GNAT User’s Guide for Native Platforms

Table of Contents

Next: , Up: (dir)   [Contents][Index]

GNAT User’s Guide for Native Platforms

GNAT User’s Guide for Native Platforms , Dec 10, 2019

AdaCore

Copyright © 2008-2020, Free Software Foundation

`GNAT, The GNU Ada Development Environment'

GCC version 10.3.0
AdaCore

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover Texts being "GNAT User’s Guide for Native Platforms", and with no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License.

• About This Guide:  
• Getting Started with GNAT:  
• The GNAT Compilation Model:  
• Building Executable Programs with GNAT:  
• GNAT Utility Programs:  
• GNAT and Program Execution:  
• Platform-Specific Information:  
• Example of Binder Output File:  
• Elaboration Order Handling in GNAT:  
• Inline Assembler:  
• GNU Free Documentation License:  
• Index:   
 — The Detailed Node Listing —

About This Guide


• What This Guide Contains:  



• What You Should Know before Reading This Guide:  



• Related Information:  



• A Note to Readers of Previous Versions of the Manual:  



• Conventions:  



Getting Started with GNAT


• Running GNAT:  



• Running a Simple Ada Program:  



• Running a Program with Multiple Units:  



• Using the gnatmake Utility:  



The GNAT Compilation Model


• Source Representation:  



• Foreign Language Representation:  



• File Naming Topics and Utilities:  



• Configuration Pragmas:  



• Generating Object Files:  



• Source Dependencies:  



• The Ada Library Information Files:  



• Binding an Ada Program:  



• GNAT and Libraries:  



• Conditional Compilation:  



• Mixed Language Programming:  



• GNAT and Other Compilation Models:  



• Using GNAT Files with External Tools:  



Foreign Language Representation


• Latin-1:  



• Other 8-Bit Codes:  



• Wide_Character Encodings:  



• Wide_Wide_Character Encodings:  



File Naming Topics and Utilities


• File Naming Rules:  



• Using Other File Names:  



• Alternative File Naming Schemes:  



• Handling Arbitrary File Naming Conventions with gnatname:  



• File Name Krunching with gnatkr:  



• Renaming Files with gnatchop:  



Handling Arbitrary File Naming Conventions with gnatname


• Arbitrary File Naming Conventions:  



• Running gnatname:  



• Switches for gnatname:  



• Examples of gnatname Usage:  



File Name Krunching with gnatkr


• About gnatkr:  



• Using gnatkr:  



• Krunching Method:  



• Examples of gnatkr Usage:  



Renaming Files with gnatchop


• Handling Files with Multiple Units:  



• Operating gnatchop in Compilation Mode:  



• Command Line for gnatchop:  



• Switches for gnatchop:  



• Examples of gnatchop Usage:  



Configuration Pragmas


• Handling of Configuration Pragmas:  



• The Configuration Pragmas Files:  



GNAT and Libraries


• Introduction to Libraries in GNAT:  



• General Ada Libraries:  



• Stand-alone Ada Libraries:  



• Rebuilding the GNAT Run-Time Library:  



General Ada Libraries


• Building a library:  



• Installing a library:  



• Using a library:  



Stand-alone Ada Libraries


• Introduction to Stand-alone Libraries:  



• Building a Stand-alone Library:  



• Creating a Stand-alone Library to be used in a non-Ada context:  



• Restrictions in Stand-alone Libraries:  



Conditional Compilation


• Modeling Conditional Compilation in Ada:  



• Preprocessing with gnatprep:  



• Integrated Preprocessing:  



Modeling Conditional Compilation in Ada


• Use of Boolean Constants:  



• Debugging - A Special Case:  



• Conditionalizing Declarations:  



• Use of Alternative Implementations:  



• Preprocessing:  



Preprocessing with gnatprep


• Preprocessing Symbols:  



• Using gnatprep:  



• Switches for gnatprep:  



• Form of Definitions File:  



• Form of Input Text for gnatprep:  



Mixed Language Programming


• Interfacing to C:  



• Calling Conventions:  



• Building Mixed Ada and C++ Programs:  



• Generating Ada Bindings for C and C++ headers:  



• Generating C Headers for Ada Specifications:  



Building Mixed Ada and C++ Programs


• Interfacing to C++:  



• Linking a Mixed C++ & Ada Program:  



• A Simple Example:  



• Interfacing with C++ constructors:  



• Interfacing with C++ at the Class Level:  



Generating Ada Bindings for C and C++ headers


• Running the Binding Generator:  



• Generating Bindings for C++ Headers:  



• Switches:  



Generating C Headers for Ada Specifications


• Running the C Header Generator:  



GNAT and Other Compilation Models


• Comparison between GNAT and C/C++ Compilation Models:  



• Comparison between GNAT and Conventional Ada Library Models:  



Using GNAT Files with External Tools


• Using Other Utility Programs with GNAT:  



• The External Symbol Naming Scheme of GNAT:  



Building Executable Programs with GNAT


• Building with gnatmake:  



• Compiling with gcc:  



• Compiler Switches:  



• Linker Switches:  



• Binding with gnatbind:  



• Linking with gnatlink:  



• Using the GNU make Utility:  



Building with gnatmake


• Running gnatmake:  



• Switches for gnatmake:  



• Mode Switches for gnatmake:  



• Notes on the Command Line:  



• How gnatmake Works:  



• Examples of gnatmake Usage:  



Compiling with gcc


• Compiling Programs:  



• Search Paths and the Run-Time Library (RTL):  



• Order of Compilation Issues:  



• Examples:  



Compiler Switches


• Alphabetical List of All Switches:  



• Output and Error Message Control:  



• Warning Message Control:  



• Debugging and Assertion Control:  



• Validity Checking:  



• Style Checking:  



• Run-Time Checks:  



• Using gcc for Syntax Checking:  



• Using gcc for Semantic Checking:  



• Compiling Different Versions of Ada:  



• Character Set Control:  



• File Naming Control:  



• Subprogram Inlining Control:  



• Auxiliary Output Control:  



• Debugging Control:  



• Exception Handling Control:  



• Units to Sources Mapping Files:  



• Code Generation Control:  



Binding with gnatbind


• Running gnatbind:  



• Switches for gnatbind:  



• Command-Line Access:  



• Search Paths for gnatbind:  



• Examples of gnatbind Usage:  



Switches for gnatbind


• Consistency-Checking Modes:  



• Binder Error Message Control:  



• Elaboration Control:  



• Output Control:  



• Dynamic Allocation Control:  



• Binding with Non-Ada Main Programs:  



• Binding Programs with No Main Subprogram:  



Linking with gnatlink


• Running gnatlink:  



• Switches for gnatlink:  



Using the GNU make Utility


• Using gnatmake in a Makefile:  



• Automatically Creating a List of Directories:  



• Generating the Command Line Switches:  



• Overcoming Command Line Length Limits:  



GNAT Utility Programs


• The File Cleanup Utility gnatclean:  



• The GNAT Library Browser gnatls:  



• The Cross-Referencing Tools gnatxref and gnatfind:  



• The Ada to HTML Converter gnathtml:  



The File Cleanup Utility gnatclean


• Running gnatclean:  



• Switches for gnatclean:  



The GNAT Library Browser gnatls


• Running gnatls:  



• Switches for gnatls:  



• Example of gnatls Usage:  



The Cross-Referencing Tools gnatxref and gnatfind


• gnatxref Switches:  



• gnatfind Switches:  



• Configuration Files for gnatxref and gnatfind:  



• Regular Expressions in gnatfind and gnatxref:  



• Examples of gnatxref Usage:  



• Examples of gnatfind Usage:  



Examples of gnatxref Usage


• General Usage:  



• Using gnatxref with vi:  



The Ada to HTML Converter gnathtml


• Invoking gnathtml:  



• Installing gnathtml:  



GNAT and Program Execution


• Running and Debugging Ada Programs:  



• Profiling:  



• Improving Performance:  



• Overflow Check Handling in GNAT:  



• Performing Dimensionality Analysis in GNAT:  



• Stack Related Facilities:  



• Memory Management Issues:  



Running and Debugging Ada Programs


• The GNAT Debugger GDB:  



• Running GDB:  



• Introduction to GDB Commands:  



• Using Ada Expressions:  



• Calling User-Defined Subprograms:  



• Using the next Command in a Function:  



• Stopping When Ada Exceptions Are Raised:  



• Ada Tasks:  



• Debugging Generic Units:  



• Remote Debugging with gdbserver:  



• GNAT Abnormal Termination or Failure to Terminate:  



• Naming Conventions for GNAT Source Files:  



• Getting Internal Debugging Information:  



• Stack Traceback:  



• Pretty-Printers for the GNAT runtime:  



Stack Traceback


• Non-Symbolic Traceback:  



• Symbolic Traceback:  



Profiling


• Profiling an Ada Program with gprof:  



Profiling an Ada Program with gprof


• Compilation for profiling:  



• Program execution:  



• Running gprof:  



• Interpretation of profiling results:  



Improving Performance


• Performance Considerations:  



• Text_IO Suggestions:  



• Reducing Size of Executables with Unused Subprogram/Data Elimination:  



Performance Considerations


• Controlling Run-Time Checks:  



• Use of Restrictions:  



• Optimization Levels:  



• Debugging Optimized Code:  



• Inlining of Subprograms:  



• Floating_Point_Operations:  



• Vectorization of loops:  



• Other Optimization Switches:  



• Optimization and Strict Aliasing:  



• Aliased Variables and Optimization:  



• Atomic Variables and Optimization:  



• Passive Task Optimization:  



Reducing Size of Executables with Unused Subprogram/Data Elimination


• About unused subprogram/data elimination:  



• Compilation options:  



• Example of unused subprogram/data elimination:  



Overflow Check Handling in GNAT


• Background:  



• Management of Overflows in GNAT:  



• Specifying the Desired Mode:  



• Default Settings:  



• Implementation Notes:  



Stack Related Facilities


• Stack Overflow Checking:  



• Static Stack Usage Analysis:  



• Dynamic Stack Usage Analysis:  



Memory Management Issues


• Some Useful Memory Pools:  



• The GNAT Debug Pool Facility:  



Platform-Specific Information


• Run-Time Libraries:  



• Specifying a Run-Time Library:  



• GNU/Linux Topics:  



• Microsoft Windows Topics:  



• Mac OS Topics:  



Run-Time Libraries


• Summary of Run-Time Configurations:  



Specifying a Run-Time Library


• Choosing the Scheduling Policy:  



GNU/Linux Topics


• Required Packages on GNU/Linux:  



Microsoft Windows Topics


• Using GNAT on Windows:  



• Using a network installation of GNAT:  



• CONSOLE and WINDOWS subsystems:  



• Temporary Files:  



• Disabling Command Line Argument Expansion:  



• Windows Socket Timeouts:  



• Mixed-Language Programming on Windows:  



• Windows Specific Add-Ons:  



Mixed-Language Programming on Windows


• Windows Calling Conventions:  



• Introduction to Dynamic Link Libraries (DLLs):  



• Using DLLs with GNAT:  



• Building DLLs with GNAT Project files:  



• Building DLLs with GNAT:  



• Building DLLs with gnatdll:  



• Ada DLLs and Finalization:  



• Creating a Spec for Ada DLLs:  



• GNAT and Windows Resources:  



• Using GNAT DLLs from Microsoft Visual Studio Applications:  



• Debugging a DLL:  



• Setting Stack Size from gnatlink:  



• Setting Heap Size from gnatlink:  



Windows Calling Conventions


• C Calling Convention:  



• Stdcall Calling Convention:  



• Win32 Calling Convention:  



• DLL Calling Convention:  



Using DLLs with GNAT


• Creating an Ada Spec for the DLL Services:  



• Creating an Import Library:  



Building DLLs with gnatdll


• Limitations When Using Ada DLLs from Ada:  



• Exporting Ada Entities:  



• Ada DLLs and Elaboration:  



Creating a Spec for Ada DLLs


• Creating the Definition File:  



• Using gnatdll:  



GNAT and Windows Resources


• Building Resources:  



• Compiling Resources:  



• Using Resources:  



Debugging a DLL


• Program and DLL Both Built with GCC/GNAT:  



• Program Built with Foreign Tools and DLL Built with GCC/GNAT:  



Windows Specific Add-Ons


• Win32Ada:  



• wPOSIX:  



Mac OS Topics


• Codesigning the Debugger:  



Elaboration Order Handling in GNAT


• Elaboration Code:  



• Elaboration Order:  



• Checking the Elaboration Order:  



• Controlling the Elaboration Order in Ada:  



• Controlling the Elaboration Order in GNAT:  



• Mixing Elaboration Models:  



• ABE Diagnostics:  



• SPARK Diagnostics:  



• Elaboration Circularities:  



• Resolving Elaboration Circularities:  



• Elaboration-related Compiler Switches:  



• Summary of Procedures for Elaboration Control:  



• Inspecting the Chosen Elaboration Order:  



Inline Assembler


• Basic Assembler Syntax:  



• A Simple Example of Inline Assembler:  



• Output Variables in Inline Assembler:  



• Input Variables in Inline Assembler:  



• Inlining Inline Assembler Code:  



• Other Asm Functionality:  



Other Asm Functionality


• The Clobber Parameter:  



• The Volatile Parameter:  












Next: , Previous: Top, Up: Top   [Contents][Index]





1 About This Guide





This guide describes the use of GNAT,
a compiler and software development
toolset for the full Ada programming language.
It documents the features of the compiler and tools, and explains
how to use them to build Ada applications.



GNAT implements Ada 95, Ada 2005 and Ada 2012, and it may also be
invoked in Ada 83 compatibility mode.
By default, GNAT assumes Ada 2012, but you can override with a
compiler switch (Compiling Different Versions of Ada)
to explicitly specify the language version.
Throughout this manual, references to ’Ada’ without a year suffix
apply to all Ada 95/2005/2012 versions of the language.





• What This Guide Contains:  



• What You Should Know before Reading This Guide:  



• Related Information:  



• A Note to Readers of Previous Versions of the Manual:  



• Conventions:  












Next: , Up: About This Guide   [Contents][Index]





1.1 What This Guide Contains




This guide contains the following chapters:






Appendices cover several additional topics:












Next: , Previous: What This Guide Contains, Up: About This Guide   [Contents][Index]





1.2 What You Should Know before Reading This Guide








This guide assumes a basic familiarity with the Ada 95 language, as
described in the International Standard ANSI/ISO/IEC-8652:1995, January
1995.
It does not require knowledge of the features introduced by Ada 2005
or Ada 2012.
Reference manuals for Ada 95, Ada 2005, and Ada 2012 are included in
the GNAT documentation package.









Next: , Previous: What You Should Know before Reading This Guide, Up: About This Guide   [Contents][Index]





1.3 Related Information




For further information about Ada and related tools, please refer to the
following documents:












Next: , Previous: Related Information, Up: About This Guide   [Contents][Index]





1.4 A Note to Readers of Previous Versions of the Manual




In early 2015 the GNAT manuals were transitioned to the
reStructuredText (rst) / Sphinx documentation generator technology.
During that process the GNAT User’s Guide was reorganized
so that related topics would be described together in the same chapter
or appendix.  Here’s a summary of the major changes realized in
the new document structure.












Previous: A Note to Readers of Previous Versions of the Manual, Up: About This Guide   [Contents][Index]





1.5 Conventions









Following are examples of the typographical and graphic conventions used
in this guide:












Next: , Previous: About This Guide, Up: Top   [Contents][Index]





2 Getting Started with GNAT




This chapter describes how to use GNAT’s command line interface to build
executable Ada programs.
On most platforms a visually oriented Integrated Development Environment
is also available, the GNAT Programming Studio (GNAT Studio).
GNAT Studio offers a graphical "look and feel", support for development in
other programming languages, comprehensive browsing features, and
many other capabilities.
For information on GNAT Studio please refer to
Using the GNAT Programming Studio.





• Running GNAT:  



• Running a Simple Ada Program:  



• Running a Program with Multiple Units:  



• Using the gnatmake Utility:  












Next: , Up: Getting Started with GNAT   [Contents][Index]





2.1 Running GNAT




Three steps are needed to create an executable file from an Ada source
file:






All three steps are most commonly handled by using the gnatmake
utility program that, given the name of the main program, automatically
performs the necessary compilation, binding and linking steps.









Next: , Previous: Running GNAT, Up: Getting Started with GNAT   [Contents][Index]





2.2 Running a Simple Ada Program




Any text editor may be used to prepare an Ada program.
(If Emacs is used, the optional Ada mode may be helpful in laying out the
program.)
The program text is a normal text file. We will assume in our initial
example that you have used your editor to prepare the following
standard format text file:





with Ada.Text_IO; use Ada.Text_IO;
procedure Hello is
begin
   Put_Line ("Hello WORLD!");
end Hello;




This file should be named hello.adb.
With the normal default file naming conventions, GNAT requires
that each file
contain a single compilation unit whose file name is the
unit name,
with periods replaced by hyphens; the
extension is ads for a
spec and adb for a body.
You can override this default file naming convention by use of the
special pragma Source_File_Name (for further information please
see Using Other File Names).
Alternatively, if you want to rename your files according to this default
convention, which is probably more convenient if you will be using GNAT
for all your compilations, then the gnatchop utility
can be used to generate correctly-named source files
(see Renaming Files with gnatchop).



You can compile the program using the following command ($ is used
as the command prompt in the examples in this document):





$ gcc -c hello.adb




gcc is the command used to run the compiler. This compiler is
capable of compiling programs in several languages, including Ada and
C. It assumes that you have given it an Ada program if the file extension is
either .ads or .adb, and it will then call
the GNAT compiler to compile the specified file.



The -c switch is required. It tells gcc to only do a
compilation. (For C programs, gcc can also do linking, but this
capability is not used directly for Ada programs, so the -c
switch must always be present.)



This compile command generates a file
hello.o, which is the object
file corresponding to your Ada program. It also generates
an ’Ada Library Information’ file hello.ali,
which contains additional information used to check
that an Ada program is consistent.
To build an executable file,
use gnatbind to bind the program
and gnatlink to link it. The
argument to both gnatbind and gnatlink is the name of the
ALI file, but the default extension of .ali can
be omitted. This means that in the most common case, the argument
is simply the name of the main program:





$ gnatbind hello
$ gnatlink hello




A simpler method of carrying out these steps is to use gnatmake,
a master program that invokes all the required
compilation, binding and linking tools in the correct order. In particular,
gnatmake automatically recompiles any sources that have been
modified since they were last compiled, or sources that depend
on such modified sources, so that ’version skew’ is avoided.







$ gnatmake hello.adb




The result is an executable program called hello, which can be
run by entering:





$ hello




assuming that the current directory is on the search path
for executable programs.



and, if all has gone well, you will see:





Hello WORLD!




appear in response to this command.









Next: , Previous: Running a Simple Ada Program, Up: Getting Started with GNAT   [Contents][Index]





2.3 Running a Program with Multiple Units




Consider a slightly more complicated example that has three files: a
main program, and the spec and body of a package:





package Greetings is
   procedure Hello;
   procedure Goodbye;
end Greetings;

with Ada.Text_IO; use Ada.Text_IO;
package body Greetings is
   procedure Hello is
   begin
      Put_Line ("Hello WORLD!");
   end Hello;

   procedure Goodbye is
   begin
      Put_Line ("Goodbye WORLD!");
   end Goodbye;
end Greetings;

with Greetings;
procedure Gmain is
begin
   Greetings.Hello;
   Greetings.Goodbye;
end Gmain;




Following the one-unit-per-file rule, place this program in the
following three separate files:






`greetings.ads'




spec of package Greetings





`greetings.adb'




body of package Greetings





`gmain.adb'




body of main program






To build an executable version of
this program, we could use four separate steps to compile, bind, and link
the program, as follows:





$ gcc -c gmain.adb
$ gcc -c greetings.adb
$ gnatbind gmain
$ gnatlink gmain




Note that there is no required order of compilation when using GNAT.
In particular it is perfectly fine to compile the main program first.
Also, it is not necessary to compile package specs in the case where
there is an accompanying body; you only need to compile the body. If you want
to submit these files to the compiler for semantic checking and not code
generation, then use the -gnatc switch:





$ gcc -c greetings.ads -gnatc




Although the compilation can be done in separate steps as in the
above example, in practice it is almost always more convenient
to use the gnatmake tool. All you need to know in this case
is the name of the main program’s source file. The effect of the above four
commands can be achieved with a single one:





$ gnatmake gmain.adb




In the next section we discuss the advantages of using gnatmake in
more detail.









Previous: Running a Program with Multiple Units, Up: Getting Started with GNAT   [Contents][Index]





2.4 Using the gnatmake Utility




If you work on a program by compiling single components at a time using
gcc, you typically keep track of the units you modify. In order to
build a consistent system, you compile not only these units, but also any
units that depend on the units you have modified.
For example, in the preceding case,
if you edit gmain.adb, you only need to recompile that file. But if
you edit greetings.ads, you must recompile both
greetings.adb and gmain.adb, because both files contain
units that depend on greetings.ads.



gnatbind will warn you if you forget one of these compilation
steps, so that it is impossible to generate an inconsistent program as a
result of forgetting to do a compilation. Nevertheless it is tedious and
error-prone to keep track of dependencies among units.
One approach to handle the dependency-bookkeeping is to use a
makefile. However, makefiles present maintenance problems of their own:
if the dependencies change as you change the program, you must make
sure that the makefile is kept up-to-date manually, which is also an
error-prone process.



The gnatmake utility takes care of these details automatically.
Invoke it using either one of the following forms:





$ gnatmake gmain.adb
$ gnatmake gmain




The argument is the name of the file containing the main program;
you may omit the extension. gnatmake
examines the environment, automatically recompiles any files that need
recompiling, and binds and links the resulting set of object files,
generating the executable file, gmain.
In a large program, it
can be extremely helpful to use gnatmake, because working out by hand
what needs to be recompiled can be difficult.



Note that gnatmake takes into account all the Ada rules that
establish dependencies among units. These include dependencies that result
from inlining subprogram bodies, and from
generic instantiation. Unlike some other
Ada make tools, gnatmake does not rely on the dependencies that were
found by the compiler on a previous compilation, which may possibly
be wrong when sources change. gnatmake determines the exact set of
dependencies from scratch each time it is run.










Next: , Previous: Getting Started with GNAT, Up: Top   [Contents][Index]





3 The GNAT Compilation Model








This chapter describes the compilation model used by GNAT. Although
similar to that used by other languages such as C and C++, this model
is substantially different from the traditional Ada compilation models,
which are based on a centralized program library. The chapter covers
the following material:








• Source Representation:  



• Foreign Language Representation:  



• File Naming Topics and Utilities:  



• Configuration Pragmas:  



• Generating Object Files:  



• Source Dependencies:  



• The Ada Library Information Files:  



• Binding an Ada Program:  



• GNAT and Libraries:  



• Conditional Compilation:  



• Mixed Language Programming:  



• GNAT and Other Compilation Models:  



• Using GNAT Files with External Tools:  












Next: , Up: The GNAT Compilation Model   [Contents][Index]





3.1 Source Representation












Ada source programs are represented in standard text files, using
Latin-1 coding. Latin-1 is an 8-bit code that includes the familiar
7-bit ASCII set, plus additional characters used for
representing foreign languages (see Foreign Language Representation
for support of non-USA character sets). The format effector characters
are represented using their standard ASCII encodings, as follows:









CharacterEffectCode


VTVertical tab16#0B#


HTHorizontal tab16#09#


CRCarriage return16#0D#


LFLine feed16#0A#


FFForm feed16#0C#








Source files are in standard text file format. In addition, GNAT will
recognize a wide variety of stream formats, in which the end of
physical lines is marked by any of the following sequences:
LF, CR, CR-LF, or LF-CR. This is useful
in accommodating files that are imported from other operating systems.







The end of a source file is normally represented by the physical end of
file. However, the control character 16#1A# (SUB) is also
recognized as signalling the end of the source file. Again, this is
provided for compatibility with other operating systems where this
code is used to represent the end of file.






Each file contains a single Ada compilation unit, including any pragmas
associated with the unit. For example, this means you must place a
package declaration (a package `spec') and the corresponding body in
separate files. An Ada `compilation' (which is a sequence of
compilation units) is represented using a sequence of files. Similarly,
you will place each subunit or child unit in a separate file.









Next: , Previous: Source Representation, Up: The GNAT Compilation Model   [Contents][Index]





3.2 Foreign Language Representation




GNAT supports the standard character sets defined in Ada as well as
several other non-standard character sets for use in localized versions
of the compiler (Character Set Control).





• Latin-1:  



• Other 8-Bit Codes:  



• Wide_Character Encodings:  



• Wide_Wide_Character Encodings:  












Next: , Up: Foreign Language Representation   [Contents][Index]





3.2.1 Latin-1






The basic character set is Latin-1. This character set is defined by ISO
standard 8859, part 1. The lower half (character codes 16#00#
... 16#7F#) is identical to standard ASCII coding, but the upper
half is used to represent additional characters. These include extended letters
used by European languages, such as French accents, the vowels with umlauts
used in German, and the extra letter A-ring used in Swedish.





For a complete list of Latin-1 codes and their encodings, see the source
file of library unit Ada.Characters.Latin_1 in file
a-chlat1.ads.
You may use any of these extended characters freely in character or
string literals. In addition, the extended characters that represent
letters can be used in identifiers.









Next: , Previous: Latin-1, Up: Foreign Language Representation   [Contents][Index]





3.2.2 Other 8-Bit Codes




GNAT also supports several other 8-bit coding schemes:










`ISO 8859-2 (Latin-2)'




Latin-2 letters allowed in identifiers, with uppercase and lowercase
equivalence.













`ISO 8859-3 (Latin-3)'




Latin-3 letters allowed in identifiers, with uppercase and lowercase
equivalence.













`ISO 8859-4 (Latin-4)'




Latin-4 letters allowed in identifiers, with uppercase and lowercase
equivalence.













`ISO 8859-5 (Cyrillic)'




ISO 8859-5 letters (Cyrillic) allowed in identifiers, with uppercase and
lowercase equivalence.













`ISO 8859-15 (Latin-9)'




ISO 8859-15 (Latin-9) letters allowed in identifiers, with uppercase and
lowercase equivalence











`IBM PC (code page 437)'




This code page is the normal default for PCs in the U.S. It corresponds
to the original IBM PC character set. This set has some, but not all, of
the extended Latin-1 letters, but these letters do not have the same
encoding as Latin-1. In this mode, these letters are allowed in
identifiers with uppercase and lowercase equivalence.











`IBM PC (code page 850)'




This code page is a modification of 437 extended to include all the
Latin-1 letters, but still not with the usual Latin-1 encoding. In this
mode, all these letters are allowed in identifiers with uppercase and
lowercase equivalence.





`Full Upper 8-bit'




Any character in the range 80-FF allowed in identifiers, and all are
considered distinct. In other words, there are no uppercase and lowercase
equivalences in this range. This is useful in conjunction with
certain encoding schemes used for some foreign character sets (e.g.,
the typical method of representing Chinese characters on the PC).





`No Upper-Half'




No upper-half characters in the range 80-FF are allowed in identifiers.
This gives Ada 83 compatibility for identifier names.






For precise data on the encodings permitted, and the uppercase and lowercase
equivalences that are recognized, see the file csets.adb in
the GNAT compiler sources. You will need to obtain a full source release
of GNAT to obtain this file.









Next: , Previous: Other 8-Bit Codes, Up: Foreign Language Representation   [Contents][Index]





3.2.3 Wide_Character Encodings




GNAT allows wide character codes to appear in character and string
literals, and also optionally in identifiers, by means of the following
possible encoding schemes:






`Hex Coding'




In this encoding, a wide character is represented by the following five
character sequence:





ESC a b c d




where a, b, c, d are the four hexadecimal
characters (using uppercase letters) of the wide character code. For
example, ESC A345 is used to represent the wide character with code
16#A345#.
This scheme is compatible with use of the full Wide_Character set.





`Upper-Half Coding'






The wide character with encoding 16#abcd# where the upper bit is on
(in other words, ’a’ is in the range 8-F) is represented as two bytes,
16#ab# and 16#cd#. The second byte cannot be a format control
character, but is not required to be in the upper half. This method can
be also used for shift-JIS or EUC, where the internal coding matches the
external coding.





`Shift JIS Coding'






A wide character is represented by a two-character sequence,
16#ab# and
16#cd#, with the restrictions described for upper-half encoding as
described above. The internal character code is the corresponding JIS
character according to the standard algorithm for Shift-JIS
conversion. Only characters defined in the JIS code set table can be
used with this encoding method.





`EUC Coding'






A wide character is represented by a two-character sequence
16#ab# and
16#cd#, with both characters being in the upper half. The internal
character code is the corresponding JIS character according to the EUC
encoding algorithm. Only characters defined in the JIS code set table
can be used with this encoding method.





`UTF-8 Coding'




A wide character is represented using
UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
10646-1/Am.2. Depending on the character value, the representation
is a one, two, or three byte sequence:





16#0000#-16#007f#: 2#0xxxxxxx#
16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx#
16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#




where the xxx bits correspond to the left-padded bits of the
16-bit character value. Note that all lower half ASCII characters
are represented as ASCII bytes and all upper half characters and
other wide characters are represented as sequences of upper-half
(The full UTF-8 scheme allows for encoding 31-bit characters as
6-byte sequences, and in the following section on wide wide
characters, the use of these sequences is documented).





`Brackets Coding'




In this encoding, a wide character is represented by the following eight
character sequence:





[ " a b c d " ]




where a, b, c, d are the four hexadecimal
characters (using uppercase letters) of the wide character code. For
example, [’A345’] is used to represent the wide character with code
16#A345#. It is also possible (though not required) to use the
Brackets coding for upper half characters. For example, the code
16#A3# can be represented as ['A3'].



This scheme is compatible with use of the full Wide_Character set,
and is also the method used for wide character encoding in some standard
ACATS (Ada Conformity Assessment Test Suite) test suite distributions.










Note: Some of these coding schemes do not permit the full use of the
Ada character set. For example, neither Shift JIS nor EUC allow the
use of the upper half of the Latin-1 set.












Previous: Wide_Character Encodings, Up: Foreign Language Representation   [Contents][Index]





3.2.4 Wide_Wide_Character Encodings




GNAT allows wide wide character codes to appear in character and string
literals, and also optionally in identifiers, by means of the following
possible encoding schemes:






`UTF-8 Coding'




A wide character is represented using
UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
10646-1/Am.2. Depending on the character value, the representation
of character codes with values greater than 16#FFFF# is a
is a four, five, or six byte sequence:





16#01_0000#-16#10_FFFF#:     11110xxx 10xxxxxx 10xxxxxx
                             10xxxxxx
16#0020_0000#-16#03FF_FFFF#: 111110xx 10xxxxxx 10xxxxxx
                             10xxxxxx 10xxxxxx
16#0400_0000#-16#7FFF_FFFF#: 1111110x 10xxxxxx 10xxxxxx
                             10xxxxxx 10xxxxxx 10xxxxxx




where the xxx bits correspond to the left-padded bits of the
32-bit character value.





`Brackets Coding'




In this encoding, a wide wide character is represented by the following ten or
twelve byte character sequence:





[ " a b c d e f " ]
[ " a b c d e f g h " ]




where a-h are the six or eight hexadecimal
characters (using uppercase letters) of the wide wide character code. For
example, ["1F4567"] is used to represent the wide wide character with code
16#001F_4567#.



This scheme is compatible with use of the full Wide_Wide_Character set,
and is also the method used for wide wide character encoding in some standard
ACATS (Ada Conformity Assessment Test Suite) test suite distributions.












Next: , Previous: Foreign Language Representation, Up: The GNAT Compilation Model   [Contents][Index]





3.3 File Naming Topics and Utilities




GNAT has a default file naming scheme and also provides the user with
a high degree of control over how the names and extensions of the
source files correspond to the Ada compilation units that they contain.





• File Naming Rules:  



• Using Other File Names:  



• Alternative File Naming Schemes:  



• Handling Arbitrary File Naming Conventions with gnatname:  



• File Name Krunching with gnatkr:  



• Renaming Files with gnatchop:  












Next: , Up: File Naming Topics and Utilities   [Contents][Index]





3.3.1 File Naming Rules




The default file name is determined by the name of the unit that the
file contains. The name is formed by taking the full expanded name of
the unit and replacing the separating dots with hyphens and using
lowercase for all letters.



An exception arises if the file name generated by the above rules starts
with one of the characters
a, g, i, or s, and the second character is a
minus. In this case, the character tilde is used in place
of the minus. The reason for this special rule is to avoid clashes with
the standard names for child units of the packages System, Ada,
Interfaces, and GNAT, which use the prefixes
s-, a-, i-, and g-,
respectively.



The file extension is .ads for a spec and
.adb for a body. The following table shows some
examples of these rules.









Source FileAda Compilation Unit


main.adsMain (spec)


main.adbMain (body)


arith_functions.adsArith_Functions (package spec)


arith_functions.adbArith_Functions (package body)


func-spec.adsFunc.Spec (child package spec)


func-spec.adbFunc.Spec (child package body)


main-sub.adbSub (subunit of Main)


a~bad.adbA.Bad (child package body)








Following these rules can result in excessively long
file names if corresponding
unit names are long (for example, if child units or subunits are
heavily nested). An option is available to shorten such long file names
(called file name ’krunching’). This may be particularly useful when
programs being developed with GNAT are to be used on operating systems
with limited file name lengths. Using gnatkr.



Of course, no file shortening algorithm can guarantee uniqueness over
all possible unit names; if file name krunching is used, it is your
responsibility to ensure no name clashes occur. Alternatively you
can specify the exact file names that you want used, as described
in the next section. Finally, if your Ada programs are migrating from a
compiler with a different naming convention, you can use the gnatchop
utility to produce source files that follow the GNAT naming conventions.
(For details see Renaming Files with gnatchop.)



Note: in the case of Windows or Mac OS operating systems, case is not
significant. So for example on Windows if the canonical name is
main-sub.adb, you can use the file name Main-Sub.adb instead.
However, case is significant for other operating systems, so for example,
if you want to use other than canonically cased file names on a Unix system,
you need to follow the procedures described in the next section.









Next: , Previous: File Naming Rules, Up: File Naming Topics and Utilities   [Contents][Index]





3.3.2 Using Other File Names






In the previous section, we have described the default rules used by
GNAT to determine the file name in which a given unit resides. It is
often convenient to follow these default rules, and if you follow them,
the compiler knows without being explicitly told where to find all
the files it needs.





However, in some cases, particularly when a program is imported from
another Ada compiler environment, it may be more convenient for the
programmer to specify which file names contain which units. GNAT allows
arbitrary file names to be used by means of the Source_File_Name pragma.
The form of this pragma is as shown in the following examples:





pragma Source_File_Name (My_Utilities.Stacks,
  Spec_File_Name => "myutilst_a.ada");
pragma Source_File_name (My_Utilities.Stacks,
  Body_File_Name => "myutilst.ada");




As shown in this example, the first argument for the pragma is the unit
name (in this example a child unit). The second argument has the form
of a named association. The identifier
indicates whether the file name is for a spec or a body;
the file name itself is given by a string literal.



The source file name pragma is a configuration pragma, which means that
normally it will be placed in the gnat.adc
file used to hold configuration
pragmas that apply to a complete compilation environment.
For more details on how the gnat.adc file is created and used
see Handling of Configuration Pragmas.





GNAT allows completely arbitrary file names to be specified using the
source file name pragma. However, if the file name specified has an
extension other than .ads or .adb it is necessary to use
a special syntax when compiling the file. The name in this case must be
preceded by the special sequence -x followed by a space and the name
of the language, here ada, as in:





$ gcc -c -x ada peculiar_file_name.sim




gnatmake handles non-standard file names in the usual manner (the
non-standard file name for the main program is simply used as the
argument to gnatmake). Note that if the extension is also non-standard,
then it must be included in the gnatmake command, it may not
be omitted.









Next: , Previous: Using Other File Names, Up: File Naming Topics and Utilities   [Contents][Index]





3.3.3 Alternative File Naming Schemes









The previous section described the use of the Source_File_Name
pragma to allow arbitrary names to be assigned to individual source files.
However, this approach requires one pragma for each file, and especially in
large systems can result in very long gnat.adc files, and also create
a maintenance problem.





GNAT also provides a facility for specifying systematic file naming schemes
other than the standard default naming scheme previously described. An
alternative scheme for naming is specified by the use of
Source_File_Name pragmas having the following format:





pragma Source_File_Name (
   Spec_File_Name  => FILE_NAME_PATTERN
 [ , Casing          => CASING_SPEC]
 [ , Dot_Replacement => STRING_LITERAL ] );

pragma Source_File_Name (
   Body_File_Name  => FILE_NAME_PATTERN
 [ , Casing          => CASING_SPEC ]
 [ , Dot_Replacement => STRING_LITERAL ] ) ;

pragma Source_File_Name (
   Subunit_File_Name  => FILE_NAME_PATTERN
 [ , Casing          => CASING_SPEC ]
 [ , Dot_Replacement => STRING_LITERAL ] ) ;

FILE_NAME_PATTERN ::= STRING_LITERAL
CASING_SPEC ::= Lowercase | Uppercase | Mixedcase




The FILE_NAME_PATTERN string shows how the file name is constructed.
It contains a single asterisk character, and the unit name is substituted
systematically for this asterisk. The optional parameter
Casing indicates
whether the unit name is to be all upper-case letters, all lower-case letters,
or mixed-case. If no
Casing parameter is used, then the default is all
lower-case.



The optional Dot_Replacement string is used to replace any periods
that occur in subunit or child unit names. If no Dot_Replacement
argument is used then separating dots appear unchanged in the resulting
file name.
Although the above syntax indicates that the
Casing argument must appear
before the Dot_Replacement argument, but it
is also permissible to write these arguments in the opposite order.



As indicated, it is possible to specify different naming schemes for
bodies, specs, and subunits. Quite often the rule for subunits is the
same as the rule for bodies, in which case, there is no need to give
a separate Subunit_File_Name rule, and in this case the
Body_File_name rule is used for subunits as well.



The separate rule for subunits can also be used to implement the rather
unusual case of a compilation environment (e.g., a single directory) which
contains a subunit and a child unit with the same unit name. Although
both units cannot appear in the same partition, the Ada Reference Manual
allows (but does not require) the possibility of the two units coexisting
in the same environment.



The file name translation works in the following steps:






As an example of the use of this mechanism, consider a commonly used scheme
in which file names are all lower case, with separating periods copied
unchanged to the resulting file name, and specs end with .1.ada, and
bodies end with .2.ada. GNAT will follow this scheme if the following
two pragmas appear:





pragma Source_File_Name
  (Spec_File_Name => ".1.ada");
pragma Source_File_Name
  (Body_File_Name => ".2.ada");




The default GNAT scheme is actually implemented by providing the following
default pragmas internally:





pragma Source_File_Name
  (Spec_File_Name => ".ads", Dot_Replacement => "-");
pragma Source_File_Name
  (Body_File_Name => ".adb", Dot_Replacement => "-");




Our final example implements a scheme typically used with one of the
Ada 83 compilers, where the separator character for subunits was ’__’
(two underscores), specs were identified by adding _.ADA, bodies
by adding .ADA, and subunits by
adding .SEP. All file names were
upper case. Child units were not present of course since this was an
Ada 83 compiler, but it seems reasonable to extend this scheme to use
the same double underscore separator for child units.





pragma Source_File_Name
  (Spec_File_Name => "_.ADA",
   Dot_Replacement => "__",
   Casing = Uppercase);
pragma Source_File_Name
  (Body_File_Name => ".ADA",
   Dot_Replacement => "__",
   Casing = Uppercase);
pragma Source_File_Name
  (Subunit_File_Name => ".SEP",
   Dot_Replacement => "__",
   Casing = Uppercase);












Next: , Previous: Alternative File Naming Schemes, Up: File Naming Topics and Utilities   [Contents][Index]





3.3.4 Handling Arbitrary File Naming Conventions with gnatname








• Arbitrary File Naming Conventions:  



• Running gnatname:  



• Switches for gnatname:  



• Examples of gnatname Usage:  












Next: , Up: Handling Arbitrary File Naming Conventions with gnatname   [Contents][Index]





3.3.4.1 Arbitrary File Naming Conventions




The GNAT compiler must be able to know the source file name of a compilation
unit.  When using the standard GNAT default file naming conventions
(.ads for specs, .adb for bodies), the GNAT compiler
does not need additional information.



When the source file names do not follow the standard GNAT default file naming
conventions, the GNAT compiler must be given additional information through
a configuration pragmas file (Configuration Pragmas)
or a project file.
When the non-standard file naming conventions are well-defined,
a small number of pragmas Source_File_Name specifying a naming pattern
(Alternative File Naming Schemes) may be sufficient. However,
if the file naming conventions are irregular or arbitrary, a number
of pragma Source_File_Name for individual compilation units
must be defined.
To help maintain the correspondence between compilation unit names and
source file names within the compiler,
GNAT provides a tool gnatname to generate the required pragmas for a
set of files.









Next: , Previous: Arbitrary File Naming Conventions, Up: Handling Arbitrary File Naming Conventions with gnatname   [Contents][Index]





3.3.4.2 Running gnatname




The usual form of the gnatname command is:





$ gnatname [ switches ]  naming_pattern  [ naming_patterns ]
    [--and [ switches ]  naming_pattern  [ naming_patterns ]]




All of the arguments are optional. If invoked without any argument,
gnatname will display its usage.



When used with at least one naming pattern, gnatname will attempt to
find all the compilation units in files that follow at least one of the
naming patterns. To find these compilation units,
gnatname will use the GNAT compiler in syntax-check-only mode on all
regular files.



One or several Naming Patterns may be given as arguments to gnatname.
Each Naming Pattern is enclosed between double quotes (or single
quotes on Windows).
A Naming Pattern is a regular expression similar to the wildcard patterns
used in file names by the Unix shells or the DOS prompt.



gnatname may be called with several sections of directories/patterns.
Sections are separated by the switch --and. In each section, there must be
at least one pattern. If no directory is specified in a section, the current
directory (or the project directory if -P is used) is implied.
The options other that the directory switches and the patterns apply globally
even if they are in different sections.



Examples of Naming Patterns are:





"*.[12].ada"
"*.ad[sb]*"
"body_*"    "spec_*"




For a more complete description of the syntax of Naming Patterns,
see the second kind of regular expressions described in g-regexp.ads
(the ’Glob’ regular expressions).



When invoked without the switch -P, gnatname will create a
configuration pragmas file gnat.adc in the current working directory,
with pragmas Source_File_Name for each file that contains a valid Ada
unit.









Next: , Previous: Running gnatname, Up: Handling Arbitrary File Naming Conventions with gnatname   [Contents][Index]





3.3.4.3 Switches for gnatname




Switches for gnatname must precede any specified Naming Pattern.



You may specify any of the following switches to gnatname:








--version




Display Copyright and version, then exit disregarding all other options.











--help




If --version was not used, display usage, then exit disregarding
all other options.





--subdirs=`dir'




Real object, library or exec directories are subdirectories <dir> of the
specified ones.





--no-backup




Do not create a backup copy of an existing project file.





--and




Start another section of directories/patterns.











-c`filename'




Create a configuration pragmas file filename (instead of the default
gnat.adc).
There may be zero, one or more space between -c and
filename.
filename may include directory information. filename must be
writable. There may be only one switch -c.
When a switch -c is
specified, no switch -P may be specified (see below).











-d`dir'




Look for source files in directory dir. There may be zero, one or more
spaces between -d and dir.
dir may end with /**, that is it may be of the form
root_dir/**. In this case, the directory root_dir and all of its
subdirectories, recursively, have to be searched for sources.
When a switch -d
is specified, the current working directory will not be searched for source
files, unless it is explicitly specified with a -d
or -D switch.
Several switches -d may be specified.
If dir is a relative path, it is relative to the directory of
the configuration pragmas file specified with switch
-c,
or to the directory of the project file specified with switch
-P or,
if neither switch -c
nor switch -P are specified, it is relative to the
current working directory. The directory
specified with switch -d must exist and be readable.











-D`filename'




Look for source files in all directories listed in text file filename.
There may be zero, one or more spaces between -D
and filename.
filename must be an existing, readable text file.
Each nonempty line in filename must be a directory.
Specifying switch -D is equivalent to specifying as many
switches -d as there are nonempty lines in
file.





-eL




Follow symbolic links when processing project files.







-f`pattern'




Foreign patterns. Using this switch, it is possible to add sources of languages
other than Ada to the list of sources of a project file.
It is only useful if a -P switch is used.
For example,





gnatname -Pprj -f"*.c" "*.ada"




will look for Ada units in all files with the .ada extension,
and will add to the list of file for project prj.gpr the C files
with extension .c.







-h




Output usage (help) information. The output is written to stdout.







-P`proj'




Create or update project file proj. There may be zero, one or more space
between -P and proj. proj may include directory
information. proj must be writable.
There may be only one switch -P.
When a switch -P is specified,
no switch -c may be specified.
On all platforms, except on VMS, when gnatname is invoked for an
existing project file <proj>.gpr, a backup copy of the project file is created
in the project directory with file name <proj>.gpr.saved_x. ’x’ is the first
non negative number that makes this backup copy a new file.







-v




Verbose mode. Output detailed explanation of behavior to stdout.
This includes name of the file written, the name of the directories to search
and, for each file in those directories whose name matches at least one of
the Naming Patterns, an indication of whether the file contains a unit,
and if so the name of the unit.











-v -v




Very Verbose mode. In addition to the output produced in verbose mode,
for each file in the searched directories whose name matches none of
the Naming Patterns, an indication is given that there is no match.







-x`pattern'




Excluded patterns. Using this switch, it is possible to exclude some files
that would match the name patterns. For example,





gnatname -x "*_nt.ada" "*.ada"




will look for Ada units in all files with the .ada extension,
except those whose names end with _nt.ada.












Previous: Switches for gnatname, Up: Handling Arbitrary File Naming Conventions with gnatname   [Contents][Index]





3.3.4.4 Examples of gnatname Usage






$ gnatname -c /home/me/names.adc -d sources "[a-z]*.ada*"




In this example, the directory /home/me must already exist
and be writable. In addition, the directory
/home/me/sources (specified by
-d sources) must exist and be readable.



Note the optional spaces after -c and -d.





$ gnatname -P/home/me/proj -x "*_nt_body.ada"
-dsources -dsources/plus -Dcommon_dirs.txt "body_*" "spec_*"




Note that several switches -d may be used,
even in conjunction with one or several switches
-D. Several Naming Patterns and one excluded pattern
are used in this example.









Next: , Previous: Handling Arbitrary File Naming Conventions with gnatname, Up: File Naming Topics and Utilities   [Contents][Index]





3.3.5 File Name Krunching with gnatkr






This section discusses the method used by the compiler to shorten
the default file names chosen for Ada units so that they do not
exceed the maximum length permitted. It also describes the
gnatkr utility that can be used to determine the result of
applying this shortening.





• About gnatkr:  



• Using gnatkr:  



• Krunching Method:  



• Examples of gnatkr Usage:  












Next: , Up: File Name Krunching with gnatkr   [Contents][Index]





3.3.5.1 About gnatkr




The default file naming rule in GNAT
is that the file name must be derived from
the unit name. The exact default rule is as follows:






The -gnatk`nn'
switch of the compiler activates a ’krunching’
circuit that limits file names to nn characters (where nn is a decimal
integer).



The gnatkr utility can be used to determine the krunched name for
a given file, when krunched to a specified maximum length.









Next: , Previous: About gnatkr, Up: File Name Krunching with gnatkr   [Contents][Index]





3.3.5.2 Using gnatkr




The gnatkr command has the form:





$ gnatkr name [ length ]




name is the uncrunched file name, derived from the name of the unit
in the standard manner described in the previous section (i.e., in particular
all dots are replaced by hyphens). The file name may or may not have an
extension (defined as a suffix of the form period followed by arbitrary
characters other than period). If an extension is present then it will
be preserved in the output. For example, when krunching hellofile.ads
to eight characters, the result will be hellofil.ads.



Note: for compatibility with previous versions of gnatkr dots may
appear in the name instead of hyphens, but the last dot will always be
taken as the start of an extension. So if gnatkr is given an argument
such as Hello.World.adb it will be treated exactly as if the first
period had been a hyphen, and for example krunching to eight characters
gives the result hellworl.adb.



Note that the result is always all lower case.
Characters of the other case are folded as required.



length represents the length of the krunched name. The default
when no argument is given is 8 characters. A length of zero stands for
unlimited, in other words do not chop except for system files where the
implied crunching length is always eight characters.



The output is the krunched name. The output has an extension only if the
original argument was a file name with an extension.









Next: , Previous: Using gnatkr, Up: File Name Krunching with gnatkr   [Contents][Index]





3.3.5.3 Krunching Method




The initial file name is determined by the name of the unit that the file
contains. The name is formed by taking the full expanded name of the
unit and replacing the separating dots with hyphens and
using lowercase
for all letters, except that a hyphen in the second character position is
replaced by a tilde if the first character is
a, i, g, or s.
The extension is .ads for a
spec and .adb for a body.
Krunching does not affect the extension, but the file name is shortened to
the specified length by following these rules:






Of course no file shortening algorithm can guarantee uniqueness over all
possible unit names, and if file name krunching is used then it is your
responsibility to ensure that no name clashes occur. The utility
program gnatkr is supplied for conveniently determining the
krunched name of a file.









Previous: Krunching Method, Up: File Name Krunching with gnatkr   [Contents][Index]





3.3.5.4 Examples of gnatkr Usage






$ gnatkr very_long_unit_name.ads      --> velounna.ads
$ gnatkr grandparent-parent-child.ads --> grparchi.ads
$ gnatkr Grandparent.Parent.Child.ads --> grparchi.ads
$ gnatkr grandparent-parent-child     --> grparchi
$ gnatkr very_long_unit_name.ads/count=6 --> vlunna.ads
$ gnatkr very_long_unit_name.ads/count=0 --> very_long_unit_name.ads










Previous: File Name Krunching with gnatkr, Up: File Naming Topics and Utilities   [Contents][Index]





3.3.6 Renaming Files with gnatchop






This section discusses how to handle files with multiple units by using
the gnatchop utility. This utility is also useful in renaming
files to meet the standard GNAT default file naming conventions.





• Handling Files with Multiple Units:  



• Operating gnatchop in Compilation Mode:  



• Command Line for gnatchop:  



• Switches for gnatchop:  



• Examples of gnatchop Usage:  












Next: , Up: Renaming Files with gnatchop   [Contents][Index]





3.3.6.1 Handling Files with Multiple Units




The basic compilation model of GNAT requires that a file submitted to the
compiler have only one unit and there be a strict correspondence
between the file name and the unit name.



The gnatchop utility allows both of these rules to be relaxed,
allowing GNAT to process files which contain multiple compilation units
and files with arbitrary file names. gnatchop
reads the specified file and generates one or more output files,
containing one unit per file. The unit and the file name correspond,
as required by GNAT.



If you want to permanently restructure a set of ’foreign’ files so that
they match the GNAT rules, and do the remaining development using the
GNAT structure, you can simply use gnatchop once, generate the
new set of files and work with them from that point on.



Alternatively, if you want to keep your files in the ’foreign’ format,
perhaps to maintain compatibility with some other Ada compilation
system, you can set up a procedure where you use gnatchop each
time you compile, regarding the source files that it writes as temporary
files that you throw away.



Note that if your file containing multiple units starts with a byte order
mark (BOM) specifying UTF-8 encoding, then the files generated by gnatchop
will each start with a copy of this BOM, meaning that they can be compiled
automatically in UTF-8 mode without needing to specify an explicit encoding.









Next: , Previous: Handling Files with Multiple Units, Up: Renaming Files with gnatchop   [Contents][Index]





3.3.6.2 Operating gnatchop in Compilation Mode




The basic function of gnatchop is to take a file with multiple units
and split it into separate files. The boundary between files is reasonably
clear, except for the issue of comments and pragmas. In default mode, the
rule is that any pragmas between units belong to the previous unit, except
that configuration pragmas always belong to the following unit. Any comments
belong to the following unit. These rules
almost always result in the right choice of
the split point without needing to mark it explicitly and most users will
find this default to be what they want. In this default mode it is incorrect to
submit a file containing only configuration pragmas, or one that ends in
configuration pragmas, to gnatchop.



However, using a special option to activate ’compilation mode’,
gnatchop
can perform another function, which is to provide exactly the semantics
required by the RM for handling of configuration pragmas in a compilation.
In the absence of configuration pragmas (at the main file level), this
option has no effect, but it causes such configuration pragmas to be handled
in a quite different manner.



First, in compilation mode, if gnatchop is given a file that consists of
only configuration pragmas, then this file is appended to the
gnat.adc file in the current directory. This behavior provides
the required behavior described in the RM for the actions to be taken
on submitting such a file to the compiler, namely that these pragmas
should apply to all subsequent compilations in the same compilation
environment. Using GNAT, the current directory, possibly containing a
gnat.adc file is the representation
of a compilation environment. For more information on the
gnat.adc file, see Handling of Configuration Pragmas.



Second, in compilation mode, if gnatchop
is given a file that starts with
configuration pragmas, and contains one or more units, then these
configuration pragmas are prepended to each of the chopped files. This
behavior provides the required behavior described in the RM for the
actions to be taken on compiling such a file, namely that the pragmas
apply to all units in the compilation, but not to subsequently compiled
units.



Finally, if configuration pragmas appear between units, they are appended
to the previous unit. This results in the previous unit being illegal,
since the compiler does not accept configuration pragmas that follow
a unit. This provides the required RM behavior that forbids configuration
pragmas other than those preceding the first compilation unit of a
compilation.



For most purposes, gnatchop will be used in default mode. The
compilation mode described above is used only if you need exactly
accurate behavior with respect to compilations, and you have files
that contain multiple units and configuration pragmas. In this
circumstance the use of gnatchop with the compilation mode
switch provides the required behavior, and is for example the mode
in which GNAT processes the ACVC tests.









Next: , Previous: Operating gnatchop in Compilation Mode, Up: Renaming Files with gnatchop   [Contents][Index]





3.3.6.3 Command Line for gnatchop




The gnatchop command has the form:





$ gnatchop switches file_name [file_name ...]
      [directory]




The only required argument is the file name of the file to be chopped.
There are no restrictions on the form of this file name. The file itself
contains one or more Ada units, in normal GNAT format, concatenated
together. As shown, more than one file may be presented to be chopped.



When run in default mode, gnatchop generates one output file in
the current directory for each unit in each of the files.



directory, if specified, gives the name of the directory to which
the output files will be written. If it is not specified, all files are
written to the current directory.



For example, given a
file called hellofiles containing





procedure Hello;

with Ada.Text_IO; use Ada.Text_IO;
procedure Hello is
begin
   Put_Line ("Hello");
end Hello;




the command





$ gnatchop hellofiles




generates two files in the current directory, one called
hello.ads containing the single line that is the procedure spec,
and the other called hello.adb containing the remaining text. The
original file is not affected. The generated files can be compiled in
the normal manner.



When gnatchop is invoked on a file that is empty or that contains only empty
lines and/or comments, gnatchop will not fail, but will not produce any
new sources.



For example, given a
file called toto.txt containing





--  Just a comment




the command





$ gnatchop toto.txt




will not produce any new file and will result in the following warnings:





toto.txt:1:01: warning: empty file, contains no compilation units
no compilation units found
no source files written










Next: , Previous: Command Line for gnatchop, Up: Renaming Files with gnatchop   [Contents][Index]





3.3.6.4 Switches for gnatchop




gnatchop recognizes the following switches:








--version




Display Copyright and version, then exit disregarding all other options.











--help




If --version was not used, display usage, then exit disregarding
all other options.











-c




Causes gnatchop to operate in compilation mode, in which
configuration pragmas are handled according to strict RM rules. See
previous section for a full description of this mode.





-gnat`xxx'




This passes the given -gnat`xxx' switch to gnat which is
used to parse the given file. Not all `xxx' options make sense,
but for example, the use of -gnati2 allows gnatchop to
process a source file that uses Latin-2 coding for identifiers.





-h




Causes gnatchop to generate a brief help summary to the standard
output file showing usage information.











-k`mm'




Limit generated file names to the specified number mm
of characters.
This is useful if the
resulting set of files is required to be interoperable with systems
which limit the length of file names.
No space is allowed between the -k and the numeric value. The numeric
value may be omitted in which case a default of -k8,
suitable for use
with DOS-like file systems, is used. If no -k switch
is present then
there is no limit on the length of file names.











-p




Causes the file modification time stamp of the input file to be
preserved and used for the time stamp of the output file(s). This may be
useful for preserving coherency of time stamps in an environment where
gnatchop is used as part of a standard build process.











-q




Causes output of informational messages indicating the set of generated
files to be suppressed. Warnings and error messages are unaffected.













-r




Generate Source_Reference pragmas. Use this switch if the output
files are regarded as temporary and development is to be done in terms
of the original unchopped file. This switch causes
Source_Reference pragmas to be inserted into each of the
generated files to refers back to the original file name and line number.
The result is that all error messages refer back to the original
unchopped file.
In addition, the debugging information placed into the object file (when
the -g switch of gcc or gnatmake is
specified)
also refers back to this original file so that tools like profilers and
debuggers will give information in terms of the original unchopped file.



If the original file to be chopped itself contains
a Source_Reference
pragma referencing a third file, then gnatchop respects
this pragma, and the generated Source_Reference pragmas
in the chopped file refer to the original file, with appropriate
line numbers. This is particularly useful when gnatchop
is used in conjunction with gnatprep to compile files that
contain preprocessing statements and multiple units.











-v




Causes gnatchop to operate in verbose mode. The version
number and copyright notice are output, as well as exact copies of
the gnat1 commands spawned to obtain the chop control information.











-w




Overwrite existing file names. Normally gnatchop regards it as a
fatal error if there is already a file with the same name as a
file it would otherwise output, in other words if the files to be
chopped contain duplicated units. This switch bypasses this
check, and causes all but the last instance of such duplicated
units to be skipped.











--GCC=`xxxx'




Specify the path of the GNAT parser to be used. When this switch is used,
no attempt is made to add the prefix to the GNAT parser executable.












Previous: Switches for gnatchop, Up: Renaming Files with gnatchop   [Contents][Index]





3.3.6.5 Examples of gnatchop Usage






$ gnatchop -w hello_s.ada prerelease/files




Chops the source file hello_s.ada. The output files will be
placed in the directory prerelease/files,
overwriting any
files with matching names in that directory (no files in the current
directory are modified).





$ gnatchop archive




Chops the source file archive
into the current directory. One
useful application of gnatchop is in sending sets of sources
around, for example in email messages. The required sources are simply
concatenated (for example, using a Unix cat
command), and then
gnatchop is used at the other end to reconstitute the original
file names.





$ gnatchop file1 file2 file3 direc




Chops all units in files file1, file2, file3, placing
the resulting files in the directory direc. Note that if any units
occur more than once anywhere within this set of files, an error message
is generated, and no files are written. To override this check, use the
-w switch,
in which case the last occurrence in the last file will
be the one that is output, and earlier duplicate occurrences for a given
unit will be skipped.









Next: , Previous: File Naming Topics and Utilities, Up: The GNAT Compilation Model   [Contents][Index]





3.4 Configuration Pragmas









Configuration pragmas include those pragmas described as
such in the Ada Reference Manual, as well as
implementation-dependent pragmas that are configuration pragmas.
See the Implementation_Defined_Pragmas chapter in the
GNAT_Reference_Manual for details on these
additional GNAT-specific configuration pragmas.
Most notably, the pragma Source_File_Name, which allows
specifying non-default names for source files, is a configuration
pragma. The following is a complete list of configuration pragmas
recognized by GNAT:





Ada_83
Ada_95
Ada_05
Ada_2005
Ada_12
Ada_2012
Allow_Integer_Address
Annotate
Assertion_Policy
Assume_No_Invalid_Values
C_Pass_By_Copy
Check_Float_Overflow
Check_Name
Check_Policy
Compile_Time_Error
Compile_Time_Warning
Compiler_Unit
Compiler_Unit_Warning
Component_Alignment
Convention_Identifier
Debug_Policy
Detect_Blocking
Default_Scalar_Storage_Order
Default_Storage_Pool
Disable_Atomic_Synchronization
Discard_Names
Elaboration_Checks
Eliminate
Enable_Atomic_Synchronization
Extend_System
Extensions_Allowed
External_Name_Casing
Fast_Math
Favor_Top_Level
Ignore_Pragma
Implicit_Packing
Initialize_Scalars
Interrupt_State
License
Locking_Policy
No_Component_Reordering
No_Heap_Finalization
No_Run_Time
No_Strict_Aliasing
Normalize_Scalars
Optimize_Alignment
Overflow_Mode
Overriding_Renamings
Partition_Elaboration_Policy
Persistent_BSS
Polling
Prefix_Exception_Messages
Priority_Specific_Dispatching
Profile
Profile_Warnings
Propagate_Exceptions
Queuing_Policy
Rational
Ravenscar
Rename_Pragma
Restricted_Run_Time
Restrictions
Restrictions_Warnings
Reviewable
Short_Circuit_And_Or
Short_Descriptors
Source_File_Name
Source_File_Name_Project
SPARK_Mode
Style_Checks
Suppress
Suppress_Exception_Locations
Task_Dispatching_Policy
Unevaluated_Use_Of_Old
Universal_Data
Unsuppress
Use_VADS_Size
Validity_Checks
Warning_As_Error
Warnings
Wide_Character_Encoding






• Handling of Configuration Pragmas:  



• The Configuration Pragmas Files:  












Next: , Up: Configuration Pragmas   [Contents][Index]





3.4.1 Handling of Configuration Pragmas




Configuration pragmas may either appear at the start of a compilation
unit, or they can appear in a configuration pragma file to apply to
all compilations performed in a given compilation environment.



GNAT also provides the gnatchop utility to provide an automatic
way to handle configuration pragmas following the semantics for
compilations (that is, files with multiple units), described in the RM.
See Operating gnatchop in Compilation Mode for details.
However, for most purposes, it will be more convenient to edit the
gnat.adc file that contains configuration pragmas directly,
as described in the following section.



In the case of Restrictions pragmas appearing as configuration
pragmas in individual compilation units, the exact handling depends on
the type of restriction.



Restrictions that require partition-wide consistency (like
No_Tasking) are
recognized wherever they appear
and can be freely inherited, e.g. from a `with'ed unit to the `with'ing
unit. This makes sense since the binder will in any case insist on seeing
consistent use, so any unit not conforming to any restrictions that are
anywhere in the partition will be rejected, and you might as well find
that out at compile time rather than at bind time.



For restrictions that do not require partition-wide consistency, e.g.
SPARK or No_Implementation_Attributes, in general the restriction applies
only to the unit in which the pragma appears, and not to any other units.



The exception is No_Elaboration_Code which always applies to the entire
object file from a compilation, i.e. to the body, spec, and all subunits.
This restriction can be specified in a configuration pragma file, or it
can be on the body and/or the spec (in eithe case it applies to all the
relevant units). It can appear on a subunit only if it has previously
appeared in the body of spec.









Previous: Handling of Configuration Pragmas, Up: Configuration Pragmas   [Contents][Index]





3.4.2 The Configuration Pragmas Files






In GNAT a compilation environment is defined by the current
directory at the time that a compile command is given. This current
directory is searched for a file whose name is gnat.adc. If
this file is present, it is expected to contain one or more
configuration pragmas that will be applied to the current compilation.
However, if the switch -gnatA is used, gnat.adc is not
considered. When taken into account, gnat.adc is added to the
dependencies, so that if gnat.adc is modified later, an invocation of
gnatmake will recompile the source.



Configuration pragmas may be entered into the gnat.adc file
either by running gnatchop on a source file that consists only of
configuration pragmas, or more conveniently by direct editing of the
gnat.adc file, which is a standard format source file.



Besides gnat.adc, additional files containing configuration
pragmas may be applied to the current compilation using the switch
-gnatec=`path' where path must designate an existing file that
contains only configuration pragmas. These configuration pragmas are
in addition to those found in gnat.adc (provided gnat.adc
is present and switch -gnatA is not used).



It is allowable to specify several switches -gnatec=, all of which
will be taken into account.



Files containing configuration pragmas specified with switches
-gnatec= are added to the dependencies, unless they are
temporary files. A file is considered temporary if its name ends in
.tmp or .TMP. Certain tools follow this naming
convention because they pass information to gcc via
temporary files that are immediately deleted; it doesn’t make sense to
depend on a file that no longer exists. Such tools include
gprbuild, gnatmake, and gnatcheck.



If you are using project file, a separate mechanism is provided using
project attributes.










Next: , Previous: Configuration Pragmas, Up: The GNAT Compilation Model   [Contents][Index]





3.5 Generating Object Files




An Ada program consists of a set of source files, and the first step in
compiling the program is to generate the corresponding object files.
These are generated by compiling a subset of these source files.
The files you need to compile are the following:











The preceding rules describe the set of files that must be compiled to
generate the object files for a program. Each object file has the same
name as the corresponding source file, except that the extension is
.o as usual.



You may wish to compile other files for the purpose of checking their
syntactic and semantic correctness. For example, in the case where a
package has a separate spec and body, you would not normally compile the
spec. However, it is convenient in practice to compile the spec to make
sure it is error-free before compiling clients of this spec, because such
compilations will fail if there is an error in the spec.



GNAT provides an option for compiling such files purely for the
purposes of checking correctness; such compilations are not required as
part of the process of building a program. To compile a file in this
checking mode, use the -gnatc switch.









Next: , Previous: Generating Object Files, Up: The GNAT Compilation Model   [Contents][Index]





3.6 Source Dependencies




A given object file clearly depends on the source file which is compiled
to produce it. Here we are using "depends" in the sense of a typical
make utility; in other words, an object file depends on a source
file if changes to the source file require the object file to be
recompiled.
In addition to this basic dependency, a given object may depend on
additional source files as follows:



















Next: , Previous: Source Dependencies, Up: The GNAT Compilation Model   [Contents][Index]





3.7 The Ada Library Information Files








Each compilation actually generates two output files. The first of these
is the normal object file that has a .o extension. The second is a
text file containing full dependency information. It has the same
name as the source file, but an .ali extension.
This file is known as the Ada Library Information (ALI) file.
The following information is contained in the ALI file.






For a full detailed description of the format of the ALI file,
see the source of the body of unit Lib.Writ, contained in file
lib-writ.adb in the GNAT compiler sources.









Next: , Previous: The Ada Library Information Files, Up: The GNAT Compilation Model   [Contents][Index]





3.8 Binding an Ada Program




When using languages such as C and C++, once the source files have been
compiled the only remaining step in building an executable program
is linking the object modules together. This means that it is possible to
link an inconsistent version of a program, in which two units have
included different versions of the same header.



The rules of Ada do not permit such an inconsistent program to be built.
For example, if two clients have different versions of the same package,
it is illegal to build a program containing these two clients.
These rules are enforced by the GNAT binder, which also determines an
elaboration order consistent with the Ada rules.



The GNAT binder is run after all the object files for a program have
been created. It is given the name of the main program unit, and from
this it determines the set of units required by the program, by reading the
corresponding ALI files. It generates error messages if the program is
inconsistent or if no valid order of elaboration exists.



If no errors are detected, the binder produces a main program, in Ada by
default, that contains calls to the elaboration procedures of those
compilation unit that require them, followed by
a call to the main program. This Ada program is compiled to generate the
object file for the main program. The name of
the Ada file is b~xxx.adb‘ (with the corresponding spec
b~xxx.ads‘) where xxx is the name of the
main program unit.



Finally, the linker is used to build the resulting executable program,
using the object from the main program from the bind step as well as the
object files for the Ada units of the program.









Next: , Previous: Binding an Ada Program, Up: The GNAT Compilation Model   [Contents][Index]





3.9 GNAT and Libraries






This section describes how to build and use libraries with GNAT, and also shows
how to recompile the GNAT run-time library. You should be familiar with the
Project Manager facility (see the `GNAT_Project_Manager' chapter of the
`GPRbuild User’s Guide') before reading this chapter.





• Introduction to Libraries in GNAT:  



• General Ada Libraries:  



• Stand-alone Ada Libraries:  



• Rebuilding the GNAT Run-Time Library:  












Next: , Up: GNAT and Libraries   [Contents][Index]





3.9.1 Introduction to Libraries in GNAT




A library is, conceptually, a collection of objects which does not have its
own main thread of execution, but rather provides certain services to the
applications that use it. A library can be either statically linked with the
application, in which case its code is directly included in the application,
or, on platforms that support it, be dynamically linked, in which case
its code is shared by all applications making use of this library.



GNAT supports both types of libraries.
In the static case, the compiled code can be provided in different ways. The
simplest approach is to provide directly the set of objects resulting from
compilation of the library source files. Alternatively, you can group the
objects into an archive using whatever commands are provided by the operating
system. For the latter case, the objects are grouped into a shared library.



In the GNAT environment, a library has three types of components:






A GNAT library may expose all its source files, which is useful for
documentation purposes. Alternatively, it may expose only the units needed by
an external user to make use of the library. That is to say, the specs
reflecting the library services along with all the units needed to compile
those specs, which can include generic bodies or any body implementing an
inlined routine. In the case of `stand-alone libraries' those exposed
units are called `interface units' (Stand-alone Ada Libraries).



All compilation units comprising an application, including those in a library,
need to be elaborated in an order partially defined by Ada’s semantics. GNAT
computes the elaboration order from the ALI files and this is why they
constitute a mandatory part of GNAT libraries.
`Stand-alone libraries' are the exception to this rule because a specific
library elaboration routine is produced independently of the application(s)
using the library.









Next: , Previous: Introduction to Libraries in GNAT, Up: GNAT and Libraries   [Contents][Index]





3.9.2 General Ada Libraries






• Building a library:  



• Installing a library:  



• Using a library:  












Next: , Up: General Ada Libraries   [Contents][Index]





3.9.2.1 Building a library




The easiest way to build a library is to use the Project Manager,
which supports a special type of project called a `Library Project'
(see the `Library Projects' section in the `GNAT Project Manager'
chapter of the `GPRbuild User’s Guide').



A project is considered a library project, when two project-level attributes
are defined in it: Library_Name and Library_Dir. In order to
control different aspects of library configuration, additional optional
project-level attributes can be specified:






The GNAT Project Manager takes full care of the library maintenance task,
including recompilation of the source files for which objects do not exist
or are not up to date, assembly of the library archive, and installation of
the library (i.e., copying associated source, object and ALI files
to the specified location).



Here is a simple library project file:





project My_Lib is
  for Source_Dirs use ("src1", "src2");
  for Object_Dir use "obj";
  for Library_Name use "mylib";
  for Library_Dir use "lib";
  for Library_Kind use "dynamic";
end My_lib;




and the compilation command to build and install the library:





$ gnatmake -Pmy_lib




It is not entirely trivial to perform manually all the steps required to
produce a library. We recommend that you use the GNAT Project Manager
for this task. In special cases where this is not desired, the necessary
steps are discussed below.



There are various possibilities for compiling the units that make up the
library: for example with a Makefile (Using the GNU make Utility) or
with a conventional script. For simple libraries, it is also possible to create
a dummy main program which depends upon all the packages that comprise the
interface of the library. This dummy main program can then be given to
gnatmake, which will ensure that all necessary objects are built.



After this task is accomplished, you should follow the standard procedure
of the underlying operating system to produce the static or shared library.



Here is an example of such a dummy program:





with My_Lib.Service1;
with My_Lib.Service2;
with My_Lib.Service3;
procedure My_Lib_Dummy is
begin
   null;
end;




Here are the generic commands that will build an archive or a shared library.





# compiling the library
$ gnatmake -c my_lib_dummy.adb

# we don't need the dummy object itself
$ rm my_lib_dummy.o my_lib_dummy.ali

# create an archive with the remaining objects
$ ar rc libmy_lib.a *.o
# some systems may require "ranlib" to be run as well

# or create a shared library
$ gcc -shared -o libmy_lib.so *.o
# some systems may require the code to have been compiled with -fPIC

# remove the object files that are now in the library
$ rm *.o

# Make the ALI files read-only so that gnatmake will not try to
# regenerate the objects that are in the library
$ chmod -w *.ali




Please note that the library must have a name of the form lib`xxx'.a
or lib`xxx'.so (or lib`xxx'.dll on Windows) in order to
be accessed by the directive -l`xxx' at link time.









Next: , Previous: Building a library, Up: General Ada Libraries   [Contents][Index]





3.9.2.2 Installing a library








If you use project files, library installation is part of the library build
process (see the `Installing a Library with Project Files' section of the
`GNAT Project Manager' chapter of the `GPRbuild User’s Guide').



When project files are not an option, it is also possible, but not recommended,
to install the library so that the sources needed to use the library are on the
Ada source path and the ALI files & libraries be on the Ada Object path (see
Search Paths and the Run-Time Library (RTL). Alternatively, the system
administrator can place general-purpose libraries in the default compiler
paths, by specifying the libraries’ location in the configuration files
ada_source_path and ada_object_path. These configuration files
must be located in the GNAT installation tree at the same place as the gcc spec
file. The location of the gcc spec file can be determined as follows:





$ gcc -v




The configuration files mentioned above have a simple format: each line
must contain one unique directory name.
Those names are added to the corresponding path
in their order of appearance in the file. The names can be either absolute
or relative; in the latter case, they are relative to where theses files
are located.



The files ada_source_path and ada_object_path might not be
present in a
GNAT installation, in which case, GNAT will look for its run-time library in
the directories adainclude (for the sources) and adalib (for the
objects and ALI files). When the files exist, the compiler does not
look in adainclude and adalib, and thus the
ada_source_path file
must contain the location for the GNAT run-time sources (which can simply
be adainclude). In the same way, the ada_object_path file must
contain the location for the GNAT run-time objects (which can simply
be adalib).



You can also specify a new default path to the run-time library at compilation
time with the switch --RTS=rts-path. You can thus choose / change
the run-time library you want your program to be compiled with. This switch is
recognized by gcc, gnatmake, gnatbind,
gnatls, gnatfind and gnatxref.



It is possible to install a library before or after the standard GNAT
library, by reordering the lines in the configuration files. In general, a
library must be installed before the GNAT library if it redefines
any part of it.









Previous: Installing a library, Up: General Ada Libraries   [Contents][Index]





3.9.2.3 Using a library




Once again, the project facility greatly simplifies the use of
libraries. In this context, using a library is just a matter of adding a
`with' clause in the user project. For instance, to make use of the
library My_Lib shown in examples in earlier sections, you can
write:





with "my_lib";
project My_Proj is
  ...
end My_Proj;




Even if you have a third-party, non-Ada library, you can still use GNAT’s
Project Manager facility to provide a wrapper for it. For example, the
following project, when `with'ed by your main project, will link with the
third-party library liba.a:





project Liba is
   for Externally_Built use "true";
   for Source_Files use ();
   for Library_Dir use "lib";
   for Library_Name use "a";
   for Library_Kind use "static";
end Liba;




This is an alternative to the use of pragma Linker_Options. It is
especially interesting in the context of systems with several interdependent
static libraries where finding a proper linker order is not easy and best be
left to the tools having visibility over project dependence information.



In order to use an Ada library manually, you need to make sure that this
library is on both your source and object path
(see Search Paths and the Run-Time Library (RTL)
and Search Paths for gnatbind). Furthermore, when the objects are grouped
in an archive or a shared library, you need to specify the desired
library at link time.



For example, you can use the library mylib installed in
/dir/my_lib_src and /dir/my_lib_obj with the following commands:





$ gnatmake -aI/dir/my_lib_src -aO/dir/my_lib_obj my_appl \\
  -largs -lmy_lib




This can be expressed more simply:





$ gnatmake my_appl




when the following conditions are met:






Note that you may also load a library dynamically at
run time given its filename, as illustrated in the GNAT plugins example
in the directory share/examples/gnat/plugins within the GNAT
install area.









Next: , Previous: General Ada Libraries, Up: GNAT and Libraries   [Contents][Index]





3.9.3 Stand-alone Ada Libraries








• Introduction to Stand-alone Libraries:  



• Building a Stand-alone Library:  



• Creating a Stand-alone Library to be used in a non-Ada context:  



• Restrictions in Stand-alone Libraries:  












Next: , Up: Stand-alone Ada Libraries   [Contents][Index]





3.9.3.1 Introduction to Stand-alone Libraries




A Stand-alone Library (abbreviated ’SAL’) is a library that contains the
necessary code to
elaborate the Ada units that are included in the library. In contrast with
an ordinary library, which consists of all sources, objects and ALI
files of the
library, a SAL may specify a restricted subset of compilation units
to serve as a library interface. In this case, the fully
self-sufficient set of files will normally consist of an objects
archive, the sources of interface units’ specs, and the ALI
files of interface units.
If an interface spec contains a generic unit or an inlined subprogram,
the body’s
source must also be provided; if the units that must be provided in the source
form depend on other units, the source and ALI files of those must
also be provided.



The main purpose of a SAL is to minimize the recompilation overhead of client
applications when a new version of the library is installed. Specifically,
if the interface sources have not changed, client applications do not need to
be recompiled. If, furthermore, a SAL is provided in the shared form and its
version, controlled by Library_Version attribute, is not changed,
then the clients do not need to be relinked.



SALs also allow the library providers to minimize the amount of library source
text exposed to the clients.  Such ’information hiding’ might be useful or
necessary for various reasons.



Stand-alone libraries are also well suited to be used in an executable whose
main routine is not written in Ada.









Next: , Previous: Introduction to Stand-alone Libraries, Up: Stand-alone Ada Libraries   [Contents][Index]





3.9.3.2 Building a Stand-alone Library




GNAT’s Project facility provides a simple way of building and installing
stand-alone libraries; see the `Stand-alone Library Projects' section
in the `GNAT Project Manager' chapter of the `GPRbuild User’s Guide'.
To be a Stand-alone Library Project, in addition to the two attributes
that make a project a Library Project (Library_Name and
Library_Dir; see the `Library Projects' section in the
`GNAT Project Manager' chapter of the `GPRbuild User’s Guide'),
the attribute Library_Interface must be defined.  For example:





for Library_Dir use "lib_dir";
for Library_Name use "dummy";
for Library_Interface use ("int1", "int1.child");




Attribute Library_Interface has a non-empty string list value,
each string in the list designating a unit contained in an immediate source
of the project file.



When a Stand-alone Library is built, first the binder is invoked to build
a package whose name depends on the library name
(b~dummy.ads/b in the example above).
This binder-generated package includes initialization and
finalization procedures whose
names depend on the library name (dummyinit and dummyfinal
in the example
above). The object corresponding to this package is included in the library.



You must ensure timely (e.g., prior to any use of interfaces in the SAL)
calling of these procedures if a static SAL is built, or if a shared SAL
is built
with the project-level attribute Library_Auto_Init set to
"false".



For a Stand-Alone Library, only the ALI files of the Interface Units
(those that are listed in attribute Library_Interface) are copied to
the Library Directory. As a consequence, only the Interface Units may be
imported from Ada units outside of the library. If other units are imported,
the binding phase will fail.



It is also possible to build an encapsulated library where not only
the code to elaborate and finalize the library is embedded but also
ensuring that the library is linked only against static
libraries. So an encapsulated library only depends on system
libraries, all other code, including the GNAT runtime, is embedded. To
build an encapsulated library the attribute
Library_Standalone must be set to encapsulated:





for Library_Dir use "lib_dir";
for Library_Name use "dummy";
for Library_Kind use "dynamic";
for Library_Interface use ("int1", "int1.child");
for Library_Standalone use "encapsulated";




The default value for this attribute is standard in which case
a stand-alone library is built.



The attribute Library_Src_Dir may be specified for a
Stand-Alone Library. Library_Src_Dir is a simple attribute that has a
single string value. Its value must be the path (absolute or relative to the
project directory) of an existing directory. This directory cannot be the
object directory or one of the source directories, but it can be the same as
the library directory. The sources of the Interface
Units of the library that are needed by an Ada client of the library will be
copied to the designated directory, called the Interface Copy directory.
These sources include the specs of the Interface Units, but they may also
include bodies and subunits, when pragmas Inline or Inline_Always
are used, or when there is a generic unit in the spec. Before the sources
are copied to the Interface Copy directory, an attempt is made to delete all
files in the Interface Copy directory.



Building stand-alone libraries by hand is somewhat tedious, but for those
occasions when it is necessary here are the steps that you need to perform:






Using SALs is not different from using other libraries
(see Using a library).









Next: , Previous: Building a Stand-alone Library, Up: Stand-alone Ada Libraries   [Contents][Index]





3.9.3.3 Creating a Stand-alone Library to be used in a non-Ada context




It is easy to adapt the SAL build procedure discussed above for use of a SAL in
a non-Ada context.



The only extra step required is to ensure that library interface subprograms
are compatible with the main program, by means of pragma Export
or pragma Convention.



Here is an example of simple library interface for use with C main program:





package My_Package is

   procedure Do_Something;
   pragma Export (C, Do_Something, "do_something");

   procedure Do_Something_Else;
   pragma Export (C, Do_Something_Else, "do_something_else");

end My_Package;




On the foreign language side, you must provide a ’foreign’ view of the
library interface; remember that it should contain elaboration routines in
addition to interface subprograms.



The example below shows the content of mylib_interface.h (note
that there is no rule for the naming of this file, any name can be used)





/* the library elaboration procedure */
extern void mylibinit (void);

/* the library finalization procedure */
extern void mylibfinal (void);

/* the interface exported by the library */
extern void do_something (void);
extern void do_something_else (void);




Libraries built as explained above can be used from any program, provided
that the elaboration procedures (named mylibinit in the previous
example) are called before the library services are used. Any number of
libraries can be used simultaneously, as long as the elaboration
procedure of each library is called.



Below is an example of a C program that uses the mylib library.





#include "mylib_interface.h"

int
main (void)
{
   /* First, elaborate the library before using it */
   mylibinit ();

   /* Main program, using the library exported entities */
   do_something ();
   do_something_else ();

   /* Library finalization at the end of the program */
   mylibfinal ();
   return 0;
}




Note that invoking any library finalization procedure generated by
gnatbind shuts down the Ada run-time environment.
Consequently, the
finalization of all Ada libraries must be performed at the end of the program.
No call to these libraries or to the Ada run-time library should be made
after the finalization phase.



Note also that special care must be taken with multi-tasks
applications. The initialization and finalization routines are not
protected against concurrent access. If such requirement is needed it
must be ensured at the application level using a specific operating
system services like a mutex or a critical-section.









Previous: Creating a Stand-alone Library to be used in a non-Ada context, Up: Stand-alone Ada Libraries   [Contents][Index]





3.9.3.4 Restrictions in Stand-alone Libraries




The pragmas listed below should be used with caution inside libraries,
as they can create incompatibilities with other Ada libraries:






When using a library that contains such pragmas, the user must make sure
that all libraries use the same pragmas with the same values. Otherwise,
Program_Error will
be raised during the elaboration of the conflicting
libraries. The usage of these pragmas and its consequences for the user
should therefore be well documented.



Similarly, the traceback in the exception occurrence mechanism should be
enabled or disabled in a consistent manner across all libraries.
Otherwise, Program_Error will be raised during the elaboration of the
conflicting libraries.



If the Version or Body_Version
attributes are used inside a library, then you need to
perform a gnatbind step that specifies all ALI files in all
libraries, so that version identifiers can be properly computed.
In practice these attributes are rarely used, so this is unlikely
to be a consideration.









Previous: Stand-alone Ada Libraries, Up: GNAT and Libraries   [Contents][Index]





3.9.4 Rebuilding the GNAT Run-Time Library














It may be useful to recompile the GNAT library in various contexts, the
most important one being the use of partition-wide configuration pragmas
such as Normalize_Scalars. A special Makefile called
Makefile.adalib is provided to that effect and can be found in
the directory containing the GNAT library. The location of this
directory depends on the way the GNAT environment has been installed and can
be determined by means of the command:





$ gnatls -v




The last entry in the object search path usually contains the
gnat library. This Makefile contains its own documentation and in
particular the set of instructions needed to rebuild a new library and
to use it.











Next: , Previous: GNAT and Libraries, Up: The GNAT Compilation Model   [Contents][Index]





3.10 Conditional Compilation




This section presents some guidelines for modeling conditional compilation in Ada and describes the
gnatprep preprocessor utility.







• Modeling Conditional Compilation in Ada:  



• Preprocessing with gnatprep:  



• Integrated Preprocessing:  












Next: , Up: Conditional Compilation   [Contents][Index]





3.10.1 Modeling Conditional Compilation in Ada




It is often necessary to arrange for a single source program
to serve multiple purposes, where it is compiled in different
ways to achieve these different goals. Some examples of the
need for this feature are






In C, or C++, the typical approach would be to use the preprocessor
that is defined as part of the language. The Ada language does not
contain such a feature. This is not an oversight, but rather a very
deliberate design decision, based on the experience that overuse of
the preprocessing features in C and C++ can result in programs that
are extremely difficult to maintain. For example, if we have ten
switches that can be on or off, this means that there are a thousand
separate programs, any one of which might not even be syntactically
correct, and even if syntactically correct, the resulting program
might not work correctly. Testing all combinations can quickly become
impossible.



Nevertheless, the need to tailor programs certainly exists, and in
this section we will discuss how this can
be achieved using Ada in general, and GNAT in particular.





• Use of Boolean Constants:  



• Debugging - A Special Case:  



• Conditionalizing Declarations:  



• Use of Alternative Implementations:  



• Preprocessing:  












Next: , Up: Modeling Conditional Compilation in Ada   [Contents][Index]





3.10.1.1 Use of Boolean Constants




In the case where the difference is simply which code
sequence is executed, the cleanest solution is to use Boolean
constants to control which code is executed.





FP_Initialize_Required : constant Boolean := True;
...
if FP_Initialize_Required then
...
end if;




Not only will the code inside the if statement not be executed if
the constant Boolean is False, but it will also be completely
deleted from the program.
However, the code is only deleted after the if statement
has been checked for syntactic and semantic correctness.
(In contrast, with preprocessors the code is deleted before the
compiler ever gets to see it, so it is not checked until the switch
is turned on.)





Typically the Boolean constants will be in a separate package,
something like:





package Config is
   FP_Initialize_Required : constant Boolean := True;
   Reset_Available        : constant Boolean := False;
   ...
end Config;




The Config package exists in multiple forms for the various targets,
with an appropriate script selecting the version of Config needed.
Then any other unit requiring conditional compilation can do a `with'
of Config to make the constants visible.









Next: , Previous: Use of Boolean Constants, Up: Modeling Conditional Compilation in Ada   [Contents][Index]





3.10.1.2 Debugging - A Special Case




A common use of conditional code is to execute statements (for example
dynamic checks, or output of intermediate results) under control of a
debug switch, so that the debugging behavior can be turned on and off.
This can be done using a Boolean constant to control whether the code
is active:





if Debugging then
   Put_Line ("got to the first stage!");
end if;




or





if Debugging and then Temperature > 999.0 then
   raise Temperature_Crazy;
end if;






Since this is a common case, there are special features to deal with
this in a convenient manner. For the case of tests, Ada 2005 has added
a pragma Assert that can be used for such tests. This pragma is modeled
on the Assert pragma that has always been available in GNAT, so this
feature may be used with GNAT even if you are not using Ada 2005 features.
The use of pragma Assert is described in the
GNAT_Reference_Manual, but as an
example, the last test could be written:





pragma Assert (Temperature <= 999.0, "Temperature Crazy");




or simply





pragma Assert (Temperature <= 999.0);




In both cases, if assertions are active and the temperature is excessive,
the exception Assert_Failure will be raised, with the given string in
the first case or a string indicating the location of the pragma in the second
case used as the exception message.





You can turn assertions on and off by using the Assertion_Policy
pragma.





This is an Ada 2005 pragma which is implemented in all modes by
GNAT. Alternatively, you can use the -gnata switch
to enable assertions from the command line, which applies to
all versions of Ada.





For the example above with the Put_Line, the GNAT-specific pragma
Debug can be used:





pragma Debug (Put_Line ("got to the first stage!"));




If debug pragmas are enabled, the argument, which must be of the form of
a procedure call, is executed (in this case, Put_Line will be called).
Only one call can be present, but of course a special debugging procedure
containing any code you like can be included in the program and then
called in a pragma Debug argument as needed.



One advantage of pragma Debug over the if Debugging then
construct is that pragma Debug can appear in declarative contexts,
such as at the very beginning of a procedure, before local declarations have
been elaborated.





Debug pragmas are enabled using either the -gnata switch that also
controls assertions, or with a separate Debug_Policy pragma.



The latter pragma is new in the Ada 2005 versions of GNAT (but it can be used
in Ada 95 and Ada 83 programs as well), and is analogous to
pragma Assertion_Policy to control assertions.



Assertion_Policy and Debug_Policy are configuration pragmas,
and thus they can appear in gnat.adc if you are not using a
project file, or in the file designated to contain configuration pragmas
in a project file.
They then apply to all subsequent compilations. In practice the use of
the -gnata switch is often the most convenient method of controlling
the status of these pragmas.



Note that a pragma is not a statement, so in contexts where a statement
sequence is required, you can’t just write a pragma on its own. You have
to add a null statement.





if ... then
   ... -- some statements
else
   pragma Assert (Num_Cases < 10);
   null;
end if;










Next: , Previous: Debugging - A Special Case, Up: Modeling Conditional Compilation in Ada   [Contents][Index]





3.10.1.3 Conditionalizing Declarations




In some cases it may be necessary to conditionalize declarations to meet
different requirements. For example we might want a bit string whose length
is set to meet some hardware message requirement.



This may be possible using declare blocks controlled
by conditional constants:





if Small_Machine then
   declare
      X : Bit_String (1 .. 10);
   begin
      ...
   end;
else
   declare
      X : Large_Bit_String (1 .. 1000);
   begin
      ...
   end;
end if;




Note that in this approach, both declarations are analyzed by the
compiler so this can only be used where both declarations are legal,
even though one of them will not be used.



Another approach is to define integer constants, e.g., Bits_Per_Word,
or Boolean constants, e.g., Little_Endian, and then write declarations
that are parameterized by these constants. For example





for Rec use
  Field1 at 0 range Boolean'Pos (Little_Endian) * 10 .. Bits_Per_Word;
end record;




If Bits_Per_Word is set to 32, this generates either





for Rec use
  Field1 at 0 range 0 .. 32;
end record;




for the big endian case, or





for Rec use record
    Field1 at 0 range 10 .. 32;
end record;




for the little endian case. Since a powerful subset of Ada expression
notation is usable for creating static constants, clever use of this
feature can often solve quite difficult problems in conditionalizing
compilation (note incidentally that in Ada 95, the little endian
constant was introduced as System.Default_Bit_Order, so you do not
need to define this one yourself).









Next: , Previous: Conditionalizing Declarations, Up: Modeling Conditional Compilation in Ada   [Contents][Index]





3.10.1.4 Use of Alternative Implementations




In some cases, none of the approaches described above are adequate. This
can occur for example if the set of declarations required is radically
different for two different configurations.



In this situation, the official Ada way of dealing with conditionalizing
such code is to write separate units for the different cases. As long as
this does not result in excessive duplication of code, this can be done
without creating maintenance problems. The approach is to share common
code as far as possible, and then isolate the code and declarations
that are different. Subunits are often a convenient method for breaking
out a piece of a unit that is to be conditionalized, with separate files
for different versions of the subunit for different targets, where the
build script selects the right one to give to the compiler.





As an example, consider a situation where a new feature in Ada 2005
allows something to be done in a really nice way. But your code must be able
to compile with an Ada 95 compiler. Conceptually you want to say:





if Ada_2005 then
   ... neat Ada 2005 code
else
   ... not quite as neat Ada 95 code
end if;




where Ada_2005 is a Boolean constant.



But this won’t work when Ada_2005 is set to False,
since the then clause will be illegal for an Ada 95 compiler.
(Recall that although such unreachable code would eventually be deleted
by the compiler, it still needs to be legal.  If it uses features
introduced in Ada 2005, it will be illegal in Ada 95.)



So instead we write





procedure Insert is separate;




Then we have two files for the subunit Insert, with the two sets of
code.
If the package containing this is called File_Queries, then we might
have two files






and the build script renames the appropriate file to file_queries-insert.adb and then carries out the compilation.



This can also be done with project files’ naming schemes. For example:





for body ("File_Queries.Insert") use "file_queries-insert-2005.ada";




Note also that with project files it is desirable to use a different extension
than ads / adb for alternative versions. Otherwise a naming
conflict may arise through another commonly used feature: to declare as part
of the project a set of directories containing all the sources obeying the
default naming scheme.



The use of alternative units is certainly feasible in all situations,
and for example the Ada part of the GNAT run-time is conditionalized
based on the target architecture using this approach. As a specific example,
consider the implementation of the AST feature in VMS. There is one
spec: s-asthan.ads which is the same for all architectures, and three
bodies:






The dummy version s-asthan.adb simply raises exceptions noting that
this operating system feature is not available, and the two remaining
versions interface with the corresponding versions of VMS to provide
VMS-compatible AST handling. The GNAT build script knows the architecture
and operating system, and automatically selects the right version,
renaming it if necessary to s-asthan.adb before the run-time build.



Another style for arranging alternative implementations is through Ada’s
access-to-subprogram facility.
In case some functionality is to be conditionally included,
you can declare an access-to-procedure variable Ref that is initialized
to designate a ’do nothing’ procedure, and then invoke Ref.all
when appropriate.
In some library package, set Ref to Proc'Access for some
procedure Proc that performs the relevant processing.
The initialization only occurs if the library package is included in the
program.
The same idea can also be implemented using tagged types and dispatching
calls.









Previous: Use of Alternative Implementations, Up: Modeling Conditional Compilation in Ada   [Contents][Index]





3.10.1.5 Preprocessing






Although it is quite possible to conditionalize code without the use of
C-style preprocessing, as described earlier in this section, it is
nevertheless convenient in some cases to use the C approach. Moreover,
older Ada compilers have often provided some preprocessing capability,
so legacy code may depend on this approach, even though it is not
standard.



To accommodate such use, GNAT provides a preprocessor (modeled to a large
extent on the various preprocessors that have been used
with legacy code on other compilers, to enable easier transition).





The preprocessor may be used in two separate modes. It can be used quite
separately from the compiler, to generate a separate output source file
that is then fed to the compiler as a separate step. This is the
gnatprep utility, whose use is fully described in
Preprocessing with gnatprep.



The preprocessing language allows such constructs as





#if DEBUG or else (PRIORITY > 4) then
   sequence of declarations
#else
   completely different sequence of declarations
#end if;




The values of the symbols DEBUG and PRIORITY can be
defined either on the command line or in a separate file.



The other way of running the preprocessor is even closer to the C style and
often more convenient. In this approach the preprocessing is integrated into
the compilation process. The compiler is given the preprocessor input which
includes #if lines etc, and then the compiler carries out the
preprocessing internally and processes the resulting output.
For more details on this approach, see Integrated Preprocessing.









Next: , Previous: Modeling Conditional Compilation in Ada, Up: Conditional Compilation   [Contents][Index]





3.10.2 Preprocessing with gnatprep








This section discusses how to use GNAT’s gnatprep utility for simple
preprocessing.
Although designed for use with GNAT, gnatprep does not depend on any
special GNAT features.
For further discussion of conditional compilation in general, see
Conditional Compilation.





• Preprocessing Symbols:  



• Using gnatprep:  



• Switches for gnatprep:  



• Form of Definitions File:  



• Form of Input Text for gnatprep:  












Next: , Up: Preprocessing with gnatprep   [Contents][Index]





3.10.2.1 Preprocessing Symbols




Preprocessing symbols are defined in `definition files' and referenced in the
sources to be preprocessed. A preprocessing symbol is an identifier, following
normal Ada (case-insensitive) rules for its syntax, with the restriction that
all characters need to be in the ASCII set (no accented letters).









Next: , Previous: Preprocessing Symbols, Up: Preprocessing with gnatprep   [Contents][Index]





3.10.2.2 Using gnatprep




To call gnatprep use:





$ gnatprep [ switches ] infile outfile [ deffile ]




where












Next: , Previous: Using gnatprep, Up: Preprocessing with gnatprep   [Contents][Index]





3.10.2.3 Switches for gnatprep









--version




Display Copyright and version, then exit disregarding all other options.











--help




If --version was not used, display usage and then exit disregarding
all other options.











-b




Causes both preprocessor lines and the lines deleted by
preprocessing to be replaced by blank lines in the output source file,
preserving line numbers in the output file.











-c




Causes both preprocessor lines and the lines deleted
by preprocessing to be retained in the output source as comments marked
with the special string "--! ". This option will result in line numbers
being preserved in the output file.











-C




Causes comments to be scanned. Normally comments are ignored by gnatprep.
If this option is specified, then comments are scanned and any $symbol
substitutions performed as in program text. This is particularly useful
when structured comments are used (e.g., for programs written in a
pre-2014 version of the SPARK Ada subset). Note that this switch is not
available when  doing integrated preprocessing (it would be useless in
this context since comments are ignored by the compiler in any case).











-D`symbol'[=`value']




Defines a new preprocessing symbol with the specified value. If no value is given
on the command line, then symbol is considered to be True. This switch
can be used in place of a definition file.











-r




Causes a Source_Reference pragma to be generated that
references the original input file, so that error messages will use
the file name of this original file. The use of this switch implies
that preprocessor lines are not to be removed from the file, so its
use will force -b mode if -c
has not been specified explicitly.



Note that if the file to be preprocessed contains multiple units, then
it will be necessary to gnatchop the output file from
gnatprep. If a Source_Reference pragma is present
in the preprocessed file, it will be respected by
gnatchop -r
so that the final chopped files will correctly refer to the original
input source file for gnatprep.











-s




Causes a sorted list of symbol names and values to be
listed on the standard output file.











-T




Use LF as line terminators when writing files. By default the line terminator
of the host (LF under unix, CR/LF under Windows) is used.











-u




Causes undefined symbols to be treated as having the value FALSE in the context
of a preprocessor test. In the absence of this option, an undefined symbol in
a #if or #elsif test will be treated as an error.











-v




Verbose mode: generates more output about work done.






Note: if neither -b nor -c is present,
then preprocessor lines and
deleted lines are completely removed from the output, unless -r is
specified, in which case -b is assumed.









Next: , Previous: Switches for gnatprep, Up: Preprocessing with gnatprep   [Contents][Index]





3.10.2.4 Form of Definitions File




The definitions file contains lines of the form:





symbol := value




where symbol is a preprocessing symbol, and value is one of the following:






Comment lines may also appear in the definitions file, starting with
the usual --,
and comments may be added to the definitions lines.









Previous: Form of Definitions File, Up: Preprocessing with gnatprep   [Contents][Index]





3.10.2.5 Form of Input Text for gnatprep




The input text may contain preprocessor conditional inclusion lines,
as well as general symbol substitution sequences.



The preprocessor conditional inclusion commands have the form:





#if <expression> [then]
   lines
#elsif <expression> [then]
   lines
#elsif <expression> [then]
   lines
...
#else
   lines
#end if;




In this example, <expression> is defined by the following grammar:





<expression> ::=  <symbol>
<expression> ::=  <symbol> = "<value>"
<expression> ::=  <symbol> = <symbol>
<expression> ::=  <symbol> = <integer>
<expression> ::=  <symbol> > <integer>
<expression> ::=  <symbol> >= <integer>
<expression> ::=  <symbol> < <integer>
<expression> ::=  <symbol> <= <integer>
<expression> ::=  <symbol> 'Defined
<expression> ::=  not <expression>
<expression> ::=  <expression> and <expression>
<expression> ::=  <expression> or <expression>
<expression> ::=  <expression> and then <expression>
<expression> ::=  <expression> or else <expression>
<expression> ::=  ( <expression> )




Note the following restriction: it is not allowed to have "and" or "or"
following "not" in the same expression without parentheses. For example, this
is not allowed:





not X or Y




This can be expressed instead as one of the following forms:





(not X) or Y
not (X or Y)




For the first test (<expression> ::= <symbol>) the symbol must have
either the value true or false, that is to say the right-hand of the
symbol definition must be one of the (case-insensitive) literals
True or False. If the value is true, then the
corresponding lines are included, and if the value is false, they are
excluded.



When comparing a symbol to an integer, the integer is any non negative
literal integer as defined in the Ada Reference Manual, such as 3, 16#FF# or
2#11#. The symbol value must also be a non negative integer. Integer values
in the range 0 .. 2**31-1 are supported.



The test (<expression> ::= <symbol>’Defined) is true only if
the symbol has been defined in the definition file or by a -D
switch on the command line. Otherwise, the test is false.



The equality tests are case insensitive, as are all the preprocessor lines.



If the symbol referenced is not defined in the symbol definitions file,
then the effect depends on whether or not switch -u
is specified. If so, then the symbol is treated as if it had the value
false and the test fails. If this switch is not specified, then
it is an error to reference an undefined symbol. It is also an error to
reference a symbol that is defined with a value other than True
or False.



The use of the not operator inverts the sense of this logical test.
The not operator cannot be combined with the or or and
operators, without parentheses. For example, "if not X or Y then" is not
allowed, but "if (not X) or Y then" and "if not (X or Y) then" are.



The then keyword is optional as shown



The # must be the first non-blank character on a line, but
otherwise the format is free form. Spaces or tabs may appear between
the # and the keyword. The keywords and the symbols are case
insensitive as in normal Ada code. Comments may be used on a
preprocessor line, but other than that, no other tokens may appear on a
preprocessor line. Any number of elsif clauses can be present,
including none at all. The else is optional, as in Ada.



The # marking the start of a preprocessor line must be the first
non-blank character on the line, i.e., it must be preceded only by
spaces or horizontal tabs.



Symbol substitution outside of preprocessor lines is obtained by using
the sequence:





$symbol




anywhere within a source line, except in a comment or within a
string literal. The identifier
following the $ must match one of the symbols defined in the symbol
definition file, and the result is to substitute the value of the
symbol in place of $symbol in the output file.



Note that although the substitution of strings within a string literal
is not possible, it is possible to have a symbol whose defined value is
a string literal. So instead of setting XYZ to hello and writing:





Header : String := "$XYZ";




you should set XYZ to "hello" and write:





Header : String := $XYZ;




and then the substitution will occur as desired.









Previous: Preprocessing with gnatprep, Up: Conditional Compilation   [Contents][Index]





3.10.3 Integrated Preprocessing




As noted above, a file to be preprocessed consists of Ada source code
in which preprocessing lines have been inserted. However,
instead of using gnatprep to explicitly preprocess a file as a separate
step before compilation, you can carry out the preprocessing implicitly
as part of compilation. Such `integrated preprocessing', which is the common
style with C, is performed when either or both of the following switches
are passed to the compiler:











Integrated preprocessing applies only to Ada source files, it is
not available for configuration pragma files.



With integrated preprocessing, the output from the preprocessor is not,
by default, written to any external file. Instead it is passed
internally to the compiler. To preserve the result of
preprocessing in a file, either run gnatprep
in standalone mode or else supply the -gnateG switch
(described below) to the compiler.



When using project files:











Note that the gnatmake switch -m will almost
always trigger recompilation for sources that are preprocessed,
because gnatmake cannot compute the checksum of the source after
preprocessing.



The actual preprocessing function is described in detail in
Preprocessing with gnatprep. This section explains the switches
that relate to integrated preprocessing.








-gnatep=`preprocessor_data_file'




This switch specifies the file name (without directory
information) of the preprocessor data file. Either place this file
in one of the source directories, or, when using project
files, reference the project file’s directory via the
project_name'Project_Dir project attribute; e.g:








project Prj is
   package Compiler is
      for Switches ("Ada") use
        ("-gnatep=" & Prj'Project_Dir & "prep.def");
   end Compiler;
end Prj;






A preprocessor data file is a text file that contains `preprocessor
control lines'.  A preprocessor control line directs the preprocessing of
either a particular source file, or, analogous to others in Ada,
all sources not specified elsewhere in  the preprocessor data file.
A preprocessor control line
can optionally identify a `definition file' that assigns values to
preprocessor symbols, as well as a list of switches that relate to
preprocessing.
Empty lines and comments (using Ada syntax) are also permitted, with no
semantic effect.



Here’s an example of a preprocessor data file:








"toto.adb"  "prep.def" -u
--  Preprocess toto.adb, using definition file prep.def
--  Undefined symbols are treated as False

* -c -DVERSION=V101
--  Preprocess all other sources without using a definition file
--  Suppressed lined are commented
--  Symbol VERSION has the value V101

"tata.adb" "prep2.def" -s
--  Preprocess tata.adb, using definition file prep2.def
--  List all symbols with their values






A preprocessor control line has the following syntax:








<preprocessor_control_line> ::=
   <preprocessor_input> [ <definition_file_name> ] { <switch> }

<preprocessor_input> ::= <source_file_name> | '*'

<definition_file_name> ::= <string_literal>

<source_file_name> := <string_literal>

<switch> := (See below for list)






Thus  each preprocessor control line starts with either a literal string or
the character ’*’:






It is an error to have two lines with the same file name or two
lines starting with the character ’*’.



After the file name or ’*’, an optional literal string specifies the name of
the definition file to be used for preprocessing
(Form of Definitions File). The definition files are found by the
compiler in one of the source directories. In some cases, when compiling
a source in a directory other than the current directory, if the definition
file is in the current directory, it may be necessary to add the current
directory as a source directory through the -I switch; otherwise
the compiler would not find the definition file.



Finally, switches similar to those of gnatprep may optionally appear:






-b




Causes both preprocessor lines and the lines deleted by
preprocessing to be replaced by blank lines, preserving the line number.
This switch is always implied; however, if specified after -c
it cancels the effect of -c.





-c




Causes both preprocessor lines and the lines deleted
by preprocessing to be retained as comments marked
with the special string ’–!’.





-D`symbol'=`new_value'




Define or redefine symbol to have new_value as its value.
The permitted form for symbol is either an Ada identifier, or any Ada reserved word
aside from if,
else, elsif, end, and, or and then.
The permitted form for new_value is a literal string, an Ada identifier or any Ada reserved
word. A symbol declared with this switch replaces a symbol with the
same name defined in a definition file.





-s




Causes a sorted list of symbol names and values to be
listed on the standard output file.





-u




Causes undefined symbols to be treated as having the value FALSE
in the context
of a preprocessor test. In the absence of this option, an undefined symbol in
a #if or #elsif test will be treated as an error.















-gnateD`symbol'[=`new_value']




Define or redefine symbol to have new_value as its value. If no value
is supplied, then the value of symbol is True.
The form of symbol is an identifier, following normal Ada (case-insensitive)
rules for its syntax, and new_value is either an arbitrary string between double
quotes or any sequence (including an empty sequence) of characters from the
set (letters, digits, period, underline).
Ada reserved words may be used as symbols, with the exceptions of if,
else, elsif, end, and, or and then.



Examples:








-gnateDToto=Tata
-gnateDFoo
-gnateDFoo=\"Foo-Bar\"






A symbol declared with this switch on the command line replaces a
symbol with the same name either in a definition file or specified with a
switch -D in the preprocessor data file.



This switch is similar to switch -D of gnatprep.





-gnateG




When integrated preprocessing is performed on source file filename.extension,
create or overwrite filename.extension.prep to contain
the result of the preprocessing.
For example if the source file is foo.adb then
the output file will be foo.adb.prep.












Next: , Previous: Conditional Compilation, Up: The GNAT Compilation Model   [Contents][Index]





3.11 Mixed Language Programming






This section describes how to develop a mixed-language program,
with a focus on combining Ada with C or C++.





• Interfacing to C:  



• Calling Conventions:  



• Building Mixed Ada and C++ Programs:  



• Generating Ada Bindings for C and C++ headers:  



• Generating C Headers for Ada Specifications:  












Next: , Up: Mixed Language Programming   [Contents][Index]





3.11.1 Interfacing to C




Interfacing Ada with a foreign language such as C involves using
compiler directives to import and/or export entity definitions in each
language – using extern statements in C, for instance, and the
Import, Export, and Convention pragmas in Ada.
A full treatment of these topics is provided in Appendix B, section 1
of the Ada Reference Manual.



There are two ways to build a program using GNAT that contains some Ada
sources and some foreign language sources, depending on whether or not
the main subprogram is written in Ada.  Here is a source example with
the main subprogram in Ada:





/* file1.c */
#include <stdio.h>

void print_num (int num)
{
  printf ("num is %d.\\n", num);
  return;
}






/* file2.c */

/* num_from_Ada is declared in my_main.adb */
extern int num_from_Ada;

int get_num (void)
{
  return num_from_Ada;
}






--  my_main.adb
procedure My_Main is

   --  Declare then export an Integer entity called num_from_Ada
   My_Num : Integer := 10;
   pragma Export (C, My_Num, "num_from_Ada");

   --  Declare an Ada function spec for Get_Num, then use
   --  C function get_num for the implementation.
   function Get_Num return Integer;
   pragma Import (C, Get_Num, "get_num");

   --  Declare an Ada procedure spec for Print_Num, then use
   --  C function print_num for the implementation.
   procedure Print_Num (Num : Integer);
   pragma Import (C, Print_Num, "print_num");

begin
   Print_Num (Get_Num);
end My_Main;




To build this example:






The last three steps can be grouped in a single command:





$ gnatmake my_main.adb -largs file1.o file2.o






If the main program is in a language other than Ada, then you may have
more than one entry point into the Ada subsystem. You must use a special
binder option to generate callable routines that initialize and
finalize the Ada units (Binding with Non-Ada Main Programs).
Calls to the initialization and finalization routines must be inserted
in the main program, or some other appropriate point in the code. The
call to initialize the Ada units must occur before the first Ada
subprogram is called, and the call to finalize the Ada units must occur
after the last Ada subprogram returns. The binder will place the
initialization and finalization subprograms into the
b~xxx.adb file where they can be accessed by your C
sources.  To illustrate, we have the following example:





/* main.c */
extern void adainit (void);
extern void adafinal (void);
extern int add (int, int);
extern int sub (int, int);

int main (int argc, char *argv[])
{
   int a = 21, b = 7;

   adainit();

   /* Should print "21 + 7 = 28" */
   printf ("%d + %d = %d\\n", a, b, add (a, b));

   /* Should print "21 - 7 = 14" */
   printf ("%d - %d = %d\\n", a, b, sub (a, b));

   adafinal();
}






--  unit1.ads
package Unit1 is
   function Add (A, B : Integer) return Integer;
   pragma Export (C, Add, "add");
end Unit1;






--  unit1.adb
package body Unit1 is
   function Add (A, B : Integer) return Integer is
   begin
      return A + B;
   end Add;
end Unit1;






--  unit2.ads
package Unit2 is
   function Sub (A, B : Integer) return Integer;
   pragma Export (C, Sub, "sub");
end Unit2;






--  unit2.adb
package body Unit2 is
   function Sub (A, B : Integer) return Integer is
   begin
      return A - B;
   end Sub;
end Unit2;




The build procedure for this application is similar to the last
example’s:






Depending on the circumstances (for example when your non-Ada main object
does not provide symbol main), you may also need to instruct the
GNAT linker not to include the standard startup objects by passing the
-nostartfiles switch to gnatlink.









Next: , Previous: Interfacing to C, Up: Mixed Language Programming   [Contents][Index]





3.11.2 Calling Conventions








GNAT follows standard calling sequence conventions and will thus interface
to any other language that also follows these conventions. The following
Convention identifiers are recognized by GNAT:












Ada




This indicates that the standard Ada calling sequence will be
used and all Ada data items may be passed without any limitations in the
case where GNAT is used to generate both the caller and callee. It is also
possible to mix GNAT generated code and code generated by another Ada
compiler. In this case, the data types should be restricted to simple
cases, including primitive types. Whether complex data types can be passed
depends on the situation. Probably it is safe to pass simple arrays, such
as arrays of integers or floats. Records may or may not work, depending
on whether both compilers lay them out identically. Complex structures
involving variant records, access parameters, tasks, or protected types,
are unlikely to be able to be passed.



Note that in the case of GNAT running
on a platform that supports HP Ada 83, a higher degree of compatibility
can be guaranteed, and in particular records are laid out in an identical
manner in the two compilers. Note also that if output from two different
compilers is mixed, the program is responsible for dealing with elaboration
issues. Probably the safest approach is to write the main program in the
version of Ada other than GNAT, so that it takes care of its own elaboration
requirements, and then call the GNAT-generated adainit procedure to ensure
elaboration of the GNAT components. Consult the documentation of the other
Ada compiler for further details on elaboration.



However, it is not possible to mix the tasking run time of GNAT and
HP Ada 83, All the tasking operations must either be entirely within
GNAT compiled sections of the program, or entirely within HP Ada 83
compiled sections of the program.













Assembler




Specifies assembler as the convention. In practice this has the
same effect as convention Ada (but is not equivalent in the sense of being
considered the same convention).













Asm




Equivalent to Assembler.
















COBOL




Data will be passed according to the conventions described
in section B.4 of the Ada Reference Manual.















C




Data will be passed according to the conventions described
in section B.3 of the Ada Reference Manual.



A note on interfacing to a C ’varargs’ function:












In C, varargs allows a function to take a variable number of
arguments. There is no direct equivalent in this to Ada. One
approach that can be used is to create a C wrapper for each
different profile and then interface to this C wrapper. For
example, to print an int value using printf,
create a C function printfi that takes two arguments, a
pointer to a string and an int, and calls printf.
Then in the Ada program, use pragma Import to
interface to printfi.



It may work on some platforms to directly interface to
a varargs function by providing a specific Ada profile
for a particular call. However, this does not work on
all platforms, since there is no guarantee that the
calling sequence for a two argument normal C function
is the same as for calling a varargs C function with
the same two arguments.















Default




Equivalent to C.













External




Equivalent to C.















C_Plus_Plus (or CPP)




This stands for C++. For most purposes this is identical to C.
See the separate description of the specialized GNAT pragmas relating to
C++ interfacing for further details.















Fortran




Data will be passed according to the conventions described
in section B.5 of the Ada Reference Manual.





Intrinsic




This applies to an intrinsic operation, as defined in the Ada
Reference Manual. If a pragma Import (Intrinsic) applies to a subprogram,
this means that the body of the subprogram is provided by the compiler itself,
usually by means of an efficient code sequence, and that the user does not
supply an explicit body for it. In an application program, the pragma may
be applied to the following sets of names:








  type Distance is new Long_Float;
  type Time     is new Long_Float;
  type Velocity is new Long_Float;
  function "/" (D : Distance; T : Time)
    return Velocity;
  pragma Import (Intrinsic, "/");

This common idiom is often programmed with a generic definition and an
explicit body. The pragma makes it simpler to introduce such declarations.
It incurs no overhead in compilation time or code size, because it is
implemented as a single machine instruction.


















Stdcall




This is relevant only to Windows implementations of GNAT,
and specifies that the Stdcall calling sequence will be used,
as defined by the NT API. Nevertheless, to ease building
cross-platform bindings this convention will be handled as a C calling
convention on non-Windows platforms.













DLL




This is equivalent to Stdcall.













Win32




This is equivalent to Stdcall.













Stubbed




This is a special convention that indicates that the compiler
should provide a stub body that raises Program_Error.






GNAT additionally provides a useful pragma Convention_Identifier
that can be used to parameterize conventions and allow additional synonyms
to be specified. For example if you have legacy code in which the convention
identifier Fortran77 was used for Fortran, you can use the configuration
pragma:





pragma Convention_Identifier (Fortran77, Fortran);




And from now on the identifier Fortran77 may be used as a convention
identifier (for example in an Import pragma) with the same
meaning as Fortran.









Next: , Previous: Calling Conventions, Up: Mixed Language Programming   [Contents][Index]





3.11.3 Building Mixed Ada and C++ Programs




A programmer inexperienced with mixed-language development may find that
building an application containing both Ada and C++ code can be a
challenge.  This section gives a few hints that should make this task easier.





• Interfacing to C++:  



• Linking a Mixed C++ & Ada Program:  



• A Simple Example:  



• Interfacing with C++ constructors:  



• Interfacing with C++ at the Class Level:  












Next: , Up: Building Mixed Ada and C++ Programs   [Contents][Index]





3.11.3.1 Interfacing to C++




GNAT supports interfacing with the G++ compiler (or any C++ compiler
generating code that is compatible with the G++ Application Binary
Interface —see ‘http://www.codesourcery.com/archives/cxx-abi’).



Interfacing can be done at 3 levels: simple data, subprograms, and
classes. In the first two cases, GNAT offers a specific Convention C_Plus_Plus
(or CPP) that behaves exactly like Convention C.
Usually, C++ mangles the names of subprograms. To generate proper mangled
names automatically, see Generating Ada Bindings for C and C++ headers).
This problem can also be addressed manually in two ways:






Interfacing at the class level can be achieved by using the GNAT specific
pragmas such as CPP_Constructor.  See the GNAT_Reference_Manual for additional information.









Next: , Previous: Interfacing to C++, Up: Building Mixed Ada and C++ Programs   [Contents][Index]





3.11.3.2 Linking a Mixed C++ & Ada Program




Usually the linker of the C++ development system must be used to link
mixed applications because most C++ systems will resolve elaboration
issues (such as calling constructors on global class instances)
transparently during the link phase. GNAT has been adapted to ease the
use of a foreign linker for the last phase. Three cases can be
considered:






Another alternative is to use the gprbuild multi-language builder
which has a large knowledge base and knows how to link Ada and C++ code
together automatically in most cases.









Next: , Previous: Linking a Mixed C++ & Ada Program, Up: Building Mixed Ada and C++ Programs   [Contents][Index]





3.11.3.3 A Simple Example




The following example, provided as part of the GNAT examples, shows how
to achieve procedural interfacing between Ada and C++ in both
directions. The C++ class A has two methods. The first method is exported
to Ada by the means of an extern C wrapper function. The second method
calls an Ada subprogram. On the Ada side, The C++ calls are modelled by
a limited record with a layout comparable to the C++ class. The Ada
subprogram, in turn, calls the C++ method. So, starting from the C++
main program, the process passes back and forth between the two
languages.



Here are the compilation commands:





$ gnatmake -c simple_cpp_interface
$ g++ -c cpp_main.C
$ g++ -c ex7.C
$ gnatbind -n simple_cpp_interface
$ gnatlink simple_cpp_interface -o cpp_main --LINK=g++ -lstdc++ ex7.o cpp_main.o




Here are the corresponding sources:





//cpp_main.C

#include "ex7.h"

extern "C" {
  void adainit (void);
  void adafinal (void);
  void method1 (A *t);
}

void method1 (A *t)
{
  t->method1 ();
}

int main ()
{
  A obj;
  adainit ();
  obj.method2 (3030);
  adafinal ();
}






//ex7.h

class Origin {
 public:
  int o_value;
};
class A : public Origin {
 public:
  void method1 (void);
  void method2 (int v);
  A();
  int   a_value;
};






//ex7.C

#include "ex7.h"
#include <stdio.h>

extern "C" { void ada_method2 (A *t, int v);}

void A::method1 (void)
{
  a_value = 2020;
  printf ("in A::method1, a_value = %d \\n",a_value);
}

void A::method2 (int v)
{
   ada_method2 (this, v);
   printf ("in A::method2, a_value = %d \\n",a_value);
}

A::A(void)
{
   a_value = 1010;
  printf ("in A::A, a_value = %d \\n",a_value);
}






-- simple_cpp_interface.ads
with System;
package Simple_Cpp_Interface is
   type A is limited
      record
         Vptr    : System.Address;
         O_Value : Integer;
         A_Value : Integer;
      end record;
   pragma Convention (C, A);

   procedure Method1 (This : in out A);
   pragma Import (C, Method1);

   procedure Ada_Method2 (This : in out A; V : Integer);
   pragma Export (C, Ada_Method2);

end Simple_Cpp_Interface;






-- simple_cpp_interface.adb
package body Simple_Cpp_Interface is

   procedure Ada_Method2 (This : in out A; V : Integer) is
   begin
      Method1 (This);
      This.A_Value := V;
   end Ada_Method2;

end Simple_Cpp_Interface;










Next: , Previous: A Simple Example, Up: Building Mixed Ada and C++ Programs   [Contents][Index]





3.11.3.4 Interfacing with C++ constructors




In order to interface with C++ constructors GNAT provides the
pragma CPP_Constructor (see the GNAT_Reference_Manual
for additional information).
In this section we present some common uses of C++ constructors
in mixed-languages programs in GNAT.



Let us assume that we need to interface with the following
C++ class:





class Root {
public:
  int  a_value;
  int  b_value;
  virtual int Get_Value ();
  Root();              // Default constructor
  Root(int v);         // 1st non-default constructor
  Root(int v, int w);  // 2nd non-default constructor
};




For this purpose we can write the following package spec (further
information on how to build this spec is available in
Interfacing with C++ at the Class Level and
Generating Ada Bindings for C and C++ headers).





with Interfaces.C; use Interfaces.C;
package Pkg_Root is
  type Root is tagged limited record
     A_Value : int;
     B_Value : int;
  end record;
  pragma Import (CPP, Root);

  function Get_Value (Obj : Root) return int;
  pragma Import (CPP, Get_Value);

  function Constructor return Root;
  pragma Cpp_Constructor (Constructor, "_ZN4RootC1Ev");

  function Constructor (v : Integer) return Root;
  pragma Cpp_Constructor (Constructor, "_ZN4RootC1Ei");

  function Constructor (v, w : Integer) return Root;
  pragma Cpp_Constructor (Constructor, "_ZN4RootC1Eii");
end Pkg_Root;




On the Ada side the constructor is represented by a function (whose
name is arbitrary) that returns the classwide type corresponding to
the imported C++ class. Although the constructor is described as a
function, it is typically a procedure with an extra implicit argument
(the object being initialized) at the implementation level. GNAT
issues the appropriate call, whatever it is, to get the object
properly initialized.



Constructors can only appear in the following contexts:






In a declaration of an object whose type is a class imported from C++,
either the default C++ constructor is implicitly called by GNAT, or
else the required C++ constructor must be explicitly called in the
expression that initializes the object. For example:





Obj1 : Root;
Obj2 : Root := Constructor;
Obj3 : Root := Constructor (v => 10);
Obj4 : Root := Constructor (30, 40);




The first two declarations are equivalent: in both cases the default C++
constructor is invoked (in the former case the call to the constructor is
implicit, and in the latter case the call is explicit in the object
declaration). Obj3 is initialized by the C++ non-default constructor
that takes an integer argument, and Obj4 is initialized by the
non-default C++ constructor that takes two integers.



Let us derive the imported C++ class in the Ada side. For example:





type DT is new Root with record
   C_Value : Natural := 2009;
end record;




In this case the components DT inherited from the C++ side must be
initialized by a C++ constructor, and the additional Ada components
of type DT are initialized by GNAT. The initialization of such an
object is done either by default, or by means of a function returning
an aggregate of type DT, or by means of an extension aggregate.





Obj5 : DT;
Obj6 : DT := Function_Returning_DT (50);
Obj7 : DT := (Constructor (30,40) with C_Value => 50);




The declaration of Obj5 invokes the default constructors: the
C++ default constructor of the parent type takes care of the initialization
of the components inherited from Root, and GNAT takes care of the default
initialization of the additional Ada components of type DT (that is,
C_Value is initialized to value 2009). The order of invocation of
the constructors is consistent with the order of elaboration required by
Ada and C++. That is, the constructor of the parent type is always called
before the constructor of the derived type.



Let us now consider a record that has components whose type is imported
from C++. For example:





type Rec1 is limited record
   Data1 : Root := Constructor (10);
   Value : Natural := 1000;
end record;

type Rec2 (D : Integer := 20) is limited record
   Rec   : Rec1;
   Data2 : Root := Constructor (D, 30);
end record;




The initialization of an object of type Rec2 will call the
non-default C++ constructors specified for the imported components.
For example:





Obj8 : Rec2 (40);




Using Ada 2005 we can use limited aggregates to initialize an object
invoking C++ constructors that differ from those specified in the type
declarations. For example:





Obj9 : Rec2 := (Rec => (Data1 => Constructor (15, 16),
                        others => <>),
                others => <>);




The above declaration uses an Ada 2005 limited aggregate to
initialize Obj9, and the C++ constructor that has two integer
arguments is invoked to initialize the Data1 component instead
of the constructor specified in the declaration of type Rec1. In
Ada 2005 the box in the aggregate indicates that unspecified components
are initialized using the expression (if any) available in the component
declaration. That is, in this case discriminant D is initialized
to value 20, Value is initialized to value 1000, and the
non-default C++ constructor that handles two integers takes care of
initializing component Data2 with values 20,30.



In Ada 2005 we can use the extended return statement to build the Ada
equivalent to C++ non-default constructors. For example:





function Constructor (V : Integer) return Rec2 is
begin
   return Obj : Rec2 := (Rec => (Data1  => Constructor (V, 20),
                                 others => <>),
                         others => <>) do
      --  Further actions required for construction of
      --  objects of type Rec2
      ...
   end record;
end Constructor;




In this example the extended return statement construct is used to
build in place the returned object whose components are initialized
by means of a limited aggregate. Any further action associated with
the constructor can be placed inside the construct.









Previous: Interfacing with C++ constructors, Up: Building Mixed Ada and C++ Programs   [Contents][Index]





3.11.3.5 Interfacing with C++ at the Class Level




In this section we demonstrate the GNAT features for interfacing with
C++ by means of an example making use of Ada 2005 abstract interface
types. This example consists of a classification of animals; classes
have been used to model our main classification of animals, and
interfaces provide support for the management of secondary
classifications. We first demonstrate a case in which the types and
constructors are defined on the C++ side and imported from the Ada
side, and latter the reverse case.



The root of our derivation will be the Animal class, with a
single private attribute (the Age of the animal), a constructor,
and two public primitives to set and get the value of this attribute.





class Animal {
 public:
   virtual void Set_Age (int New_Age);
   virtual int Age ();
   Animal() {Age_Count = 0;};
 private:
   int Age_Count;
};




Abstract interface types are defined in C++ by means of classes with pure
virtual functions and no data members. In our example we will use two
interfaces that provide support for the common management of Carnivore
and Domestic animals:





class Carnivore {
public:
   virtual int Number_Of_Teeth () = 0;
};

class Domestic {
public:
   virtual void Set_Owner (char* Name) = 0;
};




Using these declarations, we can now say that a Dog is an animal that is
both Carnivore and Domestic, that is:





class Dog : Animal, Carnivore, Domestic {
 public:
   virtual int  Number_Of_Teeth ();
   virtual void Set_Owner (char* Name);

   Dog(); // Constructor
 private:
   int  Tooth_Count;
   char *Owner;
};




In the following examples we will assume that the previous declarations are
located in a file named animals.h. The following package demonstrates
how to import these C++ declarations from the Ada side:





with Interfaces.C.Strings; use Interfaces.C.Strings;
package Animals is
  type Carnivore is limited interface;
  pragma Convention (C_Plus_Plus, Carnivore);
  function Number_Of_Teeth (X : Carnivore)
     return Natural is abstract;

  type Domestic is limited interface;
  pragma Convention (C_Plus_Plus, Domestic);
  procedure Set_Owner
    (X    : in out Domestic;
     Name : Chars_Ptr) is abstract;

  type Animal is tagged limited record
    Age : Natural;
  end record;
  pragma Import (C_Plus_Plus, Animal);

  procedure Set_Age (X : in out Animal; Age : Integer);
  pragma Import (C_Plus_Plus, Set_Age);

  function Age (X : Animal) return Integer;
  pragma Import (C_Plus_Plus, Age);

  function New_Animal return Animal;
  pragma CPP_Constructor (New_Animal);
  pragma Import (CPP, New_Animal, "_ZN6AnimalC1Ev");

  type Dog is new Animal and Carnivore and Domestic with record
    Tooth_Count : Natural;
    Owner       : Chars_Ptr;
  end record;
  pragma Import (C_Plus_Plus, Dog);

  function Number_Of_Teeth (A : Dog) return Natural;
  pragma Import (C_Plus_Plus, Number_Of_Teeth);

  procedure Set_Owner (A : in out Dog; Name : Chars_Ptr);
  pragma Import (C_Plus_Plus, Set_Owner);

  function New_Dog return Dog;
  pragma CPP_Constructor (New_Dog);
  pragma Import (CPP, New_Dog, "_ZN3DogC2Ev");
end Animals;




Thanks to the compatibility between GNAT run-time structures and the C++ ABI,
interfacing with these C++ classes is easy. The only requirement is that all
the primitives and components must be declared exactly in the same order in
the two languages.



Regarding the abstract interfaces, we must indicate to the GNAT compiler by
means of a pragma Convention (C_Plus_Plus), the convention used to pass
the arguments to the called primitives will be the same as for C++. For the
imported classes we use pragma Import with convention C_Plus_Plus
to indicate that they have been defined on the C++ side; this is required
because the dispatch table associated with these tagged types will be built
in the C++ side and therefore will not contain the predefined Ada primitives
which Ada would otherwise expect.



As the reader can see there is no need to indicate the C++ mangled names
associated with each subprogram because it is assumed that all the calls to
these primitives will be dispatching calls. The only exception is the
constructor, which must be registered with the compiler by means of
pragma CPP_Constructor and needs to provide its associated C++
mangled name because the Ada compiler generates direct calls to it.



With the above packages we can now declare objects of type Dog on the Ada side
and dispatch calls to the corresponding subprograms on the C++ side. We can
also extend the tagged type Dog with further fields and primitives, and
override some of its C++ primitives on the Ada side. For example, here we have
a type derivation defined on the Ada side that inherits all the dispatching
primitives of the ancestor from the C++ side.





with Animals; use Animals;
package Vaccinated_Animals is
  type Vaccinated_Dog is new Dog with null record;
  function Vaccination_Expired (A : Vaccinated_Dog) return Boolean;
end Vaccinated_Animals;




It is important to note that, because of the ABI compatibility, the programmer
does not need to add any further information to indicate either the object
layout or the dispatch table entry associated with each dispatching operation.



Now let us define all the types and constructors on the Ada side and export
them to C++, using the same hierarchy of our previous example:





with Interfaces.C.Strings;
use Interfaces.C.Strings;
package Animals is
  type Carnivore is limited interface;
  pragma Convention (C_Plus_Plus, Carnivore);
  function Number_Of_Teeth (X : Carnivore)
     return Natural is abstract;

  type Domestic is limited interface;
  pragma Convention (C_Plus_Plus, Domestic);
  procedure Set_Owner
    (X    : in out Domestic;
     Name : Chars_Ptr) is abstract;

  type Animal is tagged record
    Age : Natural;
  end record;
  pragma Convention (C_Plus_Plus, Animal);

  procedure Set_Age (X : in out Animal; Age : Integer);
  pragma Export (C_Plus_Plus, Set_Age);

  function Age (X : Animal) return Integer;
  pragma Export (C_Plus_Plus, Age);

  function New_Animal return Animal'Class;
  pragma Export (C_Plus_Plus, New_Animal);

  type Dog is new Animal and Carnivore and Domestic with record
    Tooth_Count : Natural;
    Owner       : String (1 .. 30);
  end record;
  pragma Convention (C_Plus_Plus, Dog);

  function Number_Of_Teeth (A : Dog) return Natural;
  pragma Export (C_Plus_Plus, Number_Of_Teeth);

  procedure Set_Owner (A : in out Dog; Name : Chars_Ptr);
  pragma Export (C_Plus_Plus, Set_Owner);

  function New_Dog return Dog'Class;
  pragma Export (C_Plus_Plus, New_Dog);
end Animals;




Compared with our previous example the only differences are the use of
pragma Convention (instead of pragma Import), and the use of
pragma Export to indicate to the GNAT compiler that the primitives will
be available to C++. Thanks to the ABI compatibility, on the C++ side there is
nothing else to be done; as explained above, the only requirement is that all
the primitives and components are declared in exactly the same order.



For completeness, let us see a brief C++ main program that uses the
declarations available in animals.h (presented in our first example) to
import and use the declarations from the Ada side, properly initializing and
finalizing the Ada run-time system along the way:





#include "animals.h"
#include <iostream>
using namespace std;

void Check_Carnivore (Carnivore *obj) {...}
void Check_Domestic (Domestic *obj)   {...}
void Check_Animal (Animal *obj)       {...}
void Check_Dog (Dog *obj)             {...}

extern "C" {
  void adainit (void);
  void adafinal (void);
  Dog* new_dog ();
}

void test ()
{
  Dog *obj = new_dog();  // Ada constructor
  Check_Carnivore (obj); // Check secondary DT
  Check_Domestic (obj);  // Check secondary DT
  Check_Animal (obj);    // Check primary DT
  Check_Dog (obj);       // Check primary DT
}

int main ()
{
  adainit ();  test();  adafinal ();
  return 0;
}










Next: , Previous: Building Mixed Ada and C++ Programs, Up: Mixed Language Programming   [Contents][Index]





3.11.4 Generating Ada Bindings for C and C++ headers










GNAT includes a binding generator for C and C++ headers which is
intended to do 95% of the tedious work of generating Ada specs from C
or C++ header files.



Note that this capability is not intended to generate 100% correct Ada specs,
and will is some cases require manual adjustments, although it can often
be used out of the box in practice.



Some of the known limitations include:






The code is generated using Ada 2012 syntax, which makes it easier to interface
with other languages. In most cases you can still use the generated binding
even if your code is compiled using earlier versions of Ada (e.g. -gnat95).





• Running the Binding Generator:  



• Generating Bindings for C++ Headers:  



• Switches:  












Next: , Up: Generating Ada Bindings for C and C++ headers   [Contents][Index]





3.11.4.1 Running the Binding Generator




The binding generator is part of the gcc compiler and can be
invoked via the -fdump-ada-spec switch, which will generate Ada
spec files for the header files specified on the command line, and all
header files needed by these files transitively. For example:





$ g++ -c -fdump-ada-spec -C /usr/include/time.h
$ gcc -c *.ads




will generate, under GNU/Linux, the following files: time_h.ads,
bits_time_h.ads, stddef_h.ads, bits_types_h.ads which
correspond to the files /usr/include/time.h,
/usr/include/bits/time.h, etc..., and will then compile these Ada specs
in Ada 2005 mode.



The -C switch tells gcc to extract comments from headers,
and will attempt to generate corresponding Ada comments.



If you want to generate a single Ada file and not the transitive closure, you
can use instead the -fdump-ada-spec-slim switch.



You can optionally specify a parent unit, of which all generated units will
be children, using -fada-spec-parent=`unit'.



Note that we recommend when possible to use the `g++' driver to
generate bindings, even for most C headers, since this will in general
generate better Ada specs. For generating bindings for C++ headers, it is
mandatory to use the `g++' command, or `gcc -x c++' which
is equivalent in this case. If `g++' cannot work on your C headers
because of incompatibilities between C and C++, then you can fallback to
gcc instead.



For an example of better bindings generated from the C++ front-end,
the name of the parameters (when available) are actually ignored by the C
front-end. Consider the following C header:





extern void foo (int variable);




with the C front-end, variable is ignored, and the above is handled as:





extern void foo (int);




generating a generic:





procedure foo (param1 : int);




with the C++ front-end, the name is available, and we generate:





procedure foo (variable : int);




In some cases, the generated bindings will be more complete or more meaningful
when defining some macros, which you can do via the -D switch. This
is for example the case with Xlib.h under GNU/Linux:





$ g++ -c -fdump-ada-spec -DXLIB_ILLEGAL_ACCESS -C /usr/include/X11/Xlib.h




The above will generate more complete bindings than a straight call without
the -DXLIB_ILLEGAL_ACCESS switch.



In other cases, it is not possible to parse a header file in a stand-alone
manner, because other include files need to be included first. In this
case, the solution is to create a small header file including the needed
#include and possible #define directives. For example, to
generate Ada bindings for readline/readline.h, you need to first
include stdio.h, so you can create a file with the following two
lines in e.g. readline1.h:





#include <stdio.h>
#include <readline/readline.h>




and then generate Ada bindings from this file:





$ g++ -c -fdump-ada-spec readline1.h










Next: , Previous: Running the Binding Generator, Up: Generating Ada Bindings for C and C++ headers   [Contents][Index]





3.11.4.2 Generating Bindings for C++ Headers




Generating bindings for C++ headers is done using the same options, always
with the `g++' compiler. Note that generating Ada spec from C++ headers is a
much more complex job and support for C++ headers is much more limited that
support for C headers. As a result, you will need to modify the resulting
bindings by hand more extensively when using C++ headers.



In this mode, C++ classes will be mapped to Ada tagged types, constructors
will be mapped using the CPP_Constructor pragma, and when possible,
multiple inheritance of abstract classes will be mapped to Ada interfaces
(see the `Interfacing to C++' section in the GNAT Reference Manual
for additional information on interfacing to C++).



For example, given the following C++ header file:





class Carnivore {
public:
   virtual int Number_Of_Teeth () = 0;
};

class Domestic {
public:
   virtual void Set_Owner (char* Name) = 0;
};

class Animal {
public:
  int Age_Count;
  virtual void Set_Age (int New_Age);
};

class Dog : Animal, Carnivore, Domestic {
 public:
  int  Tooth_Count;
  char *Owner;

  virtual int  Number_Of_Teeth ();
  virtual void Set_Owner (char* Name);

  Dog();
};




The corresponding Ada code is generated:





package Class_Carnivore is
  type Carnivore is limited interface;
  pragma Import (CPP, Carnivore);

  function Number_Of_Teeth (this : access Carnivore) return int is abstract;
end;
use Class_Carnivore;

package Class_Domestic is
  type Domestic is limited interface;
  pragma Import (CPP, Domestic);

  procedure Set_Owner
    (this : access Domestic;
     Name : Interfaces.C.Strings.chars_ptr) is abstract;
end;
use Class_Domestic;

package Class_Animal is
  type Animal is tagged limited record
    Age_Count : aliased int;
  end record;
  pragma Import (CPP, Animal);

  procedure Set_Age (this : access Animal; New_Age : int);
  pragma Import (CPP, Set_Age, "_ZN6Animal7Set_AgeEi");
end;
use Class_Animal;

package Class_Dog is
  type Dog is new Animal and Carnivore and Domestic with record
    Tooth_Count : aliased int;
    Owner : Interfaces.C.Strings.chars_ptr;
  end record;
  pragma Import (CPP, Dog);

  function Number_Of_Teeth (this : access Dog) return int;
  pragma Import (CPP, Number_Of_Teeth, "_ZN3Dog15Number_Of_TeethEv");

  procedure Set_Owner
    (this : access Dog; Name : Interfaces.C.Strings.chars_ptr);
  pragma Import (CPP, Set_Owner, "_ZN3Dog9Set_OwnerEPc");

  function New_Dog return Dog;
  pragma CPP_Constructor (New_Dog);
  pragma Import (CPP, New_Dog, "_ZN3DogC1Ev");
end;
use Class_Dog;










Previous: Generating Bindings for C++ Headers, Up: Generating Ada Bindings for C and C++ headers   [Contents][Index]





3.11.4.3 Switches









-fdump-ada-spec




Generate Ada spec files for the given header files transitively (including
all header files that these headers depend upon).











-fdump-ada-spec-slim




Generate Ada spec files for the header files specified on the command line
only.











-fada-spec-parent=`unit'




Specifies that all files generated by -fdump-ada-spec are
to be child units of the specified parent unit.











-C




Extract comments from headers and generate Ada comments in the Ada spec files.












Previous: Generating Ada Bindings for C and C++ headers, Up: Mixed Language Programming   [Contents][Index]





3.11.5 Generating C Headers for Ada Specifications








GNAT includes a C header generator for Ada specifications which supports
Ada types that have a direct mapping to C types. This includes in particular
support for:








• Running the C Header Generator:  












Up: Generating C Headers for Ada Specifications   [Contents][Index]





3.11.5.1 Running the C Header Generator




The C header generator is part of the GNAT compiler and can be invoked via
the -gnatceg combination of switches, which will generate a .h
file corresponding to the given input file (Ada spec or body). Note that
only spec files are processed in any case, so giving a spec or a body file
as input is equivalent. For example:





$ gcc -c -gnatceg pack1.ads




will generate a self-contained file called pack1.h including
common definitions from the Ada Standard package, followed by the
definitions included in pack1.ads, as well as all the other units
withed by this file.



For instance, given the following Ada files:





package Pack2 is
   type Int is range 1 .. 10;
end Pack2;






with Pack2;

package Pack1 is
   type Rec is record
      Field1, Field2 : Pack2.Int;
   end record;

   Global : Rec := (1, 2);

   procedure Proc1 (R : Rec);
   procedure Proc2 (R : in out Rec);
end Pack1;




The above gcc command will generate the following pack1.h file:





/* Standard definitions skipped */
#ifndef PACK2_ADS
#define PACK2_ADS
typedef short_short_integer pack2__TintB;
typedef pack2__TintB pack2__int;
#endif /* PACK2_ADS */

#ifndef PACK1_ADS
#define PACK1_ADS
typedef struct _pack1__rec {
  pack2__int field1;
  pack2__int field2;
} pack1__rec;
extern pack1__rec pack1__global;
extern void pack1__proc1(const pack1__rec r);
extern void pack1__proc2(pack1__rec *r);
#endif /* PACK1_ADS */




You can then include pack1.h from a C source file and use the types,
call subprograms, reference objects, and constants.









Next: , Previous: Mixed Language Programming, Up: The GNAT Compilation Model   [Contents][Index]





3.12 GNAT and Other Compilation Models




This section compares the GNAT model with the approaches taken in
other environents, first the C/C++ model and then the mechanism that
has been used in other Ada systems, in particular those traditionally
used for Ada 83.





• Comparison between GNAT and C/C++ Compilation Models:  



• Comparison between GNAT and Conventional Ada Library Models:  












Next: , Up: GNAT and Other Compilation Models   [Contents][Index]





3.12.1 Comparison between GNAT and C/C++ Compilation Models




The GNAT model of compilation is close to the C and C++ models. You can
think of Ada specs as corresponding to header files in C. As in C, you
don’t need to compile specs; they are compiled when they are used. The
Ada `with' is similar in effect to the #include of a C
header.



One notable difference is that, in Ada, you may compile specs separately
to check them for semantic and syntactic accuracy. This is not always
possible with C headers because they are fragments of programs that have
less specific syntactic or semantic rules.



The other major difference is the requirement for running the binder,
which performs two important functions. First, it checks for
consistency. In C or C++, the only defense against assembling
inconsistent programs lies outside the compiler, in a makefile, for
example. The binder satisfies the Ada requirement that it be impossible
to construct an inconsistent program when the compiler is used in normal
mode.





The other important function of the binder is to deal with elaboration
issues. There are also elaboration issues in C++ that are handled
automatically. This automatic handling has the advantage of being
simpler to use, but the C++ programmer has no control over elaboration.
Where gnatbind might complain there was no valid order of
elaboration, a C++ compiler would simply construct a program that
malfunctioned at run time.









Previous: Comparison between GNAT and C/C++ Compilation Models, Up: GNAT and Other Compilation Models   [Contents][Index]





3.12.2 Comparison between GNAT and Conventional Ada Library Models




This section is intended for Ada programmers who have
used an Ada compiler implementing the traditional Ada library
model, as described in the Ada Reference Manual.





In GNAT, there is no ’library’ in the normal sense. Instead, the set of
source files themselves acts as the library. Compiling Ada programs does
not generate any centralized information, but rather an object file and
a ALI file, which are of interest only to the binder and linker.
In a traditional system, the compiler reads information not only from
the source file being compiled, but also from the centralized library.
This means that the effect of a compilation depends on what has been
previously compiled. In particular:






In GNAT, compiling one unit never affects the compilation of any other
units because the compiler reads only source files. Only changes to source
files can affect the results of a compilation. In particular:






The most important result of these differences is that order of compilation
is never significant in GNAT. There is no situation in which one is
required to do one compilation before another. What shows up as order of
compilation requirements in the traditional Ada library becomes, in
GNAT, simple source dependencies; in other words, there is only a set
of rules saying what source files must be present when a file is
compiled.









Previous: GNAT and Other Compilation Models, Up: The GNAT Compilation Model   [Contents][Index]





3.13 Using GNAT Files with External Tools




This section explains how files that are produced by GNAT may be
used with tools designed for other languages.





• Using Other Utility Programs with GNAT:  



• The External Symbol Naming Scheme of GNAT:  












Next: , Up: Using GNAT Files with External Tools   [Contents][Index]





3.13.1 Using Other Utility Programs with GNAT




The object files generated by GNAT are in standard system format and in
particular the debugging information uses this format. This means
programs generated by GNAT can be used with existing utilities that
depend on these formats.



In general, any utility program that works with C will also often work with
Ada programs generated by GNAT. This includes software utilities such as
gprof (a profiling program), gdb (the FSF debugger), and utilities such
as Purify.









Previous: Using Other Utility Programs with GNAT, Up: Using GNAT Files with External Tools   [Contents][Index]





3.13.2 The External Symbol Naming Scheme of GNAT




In order to interpret the output from GNAT, when using tools that are
originally intended for use with other languages, it is useful to
understand the conventions used to generate link names from the Ada
entity names.



All link names are in all lowercase letters. With the exception of library
procedure names, the mechanism used is simply to use the full expanded
Ada name with dots replaced by double underscores. For example, suppose
we have the following package spec:





package QRS is
   MN : Integer;
end QRS;






The variable MN has a full expanded Ada name of QRS.MN, so
the corresponding link name is qrs__mn.
Of course if a pragma Export is used this may be overridden:





package Exports is
   Var1 : Integer;
   pragma Export (Var1, C, External_Name => "var1_name");
   Var2 : Integer;
   pragma Export (Var2, C, Link_Name => "var2_link_name");
end Exports;




In this case, the link name for Var1 is whatever link name the
C compiler would assign for the C function var1_name. This typically
would be either var1_name or _var1_name, depending on operating
system conventions, but other possibilities exist. The link name for
Var2 is var2_link_name, and this is not operating system
dependent.



One exception occurs for library level procedures. A potential ambiguity
arises between the required name _main for the C main program,
and the name we would otherwise assign to an Ada library level procedure
called Main (which might well not be the main program).



To avoid this ambiguity, we attach the prefix _ada_ to such
names. So if we have a library level procedure such as:





procedure Hello (S : String);




the external name of this procedure will be _ada_hello.










Next: , Previous: The GNAT Compilation Model, Up: Top   [Contents][Index]





4 Building Executable Programs with GNAT




This chapter describes first the gnatmake tool
(Building with gnatmake),
which automatically determines the set of sources
needed by an Ada compilation unit and executes the necessary
(re)compilations, binding and linking.
It also explains how to use each tool individually: the
compiler (gcc, see Compiling with gcc),
binder (gnatbind, see Binding with gnatbind),
and linker (gnatlink, see Linking with gnatlink)
to build executable programs.
Finally, this chapter provides examples of
how to make use of the general GNU make mechanism
in a GNAT context (see Using the GNU make Utility).






• Building with gnatmake:  



• Compiling with gcc:  



• Compiler Switches:  



• Linker Switches:  



• Binding with gnatbind:  



• Linking with gnatlink:  



• Using the GNU make Utility:  












Next: , Up: Building Executable Programs with GNAT   [Contents][Index]





4.1 Building with gnatmake






A typical development cycle when working on an Ada program consists of
the following steps:




    

  1.  Edit some sources to fix bugs;


  2.  Add enhancements;


  3.  Compile all sources affected;


  4.  Rebind and relink; and


  5.  Test.






The third step in particular can be tricky, because not only do the modified
files have to be compiled, but any files depending on these files must also be
recompiled. The dependency rules in Ada can be quite complex, especially
in the presence of overloading, use clauses, generics and inlined
subprograms.



gnatmake automatically takes care of the third and fourth steps
of this process. It determines which sources need to be compiled,
compiles them, and binds and links the resulting object files.



Unlike some other Ada make programs, the dependencies are always
accurately recomputed from the new sources. The source based approach of
the GNAT compilation model makes this possible. This means that if
changes to the source program cause corresponding changes in
dependencies, they will always be tracked exactly correctly by
gnatmake.



Note that for advanced forms of project structure, we recommend creating
a project file as explained in the `GNAT_Project_Manager' chapter in the
`GPRbuild User’s Guide', and using the
gprbuild tool which supports building with project files and works similarly
to gnatmake.





• Running gnatmake:  



• Switches for gnatmake:  



• Mode Switches for gnatmake:  



• Notes on the Command Line:  



• How gnatmake Works:  



• Examples of gnatmake Usage:  












Next: , Up: Building with gnatmake   [Contents][Index]





4.1.1 Running gnatmake




The usual form of the gnatmake command is





$ gnatmake [<switches>] <file_name> [<file_names>] [<mode_switches>]




The only required argument is one file_name, which specifies
a compilation unit that is a main program. Several file_names can be
specified: this will result in several executables being built.
If switches are present, they can be placed before the first
file_name, between file_names or after the last file_name.
If mode_switches are present, they must always be placed after
the last file_name and all switches.



If you are using standard file extensions (.adb and
.ads), then the
extension may be omitted from the file_name arguments. However, if
you are using non-standard extensions, then it is required that the
extension be given. A relative or absolute directory path can be
specified in a file_name, in which case, the input source file will
be searched for in the specified directory only. Otherwise, the input
source file will first be searched in the directory where
gnatmake was invoked and if it is not found, it will be search on
the source path of the compiler as described in
Search Paths and the Run-Time Library (RTL).



All gnatmake output (except when you specify -M) is sent to
stderr. The output produced by the
-M switch is sent to stdout.









Next: , Previous: Running gnatmake, Up: Building with gnatmake   [Contents][Index]





4.1.2 Switches for gnatmake




You may specify any of the following switches to gnatmake:








--version




Display Copyright and version, then exit disregarding all other options.











--help




If --version was not used, display usage, then exit disregarding
all other options.











--GCC=`compiler_name'




Program used for compiling. The default is gcc. You need to use
quotes around compiler_name if compiler_name contains
spaces or other separator characters.
As an example --GCC="foo -x  -y"
will instruct gnatmake to use foo -x -y as your
compiler. A limitation of this syntax is that the name and path name of
the executable itself must not include any embedded spaces. Note that
switch -c is always inserted after your command name. Thus in the
above example the compiler command that will be used by gnatmake
will be foo -c -x -y. If several --GCC=compiler_name are
used, only the last compiler_name is taken into account. However,
all the additional switches are also taken into account. Thus,
--GCC="foo -x -y" --GCC="bar -z -t" is equivalent to
--GCC="bar -x -y -z -t".











--GNATBIND=`binder_name'




Program used for binding. The default is gnatbind. You need to
use quotes around binder_name if binder_name contains spaces
or other separator characters.
As an example --GNATBIND="bar -x  -y"
will instruct gnatmake to use bar -x -y as your
binder. Binder switches that are normally appended by gnatmake
to gnatbind are now appended to the end of bar -x -y.
A limitation of this syntax is that the name and path name of the executable
itself must not include any embedded spaces.











--GNATLINK=`linker_name'




Program used for linking. The default is gnatlink. You need to
use quotes around linker_name if linker_name contains spaces
or other separator characters.
As an example --GNATLINK="lan -x  -y"
will instruct gnatmake to use lan -x -y as your
linker. Linker switches that are normally appended by gnatmake to
gnatlink are now appended to the end of lan -x -y.
A limitation of this syntax is that the name and path name of the executable
itself must not include any embedded spaces.





--create-map-file




When linking an executable, create a map file. The name of the map file
has the same name as the executable with extension ".map".





--create-map-file=`mapfile'




When linking an executable, create a map file with the specified name.











--create-missing-dirs




When using project files (-P`project'), automatically create
missing object directories, library directories and exec
directories.





--single-compile-per-obj-dir




Disallow simultaneous compilations in the same object directory when
project files are used.





--subdirs=`subdir'




Actual object directory of each project file is the subdirectory subdir of the
object directory specified or defaulted in the project file.





--unchecked-shared-lib-imports




By default, shared library projects are not allowed to import static library
projects. When this switch is used on the command line, this restriction is
relaxed.





--source-info=`source info file'




Specify a source info file. This switch is active only when project files
are used. If the source info file is specified as a relative path, then it is
relative to the object directory of the main project. If the source info file
does not exist, then after the Project Manager has successfully parsed and
processed the project files and found the sources, it creates the source info
file. If the source info file already exists and can be read successfully,
then the Project Manager will get all the needed information about the sources
from the source info file and will not look for them. This reduces the time
to process the project files, especially when looking for sources that take a
long time. If the source info file exists but cannot be parsed successfully,
the Project Manager will attempt to recreate it. If the Project Manager fails
to create the source info file, a message is issued, but gnatmake does not
fail. gnatmake "trusts" the source info file. This means that
if the source files have changed (addition, deletion, moving to a different
source directory), then the source info file need to be deleted and recreated.











-a




Consider all files in the make process, even the GNAT internal system
files (for example, the predefined Ada library files), as well as any
locked files. Locked files are files whose ALI file is write-protected.
By default,
gnatmake does not check these files,
because the assumption is that the GNAT internal files are properly up
to date, and also that any write protected ALI files have been properly
installed. Note that if there is an installation problem, such that one
of these files is not up to date, it will be properly caught by the
binder.
You may have to specify this switch if you are working on GNAT
itself. The switch -a is also useful
in conjunction with -f
if you need to recompile an entire application,
including run-time files, using special configuration pragmas,
such as a Normalize_Scalars pragma.



By default
gnatmake -a compiles all GNAT
internal files with
gcc -c -gnatpg rather than gcc -c.











-b




Bind only. Can be combined with -c to do
compilation and binding, but no link.
Can be combined with -l
to do binding and linking. When not combined with
-c
all the units in the closure of the main program must have been previously
compiled and must be up to date. The root unit specified by file_name
may be given without extension, with the source extension or, if no GNAT
Project File is specified, with the ALI file extension.











-c




Compile only. Do not perform binding, except when -b
is also specified. Do not perform linking, except if both
-b and
-l are also specified.
If the root unit specified by file_name is not a main unit, this is the
default. Otherwise gnatmake will attempt binding and linking
unless all objects are up to date and the executable is more recent than
the objects.











-C




Use a temporary mapping file. A mapping file is a way to communicate
to the compiler two mappings: from unit names to file names (without
any directory information) and from file names to path names (with
full directory information). A mapping file can make the compiler’s
file searches faster, especially if there are many source directories,
or the sources are read over a slow network connection. If
-P is used, a mapping file is always used, so
-C is unnecessary; in this case the mapping file
is initially populated based on the project file. If
-C is used without
-P,
the mapping file is initially empty. Each invocation of the compiler
will add any newly accessed sources to the mapping file.











-C=`file'




Use a specific mapping file. The file, specified as a path name (absolute or
relative) by this switch, should already exist, otherwise the switch is
ineffective. The specified mapping file will be communicated to the compiler.
This switch is not compatible with a project file
(-P‘file‘) or with multiple compiling processes
(-jnnn, when nnn is greater than 1).











-d




Display progress for each source, up to date or not, as a single line:





completed x out of y (zz%)




If the file needs to be compiled this is displayed after the invocation of
the compiler. These lines are displayed even in quiet output mode.











-D `dir'




Put all object files and ALI file in directory dir.
If the -D switch is not used, all object files
and ALI files go in the current working directory.



This switch cannot be used when using a project file.











-eI`nnn'




Indicates that the main source is a multi-unit source and the rank of the unit
in the source file is nnn. nnn needs to be a positive number and a valid
index in the source. This switch cannot be used when gnatmake is
invoked for several mains.













-eL




Follow all symbolic links when processing project files.
This should be used if your project uses symbolic links for files or
directories, but is not needed in other cases.





This also assumes that no directory matches the naming scheme for files (for
instance that you do not have a directory called "sources.ads" when using the
default GNAT naming scheme).



When you do not have to use this switch (i.e., by default), gnatmake is able to
save a lot of system calls (several per source file and object file), which
can result in a significant speed up to load and manipulate a project file,
especially when using source files from a remote system.











-eS




Output the commands for the compiler, the binder and the linker
on standard output,
instead of standard error.











-f




Force recompilations. Recompile all sources, even though some object
files may be up to date, but don’t recompile predefined or GNAT internal
files or locked files (files with a write-protected ALI file),
unless the -a switch is also specified.











-F




When using project files, if some errors or warnings are detected during
parsing and verbose mode is not in effect (no use of switch
-v), then error lines start with the full path name of the project
file, rather than its simple file name.











-g




Enable debugging. This switch is simply passed to the compiler and to the
linker.











-i




In normal mode, gnatmake compiles all object files and ALI files
into the current directory. If the -i switch is used,
then instead object files and ALI files that already exist are overwritten
in place. This means that once a large project is organized into separate
directories in the desired manner, then gnatmake will automatically
maintain and update this organization. If no ALI files are found on the
Ada object path (see Search Paths and the Run-Time Library (RTL)),
the new object and ALI files are created in the
directory containing the source being compiled. If another organization
is desired, where objects and sources are kept in different directories,
a useful technique is to create dummy ALI files in the desired directories.
When detecting such a dummy file, gnatmake will be forced to
recompile the corresponding source file, and it will be put the resulting
object and ALI files in the directory where it found the dummy file.













-j`n'




Use n processes to carry out the (re)compilations. On a multiprocessor
machine compilations will occur in parallel. If n is 0, then the
maximum number of parallel compilations is the number of core processors
on the platform. In the event of compilation errors, messages from various
compilations might get interspersed (but gnatmake will give you the
full ordered list of failing compiles at the end). If this is problematic,
rerun the make process with n set to 1 to get a clean list of messages.











-k




Keep going. Continue as much as possible after a compilation error. To
ease the programmer’s task in case of compilation errors, the list of
sources for which the compile fails is given when gnatmake
terminates.



If gnatmake is invoked with several file_names and with this
switch, if there are compilation errors when building an executable,
gnatmake will not attempt to build the following executables.











-l




Link only. Can be combined with -b to binding
and linking. Linking will not be performed if combined with
-c
but not with -b.
When not combined with -b
all the units in the closure of the main program must have been previously
compiled and must be up to date, and the main program needs to have been bound.
The root unit specified by file_name
may be given without extension, with the source extension or, if no GNAT
Project File is specified, with the ALI file extension.











-m




Specify that the minimum necessary amount of recompilations
be performed. In this mode gnatmake ignores time
stamp differences when the only
modifications to a source file consist in adding/removing comments,
empty lines, spaces or tabs. This means that if you have changed the
comments in a source file or have simply reformatted it, using this
switch will tell gnatmake not to recompile files that depend on it
(provided other sources on which these files depend have undergone no
semantic modifications). Note that the debugging information may be
out of date with respect to the sources if the -m switch causes
a compilation to be switched, so the use of this switch represents a
trade-off between compilation time and accurate debugging information.














-M




Check if all objects are up to date. If they are, output the object
dependences to stdout in a form that can be directly exploited in
a Makefile. By default, each source file is prefixed with its
(relative or absolute) directory name. This name is whatever you
specified in the various -aI
and -I switches. If you use
gnatmake -M  -q
(see below), only the source file names,
without relative paths, are output. If you just specify the  -M
switch, dependencies of the GNAT internal system files are omitted. This
is typically what you want. If you also specify
the -a switch,
dependencies of the GNAT internal files are also listed. Note that
dependencies of the objects in external Ada libraries (see
switch  -aL`dir' in the following list)
are never reported.











-n




Don’t compile, bind, or link. Checks if all objects are up to date.
If they are not, the full name of the first file that needs to be
recompiled is printed.
Repeated use of this option, followed by compiling the indicated source
file, will eventually result in recompiling all required units.











-o `exec_name'




Output executable name. The name of the final executable program will be
exec_name. If the -o switch is omitted the default
name for the executable will be the name of the input file in appropriate form
for an executable file on the host system.



This switch cannot be used when invoking gnatmake with several
file_names.











-p




Same as --create-missing-dirs











-P`project'




Use project file project. Only one such switch can be used.












-q




Quiet. When this flag is not set, the commands carried out by
gnatmake are displayed.











-s




Recompile if compiler switches have changed since last compilation.
All compiler switches but -I and -o are taken into account in the
following way:
orders between different ’first letter’ switches are ignored, but
orders between same switches are taken into account. For example,
-O -O2 is different than -O2 -O, but -g -O
is equivalent to -O -g.



This switch is recommended when Integrated Preprocessing is used.











-u




Unique. Recompile at most the main files. It implies -c. Combined with
-f, it is equivalent to calling the compiler directly. Note that using
-u with a project file and no main has a special meaning.












-U




When used without a project file or with one or several mains on the command
line, is equivalent to -u. When used with a project file and no main
on the command line, all sources of all project files are checked and compiled
if not up to date, and libraries are rebuilt, if necessary.











-v




Verbose. Display the reason for all recompilations gnatmake
decides are necessary, with the highest verbosity level.











-vl




Verbosity level Low. Display fewer lines than in verbosity Medium.











-vm




Verbosity level Medium. Potentially display fewer lines than in verbosity High.











-vh




Verbosity level High. Equivalent to -v.





-vP`x'




Indicate the verbosity of the parsing of GNAT project files.
See Switches Related to Project Files.











-x




Indicate that sources that are not part of any Project File may be compiled.
Normally, when using Project Files, only sources that are part of a Project
File may be compile. When this switch is used, a source outside of all Project
Files may be compiled. The ALI file and the object file will be put in the
object directory of the main Project. The compilation switches used will only
be those specified on the command line. Even when
-x is used, mains specified on the
command line need to be sources of a project file.





-X`name'=`value'




Indicate that external variable name has the value value.
The Project Manager will use this value for occurrences of
external(name) when parsing the project file.
Switches Related to Project Files.











-z




No main subprogram. Bind and link the program even if the unit name
given on the command line is a package name. The resulting executable
will execute the elaboration routines of the package and its closure,
then the finalization routines.







GCC switches




Any uppercase or multi-character switch that is not a gnatmake switch
is passed to gcc (e.g., -O, -gnato, etc.)




Source and library search path switches









-aI`dir'




When looking for source files also look in directory dir.
The order in which source files search is undertaken is
described in Search Paths and the Run-Time Library (RTL).











-aL`dir'




Consider dir as being an externally provided Ada library.
Instructs gnatmake to skip compilation units whose .ALI
files have been located in directory dir. This allows you to have
missing bodies for the units in dir and to ignore out of date bodies
for the same units. You still need to specify
the location of the specs for these units by using the switches
-aI`dir'  or -I`dir'.
Note: this switch is provided for compatibility with previous versions
of gnatmake. The easier method of causing standard libraries
to be excluded from consideration is to write-protect the corresponding
ALI files.











-aO`dir'




When searching for library and object files, look in directory
dir. The order in which library files are searched is described in
Search Paths for gnatbind.














-A`dir'




Equivalent to -aL`dir' -aI`dir'.







-I`dir'




Equivalent to -aO`dir' -aI`dir'.














-I-




Do not look for source files in the directory containing the source
file named in the command line.
Do not look for ALI or object files in the directory
where gnatmake was invoked.













-L`dir'




Add directory dir to the list of directories in which the linker
will search for libraries. This is equivalent to
-largs -L`dir'.
Furthermore, under Windows, the sources pointed to by the libraries path
set in the registry are not searched for.











-nostdinc




Do not look for source files in the system default directory.











-nostdlib




Do not look for library files in the system default directory.











--RTS=`rts-path'




Specifies the default location of the run-time library. GNAT looks for the
run-time
in the following directories, and stops as soon as a valid run-time is found
(adainclude or ada_source_path, and adalib or
ada_object_path present):
















Next: , Previous: Switches for gnatmake, Up: Building with gnatmake   [Contents][Index]





4.1.3 Mode Switches for gnatmake




The mode switches (referred to as mode_switches) allow the
inclusion of switches that are to be passed to the compiler itself, the
binder or the linker. The effect of a mode switch is to cause all
subsequent switches up to the end of the switch list, or up to the next
mode switch, to be interpreted as switches to be passed on to the
designated component of GNAT.








-cargs `switches'




Compiler switches. Here switches is a list of switches
that are valid switches for gcc. They will be passed on to
all compile steps performed by gnatmake.











-bargs `switches'




Binder switches. Here switches is a list of switches
that are valid switches for gnatbind. They will be passed on to
all bind steps performed by gnatmake.











-largs `switches'




Linker switches. Here switches is a list of switches
that are valid switches for gnatlink. They will be passed on to
all link steps performed by gnatmake.











-margs `switches'




Make switches. The switches are directly interpreted by gnatmake,
regardless of any previous occurrence of -cargs, -bargs
or -largs.












Next: , Previous: Mode Switches for gnatmake, Up: Building with gnatmake   [Contents][Index]





4.1.4 Notes on the Command Line




This section contains some additional useful notes on the operation
of the gnatmake command.














Next: , Previous: Notes on the Command Line, Up: Building with gnatmake   [Contents][Index]





4.1.5 How gnatmake Works




Generally gnatmake automatically performs all necessary
recompilations and you don’t need to worry about how it works. However,
it may be useful to have some basic understanding of the gnatmake
approach and in particular to understand how it uses the results of
previous compilations without incorrectly depending on them.



First a definition: an object file is considered `up to date' if the
corresponding ALI file exists and if all the source files listed in the
dependency section of this ALI file have time stamps matching those in
the ALI file. This means that neither the source file itself nor any
files that it depends on have been modified, and hence there is no need
to recompile this file.



gnatmake works by first checking if the specified main unit is up
to date. If so, no compilations are required for the main unit. If not,
gnatmake compiles the main program to build a new ALI file that
reflects the latest sources. Then the ALI file of the main unit is
examined to find all the source files on which the main program depends,
and gnatmake recursively applies the above procedure on all these
files.



This process ensures that gnatmake only trusts the dependencies
in an existing ALI file if they are known to be correct. Otherwise it
always recompiles to determine a new, guaranteed accurate set of
dependencies. As a result the program is compiled ’upside down’ from what may
be more familiar as the required order of compilation in some other Ada
systems. In particular, clients are compiled before the units on which
they depend. The ability of GNAT to compile in any order is critical in
allowing an order of compilation to be chosen that guarantees that
gnatmake will recompute a correct set of new dependencies if
necessary.



When invoking gnatmake with several file_names, if a unit is
imported by several of the executables, it will be recompiled at most once.



Note: when using non-standard naming conventions
(Using Other File Names), changing through a configuration pragmas
file the version of a source and invoking gnatmake to recompile may
have no effect, if the previous version of the source is still accessible
by gnatmake. It may be necessary to use the switch
-f.









Previous: How gnatmake Works, Up: Building with gnatmake   [Contents][Index]





4.1.6 Examples of gnatmake Usage







`gnatmake hello.adb'




Compile all files necessary to bind and link the main program
hello.adb (containing unit Hello) and bind and link the
resulting object files to generate an executable file hello.





`gnatmake main1 main2 main3'




Compile all files necessary to bind and link the main programs
main1.adb (containing unit Main1), main2.adb
(containing unit Main2) and main3.adb
(containing unit Main3) and bind and link the resulting object files
to generate three executable files main1,
main2  and main3.





`gnatmake -q Main_Unit -cargs -O2 -bargs -l'




Compile all files necessary to bind and link the main program unit
Main_Unit (from file main_unit.adb). All compilations will
be done with optimization level 2 and the order of elaboration will be
listed by the binder. gnatmake will operate in quiet mode, not
displaying commands it is executing.












Next: , Previous: Building with gnatmake, Up: Building Executable Programs with GNAT   [Contents][Index]





4.2 Compiling with gcc




This section discusses how to compile Ada programs using the gcc
command. It also describes the set of switches
that can be used to control the behavior of the compiler.





• Compiling Programs:  



• Search Paths and the Run-Time Library (RTL):  



• Order of Compilation Issues:  



• Examples:  












Next: , Up: Compiling with gcc   [Contents][Index]





4.2.1 Compiling Programs




The first step in creating an executable program is to compile the units
of the program using the gcc command. You must compile the
following files:






You need `not' compile the following files






because they are compiled as part of compiling related units. GNAT
package specs
when the corresponding body is compiled, and subunits when the parent is
compiled.





If you attempt to compile any of these files, you will get one of the
following error messages (where fff is the name of the file you
compiled):








cannot generate code for file ``fff`` (package spec)
to check package spec, use -gnatc

cannot generate code for file ``fff`` (missing subunits)
to check parent unit, use -gnatc

cannot generate code for file ``fff`` (subprogram spec)
to check subprogram spec, use -gnatc

cannot generate code for file ``fff`` (subunit)
to check subunit, use -gnatc






As indicated by the above error messages, if you want to submit
one of these files to the compiler to check for correct semantics
without generating code, then use the -gnatc switch.



The basic command for compiling a file containing an Ada unit is:





$ gcc -c [switches] <file name>




where file name is the name of the Ada file (usually
having an extension .ads for a spec or .adb for a body).
You specify the
-c switch to tell gcc to compile, but not link, the file.
The result of a successful compilation is an object file, which has the
same name as the source file but an extension of .o and an Ada
Library Information (ALI) file, which also has the same name as the
source file, but with .ali as the extension. GNAT creates these
two output files in the current directory, but you may specify a source
file in any directory using an absolute or relative path specification
containing the directory information.



TESTING: the --foobar`NN' switch





gcc is actually a driver program that looks at the extensions of
the file arguments and loads the appropriate compiler. For example, the
GNU C compiler is cc1, and the Ada compiler is gnat1.
These programs are in directories known to the driver program (in some
configurations via environment variables you set), but need not be in
your path. The gcc driver also calls the assembler and any other
utilities needed to complete the generation of the required object
files.



It is possible to supply several file names on the same gcc
command. This causes gcc to call the appropriate compiler for
each file. For example, the following command lists two separate
files to be compiled:





$ gcc -c x.adb y.adb




calls gnat1 (the Ada compiler) twice to compile x.adb and
y.adb.
The compiler generates two object files x.o and y.o
and the two ALI files x.ali and y.ali.



Any switches apply to all the files listed, see Compiler Switches for a
list of available gcc switches.









Next: , Previous: Compiling Programs, Up: Compiling with gcc   [Contents][Index]





4.2.2 Search Paths and the Run-Time Library (RTL)




With the GNAT source-based library system, the compiler must be able to
find source files for units that are needed by the unit being compiled.
Search paths are used to guide this process.



The compiler compiles one source file whose name must be given
explicitly on the command line. In other words, no searching is done
for this file. To find all other source files that are needed (the most
common being the specs of units), the compiler examines the following
directories, in the following order:






Specifying the switch -I-
inhibits the use of the directory
containing the source file named in the command line. You can still
have this directory on your search path, but in this case it must be
explicitly requested with a -I switch.



Specifying the switch -nostdinc
inhibits the search of the default location for the GNAT Run Time
Library (RTL) source files.



The compiler outputs its object files and ALI files in the current
working directory.
Caution: The object file can be redirected with the -o switch;
however, gcc and gnat1 have not been coordinated on this
so the ALI file will not go to the right place. Therefore, you should
avoid using the -o switch.





The packages Ada, System, and Interfaces and their
children make up the GNAT RTL, together with the simple System.IO
package used in the "Hello World" example. The sources for these units
are needed by the compiler and are kept together in one directory. Not
all of the bodies are needed, but all of the sources are kept together
anyway. In a normal installation, you need not specify these directory
names when compiling or binding. Either the environment variables or
the built-in defaults cause these files to be found.



In addition to the language-defined hierarchies (System, Ada and
Interfaces), the GNAT distribution provides a fourth hierarchy,
consisting of child units of GNAT. This is a collection of generally
useful types, subprograms, etc. See the GNAT_Reference_Manual
for further details.



Besides simplifying access to the RTL, a major use of search paths is
in compiling sources from multiple directories. This can make
development environments much more flexible.









Next: , Previous: Search Paths and the Run-Time Library RTL, Up: Compiling with gcc   [Contents][Index]





4.2.3 Order of Compilation Issues




If, in our earlier example, there was a spec for the hello
procedure, it would be contained in the file hello.ads; yet this
file would not have to be explicitly compiled. This is the result of the
model we chose to implement library management. Some of the consequences
of this model are as follows:












Previous: Order of Compilation Issues, Up: Compiling with gcc   [Contents][Index]





4.2.4 Examples




The following are some typical Ada compilation command line examples:





$ gcc -c xyz.adb




Compile body in file xyz.adb with all default options.





$ gcc -c -O2 -gnata xyz-def.adb




Compile the child unit package in file xyz-def.adb with extensive
optimizations, and pragma Assert/Debug statements
enabled.





$ gcc -c -gnatc abc-def.adb




Compile the subunit in file abc-def.adb in semantic-checking-only
mode.









Next: , Previous: Compiling with gcc, Up: Building Executable Programs with GNAT   [Contents][Index]





4.3 Compiler Switches




The gcc command accepts switches that control the
compilation process. These switches are fully described in this section:
first an alphabetical listing of all switches with a brief description,
and then functionally grouped sets of switches with more detailed
information.



More switches exist for GCC than those documented here, especially
for specific targets. However, their use is not recommended as
they may change code generation in ways that are incompatible with
the Ada run-time library, or can cause inconsistencies between
compilation units.





• Alphabetical List of All Switches:  



• Output and Error Message Control:  



• Warning Message Control:  



• Debugging and Assertion Control:  



• Validity Checking:  



• Style Checking:  



• Run-Time Checks:  



• Using gcc for Syntax Checking:  



• Using gcc for Semantic Checking:  



• Compiling Different Versions of Ada:  



• Character Set Control:  



• File Naming Control:  



• Subprogram Inlining Control:  



• Auxiliary Output Control:  



• Debugging Control:  



• Exception Handling Control:  



• Units to Sources Mapping Files:  



• Code Generation Control:  












Next: , Up: Compiler Switches   [Contents][Index]





4.3.1 Alphabetical List of All Switches









-b `target'




Compile your program to run on target, which is the name of a
system configuration. You must have a GNAT cross-compiler built if
target is not the same as your host system.











-B`dir'




Load compiler executables (for example, gnat1, the Ada compiler)
from dir instead of the default location. Only use this switch
when multiple versions of the GNAT compiler are available.
See the "Options for Directory Search" section in the
Using the GNU Compiler Collection (GCC) manual for further details.
You would normally use the -b or -V switch instead.











-c




Compile. Always use this switch when compiling Ada programs.



Note: for some other languages when using gcc, notably in
the case of C and C++, it is possible to use
use gcc without a -c switch to
compile and link in one step. In the case of GNAT, you
cannot use this approach, because the binder must be run
and gcc cannot be used to run the GNAT binder.











-fcallgraph-info[=su,da]




Makes the compiler output callgraph information for the program, on a
per-file basis. The information is generated in the VCG format.  It can
be decorated with additional, per-node and/or per-edge information, if a
list of comma-separated markers is additionally specified. When the
su marker is specified, the callgraph is decorated with stack usage
information; it is equivalent to -fstack-usage. When the da
marker is specified, the callgraph is decorated with information about
dynamically allocated objects.











-fdump-scos




Generates SCO (Source Coverage Obligation) information in the ALI file.
This information is used by advanced coverage tools. See unit SCOs
in the compiler sources for details in files scos.ads and
scos.adb.











-fgnat-encodings=[all|gdb|minimal]




This switch controls the balance between GNAT encodings and standard DWARF
emitted in the debug information.











-flto[=`n']




Enables Link Time Optimization. This switch must be used in conjunction
with the -Ox switches (but not with the -gnatn switch
since it is a full replacement for the latter) and instructs the compiler
to defer most optimizations until the link stage. The advantage of this
approach is that the compiler can do a whole-program analysis and choose
the best interprocedural optimization strategy based on a complete view
of the program, instead of a fragmentary view with the usual approach.
This can also speed up the compilation of big programs and reduce the
size of the executable, compared with a traditional per-unit compilation
with inlining across units enabled by the -gnatn switch.
The drawback of this approach is that it may require more memory and that
the debugging information generated by -g with it might be hardly usable.
The switch, as well as the accompanying -Ox switches, must be
specified both for the compilation and the link phases.
If the n parameter is specified, the optimization and final code
generation at link time are executed using n parallel jobs by
means of an installed make program.











-fno-inline




Suppresses all inlining, unless requested with pragma Inline_Always. The
effect is enforced regardless of other optimization or inlining switches.
Note that inlining can also be suppressed on a finer-grained basis with
pragma No_Inline.











-fno-inline-functions




Suppresses automatic inlining of subprograms, which is enabled
if -O3 is used.











-fno-inline-small-functions




Suppresses automatic inlining of small subprograms, which is enabled
if -O2 is used.











-fno-inline-functions-called-once




Suppresses inlining of subprograms local to the unit and called once
from within it, which is enabled if -O1 is used.











-fno-ivopts




Suppresses high-level loop induction variable optimizations, which are
enabled if -O1 is used. These optimizations are generally
profitable but, for some specific cases of loops with numerous uses
of the iteration variable that follow a common pattern, they may end
up destroying the regularity that could be exploited at a lower level
and thus producing inferior code.











-fno-strict-aliasing




Causes the compiler to avoid assumptions regarding non-aliasing
of objects of different types. See
Optimization and Strict Aliasing for details.











-fno-strict-overflow




Causes the compiler to avoid assumptions regarding the rules of signed
integer overflow. These rules specify that signed integer overflow will
result in a Constraint_Error exception at run time and are enforced in
default mode by the compiler, so this switch should not be necessary in
normal operating mode. It might be useful in conjunction with -gnato0
for very peculiar cases of low-level programming.











-fstack-check




Activates stack checking.
See Stack Overflow Checking for details.











-fstack-usage




Makes the compiler output stack usage information for the program, on a
per-subprogram basis. See Static Stack Usage Analysis for details.











-g




Generate debugging information. This information is stored in the object
file and copied from there to the final executable file by the linker,
where it can be read by the debugger. You must use the
-g switch if you plan on using the debugger.











-gnat05




Allow full Ada 2005 features.











-gnat12




Allow full Ada 2012 features.













-gnat2005




Allow full Ada 2005 features (same as -gnat05)











-gnat2012




Allow full Ada 2012 features (same as -gnat12)





-gnat83




Enforce Ada 83 restrictions.











-gnat95




Enforce Ada 95 restrictions.



Note: for compatibility with some Ada 95 compilers which support only
the overriding keyword of Ada 2005, the -gnatd.D switch can
be used along with -gnat95 to achieve a similar effect with GNAT.



-gnatd.D instructs GNAT to consider overriding as a keyword
and handle its associated semantic checks, even in Ada 95 mode.











-gnata




Assertions enabled. Pragma Assert and pragma Debug to be
activated. Note that these pragmas can also be controlled using the
configuration pragmas Assertion_Policy and Debug_Policy.
It also activates pragmas Check, Precondition, and
Postcondition. Note that these pragmas can also be controlled
using the configuration pragma Check_Policy. In Ada 2012, it
also activates all assertions defined in the RM as aspects: preconditions,
postconditions, type invariants and (sub)type predicates. In all Ada modes,
corresponding pragmas for type invariants and (sub)type predicates are
also activated. The default is that all these assertions are disabled,
and have no effect, other than being checked for syntactic validity, and
in the case of subtype predicates, constructions such as membership tests
still test predicates even if assertions are turned off.











-gnatA




Avoid processing gnat.adc. If a gnat.adc file is present,
it will be ignored.











-gnatb




Generate brief messages to stderr even if verbose mode set.











-gnatB




Assume no invalid (bad) values except for ’Valid attribute use
(Validity Checking).











-gnatc




Check syntax and semantics only (no code generation attempted). When the
compiler is invoked by gnatmake, if the switch -gnatc is
only given to the compiler (after -cargs or in package Compiler of
the project file, gnatmake will fail because it will not find the
object file after compilation. If gnatmake is called with
-gnatc as a builder switch (before -cargs or in package
Builder of the project file) then gnatmake will not fail because
it will not look for the object files after compilation, and it will not try
to build and link.











-gnatC




Generate CodePeer intermediate format (no code generation attempted).
This switch will generate an intermediate representation suitable for
use by CodePeer (.scil files). This switch is not compatible with
code generation (it will, among other things, disable some switches such
as -gnatn, and enable others such as -gnata).











-gnatd




Specify debug options for the compiler. The string of characters after
the -gnatd specify the specific debug options. The possible
characters are 0-9, a-z, A-Z, optionally preceded by a dot. See
compiler source file debug.adb for details of the implemented
debug options. Certain debug options are relevant to applications
programmers, and these are documented at appropriate points in this
users guide.











-gnatD




Create expanded source files for source level debugging. This switch
also suppresses generation of cross-reference information
(see -gnatx). Note that this switch is not allowed if a previous
-gnatR switch has been given, since these two switches are not compatible.











-gnateA




Check that the actual parameters of a subprogram call are not aliases of one
another. To qualify as aliasing, the actuals must denote objects of a composite
type, their memory locations must be identical or overlapping, and at least one
of the corresponding formal parameters must be of mode OUT or IN OUT.





type Rec_Typ is record
   Data : Integer := 0;
end record;

function Self (Val : Rec_Typ) return Rec_Typ is
begin
   return Val;
end Self;

procedure Detect_Aliasing (Val_1 : in out Rec_Typ; Val_2 : Rec_Typ) is
begin
   null;
end Detect_Aliasing;

Obj : Rec_Typ;

Detect_Aliasing (Obj, Obj);
Detect_Aliasing (Obj, Self (Obj));




In the example above, the first call to Detect_Aliasing fails with a
Program_Error at run time because the actuals for Val_1 and
Val_2 denote the same object. The second call executes without raising
an exception because Self(Obj) produces an anonymous object which does
not share the memory location of Obj.











-gnatec=`path'




Specify a configuration pragma file
(the equal sign is optional)
(The Configuration Pragmas Files).











-gnateC




Generate CodePeer messages in a compiler-like format. This switch is only
effective if -gnatcC is also specified and requires an installation
of CodePeer.











-gnated




Disable atomic synchronization











-gnateDsymbol[=`value']




Defines a symbol, associated with value, for preprocessing.
(Integrated Preprocessing).











-gnateE




Generate extra information in exception messages. In particular, display
extra column information and the value and range associated with index and
range check failures, and extra column information for access checks.
In cases where the compiler is able to determine at compile time that
a check will fail, it gives a warning, and the extra information is not
produced at run time.











-gnatef




Display full source path name in brief error messages.











-gnateF




Check for overflow on all floating-point operations, including those
for unconstrained predefined types. See description of pragma
Check_Float_Overflow in GNAT RM.








-gnateg
-gnatceg






The -gnatc switch must always be specified before this switch, e.g.
-gnatceg. Generate a C header from the Ada input file. See
Generating C Headers for Ada Specifications for more
information.









-gnateG




Save result of preprocessing in a text file.











-gnatei`nnn'




Set maximum number of instantiations during compilation of a single unit to
nnn. This may be useful in increasing the default maximum of 8000 for
the rare case when a single unit legitimately exceeds this limit.











-gnateI`nnn'




Indicates that the source is a multi-unit source and that the index of the
unit to compile is nnn. nnn needs to be a positive number and need
to be a valid index in the multi-unit source.











-gnatel




This switch can be used with the static elaboration model to issue info
messages showing
where implicit pragma Elaborate and pragma Elaborate_All
are generated. This is useful in diagnosing elaboration circularities
caused by these implicit pragmas when using the static elaboration
model. See See the section in this guide on elaboration checking for
further details. These messages are not generated by default, and are
intended only for temporary use when debugging circularity problems.











-gnateL




This switch turns off the info messages about implicit elaboration pragmas.











-gnatem=`path'




Specify a mapping file
(the equal sign is optional)
(Units to Sources Mapping Files).











-gnatep=`file'




Specify a preprocessing data file
(the equal sign is optional)
(Integrated Preprocessing).











-gnateP




Turn categorization dependency errors into warnings.
Ada requires that units that WITH one another have compatible categories, for
example a Pure unit cannot WITH a Preelaborate unit. If this switch is used,
these errors become warnings (which can be ignored, or suppressed in the usual
manner). This can be useful in some specialized circumstances such as the
temporary use of special test software.











-gnateS




Synonym of -fdump-scos, kept for backwards compatibility.











-gnatet=`path'




Generate target dependent information. The format of the output file is
described in the section about switch -gnateT.











-gnateT=`path'




Read target dependent information, such as endianness or sizes and alignments
of base type. If this switch is passed, the default target dependent
information of the compiler is replaced by the one read from the input file.
This is used by tools other than the compiler, e.g. to do
semantic analysis of programs that will run on some other target than
the machine on which the tool is run.



The following target dependent values should be defined,
where Nat denotes a natural integer value, Pos denotes a
positive integer value, and fields marked with a question mark are
boolean fields, where a value of 0 is False, and a value of 1 is True:





Bits_BE                    : Nat; -- Bits stored big-endian?
Bits_Per_Unit              : Pos; -- Bits in a storage unit
Bits_Per_Word              : Pos; -- Bits in a word
Bytes_BE                   : Nat; -- Bytes stored big-endian?
Char_Size                  : Pos; -- Standard.Character'Size
Double_Float_Alignment     : Nat; -- Alignment of double float
Double_Scalar_Alignment    : Nat; -- Alignment of double length scalar
Double_Size                : Pos; -- Standard.Long_Float'Size
Float_Size                 : Pos; -- Standard.Float'Size
Float_Words_BE             : Nat; -- Float words stored big-endian?
Int_Size                   : Pos; -- Standard.Integer'Size
Long_Double_Size           : Pos; -- Standard.Long_Long_Float'Size
Long_Long_Size             : Pos; -- Standard.Long_Long_Integer'Size
Long_Size                  : Pos; -- Standard.Long_Integer'Size
Maximum_Alignment          : Pos; -- Maximum permitted alignment
Max_Unaligned_Field        : Pos; -- Maximum size for unaligned bit field
Pointer_Size               : Pos; -- System.Address'Size
Short_Enums                : Nat; -- Foreign enums use short size?
Short_Size                 : Pos; -- Standard.Short_Integer'Size
Strict_Alignment           : Nat; -- Strict alignment?
System_Allocator_Alignment : Nat; -- Alignment for malloc calls
Wchar_T_Size               : Pos; -- Interfaces.C.wchar_t'Size
Words_BE                   : Nat; -- Words stored big-endian?




Bits_Per_Unit is the number of bits in a storage unit, the equivalent of
GCC macro BITS_PER_UNIT documented as follows: Define this macro to be the number of bits in an addressable storage unit (byte); normally 8.



Bits_Per_Word is the number of bits in a machine word, the equivalent of
GCC macro BITS_PER_WORD documented as follows: Number of bits in a word; normally 32.



Double_Float_Alignment, if not zero, is the maximum alignment that the
compiler can choose by default for a 64-bit floating-point type or object.



Double_Scalar_Alignment, if not zero, is the maximum alignment that the
compiler can choose by default for a 64-bit or larger scalar type or object.



Maximum_Alignment is the maximum alignment that the compiler can choose
by default for a type or object, which is also the maximum alignment that can
be specified in GNAT. It is computed for GCC backends as BIGGEST_ALIGNMENT
/ BITS_PER_UNIT where GCC macro BIGGEST_ALIGNMENT is documented as
follows: Biggest alignment that any data type can require on this machine, in bits.



Max_Unaligned_Field is the maximum size for unaligned bit field, which is
64 for the majority of GCC targets (but can be different on some targets like
AAMP).



Strict_Alignment is the equivalent of GCC macro STRICT_ALIGNMENT
documented as follows: Define this macro to be the value 1 if instructions will fail to work if given data not on the nominal alignment. If instructions will merely go slower in that case, define this macro as 0.



System_Allocator_Alignment is the guaranteed alignment of data returned
by calls to malloc.



The format of the input file is as follows. First come the values of
the variables defined above, with one line per value:





name  value




where name is the name of the parameter, spelled out in full,
and cased as in the above list, and value is an unsigned decimal
integer. Two or more blanks separates the name from the value.



All the variables must be present, in alphabetical order (i.e. the
same order as the list above).



Then there is a blank line to separate the two parts of the file. Then
come the lines showing the floating-point types to be registered, with
one line per registered mode:





name  digs float_rep size alignment




where name is the string name of the type (which can have
single spaces embedded in the name (e.g. long double), digs is
the number of digits for the floating-point type, float_rep is
the float representation (I/V/A for IEEE-754-Binary, Vax_Native,
AAMP), size is the size in bits, alignment is the
alignment in bits. The name is followed by at least two blanks, fields
are separated by at least one blank, and a LF character immediately
follows the alignment field.



Here is an example of a target parameterization file:





Bits_BE                       0
Bits_Per_Unit                 8
Bits_Per_Word                64
Bytes_BE                      0
Char_Size                     8
Double_Float_Alignment        0
Double_Scalar_Alignment       0
Double_Size                  64
Float_Size                   32
Float_Words_BE                0
Int_Size                     64
Long_Double_Size            128
Long_Long_Size               64
Long_Size                    64
Maximum_Alignment            16
Max_Unaligned_Field          64
Pointer_Size                 64
Short_Size                   16
Strict_Alignment              0
System_Allocator_Alignment   16
Wchar_T_Size                 32
Words_BE                      0

float         15  I  64  64
double        15  I  64  64
long double   18  I  80 128
TF            33  I 128 128













-gnateu




Ignore unrecognized validity, warning, and style switches that
appear after this switch is given. This may be useful when
compiling sources developed on a later version of the compiler
with an earlier version. Of course the earlier version must
support this switch.











-gnateV




Check that all actual parameters of a subprogram call are valid according to
the rules of validity checking (Validity Checking).











-gnateY




Ignore all STYLE_CHECKS pragmas. Full legality checks
are still carried out, but the pragmas have no effect
on what style checks are active. This allows all style
checking options to be controlled from the command line.











-gnatE




Dynamic elaboration checking mode enabled. For further details see
Elaboration Order Handling in GNAT.











-gnatf




Full errors. Multiple errors per line, all undefined references, do not
attempt to suppress cascaded errors.











-gnatF




Externals names are folded to all uppercase.











-gnatg




Internal GNAT implementation mode. This should not be used for applications
programs, it is intended only for use by the compiler and its run-time
library. For documentation, see the GNAT sources. Note that -gnatg
implies -gnatw.ge and -gnatyg so that all standard
warnings and all standard style options are turned on. All warnings and style
messages are treated as errors.











-gnatG=nn




List generated expanded code in source form.











-gnath




Output usage information. The output is written to stdout.











-gnatH




Legacy elaboration-checking mode enabled. When this switch is in effect,
the pre-18.x access-before-elaboration model becomes the de facto model.
For further details see Elaboration Order Handling in GNAT.











-gnati`c'




Identifier character set (c = 1/2/3/4/8/9/p/f/n/w).
For details of the possible selections for c,
see Character Set Control.











-gnatI




Ignore representation clauses. When this switch is used,
representation clauses are treated as comments. This is useful
when initially porting code where you want to ignore rep clause
problems, and also for compiling foreign code (particularly
for use with ASIS). The representation clauses that are ignored
are: enumeration_representation_clause, record_representation_clause,
and attribute_definition_clause for the following attributes:
Address, Alignment, Bit_Order, Component_Size, Machine_Radix,
Object_Size, Scalar_Storage_Order, Size, Small, Stream_Size,
and Value_Size. Pragma Default_Scalar_Storage_Order is also ignored.
Note that this option should be used only for compiling – the
code is likely to malfunction at run time.



Note that when -gnatct is used to generate trees for input
into ASIS tools, these representation clauses are removed
from the tree and ignored. This means that the tool will not see them.











-gnatj`nn'




Reformat error messages to fit on nn character lines











-gnatJ




Permissive elaboration-checking mode enabled. When this switch is in effect,
the post-18.x access-before-elaboration model ignores potential issues with:






and does not emit compile-time diagnostics or run-time checks. For further
details see Elaboration Order Handling in GNAT.











-gnatk=`n'




Limit file names to n (1-999) characters (k = krunch).











-gnatl




Output full source listing with embedded error messages.











-gnatL




Used in conjunction with -gnatG or -gnatD to intersperse original
source lines (as comment lines with line numbers) in the expanded
source output.











-gnatm=`n'




Limit number of detected error or warning messages to n
where n is in the range 1..999999. The default setting if
no switch is given is 9999. If the number of warnings reaches this
limit, then a message is output and further warnings are suppressed,
but the compilation is continued. If the number of error messages
reaches this limit, then a message is output and the compilation
is abandoned. The equal sign here is optional. A value of zero
means that no limit applies.











-gnatn[12]




Activate inlining across units for subprograms for which pragma Inline
is specified. This inlining is performed by the GCC back-end. An optional
digit sets the inlining level: 1 for moderate inlining across units
or 2 for full inlining across units. If no inlining level is specified,
the compiler will pick it based on the optimization level.











-gnatN




Activate front end inlining for subprograms for which
pragma Inline is specified. This inlining is performed
by the front end and will be visible in the
-gnatG output.



When using a gcc-based back end (in practice this means using any version
of GNAT other than the JGNAT, .NET or GNAAMP versions), then the use of
-gnatN is deprecated, and the use of -gnatn is preferred.
Historically front end inlining was more extensive than the gcc back end
inlining, but that is no longer the case.











-gnato0




Suppresses overflow checking. This causes the behavior of the compiler to
match the default for older versions where overflow checking was suppressed
by default. This is equivalent to having
pragma Suppress (Overflow_Check) in a configuration pragma file.











-gnato??




Set default mode for handling generation of code to avoid intermediate
arithmetic overflow. Here ?? is two digits, a
single digit, or nothing. Each digit is one of the digits 1
through 3:






DigitInterpretation


`1'All intermediate overflows checked against base type (STRICT)


`2'Minimize intermediate overflows (MINIMIZED)


`3'Eliminate intermediate overflows (ELIMINATED)






If only one digit appears, then it applies to all
cases; if two digits are given, then the first applies outside
assertions, pre/postconditions, and type invariants, and the second
applies within assertions, pre/postconditions, and type invariants.



If no digits follow the -gnato, then it is equivalent to
-gnato11,
causing all intermediate overflows to be handled in strict
mode.



This switch also causes arithmetic overflow checking to be performed
(as though pragma Unsuppress (Overflow_Check) had been specified).



The default if no option -gnato is given is that overflow handling
is in STRICT mode (computations done using the base type), and that
overflow checking is enabled.



Note that division by zero is a separate check that is not
controlled by this switch (divide-by-zero checking is on by default).



See also Specifying the Desired Mode.











-gnatp




Suppress all checks. See Run-Time Checks for details. This switch
has no effect if cancelled by a subsequent -gnat-p switch.











-gnat-p




Cancel effect of previous -gnatp switch.











-gnatP




Enable polling. This is required on some systems (notably Windows NT) to
obtain asynchronous abort and asynchronous transfer of control capability.
See Pragma_Polling in the GNAT_Reference_Manual for full
details.











-gnatq




Don’t quit. Try semantics, even if parse errors.











-gnatQ




Don’t quit. Generate ALI and tree files even if illegalities.
Note that code generation is still suppressed in the presence of any
errors, so even with -gnatQ no object file is generated.











-gnatr




Treat pragma Restrictions as Restriction_Warnings.











-gnatR[0|1|2|3|4][e][j][m][s]




Output representation information for declared types, objects and
subprograms. Note that this switch is not allowed if a previous
-gnatD switch has been given, since these two switches
are not compatible.











-gnats




Syntax check only.











-gnatS




Print package Standard.











-gnatt




Generate tree output file.











-gnatT`nnn'




All compiler tables start at nnn times usual starting size.











-gnatu




List units for this compilation.











-gnatU




Tag all error messages with the unique string ’error:’











-gnatv




Verbose mode. Full error output with source lines to stdout.











-gnatV




Control level of validity checking (Validity Checking).











-gnatw`xxx'




Warning mode where
xxx is a string of option letters that denotes
the exact warnings that
are enabled or disabled (Warning Message Control).











-gnatW`e'




Wide character encoding method
(e=n/h/u/s/e/8).











-gnatx




Suppress generation of cross-reference information.











-gnatX




Enable GNAT implementation extensions and latest Ada version.











-gnaty




Enable built-in style checks (Style Checking).











-gnatz`m'




Distribution stub generation and compilation
(m=r/c for receiver/caller stubs).











-I`dir'






Direct GNAT to search the dir directory for source files needed by
the current compilation
(see Search Paths and the Run-Time Library (RTL)).











-I-






Except for the source file named in the command line, do not look for source
files in the directory containing the source file named in the command line
(see Search Paths and the Run-Time Library (RTL)).











-o `file'




This switch is used in gcc to redirect the generated object file
and its associated ALI file. Beware of this switch with GNAT, because it may
cause the object file and ALI file to have different names which in turn
may confuse the binder and the linker.











-nostdinc




Inhibit the search of the default location for the GNAT Run Time
Library (RTL) source files.











-nostdlib




Inhibit the search of the default location for the GNAT Run Time
Library (RTL) ALI files.











-O[`n']




n controls the optimization level:






`n'Effect


`0'No optimization, the default setting if no -O appears


`1'Normal optimization, the default if you specify -O without an
operand. A good compromise between code quality and compilation
time.


`2'Extensive optimization, may improve execution time, possibly at
the cost of substantially increased compilation time.


`3'Same as -O2, and also includes inline expansion for small
subprograms in the same unit.


`s'Optimize space usage






See also Optimization Levels.











-pass-exit-codes




Catch exit codes from the compiler and use the most meaningful as
exit status.











--RTS=`rts-path'




Specifies the default location of the run-time library. Same meaning as the
equivalent gnatmake flag (Switches for gnatmake).











-S




Used in place of -c to
cause the assembler source file to be
generated, using .s as the extension,
instead of the object file.
This may be useful if you need to examine the generated assembly code.











-fverbose-asm




Used in conjunction with -S
to cause the generated assembly code file to be annotated with variable
names, making it significantly easier to follow.











-v




Show commands generated by the gcc driver. Normally used only for
debugging purposes or if you need to be sure what version of the
compiler you are executing.











-V `ver'




Execute ver version of the compiler. This is the gcc
version, not the GNAT version.











-w




Turn off warnings generated by the back end of the compiler. Use of
this switch also causes the default for front end warnings to be set
to suppress (as though -gnatws had appeared at the start of
the options).








You may combine a sequence of GNAT switches into a single switch. For
example, the combined switch








-gnatofi3






is equivalent to specifying the following sequence of switches:








-gnato -gnatf -gnati3






The following restrictions apply to the combination of switches
in this manner:












Next: , Previous: Alphabetical List of All Switches, Up: Compiler Switches   [Contents][Index]





4.3.2 Output and Error Message Control






The standard default format for error messages is called ’brief format’.
Brief format messages are written to stderr (the standard error
file) and have the following form:





e.adb:3:04: Incorrect spelling of keyword "function"
e.adb:4:20: ";" should be "is"




The first integer after the file name is the line number in the file,
and the second integer is the column number within the line.
GNAT Studio can parse the error messages
and point to the referenced character.
The following switches provide control over the error message
format:








-gnatv




The v stands for verbose.
The effect of this setting is to write long-format error
messages to stdout (the standard output file.
The same program compiled with the
-gnatv switch would generate:





3. funcion X (Q : Integer)
   |
>>> Incorrect spelling of keyword "function"
4. return Integer;
                 |
>>> ";" should be "is"




The vertical bar indicates the location of the error, and the >>>
prefix can be used to search for error messages. When this switch is
used the only source lines output are those with errors.











-gnatl




The l stands for list.
This switch causes a full listing of
the file to be generated. In the case where a body is
compiled, the corresponding spec is also listed, along
with any subunits. Typical output from compiling a package
body p.adb might look like:





Compiling: p.adb

     1. package body p is
     2.    procedure a;
     3.    procedure a is separate;
     4. begin
     5.    null
               |
        >>> missing ";"

     6. end;

Compiling: p.ads

     1. package p is
     2.    pragma Elaborate_Body
                                |
        >>> missing ";"

     3. end p;

Compiling: p-a.adb

     1. separate p
                |
        >>> missing "("

     2. procedure a is
     3. begin
     4.    null
               |
        >>> missing ";"

     5. end;




When you specify the -gnatv or -gnatl switches and
standard output is redirected, a brief summary is written to
stderr (standard error) giving the number of error messages and
warning messages generated.











-gnatl=`fname'




This has the same effect as -gnatl except that the output is
written to a file instead of to standard output. If the given name
fname does not start with a period, then it is the full name
of the file to be written. If fname is an extension, it is
appended to the name of the file being compiled. For example, if
file xyz.adb is compiled with -gnatl=.lst,
then the output is written to file xyz.adb.lst.











-gnatU




This switch forces all error messages to be preceded by the unique
string ’error:’. This means that error messages take a few more
characters in space, but allows easy searching for and identification
of error messages.











-gnatb




The b stands for brief.
This switch causes GNAT to generate the
brief format error messages to stderr (the standard error
file) as well as the verbose
format message or full listing (which as usual is written to
stdout (the standard output file).











-gnatm=`n'




The m stands for maximum.
n is a decimal integer in the
range of 1 to 999999 and limits the number of error or warning
messages to be generated. For example, using
-gnatm2 might yield





e.adb:3:04: Incorrect spelling of keyword "function"
e.adb:5:35: missing ".."
fatal error: maximum number of errors detected
compilation abandoned




The default setting if
no switch is given is 9999. If the number of warnings reaches this
limit, then a message is output and further warnings are suppressed,
but the compilation is continued. If the number of error messages
reaches this limit, then a message is output and the compilation
is abandoned. A value of zero means that no limit applies.



Note that the equal sign is optional, so the switches
-gnatm2 and -gnatm=2 are equivalent.











-gnatf







The f stands for full.
Normally, the compiler suppresses error messages that are likely to be
redundant. This switch causes all error
messages to be generated. In particular, in the case of
references to undefined variables. If a given variable is referenced
several times, the normal format of messages is





e.adb:7:07: "V" is undefined (more references follow)




where the parenthetical comment warns that there are additional
references to the variable V. Compiling the same program with the
-gnatf switch yields





e.adb:7:07: "V" is undefined
e.adb:8:07: "V" is undefined
e.adb:8:12: "V" is undefined
e.adb:8:16: "V" is undefined
e.adb:9:07: "V" is undefined
e.adb:9:12: "V" is undefined




The -gnatf switch also generates additional information for
some error messages.  Some examples are:















-gnatjnn




In normal operation mode (or if -gnatj0 is used), then error messages
with continuation lines are treated as though the continuation lines were
separate messages (and so a warning with two continuation lines counts as
three warnings, and is listed as three separate messages).



If the -gnatjnn switch is used with a positive value for nn, then
messages are output in a different manner. A message and all its continuation
lines are treated as a unit, and count as only one warning or message in the
statistics totals. Furthermore, the message is reformatted so that no line
is longer than nn characters.











-gnatq




The q stands for quit (really ’don’t quit’).
In normal operation mode, the compiler first parses the program and
determines if there are any syntax errors. If there are, appropriate
error messages are generated and compilation is immediately terminated.
This switch tells
GNAT to continue with semantic analysis even if syntax errors have been
found. This may enable the detection of more errors in a single run. On
the other hand, the semantic analyzer is more likely to encounter some
internal fatal error when given a syntactically invalid tree.











-gnatQ




In normal operation mode, the ALI file is not generated if any
illegalities are detected in the program. The use of -gnatQ forces
generation of the ALI file. This file is marked as being in
error, so it cannot be used for binding purposes, but it does contain
reasonably complete cross-reference information, and thus may be useful
for use by tools (e.g., semantic browsing tools or integrated development
environments) that are driven from the ALI file. This switch
implies -gnatq, since the semantic phase must be run to get a
meaningful ALI file.



In addition, if -gnatt is also specified, then the tree file is
generated even if there are illegalities. It may be useful in this case
to also specify -gnatq to ensure that full semantic processing
occurs. The resulting tree file can be processed by ASIS, for the purpose
of providing partial information about illegal units, but if the error
causes the tree to be badly malformed, then ASIS may crash during the
analysis.



When -gnatQ is used and the generated ALI file is marked as
being in error, gnatmake will attempt to recompile the source when it
finds such an ALI file, including with switch -gnatc.



Note that -gnatQ has no effect if -gnats is specified,
since ALI files are never generated if -gnats is set.












Next: , Previous: Output and Error Message Control, Up: Compiler Switches   [Contents][Index]





4.3.3 Warning Message Control






In addition to error messages, which correspond to illegalities as defined
in the Ada Reference Manual, the compiler detects two kinds of warning
situations.



First, the compiler considers some constructs suspicious and generates a
warning message to alert you to a possible error. Second, if the
compiler detects a situation that is sure to raise an exception at
run time, it generates a warning message. The following shows an example
of warning messages:





e.adb:4:24: warning: creation of object may raise Storage_Error
e.adb:10:17: warning: static value out of range
e.adb:10:17: warning: "Constraint_Error" will be raised at run time




GNAT considers a large number of situations as appropriate
for the generation of warning messages. As always, warnings are not
definite indications of errors. For example, if you do an out-of-range
assignment with the deliberate intention of raising a
Constraint_Error exception, then the warning that may be
issued does not indicate an error. Some of the situations for which GNAT
issues warnings (at least some of the time) are given in the following
list. This list is not complete, and new warnings are often added to
subsequent versions of GNAT. The list is intended to give a general idea
of the kinds of warnings that are generated.






The following section lists compiler switches that are available
to control the handling of warning messages. It is also possible
to exercise much finer control over what warnings are issued and
suppressed using the GNAT pragma Warnings (see the description
of the pragma in the GNAT_Reference_manual).








-gnatwa




`Activate most optional warnings.'



This switch activates most optional warning messages. See the remaining list
in this section for details on optional warning messages that can be
individually controlled.  The warnings that are not turned on by this
switch are:






All other optional warnings are turned on.











-gnatwA




`Suppress all optional errors.'



This switch suppresses all optional warning messages, see remaining list
in this section for details on optional warning messages that can be
individually controlled. Note that unlike switch -gnatws, the
use of switch -gnatwA does not suppress warnings that are
normally given unconditionally and cannot be individually controlled
(for example, the warning about a missing exit path in a function).
Also, again unlike switch -gnatws, warnings suppressed by
the use of switch -gnatwA can be individually turned back
on. For example the use of switch -gnatwA followed by
switch -gnatwd will suppress all optional warnings except
the warnings for implicit dereferencing.











-gnatw.a




`Activate warnings on failing assertions.'





This switch activates warnings for assertions where the compiler can tell at
compile time that the assertion will fail. Note that this warning is given
even if assertions are disabled. The default is that such warnings are
generated.











-gnatw.A




`Suppress warnings on failing assertions.'





This switch suppresses warnings for assertions where the compiler can tell at
compile time that the assertion will fail.











-gnatw_a




`Activate warnings on anonymous allocators.'





This switch activates warnings for allocators of anonymous access types,
which can involve run-time accessibility checks and lead to unexpected
accessibility violations. For more details on the rules involved, see
RM 3.10.2 (14).











-gnatw_A




`Supress warnings on anonymous allocators.'





This switch suppresses warnings for anonymous access type allocators.











-gnatwb




`Activate warnings on bad fixed values.'









This switch activates warnings for static fixed-point expressions whose
value is not an exact multiple of Small. Such values are implementation
dependent, since an implementation is free to choose either of the multiples
that surround the value. GNAT always chooses the closer one, but this is not
required behavior, and it is better to specify a value that is an exact
multiple, ensuring predictable execution. The default is that such warnings
are not generated.











-gnatwB




`Suppress warnings on bad fixed values.'



This switch suppresses warnings for static fixed-point expressions whose
value is not an exact multiple of Small.











-gnatw.b




`Activate warnings on biased representation.'





This switch activates warnings when a size clause, value size clause, component
clause, or component size clause forces the use of biased representation for an
integer type (e.g. representing a range of 10..11 in a single bit by using 0/1
to represent 10/11). The default is that such warnings are generated.











-gnatw.B




`Suppress warnings on biased representation.'



This switch suppresses warnings for representation clauses that force the use
of biased representation.











-gnatwc




`Activate warnings on conditionals.'






This switch activates warnings for conditional expressions used in
tests that are known to be True or False at compile time. The default
is that such warnings are not generated.
Note that this warning does
not get issued for the use of boolean variables or constants whose
values are known at compile time, since this is a standard technique
for conditional compilation in Ada, and this would generate too many
false positive warnings.



This warning option also activates a special test for comparisons using
the operators ’>=’ and’ <=’.
If the compiler can tell that only the equality condition is possible,
then it will warn that the ’>’ or ’<’ part of the test
is useless and that the operator could be replaced by ’=’.
An example would be comparing a Natural variable <= 0.



This warning option also generates warnings if
one or both tests is optimized away in a membership test for integer
values if the result can be determined at compile time. Range tests on
enumeration types are not included, since it is common for such tests
to include an end point.



This warning can also be turned on using -gnatwa.











-gnatwC




`Suppress warnings on conditionals.'



This switch suppresses warnings for conditional expressions used in
tests that are known to be True or False at compile time.











-gnatw.c




`Activate warnings on missing component clauses.'






This switch activates warnings for record components where a record
representation clause is present and has component clauses for the
majority, but not all, of the components. A warning is given for each
component for which no component clause is present.











-gnatw.C




`Suppress warnings on missing component clauses.'



This switch suppresses warnings for record components that are
missing a component clause in the situation described above.











-gnatw_c




`Activate warnings on unknown condition in Compile_Time_Warning.'







This switch activates warnings on a pragma Compile_Time_Warning
or Compile_Time_Error whose condition has a value that is not
known at compile time.
The default is that such warnings are generated.











-gnatw_C




`Suppress warnings on unknown condition in Compile_Time_Warning.'



This switch supresses warnings on a pragma Compile_Time_Warning
or Compile_Time_Error whose condition has a value that is not
known at compile time.











-gnatwd




`Activate warnings on implicit dereferencing.'



If this switch is set, then the use of a prefix of an access type
in an indexed component, slice, or selected component without an
explicit .all will generate a warning. With this warning
enabled, access checks occur only at points where an explicit
.all appears in the source code (assuming no warnings are
generated as a result of this switch). The default is that such
warnings are not generated.











-gnatwD




`Suppress warnings on implicit dereferencing.'








This switch suppresses warnings for implicit dereferences in
indexed components, slices, and selected components.











-gnatw.d




`Activate tagging of warning and info messages.'



If this switch is set, then warning messages are tagged, with one of the
following strings:







    

  • - `[-gnatw?]'
Used to tag warnings controlled by the switch -gnatwx where x
is a letter a-z.


  • - `[-gnatw.?]'
Used to tag warnings controlled by the switch -gnatw.x where x
is a letter a-z.


  • - `[-gnatel]'
Used to tag elaboration information (info) messages generated when the
static model of elaboration is used and the -gnatel switch is set.


  • - `[restriction warning]'
Used to tag warning messages for restriction violations, activated by use
of the pragma Restriction_Warnings.


  • - `[warning-as-error]'
Used to tag warning messages that have been converted to error messages by
use of the pragma Warning_As_Error. Note that such warnings are prefixed by
the string "error: " rather than "warning: ".


  • - `[enabled by default]'
Used to tag all other warnings that are always given by default, unless
warnings are completely suppressed using pragma `Warnings(Off)' or
the switch -gnatws.















-gnatw.D




`Deactivate tagging of warning and info messages messages.'



If this switch is set, then warning messages return to the default
mode in which warnings and info messages are not tagged as described above for
-gnatw.d.














-gnatwe




`Treat warnings and style checks as errors.'



This switch causes warning messages and style check messages to be
treated as errors.
The warning string still appears, but the warning messages are counted
as errors, and prevent the generation of an object file. Note that this
is the only -gnatw switch that affects the handling of style check messages.
Note also that this switch has no effect on info (information) messages, which
are not treated as errors if this switch is present.











-gnatw.e




`Activate every optional warning.'






This switch activates all optional warnings, including those which
are not activated by -gnatwa. The use of this switch is not
recommended for normal use. If you turn this switch on, it is almost
certain that you will get large numbers of useless warnings. The
warnings that are excluded from -gnatwa are typically highly
specialized warnings that are suitable for use only in code that has
been specifically designed according to specialized coding rules.














-gnatwE




`Treat all run-time exception warnings as errors.'



This switch causes warning messages regarding errors that will be raised
during run-time execution to be treated as errors.











-gnatwf




`Activate warnings on unreferenced formals.'






This switch causes a warning to be generated if a formal parameter
is not referenced in the body of the subprogram. This warning can
also be turned on using -gnatwu. The
default is that these warnings are not generated.











-gnatwF




`Suppress warnings on unreferenced formals.'



This switch suppresses warnings for unreferenced formal
parameters. Note that the
combination -gnatwu followed by -gnatwF has the
effect of warning on unreferenced entities other than subprogram
formals.











-gnatwg




`Activate warnings on unrecognized pragmas.'






This switch causes a warning to be generated if an unrecognized
pragma is encountered. Apart from issuing this warning, the
pragma is ignored and has no effect. The default
is that such warnings are issued (satisfying the Ada Reference
Manual requirement that such warnings appear).











-gnatwG




`Suppress warnings on unrecognized pragmas.'



This switch suppresses warnings for unrecognized pragmas.











-gnatw.g




`Warnings used for GNAT sources.'



This switch sets the warning categories that are used by the standard
GNAT style. Currently this is equivalent to
-gnatwAao.q.s.CI.V.X.Z
but more warnings may be added in the future without advanced notice.











-gnatwh




`Activate warnings on hiding.'





This switch activates warnings on hiding declarations that are considered
potentially confusing. Not all cases of hiding cause warnings; for example an
overriding declaration hides an implicit declaration, which is just normal
code. The default is that warnings on hiding are not generated.











-gnatwH




`Suppress warnings on hiding.'



This switch suppresses warnings on hiding declarations.











-gnatw.h




`Activate warnings on holes/gaps in records.'





This switch activates warnings on component clauses in record
representation clauses that leave holes (gaps) in the record layout.
If this warning option is active, then record representation clauses
should specify a contiguous layout, adding unused fill fields if needed.











-gnatw.H




`Suppress warnings on holes/gaps in records.'



This switch suppresses warnings on component clauses in record
representation clauses that leave holes (haps) in the record layout.











-gnatwi




`Activate warnings on implementation units.'



This switch activates warnings for a `with' of an internal GNAT
implementation unit, defined as any unit from the Ada,
Interfaces, GNAT,
or System
hierarchies that is not
documented in either the Ada Reference Manual or the GNAT
Programmer’s Reference Manual. Such units are intended only
for internal implementation purposes and should not be `with'ed
by user programs. The default is that such warnings are generated











-gnatwI




`Disable warnings on implementation units.'



This switch disables warnings for a `with' of an internal GNAT
implementation unit.











-gnatw.i




`Activate warnings on overlapping actuals.'



This switch enables a warning on statically detectable overlapping actuals in
a subprogram call, when one of the actuals is an in-out parameter, and the
types of the actuals are not by-copy types. This warning is off by default.











-gnatw.I




`Disable warnings on overlapping actuals.'



This switch disables warnings on overlapping actuals in a call..











-gnatwj




`Activate warnings on obsolescent features (Annex J).'








If this warning option is activated, then warnings are generated for
calls to subprograms marked with pragma Obsolescent and
for use of features in Annex J of the Ada Reference Manual. In the
case of Annex J, not all features are flagged. In particular use
of the renamed packages (like Text_IO) and use of package
ASCII are not flagged, since these are very common and
would generate many annoying positive warnings. The default is that
such warnings are not generated.



In addition to the above cases, warnings are also generated for
GNAT features that have been provided in past versions but which
have been superseded (typically by features in the new Ada standard).
For example, pragma Ravenscar will be flagged since its
function is replaced by pragma Profile(Ravenscar), and
pragma Interface_Name will be flagged since its function
is replaced by pragma Import.



Note that this warning option functions differently from the
restriction No_Obsolescent_Features in two respects.
First, the restriction applies only to annex J features.
Second, the restriction does flag uses of package ASCII.











-gnatwJ




`Suppress warnings on obsolescent features (Annex J).'



This switch disables warnings on use of obsolescent features.











-gnatw.j




`Activate warnings on late declarations of tagged type primitives.'



This switch activates warnings on visible primitives added to a
tagged type after deriving a private extension from it.











-gnatw.J




`Suppress warnings on late declarations of tagged type primitives.'



This switch suppresses warnings on visible primitives added to a
tagged type after deriving a private extension from it.











-gnatwk




`Activate warnings on variables that could be constants.'



This switch activates warnings for variables that are initialized but
never modified, and then could be declared constants. The default is that
such warnings are not given.











-gnatwK




`Suppress warnings on variables that could be constants.'



This switch disables warnings on variables that could be declared constants.











-gnatw.k




`Activate warnings on redefinition of names in standard.'



This switch activates warnings for declarations that declare a name that
is defined in package Standard. Such declarations can be confusing,
especially since the names in package Standard continue to be directly
visible, meaning that use visibiliy on such redeclared names does not
work as expected. Names of discriminants and components in records are
not included in this check.











-gnatw.K




`Suppress warnings on redefinition of names in standard.'



This switch activates warnings for declarations that declare a name that
is defined in package Standard.











-gnatwl




`Activate warnings for elaboration pragmas.'






This switch activates warnings for possible elaboration problems,
including suspicious use
of Elaborate pragmas, when using the static elaboration model, and
possible situations that may raise Program_Error when using the
dynamic elaboration model.
See the section in this guide on elaboration checking for further details.
The default is that such warnings
are not generated.











-gnatwL




`Suppress warnings for elaboration pragmas.'



This switch suppresses warnings for possible elaboration problems.











-gnatw.l




`List inherited aspects.'



This switch causes the compiler to list inherited invariants,
preconditions, and postconditions from Type_Invariant’Class, Invariant’Class,
Pre’Class, and Post’Class aspects. Also list inherited subtype predicates.











-gnatw.L




`Suppress listing of inherited aspects.'



This switch suppresses listing of inherited aspects.











-gnatwm




`Activate warnings on modified but unreferenced variables.'



This switch activates warnings for variables that are assigned (using
an initialization value or with one or more assignment statements) but
whose value is never read. The warning is suppressed for volatile
variables and also for variables that are renamings of other variables
or for which an address clause is given.
The default is that these warnings are not given.











-gnatwM




`Disable warnings on modified but unreferenced variables.'



This switch disables warnings for variables that are assigned or
initialized, but never read.











-gnatw.m




`Activate warnings on suspicious modulus values.'



This switch activates warnings for modulus values that seem suspicious.
The cases caught are where the size is the same as the modulus (e.g.
a modulus of 7 with a size of 7 bits), and modulus values of 32 or 64
with no size clause. The guess in both cases is that 2**x was intended
rather than x. In addition expressions of the form 2*x for small x
generate a warning (the almost certainly accurate guess being that
2**x was intended). The default is that these warnings are given.











-gnatw.M




`Disable warnings on suspicious modulus values.'



This switch disables warnings for suspicious modulus values.











-gnatwn




`Set normal warnings mode.'



This switch sets normal warning mode, in which enabled warnings are
issued and treated as warnings rather than errors. This is the default
mode. the switch -gnatwn can be used to cancel the effect of
an explicit -gnatws or
-gnatwe. It also cancels the effect of the
implicit -gnatwe that is activated by the
use of -gnatg.














-gnatw.n




`Activate warnings on atomic synchronization.'



This switch actives warnings when an access to an atomic variable
requires the generation of atomic synchronization code. These
warnings are off by default.











-gnatw.N




`Suppress warnings on atomic synchronization.'






This switch suppresses warnings when an access to an atomic variable
requires the generation of atomic synchronization code.














-gnatwo




`Activate warnings on address clause overlays.'



This switch activates warnings for possibly unintended initialization
effects of defining address clauses that cause one variable to overlap
another. The default is that such warnings are generated.











-gnatwO




`Suppress warnings on address clause overlays.'



This switch suppresses warnings on possibly unintended initialization
effects of defining address clauses that cause one variable to overlap
another.











-gnatw.o




`Activate warnings on modified but unreferenced out parameters.'



This switch activates warnings for variables that are modified by using
them as actuals for a call to a procedure with an out mode formal, where
the resulting assigned value is never read. It is applicable in the case
where there is more than one out mode formal. If there is only one out
mode formal, the warning is issued by default (controlled by -gnatwu).
The warning is suppressed for volatile
variables and also for variables that are renamings of other variables
or for which an address clause is given.
The default is that these warnings are not given.











-gnatw.O




`Disable warnings on modified but unreferenced out parameters.'



This switch suppresses warnings for variables that are modified by using
them as actuals for a call to a procedure with an out mode formal, where
the resulting assigned value is never read.














-gnatwp




`Activate warnings on ineffective pragma Inlines.'



This switch activates warnings for failure of front end inlining
(activated by -gnatN) to inline a particular call. There are
many reasons for not being able to inline a call, including most
commonly that the call is too complex to inline. The default is
that such warnings are not given.
Warnings on ineffective inlining by the gcc back-end can be activated
separately, using the gcc switch -Winline.











-gnatwP




`Suppress warnings on ineffective pragma Inlines.'



This switch suppresses warnings on ineffective pragma Inlines. If the
inlining mechanism cannot inline a call, it will simply ignore the
request silently.














-gnatw.p




`Activate warnings on parameter ordering.'



This switch activates warnings for cases of suspicious parameter
ordering when the list of arguments are all simple identifiers that
match the names of the formals, but are in a different order. The
warning is suppressed if any use of named parameter notation is used,
so this is the appropriate way to suppress a false positive (and
serves to emphasize that the "misordering" is deliberate). The
default is that such warnings are not given.











-gnatw.P




`Suppress warnings on parameter ordering.'



This switch suppresses warnings on cases of suspicious parameter
ordering.














-gnatwq




`Activate warnings on questionable missing parentheses.'



This switch activates warnings for cases where parentheses are not used and
the result is potential ambiguity from a readers point of view. For example
(not a > b) when a and b are modular means ((not a) > b) and very likely the
programmer intended (not (a > b)). Similarly (-x mod 5) means (-(x mod 5)) and
quite likely ((-x) mod 5) was intended. In such situations it seems best to
follow the rule of always parenthesizing to make the association clear, and
this warning switch warns if such parentheses are not present. The default
is that these warnings are given.











-gnatwQ




`Suppress warnings on questionable missing parentheses.'



This switch suppresses warnings for cases where the association is not
clear and the use of parentheses is preferred.














-gnatw.q




`Activate warnings on questionable layout of record types.'



This switch activates warnings for cases where the default layout of
a record type, that is to say the layout of its components in textual
order of the source code, would very likely cause inefficiencies in
the code generated by the compiler, both in terms of space and speed
during execution. One warning is issued for each problematic component
without representation clause in the nonvariant part and then in each
variant recursively, if any.



The purpose of these warnings is neither to prescribe an optimal layout
nor to force the use of representation clauses, but rather to get rid of
the most blatant inefficiencies in the layout. Therefore, the default
layout is matched against the following synthetic ordered layout and
the deviations are flagged on a component-by-component basis:






for the nonvariant part and for each variant recursively, if any.



The exact wording of the warning depends on whether the compiler is allowed
to reorder the components in the record type or precluded from doing it by
means of pragma No_Component_Reordering.



The default is that these warnings are not given.











-gnatw.Q




`Suppress warnings on questionable layout of record types.'



This switch suppresses warnings for cases where the default layout of
a record type would very likely cause inefficiencies.











-gnatwr




`Activate warnings on redundant constructs.'



This switch activates warnings for redundant constructs. The following
is the current list of constructs regarded as redundant:






The default is that warnings for redundant constructs are not given.











-gnatwR




`Suppress warnings on redundant constructs.'



This switch suppresses warnings for redundant constructs.











-gnatw.r




`Activate warnings for object renaming function.'



This switch activates warnings for an object renaming that renames a
function call, which is equivalent to a constant declaration (as
opposed to renaming the function itself).  The default is that these
warnings are given.











-gnatw.R




`Suppress warnings for object renaming function.'



This switch suppresses warnings for object renaming function.











-gnatw_r




`Activate warnings for out-of-order record representation clauses.'



This switch activates warnings for record representation clauses,
if the order of component declarations, component clauses,
and bit-level layout do not all agree.
The default is that these warnings are not given.











-gnatw_R




`Suppress warnings for out-of-order record representation clauses.'











-gnatws




`Suppress all warnings.'



This switch completely suppresses the
output of all warning messages from the GNAT front end, including
both warnings that can be controlled by switches described in this
section, and those that are normally given unconditionally. The
effect of this suppress action can only be cancelled by a subsequent
use of the switch -gnatwn.



Note that switch -gnatws does not suppress
warnings from the gcc back end.
To suppress these back end warnings as well, use the switch -w
in addition to -gnatws. Also this switch has no effect on the
handling of style check messages.













-gnatw.s




`Activate warnings on overridden size clauses.'



This switch activates warnings on component clauses in record
representation clauses where the length given overrides that
specified by an explicit size clause for the component type. A
warning is similarly given in the array case if a specified
component size overrides an explicit size clause for the array
component type.











-gnatw.S




`Suppress warnings on overridden size clauses.'



This switch suppresses warnings on component clauses in record
representation clauses that override size clauses, and similar
warnings when an array component size overrides a size clause.

















-gnatwt




`Activate warnings for tracking of deleted conditional code.'



This switch activates warnings for tracking of code in conditionals (IF and
CASE statements) that is detected to be dead code which cannot be executed, and
which is removed by the front end. This warning is off by default. This may be
useful for detecting deactivated code in certified applications.











-gnatwT




`Suppress warnings for tracking of deleted conditional code.'



This switch suppresses warnings for tracking of deleted conditional code.











-gnatw.t




`Activate warnings on suspicious contracts.'



This switch activates warnings on suspicious contracts. This includes
warnings on suspicious postconditions (whether a pragma Postcondition or a
Post aspect in Ada 2012) and suspicious contract cases (pragma or aspect
Contract_Cases). A function postcondition or contract case is suspicious
when no postcondition or contract case for this function mentions the result
of the function.  A procedure postcondition or contract case is suspicious
when it only refers to the pre-state of the procedure, because in that case
it should rather be expressed as a precondition. This switch also controls
warnings on suspicious cases of expressions typically found in contracts like
quantified expressions and uses of Update attribute. The default is that such
warnings are generated.











-gnatw.T




`Suppress warnings on suspicious contracts.'



This switch suppresses warnings on suspicious contracts.











-gnatwu




`Activate warnings on unused entities.'



This switch activates warnings to be generated for entities that
are declared but not referenced, and for units that are `with'ed
and not
referenced. In the case of packages, a warning is also generated if
no entities in the package are referenced. This means that if a with’ed
package is referenced but the only references are in use
clauses or renames
declarations, a warning is still generated. A warning is also generated
for a generic package that is `with'ed but never instantiated.
In the case where a package or subprogram body is compiled, and there
is a `with' on the corresponding spec
that is only referenced in the body,
a warning is also generated, noting that the
`with' can be moved to the body. The default is that
such warnings are not generated.
This switch also activates warnings on unreferenced formals
(it includes the effect of -gnatwf).











-gnatwU




`Suppress warnings on unused entities.'



This switch suppresses warnings for unused entities and packages.
It also turns off warnings on unreferenced formals (and thus includes
the effect of -gnatwF).











-gnatw.u




`Activate warnings on unordered enumeration types.'



This switch causes enumeration types to be considered as conceptually
unordered, unless an explicit pragma Ordered is given for the type.
The effect is to generate warnings in clients that use explicit comparisons
or subranges, since these constructs both treat objects of the type as
ordered. (A `client' is defined as a unit that is other than the unit in
which the type is declared, or its body or subunits.) Please refer to
the description of pragma Ordered in the
GNAT Reference Manual for further details.
The default is that such warnings are not generated.











-gnatw.U




`Deactivate warnings on unordered enumeration types.'



This switch causes all enumeration types to be considered as ordered, so
that no warnings are given for comparisons or subranges for any type.













-gnatwv




`Activate warnings on unassigned variables.'



This switch activates warnings for access to variables which
may not be properly initialized. The default is that
such warnings are generated.











-gnatwV




`Suppress warnings on unassigned variables.'



This switch suppresses warnings for access to variables which
may not be properly initialized.
For variables of a composite type, the warning can also be suppressed in
Ada 2005 by using a default initialization with a box. For example, if
Table is an array of records whose components are only partially uninitialized,
then the following code:





Tab : Table := (others => <>);




will suppress warnings on subsequent statements that access components
of variable Tab.













-gnatw.v




`Activate info messages for non-default bit order.'



This switch activates messages (labeled "info", they are not warnings,
just informational messages) about the effects of non-default bit-order
on records to which a component clause is applied. The effect of specifying
non-default bit ordering is a bit subtle (and changed with Ada 2005), so
these messages, which are given by default, are useful in understanding the
exact consequences of using this feature.











-gnatw.V




`Suppress info messages for non-default bit order.'



This switch suppresses information messages for the effects of specifying
non-default bit order on record components with component clauses.













-gnatww




`Activate warnings on wrong low bound assumption.'



This switch activates warnings for indexing an unconstrained string parameter
with a literal or S’Length. This is a case where the code is assuming that the
low bound is one, which is in general not true (for example when a slice is
passed). The default is that such warnings are generated.











-gnatwW




`Suppress warnings on wrong low bound assumption.'



This switch suppresses warnings for indexing an unconstrained string parameter
with a literal or S’Length. Note that this warning can also be suppressed
in a particular case by adding an assertion that the lower bound is 1,
as shown in the following example:





procedure K (S : String) is
   pragma Assert (S'First = 1);
   ...















-gnatw.w




`Activate warnings on Warnings Off pragmas.'



This switch activates warnings for use of pragma Warnings (Off, entity)
where either the pragma is entirely useless (because it suppresses no
warnings), or it could be replaced by pragma Unreferenced or
pragma Unmodified.
Also activates warnings for the case of
Warnings (Off, String), where either there is no matching
Warnings (On, String), or the Warnings (Off) did not suppress any warning.
The default is that these warnings are not given.











-gnatw.W




`Suppress warnings on unnecessary Warnings Off pragmas.'



This switch suppresses warnings for use of pragma Warnings (Off, ...).













-gnatwx




`Activate warnings on Export/Import pragmas.'



This switch activates warnings on Export/Import pragmas when
the compiler detects a possible conflict between the Ada and
foreign language calling sequences. For example, the use of
default parameters in a convention C procedure is dubious
because the C compiler cannot supply the proper default, so
a warning is issued. The default is that such warnings are
generated.











-gnatwX




`Suppress warnings on Export/Import pragmas.'



This switch suppresses warnings on Export/Import pragmas.
The sense of this is that you are telling the compiler that
you know what you are doing in writing the pragma, and it
should not complain at you.











-gnatw.x




`Activate warnings for No_Exception_Propagation mode.'



This switch activates warnings for exception usage when pragma Restrictions
(No_Exception_Propagation) is in effect. Warnings are given for implicit or
explicit exception raises which are not covered by a local handler, and for
exception handlers which do not cover a local raise. The default is that
these warnings are given for units that contain exception handlers.





-gnatw.X




`Disable warnings for No_Exception_Propagation mode.'



This switch disables warnings for exception usage when pragma Restrictions
(No_Exception_Propagation) is in effect.













-gnatwy




`Activate warnings for Ada compatibility issues.'



For the most part, newer versions of Ada are upwards compatible
with older versions. For example, Ada 2005 programs will almost
always work when compiled as Ada 2012.
However there are some exceptions (for example the fact that
some is now a reserved word in Ada 2012). This
switch activates several warnings to help in identifying
and correcting such incompatibilities. The default is that
these warnings are generated. Note that at one point Ada 2005
was called Ada 0Y, hence the choice of character.













-gnatwY




`Disable warnings for Ada compatibility issues.'



This switch suppresses the warnings intended to help in identifying
incompatibilities between Ada language versions.













-gnatw.y




`Activate information messages for why package spec needs body.'



There are a number of cases in which a package spec needs a body.
For example, the use of pragma Elaborate_Body, or the declaration
of a procedure specification requiring a completion. This switch
causes information messages to be output showing why a package
specification requires a body. This can be useful in the case of
a large package specification which is unexpectedly requiring a
body. The default is that such information messages are not output.













-gnatw.Y




`Disable information messages for why package spec needs body.'



This switch suppresses the output of information messages showing why
a package specification needs a body.













-gnatwz




`Activate warnings on unchecked conversions.'



This switch activates warnings for unchecked conversions
where the types are known at compile time to have different
sizes. The default is that such warnings are generated. Warnings are also
generated for subprogram pointers with different conventions.











-gnatwZ




`Suppress warnings on unchecked conversions.'



This switch suppresses warnings for unchecked conversions
where the types are known at compile time to have different
sizes or conventions.













-gnatw.z




`Activate warnings for size not a multiple of alignment.'



This switch activates warnings for cases of array and record types
with specified Size and Alignment attributes where the
size is not a multiple of the alignment, resulting in an object
size that is greater than the specified size. The default
is that such warnings are generated.













-gnatw.Z




`Suppress warnings for size not a multiple of alignment.'



This switch suppresses warnings for cases of array and record types
with specified Size and Alignment attributes where the
size is not a multiple of the alignment, resulting in an object
size that is greater than the specified size. The warning can also
be suppressed by giving an explicit Object_Size value.











-Wunused




The warnings controlled by the -gnatw switch are generated by
the front end of the compiler. The GCC back end can provide
additional warnings and they are controlled by the -W switch.
For example, -Wunused activates back end
warnings for entities that are declared but not referenced.











-Wuninitialized




Similarly, -Wuninitialized activates
the back end warning for uninitialized variables. This switch must be
used in conjunction with an optimization level greater than zero.











-Wstack-usage=`len'




Warn if the stack usage of a subprogram might be larger than len bytes.
See Static Stack Usage Analysis for details.











-Wall




This switch enables most warnings from the GCC back end.
The code generator detects a number of warning situations that are missed
by the GNAT front end, and this switch can be used to activate them.
The use of this switch also sets the default front end warning mode to
-gnatwa, that is, most front end warnings activated as well.











-w




Conversely, this switch suppresses warnings from the GCC back end.
The use of this switch also sets the default front end warning mode to
-gnatws, that is, front end warnings suppressed as well.











-Werror




This switch causes warnings from the GCC back end to be treated as
errors.  The warning string still appears, but the warning messages are
counted as errors, and prevent the generation of an object file.






A string of warning parameters can be used in the same parameter. For example:





-gnatwaGe




will turn on all optional warnings except for unrecognized pragma warnings,
and also specify that warnings should be treated as errors.



When no switch -gnatw is used, this is equivalent to:

















Next: , Previous: Warning Message Control, Up: Compiler Switches   [Contents][Index]





4.3.4 Debugging and Assertion Control









-gnata


















The -gnata option is equivalent to the following Assertion_Policy pragma:





pragma Assertion_Policy (Check);




Which is a shorthand for:





pragma Assertion_Policy
  (Assert               => Check,
   Static_Predicate     => Check,
   Dynamic_Predicate    => Check,
   Pre                  => Check,
   Pre'Class            => Check,
   Post                 => Check,
   Post'Class           => Check,
   Type_Invariant       => Check,
   Type_Invariant'Class => Check);




The pragmas Assert and Debug normally have no effect and
are ignored. This switch, where a stands for ’assert’, causes
pragmas Assert and Debug to be activated. This switch also
causes preconditions, postconditions, subtype predicates, and
type invariants to be activated.



The pragmas have the form:





pragma Assert (<Boolean-expression> [, <static-string-expression>])
pragma Debug (<procedure call>)
pragma Type_Invariant (<type-local-name>, <Boolean-expression>)
pragma Predicate (<type-local-name>, <Boolean-expression>)
pragma Precondition (<Boolean-expression>, <string-expression>)
pragma Postcondition (<Boolean-expression>, <string-expression>)




The aspects have the form:





with [Pre|Post|Type_Invariant|Dynamic_Predicate|Static_Predicate]
  => <Boolean-expression>;




The Assert pragma causes Boolean-expression to be tested.
If the result is True, the pragma has no effect (other than
possible side effects from evaluating the expression). If the result is
False, the exception Assert_Failure declared in the package
System.Assertions is raised (passing static-string-expression, if
present, as the message associated with the exception). If no string
expression is given, the default is a string containing the file name and
line number of the pragma.



The Debug pragma causes procedure to be called. Note that
pragma Debug may appear within a declaration sequence, allowing
debugging procedures to be called between declarations.



For the aspect specification, the Boolean-expression is evaluated.
If the result is True, the aspect has no effect. If the result
is False, the exception Assert_Failure is raised.












Next: , Previous: Debugging and Assertion Control, Up: Compiler Switches   [Contents][Index]





4.3.5 Validity Checking






The Ada Reference Manual defines the concept of invalid values (see
RM 13.9.1). The primary source of invalid values is uninitialized
variables. A scalar variable that is left uninitialized may contain
an invalid value; the concept of invalid does not apply to access or
composite types.



It is an error to read an invalid value, but the RM does not require
run-time checks to detect such errors, except for some minimal
checking to prevent erroneous execution (i.e. unpredictable
behavior). This corresponds to the -gnatVd switch below,
which is the default. For example, by default, if the expression of a
case statement is invalid, it will raise Constraint_Error rather than
causing a wild jump, and if an array index on the left-hand side of an
assignment is invalid, it will raise Constraint_Error rather than
overwriting an arbitrary memory location.



The -gnatVa may be used to enable additional validity checks,
which are not required by the RM. These checks are often very
expensive (which is why the RM does not require them). These checks
are useful in tracking down uninitialized variables, but they are
not usually recommended for production builds, and in particular
we do not recommend using these extra validity checking options in
combination with optimization, since this can confuse the optimizer.
If performance is a consideration, leading to the need to optimize,
then the validity checking options should not be used.



The other -gnatV`x' switches below allow finer-grained
control; you can enable whichever validity checks you desire. However,
for most debugging purposes, -gnatVa is sufficient, and the
default -gnatVd (i.e. standard Ada behavior) is usually
sufficient for non-debugging use.



The -gnatB switch tells the compiler to assume that all
values are valid (that is, within their declared subtype range)
except in the context of a use of the Valid attribute. This means
the compiler can generate more efficient code, since the range
of values is better known at compile time. However, an uninitialized
variable can cause wild jumps and memory corruption in this mode.



The -gnatV`x' switch allows control over the validity
checking mode as described below.
The x argument is a string of letters that
indicate validity checks that are performed or not performed in addition
to the default checks required by Ada as described above.








-gnatVa




`All validity checks.'



All validity checks are turned on.
That is, -gnatVa is
equivalent to gnatVcdfimorst.











-gnatVc




`Validity checks for copies.'



The right hand side of assignments, and the initializing values of
object declarations are validity checked.











-gnatVd




`Default (RM) validity checks.'



Some validity checks are done by default following normal Ada semantics
(RM 13.9.1 (9-11)).
A check is done in case statements that the expression is within the range
of the subtype. If it is not, Constraint_Error is raised.
For assignments to array components, a check is done that the expression used
as index is within the range. If it is not, Constraint_Error is raised.
Both these validity checks may be turned off using switch -gnatVD.
They are turned on by default. If -gnatVD is specified, a subsequent
switch -gnatVd will leave the checks turned on.
Switch -gnatVD should be used only if you are sure that all such
expressions have valid values. If you use this switch and invalid values
are present, then the program is erroneous, and wild jumps or memory
overwriting may occur.











-gnatVe




`Validity checks for elementary components.'



In the absence of this switch, assignments to record or array components are
not validity checked, even if validity checks for assignments generally
(-gnatVc) are turned on. In Ada, assignment of composite values do not
require valid data, but assignment of individual components does. So for
example, there is a difference between copying the elements of an array with a
slice assignment, compared to assigning element by element in a loop. This
switch allows you to turn off validity checking for components, even when they
are assigned component by component.











-gnatVf




`Validity checks for floating-point values.'



In the absence of this switch, validity checking occurs only for discrete
values. If -gnatVf is specified, then validity checking also applies
for floating-point values, and NaNs and infinities are considered invalid,
as well as out of range values for constrained types. Note that this means
that standard IEEE infinity mode is not allowed. The exact contexts
in which floating-point values are checked depends on the setting of other
options. For example, -gnatVif or -gnatVfi
(the order does not matter) specifies that floating-point parameters of mode
in should be validity checked.











-gnatVi




`Validity checks for ‘‘in‘‘ mode parameters.'



Arguments for parameters of mode in are validity checked in function
and procedure calls at the point of call.











-gnatVm




`Validity checks for ‘‘in out‘‘ mode parameters.'



Arguments for parameters of mode in out are validity checked in
procedure calls at the point of call. The 'm' here stands for
modify, since this concerns parameters that can be modified by the call.
Note that there is no specific option to test out parameters,
but any reference within the subprogram will be tested in the usual
manner, and if an invalid value is copied back, any reference to it
will be subject to validity checking.











-gnatVn




`No validity checks.'



This switch turns off all validity checking, including the default checking
for case statements and left hand side subscripts. Note that the use of
the switch -gnatp suppresses all run-time checks, including
validity checks, and thus implies -gnatVn. When this switch
is used, it cancels any other -gnatV previously issued.











-gnatVo




`Validity checks for operator and attribute operands.'



Arguments for predefined operators and attributes are validity checked.
This includes all operators in package Standard,
the shift operators defined as intrinsic in package Interfaces
and operands for attributes such as Pos. Checks are also made
on individual component values for composite comparisons, and on the
expressions in type conversions and qualified expressions. Checks are
also made on explicit ranges using .. (e.g., slices, loops etc).











-gnatVp




`Validity checks for parameters.'



This controls the treatment of parameters within a subprogram (as opposed
to -gnatVi and -gnatVm which control validity testing
of parameters on a call. If either of these call options is used, then
normally an assumption is made within a subprogram that the input arguments
have been validity checking at the point of call, and do not need checking
again within a subprogram). If -gnatVp is set, then this assumption
is not made, and parameters are not assumed to be valid, so their validity
will be checked (or rechecked) within the subprogram.











-gnatVr




`Validity checks for function returns.'



The expression in return statements in functions is validity
checked.











-gnatVs




`Validity checks for subscripts.'



All subscripts expressions are checked for validity, whether they appear
on the right side or left side (in default mode only left side subscripts
are validity checked).











-gnatVt




`Validity checks for tests.'



Expressions used as conditions in if, while or exit
statements are checked, as well as guard expressions in entry calls.






The -gnatV switch may be followed by a string of letters
to turn on a series of validity checking options.
For example, -gnatVcr
specifies that in addition to the default validity checking, copies and
function return expressions are to be validity checked.
In order to make it easier to specify the desired combination of effects,
the upper case letters CDFIMORST may
be used to turn off the corresponding lower case option.
Thus -gnatVaM turns on all validity checking options except for
checking of in out parameters.



The specification of additional validity checking generates extra code (and
in the case of -gnatVa the code expansion can be substantial).
However, these additional checks can be very useful in detecting
uninitialized variables, incorrect use of unchecked conversion, and other
errors leading to invalid values. The use of pragma Initialize_Scalars
is useful in conjunction with the extra validity checking, since this
ensures that wherever possible uninitialized variables have invalid values.



See also the pragma Validity_Checks which allows modification of
the validity checking mode at the program source level, and also allows for
temporary disabling of validity checks.









Next: , Previous: Validity Checking, Up: Compiler Switches   [Contents][Index]





4.3.6 Style Checking








The -gnatyx switch causes the compiler to
enforce specified style rules. A limited set of style rules has been used
in writing the GNAT sources themselves. This switch allows user programs
to activate all or some of these checks. If the source program fails a
specified style check, an appropriate message is given, preceded by
the character sequence ’(style)’. This message does not prevent
successful compilation (unless the -gnatwe switch is used).



Note that this is by no means intended to be a general facility for
checking arbitrary coding standards. It is simply an embedding of the
style rules we have chosen for the GNAT sources. If you are starting
a project which does not have established style standards, you may
find it useful to adopt the entire set of GNAT coding standards, or
some subset of them.




The string x is a sequence of letters or digits
indicating the particular style
checks to be performed. The following checks are defined:








-gnaty0




`Specify indentation level.'



If a digit from 1-9 appears
in the string after -gnaty
then proper indentation is checked, with the digit indicating the
indentation level required. A value of zero turns off this style check.
The general style of required indentation is as specified by
the examples in the Ada Reference Manual. Full line comments must be
aligned with the -- starting on a column that is a multiple of
the alignment level, or they may be aligned the same way as the following
non-blank line (this is useful when full line comments appear in the middle
of a statement, or they may be aligned with the source line on the previous
non-blank line.











-gnatya




`Check attribute casing.'



Attribute names, including the case of keywords such as digits
used as attributes names, must be written in mixed case, that is, the
initial letter and any letter following an underscore must be uppercase.
All other letters must be lowercase.











-gnatyA




`Use of array index numbers in array attributes.'



When using the array attributes First, Last, Range,
or Length, the index number must be omitted for one-dimensional arrays
and is required for multi-dimensional arrays.











-gnatyb




`Blanks not allowed at statement end.'



Trailing blanks are not allowed at the end of statements. The purpose of this
rule, together with h (no horizontal tabs), is to enforce a canonical format
for the use of blanks to separate source tokens.











-gnatyB




`Check Boolean operators.'



The use of AND/OR operators is not permitted except in the cases of modular
operands, array operands, and simple stand-alone boolean variables or
boolean constants. In all other cases and then/or else are
required.











-gnatyc




`Check comments, double space.'



Comments must meet the following set of rules:















-gnatyC




`Check comments, single space.'



This is identical to c except that only one space
is required following the -- of a comment instead of two.











-gnatyd




`Check no DOS line terminators present.'



All lines must be terminated by a single ASCII.LF
character (in particular the DOS line terminator sequence CR/LF is not
allowed).











-gnatyD




`Check declared identifiers in mixed case.'



Declared identifiers must be in mixed case, as in
This_Is_An_Identifier. Use -gnatyr in addition to ensure
that references match declarations.











-gnatye




`Check end/exit labels.'



Optional labels on end statements ending subprograms and on
exit statements exiting named loops, are required to be present.











-gnatyf




`No form feeds or vertical tabs.'



Neither form feeds nor vertical tab characters are permitted
in the source text.











-gnatyg




`GNAT style mode.'



The set of style check switches is set to match that used by the GNAT sources.
This may be useful when developing code that is eventually intended to be
incorporated into GNAT. Currently this is equivalent to -gnatyydISux)
but additional style switches may be added to this set in the future without
advance notice.











-gnatyh




`No horizontal tabs.'



Horizontal tab characters are not permitted in the source text.
Together with the b (no blanks at end of line) check, this
enforces a canonical form for the use of blanks to separate
source tokens.











-gnatyi




`Check if-then layout.'



The keyword then must appear either on the same
line as corresponding if, or on a line on its own, lined
up under the if.











-gnatyI




`check mode IN keywords.'



Mode in (the default mode) is not
allowed to be given explicitly. in out is fine,
but not in on its own.











-gnatyk




`Check keyword casing.'



All keywords must be in lower case (with the exception of keywords
such as digits used as attribute names to which this check
does not apply).











-gnatyl




`Check layout.'



Layout of statement and declaration constructs must follow the
recommendations in the Ada Reference Manual, as indicated by the
form of the syntax rules. For example an else keyword must
be lined up with the corresponding if keyword.



There are two respects in which the style rule enforced by this check
option are more liberal than those in the Ada Reference Manual. First
in the case of record declarations, it is permissible to put the
record keyword on the same line as the type keyword, and
then the end in end record must line up under type.
This is also permitted when the type declaration is split on two lines.
For example, any of the following three layouts is acceptable:





type q is record
   a : integer;
   b : integer;
end record;

type q is
   record
      a : integer;
      b : integer;
   end record;

type q is
   record
      a : integer;
      b : integer;
end record;




Second, in the case of a block statement, a permitted alternative
is to put the block label on the same line as the declare or
begin keyword, and then line the end keyword up under
the block label. For example both the following are permitted:





Block : declare
   A : Integer := 3;
begin
   Proc (A, A);
end Block;

Block :
   declare
      A : Integer := 3;
   begin
      Proc (A, A);
   end Block;




The same alternative format is allowed for loops. For example, both of
the following are permitted:





Clear : while J < 10 loop
   A (J) := 0;
end loop Clear;

Clear :
   while J < 10 loop
      A (J) := 0;
   end loop Clear;













-gnatyL




`Set maximum nesting level.'



The maximum level of nesting of constructs (including subprograms, loops,
blocks, packages, and conditionals) may not exceed the given value
`nnn'. A value of zero disconnects this style check.











-gnatym




`Check maximum line length.'



The length of source lines must not exceed 79 characters, including
any trailing blanks. The value of 79 allows convenient display on an
80 character wide device or window, allowing for possible special
treatment of 80 character lines. Note that this count is of
characters in the source text. This means that a tab character counts
as one character in this count and a wide character sequence counts as
a single character (however many bytes are needed in the encoding).











-gnatyM




`Set maximum line length.'



The length of lines must not exceed the
given value `nnn'. The maximum value that can be specified is 32767.
If neither style option for setting the line length is used, then the
default is 255. This also controls the maximum length of lexical elements,
where the only restriction is that they must fit on a single line.











-gnatyn




`Check casing of entities in Standard.'



Any identifier from Standard must be cased
to match the presentation in the Ada Reference Manual (for example,
Integer and ASCII.NUL).











-gnatyN




`Turn off all style checks.'



All style check options are turned off.











-gnatyo




`Check order of subprogram bodies.'



All subprogram bodies in a given scope
(e.g., a package body) must be in alphabetical order. The ordering
rule uses normal Ada rules for comparing strings, ignoring casing
of letters, except that if there is a trailing numeric suffix, then
the value of this suffix is used in the ordering (e.g., Junk2 comes
before Junk10).











-gnatyO




`Check that overriding subprograms are explicitly marked as such.'



This applies to all subprograms of a derived type that override a primitive
operation of the type, for both tagged and untagged types. In particular,
the declaration of a primitive operation of a type extension that overrides
an inherited operation must carry an overriding indicator. Another case is
the declaration of a function that overrides a predefined operator (such
as an equality operator).











-gnatyp




`Check pragma casing.'



Pragma names must be written in mixed case, that is, the
initial letter and any letter following an underscore must be uppercase.
All other letters must be lowercase. An exception is that SPARK_Mode is
allowed as an alternative for Spark_Mode.











-gnatyr




`Check references.'



All identifier references must be cased in the same way as the
corresponding declaration. No specific casing style is imposed on
identifiers. The only requirement is for consistency of references
with declarations.











-gnatys




`Check separate specs.'



Separate declarations (’specs’) are required for subprograms (a
body is not allowed to serve as its own declaration). The only
exception is that parameterless library level procedures are
not required to have a separate declaration. This exception covers
the most frequent form of main program procedures.











-gnatyS




`Check no statements after then/else.'



No statements are allowed
on the same line as a then or else keyword following the
keyword in an if statement. or else and and then are not
affected, and a special exception allows a pragma to appear after else.











-gnatyt




`Check token spacing.'



The following token spacing rules are enforced:






Exactly one blank (and no other white space) must appear between
a not token and a following in token.











-gnatyu




`Check unnecessary blank lines.'



Unnecessary blank lines are not allowed. A blank line is considered
unnecessary if it appears at the end of the file, or if more than
one blank line occurs in sequence.











-gnatyx




`Check extra parentheses.'



Unnecessary extra level of parentheses (C-style) are not allowed
around conditions in if statements, while statements and
exit statements.











-gnatyy




`Set all standard style check options.'



This is equivalent to gnaty3aAbcefhiklmnprst, that is all checking
options enabled with the exception of -gnatyB, -gnatyd,
-gnatyI, -gnatyLnnn, -gnatyo, -gnatyO,
-gnatyS, -gnatyu, and -gnatyx.











-gnaty-




`Remove style check options.'



This causes any subsequent options in the string to act as canceling the
corresponding style check option. To cancel maximum nesting level control,
use the L parameter without any integer value after that, because any
digit following `-' in the parameter string of the -gnaty
option will be treated as canceling the indentation check. The same is true
for the M parameter. y and N parameters are not
allowed after `-'.











-gnaty+




`Enable style check options.'



This causes any subsequent options in the string to enable the corresponding
style check option. That is, it cancels the effect of a previous -,
if any.








In the above rules, appearing in column one is always permitted, that is,
counts as meeting either a requirement for a required preceding space,
or as meeting a requirement for no preceding space.



Appearing at the end of a line is also always permitted, that is, counts
as meeting either a requirement for a following space, or as meeting
a requirement for no following space.



If any of these style rules is violated, a message is generated giving
details on the violation. The initial characters of such messages are
always ’(style)’. Note that these messages are treated as warning
messages, so they normally do not prevent the generation of an object
file. The -gnatwe switch can be used to treat warning messages,
including style messages, as fatal errors.



The switch -gnaty on its own (that is not
followed by any letters or digits) is equivalent
to the use of -gnatyy as described above, that is all
built-in standard style check options are enabled.



The switch -gnatyN clears any previously set style checks.









Next: , Previous: Style Checking, Up: Compiler Switches   [Contents][Index]





4.3.7 Run-Time Checks

















By default, the following checks are suppressed: stack overflow
checks, and checks for access before elaboration on subprogram
calls. All other checks, including overflow checks, range checks and
array bounds checks, are turned on by default. The following gcc
switches refine this default behavior.








-gnatp









This switch causes the unit to be compiled
as though pragma Suppress (All_checks)
had been present in the source. Validity checks are also eliminated (in
other words -gnatp also implies -gnatVn.
Use this switch to improve the performance
of the code at the expense of safety in the presence of invalid data or
program bugs.



Note that when checks are suppressed, the compiler is allowed, but not
required, to omit the checking code. If the run-time cost of the
checking code is zero or near-zero, the compiler will generate it even
if checks are suppressed. In particular, if the compiler can prove
that a certain check will necessarily fail, it will generate code to
do an unconditional ’raise’, even if checks are suppressed. The
compiler warns in this case. Another case in which checks may not be
eliminated is when they are embedded in certain run-time routines such
as math library routines.



Of course, run-time checks are omitted whenever the compiler can prove
that they will not fail, whether or not checks are suppressed.



Note that if you suppress a check that would have failed, program
execution is erroneous, which means the behavior is totally
unpredictable. The program might crash, or print wrong answers, or
do anything else. It might even do exactly what you wanted it to do
(and then it might start failing mysteriously next week or next
year). The compiler will generate code based on the assumption that
the condition being checked is true, which can result in erroneous
execution if that assumption is wrong.



The checks subject to suppression include all the checks defined by the Ada
standard, the additional implementation defined checks Alignment_Check,
Duplicated_Tag_Check, Predicate_Check, Container_Checks, Tampering_Check,
and Validity_Check, as well as any checks introduced using pragma Check_Name.
Note that Atomic_Synchronization is not automatically suppressed by use of this option.



If the code depends on certain checks being active, you can use
pragma Unsuppress either as a configuration pragma or as
a local pragma to make sure that a specified check is performed
even if gnatp is specified.



The -gnatp switch has no effect if a subsequent
-gnat-p switch appears.


















-gnat-p




This switch cancels the effect of a previous gnatp switch.


















-gnato??




This switch controls the mode used for computing intermediate
arithmetic integer operations, and also enables overflow checking.
For a full description of overflow mode and checking control, see
the ’Overflow Check Handling in GNAT’ appendix in this
User’s Guide.



Overflow checks are always enabled by this switch. The argument
controls the mode, using the codes






`1 = STRICT'




In STRICT mode, intermediate operations are always done using the
base type, and overflow checking ensures that the result is within
the base type range.





`2 = MINIMIZED'




In MINIMIZED mode, overflows in intermediate operations are avoided
where possible by using a larger integer type for the computation
(typically Long_Long_Integer). Overflow checking ensures that
the result fits in this larger integer type.





`3 = ELIMINATED'




In ELIMINATED mode, overflows in intermediate operations are avoided
by using multi-precision arithmetic. In this case, overflow checking
has no effect on intermediate operations (since overflow is impossible).






If two digits are present after -gnato then the first digit
sets the mode for expressions outside assertions, and the second digit
sets the mode for expressions within assertions. Here assertions is used
in the technical sense (which includes for example precondition and
postcondition expressions).



If one digit is present, the corresponding mode is applicable to both
expressions within and outside assertion expressions.



If no digits are present, the default is to enable overflow checks
and set STRICT mode for both kinds of expressions. This is compatible
with the use of -gnato in previous versions of GNAT.





Note that the -gnato?? switch does not affect the code generated
for any floating-point operations; it applies only to integer semantics.
For floating-point, GNAT has the Machine_Overflows
attribute set to False and the normal mode of operation is to
generate IEEE NaN and infinite values on overflow or invalid operations
(such as dividing 0.0 by 0.0).



The reason that we distinguish overflow checking from other kinds of
range constraint checking is that a failure of an overflow check, unlike
for example the failure of a range check, can result in an incorrect
value, but cannot cause random memory destruction (like an out of range
subscript), or a wild jump (from an out of range case value). Overflow
checking is also quite expensive in time and space, since in general it
requires the use of double length arithmetic.



Note again that the default is -gnato11 (equivalent to -gnato1),
so overflow checking is performed in STRICT mode by default.
















-gnatE




Enables dynamic checks for access-before-elaboration
on subprogram calls and generic instantiations.
Note that -gnatE is not necessary for safety, because in the
default mode, GNAT ensures statically that the checks would not fail.
For full details of the effect and use of this switch,
Compiling with gcc.
















-fstack-check




Activates stack overflow checking. For full details of the effect and use of
this switch see Stack Overflow Checking.








The setting of these switches only controls the default setting of the
checks. You may modify them using either Suppress (to remove
checks) or Unsuppress (to add back suppressed checks) pragmas in
the program source.









Next: , Previous: Run-Time Checks, Up: Compiler Switches   [Contents][Index]





4.3.8 Using gcc for Syntax Checking









-gnats




The s stands for ’syntax’.



Run GNAT in syntax checking only mode. For
example, the command





$ gcc -c -gnats x.adb




compiles file x.adb in syntax-check-only mode. You can check a
series of files in a single command
, and can use wildcards to specify such a group of files.
Note that you must specify the -c (compile
only) flag in addition to the -gnats flag.



You may use other switches in conjunction with -gnats. In
particular, -gnatl and -gnatv are useful to control the
format of any generated error messages.



When the source file is empty or contains only empty lines and/or comments,
the output is a warning:





$ gcc -c -gnats -x ada toto.txt
toto.txt:1:01: warning: empty file, contains no compilation units
$




Otherwise, the output is simply the error messages, if any. No object file or
ALI file is generated by a syntax-only compilation. Also, no units other
than the one specified are accessed. For example, if a unit X
`with's a unit Y, compiling unit X in syntax
check only mode does not access the source file containing unit
Y.






Normally, GNAT allows only a single unit in a source file. However, this
restriction does not apply in syntax-check-only mode, and it is possible
to check a file containing multiple compilation units concatenated
together. This is primarily used by the gnatchop utility
(Renaming Files with gnatchop).












Next: , Previous: Using gcc for Syntax Checking, Up: Compiler Switches   [Contents][Index]





4.3.9 Using gcc for Semantic Checking









-gnatc




The c stands for ’check’.
Causes the compiler to operate in semantic check mode,
with full checking for all illegalities specified in the
Ada Reference Manual, but without generation of any object code
(no object file is generated).



Because dependent files must be accessed, you must follow the GNAT
semantic restrictions on file structuring to operate in this mode:






The output consists of error messages as appropriate. No object file is
generated. An ALI file is generated for use in the context of
cross-reference tools, but this file is marked as not being suitable
for binding (since no object file is generated).
The checking corresponds exactly to the notion of
legality in the Ada Reference Manual.



Any unit can be compiled in semantics-checking-only mode, including
units that would not normally be compiled (subunits,
and specifications where a separate body is present).












Next: , Previous: Using gcc for Semantic Checking, Up: Compiler Switches   [Contents][Index]





4.3.10 Compiling Different Versions of Ada




The switches described in this section allow you to explicitly specify
the version of the Ada language that your programs are written in.
The default mode is Ada 2012,
but you can also specify Ada 95, Ada 2005 mode, or
indicate Ada 83 compatibility mode.















-gnat83 (Ada 83 Compatibility Mode)




Although GNAT is primarily an Ada 95 / Ada 2005 compiler, this switch
specifies that the program is to be compiled in Ada 83 mode. With
-gnat83, GNAT rejects most post-Ada 83 extensions and applies Ada 83
semantics where this can be done easily.
It is not possible to guarantee this switch does a perfect
job; some subtle tests, such as are
found in earlier ACVC tests (and that have been removed from the ACATS suite
for Ada 95), might not compile correctly.
Nevertheless, this switch may be useful in some circumstances, for example
where, due to contractual reasons, existing code needs to be maintained
using only Ada 83 features.



With few exceptions (most notably the need to use <> on
unconstrained 

generic formal parameters,
the use of the new Ada 95 / Ada 2005
reserved words, and the use of packages
with optional bodies), it is not necessary to specify the
-gnat83 switch when compiling Ada 83 programs, because, with rare
exceptions, Ada 95 and Ada 2005 are upwardly compatible with Ada 83. Thus
a correct Ada 83 program is usually also a correct program
in these later versions of the language standard. For further information
please refer to the `Compatibility and Porting Guide' chapter in the
GNAT Reference Manual.













-gnat95 (Ada 95 mode)




This switch directs the compiler to implement the Ada 95 version of the
language.
Since Ada 95 is almost completely upwards
compatible with Ada 83, Ada 83 programs may generally be compiled using
this switch (see the description of the -gnat83 switch for further
information about Ada 83 mode).
If an Ada 2005 program is compiled in Ada 95 mode,
uses of the new Ada 2005 features will cause error
messages or warnings.



This switch also can be used to cancel the effect of a previous
-gnat83, -gnat05/2005, or -gnat12/2012
switch earlier in the command line.















-gnat05 or -gnat2005 (Ada 2005 mode)




This switch directs the compiler to implement the Ada 2005 version of the
language, as documented in the official Ada standards document.
Since Ada 2005 is almost completely upwards
compatible with Ada 95 (and thus also with Ada 83), Ada 83 and Ada 95 programs
may generally be compiled using this switch (see the description of the
-gnat83 and -gnat95 switches for further
information).















-gnat12 or -gnat2012 (Ada 2012 mode)




This switch directs the compiler to implement the Ada 2012 version of the
language (also the default).
Since Ada 2012 is almost completely upwards
compatible with Ada 2005 (and thus also with Ada 83, and Ada 95),
Ada 83 and Ada 95 programs
may generally be compiled using this switch (see the description of the
-gnat83, -gnat95, and -gnat05/2005 switches
for further information).















-gnatX (Enable GNAT Extensions)




This switch directs the compiler to implement the latest version of the
language (currently Ada 2012) and also to enable certain GNAT implementation
extensions that are not part of any Ada standard. For a full list of these
extensions, see the GNAT reference manual.












Next: , Previous: Compiling Different Versions of Ada, Up: Compiler Switches   [Contents][Index]





4.3.11 Character Set Control









-gnati`c'




Normally GNAT recognizes the Latin-1 character set in source program
identifiers, as described in the Ada Reference Manual.
This switch causes
GNAT to recognize alternate character sets in identifiers. c is a
single character  indicating the character set, as follows:






`1'ISO 8859-1 (Latin-1) identifiers


`2'ISO 8859-2 (Latin-2) letters allowed in identifiers


`3'ISO 8859-3 (Latin-3) letters allowed in identifiers


`4'ISO 8859-4 (Latin-4) letters allowed in identifiers


`5'ISO 8859-5 (Cyrillic) letters allowed in identifiers


`9'ISO 8859-15 (Latin-9) letters allowed in identifiers


`p'IBM PC letters (code page 437) allowed in identifiers


`8'IBM PC letters (code page 850) allowed in identifiers


`f'Full upper-half codes allowed in identifiers


`n'No upper-half codes allowed in identifiers


`w'Wide-character codes (that is, codes greater than 255)
allowed in identifiers






See Foreign Language Representation for full details on the
implementation of these character sets.











-gnatW`e'




Specify the method of encoding for wide characters.
e is one of the following:






`h'Hex encoding (brackets coding also recognized)


`u'Upper half encoding (brackets encoding also recognized)


`s'Shift/JIS encoding (brackets encoding also recognized)


`e'EUC encoding (brackets encoding also recognized)


`8'UTF-8 encoding (brackets encoding also recognized)


`b'Brackets encoding only (default value)






For full details on these encoding
methods see Wide_Character Encodings.
Note that brackets coding is always accepted, even if one of the other
options is specified, so for example -gnatW8 specifies that both
brackets and UTF-8 encodings will be recognized. The units that are
with’ed directly or indirectly will be scanned using the specified
representation scheme, and so if one of the non-brackets scheme is
used, it must be used consistently throughout the program. However,
since brackets encoding is always recognized, it may be conveniently
used in standard libraries, allowing these libraries to be used with
any of the available coding schemes.



Note that brackets encoding only applies to program text. Within comments,
brackets are considered to be normal graphic characters, and bracket sequences
are never recognized as wide characters.



If no -gnatW? parameter is present, then the default
representation is normally Brackets encoding only. However, if the
first three characters of the file are 16#EF# 16#BB# 16#BF# (the standard
byte order mark or BOM for UTF-8), then these three characters are
skipped and the default representation for the file is set to UTF-8.



Note that the wide character representation that is specified (explicitly
or by default) for the main program also acts as the default encoding used
for Wide_Text_IO files if not specifically overridden by a WCEM form
parameter.






When no -gnatW? is specified, then characters (other than wide
characters represented using brackets notation) are treated as 8-bit
Latin-1 codes. The codes recognized are the Latin-1 graphic characters,
and ASCII format effectors (CR, LF, HT, VT). Other lower half control
characters in the range 16#00#..16#1F# are not accepted in program text
or in comments. Upper half control characters (16#80#..16#9F#) are rejected
in program text, but allowed and ignored in comments. Note in particular
that the Next Line (NEL) character whose encoding is 16#85# is not recognized
as an end of line in this default mode. If your source program contains
instances of the NEL character used as a line terminator,
you must use UTF-8 encoding for the whole
source program. In default mode, all lines must be ended by a standard
end of line sequence (CR, CR/LF, or LF).



Note that the convention of simply accepting all upper half characters in
comments means that programs that use standard ASCII for program text, but
UTF-8 encoding for comments are accepted in default mode, providing that the
comments are ended by an appropriate (CR, or CR/LF, or LF) line terminator.
This is a common mode for many programs with foreign language comments.









Next: , Previous: Character Set Control, Up: Compiler Switches   [Contents][Index]





4.3.12 File Naming Control









-gnatk`n'




Activates file name ’krunching’. n, a decimal integer in the range
1-999, indicates the maximum allowable length of a file name (not
including the .ads or .adb extension). The default is not
to enable file name krunching.



For the source file naming rules, File Naming Rules.












Next: , Previous: File Naming Control, Up: Compiler Switches   [Contents][Index]





4.3.13 Subprogram Inlining Control









-gnatn[12]




The n here is intended to suggest the first syllable of the word ’inline’.
GNAT recognizes and processes Inline pragmas. However, for inlining to
actually occur, optimization must be enabled and, by default, inlining of
subprograms across units is not performed. If you want to additionally
enable inlining of subprograms specified by pragma Inline across units,
you must also specify this switch.



In the absence of this switch, GNAT does not attempt inlining across units
and does not access the bodies of subprograms for which pragma Inline is
specified if they are not in the current unit.



You can optionally specify the inlining level: 1 for moderate inlining across
units, which is a good compromise between compilation times and performances
at run time, or 2 for full inlining across units, which may bring about
longer compilation times. If no inlining level is specified, the compiler will
pick it based on the optimization level: 1 for -O1, -O2 or
-Os and 2 for -O3.



If you specify this switch the compiler will access these bodies,
creating an extra source dependency for the resulting object file, and
where possible, the call will be inlined.
For further details on when inlining is possible
see Inlining of Subprograms.











-gnatN




This switch activates front-end inlining which also
generates additional dependencies.



When using a gcc-based back end (in practice this means using any version
of GNAT other than the JGNAT, .NET or GNAAMP versions), then the use of
-gnatN is deprecated, and the use of -gnatn is preferred.
Historically front end inlining was more extensive than the gcc back end
inlining, but that is no longer the case.












Next: , Previous: Subprogram Inlining Control, Up: Compiler Switches   [Contents][Index]





4.3.14 Auxiliary Output Control














-gnatt




Causes GNAT to write the internal tree for a unit to a file (with the
extension .adt.
This not normally required, but is used by separate analysis tools.
Typically
these tools do the necessary compilations automatically, so you should
not have to specify this switch in normal operation.
Note that the combination of switches -gnatct
generates a tree in the form required by ASIS applications.











-gnatu




Print a list of units required by this compilation on stdout.
The listing includes all units on which the unit being compiled depends
either directly or indirectly.











-pass-exit-codes




If this switch is not used, the exit code returned by gcc when
compiling multiple files indicates whether all source files have
been successfully used to generate object files or not.



When -pass-exit-codes is used, gcc exits with an extended
exit status and allows an integrated development environment to better
react to a compilation failure. Those exit status are:






`5'There was an error in at least one source file.


`3'At least one source file did not generate an object file.


`2'The compiler died unexpectedly (internal error for example).


`0'An object file has been generated for every source file.
















Next: , Previous: Auxiliary Output Control, Up: Compiler Switches   [Contents][Index]





4.3.15 Debugging Control
















-gnatd`x'




Activate internal debugging switches. x is a letter or digit, or
string of letters or digits, which specifies the type of debugging
outputs desired. Normally these are used only for internal development
or system debugging purposes. You can find full documentation for these
switches in the body of the Debug unit in the compiler source
file debug.adb.











-gnatG[=`nn']




This switch causes the compiler to generate auxiliary output containing
a pseudo-source listing of the generated expanded code. Like most Ada
compilers, GNAT works by first transforming the high level Ada code into
lower level constructs. For example, tasking operations are transformed
into calls to the tasking run-time routines. A unique capability of GNAT
is to list this expanded code in a form very close to normal Ada source.
This is very useful in understanding the implications of various Ada
usage on the efficiency of the generated code. There are many cases in
Ada (e.g., the use of controlled types), where simple Ada statements can
generate a lot of run-time code. By using -gnatG you can identify
these cases, and consider whether it may be desirable to modify the coding
approach to improve efficiency.



The optional parameter nn if present after -gnatG specifies an
alternative maximum line length that overrides the normal default of 72.
This value is in the range 40-999999, values less than 40 being silently
reset to 40. The equal sign is optional.



The format of the output is very similar to standard Ada source, and is
easily understood by an Ada programmer. The following special syntactic
additions correspond to low level features used in the generated code that
do not have any exact analogies in pure Ada source form. The following
is a partial list of these special constructions. See the spec
of package Sprint in file sprint.ads for a full list.





If the switch -gnatL is used in conjunction with
-gnatG, then the original source lines are interspersed
in the expanded source (as comment lines with the original line number).






new `xxx' [storage_pool = `yyy']




Shows the storage pool being used for an allocator.





at end `procedure-name';




Shows the finalization (cleanup) procedure for a scope.





(if `expr' then `expr' else `expr')




Conditional expression equivalent to the x?y:z construction in C.





`target'^(`source')




A conversion with floating-point truncation instead of rounding.





`target'?(`source')




A conversion that bypasses normal Ada semantic checking. In particular
enumeration types and fixed-point types are treated simply as integers.





`target'?^(`source')




Combines the above two cases.






`x' #/ `y'



`x' #mod `y'



`x' # `y'






`x' #rem `y'




A division or multiplication of fixed-point values which are treated as
integers without any kind of scaling.





free `expr' [storage_pool = `xxx']




Shows the storage pool associated with a free statement.





[subtype or type declaration]




Used to list an equivalent declaration for an internally generated
type that is referenced elsewhere in the listing.





freeze `type-name' [`actions']




Shows the point at which type-name is frozen, with possible
associated actions to be performed at the freeze point.





reference `itype'




Reference (and hence definition) to internal type itype.





`function-name'! (`arg', `arg', `arg')




Intrinsic function call.





`label-name' : label




Declaration of label labelname.





#$ `subprogram-name'




An implicit call to a run-time support routine
(to meet the requirement of H.3.1(9) in a
convenient manner).





`expr' && `expr' && `expr' ... && `expr'




A multiple concatenation (same effect as expr & expr &
expr, but handled more efficiently).





[constraint_error]




Raise the Constraint_Error exception.





`expression''reference




A pointer to the result of evaluating {expression}.





`target-type'!(`source-expression')




An unchecked conversion of source-expression to target-type.





[`numerator'/`denominator']




Used to represent internal real literals (that) have no exact
representation in base 2-16 (for example, the result of compile time
evaluation of the expression 1.0/27.0).















-gnatD[=nn]




When used in conjunction with -gnatG, this switch causes
the expanded source, as described above for
-gnatG to be written to files with names
xxx.dg, where xxx is the normal file name,
instead of to the standard output file. For
example, if the source file name is hello.adb, then a file
hello.adb.dg will be written.  The debugging
information generated by the gcc -g switch
will refer to the generated xxx.dg file. This allows
you to do source level debugging using the generated code which is
sometimes useful for complex code, for example to find out exactly
which part of a complex construction raised an exception. This switch
also suppresses generation of cross-reference information (see
-gnatx) since otherwise the cross-reference information
would refer to the .dg file, which would cause
confusion since this is not the original source file.



Note that -gnatD actually implies -gnatG
automatically, so it is not necessary to give both options.
In other words -gnatD is equivalent to -gnatDG).





If the switch -gnatL is used in conjunction with
-gnatDG, then the original source lines are interspersed
in the expanded source (as comment lines with the original line number).



The optional parameter nn if present after -gnatD specifies an
alternative maximum line length that overrides the normal default of 72.
This value is in the range 40-999999, values less than 40 being silently
reset to 40. The equal sign is optional.













-gnatr




This switch causes pragma Restrictions to be treated as Restriction_Warnings
so that violation of restrictions causes warnings rather than illegalities.
This is useful during the development process when new restrictions are added
or investigated. The switch also causes pragma Profile to be treated as
Profile_Warnings, and pragma Restricted_Run_Time and pragma Ravenscar set
restriction warnings rather than restrictions.











-gnatR[0|1|2|3|4][e][j][m][s]




This switch controls output from the compiler of a listing showing
representation information for declared types, objects and subprograms.
For -gnatR0, no information is output (equivalent to omitting
the -gnatR switch). For -gnatR1 (which is the default,
so -gnatR with no parameter has the same effect), size and
alignment information is listed for declared array and record types.



For -gnatR2, size and alignment information is listed for all
declared types and objects. The Linker_Section is also listed for any
entity for which the Linker_Section is set explicitly or implicitly (the
latter case occurs for objects of a type for which a Linker_Section
is set).



For -gnatR3, symbolic expressions for values that are computed
at run time for records are included. These symbolic expressions have
a mostly obvious format with #n being used to represent the value of the
n’th discriminant. See source files repinfo.ads/adb in the
GNAT sources for full details on the format of -gnatR3 output.



For -gnatR4, information for relevant compiler-generated types
is also listed, i.e. when they are structurally part of other declared
types and objects.



If the switch is followed by an e (e.g. -gnatR2e), then
extended representation information for record sub-components of records
is included.



If the switch is followed by an m (e.g. -gnatRm), then
subprogram conventions and parameter passing mechanisms for all the
subprograms are included.



If the switch is followed by a j (e.g., -gnatRj), then
the output is in the JSON data interchange format specified by the
ECMA-404 standard. The semantic description of this JSON output is
available in the specification of the Repinfo unit present in the
compiler sources.



If the switch is followed by an s (e.g., -gnatR3s), then
the output is to a file with the name file.rep where file is
the name of the corresponding source file, except if j is also
specified, in which case the file name is file.json.



Note that it is possible for record components to have zero size. In
this case, the component clause uses an obvious extension of permitted
Ada syntax, for example at 0 range 0 .. -1.











-gnatS




The use of the switch -gnatS for an
Ada compilation will cause the compiler to output a
representation of package Standard in a form very
close to standard Ada. It is not quite possible to
do this entirely in standard Ada (since new
numeric base types cannot be created in standard
Ada), but the output is easily
readable to any Ada programmer, and is useful to
determine the characteristics of target dependent
types in package Standard.











-gnatx




Normally the compiler generates full cross-referencing information in
the ALI file. This information is used by a number of tools,
including gnatfind and gnatxref. The -gnatx switch
suppresses this information. This saves some space and may slightly
speed up compilation, but means that these tools cannot be used.











-fgnat-encodings=[all|gdb|minimal]




This switch controls the balance between GNAT encodings and standard DWARF
emitted in the debug information.



Historically, old debug formats like stabs were not powerful enough to
express some Ada types (for instance, variant records or fixed-point types).
To work around this, GNAT introduced proprietary encodings that embed the
missing information ("GNAT encodings").



Recent versions of the DWARF debug information format are now able to
correctly describe most of these Ada constructs ("standard DWARF"). As
third-party tools started to use this format, GNAT has been enhanced to
generate it. However, most tools (including GDB) are still relying on GNAT
encodings.



To support all tools, GNAT needs to be versatile about the balance between
generation of GNAT encodings and standard DWARF. This is what
-fgnat-encodings is about.
















Next: , Previous: Debugging Control, Up: Compiler Switches   [Contents][Index]





4.3.16 Exception Handling Control




GNAT uses two methods for handling exceptions at run time. The
setjmp/longjmp method saves the context when entering
a frame with an exception handler. Then when an exception is
raised, the context can be restored immediately, without the
need for tracing stack frames. This method provides very fast
exception propagation, but introduces significant overhead for
the use of exception handlers, even if no exception is raised.



The other approach is called ’zero cost’ exception handling.
With this method, the compiler builds static tables to describe
the exception ranges. No dynamic code is required when entering
a frame containing an exception handler. When an exception is
raised, the tables are used to control a back trace of the
subprogram invocation stack to locate the required exception
handler. This method has considerably poorer performance for
the propagation of exceptions, but there is no overhead for
exception handlers if no exception is raised. Note that in this
mode and in the context of mixed Ada and C/C++ programming,
to propagate an exception through a C/C++ code, the C/C++ code
must be compiled with the -funwind-tables GCC’s
option.



The following switches may be used to control which of the
two exception handling methods is used.








--RTS=sjlj




This switch causes the setjmp/longjmp run-time (when available) to be used
for exception handling. If the default
mechanism for the target is zero cost exceptions, then
this switch can be used to modify this default, and must be
used for all units in the partition.
This option is rarely used. One case in which it may be
advantageous is if you have an application where exception
raising is common and the overall performance of the
application is improved by favoring exception propagation.













--RTS=zcx




This switch causes the zero cost approach to be used
for exception handling. If this is the default mechanism for the
target (see below), then this switch is unneeded. If the default
mechanism for the target is setjmp/longjmp exceptions, then
this switch can be used to modify this default, and must be
used for all units in the partition.
This option can only be used if the zero cost approach
is available for the target in use, otherwise it will generate an error.






The same option --RTS must be used both for gcc
and gnatbind. Passing this option to gnatmake
(Switches for gnatmake) will ensure the required consistency
through the compilation and binding steps.









Next: , Previous: Exception Handling Control, Up: Compiler Switches   [Contents][Index]





4.3.17 Units to Sources Mapping Files









-gnatem=`path'




A mapping file is a way to communicate to the compiler two mappings:
from unit names to file names (without any directory information) and from
file names to path names (with full directory information). These mappings
are used by the compiler to short-circuit the path search.



The use of mapping files is not required for correct operation of the
compiler, but mapping files can improve efficiency, particularly when
sources are read over a slow network connection. In normal operation,
you need not be concerned with the format or use of mapping files,
and the -gnatem switch is not a switch that you would use
explicitly. It is intended primarily for use by automatic tools such as
gnatmake running under the project file facility. The
description here of the format of mapping files is provided
for completeness and for possible use by other tools.



A mapping file is a sequence of sets of three lines. In each set, the
first line is the unit name, in lower case, with %s appended
for specs and %b appended for bodies; the second line is the
file name; and the third line is the path name.



Example:





main%b
main.2.ada
/gnat/project1/sources/main.2.ada




When the switch -gnatem is specified, the compiler will
create in memory the two mappings from the specified file. If there is
any problem (nonexistent file, truncated file or duplicate entries),
no mapping will be created.



Several -gnatem switches may be specified; however, only the
last one on the command line will be taken into account.



When using a project file, gnatmake creates a temporary
mapping file and communicates it to the compiler using this switch.












Previous: Units to Sources Mapping Files, Up: Compiler Switches   [Contents][Index]





4.3.18 Code Generation Control




The GCC technology provides a wide range of target dependent
-m switches for controlling
details of code generation with respect to different versions of
architectures. This includes variations in instruction sets (e.g.,
different members of the power pc family), and different requirements
for optimal arrangement of instructions (e.g., different members of
the x86 family). The list of available -m switches may be
found in the GCC documentation.



Use of these -m switches may in some cases result in improved
code performance.



The GNAT technology is tested and qualified without any
-m switches,
so generally the most reliable approach is to avoid the use of these
switches. However, we generally expect most of these switches to work
successfully with GNAT, and many customers have reported successful
use of these options.



Our general advice is to avoid the use of -m switches unless
special needs lead to requirements in this area. In particular,
there is no point in using -m switches to improve performance
unless you actually see a performance improvement.









Next: , Previous: Compiler Switches, Up: Building Executable Programs with GNAT   [Contents][Index]





4.4 Linker Switches




Linker switches can be specified after -largs builder switch.








-fuse-ld=`name'




Linker to be used. The default is bfd for ld.bfd,
the alternative being gold for ld.gold. The later is
a more recent and faster linker, but only available on GNU/Linux
platforms.












Next: , Previous: Linker Switches, Up: Building Executable Programs with GNAT   [Contents][Index]





4.5 Binding with gnatbind






This chapter describes the GNAT binder, gnatbind, which is used
to bind compiled GNAT objects.



The gnatbind program performs four separate functions:








• Running gnatbind:  



• Switches for gnatbind:  



• Command-Line Access:  



• Search Paths for gnatbind:  



• Examples of gnatbind Usage:  












Next: , Up: Binding with gnatbind   [Contents][Index]





4.5.1 Running gnatbind




The form of the gnatbind command is





$ gnatbind [ switches ] mainprog[.ali] [ switches ]




where mainprog.adb is the Ada file containing the main program
unit body. gnatbind constructs an Ada
package in two files whose names are
b~mainprog.ads, and b~mainprog.adb.
For example, if given the
parameter hello.ali, for a main program contained in file
hello.adb, the binder output files would be b~hello.ads
and b~hello.adb.



When doing consistency checking, the binder takes into consideration
any source files it can locate. For example, if the binder determines
that the given main program requires the package Pack, whose
.ALI
file is pack.ali and whose corresponding source spec file is
pack.ads, it attempts to locate the source file pack.ads
(using the same search path conventions as previously described for the
gcc command). If it can locate this source file, it checks that
the time stamps
or source checksums of the source and its references to in ALI files
match. In other words, any ALI files that mentions this spec must have
resulted from compiling this version of the source file (or in the case
where the source checksums match, a version close enough that the
difference does not matter).






The effect of this consistency checking, which includes source files, is
that the binder ensures that the program is consistent with the latest
version of the source files that can be located at bind time. Editing a
source file without compiling files that depend on the source file cause
error messages to be generated by the binder.



For example, suppose you have a main program hello.adb and a
package P, from file p.ads and you perform the following
steps:






At this point, the file p.ali contains an out-of-date time stamp
because the file p.ads has been edited. The attempt at binding
fails, and the binder generates the following error messages:





error: "hello.adb" must be recompiled ("p.ads" has been modified)
error: "p.ads" has been modified and must be recompiled




Now both files must be recompiled as indicated, and then the bind can
succeed, generating a main program. You need not normally be concerned
with the contents of this file, but for reference purposes a sample
binder output file is given in Example of Binder Output File.



In most normal usage, the default mode of gnatbind which is to
generate the main package in Ada, as described in the previous section.
In particular, this means that any Ada programmer can read and understand
the generated main program. It can also be debugged just like any other
Ada code provided the -g switch is used for
gnatbind and gnatlink.









Next: , Previous: Running gnatbind, Up: Binding with gnatbind   [Contents][Index]





4.5.2 Switches for gnatbind




The following switches are available with gnatbind; details will
be presented in subsequent sections.








--version




Display Copyright and version, then exit disregarding all other options.











--help




If --version was not used, display usage, then exit disregarding
all other options.











-a




Indicates that, if supported by the platform, the adainit procedure should
be treated as an initialisation routine by the linker (a constructor). This
is intended to be used by the Project Manager to automatically initialize
shared Stand-Alone Libraries.











-aO




Specify directory to be searched for ALI files.











-aI




Specify directory to be searched for source file.











-A[=`filename']




Output ALI list (to standard output or to the named file).











-b




Generate brief messages to stderr even if verbose mode set.











-c




Check only, no generation of binder output file.











-d`nn'[k|m]




This switch can be used to change the default task stack size value
to a specified size nn, which is expressed in bytes by default, or
in kilobytes when suffixed with k or in megabytes when suffixed
with m.
In the absence of a [k|m] suffix, this switch is equivalent,
in effect, to completing all task specs with





pragma Storage_Size (nn);




When they do not already have such a pragma.











-D`nn'[k|m]




Set the default secondary stack size to nn. The suffix indicates whether
the size is in bytes (no suffix), kilobytes (k suffix) or megabytes
(m suffix).



The secondary stack holds objects of unconstrained types that are returned by
functions, for example unconstrained Strings. The size of the secondary stack
can be dynamic or fixed depending on the target.



For most targets, the secondary stack grows on demand and is implemented as
a chain of blocks in the heap. In this case, the default secondary stack size
determines the initial size of the secondary stack for each task and the
smallest amount the secondary stack can grow by.



For Ravenscar, ZFP, and Cert run-times the size of the secondary stack is
fixed. This switch can be used to change the default size of these stacks.
The default secondary stack size can be overridden on a per-task basis if
individual tasks have different secondary stack requirements. This is
achieved through the Secondary_Stack_Size aspect that takes the size of the
secondary stack in bytes.











-e




Output complete list of elaboration-order dependencies.











-Ea




Store tracebacks in exception occurrences when the target supports it.
The "a" is for "address"; tracebacks will contain hexadecimal addresses,
unless symbolic tracebacks are enabled.



See also the packages GNAT.Traceback and
GNAT.Traceback.Symbolic for more information.
Note that on x86 ports, you must not use -fomit-frame-pointer
gcc option.











-Es




Store tracebacks in exception occurrences when the target supports it.
The "s" is for "symbolic"; symbolic tracebacks are enabled.











-E




Currently the same as -Ea.











-f`elab-order'




Force elaboration order. For further details see Elaboration Control
and Elaboration Order Handling in GNAT.











-F




Force the checks of elaboration flags. gnatbind does not normally
generate checks of elaboration flags for the main executable, except when
a Stand-Alone Library is used. However, there are cases when this cannot be
detected by gnatbind. An example is importing an interface of a Stand-Alone
Library through a pragma Import and only specifying through a linker switch
this Stand-Alone Library. This switch is used to guarantee that elaboration
flag checks are generated.











-h




Output usage (help) information.











-H




Legacy elaboration order model enabled. For further details see
Elaboration Order Handling in GNAT.











-H32




Use 32-bit allocations for __gnat_malloc (and thus for access types).
For further details see Dynamic Allocation Control.













-H64




Use 64-bit allocations for __gnat_malloc (and thus for access types).
For further details see Dynamic Allocation Control.







-I




Specify directory to be searched for source and ALI files.







-I-




Do not look for sources in the current directory where gnatbind was
invoked, and do not look for ALI files in the directory containing the
ALI file named in the gnatbind command line.







-l




Output chosen elaboration order.







-L`xxx'




Bind the units for library building. In this case the adainit and
adafinal procedures (Binding with Non-Ada Main Programs)
are renamed to `xxx'init and
`xxx'final.
Implies -n.
(GNAT and Libraries, for more details.)







-M`xyz'




Rename generated main program from main to xyz. This option is
supported on cross environments only.







-m`n'




Limit number of detected errors or warnings to n, where n is
in the range 1..999999. The default value if no switch is
given is 9999. If the number of warnings reaches this limit, then a
message is output and further warnings are suppressed, the bind
continues in this case. If the number of errors reaches this
limit, then a message is output and the bind is abandoned.
A value of zero means that no limit is enforced. The equal
sign is optional.







-minimal




Generate a binder file suitable for space-constrained applications. When
active, binder-generated objects not required for program operation are no
longer generated. `Warning:' this option comes with the following
limitations:










-n




No main program.







-nostdinc




Do not look for sources in the system default directory.







-nostdlib




Do not look for library files in the system default directory.







--RTS=`rts-path'




Specifies the default location of the run-time library. Same meaning as the
equivalent gnatmake flag (Switches for gnatmake).







-o `file'




Name the output file file (default is b~`xxx.adb‘).
Note that if this option is used, then linking must be done manually,
gnatlink cannot be used.







-O[=`filename']




Output object list (to standard output or to the named file).







-p




Pessimistic (worst-case) elaboration order.







-P




Generate binder file suitable for CodePeer.







-R




Output closure source list, which includes all non-run-time units that are
included in the bind.







-Ra




Like -R but the list includes run-time units.







-s




Require all source files to be present.







-S`xxx'




Specifies the value to be used when detecting uninitialized scalar
objects with pragma Initialize_Scalars.
The xxx string specified with the switch is one of:








In addition, you can specify -Sev to indicate that the value is
to be set at run time. In this case, the program will look for an environment
variable of the form GNAT_INIT_SCALARS=`yy', where yy is one
of in/lo/hi/`xx' with the same meanings as above.
If no environment variable is found, or if it does not have a valid value,
then the default is in (invalid values).











-static




Link against a static GNAT run-time.







-shared




Link against a shared GNAT run-time when available.







-t




Tolerate time stamp and other consistency errors.







-T`n'




Set the time slice value to n milliseconds. If the system supports
the specification of a specific time slice value, then the indicated value
is used. If the system does not support specific time slice values, but
does support some general notion of round-robin scheduling, then any
nonzero value will activate round-robin scheduling.



A value of zero is treated specially. It turns off time
slicing, and in addition, indicates to the tasking run-time that the
semantics should match as closely as possible the Annex D
requirements of the Ada RM, and in particular sets the default
scheduling policy to FIFO_Within_Priorities.







-u`n'




Enable dynamic stack usage, with n results stored and displayed
at program termination. A result is generated when a task
terminates. Results that can’t be stored are displayed on the fly, at
task termination. This option is currently not supported on Itanium
platforms. (See Dynamic Stack Usage Analysis for details.)







-v




Verbose mode. Write error messages, header, summary output to
stdout.







-V`key'=`value'




Store the given association of key to value in the bind environment.
Values stored this way can be retrieved at run time using
GNAT.Bind_Environment.







-w`x'




Warning mode; x = s/e for suppress/treat as error.







-Wx`e'




Override default wide character encoding for standard Text_IO files.







-x




Exclude source files (check object consistency only).







-X`nnn'




Set default exit status value, normally 0 for POSIX compliance.







-y




Enable leap seconds support in Ada.Calendar and its children.







-z




No main subprogram.






You may obtain this listing of switches by running gnatbind with
no arguments.





• Consistency-Checking Modes:  



• Binder Error Message Control:  



• Elaboration Control:  



• Output Control:  



• Dynamic Allocation Control:  



• Binding with Non-Ada Main Programs:  



• Binding Programs with No Main Subprogram:  












Next: , Up: Switches for gnatbind   [Contents][Index]





4.5.2.1 Consistency-Checking Modes




As described earlier, by default gnatbind checks
that object files are consistent with one another and are consistent
with any source files it can locate. The following switches control binder
access to sources.













-s




Require source files to be present. In this mode, the binder must be
able to locate all source files that are referenced, in order to check
their consistency. In normal mode, if a source file cannot be located it
is simply ignored. If you specify this switch, a missing source
file is an error.







-Wx`e'




Override default wide character encoding for standard Text_IO files.
Normally the default wide character encoding method used for standard
[Wide_[Wide_]]Text_IO files is taken from the encoding specified for
the main source input (see description of switch
-gnatWx for the compiler). The
use of this switch for the binder (which has the same set of
possible arguments) overrides this default as specified.







-x




Exclude source files. In this mode, the binder only checks that ALI
files are consistent with one another. Source files are not accessed.
The binder runs faster in this mode, and there is still a guarantee that
the resulting program is self-consistent.
If a source file has been edited since it was last compiled, and you
specify this switch, the binder will not detect that the object
file is out of date with respect to the source file. Note that this is the
mode that is automatically used by gnatmake because in this
case the checking against sources has already been performed by
gnatmake in the course of compilation (i.e., before binding).












Next: , Previous: Consistency-Checking Modes, Up: Switches for gnatbind   [Contents][Index]





4.5.2.2 Binder Error Message Control




The following switches provide control over the generation of error
messages from the binder:













-v




Verbose mode. In the normal mode, brief error messages are generated to
stderr. If this switch is present, a header is written
to stdout and any error messages are directed to stdout.
All that is written to stderr is a brief summary message.







-b




Generate brief error messages to stderr even if verbose mode is
specified. This is relevant only when used with the
-v switch.







-m`n'




Limits the number of error messages to n, a decimal integer in the
range 1-999. The binder terminates immediately if this limit is reached.







-M`xxx'




Renames the generated main program from main to xxx.
This is useful in the case of some cross-building environments, where
the actual main program is separate from the one generated
by gnatbind.









-ws




Suppress all warning messages.







-we




Treat any warning messages as fatal errors.















-t




The binder performs a number of consistency checks including:






Normally failure of such checks, in accordance with the consistency
requirements of the Ada Reference Manual, causes error messages to be
generated which abort the binder and prevent the output of a binder
file and subsequent link to obtain an executable.



The -t switch converts these error messages
into warnings, so that
binding and linking can continue to completion even in the presence of such
errors. The result may be a failed link (due to missing symbols), or a
non-functional executable which has undefined semantics.







Note: This means that -t should be used only in unusual situations,
with extreme care.
















Next: , Previous: Binder Error Message Control, Up: Switches for gnatbind   [Contents][Index]





4.5.2.3 Elaboration Control




The following switches provide additional control over the elaboration
order. For further details see Elaboration Order Handling in GNAT.








-f`elab-order'




Force elaboration order.



elab-order should be the name of a "forced elaboration order file", that
is, a text file containing library item names, one per line. A name of the
form "some.unit%s" or "some.unit (spec)" denotes the spec of Some.Unit. A
name of the form "some.unit%b" or "some.unit (body)" denotes the body of
Some.Unit. Each pair of lines is taken to mean that there is an elaboration
dependence of the second line on the first. For example, if the file
contains:





this (spec)
this (body)
that (spec)
that (body)




then the spec of This will be elaborated before the body of This, and the
body of This will be elaborated before the spec of That, and the spec of That
will be elaborated before the body of That. The first and last of these three
dependences are already required by Ada rules, so this file is really just
forcing the body of This to be elaborated before the spec of That.



The given order must be consistent with Ada rules, or else gnatbind will
give elaboration cycle errors. For example, if you say x (body) should be
elaborated before x (spec), there will be a cycle, because Ada rules require
x (spec) to be elaborated before x (body); you can’t have the spec and body
both elaborated before each other.



If you later add "with That;" to the body of This, there will be a cycle, in
which case you should erase either "this (body)" or "that (spec)" from the
above forced elaboration order file.



Blank lines and Ada-style comments are ignored. Unit names that do not exist
in the program are ignored. Units in the GNAT predefined library are also
ignored.











-p




Pessimistic elaboration order



This switch is only applicable to the pre-20.x legacy elaboration models.
The post-20.x elaboration model uses a more informed approach of ordering
the units.



Normally the binder attempts to choose an elaboration order that is likely to
minimize the likelihood of an elaboration order error resulting in raising a
Program_Error exception. This switch reverses the action of the binder,
and requests that it deliberately choose an order that is likely to maximize
the likelihood of an elaboration error. This is useful in ensuring
portability and avoiding dependence on accidental fortuitous elaboration
ordering.



Normally it only makes sense to use the -p switch if dynamic
elaboration checking is used (-gnatE switch used for compilation).
This is because in the default static elaboration mode, all necessary
Elaborate and Elaborate_All pragmas are implicitly inserted.
These implicit pragmas are still respected by the binder in -p
mode, so a safe elaboration order is assured.



Note that -p is not intended for production use; it is more for
debugging/experimental use.












Next: , Previous: Elaboration Control, Up: Switches for gnatbind   [Contents][Index]





4.5.2.4 Output Control




The following switches allow additional control over the output
generated by the binder.













-c




Check only. Do not generate the binder output file. In this mode the
binder performs all error checks but does not generate an output file.







-e




Output complete list of elaboration-order dependencies, showing the
reason for each dependency. This output can be rather extensive but may
be useful in diagnosing problems with elaboration order. The output is
written to stdout.







-h




Output usage information. The output is written to stdout.







-K




Output linker options to stdout. Includes library search paths,
contents of pragmas Ident and Linker_Options, and libraries added
by gnatbind.







-l




Output chosen elaboration order. The output is written to stdout.







-O




Output full names of all the object files that must be linked to provide
the Ada component of the program. The output is written to stdout.
This list includes the files explicitly supplied and referenced by the user
as well as implicitly referenced run-time unit files. The latter are
omitted if the corresponding units reside in shared libraries. The
directory names for the run-time units depend on the system configuration.







-o `file'




Set name of output file to file instead of the normal
b~`mainprog.adb‘ default. Note that file denote the Ada
binder generated body filename.
Note that if this option is used, then linking must be done manually.
It is not possible to use gnatlink in this case, since it cannot locate
the binder file.







-r




Generate list of pragma Restrictions that could be applied to
the current unit. This is useful for code audit purposes, and also may
be used to improve code generation in some cases.












Next: , Previous: Output Control, Up: Switches for gnatbind   [Contents][Index]





4.5.2.5 Dynamic Allocation Control




The heap control switches – -H32 and -H64 –
determine whether dynamic allocation uses 32-bit or 64-bit memory.
They only affect compiler-generated allocations via __gnat_malloc;
explicit calls to malloc and related functions from the C
run-time library are unaffected.






-H32




Allocate memory on 32-bit heap





-H64




Allocate memory on 64-bit heap.  This is the default
unless explicitly overridden by a 'Size clause on the access type.






These switches are only effective on VMS platforms.









Next: , Previous: Dynamic Allocation Control, Up: Switches for gnatbind   [Contents][Index]





4.5.2.6 Binding with Non-Ada Main Programs




The description so far has assumed that the main
program is in Ada, and that the task of the binder is to generate a
corresponding function main that invokes this Ada main
program. GNAT also supports the building of executable programs where
the main program is not in Ada, but some of the called routines are
written in Ada and compiled using GNAT (Mixed Language Programming).
The following switch is used in this situation:













-n




No main program. The main program is not in Ada.






In this case, most of the functions of the binder are still required,
but instead of generating a main program, the binder generates a file
containing the following callable routines:











adainit




You must call this routine to initialize the Ada part of the program by
calling the necessary elaboration routines. A call to adainit is
required before the first call to an Ada subprogram.



Note that it is assumed that the basic execution environment must be setup
to be appropriate for Ada execution at the point where the first Ada
subprogram is called. In particular, if the Ada code will do any
floating-point operations, then the FPU must be setup in an appropriate
manner. For the case of the x86, for example, full precision mode is
required. The procedure GNAT.Float_Control.Reset may be used to ensure
that the FPU is in the right state.











adafinal




You must call this routine to perform any library-level finalization
required by the Ada subprograms. A call to adafinal is required
after the last call to an Ada subprogram, and before the program
terminates.













If the -n switch
is given, more than one ALI file may appear on
the command line for gnatbind. The normal closure
calculation is performed for each of the specified units. Calculating
the closure means finding out the set of units involved by tracing
`with' references. The reason it is necessary to be able to
specify more than one ALI file is that a given program may invoke two or
more quite separate groups of Ada units.



The binder takes the name of its output file from the last specified ALI
file, unless overridden by the use of the -o file.





The output is an Ada unit in source form that can be compiled with GNAT.
This compilation occurs automatically as part of the gnatlink
processing.



Currently the GNAT run-time requires a FPU using 80 bits mode
precision. Under targets where this is not the default it is required to
call GNAT.Float_Control.Reset before using floating point numbers (this
include float computation, float input and output) in the Ada code. A
side effect is that this could be the wrong mode for the foreign code
where floating point computation could be broken after this call.









Previous: Binding with Non-Ada Main Programs, Up: Switches for gnatbind   [Contents][Index]





4.5.2.7 Binding Programs with No Main Subprogram




It is possible to have an Ada program which does not have a main
subprogram. This program will call the elaboration routines of all the
packages, then the finalization routines.



The following switch is used to bind programs organized in this manner:













-z




Normally the binder checks that the unit name given on the command line
corresponds to a suitable main subprogram. When this switch is used,
a list of ALI files can be given, and the execution of the program
consists of elaboration of these units in an appropriate order. Note
that the default wide character encoding method for standard Text_IO
files is always set to Brackets if this switch is set (you can use
the binder switch
-Wx to override this default).












Next: , Previous: Switches for gnatbind, Up: Binding with gnatbind   [Contents][Index]





4.5.3 Command-Line Access




The package Ada.Command_Line provides access to the command-line
arguments and program name. In order for this interface to operate
correctly, the two variables





int gnat_argc;
char **gnat_argv;








are declared in one of the GNAT library routines. These variables must
be set from the actual argc and argv values passed to the
main program. With no `n' present, gnatbind
generates the C main program to automatically set these variables.
If the `n' switch is used, there is no automatic way to
set these variables. If they are not set, the procedures in
Ada.Command_Line will not be available, and any attempt to use
them will raise Constraint_Error. If command line access is
required, your main program must set gnat_argc and
gnat_argv from the argc and argv values passed to
it.









Next: , Previous: Command-Line Access, Up: Binding with gnatbind   [Contents][Index]





4.5.4 Search Paths for gnatbind




The binder takes the name of an ALI file as its argument and needs to
locate source files as well as other ALI files to verify object consistency.



For source files, it follows exactly the same search rules as gcc
(see Search Paths and the Run-Time Library (RTL)). For ALI files the
directories searched are:












In the binder the switch -I
is used to specify both source and
library file paths. Use -aI
instead if you want to specify
source paths only, and -aO
if you want to specify library paths
only. This means that for the binder
-I`dir' is equivalent to
-aI`dir'
-aO``dir'.
The binder generates the bind file (a C language source file) in the
current working directory.











The packages Ada, System, and Interfaces and their
children make up the GNAT Run-Time Library, together with the package
GNAT and its children, which contain a set of useful additional
library functions provided by GNAT. The sources for these units are
needed by the compiler and are kept together in one directory. The ALI
files and object files generated by compiling the RTL are needed by the
binder and the linker and are kept together in one directory, typically
different from the directory containing the sources. In a normal
installation, you need not specify these directory names when compiling
or binding. Either the environment variables or the built-in defaults
cause these files to be found.



Besides simplifying access to the RTL, a major use of search paths is
in compiling sources from multiple directories. This can make
development environments much more flexible.









Previous: Search Paths for gnatbind, Up: Binding with gnatbind   [Contents][Index]





4.5.5 Examples of gnatbind Usage




Here are some examples of gnatbind invovations:








gnatbind hello




The main program Hello (source program in hello.adb) is
bound using the standard switch settings. The generated main program is
b~hello.adb. This is the normal, default use of the binder.





gnatbind hello -o mainprog.adb




The main program Hello (source program in hello.adb) is
bound using the standard switch settings. The generated main program is
mainprog.adb with the associated spec in
mainprog.ads. Note that you must specify the body here not the
spec. Note that if this option is used, then linking must be done manually,
since gnatlink will not be able to find the generated file.










Next: , Previous: Binding with gnatbind, Up: Building Executable Programs with GNAT   [Contents][Index]





4.6 Linking with gnatlink






This chapter discusses gnatlink, a tool that links
an Ada program and builds an executable file. This utility
invokes the system linker (via the gcc command)
with a correct list of object files and library references.
gnatlink automatically determines the list of files and
references for the Ada part of a program. It uses the binder file
generated by the gnatbind to determine this list.





• Running gnatlink:  



• Switches for gnatlink:  












Next: , Up: Linking with gnatlink   [Contents][Index]





4.6.1 Running gnatlink




The form of the gnatlink command is





$ gnatlink [ switches ] mainprog [.ali]
           [ non-Ada objects ] [ linker options ]




The arguments of gnatlink (switches, main ALI file,
non-Ada objects
or linker options) may be in any order, provided that no non-Ada object may
be mistaken for a main ALI file.
Any file name F without the .ali
extension will be taken as the main ALI file if a file exists
whose name is the concatenation of F and .ali.



mainprog.ali references the ALI file of the main program.
The .ali extension of this file can be omitted. From this
reference, gnatlink locates the corresponding binder file
b~mainprog.adb and, using the information in this file along
with the list of non-Ada objects and linker options, constructs a
linker command file to create the executable.



The arguments other than the gnatlink switches and the main
ALI file are passed to the linker uninterpreted.
They typically include the names of
object files for units written in other languages than Ada and any library
references required to resolve references in any of these foreign language
units, or in Import pragmas in any Ada units.



linker options is an optional list of linker specific
switches.
The default linker called by gnatlink is gcc which in
turn calls the appropriate system linker.



One useful option for the linker is -s: it reduces the size of the
executable by removing all symbol table and relocation information from the
executable.



Standard options for the linker such as -lmy_lib or
-Ldir can be added as is.
For options that are not recognized by
gcc as linker options, use the gcc switches
-Xlinker or -Wl,.



Refer to the GCC documentation for
details.



Here is an example showing how to generate a linker map:





$ gnatlink my_prog -Wl,-Map,MAPFILE




Using linker options it is possible to set the program stack and
heap size.
See Setting Stack Size from gnatlink and
Setting Heap Size from gnatlink.



gnatlink determines the list of objects required by the Ada
program and prepends them to the list of objects passed to the linker.
gnatlink also gathers any arguments set by the use of
pragma Linker_Options and adds them to the list of arguments
presented to the linker.









Previous: Running gnatlink, Up: Linking with gnatlink   [Contents][Index]





4.6.2 Switches for gnatlink




The following switches are available with the gnatlink utility:








--version




Display Copyright and version, then exit disregarding all other options.











--help




If --version was not used, display usage, then exit disregarding
all other options.













-f




On some targets, the command line length is limited, and gnatlink
will generate a separate file for the linker if the list of object files
is too long.
The -f switch forces this file
to be generated even if
the limit is not exceeded. This is useful in some cases to deal with
special situations where the command line length is exceeded.














-g




The option to include debugging information causes the Ada bind file (in
other words, b~mainprog.adb) to be compiled with -g.
In addition, the binder does not delete the b~mainprog.adb,
b~mainprog.o and b~mainprog.ali files.
Without -g, the binder removes these files by default.











-n




Do not compile the file generated by the binder. This may be used when
a link is rerun with different options, but there is no need to recompile
the binder file.











-v




Verbose mode. Causes additional information to be output, including a full
list of the included object files.
This switch option is most useful when you want
to see what set of object files are being used in the link step.











-v -v




Very verbose mode. Requests that the compiler operate in verbose mode when
it compiles the binder file, and that the system linker run in verbose mode.











-o `exec-name'




exec-name specifies an alternate name for the generated
executable program. If this switch is omitted, the executable has the same
name as the main unit. For example, gnatlink try.ali creates
an executable called try.











-B`dir'




Load compiler executables (for example, gnat1, the Ada compiler)
from dir instead of the default location. Only use this switch
when multiple versions of the GNAT compiler are available.
See the Directory Options section in The_GNU_Compiler_Collection
for further details. You would normally use the -b or
-V switch instead.











-M




When linking an executable, create a map file. The name of the map file
has the same name as the executable with extension ".map".











-M=`mapfile'




When linking an executable, create a map file. The name of the map file is
mapfile.











--GCC=`compiler_name'




Program used for compiling the binder file. The default is
gcc. You need to use quotes around compiler_name if
compiler_name contains spaces or other separator characters.
As an example --GCC="foo -x -y" will instruct gnatlink to
use foo -x -y as your compiler. Note that switch -c is always
inserted after your command name. Thus in the above example the compiler
command that will be used by gnatlink will be foo -c -x -y.
A limitation of this syntax is that the name and path name of the executable
itself must not include any embedded spaces. If the compiler executable is
different from the default one (gcc or <prefix>-gcc), then the back-end
switches in the ALI file are not used to compile the binder generated source.
For example, this is the case with --GCC="foo -x -y". But the back end
switches will be used for --GCC="gcc -gnatv". If several
--GCC=compiler_name are used, only the last compiler_name
is taken into account. However, all the additional switches are also taken
into account. Thus,
--GCC="foo -x -y" --GCC="bar -z -t" is equivalent to
--GCC="bar -x -y -z -t".











--LINK=`name'




name is the name of the linker to be invoked. This is especially
useful in mixed language programs since languages such as C++ require
their own linker to be used. When this switch is omitted, the default
name for the linker is gcc. When this switch is used, the
specified linker is called instead of gcc with exactly the same
parameters that would have been passed to gcc so if the desired
linker requires different parameters it is necessary to use a wrapper
script that massages the parameters before invoking the real linker. It
may be useful to control the exact invocation by using the verbose
switch.












Previous: Linking with gnatlink, Up: Building Executable Programs with GNAT   [Contents][Index]





4.7 Using the GNU make Utility







This chapter offers some examples of makefiles that solve specific
problems. It does not explain how to write a makefile, nor does it try to replace the
gnatmake utility (Building with gnatmake).



All the examples in this section are specific to the GNU version of
make. Although make is a standard utility, and the basic language
is the same, these examples use some advanced features found only in
GNU make.





• Using gnatmake in a Makefile:  



• Automatically Creating a List of Directories:  



• Generating the Command Line Switches:  



• Overcoming Command Line Length Limits:  












Next: , Up: Using the GNU make Utility   [Contents][Index]





4.7.1 Using gnatmake in a Makefile





Complex project organizations can be handled in a very powerful way by
using GNU make combined with gnatmake. For instance, here is a Makefile
which allows you to build each subsystem of a big project into a separate
shared library. Such a makefile allows you to significantly reduce the link
time of very big applications while maintaining full coherence at
each step of the build process.



The list of dependencies are handled automatically by
gnatmake. The Makefile is simply used to call gnatmake in each of
the appropriate directories.



Note that you should also read the example on how to automatically
create the list of directories
(Automatically Creating a List of Directories)
which might help you in case your project has a lot of subdirectories.





## This Makefile is intended to be used with the following directory
## configuration:
##  - The sources are split into a series of csc (computer software components)
##    Each of these csc is put in its own directory.
##    Their name are referenced by the directory names.
##    They will be compiled into shared library (although this would also work
##    with static libraries
##  - The main program (and possibly other packages that do not belong to any
##    csc is put in the top level directory (where the Makefile is).
##       toplevel_dir __ first_csc  (sources) __ lib (will contain the library)
##                    \\_ second_csc (sources) __ lib (will contain the library)
##                    \\_ ...
## Although this Makefile is build for shared library, it is easy to modify
## to build partial link objects instead (modify the lines with -shared and
## gnatlink below)
##
## With this makefile, you can change any file in the system or add any new
## file, and everything will be recompiled correctly (only the relevant shared
## objects will be recompiled, and the main program will be re-linked).

# The list of computer software component for your project. This might be
# generated automatically.
CSC_LIST=aa bb cc

# Name of the main program (no extension)
MAIN=main

# If we need to build objects with -fPIC, uncomment the following line
#NEED_FPIC=-fPIC

# The following variable should give the directory containing libgnat.so
# You can get this directory through 'gnatls -v'. This is usually the last
# directory in the Object_Path.
GLIB=...

# The directories for the libraries
# (This macro expands the list of CSC to the list of shared libraries, you
# could simply use the expanded form:
# LIB_DIR=aa/lib/libaa.so bb/lib/libbb.so cc/lib/libcc.so
LIB_DIR=${foreach dir,${CSC_LIST},${dir}/lib/lib${dir}.so}

${MAIN}: objects ${LIB_DIR}
    gnatbind ${MAIN} ${CSC_LIST:%=-aO%/lib} -shared
    gnatlink ${MAIN} ${CSC_LIST:%=-l%}

objects::
    # recompile the sources
    gnatmake -c -i ${MAIN}.adb ${NEED_FPIC} ${CSC_LIST:%=-I%}

# Note: In a future version of GNAT, the following commands will be simplified
# by a new tool, gnatmlib
${LIB_DIR}:
    mkdir -p ${dir $@ }
    cd ${dir $@ } && gcc -shared -o ${notdir $@ } ../*.o -L${GLIB} -lgnat
    cd ${dir $@ } && cp -f ../*.ali .

# The dependencies for the modules
# Note that we have to force the expansion of *.o, since in some cases
# make won't be able to do it itself.
aa/lib/libaa.so: ${wildcard aa/*.o}
bb/lib/libbb.so: ${wildcard bb/*.o}
cc/lib/libcc.so: ${wildcard cc/*.o}

# Make sure all of the shared libraries are in the path before starting the
# program
run::
    LD_LIBRARY_PATH=`pwd`/aa/lib:`pwd`/bb/lib:`pwd`/cc/lib ./${MAIN}

clean::
    ${RM} -rf ${CSC_LIST:%=%/lib}
    ${RM} ${CSC_LIST:%=%/*.ali}
    ${RM} ${CSC_LIST:%=%/*.o}
    ${RM} *.o *.ali ${MAIN}










Next: , Previous: Using gnatmake in a Makefile, Up: Using the GNU make Utility   [Contents][Index]





4.7.2 Automatically Creating a List of Directories




In most makefiles, you will have to specify a list of directories, and
store it in a variable. For small projects, it is often easier to
specify each of them by hand, since you then have full control over what
is the proper order for these directories, which ones should be
included.



However, in larger projects, which might involve hundreds of
subdirectories, it might be more convenient to generate this list
automatically.



The example below presents two methods. The first one, although less
general, gives you more control over the list. It involves wildcard
characters, that are automatically expanded by make. Its
shortcoming is that you need to explicitly specify some of the
organization of your project, such as for instance the directory tree
depth, whether some directories are found in a separate tree, etc.



The second method is the most general one. It requires an external
program, called find, which is standard on all Unix systems. All
the directories found under a given root directory will be added to the
list.





# The examples below are based on the following directory hierarchy:
# All the directories can contain any number of files
# ROOT_DIRECTORY ->  a  ->  aa  ->  aaa
#                       ->  ab
#                       ->  ac
#                ->  b  ->  ba  ->  baa
#                       ->  bb
#                       ->  bc
# This Makefile creates a variable called DIRS, that can be reused any time
# you need this list (see the other examples in this section)

# The root of your project's directory hierarchy
ROOT_DIRECTORY=.

####
# First method: specify explicitly the list of directories
# This allows you to specify any subset of all the directories you need.
####

DIRS := a/aa/ a/ab/ b/ba/

####
# Second method: use wildcards
# Note that the argument(s) to wildcard below should end with a '/'.
# Since wildcards also return file names, we have to filter them out
# to avoid duplicate directory names.
# We thus use make's ``dir`` and ``sort`` functions.
# It sets DIRs to the following value (note that the directories aaa and baa
# are not given, unless you change the arguments to wildcard).
# DIRS= ./a/a/ ./b/ ./a/aa/ ./a/ab/ ./a/ac/ ./b/ba/ ./b/bb/ ./b/bc/
####

DIRS := ${sort ${dir ${wildcard ${ROOT_DIRECTORY}/*/
                    ${ROOT_DIRECTORY}/*/*/}}}

####
# Third method: use an external program
# This command is much faster if run on local disks, avoiding NFS slowdowns.
# This is the most complete command: it sets DIRs to the following value:
# DIRS= ./a ./a/aa ./a/aa/aaa ./a/ab ./a/ac ./b ./b/ba ./b/ba/baa ./b/bb ./b/bc
####

DIRS := ${shell find ${ROOT_DIRECTORY} -type d -print}










Next: , Previous: Automatically Creating a List of Directories, Up: Using the GNU make Utility   [Contents][Index]





4.7.3 Generating the Command Line Switches




Once you have created the list of directories as explained in the
previous section (Automatically Creating a List of Directories),
you can easily generate the command line arguments to pass to gnatmake.



For the sake of completeness, this example assumes that the source path
is not the same as the object path, and that you have two separate lists
of directories.





# see "Automatically creating a list of directories" to create
# these variables
SOURCE_DIRS=
OBJECT_DIRS=

GNATMAKE_SWITCHES := ${patsubst %,-aI%,${SOURCE_DIRS}}
GNATMAKE_SWITCHES += ${patsubst %,-aO%,${OBJECT_DIRS}}

all:
        gnatmake ${GNATMAKE_SWITCHES} main_unit










Previous: Generating the Command Line Switches, Up: Using the GNU make Utility   [Contents][Index]





4.7.4 Overcoming Command Line Length Limits




One problem that might be encountered on big projects is that many
operating systems limit the length of the command line. It is thus hard to give
gnatmake the list of source and object directories.



This example shows how you can set up environment variables, which will
make gnatmake behave exactly as if the directories had been
specified on the command line, but have a much higher length limit (or
even none on most systems).



It assumes that you have created a list of directories in your Makefile,
using one of the methods presented in
Automatically Creating a List of Directories.
For the sake of completeness, we assume that the object
path (where the ALI files are found) is different from the sources patch.



Note a small trick in the Makefile below: for efficiency reasons, we
create two temporary variables (SOURCE_LIST and OBJECT_LIST), that are
expanded immediately by make. This way we overcome the standard
make behavior which is to expand the variables only when they are
actually used.



On Windows, if you are using the standard Windows command shell, you must
replace colons with semicolons in the assignments to these variables.





# In this example, we create both ADA_INCLUDE_PATH and ADA_OBJECTS_PATH.
# This is the same thing as putting the -I arguments on the command line.
# (the equivalent of using -aI on the command line would be to define
#  only ADA_INCLUDE_PATH, the equivalent of -aO is ADA_OBJECTS_PATH).
# You can of course have different values for these variables.
#
# Note also that we need to keep the previous values of these variables, since
# they might have been set before running 'make' to specify where the GNAT
# library is installed.

# see "Automatically creating a list of directories" to create these
# variables
SOURCE_DIRS=
OBJECT_DIRS=

empty:=
space:=${empty} ${empty}
SOURCE_LIST := ${subst ${space},:,${SOURCE_DIRS}}
OBJECT_LIST := ${subst ${space},:,${OBJECT_DIRS}}
ADA_INCLUDE_PATH += ${SOURCE_LIST}
ADA_OBJECTS_PATH += ${OBJECT_LIST}
export ADA_INCLUDE_PATH
export ADA_OBJECTS_PATH

all:
        gnatmake main_unit










Next: , Previous: Building Executable Programs with GNAT, Up: Top   [Contents][Index]





5 GNAT Utility Programs




This chapter describes a number of utility programs:







Other GNAT utilities are described elsewhere in this manual:








• The File Cleanup Utility gnatclean:  



• The GNAT Library Browser gnatls:  



• The Cross-Referencing Tools gnatxref and gnatfind:  



• The Ada to HTML Converter gnathtml:  












Next: , Up: GNAT Utility Programs   [Contents][Index]





5.1 The File Cleanup Utility gnatclean








gnatclean is a tool that allows the deletion of files produced by the
compiler, binder and linker, including ALI files, object files, tree files,
expanded source files, library files, interface copy source files, binder
generated files and executable files.





• Running gnatclean:  



• Switches for gnatclean:  












Next: , Up: The File Cleanup Utility gnatclean   [Contents][Index]





5.1.1 Running gnatclean




The gnatclean command has the form:








$ gnatclean switches names






where names is a list of source file names. Suffixes .ads and
adb may be omitted. If a project file is specified using switch
-P, then names may be completely omitted.



In normal mode, gnatclean delete the files produced by the compiler and,
if switch -c is not specified, by the binder and
the linker. In informative-only mode, specified by switch
-n, the list of files that would have been deleted in
normal mode is listed, but no file is actually deleted.









Previous: Running gnatclean, Up: The File Cleanup Utility gnatclean   [Contents][Index]





5.1.2 Switches for gnatclean




gnatclean recognizes the following switches:








--version




Display copyright and version, then exit disregarding all other options.











--help




If --version was not used, display usage, then exit disregarding
all other options.





--subdirs=`subdir'




Actual object directory of each project file is the subdirectory subdir of the
object directory specified or defaulted in the project file.





--unchecked-shared-lib-imports




By default, shared library projects are not allowed to import static library
projects. When this switch is used on the command line, this restriction is
relaxed.











-c




Only attempt to delete the files produced by the compiler, not those produced
by the binder or the linker. The files that are not to be deleted are library
files, interface copy files, binder generated files and executable files.











-D `dir'




Indicate that ALI and object files should normally be found in directory dir.











-F




When using project files, if some errors or warnings are detected during
parsing and verbose mode is not in effect (no use of switch
-v), then error lines start with the full path name of the project
file, rather than its simple file name.











-h




Output a message explaining the usage of gnatclean.











-n




Informative-only mode. Do not delete any files. Output the list of the files
that would have been deleted if this switch was not specified.











-P`project'




Use project file project. Only one such switch can be used.
When cleaning a project file, the files produced by the compilation of the
immediate sources or inherited sources of the project files are to be
deleted. This is not depending on the presence or not of executable names
on the command line.











-q




Quiet output. If there are no errors, do not output anything, except in
verbose mode (switch -v) or in informative-only mode
(switch -n).











-r




When a project file is specified (using switch -P),
clean all imported and extended project files, recursively. If this switch
is not specified, only the files related to the main project file are to be
deleted. This switch has no effect if no project file is specified.











-v




Verbose mode.











-vP`x'




Indicates the verbosity of the parsing of GNAT project files.
Switches Related to Project Files.











-X`name'=`value'




Indicates that external variable name has the value value.
The Project Manager will use this value for occurrences of
external(name) when parsing the project file.
See Switches Related to Project Files.











-aO`dir'




When searching for ALI and object files, look in directory dir.











-I`dir'




Equivalent to -aO`dir'.














-I-




Do not look for ALI or object files in the directory
where gnatclean was invoked.












Next: , Previous: The File Cleanup Utility gnatclean, Up: GNAT Utility Programs   [Contents][Index]





5.2 The GNAT Library Browser gnatls








gnatls is a tool that outputs information about compiled
units. It gives the relationship between objects, unit names and source
files. It can also be used to check the source dependencies of a unit
as well as various characteristics.





• Running gnatls:  



• Switches for gnatls:  



• Example of gnatls Usage:  












Next: , Up: The GNAT Library Browser gnatls   [Contents][Index]





5.2.1 Running gnatls




The gnatls command has the form








$ gnatls switches object_or_ali_file






The main argument is the list of object or ali files
(see The Ada Library Information Files)
for which information is requested.



In normal mode, without additional option, gnatls produces a
four-column listing. Each line represents information for a specific
object. The first column gives the full path of the object, the second
column gives the name of the principal unit in this object, the third
column gives the status of the source and the fourth column gives the
full path of the source representing this unit.
Here is a simple example of use:








$ gnatls *.o
./demo1.o            demo1            DIF demo1.adb
./demo2.o            demo2             OK demo2.adb
./hello.o            h1                OK hello.adb
./instr-child.o      instr.child      MOK instr-child.adb
./instr.o            instr             OK instr.adb
./tef.o              tef              DIF tef.adb
./text_io_example.o  text_io_example   OK text_io_example.adb
./tgef.o             tgef             DIF tgef.adb






The first line can be interpreted as follows: the main unit which is
contained in
object file demo1.o is demo1, whose main source is in
demo1.adb. Furthermore, the version of the source used for the
compilation of demo1 has been modified (DIF). Each source file has a status
qualifier which can be:






`OK (unchanged)'




The version of the source file used for the compilation of the
specified unit corresponds exactly to the actual source file.





`MOK (slightly modified)'




The version of the source file used for the compilation of the
specified unit differs from the actual source file but not enough to
require recompilation. If you use gnatmake with the option
-m (minimal recompilation), a file marked
MOK will not be recompiled.





`DIF (modified)'




No version of the source found on the path corresponds to the source
used to build this object.





`??? (file not found)'




No source file was found for this unit.





`HID (hidden,  unchanged version not first on PATH)'




The version of the source that corresponds exactly to the source used
for compilation has been found on the path but it is hidden by another
version of the same source that has been modified.












Next: , Previous: Running gnatls, Up: The GNAT Library Browser gnatls   [Contents][Index]





5.2.2 Switches for gnatls




gnatls recognizes the following switches:








--version




Display copyright and version, then exit disregarding all other options.











--help




If --version was not used, display usage, then exit disregarding
all other options.











-a




Consider all units, including those of the predefined Ada library.
Especially useful with -d.











-d




List sources from which specified units depend on.











-h




Output the list of options.











-o




Only output information about object files.











-s




Only output information about source files.











-u




Only output information about compilation units.











-files=`file'




Take as arguments the files listed in text file file.
Text file file may contain empty lines that are ignored.
Each nonempty line should contain the name of an existing file.
Several such switches may be specified simultaneously.

















-aO`dir', -aI`dir', -I`dir', -I-, -nostdinc




Source path manipulation. Same meaning as the equivalent gnatmake
flags (Switches for gnatmake).











-aP`dir'




Add dir at the beginning of the project search dir.











--RTS=`rts-path'




Specifies the default location of the runtime library. Same meaning as the
equivalent gnatmake flag (Switches for gnatmake).











-v




Verbose mode. Output the complete source, object and project paths. Do not use
the default column layout but instead use long format giving as much as
information possible on each requested units, including special
characteristics such as:
















Previous: Switches for gnatls, Up: The GNAT Library Browser gnatls   [Contents][Index]





5.2.3 Example of gnatls Usage




Example of using the verbose switch. Note how the source and
object paths are affected by the -I switch.








$ gnatls -v -I.. demo1.o

GNATLS 5.03w (20041123-34)
Copyright 1997-2004 Free Software Foundation, Inc.

Source Search Path:
   <Current_Directory>
   ../
   /home/comar/local/adainclude/

Object Search Path:
   <Current_Directory>
   ../
   /home/comar/local/lib/gcc-lib/x86-linux/3.4.3/adalib/

Project Search Path:
   <Current_Directory>
   /home/comar/local/lib/gnat/

./demo1.o
   Unit =>
     Name   => demo1
     Kind   => subprogram body
     Flags  => No_Elab_Code
     Source => demo1.adb    modified






The following is an example of use of the dependency list.
Note the use of the -s switch
which gives a straight list of source files. This can be useful for
building specialized scripts.








$ gnatls -d demo2.o
./demo2.o   demo2        OK demo2.adb
                         OK gen_list.ads
                         OK gen_list.adb
                         OK instr.ads
                         OK instr-child.ads

$ gnatls -d -s -a demo1.o
demo1.adb
/home/comar/local/adainclude/ada.ads
/home/comar/local/adainclude/a-finali.ads
/home/comar/local/adainclude/a-filico.ads
/home/comar/local/adainclude/a-stream.ads
/home/comar/local/adainclude/a-tags.ads
gen_list.ads
gen_list.adb
/home/comar/local/adainclude/gnat.ads
/home/comar/local/adainclude/g-io.ads
instr.ads
/home/comar/local/adainclude/system.ads
/home/comar/local/adainclude/s-exctab.ads
/home/comar/local/adainclude/s-finimp.ads
/home/comar/local/adainclude/s-finroo.ads
/home/comar/local/adainclude/s-secsta.ads
/home/comar/local/adainclude/s-stalib.ads
/home/comar/local/adainclude/s-stoele.ads
/home/comar/local/adainclude/s-stratt.ads
/home/comar/local/adainclude/s-tasoli.ads
/home/comar/local/adainclude/s-unstyp.ads
/home/comar/local/adainclude/unchconv.ads












Next: , Previous: The GNAT Library Browser gnatls, Up: GNAT Utility Programs   [Contents][Index]





5.3 The Cross-Referencing Tools gnatxref and gnatfind








The compiler generates cross-referencing information (unless
you set the -gnatx switch), which are saved in the .ali files.
This information indicates where in the source each entity is declared and
referenced. Note that entities in package Standard are not included, but
entities in all other predefined units are included in the output.



Before using any of these two tools, you need to compile successfully your
application, so that GNAT gets a chance to generate the cross-referencing
information.



The two tools gnatxref and gnatfind take advantage of this
information to provide the user with the capability to easily locate the
declaration and references to an entity. These tools are quite similar,
the difference being that gnatfind is intended for locating
definitions and/or references to a specified entity or entities, whereas
gnatxref is oriented to generating a full report of all
cross-references.



To use these tools, you must not compile your application using the
-gnatx switch on the gnatmake command line
(see Building with gnatmake). Otherwise, cross-referencing
information will not be generated.





• gnatxref Switches:  



• gnatfind Switches:  



• Configuration Files for gnatxref and gnatfind:  



• Regular Expressions in gnatfind and gnatxref:  



• Examples of gnatxref Usage:  



• Examples of gnatfind Usage:  












Next: , Up: The Cross-Referencing Tools gnatxref and gnatfind   [Contents][Index]





5.3.1 gnatxref Switches




The command invocation for gnatxref is:








$ gnatxref [ switches ] sourcefile1 [ sourcefile2 ... ]






where






sourcefile1 [, sourcefile2 ...]




identify the source files for which a report is to be generated. The
withed units will be processed too. You must provide at least one file.



These file names are considered to be regular expressions, so for instance
specifying source*.adb is the same as giving every file in the current
directory whose name starts with source and whose extension is
adb.



You shouldn’t specify any directory name, just base names. gnatxref
and gnatfind will be able to locate these files by themselves using
the source path. If you specify directories, no result is produced.






The following switches are available for gnatxref:








--version




Display copyright and version, then exit disregarding all other options.











--help




If --version was not used, display usage, then exit disregarding
all other options.











-a




If this switch is present, gnatfind and gnatxref will parse
the read-only files found in the library search path. Otherwise, these files
will be ignored. This option can be used to protect Gnat sources or your own
libraries from being parsed, thus making gnatfind and gnatxref
much faster, and their output much smaller. Read-only here refers to access
or permissions status in the file system for the current user.











-aI`DIR'




When looking for source files also look in directory DIR. The order in which
source file search is undertaken is the same as for gnatmake.











aO`DIR'




When -searching for library and object files, look in directory
DIR. The order in which library files are searched is the same as for
gnatmake.











-nostdinc




Do not look for sources in the system default directory.











-nostdlib




Do not look for library files in the system default directory.











--ext=`extension'




Specify an alternate ali file extension. The default is ali and other
extensions (e.g. gli for C/C++ sources) may be specified via this switch.
Note that if this switch overrides the default, only the new extension will
be considered.











--RTS=`rts-path'




Specifies the default location of the runtime library. Same meaning as the
equivalent gnatmake flag (Switches for gnatmake).











-d




If this switch is set gnatxref will output the parent type
reference for each matching derived types.











-f




If this switch is set, the output file names will be preceded by their
directory (if the file was found in the search path). If this switch is
not set, the directory will not be printed.











-g




If this switch is set, information is output only for library-level
entities, ignoring local entities. The use of this switch may accelerate
gnatfind and gnatxref.











-I`DIR'




Equivalent to -aODIR -aIDIR.











-p`FILE'




Specify a configuration file to use to list the source and object directories.



If a file is specified, then the content of the source directory and object
directory lines are added as if they had been specified respectively
by -aI and -aO.



See Configuration Files for gnatxref and gnatfind for the syntax
of this configuration file.





-u




Output only unused symbols. This may be really useful if you give your
main compilation unit on the command line, as gnatxref will then
display every unused entity and ’with’ed package.





-v




Instead of producing the default output, gnatxref will generate a
tags file that can be used by vi. For examples how to use this
feature, see Examples of gnatxref Usage. The tags file is output
to the standard output, thus you will have to redirect it to a file.






All these switches may be in any order on the command line, and may even
appear after the file names. They need not be separated by spaces, thus
you can say gnatxref -ag instead of gnatxref -a -g.









Next: , Previous: gnatxref Switches, Up: The Cross-Referencing Tools gnatxref and gnatfind   [Contents][Index]





5.3.2 gnatfind Switches




The command invocation for gnatfind is:








$ gnatfind [ switches ]  pattern[:sourcefile[:line[:column]]]
      [file1 file2 ...]






with the following iterpretation of the command arguments:






`pattern'




An entity will be output only if it matches the regular expression found
in `pattern', see Regular Expressions in gnatfind and gnatxref.



Omitting the pattern is equivalent to specifying *, which
will match any entity. Note that if you do not provide a pattern, you
have to provide both a sourcefile and a line.



Entity names are given in Latin-1, with uppercase/lowercase equivalence
for matching purposes. At the current time there is no support for
8-bit codes other than Latin-1, or for wide characters in identifiers.





`sourcefile'




gnatfind will look for references, bodies or declarations
of symbols referenced in sourcefile, at line line
and column column. See Examples of gnatfind Usage
for syntax examples.





`line'




A decimal integer identifying the line number containing
the reference to the entity (or entities) to be located.





`column'




A decimal integer identifying the exact location on the
line of the first character of the identifier for the
entity reference. Columns are numbered from 1.





`file1 file2 ...'




The search will be restricted to these source files. If none are given, then
the search will be conducted for every library file in the search path.
These files must appear only after the pattern or sourcefile.



These file names are considered to be regular expressions, so for instance
specifying source*.adb is the same as giving every file in the current
directory whose name starts with source and whose extension is
adb.



The location of the spec of the entity will always be displayed, even if it
isn’t in one of file1, file2, ... The
occurrences of the entity in the separate units of the ones given on the
command line will also be displayed.



Note that if you specify at least one file in this part, gnatfind may
sometimes not be able to find the body of the subprograms.






At least one of ’sourcefile’ or ’pattern’ has to be present on
the command line.



The following switches are available:








--version




Display copyright and version, then exit disregarding all other options.











--help




If --version was not used, display usage, then exit disregarding
all other options.











-a




If this switch is present, gnatfind and gnatxref will parse
the read-only files found in the library search path. Otherwise, these files
will be ignored. This option can be used to protect Gnat sources or your own
libraries from being parsed, thus making gnatfind and gnatxref
much faster, and their output much smaller. Read-only here refers to access
or permission status in the file system for the current user.











-aI`DIR'




When looking for source files also look in directory DIR. The order in which
source file search is undertaken is the same as for gnatmake.











-aO`DIR'




When searching for library and object files, look in directory
DIR. The order in which library files are searched is the same as for
gnatmake.











-nostdinc




Do not look for sources in the system default directory.











-nostdlib




Do not look for library files in the system default directory.











--ext=`extension'




Specify an alternate ali file extension. The default is ali and other
extensions may be specified via this switch. Note that if this switch
overrides the default, only the new extension will be considered.











--RTS=`rts-path'




Specifies the default location of the runtime library. Same meaning as the
equivalent gnatmake flag (Switches for gnatmake).











-d




If this switch is set, then gnatfind will output the parent type
reference for each matching derived types.











-e




By default, gnatfind accept the simple regular expression set for
pattern. If this switch is set, then the pattern will be
considered as full Unix-style regular expression.











-f




If this switch is set, the output file names will be preceded by their
directory (if the file was found in the search path). If this switch is
not set, the directory will not be printed.











-g




If this switch is set, information is output only for library-level
entities, ignoring local entities. The use of this switch may accelerate
gnatfind and gnatxref.











-I`DIR'




Equivalent to -aODIR -aIDIR.











-p`FILE'




Specify a configuration file to use to list the source and object directories.



If a file is specified, then the content of the source directory and object
directory lines are added as if they had been specified respectively
by -aI and -aO.



See Configuration Files for gnatxref and gnatfind for the syntax
of this configuration file.











-r




By default, gnatfind will output only the information about the
declaration, body or type completion of the entities. If this switch is
set, the gnatfind will locate every reference to the entities in
the files specified on the command line (or in every file in the search
path if no file is given on the command line).











-s




If this switch is set, then gnatfind will output the content
of the Ada source file lines were the entity was found.











-t




If this switch is set, then gnatfind will output the type hierarchy for
the specified type. It act like -d option but recursively from parent
type to parent type. When this switch is set it is not possible to
specify more than one file.






All these switches may be in any order on the command line, and may even
appear after the file names. They need not be separated by spaces, thus
you can say gnatxref -ag instead of
gnatxref -a -g.



As stated previously, gnatfind will search in every directory in the
search path. You can force it to look only in the current directory if
you specify * at the end of the command line.









Next: , Previous: gnatfind Switches, Up: The Cross-Referencing Tools gnatxref and gnatfind   [Contents][Index]





5.3.3 Configuration Files for gnatxref and gnatfind




Configuration files are used by gnatxref and gnatfind to specify
the list of source and object directories to consider. They can be
specified via the -p switch.



The following lines can be included, in any order in the file:






Any other line will be silently ignored.









Next: , Previous: Configuration Files for gnatxref and gnatfind, Up: The Cross-Referencing Tools gnatxref and gnatfind   [Contents][Index]





5.3.4 Regular Expressions in gnatfind and gnatxref




As specified in the section about gnatfind, the pattern can be a
regular expression. Two kinds of regular expressions
are recognized:












Next: , Previous: Regular Expressions in gnatfind and gnatxref, Up: The Cross-Referencing Tools gnatxref and gnatfind   [Contents][Index]





5.3.5 Examples of gnatxref Usage






• General Usage:  



• Using gnatxref with vi:  












Next: , Up: Examples of gnatxref Usage   [Contents][Index]





5.3.5.1 General Usage




For the following examples, we will consider the following units:








main.ads:
1: with Bar;
2: package Main is
3:     procedure Foo (B : in Integer);
4:     C : Integer;
5: private
6:     D : Integer;
7: end Main;

main.adb:
1: package body Main is
2:     procedure Foo (B : in Integer) is
3:     begin
4:        C := B;
5:        D := B;
6:        Bar.Print (B);
7:        Bar.Print (C);
8:     end Foo;
9: end Main;

bar.ads:
1: package Bar is
2:     procedure Print (B : Integer);
3: end bar;






The first thing to do is to recompile your application (for instance, in
that case just by doing a gnatmake main, so that GNAT generates
the cross-referencing information.
You can then issue any of the following commands:

















Previous: General Usage, Up: Examples of gnatxref Usage   [Contents][Index]





5.3.5.2 Using gnatxref with vi




gnatxref can generate a tags file output, which can be used
directly from vi. Note that the standard version of vi
will not work properly with overloaded symbols. Consider using another
free implementation of vi, such as vim.








$ gnatxref -v gnatfind.adb > tags






The following command will generate the tags file for gnatfind itself
(if the sources are in the search path!):








$ gnatxref -v gnatfind.adb > tags






From vi, you can then use the command :tag `entity'
(replacing entity by whatever you are looking for), and vi will
display a new file with the corresponding declaration of entity.









Previous: Examples of gnatxref Usage, Up: The Cross-Referencing Tools gnatxref and gnatfind   [Contents][Index]





5.3.6 Examples of gnatfind Usage













Previous: The Cross-Referencing Tools gnatxref and gnatfind, Up: GNAT Utility Programs   [Contents][Index]





5.4 The Ada to HTML Converter gnathtml






gnathtml is a Perl script that allows Ada source files to be browsed using
standard Web browsers. For installation information, see Installing gnathtml.



Ada reserved keywords are highlighted in a bold font and Ada comments in
a blue font. Unless your program was compiled with the gcc -gnatx
switch to suppress the generation of cross-referencing information, user
defined variables and types will appear in a different color; you will
be able to click on any identifier and go to its declaration.





• Invoking gnathtml:  



• Installing gnathtml:  












Next: , Up: The Ada to HTML Converter gnathtml   [Contents][Index]





5.4.1 Invoking gnathtml




The command line is as follows:








$ perl gnathtml.pl [ switches ] ada-files






You can specify as many Ada files as you want. gnathtml will generate
an html file for every ada file, and a global file called index.htm.
This file is an index of every identifier defined in the files.



The following switches are available:








83




Only the Ada 83 subset of keywords will be highlighted.











cc `color'




This option allows you to change the color used for comments. The default
value is green. The color argument can be any name accepted by html.











d




If the Ada files depend on some other files (for instance through
with clauses, the latter files will also be converted to html.
Only the files in the user project will be converted to html, not the files
in the run-time library itself.











D




This command is the same as -d above, but gnathtml will
also look for files in the run-time library, and generate html files for them.











ext `extension'




This option allows you to change the extension of the generated HTML files.
If you do not specify an extension, it will default to htm.











f




By default, gnathtml will generate html links only for global entities
(’with’ed units, global variables and types,...). If you specify
-f on the command line, then links will be generated for local
entities too.











l `number'




If this switch is provided and number is not 0, then
gnathtml will number the html files every number line.











I `dir'




Specify a directory to search for library files (.ALI files) and
source files. You can provide several -I switches on the command line,
and the directories will be parsed in the order of the command line.











o `dir'




Specify the output directory for html files. By default, gnathtml will
saved the generated html files in a subdirectory named html/.











p `file'




If you are using Emacs and the most recent Emacs Ada mode, which provides
a full Integrated Development Environment for compiling, checking,
running and debugging applications, you may use .gpr files
to give the directories where Emacs can find sources and object files.



Using this switch, you can tell gnathtml to use these files.
This allows you to get an html version of your application, even if it
is spread over multiple directories.











sc `color'




This switch allows you to change the color used for symbol
definitions.
The default value is red. The color argument can be any name accepted by html.











t `file'




This switch provides the name of a file. This file contains a list of
file names to be converted, and the effect is exactly as though they had
appeared explicitly on the command line. This
is the recommended way to work around the command line length limit on some
systems.












Previous: Invoking gnathtml, Up: The Ada to HTML Converter gnathtml   [Contents][Index]





5.4.2 Installing gnathtml




Perl needs to be installed on your machine to run this script.
Perl is freely available for almost every architecture and
operating system via the Internet.



On Unix systems, you  may want to modify  the  first line of  the script
gnathtml,  to explicitly  specify  where Perl
is located. The syntax of this line is:








#!full_path_name_to_perl






Alternatively, you may run the script using the following command line:








$ perl gnathtml.pl [ switches ] files
























Next: , Previous: GNAT Utility Programs, Up: Top   [Contents][Index]





6 GNAT and Program Execution




This chapter covers several topics:








• Running and Debugging Ada Programs:  



• Profiling:  



• Improving Performance:  



• Overflow Check Handling in GNAT:  



• Performing Dimensionality Analysis in GNAT:  



• Stack Related Facilities:  



• Memory Management Issues:  












Next: , Up: GNAT and Program Execution   [Contents][Index]





6.1 Running and Debugging Ada Programs






This section discusses how to debug Ada programs.



An incorrect Ada program may be handled in three ways by the GNAT compiler:












• The GNAT Debugger GDB:  



• Running GDB:  



• Introduction to GDB Commands:  



• Using Ada Expressions:  



• Calling User-Defined Subprograms:  



• Using the next Command in a Function:  



• Stopping When Ada Exceptions Are Raised:  



• Ada Tasks:  



• Debugging Generic Units:  



• Remote Debugging with gdbserver:  



• GNAT Abnormal Termination or Failure to Terminate:  



• Naming Conventions for GNAT Source Files:  



• Getting Internal Debugging Information:  



• Stack Traceback:  



• Pretty-Printers for the GNAT runtime:  












Next: , Up: Running and Debugging Ada Programs   [Contents][Index]





6.1.1 The GNAT Debugger GDB




GDB is a general purpose, platform-independent debugger that
can be used to debug mixed-language programs compiled with gcc,
and in particular is capable of debugging Ada programs compiled with
GNAT. The latest versions of GDB are Ada-aware and can handle
complex Ada data structures.



See Debugging with GDB,
for full details on the usage of GDB, including a section on
its usage on programs. This manual should be consulted for full
details. The section that follows is a brief introduction to the
philosophy and use of GDB.



When GNAT programs are compiled, the compiler optionally writes debugging
information into the generated object file, including information on
line numbers, and on declared types and variables. This information is
separate from the generated code. It makes the object files considerably
larger, but it does not add to the size of the actual executable that
will be loaded into memory, and has no impact on run-time performance. The
generation of debug information is triggered by the use of the
-g switch in the gcc or gnatmake command
used to carry out the compilations. It is important to emphasize that
the use of these options does not change the generated code.



The debugging information is written in standard system formats that
are used by many tools, including debuggers and profilers. The format
of the information is typically designed to describe C types and
semantics, but GNAT implements a translation scheme which allows full
details about Ada types and variables to be encoded into these
standard C formats. Details of this encoding scheme may be found in
the file exp_dbug.ads in the GNAT source distribution. However, the
details of this encoding are, in general, of no interest to a user,
since GDB automatically performs the necessary decoding.



When a program is bound and linked, the debugging information is
collected from the object files, and stored in the executable image of
the program. Again, this process significantly increases the size of
the generated executable file, but it does not increase the size of
the executable program itself. Furthermore, if this program is run in
the normal manner, it runs exactly as if the debug information were
not present, and takes no more actual memory.



However, if the program is run under control of GDB, the
debugger is activated.  The image of the program is loaded, at which
point it is ready to run.  If a run command is given, then the program
will run exactly as it would have if GDB were not present. This
is a crucial part of the GDB design philosophy.  GDB is
entirely non-intrusive until a breakpoint is encountered.  If no
breakpoint is ever hit, the program will run exactly as it would if no
debugger were present. When a breakpoint is hit, GDB accesses
the debugging information and can respond to user commands to inspect
variables, and more generally to report on the state of execution.









Next: , Previous: The GNAT Debugger GDB, Up: Running and Debugging Ada Programs   [Contents][Index]





6.1.2 Running GDB




This section describes how to initiate the debugger.



The debugger can be launched from a GNAT Studio menu or
directly from the command line. The description below covers the latter use.
All the commands shown can be used in the GNAT Studio debug console window,
but there are usually more GUI-based ways to achieve the same effect.



The command to run GDB is








$ gdb program






where program is the name of the executable file. This
activates the debugger and results in a prompt for debugger commands.
The simplest command is simply run, which causes the program to run
exactly as if the debugger were not present. The following section
describes some of the additional commands that can be given to GDB.









Next: , Previous: Running GDB, Up: Running and Debugging Ada Programs   [Contents][Index]





6.1.3 Introduction to GDB Commands




GDB contains a large repertoire of commands.
See Debugging with GDB for extensive documentation on the use
of these commands, together with examples of their use. Furthermore,
the command `help' invoked from within GDB activates a simple help
facility which summarizes the available commands and their options.
In this section we summarize a few of the most commonly
used commands to give an idea of what GDB is about. You should create
a simple program with debugging information and experiment with the use of
these GDB commands on the program as you read through the
following section.






The above list is a very short introduction to the commands that
GDB provides. Important additional capabilities, including conditional
breakpoints, the ability to execute command sequences on a breakpoint,
the ability to debug at the machine instruction level and many other
features are described in detail in Debugging with GDB.
Note that most commands can be abbreviated
(for example, c for continue, bt for backtrace).









Next: , Previous: Introduction to GDB Commands, Up: Running and Debugging Ada Programs   [Contents][Index]





6.1.4 Using Ada Expressions






GDB supports a fairly large subset of Ada expression syntax, with some
extensions. The philosophy behind the design of this subset is











Thus, for brevity, the debugger acts as if there were
implicit with and use clauses in effect for all user-written
packages, thus making it unnecessary to fully qualify most names with
their packages, regardless of context. Where this causes ambiguity,
GDB asks the user’s intent.



For details on the supported Ada syntax, see Debugging with GDB.









Next: , Previous: Using Ada Expressions, Up: Running and Debugging Ada Programs   [Contents][Index]





6.1.5 Calling User-Defined Subprograms




An important capability of GDB is the ability to call user-defined
subprograms while debugging. This is achieved simply by entering
a subprogram call statement in the form:








call subprogram-name (parameters)






The keyword call can be omitted in the normal case where the
subprogram-name does not coincide with any of the predefined
GDB commands.



The effect is to invoke the given subprogram, passing it the
list of parameters that is supplied. The parameters can be expressions and
can include variables from the program being debugged. The
subprogram must be defined
at the library level within your program, and GDB will call the
subprogram within the environment of your program execution (which
means that the subprogram is free to access or even modify variables
within your program).



The most important use of this facility is in allowing the inclusion of
debugging routines that are tailored to particular data structures
in your program. Such debugging routines can be written to provide a suitably
high-level description of an abstract type, rather than a low-level dump
of its physical layout. After all, the standard
GDB print command only knows the physical layout of your
types, not their abstract meaning. Debugging routines can provide information
at the desired semantic level and are thus enormously useful.



For example, when debugging GNAT itself, it is crucial to have access to
the contents of the tree nodes used to represent the program internally.
But tree nodes are represented simply by an integer value (which in turn
is an index into a table of nodes).
Using the print command on a tree node would simply print this integer
value, which is not very useful. But the PN routine (defined in file
treepr.adb in the GNAT sources) takes a tree node as input, and displays
a useful high level representation of the tree node, which includes the
syntactic category of the node, its position in the source, the integers
that denote descendant nodes and parent node, as well as varied
semantic information. To study this example in more detail, you might want to
look at the body of the PN procedure in the stated file.



Another useful application of this capability is to deal with situations of
complex data which are not handled suitably by GDB. For example, if you specify
Convention Fortran for a multi-dimensional array, GDB does not know that
the ordering of array elements has been switched and will not properly
address the array elements. In such a case, instead of trying to print the
elements directly from GDB, you can write a callable procedure that prints
the elements in the desired format.









Next: , Previous: Calling User-Defined Subprograms, Up: Running and Debugging Ada Programs   [Contents][Index]





6.1.6 Using the `next' Command in a Function




When you use the next command in a function, the current source
location will advance to the next statement as usual. A special case
arises in the case of a return statement.



Part of the code for a return statement is the ’epilogue’ of the function.
This is the code that returns to the caller. There is only one copy of
this epilogue code, and it is typically associated with the last return
statement in the function if there is more than one return. In some
implementations, this epilogue is associated with the first statement
of the function.



The result is that if you use the next command from a return
statement that is not the last return statement of the function you
may see a strange apparent jump to the last return statement or to
the start of the function. You should simply ignore this odd jump.
The value returned is always that from the first return statement
that was stepped through.









Next: , Previous: Using the next Command in a Function, Up: Running and Debugging Ada Programs   [Contents][Index]





6.1.7 Stopping When Ada Exceptions Are Raised






You can set catchpoints that stop the program execution when your program
raises selected exceptions.














Next: , Previous: Stopping When Ada Exceptions Are Raised, Up: Running and Debugging Ada Programs   [Contents][Index]





6.1.8 Ada Tasks




GDB allows the following task-related commands:
















For more detailed information on the tasking support,
see Debugging with GDB.













Next: , Previous: Ada Tasks, Up: Running and Debugging Ada Programs   [Contents][Index]





6.1.9 Debugging Generic Units




GNAT always uses code expansion for generic instantiation. This means that
each time an instantiation occurs, a complete copy of the original code is
made, with appropriate substitutions of formals by actuals.



It is not possible to refer to the original generic entities in
GDB, but it is always possible to debug a particular instance of
a generic, by using the appropriate expanded names. For example, if we have








procedure g is

   generic package k is
      procedure kp (v1 : in out integer);
   end k;

   package body k is
      procedure kp (v1 : in out integer) is
      begin
         v1 := v1 + 1;
      end kp;
   end k;

   package k1 is new k;
   package k2 is new k;

   var : integer := 1;

begin
   k1.kp (var);
   k2.kp (var);
   k1.kp (var);
   k2.kp (var);
end;






Then to break on a call to procedure kp in the k2 instance, simply
use the command:








(gdb) break g.k2.kp






When the breakpoint occurs, you can step through the code of the
instance in the normal manner and examine the values of local variables, as for
other units.











Next: , Previous: Debugging Generic Units, Up: Running and Debugging Ada Programs   [Contents][Index]





6.1.10 Remote Debugging with gdbserver




On platforms where gdbserver is supported, it is possible to use this tool
to debug your application remotely.  This can be useful in situations
where the program needs to be run on a target host that is different
from the host used for development, particularly when the target has
a limited amount of resources (either CPU and/or memory).



To do so, start your program using gdbserver on the target machine.
gdbserver then automatically suspends the execution of your program
at its entry point, waiting for a debugger to connect to it.  The
following commands starts an application and tells gdbserver to
wait for a connection with the debugger on localhost port 4444.








$ gdbserver localhost:4444 program
Process program created; pid = 5685
Listening on port 4444






Once gdbserver has started listening, we can tell the debugger to establish
a connection with this gdbserver, and then start the same debugging session
as if the program was being debugged on the same host, directly under
the control of GDB.








$ gdb program
(gdb) target remote targethost:4444
Remote debugging using targethost:4444
0x00007f29936d0af0 in ?? () from /lib64/ld-linux-x86-64.so.
(gdb) b foo.adb:3
Breakpoint 1 at 0x401f0c: file foo.adb, line 3.
(gdb) continue
Continuing.

Breakpoint 1, foo () at foo.adb:4
4       end foo;






It is also possible to use gdbserver to attach to an already running
program, in which case the execution of that program is simply suspended
until the connection between the debugger and gdbserver is established.



For more information on how to use gdbserver, see the `Using the gdbserver Program'
section in Debugging with GDB.
GNAT provides support for gdbserver on x86-linux, x86-windows and x86_64-linux.











Next: , Previous: Remote Debugging with gdbserver, Up: Running and Debugging Ada Programs   [Contents][Index]





6.1.11 GNAT Abnormal Termination or Failure to Terminate




When presented with programs that contain serious errors in syntax
or semantics,
GNAT may on rare occasions  experience problems in operation, such
as aborting with a
segmentation fault or illegal memory access, raising an internal
exception, terminating abnormally, or failing to terminate at all.
In such cases, you can activate
various features of GNAT that can help you pinpoint the construct in your
program that is the likely source of the problem.



The following strategies are presented in increasing order of
difficulty, corresponding to your experience in using GNAT and your
familiarity with compiler internals.

















Next: , Previous: GNAT Abnormal Termination or Failure to Terminate, Up: Running and Debugging Ada Programs   [Contents][Index]





6.1.12 Naming Conventions for GNAT Source Files




In order to examine the workings of the GNAT system, the following
brief description of its organization may be helpful:












Next: , Previous: Naming Conventions for GNAT Source Files, Up: Running and Debugging Ada Programs   [Contents][Index]





6.1.13 Getting Internal Debugging Information




Most compilers have internal debugging switches and modes. GNAT
does also, except GNAT internal debugging switches and modes are not
secret. A summary and full description of all the compiler and binder
debug flags are in the file debug.adb. You must obtain the
sources of the compiler to see the full detailed effects of these flags.



The switches that print the source of the program (reconstructed from
the internal tree) are of general interest for user programs, as are the
options to print
the full internal tree, and the entity table (the symbol table
information). The reconstructed source provides a readable version of the
program after the front-end has completed analysis and  expansion,
and is useful when studying the performance of specific constructs.
For example, constraint checks are indicated, complex aggregates
are replaced with loops and assignments, and tasking primitives
are replaced with run-time calls.















Next: , Previous: Getting Internal Debugging Information, Up: Running and Debugging Ada Programs   [Contents][Index]





6.1.14 Stack Traceback




Traceback is a mechanism to display the sequence of subprogram calls that
leads to a specified execution point in a program. Often (but not always)
the execution point is an instruction at which an exception has been raised.
This mechanism is also known as `stack unwinding' because it obtains
its information by scanning the run-time stack and recovering the activation
records of all active subprograms. Stack unwinding is one of the most
important tools for program debugging.



The first entry stored in traceback corresponds to the deepest calling level,
that is to say the subprogram currently executing the instruction
from which we want to obtain the traceback.



Note that there is no runtime performance penalty when stack traceback
is enabled, and no exception is raised during program execution.








• Non-Symbolic Traceback:  



• Symbolic Traceback:  












Next: , Up: Stack Traceback   [Contents][Index]





6.1.14.1 Non-Symbolic Traceback




Note: this feature is not supported on all platforms. See
GNAT.Traceback spec in g-traceb.ads
for a complete list of supported platforms.




Tracebacks From an Unhandled Exception




A runtime non-symbolic traceback is a list of addresses of call instructions.
To enable this feature you must use the -E
gnatbind option. With this option a stack traceback is stored as part
of exception information. You can retrieve this information using the
addr2line tool.



Here is a simple example:








procedure STB is

   procedure P1 is
   begin
      raise Constraint_Error;
   end P1;

   procedure P2 is
   begin
      P1;
   end P2;

begin
   P2;
end STB;






$ gnatmake stb -bargs -E
$ stb

Execution terminated by unhandled exception
Exception name: CONSTRAINT_ERROR
Message: stb.adb:5
Call stack traceback locations:
0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4






As we see the traceback lists a sequence of addresses for the unhandled
exception CONSTRAINT_ERROR raised in procedure P1. It is easy to
guess that this exception come from procedure P1. To translate these
addresses into the source lines where the calls appear, the
addr2line tool, described below, is invaluable. The use of this tool
requires the program to be compiled with debug information.








$ gnatmake -g stb -bargs -E
$ stb

Execution terminated by unhandled exception
Exception name: CONSTRAINT_ERROR
Message: stb.adb:5
Call stack traceback locations:
0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4

$ addr2line --exe=stb 0x401373 0x40138b 0x40139c 0x401335 0x4011c4
   0x4011f1 0x77e892a4

00401373 at d:/stb/stb.adb:5
0040138B at d:/stb/stb.adb:10
0040139C at d:/stb/stb.adb:14
00401335 at d:/stb/b~stb.adb:104
004011C4 at /build/.../crt1.c:200
004011F1 at /build/.../crt1.c:222
77E892A4 in ?? at ??:0






The addr2line tool has several other useful options:









--functionsto get the function name corresponding to any location


--demangle=gnatto use the gnat decoding mode for the function names.
Note that for binutils version 2.9.x the option is
simply --demangle.








$ addr2line --exe=stb --functions --demangle=gnat 0x401373 0x40138b
   0x40139c 0x401335 0x4011c4 0x4011f1

00401373 in stb.p1 at d:/stb/stb.adb:5
0040138B in stb.p2 at d:/stb/stb.adb:10
0040139C in stb at d:/stb/stb.adb:14
00401335 in main at d:/stb/b~stb.adb:104
004011C4 in <__mingw_CRTStartup> at /build/.../crt1.c:200
004011F1 in <mainCRTStartup> at /build/.../crt1.c:222






From this traceback we can see that the exception was raised in
stb.adb at line 5, which was reached from a procedure call in
stb.adb at line 10, and so on. The b~std.adb is the binder file,
which contains the call to the main program.
Running gnatbind. The remaining entries are assorted runtime routines,
and the output will vary from platform to platform.



It is also possible to use GDB with these traceback addresses to debug
the program. For example, we can break at a given code location, as reported
in the stack traceback:








$ gdb -nw stb






Furthermore, this feature is not implemented inside Windows DLL. Only
the non-symbolic traceback is reported in this case.








(gdb) break *0x401373
Breakpoint 1 at 0x401373: file stb.adb, line 5.






It is important to note that the stack traceback addresses
do not change when debug information is included. This is particularly useful
because it makes it possible to release software without debug information (to
minimize object size), get a field report that includes a stack traceback
whenever an internal bug occurs, and then be able to retrieve the sequence
of calls with the same program compiled with debug information.




Tracebacks From Exception Occurrences




Non-symbolic tracebacks are obtained by using the -E binder argument.
The stack traceback is attached to the exception information string, and can
be retrieved in an exception handler within the Ada program, by means of the
Ada facilities defined in Ada.Exceptions. Here is a simple example:








with Ada.Text_IO;
with Ada.Exceptions;

procedure STB is

   use Ada;
   use Ada.Exceptions;

   procedure P1 is
      K : Positive := 1;
   begin
      K := K - 1;
   exception
      when E : others =>
         Text_IO.Put_Line (Exception_Information (E));
   end P1;

   procedure P2 is
   begin
      P1;
   end P2;

begin
   P2;
end STB;






This program will output:








$ stb

Exception name: CONSTRAINT_ERROR
Message: stb.adb:12
Call stack traceback locations:
0x4015e4 0x401633 0x401644 0x401461 0x4011c4 0x4011f1 0x77e892a4







Tracebacks From Anywhere in a Program




It is also possible to retrieve a stack traceback from anywhere in a
program. For this you need to
use the GNAT.Traceback API. This package includes a procedure called
Call_Chain that computes a complete stack traceback, as well as useful
display procedures described below. It is not necessary to use the
-E gnatbind option in this case, because the stack traceback mechanism
is invoked explicitly.



In the following example we compute a traceback at a specific location in
the program, and we display it using GNAT.Debug_Utilities.Image to
convert addresses to strings:








with Ada.Text_IO;
with GNAT.Traceback;
with GNAT.Debug_Utilities;

procedure STB is

   use Ada;
   use GNAT;
   use GNAT.Traceback;

   procedure P1 is
      TB  : Tracebacks_Array (1 .. 10);
      --  We are asking for a maximum of 10 stack frames.
      Len : Natural;
      --  Len will receive the actual number of stack frames returned.
   begin
      Call_Chain (TB, Len);

      Text_IO.Put ("In STB.P1 : ");

      for K in 1 .. Len loop
         Text_IO.Put (Debug_Utilities.Image (TB (K)));
         Text_IO.Put (' ');
      end loop;

      Text_IO.New_Line;
   end P1;

   procedure P2 is
   begin
      P1;
   end P2;

begin
   P2;
end STB;






$ gnatmake -g stb
$ stb

In STB.P1 : 16#0040_F1E4# 16#0040_14F2# 16#0040_170B# 16#0040_171C#
16#0040_1461# 16#0040_11C4# 16#0040_11F1# 16#77E8_92A4#






You can then get further information by invoking the addr2line
tool as described earlier (note that the hexadecimal addresses
need to be specified in C format, with a leading ’0x’).












Previous: Non-Symbolic Traceback, Up: Stack Traceback   [Contents][Index]





6.1.14.2 Symbolic Traceback




A symbolic traceback is a stack traceback in which procedure names are
associated with each code location.



Note that this feature is not supported on all platforms. See
GNAT.Traceback.Symbolic spec in g-trasym.ads for a complete
list of currently supported platforms.



Note that the symbolic traceback requires that the program be compiled
with debug information. If it is not compiled with debug information
only the non-symbolic information will be valid.




Tracebacks From Exception Occurrences




Here is an example:








with Ada.Text_IO;
with GNAT.Traceback.Symbolic;

procedure STB is

   procedure P1 is
   begin
      raise Constraint_Error;
   end P1;

   procedure P2 is
   begin
      P1;
   end P2;

   procedure P3 is
   begin
      P2;
   end P3;

begin
   P3;
exception
   when E : others =>
      Ada.Text_IO.Put_Line (GNAT.Traceback.Symbolic.Symbolic_Traceback (E));
end STB;






$ gnatmake -g .\stb -bargs -E
$ stb

0040149F in stb.p1 at stb.adb:8
004014B7 in stb.p2 at stb.adb:13
004014CF in stb.p3 at stb.adb:18
004015DD in ada.stb at stb.adb:22
00401461 in main at b~stb.adb:168
004011C4 in __mingw_CRTStartup at crt1.c:200
004011F1 in mainCRTStartup at crt1.c:222
77E892A4 in ?? at ??:0






In the above example the .\ syntax in the gnatmake command
is currently required by addr2line for files that are in
the current working directory.
Moreover, the exact sequence of linker options may vary from platform
to platform.
The above -largs section is for Windows platforms. By contrast,
under Unix there is no need for the -largs section.
Differences across platforms are due to details of linker implementation.




Tracebacks From Anywhere in a Program




It is possible to get a symbolic stack traceback
from anywhere in a program, just as for non-symbolic tracebacks.
The first step is to obtain a non-symbolic
traceback, and then call Symbolic_Traceback to compute the symbolic
information. Here is an example:








with Ada.Text_IO;
with GNAT.Traceback;
with GNAT.Traceback.Symbolic;

procedure STB is

   use Ada;
   use GNAT.Traceback;
   use GNAT.Traceback.Symbolic;

   procedure P1 is
      TB  : Tracebacks_Array (1 .. 10);
      --  We are asking for a maximum of 10 stack frames.
      Len : Natural;
      --  Len will receive the actual number of stack frames returned.
   begin
      Call_Chain (TB, Len);
      Text_IO.Put_Line (Symbolic_Traceback (TB (1 .. Len)));
   end P1;

   procedure P2 is
   begin
      P1;
   end P2;

begin
   P2;
end STB;







Automatic Symbolic Tracebacks




Symbolic tracebacks may also be enabled by using the -Es switch to gnatbind (as
in gprbuild -g ... -bargs -Es).
This will cause the Exception_Information to contain a symbolic traceback,
which will also be printed if an unhandled exception terminates the
program.









Previous: Stack Traceback, Up: Running and Debugging Ada Programs   [Contents][Index]





6.1.15 Pretty-Printers for the GNAT runtime




As discussed in Calling User-Defined Subprograms, GDB’s
print command only knows about the physical layout of program data
structures and therefore normally displays only low-level dumps, which
are often hard to understand.



An example of this is when trying to display the contents of an Ada
standard container, such as Ada.Containers.Ordered_Maps.Map:








with Ada.Containers.Ordered_Maps;

procedure PP is
   package Int_To_Nat is
      new Ada.Containers.Ordered_Maps (Integer, Natural);

   Map : Int_To_Nat.Map;
begin
   Map.Insert (1, 10);
   Map.Insert (2, 20);
   Map.Insert (3, 30);

   Map.Clear; --  BREAK HERE
end PP;






When this program is built with debugging information and run under
GDB up to the Map.Clear statement, trying to print Map will
yield information that is only relevant to the developers of our standard
containers:








(gdb) print map
$1 = (
  tree => (
    first => 0x64e010,
    last => 0x64e070,
    root => 0x64e040,
    length => 3,
    tc => (
      busy => 0,
      lock => 0
    )
  )
)






Fortunately, GDB has a feature called pretty-printers1,
which allows customizing how GDB displays data structures. The GDB
shipped with GNAT embeds such pretty-printers for the most common
containers in the standard library.  To enable them, either run the
following command manually under GDB or add it to your .gdbinit file:








python import gnatdbg; gnatdbg.setup()






Once this is done, GDB’s print command will automatically use
these pretty-printers when appropriate. Using the previous example:








(gdb) print map
$1 = pp.int_to_nat.map of length 3 = {
  [1] = 10,
  [2] = 20,
  [3] = 30
}






Pretty-printers are invoked each time GDB tries to display a value,
including when displaying the arguments of a called subprogram (in
GDB’s backtrace command) or when printing the value returned by a
function (in GDB’s finish command).



To display a value without involving pretty-printers, print can be
invoked with its /r option:








(gdb) print/r map
$1 = (
  tree => (...






Finer control of pretty-printers is also possible: see GDB’s online documentation2
for more information.











Next: , Previous: Running and Debugging Ada Programs, Up: GNAT and Program Execution   [Contents][Index]





6.2 Profiling




This section describes how to use the gprof profiler tool on Ada programs.









• Profiling an Ada Program with gprof:  












Up: Profiling   [Contents][Index]





6.2.1 Profiling an Ada Program with gprof




This section is not meant to be an exhaustive documentation of gprof.
Full documentation for it can be found in the GNU Profiler User’s Guide
documentation that is part of this GNAT distribution.



Profiling a program helps determine the parts of a program that are executed
most often, and are therefore the most time-consuming.



gprof is the standard GNU profiling tool; it has been enhanced to
better handle Ada programs and multitasking.
It is currently supported on the following platforms






In order to profile a program using gprof, several steps are needed:




    

  1.  Instrument the code, which requires a full recompilation of the project with the
proper switches.


  2.  Execute the program under the analysis conditions, i.e. with the desired
input.


  3.  Analyze the results using the gprof tool.




The following sections detail the different steps, and indicate how
to interpret the results.





• Compilation for profiling:  



• Program execution:  



• Running gprof:  



• Interpretation of profiling results:  












Next: , Up: Profiling an Ada Program with gprof   [Contents][Index]





6.2.1.1 Compilation for profiling










In order to profile a program the first step is to tell the compiler
to generate the necessary profiling information. The compiler switch to be used
is -pg, which must be added to other compilation switches. This
switch needs to be specified both during compilation and link stages, and can
be specified once when using gnatmake:








$ gnatmake -f -pg -P my_project






Note that only the objects that were compiled with the -pg switch will
be profiled; if you need to profile your whole project, use the -f
gnatmake switch to force full recompilation.









Next: , Previous: Compilation for profiling, Up: Profiling an Ada Program with gprof   [Contents][Index]





6.2.1.2 Program execution




Once the program has been compiled for profiling, you can run it as usual.



The only constraint imposed by profiling is that the program must terminate
normally. An interrupted program (via a Ctrl-C, kill, etc.) will not be
properly analyzed.



Once the program completes execution, a data file called gmon.out is
generated in the directory where the program was launched from. If this file
already exists, it will be overwritten.









Next: , Previous: Program execution, Up: Profiling an Ada Program with gprof   [Contents][Index]





6.2.1.3 Running gprof




The gprof tool is called as follow:








$ gprof my_prog gmon.out






or simply:








$  gprof my_prog






The complete form of the gprof command line is the following:








$ gprof [switches] [executable [data-file]]






gprof supports numerous switches. The order of these
switch does not matter. The full list of options can be found in
the GNU Profiler User’s Guide documentation that comes with this documentation.



The following is the subset of those switches that is most relevant:








--demangle[=`style'], --no-demangle




These options control whether symbol names should be demangled when
printing output.  The default is to demangle C++ symbols.  The
--no-demangle option may be used to turn off demangling. Different
compilers have different mangling styles.  The optional demangling style
argument can be used to choose an appropriate demangling style for your
compiler, in particular Ada symbols generated by GNAT can be demangled using
--demangle=gnat.











-e `function_name'




The -e `function' option tells gprof not to print
information about the function function_name (and its
children...) in the call graph.  The function will still be listed
as a child of any functions that call it, but its index number will be
shown as [not printed].  More than one -e option may be
given; only one function_name may be indicated with each -e
option.











-E `function_name'




The -E `function' option works like the -e option, but
execution time spent in the function (and children who were not called from
anywhere else), will not be used to compute the percentages-of-time for
the call graph.  More than one -E option may be given; only one
function_name may be indicated with each -E` option.











-f `function_name'




The -f `function' option causes gprof to limit the
call graph to the function function_name and its children (and
their children...).  More than one -f option may be given;
only one function_name may be indicated with each -f
option.











-F `function_name'




The -F `function' option works like the -f option, but
only time spent in the function and its children (and their
children...) will be used to determine total-time and
percentages-of-time for the call graph.  More than one -F option
may be given; only one function_name may be indicated with each
-F option.  The -F option overrides the -E option.












Previous: Running gprof, Up: Profiling an Ada Program with gprof   [Contents][Index]





6.2.1.4 Interpretation of profiling results




The results of the profiling analysis are represented by two arrays: the
’flat profile’ and the ’call graph’. Full documentation of those outputs
can be found in the GNU Profiler User’s Guide.



The flat profile shows the time spent in each function of the program, and how
many time it has been called. This allows you to locate easily the most
time-consuming functions.



The call graph shows, for each subprogram, the subprograms that call it,
and the subprograms that it calls. It also provides an estimate of the time
spent in each of those callers/called subprograms.









Next: , Previous: Profiling, Up: GNAT and Program Execution   [Contents][Index]





6.3 Improving Performance






This section presents several topics related to program performance.
It first describes some of the tradeoffs that need to be considered
and some of the techniques for making your program run faster.



It then documents the unused subprogram/data elimination feature,
which can reduce the size of program executables.





• Performance Considerations:  



• Text_IO Suggestions:  



• Reducing Size of Executables with Unused Subprogram/Data Elimination:  












Next: , Up: Improving Performance   [Contents][Index]





6.3.1 Performance Considerations




The GNAT system provides a number of options that allow a trade-off
between






The defaults (if no options are selected) aim at improving the speed
of compilation and minimizing dependences, at the expense of performance
of the generated code:






These options are suitable for most program development purposes. This
section describes how you can modify these choices, and also provides
some guidelines on debugging optimized code.





• Controlling Run-Time Checks:  



• Use of Restrictions:  



• Optimization Levels:  



• Debugging Optimized Code:  



• Inlining of Subprograms:  



• Floating_Point_Operations:  



• Vectorization of loops:  



• Other Optimization Switches:  



• Optimization and Strict Aliasing:  



• Aliased Variables and Optimization:  



• Atomic Variables and Optimization:  



• Passive Task Optimization:  












Next: , Up: Performance Considerations   [Contents][Index]





6.3.1.1 Controlling Run-Time Checks




By default, GNAT generates all run-time checks, except stack overflow
checks, and checks for access before elaboration on subprogram
calls. The latter are not required in default mode, because all
necessary checking is done at compile time.







The gnat switch, -gnatp allows this default to be modified. See
Run-Time Checks.



Our experience is that the default is suitable for most development
purposes.



Elaboration checks are off by default, and also not needed by default, since
GNAT uses a static elaboration analysis approach that avoids the need for
run-time checking. This manual contains a full chapter discussing the issue
of elaboration checks, and if the default is not satisfactory for your use,
you should read this chapter.



For validity checks, the minimal checks required by the Ada Reference
Manual (for case statements and assignments to array elements) are on
by default. These can be suppressed by use of the -gnatVn switch.
Note that in Ada 83, there were no validity checks, so if the Ada 83 mode
is acceptable (or when comparing GNAT performance with an Ada 83 compiler),
it may be reasonable to routinely use -gnatVn. Validity checks
are also suppressed entirely if -gnatp is used.
















Note that the setting of the switches controls the default setting of
the checks. They may be modified using either pragma Suppress (to
remove checks) or pragma Unsuppress (to add back suppressed
checks) in the program source.









Next: , Previous: Controlling Run-Time Checks, Up: Performance Considerations   [Contents][Index]





6.3.1.2 Use of Restrictions




The use of pragma Restrictions allows you to control which features are
permitted in your program. Apart from the obvious point that if you avoid
relatively expensive features like finalization (enforceable by the use
of pragma Restrictions (No_Finalization), the use of this pragma does not
affect the generated code in most cases.



One notable exception to this rule is that the possibility of task abort
results in some distributed overhead, particularly if finalization or
exception handlers are used. The reason is that certain sections of code
have to be marked as non-abortable.



If you use neither the abort statement, nor asynchronous transfer
of control (select ... then abort), then this distributed overhead
is removed, which may have a general positive effect in improving
overall performance.  Especially code involving frequent use of tasking
constructs and controlled types will show much improved performance.
The relevant restrictions pragmas are








pragma Restrictions (No_Abort_Statements);
pragma Restrictions (Max_Asynchronous_Select_Nesting => 0);






It is recommended that these restriction pragmas be used if possible. Note
that this also means that you can write code without worrying about the
possibility of an immediate abort at any point.









Next: , Previous: Use of Restrictions, Up: Performance Considerations   [Contents][Index]





6.3.1.3 Optimization Levels






Without any optimization option,
the compiler’s goal is to reduce the cost of
compilation and to make debugging produce the expected results.
Statements are independent: if you stop the program with a breakpoint between
statements, you can then assign a new value to any variable or change
the program counter to any other statement in the subprogram and get exactly
the results you would expect from the source code.



Turning on optimization makes the compiler attempt to improve the
performance and/or code size at the expense of compilation time and
possibly the ability to debug the program.



If you use multiple
-O options, with or without level numbers,
the last such option is the one that is effective.



The default is optimization off. This results in the fastest compile
times, but GNAT makes absolutely no attempt to optimize, and the
generated programs are considerably larger and slower than when
optimization is enabled. You can use the
-O switch (the permitted forms are -O0, -O1
-O2, -O3, and -Os)
to gcc to control the optimization level:






Higher optimization levels perform more global transformations on the
program and apply more expensive analysis algorithms in order to generate
faster and more compact code. The price in compilation time, and the
resulting improvement in execution time,
both depend on the particular application and the hardware environment.
You should experiment to find the best level for your application.



Since the precise set of optimizations done at each level will vary from
release to release (and sometime from target to target), it is best to think
of the optimization settings in general terms.
See the `Options That Control Optimization' section in
Using the GNU Compiler Collection (GCC)
for details about
the -O settings and a number of -f options that
individually enable or disable specific optimizations.



Unlike some other compilation systems, gcc has
been tested extensively at all optimization levels. There are some bugs
which appear only with optimization turned on, but there have also been
bugs which show up only in `unoptimized' code. Selecting a lower
level of optimization does not improve the reliability of the code
generator, which in practice is highly reliable at all optimization
levels.



Note regarding the use of -O3: The use of this optimization level
ought not to be automatically preferred over that of level -O2,
since it often results in larger executables which may run more slowly.
See further discussion of this point in Inlining of Subprograms.









Next: , Previous: Optimization Levels, Up: Performance Considerations   [Contents][Index]





6.3.1.4 Debugging Optimized Code








Although it is possible to do a reasonable amount of debugging at
nonzero optimization levels,
the higher the level the more likely that
source-level constructs will have been eliminated by optimization.
For example, if a loop is strength-reduced, the loop
control variable may be completely eliminated and thus cannot be
displayed in the debugger.
This can only happen at -O2 or -O3.
Explicit temporary variables that you code might be eliminated at
level -O1 or higher.





The use of the -g switch,
which is needed for source-level debugging,
affects the size of the program executable on disk,
and indeed the debugging information can be quite large.
However, it has no effect on the generated code (and thus does not
degrade performance)



Since the compiler generates debugging tables for a compilation unit before
it performs optimizations, the optimizing transformations may invalidate some
of the debugging data.  You therefore need to anticipate certain
anomalous situations that may arise while debugging optimized code.
These are the most common cases:






In light of such anomalies, a recommended technique is to use -O0
early in the software development cycle, when extensive debugging capabilities
are most needed, and then move to -O1 and later -O2 as
the debugger becomes less critical.
Whether to use the -g switch in the release version is
a release management issue.
Note that if you use -g you can then use the strip program
on the resulting executable,
which removes both debugging information and global symbols.









Next: , Previous: Debugging Optimized Code, Up: Performance Considerations   [Contents][Index]





6.3.1.5 Inlining of Subprograms




A call to a subprogram in the current unit is inlined if all the
following conditions are met:






Calls to subprograms in `with'ed units are normally not inlined.
To achieve actual inlining (that is, replacement of the call by the code
in the body of the subprogram), the following conditions must all be true:






Even if all these conditions are met, it may not be possible for
the compiler to inline the call, due to the length of the body,
or features in the body that make it impossible for the compiler
to do the inlining.



Note that specifying the -gnatn switch causes additional
compilation dependencies. Consider the following:








package R is
   procedure Q;
   pragma Inline (Q);
end R;
package body R is
   ...
end R;

with R;
procedure Main is
begin
   ...
   R.Q;
end Main;






With the default behavior (no -gnatn switch specified), the
compilation of the Main procedure depends only on its own source,
main.adb, and the spec of the package in file r.ads. This
means that editing the body of R does not require recompiling
Main.



On the other hand, the call R.Q is not inlined under these
circumstances. If the -gnatn switch is present when Main
is compiled, the call will be inlined if the body of Q is small
enough, but now Main depends on the body of R in
r.adb as well as on the spec. This means that if this body is edited,
the main program must be recompiled. Note that this extra dependency
occurs whether or not the call is in fact inlined by gcc.



The use of front end inlining with -gnatN generates similar
additional dependencies.





Note: The -fno-inline switch overrides all other conditions and ensures that
no inlining occurs, unless requested with pragma Inline_Always for gcc
back-ends. The extra dependences resulting from -gnatn will still be active,
even if this switch is used to suppress the resulting inlining actions.





Note: The -fno-inline-functions switch can be used to prevent
automatic inlining of subprograms if -O3 is used.





Note: The -fno-inline-small-functions switch can be used to prevent
automatic inlining of small subprograms if -O2 is used.





Note: The -fno-inline-functions-called-once switch
can be used to prevent inlining of subprograms local to the unit
and called once from within it if -O1 is used.



Note regarding the use of -O3: -gnatn is made up of two
sub-switches -gnatn1 and -gnatn2 that can be directly
specified in lieu of it, -gnatn being translated into one of them
based on the optimization level. With -O2 or below, -gnatn
is equivalent to -gnatn1 which activates pragma Inline with
moderate inlining across modules. With -O3, -gnatn is
equivalent to -gnatn2 which activates pragma Inline with
full inlining across modules. If you have used pragma Inline in
appropriate cases, then it is usually much better to use -O2
and -gnatn and avoid the use of -O3 which has the additional
effect of inlining subprograms you did not think should be inlined. We have
found that the use of -O3 may slow down the compilation and increase
the code size by performing excessive inlining, leading to increased
instruction cache pressure from the increased code size and thus minor
performance improvements. So the bottom line here is that you should not
automatically assume that -O3 is better than -O2, and
indeed you should use -O3 only if tests show that it actually
improves performance for your program.









Next: , Previous: Inlining of Subprograms, Up: Performance Considerations   [Contents][Index]





6.3.1.6 Floating_Point_Operations






On almost all targets, GNAT maps Float and Long_Float to the 32-bit and
64-bit standard IEEE floating-point representations, and operations will
use standard IEEE arithmetic as provided by the processor. On most, but
not all, architectures, the attribute Machine_Overflows is False for these
types, meaning that the semantics of overflow is implementation-defined.
In the case of GNAT, these semantics correspond to the normal IEEE
treatment of infinities and NaN (not a number) values. For example,
1.0 / 0.0 yields plus infinitiy and 0.0 / 0.0 yields a NaN. By
avoiding explicit overflow checks, the performance is greatly improved
on many targets. However, if required, floating-point overflow can be
enabled by the use of the pragma Check_Float_Overflow.



Another consideration that applies specifically to x86 32-bit
architectures is which form of floating-point arithmetic is used.
By default the operations use the old style x86 floating-point,
which implements an 80-bit extended precision form (on these
architectures the type Long_Long_Float corresponds to that form).
In addition, generation of efficient code in this mode means that
the extended precision form will be used for intermediate results.
This may be helpful in improving the final precision of a complex
expression. However it means that the results obtained on the x86
will be different from those on other architectures, and for some
algorithms, the extra intermediate precision can be detrimental.



In addition to this old-style floating-point, all modern x86 chips
implement an alternative floating-point operation model referred
to as SSE2. In this model there is no extended form, and furthermore
execution performance is significantly enhanced. To force GNAT to use
this more modern form, use both of the switches:






-msse2 -mfpmath=sse




A unit compiled with these switches will automatically use the more
efficient SSE2 instruction set for Float and Long_Float operations.
Note that the ABI has the same form for both floating-point models,
so it is permissible to mix units compiled with and without these
switches.









Next: , Previous: Floating_Point_Operations, Up: Performance Considerations   [Contents][Index]





6.3.1.7 Vectorization of loops






You can take advantage of the auto-vectorizer present in the gcc
back end to vectorize loops with GNAT.  The corresponding command line switch
is -ftree-vectorize but, as it is enabled by default at -O3
and other aggressive optimizations helpful for vectorization also are enabled
by default at this level, using -O3 directly is recommended.



You also need to make sure that the target architecture features a supported
SIMD instruction set.  For example, for the x86 architecture, you should at
least specify -msse2 to get significant vectorization (but you don’t
need to specify it for x86-64 as it is part of the base 64-bit architecture).
Similarly, for the PowerPC architecture, you should specify -maltivec.



The preferred loop form for vectorization is the for iteration scheme.
Loops with a while iteration scheme can also be vectorized if they are
very simple, but the vectorizer will quickly give up otherwise.  With either
iteration scheme, the flow of control must be straight, in particular no
exit statement may appear in the loop body.  The loop may however
contain a single nested loop, if it can be vectorized when considered alone:








A : array (1..4, 1..4) of Long_Float;
S : array (1..4) of Long_Float;

procedure Sum is
begin
   for I in A'Range(1) loop
      for J in A'Range(2) loop
         S (I) := S (I) + A (I, J);
      end loop;
   end loop;
end Sum;






The vectorizable operations depend on the targeted SIMD instruction set, but
the adding and some of the multiplying operators are generally supported, as
well as the logical operators for modular types. Note that compiling
with -gnatp might well reveal cases where some checks do thwart
vectorization.



Type conversions may also prevent vectorization if they involve semantics that
are not directly supported by the code generator or the SIMD instruction set.
A typical example is direct conversion from floating-point to integer types.
The solution in this case is to use the following idiom:








Integer (S'Truncation (F))






if S is the subtype of floating-point object F.



In most cases, the vectorizable loops are loops that iterate over arrays.
All kinds of array types are supported, i.e. constrained array types with
static bounds:








type Array_Type is array (1 .. 4) of Long_Float;






constrained array types with dynamic bounds:








type Array_Type is array (1 .. Q.N) of Long_Float;

type Array_Type is array (Q.K .. 4) of Long_Float;

type Array_Type is array (Q.K .. Q.N) of Long_Float;






or unconstrained array types:








type Array_Type is array (Positive range <>) of Long_Float;






The quality of the generated code decreases when the dynamic aspect of the
array type increases, the worst code being generated for unconstrained array
types.  This is so because, the less information the compiler has about the
bounds of the array, the more fallback code it needs to generate in order to
fix things up at run time.



It is possible to specify that a given loop should be subject to vectorization
preferably to other optimizations by means of pragma Loop_Optimize:








pragma Loop_Optimize (Vector);






placed immediately within the loop will convey the appropriate hint to the
compiler for this loop.



It is also possible to help the compiler generate better vectorized code
for a given loop by asserting that there are no loop-carried dependencies
in the loop.  Consider for example the procedure:








type Arr is array (1 .. 4) of Long_Float;

procedure Add (X, Y : not null access Arr; R : not null access Arr) is
begin
  for I in Arr'Range loop
    R(I) := X(I) + Y(I);
  end loop;
end;






By default, the compiler cannot unconditionally vectorize the loop because
assigning to a component of the array designated by R in one iteration could
change the value read from the components of the array designated by X or Y
in a later iteration.  As a result, the compiler will generate two versions
of the loop in the object code, one vectorized and the other not vectorized,
as well as a test to select the appropriate version at run time.  This can
be overcome by another hint:








pragma Loop_Optimize (Ivdep);






placed immediately within the loop will tell the compiler that it can safely
omit the non-vectorized version of the loop as well as the run-time test.









Next: , Previous: Vectorization of loops, Up: Performance Considerations   [Contents][Index]





6.3.1.8 Other Optimization Switches






Since GNAT uses the gcc back end, all the specialized
gcc optimization switches are potentially usable. These switches
have not been extensively tested with GNAT but can generally be expected
to work. Examples of switches in this category are -funroll-loops
and the various target-specific -m options (in particular, it has
been observed that -march=xxx can significantly improve performance
on appropriate machines). For full details of these switches, see
the `Submodel Options' section in the `Hardware Models and Configurations'
chapter of Using the GNU Compiler Collection (GCC).









Next: , Previous: Other Optimization Switches, Up: Performance Considerations   [Contents][Index]





6.3.1.9 Optimization and Strict Aliasing










The strong typing capabilities of Ada allow an optimizer to generate
efficient code in situations where other languages would be forced to
make worst case assumptions preventing such optimizations. Consider
the following example:








procedure R is
   type Int1 is new Integer;
   type Int2 is new Integer;
   type Int1A is access Int1;
   type Int2A is access Int2;
   Int1V : Int1A;
   Int2V : Int2A;
   ...

begin
   ...
   for J in Data'Range loop
      if Data (J) = Int1V.all then
         Int2V.all := Int2V.all + 1;
      end if;
   end loop;
   ...
end R;






In this example, since the variable Int1V can only access objects
of type Int1, and Int2V can only access objects of type
Int2, there is no possibility that the assignment to
Int2V.all affects the value of Int1V.all. This means that
the compiler optimizer can "know" that the value Int1V.all is constant
for all iterations of the loop and avoid the extra memory reference
required to dereference it each time through the loop.



This kind of optimization, called strict aliasing analysis, is
triggered by specifying an optimization level of -O2 or
higher or -Os and allows GNAT to generate more efficient code
when access values are involved.



However, although this optimization is always correct in terms of
the formal semantics of the Ada Reference Manual, difficulties can
arise if features like Unchecked_Conversion are used to break
the typing system. Consider the following complete program example:








package p1 is
   type int1 is new integer;
   type int2 is new integer;
   type a1 is access int1;
   type a2 is access int2;
end p1;

with p1; use p1;
package p2 is
   function to_a2 (Input : a1) return a2;
end p2;

with Unchecked_Conversion;
package body p2 is
   function to_a2 (Input : a1) return a2 is
      function to_a2u is
        new Unchecked_Conversion (a1, a2);
   begin
      return to_a2u (Input);
   end to_a2;
end p2;

with p2; use p2;
with p1; use p1;
with Text_IO; use Text_IO;
procedure m is
   v1 : a1 := new int1;
   v2 : a2 := to_a2 (v1);
begin
   v1.all := 1;
   v2.all := 0;
   put_line (int1'image (v1.all));
end;






This program prints out 0 in -O0 or -O1
mode, but it prints out 1 in -O2 mode. That’s
because in strict aliasing mode, the compiler can and
does assume that the assignment to v2.all could not
affect the value of v1.all, since different types
are involved.



This behavior is not a case of non-conformance with the standard, since
the Ada RM specifies that an unchecked conversion where the resulting
bit pattern is not a correct value of the target type can result in an
abnormal value and attempting to reference an abnormal value makes the
execution of a program erroneous.  That’s the case here since the result
does not point to an object of type int2.  This means that the
effect is entirely unpredictable.



However, although that explanation may satisfy a language
lawyer, in practice an applications programmer expects an
unchecked conversion involving pointers to create true
aliases and the behavior of printing 1 seems plain wrong.
In this case, the strict aliasing optimization is unwelcome.



Indeed the compiler recognizes this possibility, and the
unchecked conversion generates a warning:








p2.adb:5:07: warning: possible aliasing problem with type "a2"
p2.adb:5:07: warning: use -fno-strict-aliasing switch for references
p2.adb:5:07: warning:  or use "pragma No_Strict_Aliasing (a2);"






Unfortunately the problem is recognized when compiling the body of
package p2, but the actual "bad" code is generated while
compiling the body of m and this latter compilation does not see
the suspicious Unchecked_Conversion.



As implied by the warning message, there are approaches you can use to
avoid the unwanted strict aliasing optimization in a case like this.



One possibility is to simply avoid the use of -O2, but
that is a bit drastic, since it throws away a number of useful
optimizations that do not involve strict aliasing assumptions.



A less drastic approach is to compile the program using the
option -fno-strict-aliasing. Actually it is only the
unit containing the dereferencing of the suspicious pointer
that needs to be compiled. So in this case, if we compile
unit m with this switch, then we get the expected
value of zero printed. Analyzing which units might need
the switch can be painful, so a more reasonable approach
is to compile the entire program with options -O2
and -fno-strict-aliasing. If the performance is
satisfactory with this combination of options, then the
advantage is that the entire issue of possible "wrong"
optimization due to strict aliasing is avoided.



To avoid the use of compiler switches, the configuration
pragma No_Strict_Aliasing with no parameters may be
used to specify that for all access types, the strict
aliasing optimization should be suppressed.



However, these approaches are still overkill, in that they causes
all manipulations of all access values to be deoptimized. A more
refined approach is to concentrate attention on the specific
access type identified as problematic.



First, if a careful analysis of uses of the pointer shows
that there are no possible problematic references, then
the warning can be suppressed by bracketing the
instantiation of Unchecked_Conversion to turn
the warning off:








pragma Warnings (Off);
function to_a2u is
  new Unchecked_Conversion (a1, a2);
pragma Warnings (On);






Of course that approach is not appropriate for this particular
example, since indeed there is a problematic reference. In this
case we can take one of two other approaches.



The first possibility is to move the instantiation of unchecked
conversion to the unit in which the type is declared. In
this example, we would move the instantiation of
Unchecked_Conversion from the body of package
p2 to the spec of package p1. Now the
warning disappears. That’s because any use of the
access type knows there is a suspicious unchecked
conversion, and the strict aliasing optimization
is automatically suppressed for the type.



If it is not practical to move the unchecked conversion to the same unit
in which the destination access type is declared (perhaps because the
source type is not visible in that unit), you may use pragma
No_Strict_Aliasing for the type. This pragma must occur in the
same declarative sequence as the declaration of the access type:








type a2 is access int2;
pragma No_Strict_Aliasing (a2);






Here again, the compiler now knows that the strict aliasing optimization
should be suppressed for any reference to type a2 and the
expected behavior is obtained.



Finally, note that although the compiler can generate warnings for
simple cases of unchecked conversions, there are tricker and more
indirect ways of creating type incorrect aliases which the compiler
cannot detect. Examples are the use of address overlays and unchecked
conversions involving composite types containing access types as
components. In such cases, no warnings are generated, but there can
still be aliasing problems. One safe coding practice is to forbid the
use of address clauses for type overlaying, and to allow unchecked
conversion only for primitive types. This is not really a significant
restriction since any possible desired effect can be achieved by
unchecked conversion of access values.



The aliasing analysis done in strict aliasing mode can certainly
have significant benefits. We have seen cases of large scale
application code where the time is increased by up to 5% by turning
this optimization off. If you have code that includes significant
usage of unchecked conversion, you might want to just stick with
-O1 and avoid the entire issue. If you get adequate
performance at this level of optimization level, that’s probably
the safest approach. If tests show that you really need higher
levels of optimization, then you can experiment with -O2
and -O2 -fno-strict-aliasing to see how much effect this
has on size and speed of the code. If you really need to use
-O2 with strict aliasing in effect, then you should
review any uses of unchecked conversion of access types,
particularly if you are getting the warnings described above.









Next: , Previous: Optimization and Strict Aliasing, Up: Performance Considerations   [Contents][Index]





6.3.1.10 Aliased Variables and Optimization






There are scenarios in which programs may
use low level techniques to modify variables
that otherwise might be considered to be unassigned. For example,
a variable can be passed to a procedure by reference, which takes
the address of the parameter and uses the address to modify the
variable’s value, even though it is passed as an IN parameter.
Consider the following example:








procedure P is
   Max_Length : constant Natural := 16;
   type Char_Ptr is access all Character;

   procedure Get_String(Buffer: Char_Ptr; Size : Integer);
   pragma Import (C, Get_String, "get_string");

   Name : aliased String (1 .. Max_Length) := (others => ' ');
   Temp : Char_Ptr;

   function Addr (S : String) return Char_Ptr is
      function To_Char_Ptr is
        new Ada.Unchecked_Conversion (System.Address, Char_Ptr);
   begin
      return To_Char_Ptr (S (S'First)'Address);
   end;

begin
   Temp := Addr (Name);
   Get_String (Temp, Max_Length);
end;






where Get_String is a C function that uses the address in Temp to
modify the variable Name. This code is dubious, and arguably
erroneous, and the compiler would be entitled to assume that
Name is never modified, and generate code accordingly.



However, in practice, this would cause some existing code that
seems to work with no optimization to start failing at high
levels of optimzization.



What the compiler does for such cases is to assume that marking
a variable as aliased indicates that some "funny business" may
be going on. The optimizer recognizes the aliased keyword and
inhibits optimizations that assume the value cannot be assigned.
This means that the above example will in fact "work" reliably,
that is, it will produce the expected results.









Next: , Previous: Aliased Variables and Optimization, Up: Performance Considerations   [Contents][Index]





6.3.1.11 Atomic Variables and Optimization






There are two considerations with regard to performance when
atomic variables are used.



First, the RM only guarantees that access to atomic variables
be atomic, it has nothing to say about how this is achieved,
though there is a strong implication that this should not be
achieved by explicit locking code. Indeed GNAT will never
generate any locking code for atomic variable access (it will
simply reject any attempt to make a variable or type atomic
if the atomic access cannot be achieved without such locking code).



That being said, it is important to understand that you cannot
assume that the entire variable will always be accessed. Consider
this example:








type R is record
   A,B,C,D : Character;
end record;
for R'Size use 32;
for R'Alignment use 4;

RV : R;
pragma Atomic (RV);
X : Character;
...
X := RV.B;






You cannot assume that the reference to RV.B
will read the entire 32-bit
variable with a single load instruction. It is perfectly legitimate if
the hardware allows it to do a byte read of just the B field. This read
is still atomic, which is all the RM requires. GNAT can and does take
advantage of this, depending on the architecture and optimization level.
Any assumption to the contrary is non-portable and risky. Even if you
examine the assembly language and see a full 32-bit load, this might
change in a future version of the compiler.



If your application requires that all accesses to RV in this
example be full 32-bit loads, you need to make a copy for the access
as in:








declare
   RV_Copy : constant R := RV;
begin
   X := RV_Copy.B;
end;






Now the reference to RV must read the whole variable.
Actually one can imagine some compiler which figures
out that the whole copy is not required (because only
the B field is actually accessed), but GNAT
certainly won’t do that, and we don’t know of any
compiler that would not handle this right, and the
above code will in practice work portably across
all architectures (that permit the Atomic declaration).



The second issue with atomic variables has to do with
the possible requirement of generating synchronization
code. For more details on this, consult the sections on
the pragmas Enable/Disable_Atomic_Synchronization in the
GNAT Reference Manual. If performance is critical, and
such synchronization code is not required, it may be
useful to disable it.









Previous: Atomic Variables and Optimization, Up: Performance Considerations   [Contents][Index]





6.3.1.12 Passive Task Optimization






A passive task is one which is sufficiently simple that
in theory a compiler could recognize it an implement it
efficiently without creating a new thread. The original design
of Ada 83 had in mind this kind of passive task optimization, but
only a few Ada 83 compilers attempted it. The problem was that
it was difficult to determine the exact conditions under which
the optimization was possible. The result is a very fragile
optimization where a very minor change in the program can
suddenly silently make a task non-optimizable.



With the revisiting of this issue in Ada 95, there was general
agreement that this approach was fundamentally flawed, and the
notion of protected types was introduced. When using protected
types, the restrictions are well defined, and you KNOW that the
operations will be optimized, and furthermore this optimized
performance is fully portable.



Although it would theoretically be possible for GNAT to attempt to
do this optimization, but it really doesn’t make sense in the
context of Ada 95, and none of the Ada 95 compilers implement
this optimization as far as we know. In particular GNAT never
attempts to perform this optimization.



In any new Ada 95 code that is written, you should always
use protected types in place of tasks that might be able to
be optimized in this manner.
Of course this does not help if you have legacy Ada 83 code
that depends on this optimization, but it is unusual to encounter
a case where the performance gains from this optimization
are significant.



Your program should work correctly without this optimization. If
you have performance problems, then the most practical
approach is to figure out exactly where these performance problems
arise, and update those particular tasks to be protected types. Note
that typically clients of the tasks who call entries, will not have
to be modified, only the task definition itself.









Next: , Previous: Performance Considerations, Up: Improving Performance   [Contents][Index]





6.3.2 Text_IO Suggestions






The Ada.Text_IO package has fairly high overheads due in part to
the requirement of maintaining page and line counts. If performance
is critical, a recommendation is to use Stream_IO instead of
Text_IO for volume output, since this package has less overhead.



If Text_IO must be used, note that by default output to the standard
output and standard error files is unbuffered (this provides better
behavior when output statements are used for debugging, or if the
progress of a program is observed by tracking the output, e.g. by
using the Unix `tail -f' command to watch redirected output.



If you are generating large volumes of output with Text_IO and
performance is an important factor, use a designated file instead
of the standard output file, or change the standard output file to
be buffered using Interfaces.C_Streams.setvbuf.









Previous: Text_IO Suggestions, Up: Improving Performance   [Contents][Index]





6.3.3 Reducing Size of Executables with Unused Subprogram/Data Elimination






This section describes how you can eliminate unused subprograms and data from
your executable just by setting options at compilation time.





• About unused subprogram/data elimination:  



• Compilation options:  



• Example of unused subprogram/data elimination:  












Next: , Up: Reducing Size of Executables with Unused Subprogram/Data Elimination   [Contents][Index]





6.3.3.1 About unused subprogram/data elimination




By default, an executable contains all code and data of its composing objects
(directly linked or coming from statically linked libraries), even data or code
never used by this executable.



This feature will allow you to eliminate such unused code from your
executable, making it smaller (in disk and in memory).



This functionality is available on all Linux platforms except for the IA-64
architecture and on all cross platforms using the ELF binary file format.
In both cases GNU binutils version 2.16 or later are required to enable it.









Next: , Previous: About unused subprogram/data elimination, Up: Reducing Size of Executables with Unused Subprogram/Data Elimination   [Contents][Index]





6.3.3.2 Compilation options




The operation of eliminating the unused code and data from the final executable
is directly performed by the linker.







In order to do this, it has to work with objects compiled with the
following options:
-ffunction-sections -fdata-sections.



These options are usable with C and Ada files.
They will place respectively each
function or data in a separate section in the resulting object file.



Once the objects and static libraries are created with these options, the
linker can perform the dead code elimination. You can do this by setting
the -Wl,--gc-sections option to gcc command or in the
-largs section of gnatmake. This will perform a
garbage collection of code and data never referenced.



If the linker performs a partial link (-r linker option), then you
will need to provide the entry point using the -e / --entry
linker option.



Note that objects compiled without the -ffunction-sections and
-fdata-sections options can still be linked with the executable.
However, no dead code elimination will be performed on those objects (they will
be linked as is).



The GNAT static library is now compiled with -ffunction-sections and
-fdata-sections on some platforms. This allows you to eliminate the unused code
and data of the GNAT library from your executable.









Previous: Compilation options, Up: Reducing Size of Executables with Unused Subprogram/Data Elimination   [Contents][Index]





6.3.3.3 Example of unused subprogram/data elimination




Here is a simple example:








with Aux;

procedure Test is
begin
   Aux.Used (10);
end Test;

package Aux is
   Used_Data   : Integer;
   Unused_Data : Integer;

   procedure Used   (Data : Integer);
   procedure Unused (Data : Integer);
end Aux;

package body Aux is
   procedure Used (Data : Integer) is
   begin
      Used_Data := Data;
   end Used;

   procedure Unused (Data : Integer) is
   begin
      Unused_Data := Data;
   end Unused;
end Aux;






Unused and Unused_Data are never referenced in this code
excerpt, and hence they may be safely removed from the final executable.








$ gnatmake test

$ nm test | grep used
020015f0 T aux__unused
02005d88 B aux__unused_data
020015cc T aux__used
02005d84 B aux__used_data

$ gnatmake test -cargs -fdata-sections -ffunction-sections \\
     -largs -Wl,--gc-sections

$ nm test | grep used
02005350 T aux__used
0201ffe0 B aux__used_data






It can be observed that the procedure Unused and the object
Unused_Data are removed by the linker when using the
appropriate options.













Next: , Previous: Improving Performance, Up: GNAT and Program Execution   [Contents][Index]





6.4 Overflow Check Handling in GNAT




This section explains how to control the handling of overflow checks.





• Background:  



• Management of Overflows in GNAT:  



• Specifying the Desired Mode:  



• Default Settings:  



• Implementation Notes:  












Next: , Up: Overflow Check Handling in GNAT   [Contents][Index]





6.4.1 Background




Overflow checks are checks that the compiler may make to ensure
that intermediate results are not out of range. For example:








A : Integer;
...
A := A + 1;






If A has the value Integer'Last, then the addition may cause
overflow since the result is out of range of the type Integer.
In this case Constraint_Error will be raised if checks are
enabled.



A trickier situation arises in examples like the following:








A, C : Integer;
...
A := (A + 1) + C;






where A is Integer'Last and C is -1.
Now the final result of the expression on the right hand side is
Integer'Last which is in range, but the question arises whether the
intermediate addition of (A + 1) raises an overflow error.



The (perhaps surprising) answer is that the Ada language
definition does not answer this question. Instead it leaves
it up to the implementation to do one of two things if overflow
checks are enabled.






If the compiler chooses the first approach, then the assignment of this
example will indeed raise Constraint_Error if overflow checking is
enabled, or result in erroneous execution if overflow checks are suppressed.



But if the compiler
chooses the second approach, then it can perform both additions yielding
the correct mathematical result, which is in range, so no exception
will be raised, and the right result is obtained, regardless of whether
overflow checks are suppressed.



Note that in the first example an
exception will be raised in either case, since if the compiler
gives the correct mathematical result for the addition, it will
be out of range of the target type of the assignment, and thus
fails the range check.



This lack of specified behavior in the handling of overflow for
intermediate results is a source of non-portability, and can thus
be problematic when programs are ported. Most typically this arises
in a situation where the original compiler did not raise an exception,
and then the application is moved to a compiler where the check is
performed on the intermediate result and an unexpected exception is
raised.



Furthermore, when using Ada 2012’s preconditions and other
assertion forms, another issue arises. Consider:








procedure P (A, B : Integer) with
  Pre => A + B <= Integer'Last;






One often wants to regard arithmetic in a context like this from
a mathematical point of view. So for example, if the two actual parameters
for a call to P are both Integer'Last, then
the precondition should be regarded as False. If we are executing
in a mode with run-time checks enabled for preconditions, then we would
like this precondition to fail, rather than raising an exception
because of the intermediate overflow.



However, the language definition leaves the specification of
whether the above condition fails (raising Assert_Error) or
causes an intermediate overflow (raising Constraint_Error)
up to the implementation.



The situation is worse in a case such as the following:








procedure Q (A, B, C : Integer) with
  Pre => A + B + C <= Integer'Last;






Consider the call








Q (A => Integer'Last, B => 1, C => -1);






From a mathematical point of view the precondition
is True, but at run time we may (but are not guaranteed to) get an
exception raised because of the intermediate overflow (and we really
would prefer this precondition to be considered True at run time).









Next: , Previous: Background, Up: Overflow Check Handling in GNAT   [Contents][Index]





6.4.2 Management of Overflows in GNAT




To deal with the portability issue, and with the problem of
mathematical versus run-time interpretation of the expressions in
assertions, GNAT provides comprehensive control over the handling
of intermediate overflow. GNAT can operate in three modes, and
furthemore, permits separate selection of operating modes for
the expressions within assertions (here the term ’assertions’
is used in the technical sense, which includes preconditions and so forth)
and for expressions appearing outside assertions.



The three modes are:






Note that these modes apply only to the evaluation of predefined
arithmetic, membership, and comparison operators for signed integer
arithmetic.



For fixed-point arithmetic, checks can be suppressed. But if checks
are enabled
then fixed-point values are always checked for overflow against the
base type for intermediate expressions (that is such checks always
operate in the equivalent of STRICT mode).



For floating-point, on nearly all architectures, Machine_Overflows
is False, and IEEE infinities are generated, so overflow exceptions
are never raised. If you want to avoid infinities, and check that
final results of expressions are in range, then you can declare a
constrained floating-point type, and range checks will be carried
out in the normal manner (with infinite values always failing all
range checks).









Next: , Previous: Management of Overflows in GNAT, Up: Overflow Check Handling in GNAT   [Contents][Index]





6.4.3 Specifying the Desired Mode






The desired mode of for handling intermediate overflow can be specified using
either the Overflow_Mode pragma or an equivalent compiler switch.
The pragma has the form








pragma Overflow_Mode ([General =>] MODE [, [Assertions =>] MODE]);






where MODE is one of






The case is ignored, so MINIMIZED, Minimized and
minimized all have the same effect.



If only the General parameter is present, then the given MODE applies
to expressions both within and outside assertions. If both arguments
are present, then General applies to expressions outside assertions,
and Assertions applies to expressions within assertions. For example:








pragma Overflow_Mode
  (General => Minimized, Assertions => Eliminated);






specifies that general expressions outside assertions be evaluated
in ’minimize intermediate overflows’ mode, and expressions within
assertions be evaluated in ’eliminate intermediate overflows’ mode.
This is often a reasonable choice, avoiding excessive overhead
outside assertions, but assuring a high degree of portability
when importing code from another compiler, while incurring
the extra overhead for assertion expressions to ensure that
the behavior at run time matches the expected mathematical
behavior.



The Overflow_Mode pragma has the same scoping and placement
rules as pragma Suppress, so it can occur either as a
configuration pragma, specifying a default for the whole
program, or in a declarative scope, where it applies to the
remaining declarations and statements in that scope.



Note that pragma Overflow_Mode does not affect whether
overflow checks are enabled or suppressed. It only controls the
method used to compute intermediate values. To control whether
overflow checking is enabled or suppressed, use pragma Suppress
or Unsuppress in the usual manner.







Additionally, a compiler switch -gnato? or -gnato??
can be used to control the checking mode default (which can be subsequently
overridden using pragmas).



Here ? is one of the digits 1 through 3:









1use base type for intermediate operations (STRICT)


2minimize intermediate overflows (MINIMIZED)


3eliminate intermediate overflows (ELIMINATED)








As with the pragma, if only one digit appears then it applies to all
cases; if two digits are given, then the first applies outside
assertions, and the second within assertions. Thus the equivalent
of the example pragma above would be
-gnato23.



If no digits follow the -gnato, then it is equivalent to
-gnato11,
causing all intermediate operations to be computed using the base
type (STRICT mode).









Next: , Previous: Specifying the Desired Mode, Up: Overflow Check Handling in GNAT   [Contents][Index]





6.4.4 Default Settings




The default mode for overflow checks is








General => Strict






which causes all computations both inside and outside assertions to use
the base type.



This retains compatibility with previous versions of
GNAT which suppressed overflow checks by default and always
used the base type for computation of intermediate results.




The 

switch -gnato (with no digits following)
is equivalent to








General => Strict






which causes overflow checking of all intermediate overflows
both inside and outside assertions against the base type.



The pragma Suppress (Overflow_Check) disables overflow
checking, but it has no effect on the method used for computing
intermediate results.



The pragma Unsuppress (Overflow_Check) enables overflow
checking, but it has no effect on the method used for computing
intermediate results.









Previous: Default Settings, Up: Overflow Check Handling in GNAT   [Contents][Index]





6.4.5 Implementation Notes




In practice on typical 64-bit machines, the MINIMIZED mode is
reasonably efficient, and can be generally used. It also helps
to ensure compatibility with code imported from some other
compiler to GNAT.



Setting all intermediate overflows checking (CHECKED mode)
makes sense if you want to
make sure that your code is compatible with any other possible
Ada implementation. This may be useful in ensuring portability
for code that is to be exported to some other compiler than GNAT.



The Ada standard allows the reassociation of expressions at
the same precedence level if no parentheses are present. For
example, A+B+C parses as though it were (A+B)+C, but
the compiler can reintepret this as A+(B+C), possibly
introducing or eliminating an overflow exception. The GNAT
compiler never takes advantage of this freedom, and the
expression A+B+C will be evaluated as (A+B)+C.
If you need the other order, you can write the parentheses
explicitly A+(B+C) and GNAT will respect this order.



The use of ELIMINATED mode will cause the compiler to
automatically include an appropriate arbitrary precision
integer arithmetic package. The compiler will make calls
to this package, though only in cases where it cannot be
sure that Long_Long_Integer is sufficient to guard against
intermediate overflows. This package does not use dynamic
allocation, but it does use the secondary stack, so an
appropriate secondary stack package must be present (this
is always true for standard full Ada, but may require
specific steps for restricted run times such as ZFP).



Although ELIMINATED mode causes expressions to use arbitrary
precision arithmetic, avoiding overflow, the final result
must be in an appropriate range. This is true even if the
final result is of type [Long_[Long_]]Integer'Base, which
still has the same bounds as its associated constrained
type at run-time.



Currently, the ELIMINATED mode is only available on target
platforms for which Long_Long_Integer is 64-bits (nearly all GNAT
platforms).









Next: , Previous: Overflow Check Handling in GNAT, Up: GNAT and Program Execution   [Contents][Index]





6.5 Performing Dimensionality Analysis in GNAT






The GNAT compiler supports dimensionality checking. The user can
specify physical units for objects, and the compiler will verify that uses
of these objects are compatible with their dimensions, in a fashion that is
familiar to engineering practice. The dimensions of algebraic expressions
(including powers with static exponents) are computed from their constituents.







This feature depends on Ada 2012 aspect specifications, and is available from
version 7.0.1 of GNAT onwards.
The GNAT-specific aspect Dimension_System
allows you to define a system of units; the aspect Dimension
then allows the user to declare dimensioned quantities within a given system.
(These aspects are described in the `Implementation Defined Aspects'
chapter of the `GNAT Reference Manual').



The major advantage of this model is that it does not require the declaration of
multiple operators for all possible combinations of types: it is only necessary
to use the proper subtypes in object declarations.







The simplest way to impose dimensionality checking on a computation is to make
use of one of the instantiations of the package System.Dim.Generic_Mks, which
are part of the GNAT library. This generic package defines a floating-point
type MKS_Type, for which a sequence of dimension names are specified,
together with their conventional abbreviations.  The following should be read
together with the full specification of the package, in file
s-digemk.ads.










type Mks_Type is new Float_Type
  with
   Dimension_System => (
     (Unit_Name => Meter,    Unit_Symbol => 'm',   Dim_Symbol => 'L'),
     (Unit_Name => Kilogram, Unit_Symbol => "kg",  Dim_Symbol => 'M'),
     (Unit_Name => Second,   Unit_Symbol => 's',   Dim_Symbol => 'T'),
     (Unit_Name => Ampere,   Unit_Symbol => 'A',   Dim_Symbol => 'I'),
     (Unit_Name => Kelvin,   Unit_Symbol => 'K',   Dim_Symbol => "Theta"),
     (Unit_Name => Mole,     Unit_Symbol => "mol", Dim_Symbol => 'N'),
     (Unit_Name => Candela,  Unit_Symbol => "cd",  Dim_Symbol => 'J'));






The package then defines a series of subtypes that correspond to these
conventional units. For example:








subtype Length is Mks_Type
  with
   Dimension => (Symbol => 'm', Meter  => 1, others => 0);






and similarly for Mass, Time, Electric_Current,
Thermodynamic_Temperature, Amount_Of_Substance, and
Luminous_Intensity (the standard set of units of the SI system).



The package also defines conventional names for values of each unit, for
example:








m   : constant Length           := 1.0;
kg  : constant Mass             := 1.0;
s   : constant Time             := 1.0;
A   : constant Electric_Current := 1.0;






as well as useful multiples of these units:








 cm  : constant Length := 1.0E-02;
 g   : constant Mass   := 1.0E-03;
 min : constant Time   := 60.0;
 day : constant Time   := 60.0 * 24.0 * min;
...






There are three instantiations of System.Dim.Generic_Mks defined in the
GNAT library:






Using one of these packages, you can then define a derived unit by providing
the aspect that specifies its dimensions within the MKS system, as well as the
string to be used for output of a value of that unit:








subtype Acceleration is Mks_Type
  with Dimension => ("m/sec^2",
                     Meter => 1,
                     Second => -2,
                     others => 0);






Here is a complete example of use:








with System.Dim.MKS; use System.Dim.Mks;
with System.Dim.Mks_IO; use System.Dim.Mks_IO;
with Text_IO; use Text_IO;
procedure Free_Fall is
  subtype Acceleration is Mks_Type
    with Dimension => ("m/sec^2", 1, 0, -2, others => 0);
  G : constant acceleration := 9.81 * m / (s ** 2);
  T : Time := 10.0*s;
  Distance : Length;

begin
  Put ("Gravitational constant: ");
  Put (G, Aft => 2, Exp => 0); Put_Line ("");
  Distance := 0.5 * G * T ** 2;
  Put ("distance travelled in 10 seconds of free fall ");
  Put (Distance, Aft => 2, Exp => 0);
  Put_Line ("");
end Free_Fall;






Execution of this program yields:








Gravitational constant:  9.81 m/sec^2
distance travelled in 10 seconds of free fall 490.50 m






However, incorrect assignments such as:








Distance := 5.0;
Distance := 5.0 * kg;






are rejected with the following diagnoses:








Distance := 5.0;
   >>> dimensions mismatch in assignment
   >>> left-hand side has dimension [L]
   >>> right-hand side is dimensionless

Distance := 5.0 * kg:
   >>> dimensions mismatch in assignment
   >>> left-hand side has dimension [L]
   >>> right-hand side has dimension [M]






The dimensions of an expression are properly displayed, even if there is
no explicit subtype for it. If we add to the program:








Put ("Final velocity: ");
Put (G * T, Aft =>2, Exp =>0);
Put_Line ("");






then the output includes:








Final velocity: 98.10 m.s**(-1)










The type Mks_Type is said to be a `dimensionable type' since it has a
Dimension_System aspect, and the subtypes Length, Mass, etc.,
are said to be `dimensioned subtypes' since each one has a Dimension
aspect.














The Dimension aspect of a dimensioned subtype S defines a mapping
from the base type’s Unit_Names to integer (or, more generally, rational)
values. This mapping is the `dimension vector' (also referred to as the
`dimensionality') for that subtype, denoted by DV(S), and thus for each
object of that subtype. Intuitively, the value specified for each
Unit_Name is the exponent associated with that unit; a zero value
means that the unit is not used. For example:








declare
   Acc : Acceleration;
   ...
begin
   ...
end;






Here DV(Acc) = DV(Acceleration) =
(Meter=>1, Kilogram=>0, Second=>-2, Ampere=>0, Kelvin=>0, Mole=>0, Candela=>0).
Symbolically, we can express this as Meter / Second**2.



The dimension vector of an arithmetic expression is synthesized from the
dimension vectors of its components, with compile-time dimensionality checks
that help prevent mismatches such as using an Acceleration where a
Length is required.



The dimension vector of the result of an arithmetic expression `expr', or
DV(`expr'), is defined as follows, assuming conventional
mathematical definitions for the vector operations that are used:






Note that, by the above rules, it is illegal to use binary "+" or "-" to
combine a dimensioned and dimensionless value.  Thus an expression such as
acc-10.0 is illegal, where acc is an object of subtype
Acceleration.



The dimensionality checks for relationals use the same rules as
for "+" and "-", except when comparing to a literal; thus








acc > len






is equivalent to








acc-len > 0.0






and is thus illegal, but








acc > 10.0






is accepted with a warning. Analogously a conditional expression requires the
same dimension vector for each branch (with no exception for literals).



The dimension vector of a type conversion T(`expr') is defined
as follows, based on the nature of T:






The dimension vector for a type qualification T'(`expr') is the same
as for the type conversion T(`expr').



An assignment statement








Source := Target;






requires DV(Source) = DV(Target), and analogously for parameter
passing (the dimension vector for the actual parameter must be equal to the
dimension vector for the formal parameter).









Next: , Previous: Performing Dimensionality Analysis in GNAT, Up: GNAT and Program Execution   [Contents][Index]





6.6 Stack Related Facilities




This section describes some useful tools associated with stack
checking and analysis. In
particular, it deals with dynamic and static stack usage measurements.





• Stack Overflow Checking:  



• Static Stack Usage Analysis:  



• Dynamic Stack Usage Analysis:  












Next: , Up: Stack Related Facilities   [Contents][Index]





6.6.1 Stack Overflow Checking








For most operating systems, gcc does not perform stack overflow
checking by default. This means that if the main environment task or
some other task exceeds the available stack space, then unpredictable
behavior will occur. Most native systems offer some level of protection by
adding a guard page at the end of each task stack. This mechanism is usually
not enough for dealing properly with stack overflow situations because
a large local variable could "jump" above the guard page.
Furthermore, when the
guard page is hit, there may not be any space left on the stack for executing
the exception propagation code. Enabling stack checking avoids
such situations.



To activate stack checking, compile all units with the gcc option
-fstack-check. For example:








$ gcc -c -fstack-check package1.adb






Units compiled with this option will generate extra instructions to check
that any use of the stack (for procedure calls or for declaring local
variables in declare blocks) does not exceed the available stack space.
If the space is exceeded, then a Storage_Error exception is raised.



For declared tasks, the default stack size is defined by the GNAT runtime,
whose size may be modified at bind time through the -d bind switch
(Switches for gnatbind). Task specific stack sizes may be set using the
Storage_Size pragma.



For the environment task, the stack size is determined by the operating system.
Consequently, to modify the size of the environment task please refer to your
operating system documentation.









Next: , Previous: Stack Overflow Checking, Up: Stack Related Facilities   [Contents][Index]





6.6.2 Static Stack Usage Analysis








A unit compiled with -fstack-usage will generate an extra file
that specifies
the maximum amount of stack used, on a per-function basis.
The file has the same
basename as the target object file with a .su extension.
Each line of this file is made up of three fields:






The second field corresponds to the size of the known part of the function
frame.



The qualifier static means that the function frame size
is purely static.
It usually means that all local variables have a static size.
In this case, the second field is a reliable measure of the function stack
utilization.



The qualifier dynamic means that the function frame size is not static.
It happens mainly when some local variables have a dynamic size. When this
qualifier appears alone, the second field is not a reliable measure
of the function stack analysis. When it is qualified with  bounded, it
means that the second field is a reliable maximum of the function stack
utilization.



A unit compiled with -Wstack-usage will issue a warning for each
subprogram whose stack usage might be larger than the specified amount of
bytes.  The wording is in keeping with the qualifier documented above.









Previous: Static Stack Usage Analysis, Up: Stack Related Facilities   [Contents][Index]





6.6.3 Dynamic Stack Usage Analysis




It is possible to measure the maximum amount of stack used by a task, by
adding a switch to gnatbind, as:








$ gnatbind -u0 file






With this option, at each task termination, its stack usage is output on
stderr.
Note that this switch is not compatible with tools like
Valgrind and DrMemory; they will report errors.



It is not always convenient to output the stack usage when the program
is still running. Hence, it is possible to delay this output until program
termination. for a given number of tasks specified as the argument of the
-u option. For instance:








$ gnatbind -u100 file






will buffer the stack usage information of the first 100 tasks to terminate and
output this info at program termination. Results are displayed in four
columns:








Index | Task Name | Stack Size | Stack Usage






where:






By default the environment task stack, the stack that contains the main unit,
is not processed. To enable processing of the environment task stack, the
environment variable GNAT_STACK_LIMIT needs to be set to the maximum size of
the environment task stack. This amount is given in kilobytes. For example:








$ set GNAT_STACK_LIMIT 1600






would specify to the analyzer that the environment task stack has a limit
of 1.6 megabytes. Any stack usage beyond this will be ignored by the analysis.



The package GNAT.Task_Stack_Usage provides facilities to get
stack-usage reports at run time. See its body for the details.









Previous: Stack Related Facilities, Up: GNAT and Program Execution   [Contents][Index]





6.7 Memory Management Issues




This section describes some useful memory pools provided in the GNAT library
and in particular the GNAT Debug Pool facility, which can be used to detect
incorrect uses of access values (including ’dangling references’).






• Some Useful Memory Pools:  



• The GNAT Debug Pool Facility:  












Next: , Up: Memory Management Issues   [Contents][Index]





6.7.1 Some Useful Memory Pools









The System.Pool_Global package offers the Unbounded_No_Reclaim_Pool
storage pool. Allocations use the standard system call malloc while
deallocations use the standard system call free. No reclamation is
performed when the pool goes out of scope. For performance reasons, the
standard default Ada allocators/deallocators do not use any explicit storage
pools but if they did, they could use this storage pool without any change in
behavior. That is why this storage pool is used  when the user
manages to make the default implicit allocator explicit as in this example:








type T1 is access Something;
 -- no Storage pool is defined for T2

type T2 is access Something_Else;
for T2'Storage_Pool use T1'Storage_Pool;
-- the above is equivalent to
for T2'Storage_Pool use System.Pool_Global.Global_Pool_Object;






The System.Pool_Local package offers the Unbounded_Reclaim_Pool storage
pool. The allocation strategy is similar to Pool_Local
except that the all
storage allocated with this pool is reclaimed when the pool object goes out of
scope. This pool provides a explicit mechanism similar to the implicit one
provided by several Ada 83 compilers for allocations performed through a local
access type and whose purpose was to reclaim memory when exiting the
scope of a given local access. As an example, the following program does not
leak memory even though it does not perform explicit deallocation:








with System.Pool_Local;
procedure Pooloc1 is
   procedure Internal is
      type A is access Integer;
      X : System.Pool_Local.Unbounded_Reclaim_Pool;
      for A'Storage_Pool use X;
      v : A;
   begin
      for I in  1 .. 50 loop
         v := new Integer;
      end loop;
   end Internal;
begin
   for I in  1 .. 100 loop
      Internal;
   end loop;
end Pooloc1;






The System.Pool_Size package implements the Stack_Bounded_Pool used when
Storage_Size is specified for an access type.
The whole storage for the pool is
allocated at once, usually on the stack at the point where the access type is
elaborated. It is automatically reclaimed when exiting the scope where the
access type is defined. This package is not intended to be used directly by the
user and it is implicitly used for each such declaration:








type T1 is access Something;
for T1'Storage_Size use 10_000;












Previous: Some Useful Memory Pools, Up: Memory Management Issues   [Contents][Index]





6.7.2 The GNAT Debug Pool Facility










The use of unchecked deallocation and unchecked conversion can easily
lead to incorrect memory references. The problems generated by such
references are usually difficult to tackle because the symptoms can be
very remote from the origin of the problem. In such cases, it is
very helpful to detect the problem as early as possible. This is the
purpose of the Storage Pool provided by GNAT.Debug_Pools.



In order to use the GNAT specific debugging pool, the user must
associate a debug pool object with each of the access types that may be
related to suspected memory problems. See Ada Reference Manual 13.11.








type Ptr is access Some_Type;
Pool : GNAT.Debug_Pools.Debug_Pool;
for Ptr'Storage_Pool use Pool;






GNAT.Debug_Pools is derived from a GNAT-specific kind of
pool: the Checked_Pool. Such pools, like standard Ada storage pools,
allow the user to redefine allocation and deallocation strategies. They
also provide a checkpoint for each dereference, through the use of
the primitive operation Dereference which is implicitly called at
each dereference of an access value.



Once an access type has been associated with a debug pool, operations on
values of the type may raise four distinct exceptions,
which correspond to four potential kinds of memory corruption:






For types associated with a Debug_Pool, dynamic allocation is performed using
the standard GNAT allocation routine. References to all allocated chunks of
memory are kept in an internal dictionary. Several deallocation strategies are
provided, whereupon the user can choose to release the memory to the system,
keep it allocated for further invalid access checks, or fill it with an easily
recognizable pattern for debug sessions. The memory pattern is the old IBM
hexadecimal convention: 16#DEADBEEF#.



See the documentation in the file g-debpoo.ads for more information on the
various strategies.



Upon each dereference, a check is made that the access value denotes a
properly allocated memory location. Here is a complete example of use of
Debug_Pools, that includes typical instances of  memory corruption:








with Gnat.Io; use Gnat.Io;
with Unchecked_Deallocation;
with Unchecked_Conversion;
with GNAT.Debug_Pools;
with System.Storage_Elements;
with Ada.Exceptions; use Ada.Exceptions;
procedure Debug_Pool_Test is

   type T is access Integer;
   type U is access all T;

   P : GNAT.Debug_Pools.Debug_Pool;
   for T'Storage_Pool use P;

   procedure Free is new Unchecked_Deallocation (Integer, T);
   function UC is new Unchecked_Conversion (U, T);
   A, B : aliased T;

   procedure Info is new GNAT.Debug_Pools.Print_Info(Put_Line);

begin
   Info (P);
   A := new Integer;
   B := new Integer;
   B := A;
   Info (P);
   Free (A);
   begin
      Put_Line (Integer'Image(B.all));
   exception
      when E : others => Put_Line ("raised: " & Exception_Name (E));
   end;
   begin
      Free (B);
   exception
      when E : others => Put_Line ("raised: " & Exception_Name (E));
   end;
   B := UC(A'Access);
   begin
      Put_Line (Integer'Image(B.all));
   exception
      when E : others => Put_Line ("raised: " & Exception_Name (E));
   end;
   begin
      Free (B);
   exception
      when E : others => Put_Line ("raised: " & Exception_Name (E));
   end;
   Info (P);
end Debug_Pool_Test;






The debug pool mechanism provides the following precise diagnostics on the
execution of this erroneous program:








Debug Pool info:
  Total allocated bytes :  0
  Total deallocated bytes :  0
  Current Water Mark:  0
  High Water Mark:  0

Debug Pool info:
  Total allocated bytes :  8
  Total deallocated bytes :  0
  Current Water Mark:  8
  High Water Mark:  8

raised: GNAT.DEBUG_POOLS.ACCESSING_DEALLOCATED_STORAGE
raised: GNAT.DEBUG_POOLS.FREEING_DEALLOCATED_STORAGE
raised: GNAT.DEBUG_POOLS.ACCESSING_NOT_ALLOCATED_STORAGE
raised: GNAT.DEBUG_POOLS.FREEING_NOT_ALLOCATED_STORAGE
Debug Pool info:
  Total allocated bytes :  8
  Total deallocated bytes :  4
  Current Water Mark:  4
  High Water Mark:  8














Next: , Previous: GNAT and Program Execution, Up: Top   [Contents][Index]





7 Platform-Specific Information




This appendix contains information relating to the implementation
of run-time libraries on various platforms and also covers
topics related to the GNAT implementation on Windows and Mac OS.





• Run-Time Libraries:  



• Specifying a Run-Time Library:  



• GNU/Linux Topics:  



• Microsoft Windows Topics:  



• Mac OS Topics:  












Next: , Up: Platform-Specific Information   [Contents][Index]





7.1 Run-Time Libraries










The GNAT run-time implementation may vary with respect to both the
underlying threads library and the exception-handling scheme.
For threads support, the default run-time will bind to the thread
package of the underlying operating system.



For exception handling, either or both of two models are supplied:















Most programs should experience a substantial speed improvement by
being compiled with a ZCX run-time.
This is especially true for
tasking applications or applications with many exception handlers.
Note however that the ZCX run-time does not support asynchronous abort
of tasks (abort and select-then-abort constructs) and will instead
implement abort by polling points in the runtime. You can also add additional
polling points explicitly if needed in your application via pragma
Abort_Defer.



This section summarizes which combinations of threads and exception support
are supplied on various GNAT platforms.





• Summary of Run-Time Configurations:  












Up: Run-Time Libraries   [Contents][Index]





7.1.1 Summary of Run-Time Configurations







PlatformRun-TimeTaskingExceptions


GNU/Linuxrts-native
(default)pthread libraryZCX


rts-sjljpthread librarySJLJ


Windowsrts-native
(default)native Win32 threadsZCX


rts-sjljnative Win32 threadsSJLJ


Mac OSrts-nativepthread libraryZCX












Next: , Previous: Run-Time Libraries, Up: Platform-Specific Information   [Contents][Index]





7.2 Specifying a Run-Time Library




The adainclude subdirectory containing the sources of the GNAT
run-time library, and the adalib subdirectory containing the
ALI files and the static and/or shared GNAT library, are located
in the gcc target-dependent area:








target=$prefix/lib/gcc/gcc-*dumpmachine*/gcc-*dumpversion*/






As indicated above, on some platforms several run-time libraries are supplied.
These libraries are installed in the target dependent area and
contain a complete source and binary subdirectory. The detailed description
below explains the differences between the different libraries in terms of
their thread support.



The default run-time library (when GNAT is installed) is `rts-native'.
This default run-time is selected by the means of soft links.
For example on x86-linux:







               $(target-dir)
              __/ /      \ \___
      _______/   /        \    \_________________
     /          /          \                     \
    /          /            \                     \
ADAINCLUDE  ADALIB      rts-native             rts-sjlj
   :          :            /    \                 /   \
   :          :           /      \               /     \
   :          :          /        \             /       \
   :          :         /          \           /         \
   +-------------> adainclude     adalib   adainclude   adalib
              :                     ^
              :                     :
              +---------------------+

              Run-Time Library Directory Structure
   (Upper-case names and dotted/dashed arrows represent soft links)




If the `rts-sjlj' library is to be selected on a permanent basis,
these soft links can be modified with the following commands:








$ cd $target
$ rm -f adainclude adalib
$ ln -s rts-sjlj/adainclude adainclude
$ ln -s rts-sjlj/adalib adalib






Alternatively, you can specify rts-sjlj/adainclude in the file
$target/ada_source_path and rts-sjlj/adalib in
$target/ada_object_path.





Selecting another run-time library temporarily can be
achieved by using the --RTS switch, e.g., --RTS=sjlj










• Choosing the Scheduling Policy:  












Up: Specifying a Run-Time Library   [Contents][Index]





7.2.1 Choosing the Scheduling Policy




When using a POSIX threads implementation, you have a choice of several
scheduling policies: SCHED_FIFO, SCHED_RR and SCHED_OTHER.



Typically, the default is SCHED_OTHER, while using SCHED_FIFO
or SCHED_RR requires special (e.g., root) privileges.









By default, GNAT uses the SCHED_OTHER policy. To specify
SCHED_FIFO,
you can use one of the following:






To specify SCHED_RR,
you should use pragma Time_Slice with a
value greater than 0.0, or else use the corresponding -T
binder option.



To make sure a program is running as root, you can put something like
this in a library package body in your application:








function geteuid return Integer;
pragma Import (C, geteuid, "geteuid");
Ignore : constant Boolean :=
  (if geteuid = 0 then True else raise Program_Error with "must be root");






It gets the effective user id, and if it’s not 0 (i.e. root), it raises
Program_Error.













Next: , Previous: Specifying a Run-Time Library, Up: Platform-Specific Information   [Contents][Index]





7.3 GNU/Linux Topics




This section describes topics that are specific to GNU/Linux platforms.





• Required Packages on GNU/Linux:  












Up: GNU/Linux Topics   [Contents][Index]





7.3.1 Required Packages on GNU/Linux




GNAT requires the C library developer’s package to be installed.
The name of of that package depends on your GNU/Linux distribution:






If using the 32-bit version of GNAT on a 64-bit version of GNU/Linux,
you’ll need the 32-bit version of the following packages:






Other GNU/Linux distributions might be choosing a different name
for those packages.











Next: , Previous: GNU/Linux Topics, Up: Platform-Specific Information   [Contents][Index]





7.4 Microsoft Windows Topics




This section describes topics that are specific to the Microsoft Windows
platforms.






• Using GNAT on Windows:  



• Using a network installation of GNAT:  



• CONSOLE and WINDOWS subsystems:  



• Temporary Files:  



• Disabling Command Line Argument Expansion:  



• Windows Socket Timeouts:  



• Mixed-Language Programming on Windows:  



• Windows Specific Add-Ons:  












Next: , Up: Microsoft Windows Topics   [Contents][Index]





7.4.1 Using GNAT on Windows




One of the strengths of the GNAT technology is that its tool set
(gcc, gnatbind, gnatlink, gnatmake, the
gdb debugger, etc.) is used in the same way regardless of the
platform.



On Windows this tool set is complemented by a number of Microsoft-specific
tools that have been provided to facilitate interoperability with Windows
when this is required. With these tools:






Immediately below are listed all known general GNAT-for-Windows restrictions.
Other restrictions about specific features like Windows Resources and DLLs
are listed in separate sections below.












Next: , Previous: Using GNAT on Windows, Up: Microsoft Windows Topics   [Contents][Index]





7.4.2 Using a network installation of GNAT




Make sure the system on which GNAT is installed is accessible from the
current machine, i.e., the install location is shared over the network.
Shared resources are accessed on Windows by means of UNC paths, which
have the format \\\\server\\sharename\\path



In order to use such a network installation, simply add the UNC path of the
bin directory of your GNAT installation in front of your PATH. For
example, if GNAT is installed in \GNAT directory of a share location
called c-drive on a machine LOKI, the following command will
make it available:








$ path \\loki\c-drive\gnat\bin;%path%`






Be aware that every compilation using the network installation results in the
transfer of large amounts of data across the network and will likely cause
serious performance penalty.









Next: , Previous: Using a network installation of GNAT, Up: Microsoft Windows Topics   [Contents][Index]





7.4.3 CONSOLE and WINDOWS subsystems










There are two main subsystems under Windows. The CONSOLE subsystem
(which is the default subsystem) will always create a console when
launching the application. This is not something desirable when the
application has a Windows GUI. To get rid of this console the
application must be using the WINDOWS subsystem. To do so
the -mwindows linker option must be specified.








$ gnatmake winprog -largs -mwindows












Next: , Previous: CONSOLE and WINDOWS subsystems, Up: Microsoft Windows Topics   [Contents][Index]





7.4.4 Temporary Files






It is possible to control where temporary files gets created by setting
the 


TMP environment variable. The file will be created:






This allows you to determine exactly where the temporary
file will be created. This is particularly useful in networked
environments where you may not have write access to some
directories.









Next: , Previous: Temporary Files, Up: Microsoft Windows Topics   [Contents][Index]





7.4.5 Disabling Command Line Argument Expansion






By default, an executable compiled for the Windows platform will do
the following postprocessing on the arguments passed on the command
line:






Note that if the program is launched from a shell such as Cygwin Bash
then quote removal might be performed by the shell.



In some contexts it might be useful to disable this feature (for example if
the program performs its own argument expansion). In order to do this, a C
symbol needs to be defined and set to 0. You can do this by
adding the following code fragment in one of your Ada units:





Do_Argv_Expansion : Integer := 0;
pragma Export (C, Do_Argv_Expansion, "__gnat_do_argv_expansion");




The results of previous examples will be respectively:





Ada.Command_Line.Argument (1) -> "*.txt"




and:





Ada.Command_Line.Argument (1) -> "'*.txt'"










Next: , Previous: Disabling Command Line Argument Expansion, Up: Microsoft Windows Topics   [Contents][Index]





7.4.6 Windows Socket Timeouts




Microsoft Windows desktops older than 8.0 and Microsoft Windows Servers
older than 2019 set a socket timeout 500 milliseconds longer than the value
set by setsockopt with SO_RCVTIMEO and SO_SNDTIMEO options. The GNAT
runtime makes a correction for the difference in the corresponding Windows
versions. For Windows Server starting with version 2019, the user must
provide a manifest file for the GNAT runtime to be able to recognize that
the Windows version does not need the timeout correction. The manifest file
should be located in the same directory as the executable file, and its file
name must match the executable name suffixed by .manifest. For example,
if the executable name is sock_wto.exe, then the manifest file name
has to be sock_wto.exe.manifest. The manifest file must contain at
least the following data:





<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
<compatibility xmlns="urn:schemas-microsoft-com:compatibility.v1">
<application>
   <!-- Windows Vista -->
   <supportedOS Id="{e2011457-1546-43c5-a5fe-008deee3d3f0}"/>
   <!-- Windows 7 -->
   <supportedOS Id="{35138b9a-5d96-4fbd-8e2d-a2440225f93a}"/>
   <!-- Windows 8 -->
   <supportedOS Id="{4a2f28e3-53b9-4441-ba9c-d69d4a4a6e38}"/>
   <!-- Windows 8.1 -->
   <supportedOS Id="{1f676c76-80e1-4239-95bb-83d0f6d0da78}"/>
   <!-- Windows 10 -->
   <supportedOS Id="{8e0f7a12-bfb3-4fe8-b9a5-48fd50a15a9a}"/>
</application>
</compatibility>
</assembly>




Without the manifest file, the socket timeout is going to be overcorrected on
these Windows Server versions and the actual time is going to be 500
milliseconds shorter than what was set with GNAT.Sockets.Set_Socket_Option.
Note that on Microsoft Windows versions where correction is necessary, there
is no way to set a socket timeout shorter than 500 ms. If a socket timeout
shorter than 500 ms is needed on these Windows versions, a call to
Check_Selector should be added before any socket read or write operations.









Next: , Previous: Windows Socket Timeouts, Up: Microsoft Windows Topics   [Contents][Index]





7.4.7 Mixed-Language Programming on Windows




Developing pure Ada applications on Windows is no different than on
other GNAT-supported platforms. However, when developing or porting an
application that contains a mix of Ada and C/C++, the choice of your
Windows C/C++ development environment conditions your overall
interoperability strategy.



If you use gcc or Microsoft C to compile the non-Ada part of
your application, there are no Windows-specific restrictions that
affect the overall interoperability with your Ada code. If you do want
to use the Microsoft tools for your C++ code, you have two choices:






In addition to the description about C main in
Mixed Language Programming section, if the C main uses a
stand-alone library it is required on x86-windows to
setup the SEH context. For this the C main must looks like this:








/* main.c */
extern void adainit (void);
extern void adafinal (void);
extern void __gnat_initialize(void*);
extern void call_to_ada (void);

int main (int argc, char *argv[])
{
  int SEH [2];

  /* Initialize the SEH context */
  __gnat_initialize (&SEH);

  adainit();

  /* Then call Ada services in the stand-alone library */

  call_to_ada();

  adafinal();
}






Note that this is not needed on x86_64-windows where the Windows
native SEH support is used.





• Windows Calling Conventions:  



• Introduction to Dynamic Link Libraries (DLLs):  



• Using DLLs with GNAT:  



• Building DLLs with GNAT Project files:  



• Building DLLs with GNAT:  



• Building DLLs with gnatdll:  



• Ada DLLs and Finalization:  



• Creating a Spec for Ada DLLs:  



• GNAT and Windows Resources:  



• Using GNAT DLLs from Microsoft Visual Studio Applications:  



• Debugging a DLL:  



• Setting Stack Size from gnatlink:  



• Setting Heap Size from gnatlink:  












Next: , Up: Mixed-Language Programming on Windows   [Contents][Index]





7.4.7.1 Windows Calling Conventions








This section pertain only to Win32. On Win64 there is a single native
calling convention. All convention specifiers are ignored on this
platform.



When a subprogram F (caller) calls a subprogram G
(callee), there are several ways to push G’s parameters on the
stack and there are several possible scenarios to clean up the stack
upon G’s return. A calling convention is an agreed upon software
protocol whereby the responsibilities between the caller (F) and
the callee (G) are clearly defined. Several calling conventions
are available for Windows:








• C Calling Convention:  



• Stdcall Calling Convention:  



• Win32 Calling Convention:  



• DLL Calling Convention:  












Next: , Up: Windows Calling Conventions   [Contents][Index]





7.4.7.2 C Calling Convention




This is the default calling convention used when interfacing to C/C++
routines compiled with either gcc or Microsoft Visual C++.



In the C calling convention subprogram parameters are pushed on the
stack by the caller from right to left. The caller itself is in charge of
cleaning up the stack after the call. In addition, the name of a routine
with C calling convention is mangled by adding a leading underscore.



The name to use on the Ada side when importing (or exporting) a routine
with C calling convention is the name of the routine. For
instance the C function:








int get_val (long);






should be imported from Ada as follows:








function Get_Val (V : Interfaces.C.long) return Interfaces.C.int;
pragma Import (C, Get_Val, External_Name => "get_val");






Note that in this particular case the External_Name parameter could
have been omitted since, when missing, this parameter is taken to be the
name of the Ada entity in lower case. When the Link_Name parameter
is missing, as in the above example, this parameter is set to be the
External_Name with a leading underscore.



When importing a variable defined in C, you should always use the C
calling convention unless the object containing the variable is part of a
DLL (in which case you should use the Stdcall calling
convention, Stdcall Calling Convention).









Next: , Previous: C Calling Convention, Up: Windows Calling Conventions   [Contents][Index]





7.4.7.3 Stdcall Calling Convention




This convention, which was the calling convention used for Pascal
programs, is used by Microsoft for all the routines in the Win32 API for
efficiency reasons. It must be used to import any routine for which this
convention was specified.



In the Stdcall calling convention subprogram parameters are pushed
on the stack by the caller from right to left. The callee (and not the
caller) is in charge of cleaning the stack on routine exit. In addition,
the name of a routine with Stdcall calling convention is mangled by
adding a leading underscore (as for the C calling convention) and a
trailing @`nn', where nn is the overall size (in
bytes) of the parameters passed to the routine.



The name to use on the Ada side when importing a C routine with a
Stdcall calling convention is the name of the C routine. The leading
underscore and trailing @`nn' are added automatically by
the compiler. For instance the Win32 function:








APIENTRY int get_val (long);






should be imported from Ada as follows:








function Get_Val (V : Interfaces.C.long) return Interfaces.C.int;
pragma Import (Stdcall, Get_Val);
--  On the x86 a long is 4 bytes, so the Link_Name is "_get_val@4"






As for the C calling convention, when the External_Name
parameter is missing, it is taken to be the name of the Ada entity in lower
case. If instead of writing the above import pragma you write:








function Get_Val (V : Interfaces.C.long) return Interfaces.C.int;
pragma Import (Stdcall, Get_Val, External_Name => "retrieve_val");






then the imported routine is _retrieve_val@4. However, if instead
of specifying the External_Name parameter you specify the
Link_Name as in the following example:








function Get_Val (V : Interfaces.C.long) return Interfaces.C.int;
pragma Import (Stdcall, Get_Val, Link_Name => "retrieve_val");






then the imported routine is retrieve_val, that is, there is no
decoration at all. No leading underscore and no Stdcall suffix
@`nn'.



This is especially important as in some special cases a DLL’s entry
point name lacks a trailing @`nn' while the exported
name generated for a call has it.



It is also possible to import variables defined in a DLL by using an
import pragma for a variable. As an example, if a DLL contains a
variable defined as:








int my_var;






then, to access this variable from Ada you should write:








My_Var : Interfaces.C.int;
pragma Import (Stdcall, My_Var);






Note that to ease building cross-platform bindings this convention
will be handled as a C calling convention on non-Windows platforms.









Next: , Previous: Stdcall Calling Convention, Up: Windows Calling Conventions   [Contents][Index]





7.4.7.4 Win32 Calling Convention




This convention, which is GNAT-specific is fully equivalent to the
Stdcall calling convention described above.









Previous: Win32 Calling Convention, Up: Windows Calling Conventions   [Contents][Index]





7.4.7.5 DLL Calling Convention




This convention, which is GNAT-specific is fully equivalent to the
Stdcall calling convention described above.









Next: , Previous: Windows Calling Conventions, Up: Mixed-Language Programming on Windows   [Contents][Index]





7.4.7.6 Introduction to Dynamic Link Libraries (DLLs)






A Dynamically Linked Library (DLL) is a library that can be shared by
several applications running under Windows. A DLL can contain any number of
routines and variables.



One advantage of DLLs is that you can change and enhance them without
forcing all the applications that depend on them to be relinked or
recompiled. However, you should be aware than all calls to DLL routines are
slower since, as you will understand below, such calls are indirect.



To illustrate the remainder of this section, suppose that an application
wants to use the services of a DLL API.dll. To use the services
provided by API.dll you must statically link against the DLL or
an import library which contains a jump table with an entry for each
routine and variable exported by the DLL. In the Microsoft world this
import library is called API.lib. When using GNAT this import
library is called either libAPI.dll.a, libapi.dll.a,
libAPI.a or libapi.a (names are case insensitive).



After you have linked your application with the DLL or the import library
and you run your application, here is what happens:






There is an additional point which is worth mentioning. In the Windows
world there are two kind of DLLs: relocatable and non-relocatable
DLLs. Non-relocatable DLLs can only be loaded at a very specific address
in the target application address space. If the addresses of two
non-relocatable DLLs overlap and these happen to be used by the same
application, a conflict will occur and the application will run
incorrectly. Hence, when possible, it is always preferable to use and
build relocatable DLLs. Both relocatable and non-relocatable DLLs are
supported by GNAT. Note that the -s linker option (see GNU Linker
User’s Guide) removes the debugging symbols from the DLL but the DLL can
still be relocated.



As a side note, an interesting difference between Microsoft DLLs and
Unix shared libraries, is the fact that on most Unix systems all public
routines are exported by default in a Unix shared library, while under
Windows it is possible (but not required) to list exported routines in
a definition file (see The Definition File).









Next: , Previous: Introduction to Dynamic Link Libraries DLLs, Up: Mixed-Language Programming on Windows   [Contents][Index]





7.4.7.7 Using DLLs with GNAT




To use the services of a DLL, say API.dll, in your Ada application
you must have:






Once you have all the above, to compile an Ada application that uses the
services of API.dll and whose main subprogram is My_Ada_App,
you simply issue the command








$ gnatmake my_ada_app -largs -lAPI






The argument -largs -lAPI at the end of the gnatmake command
tells the GNAT linker to look for an import library. The linker will
look for a library name in this specific order:






The first three are the GNU style import libraries. The third is the
Microsoft style import libraries. The last two are the actual DLL names.



Note that if the Ada package spec for API.dll contains the
following pragma








pragma Linker_Options ("-lAPI");






you do not have to add -largs -lAPI at the end of the
gnatmake command.



If any one of the items above is missing you will have to create it
yourself. The following sections explain how to do so using as an
example a fictitious DLL called API.dll.





• Creating an Ada Spec for the DLL Services:  



• Creating an Import Library:  












Next: , Up: Using DLLs with GNAT   [Contents][Index]





7.4.7.8 Creating an Ada Spec for the DLL Services




A DLL typically comes with a C/C++ header file which provides the
definitions of the routines and variables exported by the DLL. The Ada
equivalent of this header file is a package spec that contains definitions
for the imported entities. If the DLL you intend to use does not come with
an Ada spec you have to generate one such spec yourself. For example if
the header file of API.dll is a file api.h containing the
following two definitions:








int some_var;
int get (char *);






then the equivalent Ada spec could be:








with Interfaces.C.Strings;
package API is
   use Interfaces;

   Some_Var : C.int;
   function Get (Str : C.Strings.Chars_Ptr) return C.int;

private
   pragma Import (C, Get);
   pragma Import (DLL, Some_Var);
end API;












Previous: Creating an Ada Spec for the DLL Services, Up: Using DLLs with GNAT   [Contents][Index]





7.4.7.9 Creating an Import Library






If a Microsoft-style import library API.lib or a GNAT-style
import library libAPI.dll.a or libAPI.a is available
with API.dll you can skip this section. You can also skip this
section if API.dll or libAPI.dll is built with GNU tools
as in this case it is possible to link directly against the
DLL. Otherwise read on.





The Definition File




As previously mentioned, and unlike Unix systems, the list of symbols
that are exported from a DLL must be provided explicitly in Windows.
The main goal of a definition file is precisely that: list the symbols
exported by a DLL. A definition file (usually a file with a .def
suffix) has the following structure:








[LIBRARY ``name``]
[DESCRIPTION ``string``]
EXPORTS
   ``symbol1``
   ``symbol2``
   ...









`LIBRARY name'




This section, which is optional, gives the name of the DLL.





`DESCRIPTION string'




This section, which is optional, gives a description string that will be
embedded in the import library.





`EXPORTS'




This section gives the list of exported symbols (procedures, functions or
variables). For instance in the case of API.dll the EXPORTS
section of API.def looks like:





EXPORTS
   some_var
   get








Note that you must specify the correct suffix (@`nn')
(see Windows Calling Conventions) for a Stdcall
calling convention function in the exported symbols list.



There can actually be other sections in a definition file, but these
sections are not relevant to the discussion at hand.



Creating a Definition File Automatically




You can automatically create the definition file API.def
(see The Definition File) from a DLL.
For that use the dlltool program as follows:








$ dlltool API.dll -z API.def --export-all-symbols




Note that if some routines in the DLL have the Stdcall convention
(Windows Calling Conventions) with stripped @`nn'
suffix then you’ll have to edit api.def to add it, and specify
-k to gnatdll when creating the import library.



Here are some hints to find the right @`nn' suffix.








GNAT-Style Import Library




To create a static import library from API.dll with the GNAT tools
you should create the .def file, then use gnatdll tool
(see Using gnatdll) as follows:








$ gnatdll -e API.def -d API.dll




gnatdll takes as input a definition file API.def and the
name of the DLL containing the services listed in the definition file
API.dll. The name of the static import library generated is
computed from the name of the definition file as follows: if the
definition file name is xyz.def, the import library name will
be libxyz.a. Note that in the previous example option
-e could have been removed because the name of the definition
file (before the .def suffix) is the same as the name of the
DLL (Using gnatdll for more information about gnatdll).




Microsoft-Style Import Library




A Microsoft import library is needed only if you plan to make an
Ada DLL available to applications developed with Microsoft
tools (Mixed-Language Programming on Windows).



To create a Microsoft-style import library for API.dll you
should create the .def file, then build the actual import library using
Microsoft’s lib utility:








$ lib -machine:IX86 -def:API.def -out:API.lib




If you use the above command the definition file API.def must
contain a line giving the name of the DLL:





LIBRARY      "API"




See the Microsoft documentation for further details about the usage of
lib.










Next: , Previous: Using DLLs with GNAT, Up: Mixed-Language Programming on Windows   [Contents][Index]





7.4.7.10 Building DLLs with GNAT Project files







There is nothing specific to Windows in the build process.
See the `Library Projects' section in the `GNAT Project Manager'
chapter of the `GPRbuild User’s Guide'.



Due to a system limitation, it is not possible under Windows to create threads
when inside the DllMain routine which is used for auto-initialization
of shared libraries, so it is not possible to have library level tasks in SALs.









Next: , Previous: Building DLLs with GNAT Project files, Up: Mixed-Language Programming on Windows   [Contents][Index]





7.4.7.11 Building DLLs with GNAT







This section explain how to build DLLs using the GNAT built-in DLL
support. With the following procedure it is straight forward to build
and use DLLs with GNAT.






At this point it is possible to use the DLL by directly linking
against it. Note that you must use the GNAT shared runtime when using
GNAT shared libraries. This is achieved by using the -shared binder
option.








$ gnatmake main -Iapilib -bargs -shared -largs -Lapilib -lAPI












Next: , Previous: Building DLLs with GNAT, Up: Mixed-Language Programming on Windows   [Contents][Index]





7.4.7.12 Building DLLs with gnatdll







Note that it is preferred to use GNAT Project files
(Building DLLs with GNAT Project files) or the built-in GNAT
DLL support (Building DLLs with GNAT) or to build DLLs.



This section explains how to build DLLs containing Ada code using
gnatdll. These DLLs will be referred to as Ada DLLs in the
remainder of this section.



The steps required to build an Ada DLL that is to be used by Ada as well as
non-Ada applications are as follows:






Note that a relocatable DLL stripped using the strip
binutils tool will not be relocatable anymore. To build a DLL without
debug information pass -largs -s to gnatdll. This
restriction does not apply to a DLL built using a Library Project.
See the `Library Projects' section in the `GNAT Project Manager'
chapter of the `GPRbuild User’s Guide'.






• Limitations When Using Ada DLLs from Ada:  



• Exporting Ada Entities:  



• Ada DLLs and Elaboration:  












Next: , Up: Building DLLs with gnatdll   [Contents][Index]





7.4.7.13 Limitations When Using Ada DLLs from Ada




When using Ada DLLs from Ada applications there is a limitation users
should be aware of. Because on Windows the GNAT run-time is not in a DLL of
its own, each Ada DLL includes a part of the GNAT run-time. Specifically,
each Ada DLL includes the services of the GNAT run-time that are necessary
to the Ada code inside the DLL. As a result, when an Ada program uses an
Ada DLL there are two independent GNAT run-times: one in the Ada DLL and
one in the main program.



It is therefore not possible to exchange GNAT run-time objects between the
Ada DLL and the main Ada program. Example of GNAT run-time objects are file
handles (e.g., Text_IO.File_Type), tasks types, protected objects
types, etc.



It is completely safe to exchange plain elementary, array or record types,
Windows object handles, etc.









Next: , Previous: Limitations When Using Ada DLLs from Ada, Up: Building DLLs with gnatdll   [Contents][Index]





7.4.7.14 Exporting Ada Entities






Building a DLL is a way to encapsulate a set of services usable from any
application. As a result, the Ada entities exported by a DLL should be
exported with the C or Stdcall calling conventions to avoid
any Ada name mangling. As an example here is an Ada package
API, spec and body, exporting two procedures, a function, and a
variable:








with Interfaces.C; use Interfaces;
package API is
   Count : C.int := 0;
   function Factorial (Val : C.int) return C.int;

   procedure Initialize_API;
   procedure Finalize_API;
   --  Initialization & Finalization routines. More in the next section.
private
   pragma Export (C, Initialize_API);
   pragma Export (C, Finalize_API);
   pragma Export (C, Count);
   pragma Export (C, Factorial);
end API;






package body API is
   function Factorial (Val : C.int) return C.int is
      Fact : C.int := 1;
   begin
      Count := Count + 1;
      for K in 1 .. Val loop
         Fact := Fact * K;
      end loop;
      return Fact;
   end Factorial;

   procedure Initialize_API is
      procedure Adainit;
      pragma Import (C, Adainit);
   begin
      Adainit;
   end Initialize_API;

   procedure Finalize_API is
      procedure Adafinal;
      pragma Import (C, Adafinal);
   begin
      Adafinal;
   end Finalize_API;
end API;






If the Ada DLL you are building will only be used by Ada applications
you do not have to export Ada entities with a C or Stdcall
convention. As an example, the previous package could be written as
follows:








package API is
   Count : Integer := 0;
   function Factorial (Val : Integer) return Integer;

   procedure Initialize_API;
   procedure Finalize_API;
   --  Initialization and Finalization routines.
end API;






package body API is
   function Factorial (Val : Integer) return Integer is
      Fact : Integer := 1;
   begin
      Count := Count + 1;
      for K in 1 .. Val loop
         Fact := Fact * K;
      end loop;
      return Fact;
   end Factorial;

   ...
   --  The remainder of this package body is unchanged.
end API;






Note that if you do not export the Ada entities with a C or
Stdcall convention you will have to provide the mangled Ada names
in the definition file of the Ada DLL
(Creating the Definition File).









Previous: Exporting Ada Entities, Up: Building DLLs with gnatdll   [Contents][Index]





7.4.7.15 Ada DLLs and Elaboration






The DLL that you are building contains your Ada code as well as all the
routines in the Ada library that are needed by it. The first thing a
user of your DLL must do is elaborate the Ada code
(Elaboration Order Handling in GNAT).



To achieve this you must export an initialization routine
(Initialize_API in the previous example), which must be invoked
before using any of the DLL services. This elaboration routine must call
the Ada elaboration routine adainit generated by the GNAT binder
(Binding with Non-Ada Main Programs). See the body of
Initialize_Api for an example. Note that the GNAT binder is
automatically invoked during the DLL build process by the gnatdll
tool (Using gnatdll).



When a DLL is loaded, Windows systematically invokes a routine called
DllMain. It would therefore be possible to call adainit
directly from DllMain without having to provide an explicit
initialization routine. Unfortunately, it is not possible to call
adainit from the DllMain if your program has library level
tasks because access to the DllMain entry point is serialized by
the system (that is, only a single thread can execute ’through’ it at a
time), which means that the GNAT run-time will deadlock waiting for the
newly created task to complete its initialization.









Next: , Previous: Building DLLs with gnatdll, Up: Mixed-Language Programming on Windows   [Contents][Index]





7.4.7.16 Ada DLLs and Finalization






When the services of an Ada DLL are no longer needed, the client code should
invoke the DLL finalization routine, if available. The DLL finalization
routine is in charge of releasing all resources acquired by the DLL. In the
case of the Ada code contained in the DLL, this is achieved by calling
routine adafinal generated by the GNAT binder
(Binding with Non-Ada Main Programs).
See the body of Finalize_Api for an
example. As already pointed out the GNAT binder is automatically invoked
during the DLL build process by the gnatdll tool
(Using gnatdll).









Next: , Previous: Ada DLLs and Finalization, Up: Mixed-Language Programming on Windows   [Contents][Index]





7.4.7.17 Creating a Spec for Ada DLLs




To use the services exported by the Ada DLL from another programming
language (e.g., C), you have to translate the specs of the exported Ada
entities in that language. For instance in the case of API.dll,
the corresponding C header file could look like:








extern int *_imp__count;
#define count (*_imp__count)
int factorial (int);






It is important to understand that when building an Ada DLL to be used by
other Ada applications, you need two different specs for the packages
contained in the DLL: one for building the DLL and the other for using
the DLL. This is because the DLL calling convention is needed to
use a variable defined in a DLL, but when building the DLL, the variable
must have either the Ada or C calling convention. As an
example consider a DLL comprising the following package API:








package API is
   Count : Integer := 0;
   ...
   --  Remainder of the package omitted.
end API;






After producing a DLL containing package API, the spec that
must be used to import API.Count from Ada code outside of the
DLL is:








package API is
   Count : Integer;
   pragma Import (DLL, Count);
end API;








• Creating the Definition File:  



• Using gnatdll:  












Next: , Up: Creating a Spec for Ada DLLs   [Contents][Index]





7.4.7.18 Creating the Definition File




The definition file is the last file needed to build the DLL. It lists
the exported symbols. As an example, the definition file for a DLL
containing only package API (where all the entities are exported
with a C calling convention) is:








EXPORTS
    count
    factorial
    finalize_api
    initialize_api






If the C calling convention is missing from package API,
then the definition file contains the mangled Ada names of the above
entities, which in this case are:








EXPORTS
    api__count
    api__factorial
    api__finalize_api
    api__initialize_api












Previous: Creating the Definition File, Up: Creating a Spec for Ada DLLs   [Contents][Index]





7.4.7.19 Using gnatdll






gnatdll is a tool to automate the DLL build process once all the Ada
and non-Ada sources that make up your DLL have been compiled.
gnatdll is actually in charge of two distinct tasks: build the
static import library for the DLL and the actual DLL. The form of the
gnatdll command is








$ gnatdll [ switches ] list-of-files [ -largs opts ]






where list-of-files is a list of ALI and object files. The object
file list must be the exact list of objects corresponding to the non-Ada
sources whose services are to be included in the DLL. The ALI file list
must be the exact list of ALI files for the corresponding Ada sources
whose services are to be included in the DLL. If list-of-files is
missing, only the static import library is generated.



You may specify any of the following switches to gnatdll:













-a[`address']




Build a non-relocatable DLL at address. If address is not
specified the default address 0x11000000 will be used. By default,
when this switch is missing, gnatdll builds relocatable DLL. We
advise the reader to build relocatable DLL.







-b `address'




Set the relocatable DLL base address. By default the address is
0x11000000.







-bargs `opts'




Binder options. Pass opts to the binder.







-d `dllfile'




dllfile is the name of the DLL. This switch must be present for
gnatdll to do anything. The name of the generated import library is
obtained algorithmically from dllfile as shown in the following
example: if dllfile is xyz.dll, the import library name is
libxyz.dll.a. The name of the definition file to use (if not specified
by option -e) is obtained algorithmically from dllfile
as shown in the following example:
if dllfile is xyz.dll, the definition
file used is xyz.def.







-e `deffile'




deffile is the name of the definition file.







-g




Generate debugging information. This information is stored in the object
file and copied from there to the final DLL file by the linker,
where it can be read by the debugger. You must use the
-g switch if you plan on using the debugger or the symbolic
stack traceback.







-h




Help mode. Displays gnatdll switch usage information.







-I`dir'




Direct gnatdll to search the dir directory for source and
object files needed to build the DLL.
(Search Paths and the Run-Time Library (RTL)).







-k




Removes the @`nn' suffix from the import library’s exported
names, but keeps them for the link names. You must specify this
option if you want to use a Stdcall function in a DLL for which
the @`nn' suffix has been removed. This is the case for most
of the Windows NT DLL for example. This option has no effect when
-n option is specified.







-l `file'




The list of ALI and object files used to build the DLL are listed in
file, instead of being given in the command line. Each line in
file contains the name of an ALI or object file.







-n




No Import. Do not create the import library.







-q




Quiet mode. Do not display unnecessary messages.







-v




Verbose mode. Display extra information.







-largs `opts'




Linker options. Pass opts to the linker.







gnatdll Example




As an example the command to build a relocatable DLL from api.adb
once api.adb has been compiled and api.def created is








$ gnatdll -d api.dll api.ali






The above command creates two files: libapi.dll.a (the import
library) and api.dll (the actual DLL). If you want to create
only the DLL, just type:








$ gnatdll -d api.dll -n api.ali






Alternatively if you want to create just the import library, type:








$ gnatdll -d api.dll







gnatdll behind the Scenes




This section details the steps involved in creating a DLL. gnatdll
does these steps for you. Unless you are interested in understanding what
goes on behind the scenes, you should skip this section.



We use the previous example of a DLL containing the Ada package API,
to illustrate the steps necessary to build a DLL. The starting point is a
set of objects that will make up the DLL and the corresponding ALI
files. In the case of this example this means that api.o and
api.ali are available. To build a relocatable DLL, gnatdll does
the following:






Using dlltool




dlltool is the low-level tool used by gnatdll to build
DLLs and static import libraries. This section summarizes the most
common dlltool switches. The form of the dlltool command
is








$ dlltool [`switches`]






dlltool switches include:








--base-file `basefile'




Read the base file basefile generated by the linker. This switch
is used to create a relocatable DLL.











--def `deffile'




Read the definition file.











--dllname `name'




Gives the name of the DLL. This switch is used to embed the name of the
DLL in the static import library generated by dlltool with switch
--output-lib.











-k




Kill @`nn' from exported names
(Windows Calling Conventions
for a discussion about Stdcall-style symbols.











--help




Prints the dlltool switches with a concise description.











--output-exp `exportfile'




Generate an export file exportfile. The export file contains the
export table (list of symbols in the DLL) and is used to create the DLL.











--output-lib `libfile'




Generate a static import library libfile.











-v




Verbose mode.











--as `assembler-name'




Use assembler-name as the assembler. The default is as.












Next: , Previous: Creating a Spec for Ada DLLs, Up: Mixed-Language Programming on Windows   [Contents][Index]





7.4.7.20 GNAT and Windows Resources







Resources are an easy way to add Windows specific objects to your
application. The objects that can be added as resources include:






For example, a version information resource can be defined as follow and
embedded into an executable or DLL:



A version information resource can be used to embed information into an
executable or a DLL. These information can be viewed using the file properties
from the Windows Explorer. Here is an example of a version information
resource:








1 VERSIONINFO
FILEVERSION     1,0,0,0
PRODUCTVERSION  1,0,0,0
BEGIN
  BLOCK "StringFileInfo"
  BEGIN
    BLOCK "080904E4"
    BEGIN
      VALUE "CompanyName", "My Company Name"
      VALUE "FileDescription", "My application"
      VALUE "FileVersion", "1.0"
      VALUE "InternalName", "my_app"
      VALUE "LegalCopyright", "My Name"
      VALUE "OriginalFilename", "my_app.exe"
      VALUE "ProductName", "My App"
      VALUE "ProductVersion", "1.0"
    END
  END

  BLOCK "VarFileInfo"
  BEGIN
    VALUE "Translation", 0x809, 1252
  END
END






The value 0809 (langID) is for the U.K English language and
04E4 (charsetID), which is equal to 1252 decimal, for
multilingual.



This section explains how to build, compile and use resources. Note that this
section does not cover all resource objects, for a complete description see
the corresponding Microsoft documentation.





• Building Resources:  



• Compiling Resources:  



• Using Resources:  












Next: , Up: GNAT and Windows Resources   [Contents][Index]





7.4.7.21 Building Resources







A resource file is an ASCII file. By convention resource files have an
.rc extension.
The easiest way to build a resource file is to use Microsoft tools
such as imagedit.exe to build bitmaps, icons and cursors and
dlgedit.exe to build dialogs.
It is always possible to build an .rc file yourself by writing a
resource script.



It is not our objective to explain how to write a resource file. A
complete description of the resource script language can be found in the
Microsoft documentation.









Next: , Previous: Building Resources, Up: GNAT and Windows Resources   [Contents][Index]





7.4.7.22 Compiling Resources











This section describes how to build a GNAT-compatible (COFF) object file
containing the resources. This is done using the Resource Compiler
windres as follows:








$ windres -i myres.rc -o myres.o






By default windres will run gcc to preprocess the .rc
file. You can specify an alternate preprocessor (usually named
cpp.exe) using the windres --preprocessor
parameter. A list of all possible options may be obtained by entering
the command windres --help.



It is also possible to use the Microsoft resource compiler rc.exe
to produce a .res file (binary resource file). See the
corresponding Microsoft documentation for further details. In this case
you need to use windres to translate the .res file to a
GNAT-compatible object file as follows:








$ windres -i myres.res -o myres.o












Previous: Compiling Resources, Up: GNAT and Windows Resources   [Contents][Index]





7.4.7.23 Using Resources







To include the resource file in your program just add the
GNAT-compatible object file for the resource(s) to the linker
arguments. With gnatmake this is done by using the -largs
option:








$ gnatmake myprog -largs myres.o












Next: , Previous: GNAT and Windows Resources, Up: Mixed-Language Programming on Windows   [Contents][Index]





7.4.7.24 Using GNAT DLLs from Microsoft Visual Studio Applications







This section describes a common case of mixed GNAT/Microsoft Visual Studio
application development, where the main program is developed using MSVS, and
is linked with a DLL developed using GNAT. Such a mixed application should
be developed following the general guidelines outlined above; below is the
cookbook-style sequence of steps to follow:




    

  1.  First develop and build the GNAT shared library using a library project
(let’s assume the project is mylib.gpr, producing the library libmylib.dll):









$ gprbuild -p mylib.gpr







    

  1.  Produce a .def file for the symbols you need to interface with, either by
hand or automatically with possibly some manual adjustments
(see Creating Definition File Automatically):









$ dlltool libmylib.dll -z libmylib.def --export-all-symbols







    

  1.  Make sure that MSVS command-line tools are accessible on the path.


  2.  Create the Microsoft-style import library (see MSVS-Style Import Library):









$ lib -machine:IX86 -def:libmylib.def -out:libmylib.lib






If you are using a 64-bit toolchain, the above becomes...








$ lib -machine:X64 -def:libmylib.def -out:libmylib.lib







    

  1.  Build the C main









$ cl /O2 /MD main.c libmylib.lib







    

  1.  Before running the executable, make sure you have set the PATH to the DLL,
or copy the DLL into into the directory containing the .exe.










Next: , Previous: Using GNAT DLLs from Microsoft Visual Studio Applications, Up: Mixed-Language Programming on Windows   [Contents][Index]





7.4.7.25 Debugging a DLL






Debugging a DLL is similar to debugging a standard program. But
we have to deal with two different executable parts: the DLL and the
program that uses it. We have the following four possibilities:






In this section we address only cases one and two above.
There is no point in trying to debug
a DLL with GNU/GDB, if there is no GDB-compatible debugging
information in it. To do so you must use a debugger compatible with the
tools suite used to build the DLL.





• Program and DLL Both Built with GCC/GNAT:  



• Program Built with Foreign Tools and DLL Built with GCC/GNAT:  












Next: , Up: Debugging a DLL   [Contents][Index]





7.4.7.26 Program and DLL Both Built with GCC/GNAT




This is the simplest case. Both the DLL and the program have GDB
compatible debugging information. It is then possible to break anywhere in
the process. Let’s suppose here that the main procedure is named
ada_main and that in the DLL there is an entry point named
ada_dll.



The DLL (Introduction to Dynamic Link Libraries (DLLs)) and
program must have been built with the debugging information (see GNAT -g
switch). Here are the step-by-step instructions for debugging it:






At this stage a breakpoint is set inside the DLL. From there on
you can use the standard approach to debug the whole program
(Running and Debugging Ada Programs).









Previous: Program and DLL Both Built with GCC/GNAT, Up: Debugging a DLL   [Contents][Index]





7.4.7.27 Program Built with Foreign Tools and DLL Built with GCC/GNAT




In this case things are slightly more complex because it is not possible to
start the main program and then break at the beginning to load the DLL and the
associated DLL debugging information. It is not possible to break at the
beginning of the program because there is no GDB debugging information,
and therefore there is no direct way of getting initial control. This
section addresses this issue by describing some methods that can be used
to break somewhere in the DLL to debug it.



First suppose that the main procedure is named main (this is for
example some C code built with Microsoft Visual C) and that there is a
DLL named test.dll containing an Ada entry point named
ada_dll.



The DLL (see Introduction to Dynamic Link Libraries (DLLs)) must have
been built with debugging information (see the GNAT -g option).




Debugging the DLL Directly







It is also possible to debug the DLL by attaching to a running process.




Attaching to a Running Process







With GDB it is always possible to debug a running process by
attaching to it. It is possible to debug a DLL this way. The limitation
of this approach is that the DLL must run long enough to perform the
attach operation. It may be useful for instance to insert a time wasting
loop in the code of the DLL to meet this criterion.






This last step will resume the process execution, and stop at
the breakpoint we have set. From there you can use the standard
approach to debug a program as described in
Running and Debugging Ada Programs.









Next: , Previous: Debugging a DLL, Up: Mixed-Language Programming on Windows   [Contents][Index]





7.4.7.28 Setting Stack Size from gnatlink




It is possible to specify the program stack size at link time. On modern
versions of Windows, starting with XP, this is mostly useful to set the size of
the main stack (environment task). The other task stacks are set with pragma
Storage_Size or with the `gnatbind -d' command.



Since older versions of Windows (2000, NT4, etc.) do not allow setting the
reserve size of individual tasks, the link-time stack size applies to all
tasks, and pragma Storage_Size has no effect.
In particular, Stack Overflow checks are made against this
link-time specified size.



This setting can be done with gnatlink using either of the following:












Previous: Setting Stack Size from gnatlink, Up: Mixed-Language Programming on Windows   [Contents][Index]





7.4.7.29 Setting Heap Size from gnatlink




Under Windows systems, it is possible to specify the program heap size from
gnatlink using either of the following:












Previous: Mixed-Language Programming on Windows, Up: Microsoft Windows Topics   [Contents][Index]





7.4.8 Windows Specific Add-Ons




This section describes the Windows specific add-ons.





• Win32Ada:  



• wPOSIX:  












Next: , Up: Windows Specific Add-Ons   [Contents][Index]





7.4.8.1 Win32Ada




Win32Ada is a binding for the Microsoft Win32 API. This binding can be
easily installed from the provided installer. To use the Win32Ada
binding you need to use a project file, and adding a single with_clause
will give you full access to the Win32Ada binding sources and ensure
that the proper libraries are passed to the linker.








with "win32ada";
project P is
   for Sources use ...;
end P;






To build the application you just need to call gprbuild for the
application’s project, here p.gpr:








gprbuild p.gpr












Previous: Win32Ada, Up: Windows Specific Add-Ons   [Contents][Index]





7.4.8.2 wPOSIX




wPOSIX is a minimal POSIX binding whose goal is to help with building
cross-platforms applications. This binding is not complete though, as
the Win32 API does not provide the necessary support for all POSIX APIs.



To use the wPOSIX binding you need to use a project file, and adding
a single with_clause will give you full access to the wPOSIX binding
sources and ensure that the proper libraries are passed to the linker.








with "wposix";
project P is
   for Sources use ...;
end P;






To build the application you just need to call gprbuild for the
application’s project, here p.gpr:








gprbuild p.gpr












Previous: Microsoft Windows Topics, Up: Platform-Specific Information   [Contents][Index]





7.5 Mac OS Topics






This section describes topics that are specific to Apple’s OS X
platform.





• Codesigning the Debugger:  












Up: Mac OS Topics   [Contents][Index]





7.5.1 Codesigning the Debugger




The Darwin Kernel requires the debugger to have special permissions
before it is allowed to control other processes. These permissions
are granted by codesigning the GDB executable. Without these
permissions, the debugger will report error messages such as:





Starting program: /x/y/foo
Unable to find Mach task port for process-id 28885: (os/kern) failure (0x5).
(please check gdb is codesigned - see taskgated(8))




Codesigning requires a certificate.  The following procedure explains
how to create one:






Once a certificate has been created, the debugger can be codesigned
as follow. In a Terminal, run the following command:








$ codesign -f -s  "gdb-cert"  <gnat_install_prefix>/bin/gdb






where "gdb-cert" should be replaced by the actual certificate
name chosen above, and <gnat_install_prefix> should be replaced by
the location where you installed GNAT.  Also, be sure that users are
in the Unix group _developer.









Next: , Previous: Platform-Specific Information, Up: Top   [Contents][Index]





8 Example of Binder Output File






This Appendix displays the source code for the output file
generated by `gnatbind' for a simple ’Hello World’ program.
Comments have been added for clarification purposes.





--  The package is called Ada_Main unless this name is actually used
--  as a unit name in the partition, in which case some other unique
--  name is used.

pragma Ada_95;
with System;
package ada_main is
   pragma Warnings (Off);

   --  The main program saves the parameters (argument count,
   --  argument values, environment pointer) in global variables
   --  for later access by other units including
   --  Ada.Command_Line.

   gnat_argc : Integer;
   gnat_argv : System.Address;
   gnat_envp : System.Address;

   --  The actual variables are stored in a library routine. This
   --  is useful for some shared library situations, where there
   --  are problems if variables are not in the library.

   pragma Import (C, gnat_argc);
   pragma Import (C, gnat_argv);
   pragma Import (C, gnat_envp);

   --  The exit status is similarly an external location

   gnat_exit_status : Integer;
   pragma Import (C, gnat_exit_status);

   GNAT_Version : constant String :=
                    "GNAT Version: Pro 7.4.0w (20141119-49)" & ASCII.NUL;
   pragma Export (C, GNAT_Version, "__gnat_version");

   Ada_Main_Program_Name : constant String := "_ada_hello" & ASCII.NUL;
   pragma Export (C, Ada_Main_Program_Name, "__gnat_ada_main_program_name");

   --  This is the generated adainit routine that performs
   --  initialization at the start of execution. In the case
   --  where Ada is the main program, this main program makes
   --  a call to adainit at program startup.

   procedure adainit;
   pragma Export (C, adainit, "adainit");

   --  This is the generated adafinal routine that performs
   --  finalization at the end of execution. In the case where
   --  Ada is the main program, this main program makes a call
   --  to adafinal at program termination.

   procedure adafinal;
   pragma Export (C, adafinal, "adafinal");

   --  This routine is called at the start of execution. It is
   --  a dummy routine that is used by the debugger to breakpoint
   --  at the start of execution.

   --  This is the actual generated main program (it would be
   --  suppressed if the no main program switch were used). As
   --  required by standard system conventions, this program has
   --  the external name main.

   function main
     (argc : Integer;
      argv : System.Address;
      envp : System.Address)
      return Integer;
   pragma Export (C, main, "main");

   --  The following set of constants give the version
   --  identification values for every unit in the bound
   --  partition. This identification is computed from all
   --  dependent semantic units, and corresponds to the
   --  string that would be returned by use of the
   --  Body_Version or Version attributes.

   --  The following Export pragmas export the version numbers
   --  with symbolic names ending in B (for body) or S
   --  (for spec) so that they can be located in a link. The
   --  information provided here is sufficient to track down
   --  the exact versions of units used in a given build.

   type Version_32 is mod 2 ** 32;
   u00001 : constant Version_32 := 16#8ad6e54a#;
   pragma Export (C, u00001, "helloB");
   u00002 : constant Version_32 := 16#fbff4c67#;
   pragma Export (C, u00002, "system__standard_libraryB");
   u00003 : constant Version_32 := 16#1ec6fd90#;
   pragma Export (C, u00003, "system__standard_libraryS");
   u00004 : constant Version_32 := 16#3ffc8e18#;
   pragma Export (C, u00004, "adaS");
   u00005 : constant Version_32 := 16#28f088c2#;
   pragma Export (C, u00005, "ada__text_ioB");
   u00006 : constant Version_32 := 16#f372c8ac#;
   pragma Export (C, u00006, "ada__text_ioS");
   u00007 : constant Version_32 := 16#2c143749#;
   pragma Export (C, u00007, "ada__exceptionsB");
   u00008 : constant Version_32 := 16#f4f0cce8#;
   pragma Export (C, u00008, "ada__exceptionsS");
   u00009 : constant Version_32 := 16#a46739c0#;
   pragma Export (C, u00009, "ada__exceptions__last_chance_handlerB");
   u00010 : constant Version_32 := 16#3aac8c92#;
   pragma Export (C, u00010, "ada__exceptions__last_chance_handlerS");
   u00011 : constant Version_32 := 16#1d274481#;
   pragma Export (C, u00011, "systemS");
   u00012 : constant Version_32 := 16#a207fefe#;
   pragma Export (C, u00012, "system__soft_linksB");
   u00013 : constant Version_32 := 16#467d9556#;
   pragma Export (C, u00013, "system__soft_linksS");
   u00014 : constant Version_32 := 16#b01dad17#;
   pragma Export (C, u00014, "system__parametersB");
   u00015 : constant Version_32 := 16#630d49fe#;
   pragma Export (C, u00015, "system__parametersS");
   u00016 : constant Version_32 := 16#b19b6653#;
   pragma Export (C, u00016, "system__secondary_stackB");
   u00017 : constant Version_32 := 16#b6468be8#;
   pragma Export (C, u00017, "system__secondary_stackS");
   u00018 : constant Version_32 := 16#39a03df9#;
   pragma Export (C, u00018, "system__storage_elementsB");
   u00019 : constant Version_32 := 16#30e40e85#;
   pragma Export (C, u00019, "system__storage_elementsS");
   u00020 : constant Version_32 := 16#41837d1e#;
   pragma Export (C, u00020, "system__stack_checkingB");
   u00021 : constant Version_32 := 16#93982f69#;
   pragma Export (C, u00021, "system__stack_checkingS");
   u00022 : constant Version_32 := 16#393398c1#;
   pragma Export (C, u00022, "system__exception_tableB");
   u00023 : constant Version_32 := 16#b33e2294#;
   pragma Export (C, u00023, "system__exception_tableS");
   u00024 : constant Version_32 := 16#ce4af020#;
   pragma Export (C, u00024, "system__exceptionsB");
   u00025 : constant Version_32 := 16#75442977#;
   pragma Export (C, u00025, "system__exceptionsS");
   u00026 : constant Version_32 := 16#37d758f1#;
   pragma Export (C, u00026, "system__exceptions__machineS");
   u00027 : constant Version_32 := 16#b895431d#;
   pragma Export (C, u00027, "system__exceptions_debugB");
   u00028 : constant Version_32 := 16#aec55d3f#;
   pragma Export (C, u00028, "system__exceptions_debugS");
   u00029 : constant Version_32 := 16#570325c8#;
   pragma Export (C, u00029, "system__img_intB");
   u00030 : constant Version_32 := 16#1ffca443#;
   pragma Export (C, u00030, "system__img_intS");
   u00031 : constant Version_32 := 16#b98c3e16#;
   pragma Export (C, u00031, "system__tracebackB");
   u00032 : constant Version_32 := 16#831a9d5a#;
   pragma Export (C, u00032, "system__tracebackS");
   u00033 : constant Version_32 := 16#9ed49525#;
   pragma Export (C, u00033, "system__traceback_entriesB");
   u00034 : constant Version_32 := 16#1d7cb2f1#;
   pragma Export (C, u00034, "system__traceback_entriesS");
   u00035 : constant Version_32 := 16#8c33a517#;
   pragma Export (C, u00035, "system__wch_conB");
   u00036 : constant Version_32 := 16#065a6653#;
   pragma Export (C, u00036, "system__wch_conS");
   u00037 : constant Version_32 := 16#9721e840#;
   pragma Export (C, u00037, "system__wch_stwB");
   u00038 : constant Version_32 := 16#2b4b4a52#;
   pragma Export (C, u00038, "system__wch_stwS");
   u00039 : constant Version_32 := 16#92b797cb#;
   pragma Export (C, u00039, "system__wch_cnvB");
   u00040 : constant Version_32 := 16#09eddca0#;
   pragma Export (C, u00040, "system__wch_cnvS");
   u00041 : constant Version_32 := 16#6033a23f#;
   pragma Export (C, u00041, "interfacesS");
   u00042 : constant Version_32 := 16#ece6fdb6#;
   pragma Export (C, u00042, "system__wch_jisB");
   u00043 : constant Version_32 := 16#899dc581#;
   pragma Export (C, u00043, "system__wch_jisS");
   u00044 : constant Version_32 := 16#10558b11#;
   pragma Export (C, u00044, "ada__streamsB");
   u00045 : constant Version_32 := 16#2e6701ab#;
   pragma Export (C, u00045, "ada__streamsS");
   u00046 : constant Version_32 := 16#db5c917c#;
   pragma Export (C, u00046, "ada__io_exceptionsS");
   u00047 : constant Version_32 := 16#12c8cd7d#;
   pragma Export (C, u00047, "ada__tagsB");
   u00048 : constant Version_32 := 16#ce72c228#;
   pragma Export (C, u00048, "ada__tagsS");
   u00049 : constant Version_32 := 16#c3335bfd#;
   pragma Export (C, u00049, "system__htableB");
   u00050 : constant Version_32 := 16#99e5f76b#;
   pragma Export (C, u00050, "system__htableS");
   u00051 : constant Version_32 := 16#089f5cd0#;
   pragma Export (C, u00051, "system__string_hashB");
   u00052 : constant Version_32 := 16#3bbb9c15#;
   pragma Export (C, u00052, "system__string_hashS");
   u00053 : constant Version_32 := 16#807fe041#;
   pragma Export (C, u00053, "system__unsigned_typesS");
   u00054 : constant Version_32 := 16#d27be59e#;
   pragma Export (C, u00054, "system__val_lluB");
   u00055 : constant Version_32 := 16#fa8db733#;
   pragma Export (C, u00055, "system__val_lluS");
   u00056 : constant Version_32 := 16#27b600b2#;
   pragma Export (C, u00056, "system__val_utilB");
   u00057 : constant Version_32 := 16#b187f27f#;
   pragma Export (C, u00057, "system__val_utilS");
   u00058 : constant Version_32 := 16#d1060688#;
   pragma Export (C, u00058, "system__case_utilB");
   u00059 : constant Version_32 := 16#392e2d56#;
   pragma Export (C, u00059, "system__case_utilS");
   u00060 : constant Version_32 := 16#84a27f0d#;
   pragma Export (C, u00060, "interfaces__c_streamsB");
   u00061 : constant Version_32 := 16#8bb5f2c0#;
   pragma Export (C, u00061, "interfaces__c_streamsS");
   u00062 : constant Version_32 := 16#6db6928f#;
   pragma Export (C, u00062, "system__crtlS");
   u00063 : constant Version_32 := 16#4e6a342b#;
   pragma Export (C, u00063, "system__file_ioB");
   u00064 : constant Version_32 := 16#ba56a5e4#;
   pragma Export (C, u00064, "system__file_ioS");
   u00065 : constant Version_32 := 16#b7ab275c#;
   pragma Export (C, u00065, "ada__finalizationB");
   u00066 : constant Version_32 := 16#19f764ca#;
   pragma Export (C, u00066, "ada__finalizationS");
   u00067 : constant Version_32 := 16#95817ed8#;
   pragma Export (C, u00067, "system__finalization_rootB");
   u00068 : constant Version_32 := 16#52d53711#;
   pragma Export (C, u00068, "system__finalization_rootS");
   u00069 : constant Version_32 := 16#769e25e6#;
   pragma Export (C, u00069, "interfaces__cB");
   u00070 : constant Version_32 := 16#4a38bedb#;
   pragma Export (C, u00070, "interfaces__cS");
   u00071 : constant Version_32 := 16#07e6ee66#;
   pragma Export (C, u00071, "system__os_libB");
   u00072 : constant Version_32 := 16#d7b69782#;
   pragma Export (C, u00072, "system__os_libS");
   u00073 : constant Version_32 := 16#1a817b8e#;
   pragma Export (C, u00073, "system__stringsB");
   u00074 : constant Version_32 := 16#639855e7#;
   pragma Export (C, u00074, "system__stringsS");
   u00075 : constant Version_32 := 16#e0b8de29#;
   pragma Export (C, u00075, "system__file_control_blockS");
   u00076 : constant Version_32 := 16#b5b2aca1#;
   pragma Export (C, u00076, "system__finalization_mastersB");
   u00077 : constant Version_32 := 16#69316dc1#;
   pragma Export (C, u00077, "system__finalization_mastersS");
   u00078 : constant Version_32 := 16#57a37a42#;
   pragma Export (C, u00078, "system__address_imageB");
   u00079 : constant Version_32 := 16#bccbd9bb#;
   pragma Export (C, u00079, "system__address_imageS");
   u00080 : constant Version_32 := 16#7268f812#;
   pragma Export (C, u00080, "system__img_boolB");
   u00081 : constant Version_32 := 16#e8fe356a#;
   pragma Export (C, u00081, "system__img_boolS");
   u00082 : constant Version_32 := 16#d7aac20c#;
   pragma Export (C, u00082, "system__ioB");
   u00083 : constant Version_32 := 16#8365b3ce#;
   pragma Export (C, u00083, "system__ioS");
   u00084 : constant Version_32 := 16#6d4d969a#;
   pragma Export (C, u00084, "system__storage_poolsB");
   u00085 : constant Version_32 := 16#e87cc305#;
   pragma Export (C, u00085, "system__storage_poolsS");
   u00086 : constant Version_32 := 16#e34550ca#;
   pragma Export (C, u00086, "system__pool_globalB");
   u00087 : constant Version_32 := 16#c88d2d16#;
   pragma Export (C, u00087, "system__pool_globalS");
   u00088 : constant Version_32 := 16#9d39c675#;
   pragma Export (C, u00088, "system__memoryB");
   u00089 : constant Version_32 := 16#445a22b5#;
   pragma Export (C, u00089, "system__memoryS");
   u00090 : constant Version_32 := 16#6a859064#;
   pragma Export (C, u00090, "system__storage_pools__subpoolsB");
   u00091 : constant Version_32 := 16#e3b008dc#;
   pragma Export (C, u00091, "system__storage_pools__subpoolsS");
   u00092 : constant Version_32 := 16#63f11652#;
   pragma Export (C, u00092, "system__storage_pools__subpools__finalizationB");
   u00093 : constant Version_32 := 16#fe2f4b3a#;
   pragma Export (C, u00093, "system__storage_pools__subpools__finalizationS");

   --  BEGIN ELABORATION ORDER
   --  ada%s
   --  interfaces%s
   --  system%s
   --  system.case_util%s
   --  system.case_util%b
   --  system.htable%s
   --  system.img_bool%s
   --  system.img_bool%b
   --  system.img_int%s
   --  system.img_int%b
   --  system.io%s
   --  system.io%b
   --  system.parameters%s
   --  system.parameters%b
   --  system.crtl%s
   --  interfaces.c_streams%s
   --  interfaces.c_streams%b
   --  system.standard_library%s
   --  system.exceptions_debug%s
   --  system.exceptions_debug%b
   --  system.storage_elements%s
   --  system.storage_elements%b
   --  system.stack_checking%s
   --  system.stack_checking%b
   --  system.string_hash%s
   --  system.string_hash%b
   --  system.htable%b
   --  system.strings%s
   --  system.strings%b
   --  system.os_lib%s
   --  system.traceback_entries%s
   --  system.traceback_entries%b
   --  ada.exceptions%s
   --  system.soft_links%s
   --  system.unsigned_types%s
   --  system.val_llu%s
   --  system.val_util%s
   --  system.val_util%b
   --  system.val_llu%b
   --  system.wch_con%s
   --  system.wch_con%b
   --  system.wch_cnv%s
   --  system.wch_jis%s
   --  system.wch_jis%b
   --  system.wch_cnv%b
   --  system.wch_stw%s
   --  system.wch_stw%b
   --  ada.exceptions.last_chance_handler%s
   --  ada.exceptions.last_chance_handler%b
   --  system.address_image%s
   --  system.exception_table%s
   --  system.exception_table%b
   --  ada.io_exceptions%s
   --  ada.tags%s
   --  ada.streams%s
   --  ada.streams%b
   --  interfaces.c%s
   --  system.exceptions%s
   --  system.exceptions%b
   --  system.exceptions.machine%s
   --  system.finalization_root%s
   --  system.finalization_root%b
   --  ada.finalization%s
   --  ada.finalization%b
   --  system.storage_pools%s
   --  system.storage_pools%b
   --  system.finalization_masters%s
   --  system.storage_pools.subpools%s
   --  system.storage_pools.subpools.finalization%s
   --  system.storage_pools.subpools.finalization%b
   --  system.memory%s
   --  system.memory%b
   --  system.standard_library%b
   --  system.pool_global%s
   --  system.pool_global%b
   --  system.file_control_block%s
   --  system.file_io%s
   --  system.secondary_stack%s
   --  system.file_io%b
   --  system.storage_pools.subpools%b
   --  system.finalization_masters%b
   --  interfaces.c%b
   --  ada.tags%b
   --  system.soft_links%b
   --  system.os_lib%b
   --  system.secondary_stack%b
   --  system.address_image%b
   --  system.traceback%s
   --  ada.exceptions%b
   --  system.traceback%b
   --  ada.text_io%s
   --  ada.text_io%b
   --  hello%b
   --  END ELABORATION ORDER

end ada_main;






pragma Ada_95;
--  The following source file name pragmas allow the generated file
--  names to be unique for different main programs. They are needed
--  since the package name will always be Ada_Main.

pragma Source_File_Name (ada_main, Spec_File_Name => "b~hello.ads");
pragma Source_File_Name (ada_main, Body_File_Name => "b~hello.adb");

pragma Suppress (Overflow_Check);
with Ada.Exceptions;

--  Generated package body for Ada_Main starts here

package body ada_main is
   pragma Warnings (Off);

   --  These values are reference counter associated to units which have
   --  been elaborated. It is also used to avoid elaborating the
   --  same unit twice.

   E72 : Short_Integer; pragma Import (Ada, E72, "system__os_lib_E");
   E13 : Short_Integer; pragma Import (Ada, E13, "system__soft_links_E");
   E23 : Short_Integer; pragma Import (Ada, E23, "system__exception_table_E");
   E46 : Short_Integer; pragma Import (Ada, E46, "ada__io_exceptions_E");
   E48 : Short_Integer; pragma Import (Ada, E48, "ada__tags_E");
   E45 : Short_Integer; pragma Import (Ada, E45, "ada__streams_E");
   E70 : Short_Integer; pragma Import (Ada, E70, "interfaces__c_E");
   E25 : Short_Integer; pragma Import (Ada, E25, "system__exceptions_E");
   E68 : Short_Integer; pragma Import (Ada, E68, "system__finalization_root_E");
   E66 : Short_Integer; pragma Import (Ada, E66, "ada__finalization_E");
   E85 : Short_Integer; pragma Import (Ada, E85, "system__storage_pools_E");
   E77 : Short_Integer; pragma Import (Ada, E77, "system__finalization_masters_E");
   E91 : Short_Integer; pragma Import (Ada, E91, "system__storage_pools__subpools_E");
   E87 : Short_Integer; pragma Import (Ada, E87, "system__pool_global_E");
   E75 : Short_Integer; pragma Import (Ada, E75, "system__file_control_block_E");
   E64 : Short_Integer; pragma Import (Ada, E64, "system__file_io_E");
   E17 : Short_Integer; pragma Import (Ada, E17, "system__secondary_stack_E");
   E06 : Short_Integer; pragma Import (Ada, E06, "ada__text_io_E");

   Local_Priority_Specific_Dispatching : constant String := "";
   Local_Interrupt_States : constant String := "";

   Is_Elaborated : Boolean := False;

   procedure finalize_library is
   begin
      E06 := E06 - 1;
      declare
         procedure F1;
         pragma Import (Ada, F1, "ada__text_io__finalize_spec");
      begin
         F1;
      end;
      E77 := E77 - 1;
      E91 := E91 - 1;
      declare
         procedure F2;
         pragma Import (Ada, F2, "system__file_io__finalize_body");
      begin
         E64 := E64 - 1;
         F2;
      end;
      declare
         procedure F3;
         pragma Import (Ada, F3, "system__file_control_block__finalize_spec");
      begin
         E75 := E75 - 1;
         F3;
      end;
      E87 := E87 - 1;
      declare
         procedure F4;
         pragma Import (Ada, F4, "system__pool_global__finalize_spec");
      begin
         F4;
      end;
      declare
         procedure F5;
         pragma Import (Ada, F5, "system__storage_pools__subpools__finalize_spec");
      begin
         F5;
      end;
      declare
         procedure F6;
         pragma Import (Ada, F6, "system__finalization_masters__finalize_spec");
      begin
         F6;
      end;
      declare
         procedure Reraise_Library_Exception_If_Any;
         pragma Import (Ada, Reraise_Library_Exception_If_Any, "__gnat_reraise_library_exception_if_any");
      begin
         Reraise_Library_Exception_If_Any;
      end;
   end finalize_library;

   -------------
   -- adainit --
   -------------

   procedure adainit is

      Main_Priority : Integer;
      pragma Import (C, Main_Priority, "__gl_main_priority");
      Time_Slice_Value : Integer;
      pragma Import (C, Time_Slice_Value, "__gl_time_slice_val");
      WC_Encoding : Character;
      pragma Import (C, WC_Encoding, "__gl_wc_encoding");
      Locking_Policy : Character;
      pragma Import (C, Locking_Policy, "__gl_locking_policy");
      Queuing_Policy : Character;
      pragma Import (C, Queuing_Policy, "__gl_queuing_policy");
      Task_Dispatching_Policy : Character;
      pragma Import (C, Task_Dispatching_Policy, "__gl_task_dispatching_policy");
      Priority_Specific_Dispatching : System.Address;
      pragma Import (C, Priority_Specific_Dispatching, "__gl_priority_specific_dispatching");
      Num_Specific_Dispatching : Integer;
      pragma Import (C, Num_Specific_Dispatching, "__gl_num_specific_dispatching");
      Main_CPU : Integer;
      pragma Import (C, Main_CPU, "__gl_main_cpu");
      Interrupt_States : System.Address;
      pragma Import (C, Interrupt_States, "__gl_interrupt_states");
      Num_Interrupt_States : Integer;
      pragma Import (C, Num_Interrupt_States, "__gl_num_interrupt_states");
      Unreserve_All_Interrupts : Integer;
      pragma Import (C, Unreserve_All_Interrupts, "__gl_unreserve_all_interrupts");
      Detect_Blocking : Integer;
      pragma Import (C, Detect_Blocking, "__gl_detect_blocking");
      Default_Stack_Size : Integer;
      pragma Import (C, Default_Stack_Size, "__gl_default_stack_size");
      Leap_Seconds_Support : Integer;
      pragma Import (C, Leap_Seconds_Support, "__gl_leap_seconds_support");

      procedure Runtime_Initialize;
      pragma Import (C, Runtime_Initialize, "__gnat_runtime_initialize");

      Finalize_Library_Objects : No_Param_Proc;
      pragma Import (C, Finalize_Library_Objects, "__gnat_finalize_library_objects");

   --  Start of processing for adainit

   begin

      --  Record various information for this partition.  The values
      --  are derived by the binder from information stored in the ali
      --  files by the compiler.

      if Is_Elaborated then
         return;
      end if;
      Is_Elaborated := True;
      Main_Priority := -1;
      Time_Slice_Value := -1;
      WC_Encoding := 'b';
      Locking_Policy := ' ';
      Queuing_Policy := ' ';
      Task_Dispatching_Policy := ' ';
      Priority_Specific_Dispatching :=
        Local_Priority_Specific_Dispatching'Address;
      Num_Specific_Dispatching := 0;
      Main_CPU := -1;
      Interrupt_States := Local_Interrupt_States'Address;
      Num_Interrupt_States := 0;
      Unreserve_All_Interrupts := 0;
      Detect_Blocking := 0;
      Default_Stack_Size := -1;
      Leap_Seconds_Support := 0;

      Runtime_Initialize;

      Finalize_Library_Objects := finalize_library'access;

      --  Now we have the elaboration calls for all units in the partition.
      --  The Elab_Spec and Elab_Body attributes generate references to the
      --  implicit elaboration procedures generated by the compiler for
      --  each unit that requires elaboration. Increment a counter of
      --  reference for each unit.

      System.Soft_Links'Elab_Spec;
      System.Exception_Table'Elab_Body;
      E23 := E23 + 1;
      Ada.Io_Exceptions'Elab_Spec;
      E46 := E46 + 1;
      Ada.Tags'Elab_Spec;
      Ada.Streams'Elab_Spec;
      E45 := E45 + 1;
      Interfaces.C'Elab_Spec;
      System.Exceptions'Elab_Spec;
      E25 := E25 + 1;
      System.Finalization_Root'Elab_Spec;
      E68 := E68 + 1;
      Ada.Finalization'Elab_Spec;
      E66 := E66 + 1;
      System.Storage_Pools'Elab_Spec;
      E85 := E85 + 1;
      System.Finalization_Masters'Elab_Spec;
      System.Storage_Pools.Subpools'Elab_Spec;
      System.Pool_Global'Elab_Spec;
      E87 := E87 + 1;
      System.File_Control_Block'Elab_Spec;
      E75 := E75 + 1;
      System.File_Io'Elab_Body;
      E64 := E64 + 1;
      E91 := E91 + 1;
      System.Finalization_Masters'Elab_Body;
      E77 := E77 + 1;
      E70 := E70 + 1;
      Ada.Tags'Elab_Body;
      E48 := E48 + 1;
      System.Soft_Links'Elab_Body;
      E13 := E13 + 1;
      System.Os_Lib'Elab_Body;
      E72 := E72 + 1;
      System.Secondary_Stack'Elab_Body;
      E17 := E17 + 1;
      Ada.Text_Io'Elab_Spec;
      Ada.Text_Io'Elab_Body;
      E06 := E06 + 1;
   end adainit;

   --------------
   -- adafinal --
   --------------

   procedure adafinal is
      procedure s_stalib_adafinal;
      pragma Import (C, s_stalib_adafinal, "system__standard_library__adafinal");

      procedure Runtime_Finalize;
      pragma Import (C, Runtime_Finalize, "__gnat_runtime_finalize");

   begin
      if not Is_Elaborated then
         return;
      end if;
      Is_Elaborated := False;
      Runtime_Finalize;
      s_stalib_adafinal;
   end adafinal;

   --  We get to the main program of the partition by using
   --  pragma Import because if we try to with the unit and
   --  call it Ada style, then not only do we waste time
   --  recompiling it, but also, we don't really know the right
   --  switches (e.g.@: identifier character set) to be used
   --  to compile it.

   procedure Ada_Main_Program;
   pragma Import (Ada, Ada_Main_Program, "_ada_hello");

   ----------
   -- main --
   ----------

   --  main is actually a function, as in the ANSI C standard,
   --  defined to return the exit status. The three parameters
   --  are the argument count, argument values and environment
   --  pointer.

   function main
     (argc : Integer;
      argv : System.Address;
      envp : System.Address)
      return Integer
   is
      --  The initialize routine performs low level system
      --  initialization using a standard library routine which
      --  sets up signal handling and performs any other
      --  required setup. The routine can be found in file
      --  a-init.c.

      procedure initialize;
      pragma Import (C, initialize, "__gnat_initialize");

      --  The finalize routine performs low level system
      --  finalization using a standard library routine. The
      --  routine is found in file a-final.c and in the standard
      --  distribution is a dummy routine that does nothing, so
      --  really this is a hook for special user finalization.

      procedure finalize;
      pragma Import (C, finalize, "__gnat_finalize");

      --  The following is to initialize the SEH exceptions

      SEH : aliased array (1 .. 2) of Integer;

      Ensure_Reference : aliased System.Address := Ada_Main_Program_Name'Address;
      pragma Volatile (Ensure_Reference);

   --  Start of processing for main

   begin
      --  Save global variables

      gnat_argc := argc;
      gnat_argv := argv;
      gnat_envp := envp;

      --  Call low level system initialization

      Initialize (SEH'Address);

      --  Call our generated Ada initialization routine

      adainit;

      --  Now we call the main program of the partition

      Ada_Main_Program;

      --  Perform Ada finalization

      adafinal;

      --  Perform low level system finalization

      Finalize;

      --  Return the proper exit status
      return (gnat_exit_status);
   end;

--  This section is entirely comments, so it has no effect on the
--  compilation of the Ada_Main package. It provides the list of
--  object files and linker options, as well as some standard
--  libraries needed for the link. The gnatlink utility parses
--  this b~hello.adb file to read these comment lines to generate
--  the appropriate command line arguments for the call to the
--  system linker. The BEGIN/END lines are used for sentinels for
--  this parsing operation.

--  The exact file names will of course depend on the environment,
--  host/target and location of files on the host system.

-- BEGIN Object file/option list
   --   ./hello.o
   --   -L./
   --   -L/usr/local/gnat/lib/gcc-lib/i686-pc-linux-gnu/2.8.1/adalib/
   --   /usr/local/gnat/lib/gcc-lib/i686-pc-linux-gnu/2.8.1/adalib/libgnat.a
-- END Object file/option list

end ada_main;




The Ada code in the above example is exactly what is generated by the
binder. We have added comments to more clearly indicate the function
of each part of the generated Ada_Main package.



The code is standard Ada in all respects, and can be processed by any
tools that handle Ada. In particular, it is possible to use the debugger
in Ada mode to debug the generated Ada_Main package. For example,
suppose that for reasons that you do not understand, your program is crashing
during elaboration of the body of Ada.Text_IO. To locate this bug,
you can place a breakpoint on the call:








Ada.Text_Io'Elab_Body;






and trace the elaboration routine for this package to find out where
the problem might be (more usually of course you would be debugging
elaboration code in your own application).










Next: , Previous: Example of Binder Output File, Up: Top   [Contents][Index]





9 Elaboration Order Handling in GNAT








This appendix describes the handling of elaboration code in Ada and GNAT, and
discusses how the order of elaboration of program units can be controlled in
GNAT, either automatically or with explicit programming features.





• Elaboration Code:  



• Elaboration Order:  



• Checking the Elaboration Order:  



• Controlling the Elaboration Order in Ada:  



• Controlling the Elaboration Order in GNAT:  



• Mixing Elaboration Models:  



• ABE Diagnostics:  



• SPARK Diagnostics:  



• Elaboration Circularities:  



• Resolving Elaboration Circularities:  



• Elaboration-related Compiler Switches:  



• Summary of Procedures for Elaboration Control:  



• Inspecting the Chosen Elaboration Order:  












Next: , Up: Elaboration Order Handling in GNAT   [Contents][Index]





9.1 Elaboration Code




Ada defines the term `execution' as the process by which a construct achieves
its run-time effect. This process is also referred to as `elaboration' for
declarations and `evaluation' for expressions.



The execution model in Ada allows for certain sections of an Ada program to be
executed prior to execution of the program itself, primarily with the intent of
initializing data. These sections are referred to as `elaboration code'.
Elaboration code is executed as follows:






In addition to the Ada terminology, this appendix defines the following terms:






Elaboration code may appear in two distinct contexts:












Next: , Previous: Elaboration Code, Up: Elaboration Order Handling in GNAT   [Contents][Index]





9.2 Elaboration Order




The sequence by which the elaboration code of all units within a partition is
executed is referred to as `elaboration order'.



Within a single unit, elaboration code is executed in sequential order.








package body Client is
   Result : ... := Server.Func;

   procedure Proc is
      package Inst is new Server.Gen;
   begin
      Inst.Eval (Result);
   end Proc;
begin
   Proc;
end Client;






In the example above, the elaboration order within package body Client is
as follows:




    

  1.  The object declaration of Result is elaborated.





  2.  The subprogram body of Proc is elaborated.


  3.  Procedure Proc is invoked.







The elaboration order of all units within a partition depends on the following
factors:






A program may have several elaboration orders depending on its structure.








package Server is
   function Func (Index : Integer) return Integer;
end Server;






package body Server is
   Results : array (1 .. 5) of Integer := (1, 2, 3, 4, 5);

   function Func (Index : Integer) return Integer is
   begin
      return Results (Index);
   end Func;
end Server;






with Server;
package Client is
   Val : constant Integer := Server.Func (3);
end Client;






with Client;
procedure Main is begin null; end Main;






The following elaboration order exhibits a fundamental problem referred to as
`access-before-elaboration' or simply `ABE'.








spec of Server
spec of Client
body of Server
body of Main






The elaboration of Server’s spec materializes function Func, making it
callable. The elaboration of Client’s spec elaborates the declaration of
Val. This invokes function Server.Func, however the body of
Server.Func has not been elaborated yet because Server’s body comes
after Client’s spec in the elaboration order. As a result, the value of
constant Val is now undefined.



Without any guarantees from the language, an undetected ABE problem may hinder
proper initialization of data, which in turn may lead to undefined behavior at
run time. To prevent such ABE problems, Ada employs dynamic checks in the same
vein as index or null exclusion checks. A failed ABE check raises exception
Program_Error.



The following elaboration order avoids the ABE problem and the program can be
successfully elaborated.








spec of Server
body of Server
spec of Client
body of Main






Ada states that a total elaboration order must exist, but it does not define
what this order is. A compiler is thus tasked with choosing a suitable
elaboration order which satisfies the dependencies imposed by `with' clauses,
unit categorization, elaboration-control pragmas, and invocations performed in
elaboration code. Ideally an order that avoids ABE problems should be chosen,
however a compiler may not always find such an order due to complications with
respect to control and data flow.









Next: , Previous: Elaboration Order, Up: Elaboration Order Handling in GNAT   [Contents][Index]





9.3 Checking the Elaboration Order




To avoid placing the entire elaboration-order burden on the programmer, Ada
provides three lines of defense:












Next: , Previous: Checking the Elaboration Order, Up: Elaboration Order Handling in GNAT   [Contents][Index]





9.4 Controlling the Elaboration Order in Ada




Ada provides several idioms and pragmas to aid the programmer with specifying
the desired elaboration order and avoiding ABE problems altogether.





















The pragmas outlined above allow a server unit to guarantee safe elaboration
use by client units. Thus it is a good rule to mark units as Pure or
Preelaborate, and if this is not possible, mark them as Elaborate_Body.



There are however situations where Pure, Preelaborate, and
Elaborate_Body are not applicable. Ada provides another set of pragmas for
use by client units to help ensure the elaboration safety of server units they
depend on.













All pragmas shown above can be summarized by the following rule:



`If a client unit elaborates a server target directly or indirectly, then if
the server unit requires a body and does not have pragma Pure, Preelaborate,
or Elaborate_Body, then the client unit should have pragma Elaborate or
Elaborate_All for the server unit.'



If the rule outlined above is not followed, then a program may fall in one of
the following states:






Note that one additional advantage of using Elaborate and Elaborate_All
is that the program continues to stay in the last state (one or more correct
orders exist) even if maintenance changes the bodies of targets.









Next: , Previous: Controlling the Elaboration Order in Ada, Up: Elaboration Order Handling in GNAT   [Contents][Index]





9.5 Controlling the Elaboration Order in GNAT




In addition to Ada semantics and rules synthesized from them, GNAT offers
three elaboration models to aid the programmer with specifying the correct
elaboration order and to diagnose elaboration problems.

























The dynamic, legacy, and static models can be relaxed using compiler switch
-gnatJ, making them more permissive. Note that in this mode, GNAT
may not diagnose certain elaboration issues or install run-time checks.









Next: , Previous: Controlling the Elaboration Order in GNAT, Up: Elaboration Order Handling in GNAT   [Contents][Index]





9.6 Mixing Elaboration Models




It is possible to mix units compiled with a different elaboration model,
however the following rules must be observed:






These rules ensure that elaboration checks are not omitted. If the rules are
violated, the binder emits a warning:








warning: "x.ads" has dynamic elaboration checks and with's
warning:   "y.ads" which has static elaboration checks






The warnings can be suppressed by binder switch -ws.









Next: , Previous: Mixing Elaboration Models, Up: Elaboration Order Handling in GNAT   [Contents][Index]





9.7 ABE Diagnostics




GNAT performs extensive diagnostics on a unit-by-unit basis for all scenarios
that invoke internal targets, regardless of whether the dynamic, SPARK, or
static model is in effect.



Note that GNAT emits warnings rather than hard errors whenever it encounters an
elaboration problem. This is because the elaboration model in effect may be too
conservative, or a particular scenario may not be invoked due conditional
execution. The warnings can be suppressed selectively with pragma Warnings
(Off) or globally with compiler switch -gnatwL.



A `guaranteed ABE' arises when the body of a target is not elaborated early
enough, and causes `all' scenarios that directly invoke the target to fail.








package body Guaranteed_ABE is
   function ABE return Integer;

   Val : constant Integer := ABE;

   function ABE return Integer is
   begin
     ...
   end ABE;
end Guaranteed_ABE;






In the example above, the elaboration of Guaranteed_ABE’s body elaborates
the declaration of Val. This invokes function ABE, however the body of
ABE has not been elaborated yet. GNAT emits the following diagnostic:








4.    Val : constant Integer := ABE;
                                |
   >>> warning: cannot call "ABE" before body seen
   >>> warning: Program_Error will be raised at run time






A `conditional ABE' arises when the body of a target is not elaborated early
enough, and causes `some' scenarios that directly invoke the target to fail.








 1. package body Conditional_ABE is
 2.    procedure Force_Body is null;
 3.
 4.    generic
 5.       with function Func return Integer;
 6.    package Gen is
 7.       Val : constant Integer := Func;
 8.    end Gen;
 9.
10.    function ABE return Integer;
11.
12.    function Cause_ABE return Boolean is
13.       package Inst is new Gen (ABE);
14.    begin
15.       ...
16.    end Cause_ABE;
17.
18.    Val : constant Boolean := Cause_ABE;
19.
20.    function ABE return Integer is
21.    begin
22.       ...
23.    end ABE;
24.
25.    Safe : constant Boolean := Cause_ABE;
26. end Conditional_ABE;






In the example above, the elaboration of package body Conditional_ABE
elaborates the declaration of Val. This invokes function Cause_ABE,
which instantiates generic unit Gen as Inst. The elaboration of
Inst invokes function ABE, however the body of ABE has not been
elaborated yet. GNAT emits the following diagnostic:








13.       package Inst is new Gen (ABE);
          |
    >>> warning: in instantiation at line 7
    >>> warning: cannot call "ABE" before body seen
    >>> warning: Program_Error may be raised at run time
    >>> warning:   body of unit "Conditional_ABE" elaborated
    >>> warning:   function "Cause_ABE" called at line 18
    >>> warning:   function "ABE" called at line 7, instance at line 13






Note that the same ABE problem does not occur with the elaboration of
declaration Safe because the body of function ABE has already been
elaborated at that point.









Next: , Previous: ABE Diagnostics, Up: Elaboration Order Handling in GNAT   [Contents][Index]





9.8 SPARK Diagnostics




GNAT enforces the SPARK rules of elaboration as defined in the SPARK Reference
Manual section 7.7 when compiler switch -gnatd.v is in effect. Note
that GNAT emits hard errors whenever it encounters a violation of the SPARK
rules.








1. with Server;
2. package body SPARK_Diagnostics with SPARK_Mode is
3.    Val : constant Integer := Server.Func;
                                      |
   >>> call to "Func" during elaboration in SPARK
   >>> unit "SPARK_Diagnostics" requires pragma "Elaborate_All" for "Server"
   >>>   body of unit "SPARK_Model" elaborated
   >>>   function "Func" called at line 3

4. end SPARK_Diagnostics;












Next: , Previous: SPARK Diagnostics, Up: Elaboration Order Handling in GNAT   [Contents][Index]





9.9 Elaboration Circularities




An `elaboration circularity' occurs whenever the elaboration of a set of
units enters a deadlocked state, where each unit is waiting for another unit
to be elaborated. This situation may be the result of improper use of `with'
clauses, elaboration-control pragmas, or invocations in elaboration code.



The following example exhibits an elaboration circularity.








with B; pragma Elaborate (B);
package A is
end A;






package B is
   procedure Force_Body;
end B;






with C;
package body B is
   procedure Force_Body is null;

   Elab : constant Integer := C.Func;
end B;






package C is
   function Func return Integer;
end C;






with A;
package body C is
   function Func return Integer is
   begin
      ...
   end Func;
end C;






The binder emits the following diagnostic:








error: Elaboration circularity detected
info:
info:    Reason:
info:
info:      unit "a (spec)" depends on its own elaboration
info:
info:    Circularity:
info:
info:      unit "a (spec)" has with clause and pragma Elaborate for unit "b (spec)"
info:      unit "b (body)" is in the closure of pragma Elaborate
info:      unit "b (body)" invokes a construct of unit "c (body)" at elaboration time
info:      unit "c (body)" has with clause for unit "a (spec)"
info:
info:    Suggestions:
info:
info:      remove pragma Elaborate for unit "b (body)" in unit "a (spec)"
info:      use the dynamic elaboration model (compiler switch -gnatE)






The diagnostic consist of the following sections:












Next: , Previous: Elaboration Circularities, Up: Elaboration Order Handling in GNAT   [Contents][Index]





9.10 Resolving Elaboration Circularities




The most desirable option from the point of view of long-term maintenance is to
rearrange the program so that the elaboration problems are avoided. One useful
technique is to place the elaboration code into separate child packages.
Another is to move some of the initialization code to explicitly invoked
subprograms, where the program controls the order of initialization explicitly.
Although this is the most desirable option, it may be impractical and involve
too much modification, especially in the case of complex legacy code.



When faced with an elaboration circularity, the programmer should also consider
the tactics given in the suggestions section of the circularity diagnostic.
Depending on the units involved in the circularity, their `with' clauses,
purity, preelaborability, presence of elaboration-control pragmas and
invocations at elaboration time, the binder may suggest one or more of the
following tactics to eliminate the circularity:






If none of the tactics suggested by the binder eliminate the elaboration
circularity, the programmer should consider using one of the legacy elaboration
models, in the following order:












Next: , Previous: Resolving Elaboration Circularities, Up: Elaboration Order Handling in GNAT   [Contents][Index]





9.11 Elaboration-related Compiler Switches




GNAT has several switches that affect the elaboration model and consequently
the elaboration order chosen by the binder.








-gnatE




Dynamic elaboration checking mode enabled



When this switch is in effect, GNAT activates the dynamic model.











-gnatel




Turn on info messages on generated Elaborate[_All] pragmas



This switch is only applicable to the pre-20.x legacy elaboration models.
The post-20.x elaboration model no longer relies on implicitly generated
Elaborate and Elaborate_All pragmas to order units.



When this switch is in effect, GNAT will emit the following supplementary
information depending on the elaboration model in effect.















-gnatH




Legacy elaboration checking mode enabled



When this switch is in effect, GNAT will utilize the pre-18.x elaboration
model.











-gnatJ




Relaxed elaboration checking mode enabled



When this switch is in effect, GNAT will not process certain scenarios,
resulting in a more permissive elaboration model. Note that this may
eliminate some diagnostics and run-time checks.











-gnatw.f




Turn on warnings for suspicious Subp’Access



When this switch is in effect, GNAT will treat 'Access of an entry,
operator, or subprogram as a potential call to the target and issue warnings:





 1. package body Attribute_Call is
 2.    function Func return Integer;
 3.    type Func_Ptr is access function return Integer;
 4.
 5.    Ptr : constant Func_Ptr := Func'Access;
                                      |
    >>> warning: "Access" attribute of "Func" before body seen
    >>> warning: possible Program_Error on later references
    >>> warning:   body of unit "Attribute_Call" elaborated
    >>> warning:   "Access" of "Func" taken at line 5

 6.
 7.    function Func return Integer is
 8.    begin
 9.       ...
10.    end Func;
11. end Attribute_Call;




In the example above, the elaboration of declaration Ptr is assigned
Func'Access before the body of Func has been elaborated.











-gnatwl




Turn on warnings for elaboration problems



When this switch is in effect, GNAT emits diagnostics in the form of warnings
concerning various elaboration problems. The warnings are enabled by default.
The switch is provided in case all warnings are suppressed, but elaboration
warnings are still desired.





-gnatwL




Turn off warnings for elaboration problems



When this switch is in effect, GNAT no longer emits any diagnostics in the
form of warnings. Selective suppression of elaboration problems is possible
using pragma Warnings (Off).





 1. package body Selective_Suppression is
 2.    function ABE return Integer;
 3.
 4.    Val_1 : constant Integer := ABE;
                                   |
    >>> warning: cannot call "ABE" before body seen
    >>> warning: Program_Error will be raised at run time

 5.
 6.    pragma Warnings (Off);
 7.    Val_2 : constant Integer := ABE;
 8.    pragma Warnings (On);
 9.
10.    function ABE return Integer is
11.    begin
12.       ...
13.    end ABE;
14. end Selective_Suppression;




Note that suppressing elaboration warnings does not eliminate run-time
checks. The example above will still fail at run time with an ABE.












Next: , Previous: Elaboration-related Compiler Switches, Up: Elaboration Order Handling in GNAT   [Contents][Index]





9.12 Summary of Procedures for Elaboration Control




A programmer should first compile the program with the default options, using
none of the binder or compiler switches. If the binder succeeds in finding an
elaboration order, then apart from possible cases involing dispatching calls
and access-to-subprogram types, the program is free of elaboration errors.



If it is important for the program to be portable to compilers other than GNAT,
then the programmer should use compiler switch -gnatel and consider
the messages about missing or implicitly created Elaborate and
Elaborate_All pragmas.



If the binder reports an elaboration circularity, the programmer has several
options:












Previous: Summary of Procedures for Elaboration Control, Up: Elaboration Order Handling in GNAT   [Contents][Index]





9.13 Inspecting the Chosen Elaboration Order




To see the elaboration order chosen by the binder, inspect the contents of file
b~xxx.adb. On certain targets, this file appears as b_xxx.adb. The
elaboration order appears as a sequence of calls to Elab_Body and
Elab_Spec, interspersed with assignments to Exxx which indicates that a
particular unit is elaborated. For example:








System.Soft_Links'Elab_Body;
E14 := True;
System.Secondary_Stack'Elab_Body;
E18 := True;
System.Exception_Table'Elab_Body;
E24 := True;
Ada.Io_Exceptions'Elab_Spec;
E67 := True;
Ada.Tags'Elab_Spec;
Ada.Streams'Elab_Spec;
E43 := True;
Interfaces.C'Elab_Spec;
E69 := True;
System.Finalization_Root'Elab_Spec;
E60 := True;
System.Os_Lib'Elab_Body;
E71 := True;
System.Finalization_Implementation'Elab_Spec;
System.Finalization_Implementation'Elab_Body;
E62 := True;
Ada.Finalization'Elab_Spec;
E58 := True;
Ada.Finalization.List_Controller'Elab_Spec;
E76 := True;
System.File_Control_Block'Elab_Spec;
E74 := True;
System.File_Io'Elab_Body;
E56 := True;
Ada.Tags'Elab_Body;
E45 := True;
Ada.Text_Io'Elab_Spec;
Ada.Text_Io'Elab_Body;
E07 := True;






Note also binder switch -l, which outputs the chosen elaboration
order and provides a more readable form of the above:








ada (spec)
interfaces (spec)
system (spec)
system.case_util (spec)
system.case_util (body)
system.concat_2 (spec)
system.concat_2 (body)
system.concat_3 (spec)
system.concat_3 (body)
system.htable (spec)
system.parameters (spec)
system.parameters (body)
system.crtl (spec)
interfaces.c_streams (spec)
interfaces.c_streams (body)
system.restrictions (spec)
system.restrictions (body)
system.standard_library (spec)
system.exceptions (spec)
system.exceptions (body)
system.storage_elements (spec)
system.storage_elements (body)
system.secondary_stack (spec)
system.stack_checking (spec)
system.stack_checking (body)
system.string_hash (spec)
system.string_hash (body)
system.htable (body)
system.strings (spec)
system.strings (body)
system.traceback (spec)
system.traceback (body)
system.traceback_entries (spec)
system.traceback_entries (body)
ada.exceptions (spec)
ada.exceptions.last_chance_handler (spec)
system.soft_links (spec)
system.soft_links (body)
ada.exceptions.last_chance_handler (body)
system.secondary_stack (body)
system.exception_table (spec)
system.exception_table (body)
ada.io_exceptions (spec)
ada.tags (spec)
ada.streams (spec)
interfaces.c (spec)
interfaces.c (body)
system.finalization_root (spec)
system.finalization_root (body)
system.memory (spec)
system.memory (body)
system.standard_library (body)
system.os_lib (spec)
system.os_lib (body)
system.unsigned_types (spec)
system.stream_attributes (spec)
system.stream_attributes (body)
system.finalization_implementation (spec)
system.finalization_implementation (body)
ada.finalization (spec)
ada.finalization (body)
ada.finalization.list_controller (spec)
ada.finalization.list_controller (body)
system.file_control_block (spec)
system.file_io (spec)
system.file_io (body)
system.val_uns (spec)
system.val_util (spec)
system.val_util (body)
system.val_uns (body)
system.wch_con (spec)
system.wch_con (body)
system.wch_cnv (spec)
system.wch_jis (spec)
system.wch_jis (body)
system.wch_cnv (body)
system.wch_stw (spec)
system.wch_stw (body)
ada.tags (body)
ada.exceptions (body)
ada.text_io (spec)
ada.text_io (body)
text_io (spec)
gdbstr (body)












Next: , Previous: Elaboration Order Handling in GNAT, Up: Top   [Contents][Index]





10 Inline Assembler






If you need to write low-level software that interacts directly
with the hardware, Ada provides two ways to incorporate assembly
language code into your program.  First, you can import and invoke
external routines written in assembly language, an Ada feature fully
supported by GNAT.  However, for small sections of code it may be simpler
or more efficient to include assembly language statements directly
in your Ada source program, using the facilities of the implementation-defined
package System.Machine_Code, which incorporates the gcc
Inline Assembler.  The Inline Assembler approach offers a number of advantages,
including the following:






This appendix presents a series of examples to show you how to use
the Inline Assembler.  Although it focuses on the Intel x86,
the general approach applies also to other processors.
It is assumed that you are familiar with Ada
and with assembly language programming.





• Basic Assembler Syntax:  



• A Simple Example of Inline Assembler:  



• Output Variables in Inline Assembler:  



• Input Variables in Inline Assembler:  



• Inlining Inline Assembler Code:  



• Other Asm Functionality:  












Next: , Up: Inline Assembler   [Contents][Index]





10.1 Basic Assembler Syntax




The assembler used by GNAT and gcc is based not on the Intel assembly
language, but rather on a language that descends from the AT&T Unix
assembler as (and which is often referred to as ’AT&T syntax’).
The following table summarizes the main features of as syntax
and points out the differences from the Intel conventions.
See the gcc as and gas (an as macro
pre-processor) documentation for further information.






`Register names' 



gcc / as: Prefix with ’%’; for example %eax 
Intel: No extra punctuation; for example eax 











`Immediate operand' 



gcc / as: Prefix with ’$’; for example $4 
Intel: No extra punctuation; for example 4 











`Address' 



gcc / as: Prefix with ’$’; for example $loc 
Intel: No extra punctuation; for example loc 











`Memory contents' 



gcc / as: No extra punctuation; for example loc 
Intel: Square brackets; for example [loc] 











`Register contents' 



gcc / as: Parentheses; for example (%eax) 
Intel: Square brackets; for example [eax] 











`Hexadecimal numbers' 



gcc / as: Leading ’0x’ (C language syntax); for example 0xA0 
Intel: Trailing ’h’; for example A0h 











`Operand size' 



gcc / as: Explicit in op code; for example movw to move a 16-bit word 
Intel: Implicit, deduced by assembler; for example mov 











`Instruction repetition' 



gcc / as: Split into two lines; for example 



rep 
stosl 



Intel: Keep on one line; for example rep stosl 











`Order of operands' 



gcc / as: Source first; for example movw $4, %eax 
Intel: Destination first; for example mov eax, 4 














Next: , Previous: Basic Assembler Syntax, Up: Inline Assembler   [Contents][Index]





10.2 A Simple Example of Inline Assembler




The following example will generate a single assembly language statement,
nop, which does nothing.  Despite its lack of run-time effect,
the example will be useful in illustrating the basics of
the Inline Assembler facility.








with System.Machine_Code; use System.Machine_Code;
procedure Nothing is
begin
   Asm ("nop");
end Nothing;






Asm is a procedure declared in package System.Machine_Code;
here it takes one parameter, a `template string' that must be a static
expression and that will form the generated instruction.
Asm may be regarded as a compile-time procedure that parses
the template string and additional parameters (none here),
from which it generates a sequence of assembly language instructions.



The examples in this chapter will illustrate several of the forms
for invoking Asm; a complete specification of the syntax
is found in the Machine_Code_Insertions section of the
GNAT Reference Manual.



Under the standard GNAT conventions, the Nothing procedure
should be in a file named nothing.adb.
You can build the executable in the usual way:








$ gnatmake nothing






However, the interesting aspect of this example is not its run-time behavior
but rather the generated assembly code.
To see this output, invoke the compiler as follows:








$  gcc -c -S -fomit-frame-pointer -gnatp nothing.adb






where the options are:






This gives a human-readable assembler version of the code. The resulting
file will have the same name as the Ada source file, but with a .s
extension. In our example, the file nothing.s has the following
contents:








.file "nothing.adb"
gcc2_compiled.:
___gnu_compiled_ada:
.text
   .align 4
.globl __ada_nothing
__ada_nothing:
#APP
   nop
#NO_APP
   jmp L1
   .align 2,0x90
L1:
   ret






The assembly code you included is clearly indicated by
the compiler, between the #APP and #NO_APP
delimiters. The character before the ’APP’ and ’NOAPP’
can differ on different targets. For example, GNU/Linux uses ’#APP’ while
on NT you will see ’/APP’.



If you make a mistake in your assembler code (such as using the
wrong size modifier, or using a wrong operand for the instruction) GNAT
will report this error in a temporary file, which will be deleted when
the compilation is finished.  Generating an assembler file will help
in such cases, since you can assemble this file separately using the
as assembler that comes with gcc.



Assembling the file using the command








$ as nothing.s






will give you error messages whose lines correspond to the assembler
input file, so you can easily find and correct any mistakes you made.
If there are no errors, as will generate an object file
nothing.out.









Next: , Previous: A Simple Example of Inline Assembler, Up: Inline Assembler   [Contents][Index]





10.3 Output Variables in Inline Assembler




The examples in this section, showing how to access the processor flags,
illustrate how to specify the destination operands for assembly language
statements.








with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Get_Flags is
   Flags : Unsigned_32;
   use ASCII;
begin
   Asm ("pushfl"          & LF & HT & -- push flags on stack
        "popl %%eax"      & LF & HT & -- load eax with flags
        "movl %%eax, %0",             -- store flags in variable
        Outputs => Unsigned_32'Asm_Output ("=g", Flags));
   Put_Line ("Flags register:" & Flags'Img);
end Get_Flags;






In order to have a nicely aligned assembly listing, we have separated
multiple assembler statements in the Asm template string with linefeed
(ASCII.LF) and horizontal tab (ASCII.HT) characters.
The resulting section of the assembly output file is:








#APP
   pushfl
   popl %eax
   movl %eax, -40(%ebp)
#NO_APP






It would have been legal to write the Asm invocation as:








Asm ("pushfl popl %%eax movl %%eax, %0")






but in the generated assembler file, this would come out as:








#APP
   pushfl popl %eax movl %eax, -40(%ebp)
#NO_APP






which is not so convenient for the human reader.



We use Ada comments
at the end of each line to explain what the assembler instructions
actually do.  This is a useful convention.



When writing Inline Assembler instructions, you need to precede each register
and variable name with a percent sign.  Since the assembler already requires
a percent sign at the beginning of a register name, you need two consecutive
percent signs for such names in the Asm template string, thus %%eax.
In the generated assembly code, one of the percent signs will be stripped off.



Names such as %0, %1, %2, etc., denote input or output
variables: operands you later define using Input or Output
parameters to Asm.
An output variable is illustrated in
the third statement in the Asm template string:








movl %%eax, %0






The intent is to store the contents of the eax register in a variable that can
be accessed in Ada.  Simply writing movl %%eax, Flags would not
necessarily work, since the compiler might optimize by using a register
to hold Flags, and the expansion of the movl instruction would not be
aware of this optimization.  The solution is not to store the result directly
but rather to advise the compiler to choose the correct operand form;
that is the purpose of the %0 output variable.



Information about the output variable is supplied in the Outputs
parameter to Asm:








Outputs => Unsigned_32'Asm_Output ("=g", Flags));






The output is defined by the Asm_Output attribute of the target type;
the general format is








Type'Asm_Output (constraint_string, variable_name)






The constraint string directs the compiler how
to store/access the associated variable.  In the example








Unsigned_32'Asm_Output ("=m", Flags);






the "m" (memory) constraint tells the compiler that the variable
Flags should be stored in a memory variable, thus preventing
the optimizer from keeping it in a register.  In contrast,








Unsigned_32'Asm_Output ("=r", Flags);






uses the "r" (register) constraint, telling the compiler to
store the variable in a register.



If the constraint is preceded by the equal character ’=’, it tells
the compiler that the variable will be used to store data into it.



In the Get_Flags example, we used the "g" (global) constraint,
allowing the optimizer to choose whatever it deems best.



There are a fairly large number of constraints, but the ones that are
most useful (for the Intel x86 processor) are the following:









`='output constraint


`g'global (i.e., can be stored anywhere)


`m'in memory


`I'a constant


`a'use eax


`b'use ebx


`c'use ecx


`d'use edx


`S'use esi


`D'use edi


`r'use one of eax, ebx, ecx or edx


`q'use one of eax, ebx, ecx, edx, esi or edi








The full set of constraints is described in the gcc and as
documentation; note that it is possible to combine certain constraints
in one constraint string.



You specify the association of an output variable with an assembler operand
through the %`n' notation, where `n' is a non-negative
integer.  Thus in








Asm ("pushfl"          & LF & HT & -- push flags on stack
     "popl %%eax"      & LF & HT & -- load eax with flags
     "movl %%eax, %0",             -- store flags in variable
     Outputs => Unsigned_32'Asm_Output ("=g", Flags));






%0 will be replaced in the expanded code by the appropriate operand,
whatever
the compiler decided for the Flags variable.



In general, you may have any number of output variables:






For example:








Asm ("movl %%eax, %0" & LF & HT &
     "movl %%ebx, %1" & LF & HT &
     "movl %%ecx, %2",
     Outputs => (Unsigned_32'Asm_Output ("=g", Var_A),   --  %0 = Var_A
                 Unsigned_32'Asm_Output ("=g", Var_B),   --  %1 = Var_B
                 Unsigned_32'Asm_Output ("=g", Var_C))); --  %2 = Var_C






where Var_A, Var_B, and Var_C are variables
in the Ada program.



As a variation on the Get_Flags example, we can use the constraints
string to direct the compiler to store the eax register into the Flags
variable, instead of including the store instruction explicitly in the
Asm template string:








with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Get_Flags_2 is
   Flags : Unsigned_32;
   use ASCII;
begin
   Asm ("pushfl"      & LF & HT & -- push flags on stack
        "popl %%eax",             -- save flags in eax
        Outputs => Unsigned_32'Asm_Output ("=a", Flags));
   Put_Line ("Flags register:" & Flags'Img);
end Get_Flags_2;






The "a" constraint tells the compiler that the Flags
variable will come from the eax register. Here is the resulting code:








#APP
   pushfl
   popl %eax
#NO_APP
   movl %eax,-40(%ebp)






The compiler generated the store of eax into Flags after
expanding the assembler code.



Actually, there was no need to pop the flags into the eax register;
more simply, we could just pop the flags directly into the program variable:








with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Get_Flags_3 is
   Flags : Unsigned_32;
   use ASCII;
begin
   Asm ("pushfl"  & LF & HT & -- push flags on stack
        "pop %0",             -- save flags in Flags
        Outputs => Unsigned_32'Asm_Output ("=g", Flags));
   Put_Line ("Flags register:" & Flags'Img);
end Get_Flags_3;












Next: , Previous: Output Variables in Inline Assembler, Up: Inline Assembler   [Contents][Index]





10.4 Input Variables in Inline Assembler




The example in this section illustrates how to specify the source operands
for assembly language statements.
The program simply increments its input value by 1:








with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Increment is

   function Incr (Value : Unsigned_32) return Unsigned_32 is
      Result : Unsigned_32;
   begin
      Asm ("incl %0",
           Outputs => Unsigned_32'Asm_Output ("=a", Result),
           Inputs  => Unsigned_32'Asm_Input ("a", Value));
      return Result;
   end Incr;

   Value : Unsigned_32;

begin
   Value := 5;
   Put_Line ("Value before is" & Value'Img);
   Value := Incr (Value);
  Put_Line ("Value after is" & Value'Img);
end Increment;






The Outputs parameter to Asm specifies
that the result will be in the eax register and that it is to be stored
in the Result variable.



The Inputs parameter looks much like the Outputs parameter,
but with an Asm_Input attribute.
The "=" constraint, indicating an output value, is not present.



You can have multiple input variables, in the same way that you can have more
than one output variable.



The parameter count (%0, %1) etc, still starts at the first output statement,
and continues with the input statements.



Just as the Outputs parameter causes the register to be stored into the
target variable after execution of the assembler statements, so does the
Inputs parameter cause its variable to be loaded into the register
before execution of the assembler statements.



Thus the effect of the Asm invocation is:






The resulting assembler file (with -O2 optimization) contains:








_increment__incr.1:
   subl $4,%esp
   movl 8(%esp),%eax
#APP
   incl %eax
#NO_APP
   movl %eax,%edx
   movl %ecx,(%esp)
   addl $4,%esp
   ret












Next: , Previous: Input Variables in Inline Assembler, Up: Inline Assembler   [Contents][Index]





10.5 Inlining Inline Assembler Code




For a short subprogram such as the Incr function in the previous
section, the overhead of the call and return (creating / deleting the stack
frame) can be significant, compared to the amount of code in the subprogram
body.  A solution is to apply Ada’s Inline pragma to the subprogram,
which directs the compiler to expand invocations of the subprogram at the
point(s) of call, instead of setting up a stack frame for out-of-line calls.
Here is the resulting program:








with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Increment_2 is

   function Incr (Value : Unsigned_32) return Unsigned_32 is
      Result : Unsigned_32;
   begin
      Asm ("incl %0",
           Outputs => Unsigned_32'Asm_Output ("=a", Result),
           Inputs  => Unsigned_32'Asm_Input ("a", Value));
      return Result;
   end Incr;
   pragma Inline (Increment);

   Value : Unsigned_32;

begin
   Value := 5;
   Put_Line ("Value before is" & Value'Img);
   Value := Increment (Value);
   Put_Line ("Value after is" & Value'Img);
end Increment_2;






Compile the program with both optimization (-O2) and inlining
(-gnatn) enabled.



The Incr function is still compiled as usual, but at the
point in Increment where our function used to be called:








pushl %edi
call _increment__incr.1






the code for the function body directly appears:








movl %esi,%eax
#APP
   incl %eax
#NO_APP
   movl %eax,%edx






thus saving the overhead of stack frame setup and an out-of-line call.









Previous: Inlining Inline Assembler Code, Up: Inline Assembler   [Contents][Index]





10.6 Other Asm Functionality




This section describes two important parameters to the Asm
procedure: Clobber, which identifies register usage;
and Volatile, which inhibits unwanted optimizations.





• The Clobber Parameter:  



• The Volatile Parameter:  












Next: , Up: Other Asm Functionality   [Contents][Index]





10.6.1 The Clobber Parameter




One of the dangers of intermixing assembly language and a compiled language
such as Ada is that the compiler needs to be aware of which registers are
being used by the assembly code.  In some cases, such as the earlier examples,
the constraint string is sufficient to indicate register usage (e.g.,
"a" for
the eax register).  But more generally, the compiler needs an explicit
identification of the registers that are used by the Inline Assembly
statements.



Using a register that the compiler doesn’t know about
could be a side effect of an instruction (like mull
storing its result in both eax and edx).
It can also arise from explicit register usage in your
assembly code; for example:








Asm ("movl %0, %%ebx" & LF & HT &
     "movl %%ebx, %1",
     Outputs => Unsigned_32'Asm_Output ("=g", Var_Out),
     Inputs  => Unsigned_32'Asm_Input  ("g", Var_In));






where the compiler (since it does not analyze the Asm template string)
does not know you are using the ebx register.



In such cases you need to supply the Clobber parameter to Asm,
to identify the registers that will be used by your assembly code:








Asm ("movl %0, %%ebx" & LF & HT &
     "movl %%ebx, %1",
     Outputs => Unsigned_32'Asm_Output ("=g", Var_Out),
     Inputs  => Unsigned_32'Asm_Input  ("g", Var_In),
     Clobber => "ebx");






The Clobber parameter is a static string expression specifying the
register(s) you are using.  Note that register names are `not' prefixed
by a percent sign. Also, if more than one register is used then their names
are separated by commas; e.g., "eax, ebx"



The Clobber parameter has several additional uses:












Previous: The Clobber Parameter, Up: Other Asm Functionality   [Contents][Index]





10.6.2 The Volatile Parameter






Compiler optimizations in the presence of Inline Assembler may sometimes have
unwanted effects.  For example, when an Asm invocation with an input
variable is inside a loop, the compiler might move the loading of the input
variable outside the loop, regarding it as a one-time initialization.



If this effect is not desired, you can disable such optimizations by setting
the Volatile parameter to True; for example:








Asm ("movl %0, %%ebx" & LF & HT &
     "movl %%ebx, %1",
     Outputs  => Unsigned_32'Asm_Output ("=g", Var_Out),
     Inputs   => Unsigned_32'Asm_Input  ("g", Var_In),
     Clobber  => "ebx",
     Volatile => True);






By default, Volatile is set to False unless there is no
Outputs parameter.



Although setting Volatile to True prevents unwanted
optimizations, it will also disable other optimizations that might be
important for efficiency. In general, you should set Volatile
to True only if the compiler’s optimizations have created
problems.









Next: , Previous: Inline Assembler, Up: Top   [Contents][Index]





11 GNU Free Documentation License




Version 1.3, 3 November 2008



Copyright  2000, 2001, 2002, 2007, 2008  Free Software Foundation, Inc
‘http://fsf.org/’



Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.



`Preamble'



The purpose of this License is to make a manual, textbook, or other
functional and useful document "free" in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or noncommercially.
Secondarily, this License preserves for the author and publisher a way
to get credit for their work, while not being considered responsible
for modifications made by others.



This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense.  It
complements the GNU General Public License, which is a copyleft
license designed for free software.



We have designed this License in order to use it for manuals for free
software, because free software needs free documentation: a free
program should come with manuals providing the same freedoms that the
software does.  But this License is not limited to software manuals;
it can be used for any textual work, regardless of subject matter or
whether it is published as a printed book.  We recommend this License
principally for works whose purpose is instruction or reference.



`1. APPLICABILITY AND DEFINITIONS'



This License applies to any manual or other work, in any medium, that
contains a notice placed by the copyright holder saying it can be
distributed under the terms of this License.  Such a notice grants a
world-wide, royalty-free license, unlimited in duration, to use that
work under the conditions stated herein.  The `Document', below,
refers to any such manual or work.  Any member of the public is a
licensee, and is addressed as "`you'".  You accept the license if you
copy, modify or distribute the work in a way requiring permission
under copyright law.



A "`Modified Version'" of the Document means any work containing the
Document or a portion of it, either copied verbatim, or with
modifications and/or translated into another language.



A "`Secondary Section'" is a named appendix or a front-matter section of
the Document that deals exclusively with the relationship of the
publishers or authors of the Document to the Document’s overall subject
(or to related matters) and contains nothing that could fall directly
within that overall subject.  (Thus, if the Document is in part a
textbook of mathematics, a Secondary Section may not explain any
mathematics.)  The relationship could be a matter of historical
connection with the subject or with related matters, or of legal,
commercial, philosophical, ethical or political position regarding
them.



The "`Invariant Sections'" are certain Secondary Sections whose titles
are designated, as being those of Invariant Sections, in the notice
that says that the Document is released under this License.  If a
section does not fit the above definition of Secondary then it is not
allowed to be designated as Invariant.  The Document may contain zero
Invariant Sections.  If the Document does not identify any Invariant
Sections then there are none.



The "`Cover Texts'" are certain short passages of text that are listed,
as Front-Cover Texts or Back-Cover Texts, in the notice that says that
the Document is released under this License.  A Front-Cover Text may
be at most 5 words, and a Back-Cover Text may be at most 25 words.



A "`Transparent'" copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the
general public, that is suitable for revising the document
straightforwardly with generic text editors or (for images composed of
pixels) generic paint programs or (for drawings) some widely available
drawing editor, and that is suitable for input to text formatters or
for automatic translation to a variety of formats suitable for input
to text formatters.  A copy made in an otherwise Transparent file
format whose markup, or absence of markup, has been arranged to thwart
or discourage subsequent modification by readers is not Transparent.
An image format is not Transparent if used for any substantial amount
of text.  A copy that is not "Transparent" is called `Opaque'.



Examples of suitable formats for Transparent copies include plain
ASCII without markup, Texinfo input format, LaTeX input format, SGML
or XML using a publicly available DTD, and standard-conforming simple
HTML, PostScript or PDF designed for human modification.  Examples of
transparent image formats include PNG, XCF and JPG.  Opaque formats
include proprietary formats that can be read and edited only by
proprietary word processors, SGML or XML for which the DTD and/or
processing tools are not generally available, and the
machine-generated HTML, PostScript or PDF produced by some word
processors for output purposes only.



The "`Title Page'" means, for a printed book, the title page itself,
plus such following pages as are needed to hold, legibly, the material
this License requires to appear in the title page.  For works in
formats which do not have any title page as such, "Title Page" means
the text near the most prominent appearance of the work’s title,
preceding the beginning of the body of the text.



The "`publisher'" means any person or entity that distributes
copies of the Document to the public.



A section "`Entitled XYZ'" means a named subunit of the Document whose
title either is precisely XYZ or contains XYZ in parentheses following
text that translates XYZ in another language.  (Here XYZ stands for a
specific section name mentioned below, such as "`Acknowledgements'",
"`Dedications'", "`Endorsements'", or "`History'".)
To "`Preserve the Title'"
of such a section when you modify the Document means that it remains a
section "Entitled XYZ" according to this definition.



The Document may include Warranty Disclaimers next to the notice which
states that this License applies to the Document.  These Warranty
Disclaimers are considered to be included by reference in this
License, but only as regards disclaiming warranties: any other
implication that these Warranty Disclaimers may have is void and has
no effect on the meaning of this License.



`2. VERBATIM COPYING'



You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License applies
to the Document are reproduced in all copies, and that you add no other
conditions whatsoever to those of this License.  You may not use
technical measures to obstruct or control the reading or further
copying of the copies you make or distribute.  However, you may accept
compensation in exchange for copies.  If you distribute a large enough
number of copies you must also follow the conditions in section 3.



You may also lend copies, under the same conditions stated above, and
you may publicly display copies.



`3. COPYING IN QUANTITY'



If you publish printed copies (or copies in media that commonly have
printed covers) of the Document, numbering more than 100, and the
Document’s license notice requires Cover Texts, you must enclose the
copies in covers that carry, clearly and legibly, all these Cover
Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on
the back cover.  Both covers must also clearly and legibly identify
you as the publisher of these copies.  The front cover must present
the full title with all words of the title equally prominent and
visible.  You may add other material on the covers in addition.
Copying with changes limited to the covers, as long as they preserve
the title of the Document and satisfy these conditions, can be treated
as verbatim copying in other respects.



If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto adjacent
pages.



If you publish or distribute Opaque copies of the Document numbering
more than 100, you must either include a machine-readable Transparent
copy along with each Opaque copy, or state in or with each Opaque copy
a computer-network location from which the general network-using
public has access to download using public-standard network protocols
a complete Transparent copy of the Document, free of added material.
If you use the latter option, you must take reasonably prudent steps,
when you begin distribution of Opaque copies in quantity, to ensure
that this Transparent copy will remain thus accessible at the stated
location until at least one year after the last time you distribute an
Opaque copy (directly or through your agents or retailers) of that
edition to the public.



It is requested, but not required, that you contact the authors of the
Document well before redistributing any large number of copies, to give
them a chance to provide you with an updated version of the Document.



`4. MODIFICATIONS'



You may copy and distribute a Modified Version of the Document under
the conditions of sections 2 and 3 above, provided that you release
the Modified Version under precisely this License, with the Modified
Version filling the role of the Document, thus licensing distribution
and modification of the Modified Version to whoever possesses a copy
of it.  In addition, you must do these things in the Modified Version:




    

  1.  Use in the Title Page (and on the covers, if any) a title distinct
from that of the Document, and from those of previous versions
(which should, if there were any, be listed in the History section
of the Document).  You may use the same title as a previous version
if the original publisher of that version gives permission.


  2.  List on the Title Page, as authors, one or more persons or entities
responsible for authorship of the modifications in the Modified
Version, together with at least five of the principal authors of the
Document (all of its principal authors, if it has fewer than five),
unless they release you from this requirement.


  3.  State on the Title page the name of the publisher of the
Modified Version, as the publisher.


  4.  Preserve all the copyright notices of the Document.


  5.  Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.


  6.  Include, immediately after the copyright notices, a license notice
giving the public permission to use the Modified Version under the
terms of this License, in the form shown in the Addendum below.


  7.  Preserve in that license notice the full lists of Invariant Sections
and required Cover Texts given in the Document’s license notice.


  8.  Include an unaltered copy of this License.


  9.  Preserve the section Entitled "History", Preserve its Title, and add
to it an item stating at least the title, year, new authors, and
publisher of the Modified Version as given on the Title Page.  If
there is no section Entitled "History" in the Document, create one
stating the title, year, authors, and publisher of the Document as
given on its Title Page, then add an item describing the Modified
Version as stated in the previous sentence.


  10.  Preserve the network location, if any, given in the Document for
public access to a Transparent copy of the Document, and likewise
the network locations given in the Document for previous versions
it was based on.  These may be placed in the "History" section.
You may omit a network location for a work that was published at
least four years before the Document itself, or if the original
publisher of the version it refers to gives permission.


  11.  For any section Entitled "Acknowledgements" or "Dedications",
Preserve the Title of the section, and preserve in the section all
the substance and tone of each of the contributor acknowledgements
and/or dedications given therein.


  12.  Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles.  Section numbers
or the equivalent are not considered part of the section titles.


  13.  Delete any section Entitled "Endorsements".  Such a section
may not be included in the Modified Version.


  14.  Do not retitle any existing section to be Entitled "Endorsements"
or to conflict in title with any Invariant Section.


  15.  Preserve any Warranty Disclaimers.




If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no material
copied from the Document, you may at your option designate some or all
of these sections as invariant.  To do this, add their titles to the
list of Invariant Sections in the Modified Version’s license notice.
These titles must be distinct from any other section titles.



You may add a section Entitled "Endorsements", provided it contains
nothing but endorsements of your Modified Version by various
parties—for example, statements of peer review or that the text has
been approved by an organization as the authoritative definition of a
standard.



You may add a passage of up to five words as a Front-Cover Text, and a
passage of up to 25 words as a Back-Cover Text, to the end of the list
of Cover Texts in the Modified Version.  Only one passage of
Front-Cover Text and one of Back-Cover Text may be added by (or
through arrangements made by) any one entity.  If the Document already
includes a cover text for the same cover, previously added by you or
by arrangement made by the same entity you are acting on behalf of,
you may not add another; but you may replace the old one, on explicit
permission from the previous publisher that added the old one.



The author(s) and publisher(s) of the Document do not by this License
give permission to use their names for publicity for or to assert or
imply endorsement of any Modified Version.



`5. COMBINING DOCUMENTS'



You may combine the Document with other documents released under this
License, under the terms defined in section 4 above for modified
versions, provided that you include in the combination all of the
Invariant Sections of all of the original documents, unmodified, and
list them all as Invariant Sections of your combined work in its
license notice, and that you preserve all their Warranty Disclaimers.



The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy.  If there are multiple Invariant Sections with the same name but
different contents, make the title of each such section unique by
adding at the end of it, in parentheses, the name of the original
author or publisher of that section if known, or else a unique number.
Make the same adjustment to the section titles in the list of
Invariant Sections in the license notice of the combined work.



In the combination, you must combine any sections Entitled "History"
in the various original documents, forming one section Entitled
"History"; likewise combine any sections Entitled "Acknowledgements",
and any sections Entitled "Dedications".  You must delete all sections
Entitled "Endorsements".



`6. COLLECTIONS OF DOCUMENTS'



You may make a collection consisting of the Document and other documents
released under this License, and replace the individual copies of this
License in the various documents with a single copy that is included in
the collection, provided that you follow the rules of this License for
verbatim copying of each of the documents in all other respects.



You may extract a single document from such a collection, and distribute
it individually under this License, provided you insert a copy of this
License into the extracted document, and follow this License in all
other respects regarding verbatim copying of that document.



`7. AGGREGATION WITH INDEPENDENT WORKS'



A compilation of the Document or its derivatives with other separate
and independent documents or works, in or on a volume of a storage or
distribution medium, is called an "aggregate" if the copyright
resulting from the compilation is not used to limit the legal rights
of the compilation’s users beyond what the individual works permit.
When the Document is included in an aggregate, this License does not
apply to the other works in the aggregate which are not themselves
derivative works of the Document.



If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half of
the entire aggregate, the Document’s Cover Texts may be placed on
covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic form.
Otherwise they must appear on printed covers that bracket the whole
aggregate.



`8. TRANSLATION'



Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section 4.
Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections.  You may include a
translation of this License, and all the license notices in the
Document, and any Warranty Disclaimers, provided that you also include
the original English version of this License and the original versions
of those notices and disclaimers.  In case of a disagreement between
the translation and the original version of this License or a notice
or disclaimer, the original version will prevail.



If a section in the Document is Entitled "Acknowledgements",
"Dedications", or "History", the requirement (section 4) to Preserve
its Title (section 1) will typically require changing the actual
title.



`9. TERMINATION'



You may not copy, modify, sublicense, or distribute the Document
except as expressly provided under this License.  Any attempt
otherwise to copy, modify, sublicense, or distribute it is void, and
will automatically terminate your rights under this License.



However, if you cease all violation of this License, then your license
from a particular copyright holder is reinstated (a) provisionally,
unless and until the copyright holder explicitly and finally
terminates your license, and (b) permanently, if the copyright holder
fails to notify you of the violation by some reasonable means prior to
60 days after the cessation.



Moreover, your license from a particular copyright holder is
reinstated permanently if the copyright holder notifies you of the
violation by some reasonable means, this is the first time you have
received notice of violation of this License (for any work) from that
copyright holder, and you cure the violation prior to 30 days after
your receipt of the notice.



Termination of your rights under this section does not terminate the
licenses of parties who have received copies or rights from you under
this License.  If your rights have been terminated and not permanently
reinstated, receipt of a copy of some or all of the same material does
not give you any rights to use it.



`10. FUTURE REVISIONS OF THIS LICENSE'



The Free Software Foundation may publish new, revised versions
of the GNU Free Documentation License from time to time.  Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns.  See
‘http://www.gnu.org/copyleft/’.



Each version of the License is given a distinguishing version number.
If the Document specifies that a particular numbered version of this
License "or any later version" applies to it, you have the option of
following the terms and conditions either of that specified version or
of any later version that has been published (not as a draft) by the
Free Software Foundation.  If the Document does not specify a version
number of this License, you may choose any version ever published (not
as a draft) by the Free Software Foundation.  If the Document
specifies that a proxy can decide which future versions of this
License can be used, that proxy’s public statement of acceptance of a
version permanently authorizes you to choose that version for the
Document.



`11. RELICENSING'



"Massive Multiauthor Collaboration Site" (or "MMC Site") means any
World Wide Web server that publishes copyrightable works and also
provides prominent facilities for anybody to edit those works.  A
public wiki that anybody can edit is an example of such a server.  A
"Massive Multiauthor Collaboration" (or "MMC") contained in the
site means any set of copyrightable works thus published on the MMC
site.



"CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0
license published by Creative Commons Corporation, a not-for-profit
corporation with a principal place of business in San Francisco,
California, as well as future copyleft versions of that license
published by that same organization.



"Incorporate" means to publish or republish a Document, in whole or
in part, as part of another Document.



An MMC is "eligible for relicensing" if it is licensed under this
License, and if all works that were first published under this License
somewhere other than this MMC, and subsequently incorporated in whole
or in part into the MMC, (1) had no cover texts or invariant sections,
and (2) were thus incorporated prior to November 1, 2008.



The operator of an MMC Site may republish an MMC contained in the site
under CC-BY-SA on the same site at any time before August 1, 2009,
provided the MMC is eligible for relicensing.



`ADDENDUM: How to use this License for your documents'



To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and
license notices just after the title page:






Copyright © YEAR  YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
A copy of the license is included in the section entitled "GNU
Free Documentation License".




If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the "with ... Texts." line with this:






with the Invariant Sections being LIST THEIR TITLES, with the
Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.




If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.



If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License,
to permit their use in free software.









Previous: GNU Free Documentation License, Up: Top   [Contents][Index]





Index




Jump to:   -
   
_
   


A
   
B
   
C
   
D
   
E
   
F
   
G
   
H
   
I
   
L
   
M
   
N
   
O
   
P
   
R
   
S
   
T
   
U
   
V
   
W
   
Z
   





Index Entry  Section


 


-


-83 (gnathtml): Invoking gnathtml


-a (gnatbind): Switches for gnatbind


-A (gnatbind): Switches for gnatbind


-a (gnatdll): Using gnatdll


-a (gnatfind): gnatfind Switches


-a (gnatls): Switches for gnatls


-a (gnatmake): Switches for gnatmake


-A (gnatmake): Switches for gnatmake


-a (gnatxref): gnatxref Switches


-aI (gnatbind): Switches for gnatbind


-aI (gnatbind): Search Paths for gnatbind


-aI (gnatls): Switches for gnatls


-aI (gnatmake): Switches for gnatmake


-aIDIR (gnatfind): gnatfind Switches


-aIDIR (gnatxref): gnatxref Switches


-aL (gnatmake): Switches for gnatmake


-aO (gnatbind): Switches for gnatbind


-aO (gnatbind): Search Paths for gnatbind


-aO (gnatclean): Switches for gnatclean


-aO (gnatls): Switches for gnatls


-aO (gnatmake): Switches for gnatmake


-aODIR (gnatfind): gnatfind Switches


-aODIR (gnatxref): gnatxref Switches


-aP (gnatls): Switches for gnatls


–as (dlltool): Using gnatdll


-b (gcc): Alphabetical List of All Switches


-B (gcc): Alphabetical List of All Switches


-b (gnatbind): Switches for gnatbind


-b (gnatbind): Binder Error Message Control


-b (gnatdll): Using gnatdll


-B (gnatlink): Switches for gnatlink


-b (gnatmake): Switches for gnatmake


-b (gnatprep): Switches for gnatprep


-bargs (gnatdll): Using gnatdll


-bargs (gnatmake): Mode Switches for gnatmake


–base-file (dlltool): Using gnatdll


-C (gcc): Switches


-c (gcc): Alphabetical List of All Switches


-c (gnatbind): Switches for gnatbind


-c (gnatbind): Output Control


-c (gnatchop): Switches for gnatchop


-c (gnatclean): Switches for gnatclean


-c (gnatmake): Switches for gnatmake


-C (gnatmake): Switches for gnatmake


-c (gnatname): Switches for gnatname


-c (gnatprep): Switches for gnatprep


-C (gnatprep): Switches for gnatprep


-C= (gnatmake): Switches for gnatmake


-cargs (gnatmake): Mode Switches for gnatmake


-cc (gnathtml): Invoking gnathtml


–create-missing-dirs (gnatmake): Switches for gnatmake


-D (gnatbind): Switches for gnatbind


-D (gnatclean): Switches for gnatclean


-d (gnatdll): Using gnatdll


-d (gnatfind): gnatfind Switches


-d (gnathtml): Invoking gnathtml


-D (gnathtml): Invoking gnathtml


-d (gnatls): Switches for gnatls


-d (gnatmake): Switches for gnatmake


-D (gnatmake): Switches for gnatmake


-d (gnatname): Switches for gnatname


-D (gnatname): Switches for gnatname


-D (gnatprep): Switches for gnatprep


-d (gnatxref): gnatxref Switches


–def (dlltool): Using gnatdll


–demangle (gprof): Running gprof


–dllname (dlltool): Using gnatdll


-dnn[k|m] (gnatbind): Switches for gnatbind


-e (gnatbind): Switches for gnatbind


-E (gnatbind): Switches for gnatbind


-e (gnatbind): Output Control


-e (gnatdll): Using gnatdll


-e (gnatfind): gnatfind Switches


-e (gprof): Running gprof


-E (gprof): Running gprof


-Ea (gnatbind): Switches for gnatbind


-eI (gnatmake): Switches for gnatmake


-eL (gnatmake): Switches for gnatmake


-Es (gnatbind): Switches for gnatbind


-eS (gnatmake): Switches for gnatmake


–ext (gnatfind): gnatfind Switches


-ext (gnathtml): Invoking gnathtml


–ext (gnatxref): gnatxref Switches


-f (gnatbind): Switches for gnatbind


-F (gnatbind): Switches for gnatbind


-f (gnatbind): Elaboration Control


-F (gnatclean): Switches for gnatclean


-f (gnatfind): gnatfind Switches


-f (gnathtml): Invoking gnathtml


-f (gnatlink): Switches for gnatlink


-f (gnatmake): Switches for gnatmake


-F (gnatmake): Switches for gnatmake


-f (gnatname): Switches for gnatname


-f (gnatxref): gnatxref Switches


-f (gprof): Running gprof


-F (gprof): Running gprof


-fada-spec-parent (gcc): Switches


-fcallgraph-info (gcc): Alphabetical List of All Switches


-fdata-sections (gcc): Compilation options


-fdump-ada-spec (gcc): Switches


-fdump-ada-spec-slim (gcc): Switches


-fdump-scos (gcc): Alphabetical List of All Switches


-ffunction-sections (gcc): Compilation options


-fgnat-encodings (gcc): Alphabetical List of All Switches


-fgnat-encodings (gcc): Debugging Control


-files (gnatls): Switches for gnatls


-flto (gcc): Alphabetical List of All Switches


-fno-inline (gcc): Alphabetical List of All Switches


-fno-inline (gcc): Inlining of Subprograms


-fno-inline-functions (gcc): Alphabetical List of All Switches


-fno-inline-functions (gcc): Inlining of Subprograms


-fno-inline-functions-called-once (gcc): Alphabetical List of All Switches


-fno-inline-functions-called-once (gcc): Inlining of Subprograms


-fno-inline-small-functions (gcc): Alphabetical List of All Switches


-fno-inline-small-functions (gcc): Inlining of Subprograms


-fno-ivopts (gcc): Alphabetical List of All Switches


-fno-strict-aliasing (gcc): Alphabetical List of All Switches


-fno-strict-overflow (gcc): Alphabetical List of All Switches


-fstack-check (gcc): Alphabetical List of All Switches


-fstack-check (gcc): Run-Time Checks


-fstack-check (gcc): Stack Overflow Checking


-fstack-usage: Static Stack Usage Analysis


-fstack-usage (gcc): Alphabetical List of All Switches


-fuse-ld=name: Linker Switches


-fverbose-asm (gcc): Alphabetical List of All Switches


-g (gcc): Alphabetical List of All Switches


-g (gcc): Debugging Optimized Code


-g (gnatdll): Using gnatdll


-g (gnatfind): gnatfind Switches


-g (gnatlink): Switches for gnatlink


-g (gnatmake): Switches for gnatmake


-g (gnatxref): gnatxref Switches


–GCC= (gnatchop): Switches for gnatchop


–GCC=compiler_name (gnatlink): Switches for gnatlink


–GCC=compiler_name (gnatmake): Switches for gnatmake


-gnat-p (gcc): Alphabetical List of All Switches


-gnat-p (gcc): Run-Time Checks


-gnat05 (gcc): Alphabetical List of All Switches


-gnat05 (gcc): Compiling Different Versions of Ada


-gnat12 (gcc): Alphabetical List of All Switches


-gnat12 (gcc): Compiling Different Versions of Ada


-gnat2005 (gcc): Alphabetical List of All Switches


-gnat2005 (gcc): Compiling Different Versions of Ada


-gnat2012 (gcc): Alphabetical List of All Switches


-gnat2012 (gcc): Compiling Different Versions of Ada


-gnat83 (gcc): Alphabetical List of All Switches


-gnat83 (gcc): Compiling Different Versions of Ada


-gnat95 (gcc): Alphabetical List of All Switches


-gnat95 (gcc): Compiling Different Versions of Ada


-gnata (gcc): Alphabetical List of All Switches


-gnatA (gcc): Alphabetical List of All Switches


-gnata (gcc): Debugging and Assertion Control


-gnata switch: Debugging - A Special Case


-gnatb (gcc): Alphabetical List of All Switches


-gnatB (gcc): Alphabetical List of All Switches


-gnatb (gcc): Output and Error Message Control


–GNATBIND=binder_name (gnatmake): Switches for gnatmake


-gnatc (gcc): Alphabetical List of All Switches


-gnatC (gcc): Alphabetical List of All Switches


-gnatc (gcc): Using gcc for Semantic Checking


-gnatd (gcc): Alphabetical List of All Switches


-gnatd (gcc): Debugging Control


-gnatD (gcc): Debugging Control


-gnatdc switch: GNAT Abnormal Termination or Failure to Terminate


-gnatD[nn] (gcc): Alphabetical List of All Switches


-gnatE (gcc): Alphabetical List of All Switches


-gnatE (gcc): Run-Time Checks


-gnatE (gnat): Elaboration-related Compiler Switches


-gnateA (gcc): Alphabetical List of All Switches


-gnatec (gcc): Alphabetical List of All Switches


-gnateC (gcc): Alphabetical List of All Switches


-gnateD (gcc): Integrated Preprocessing


-gnated (gcc): Alphabetical List of All Switches


-gnateD (gcc): Alphabetical List of All Switches


-gnateE (gcc): Alphabetical List of All Switches


-gnatef (gcc): Alphabetical List of All Switches


-gnateF (gcc): Alphabetical List of All Switches


-gnateg (gcc): Alphabetical List of All Switches


-gnateG (gcc): Alphabetical List of All Switches


-gnatei (gcc): Alphabetical List of All Switches


-gnateI (gcc): Alphabetical List of All Switches


-gnatel (gcc): Alphabetical List of All Switches


-gnatel (gcc): Alphabetical List of All Switches


-gnatel (gnat): Elaboration-related Compiler Switches


-gnatem (gcc): Alphabetical List of All Switches


-gnatem (gcc): Units to Sources Mapping Files


-gnatep (gcc): Integrated Preprocessing


-gnatep (gcc): Alphabetical List of All Switches


-gnateP (gcc): Alphabetical List of All Switches


-gnateS (gcc): Alphabetical List of All Switches


-gnateT (gcc): Alphabetical List of All Switches


-gnatet=file (gcc): Alphabetical List of All Switches


-gnateu (gcc): Alphabetical List of All Switches


-gnateV (gcc): Alphabetical List of All Switches


-gnateY (gcc): Alphabetical List of All Switches


-gnatf (gcc): Alphabetical List of All Switches


-gnatF (gcc): Alphabetical List of All Switches


-gnatf (gcc): Output and Error Message Control


-gnatg (gcc): Alphabetical List of All Switches


-gnatG (gcc): Debugging Control


-gnatG[nn] (gcc): Alphabetical List of All Switches


-gnath (gcc): Alphabetical List of All Switches


-gnatH (gcc): Alphabetical List of All Switches


-gnatH (gnat): Elaboration-related Compiler Switches


-gnati (gcc): Alphabetical List of All Switches


-gnatI (gcc): Alphabetical List of All Switches


-gnati (gcc): Character Set Control


-gnatJ (gcc): Alphabetical List of All Switches


-gnatJ (gnat): Elaboration-related Compiler Switches


-gnatjnn (gcc): Alphabetical List of All Switches


-gnatjnn (gcc): Output and Error Message Control


-gnatk (gcc): Alphabetical List of All Switches


-gnatk (gcc): File Naming Control


-gnatl (gcc): Alphabetical List of All Switches


-gnatL (gcc): Alphabetical List of All Switches


-gnatl (gcc): Output and Error Message Control


-gnatL (gcc): Debugging Control


-gnatL (gcc): Debugging Control


-gnatl=fname (gcc): Output and Error Message Control


–GNATLINK=linker_name (gnatmake): Switches for gnatmake


-gnatm (gcc): Alphabetical List of All Switches


-gnatm (gcc): Output and Error Message Control


-gnatn (gcc): Alphabetical List of All Switches


-gnatN (gcc): Alphabetical List of All Switches


-gnatn (gcc): Subprogram Inlining Control


-gnatN (gcc): Subprogram Inlining Control


-gnatn switch: Source Dependencies


-gnatN switch: Source Dependencies


-gnato (gcc): Controlling Run-Time Checks


-gnato (gcc): Default Settings


-gnato0 (gcc): Alphabetical List of All Switches


-gnato? (gcc): Specifying the Desired Mode


-gnato?? (gcc): Alphabetical List of All Switches


-gnato?? (gcc): Run-Time Checks


-gnato?? (gcc): Specifying the Desired Mode


-gnatp (gcc): Alphabetical List of All Switches


-gnatP (gcc): Alphabetical List of All Switches


-gnatp (gcc): Run-Time Checks


-gnatp (gcc): Controlling Run-Time Checks


-gnatq (gcc): Alphabetical List of All Switches


-gnatQ (gcc): Alphabetical List of All Switches


-gnatq (gcc): Output and Error Message Control


-gnatQ (gcc): Output and Error Message Control


-gnatr (gcc): Alphabetical List of All Switches


-gnatR (gcc): Alphabetical List of All Switches


-gnatr (gcc): Debugging Control


-gnatR (gcc): Debugging Control


-gnats (gcc): Alphabetical List of All Switches


-gnatS (gcc): Alphabetical List of All Switches


-gnats (gcc): Using gcc for Syntax Checking


-gnatS (gcc): Debugging Control


-gnatt (gcc): Alphabetical List of All Switches


-gnatT (gcc): Alphabetical List of All Switches


-gnatt (gcc): Auxiliary Output Control


-gnatu (gcc): Alphabetical List of All Switches


-gnatU (gcc): Alphabetical List of All Switches


-gnatU (gcc): Output and Error Message Control


-gnatu (gcc): Auxiliary Output Control


-gnatv (gcc): Alphabetical List of All Switches


-gnatV (gcc): Alphabetical List of All Switches


-gnatv (gcc): Output and Error Message Control


-gnatVa (gcc): Validity Checking


-gnatVc (gcc): Validity Checking


-gnatVd (gcc): Validity Checking


-gnatVe (gcc): Validity Checking


-gnatVf (gcc): Validity Checking


-gnatVi (gcc): Validity Checking


-gnatVm (gcc): Validity Checking


-gnatVn (gcc): Validity Checking


-gnatVo (gcc): Validity Checking


-gnatVp (gcc): Validity Checking


-gnatVr (gcc): Validity Checking


-gnatVs (gcc): Validity Checking


-gnatVt (gcc): Validity Checking


-gnatw (gcc): Alphabetical List of All Switches


-gnatW (gcc): Alphabetical List of All Switches


-gnatW (gcc): Character Set Control


-gnatw.a (gcc): Warning Message Control


-gnatw.A (gcc): Warning Message Control


-gnatw.b (gcc): Warning Message Control


-gnatw.c (gcc): Warning Message Control


-gnatw.C (gcc): Warning Message Control


-gnatw.d (gcc): Warning Message Control


-gnatw.d (gcc): Warning Message Control


-gnatw.e (gcc): Warning Message Control


-gnatw.f (gnat): Elaboration-related Compiler Switches


-gnatw.g (gcc): Warning Message Control


-gnatw.h (gcc): Warning Message Control


-gnatw.H (gcc): Warning Message Control


-gnatw.i (gcc): Warning Message Control


-gnatw.I (gcc): Warning Message Control


-gnatw.j (gcc): Warning Message Control


-gnatw.J (gcc): Warning Message Control


-gnatw.k (gcc): Warning Message Control


-gnatw.l (gcc): Warning Message Control


-gnatw.L (gcc): Warning Message Control


-gnatw.m (gcc): Warning Message Control


-gnatw.M (gcc): Warning Message Control


-gnatw.n (gcc): Warning Message Control


-gnatw.N (gcc): Warning Message Control


-gnatw.o (gcc): Warning Message Control


-gnatw.O (gcc): Warning Message Control


-gnatw.p (gcc): Warning Message Control


-gnatw.P (gcc): Warning Message Control


-gnatw.q (gcc): Warning Message Control


-gnatw.Q (gcc): Warning Message Control


-gnatw.r (gcc): Warning Message Control


-gnatw.R (gcc): Warning Message Control


-gnatw.s (gcc): Warning Message Control


-gnatw.S (gcc): Warning Message Control


-gnatw.t (gcc): Warning Message Control


-gnatw.T (gcc): Warning Message Control


-gnatw.u (gcc): Warning Message Control


-gnatw.U (gcc): Warning Message Control


-gnatw.v (gcc): Warning Message Control


-gnatw.V (gcc): Warning Message Control


-gnatw.w (gcc): Warning Message Control


-gnatw.W (gcc): Warning Message Control


-gnatw.y (gcc): Warning Message Control


-gnatw.Y (gcc): Warning Message Control


-gnatw.z (gcc): Warning Message Control


-gnatw.Z (gcc): Warning Message Control


-gnatwa (gcc): Warning Message Control


-gnatwA (gcc): Warning Message Control


-gnatwb (gcc): Warning Message Control


-gnatwB (gcc): Warning Message Control


-gnatwB (gcc): Warning Message Control


-gnatwc (gcc): Warning Message Control


-gnatwC (gcc): Warning Message Control


-gnatwd (gcc): Warning Message Control


-gnatwD (gcc): Warning Message Control


-gnatwe (gcc): Warning Message Control


-gnatwE (gcc): Warning Message Control


-gnatwf (gcc): Warning Message Control


-gnatwF (gcc): Warning Message Control


-gnatwg (gcc): Warning Message Control


-gnatwG (gcc): Warning Message Control


-gnatwh (gcc): Warning Message Control


-gnatwH (gcc): Warning Message Control


-gnatwi (gcc): Warning Message Control


-gnatwI (gcc): Warning Message Control


-gnatwj (gcc): Warning Message Control


-gnatwJ (gcc): Warning Message Control


-gnatwk (gcc): Warning Message Control


-gnatwK (gcc): Warning Message Control


-gnatwK (gcc): Warning Message Control


-gnatwl (gcc): Warning Message Control


-gnatwL (gcc): Warning Message Control


-gnatwl (gnat): Elaboration-related Compiler Switches


-gnatwm (gcc): Warning Message Control


-gnatwM (gcc): Warning Message Control


-gnatwm (gcc): Warning Message Control


-gnatwn (gcc): Warning Message Control


-gnatwo (gcc): Warning Message Control


-gnatwO (gcc): Warning Message Control


-gnatwp (gcc): Warning Message Control


-gnatwP (gcc): Warning Message Control


-gnatwq (gcc): Warning Message Control


-gnatwQ (gcc): Warning Message Control


-gnatwr (gcc): Warning Message Control


-gnatwR (gcc): Warning Message Control


-gnatws (gcc): Warning Message Control


-gnatwt (gcc): Warning Message Control


-gnatwT (gcc): Warning Message Control


-gnatwu (gcc): Warning Message Control


-gnatwU (gcc): Warning Message Control


-gnatwv (gcc): Warning Message Control


-gnatwV (gcc): Warning Message Control


-gnatww (gcc): Warning Message Control


-gnatwW (gcc): Warning Message Control


-gnatwx (gcc): Warning Message Control


-gnatwX (gcc): Warning Message Control


-gnatwy (gcc): Warning Message Control


-gnatwY (gcc): Warning Message Control


-gnatwz (gcc): Warning Message Control


-gnatwZ (gcc): Warning Message Control


-gnatw_a: Warning Message Control


-gnatw_A: Warning Message Control


-gnatw_c (gcc): Warning Message Control


-gnatw_C (gcc): Warning Message Control


-gnatw_r (gcc): Warning Message Control


-gnatw_R (gcc): Warning Message Control


-gnatx (gcc): Alphabetical List of All Switches


-gnatX (gcc): Alphabetical List of All Switches


-gnatX (gcc): Compiling Different Versions of Ada


-gnatx (gcc): Debugging Control


-gnaty (gcc): Alphabetical List of All Switches


-gnaty (gcc): Style Checking


-gnaty+ (gcc): Style Checking


-gnaty- (gcc): Style Checking


-gnatya (gcc): Style Checking


-gnatyA (gcc): Style Checking


-gnatyb (gcc): Style Checking


-gnatyB (gcc): Style Checking


-gnatyc (gcc): Style Checking


-gnatyC (gcc): Style Checking


-gnatyd (gcc): Style Checking


-gnatyD (gcc): Style Checking


-gnatye (gcc): Style Checking


-gnatyf (gcc): Style Checking


-gnatyg (gcc): Style Checking


-gnatyh (gcc): Style Checking


-gnatyi (gcc): Style Checking


-gnatyI (gcc): Style Checking


-gnatyk (gcc): Style Checking


-gnatyl (gcc): Style Checking


-gnatyLnnn (gcc): Style Checking


-gnatym (gcc): Style Checking


-gnatyMnnn (gcc): Style Checking


-gnatyn (gcc): Style Checking


-gnatyN (gcc): Style Checking


-gnatyo (gcc): Style Checking


-gnatyO (gcc): Style Checking


-gnatyp (gcc): Style Checking


-gnatyr (gcc): Style Checking


-gnatys (gcc): Style Checking


-gnatyS (gcc): Style Checking


-gnatyt (gcc): Style Checking


-gnatyu (gcc): Style Checking


-gnatyx (gcc): Style Checking


-gnatyy (gcc): Style Checking


-gnaty[0-9] (gcc): Style Checking


-gnatz (gcc): Alphabetical List of All Switches


-h (gnatbind): Switches for gnatbind


-H (gnatbind): Switches for gnatbind


-h (gnatbind): Output Control


-h (gnatclean): Switches for gnatclean


-h (gnatdll): Using gnatdll


-h (gnatls): Switches for gnatls


-h (gnatname): Switches for gnatname


-H32 (gnatbind): Switches for gnatbind


-H64 (gnatbind): Switches for gnatbind


–help (dlltool): Using gnatdll


–help (gnatbind): Switches for gnatbind


–help (gnatchop): Switches for gnatchop


–help (gnatclean): Switches for gnatclean


–help (gnatfind): gnatfind Switches


–help (gnatlink): Switches for gnatlink


–help (gnatls): Switches for gnatls


–help (gnatmake): Switches for gnatmake


–help (gnatname): Switches for gnatname


–help (gnatprep): Switches for gnatprep


–help (gnatxref): gnatxref Switches


-I (gcc): Alphabetical List of All Switches


-I (gnatbind): Switches for gnatbind


-I (gnatbind): Search Paths for gnatbind


-I (gnatclean): Switches for gnatclean


-I (gnatdll): Using gnatdll


-I (gnathtml): Invoking gnathtml


-I (gnatls): Switches for gnatls


-i (gnatmake): Switches for gnatmake


-I (gnatmake): Switches for gnatmake


-I- (gcc): Alphabetical List of All Switches


-I- (gnatbind): Switches for gnatbind


-I- (gnatclean): Switches for gnatclean


-I- (gnatls): Switches for gnatls


-I- (gnatmake): Switches for gnatmake


-IDIR (gnatfind): gnatfind Switches


-IDIR (gnatxref): gnatxref Switches


-j (gnatmake): Switches for gnatmake


-k (dlltool): Using gnatdll


-K (gnatbind): Output Control


-k (gnatchop): Switches for gnatchop


-k (gnatdll): Using gnatdll


-k (gnatmake): Switches for gnatmake


-l (gnatbind): Switches for gnatbind


-L (gnatbind): Switches for gnatbind


-l (gnatbind): Output Control


-l (gnatdll): Using gnatdll


-l (gnathtml): Invoking gnathtml


-l (gnatmake): Switches for gnatmake


-L (gnatmake): Switches for gnatmake


-largs (gnatdll): Using gnatdll


-largs (gnatmake): Mode Switches for gnatmake


–LINK= (gnatlink): Switches for gnatlink


-M (gnatbind): Switches for gnatbind


-m (gnatbind): Switches for gnatbind


-m (gnatbind): Binder Error Message Control


-M (gnatbind): Binder Error Message Control


-M (gnatlink): Switches for gnatlink


-m (gnatmake): Switches for gnatmake


-M (gnatmake): Switches for gnatmake


-M= (gnatlink): Switches for gnatlink


-margs (gnatmake): Mode Switches for gnatmake


-minimal (gnatbind): Switches for gnatbind


-mwindows: CONSOLE and WINDOWS subsystems


-n (gnatbind): Switches for gnatbind


-n (gnatbind): Binding with Non-Ada Main Programs


-n (gnatbind): Binding with Non-Ada Main Programs


-n (gnatclean): Switches for gnatclean


-n (gnatdll): Using gnatdll


-n (gnatlink): Switches for gnatlink


-n (gnatmake): Switches for gnatmake


-nostdinc (gcc): Alphabetical List of All Switches


-nostdinc (gnatbind): Switches for gnatbind


-nostdinc (gnatfind): gnatfind Switches


-nostdinc (gnatmake): Switches for gnatmake


-nostdinc (gnatxref): gnatxref Switches


-nostdlib (gcc): Alphabetical List of All Switches


-nostdlib (gnatbind): Switches for gnatbind


-nostdlib (gnatfind): gnatfind Switches


-nostdlib (gnatmake): Switches for gnatmake


-nostdlib (gnatxref): gnatxref Switches


-o (gcc): Alphabetical List of All Switches


-O (gcc): Alphabetical List of All Switches


-O (gcc): Optimization Levels


-o (gnatbind): Switches for gnatbind


-O (gnatbind): Switches for gnatbind


-O (gnatbind): Output Control


-o (gnatbind): Output Control


-o (gnatbind): Binding with Non-Ada Main Programs


-o (gnathtml): Invoking gnathtml


-o (gnatlink): Switches for gnatlink


-o (gnatls): Switches for gnatls


-o (gnatmake): Switches for gnatmake


–output-exp (dlltool): Using gnatdll


–output-lib (dlltool): Using gnatdll


-p (gnatbind): Switches for gnatbind


-P (gnatbind): Switches for gnatbind


-p (gnatbind): Elaboration Control


-p (gnatchop): Switches for gnatchop


-P (gnatclean): Switches for gnatclean


-p (gnathtml): Invoking gnathtml


-p (gnatmake): Switches for gnatmake


-P (gnatmake): Switches for gnatmake


-P (gnatname): Switches for gnatname


-pass-exit-codes (gcc): Alphabetical List of All Switches


-pass-exit-codes (gcc): Auxiliary Output Control


-pFILE (gnatfind): gnatfind Switches


-pFILE (gnatxref): gnatxref Switches


-pg (gcc): Compilation for profiling


-pg (gnatlink): Compilation for profiling


-q (gnatchop): Switches for gnatchop


-q (gnatclean): Switches for gnatclean


-q (gnatdll): Using gnatdll


-q (gnatmake): Switches for gnatmake


-R (gnatbind): Switches for gnatbind


-r (gnatbind): Output Control


-r (gnatchop): Switches for gnatchop


-r (gnatclean): Switches for gnatclean


-r (gnatfind): gnatfind Switches


-r (gnatprep): Switches for gnatprep


-Ra (gnatbind): Switches for gnatbind


–RTS (gcc): Alphabetical List of All Switches


–RTS (gnatbind): Switches for gnatbind


–RTS (gnatfind): gnatfind Switches


–RTS (gnatls): Switches for gnatls


–RTS (gnatmake): Switches for gnatmake


–RTS (gnatxref): gnatxref Switches


–RTS option: Specifying a Run-Time Library


–RTS=sjlj (gnatmake): Exception Handling Control


–RTS=zcx (gnatmake): Exception Handling Control


-S (gcc): Alphabetical List of All Switches


-s (gnatbind): Switches for gnatbind


-S (gnatbind): Switches for gnatbind


-s (gnatbind): Consistency-Checking Modes


-s (gnatfind): gnatfind Switches


-s (gnatls): Switches for gnatls


-s (gnatmake): Switches for gnatmake


-s (gnatprep): Switches for gnatprep


-sc (gnathtml): Invoking gnathtml


-shared (gnatbind): Switches for gnatbind


-static (gnatbind): Switches for gnatbind


-t (gnatbind): Switches for gnatbind


-T (gnatbind): Switches for gnatbind


-t (gnatbind): Binder Error Message Control


-t (gnatfind): gnatfind Switches


-t (gnathtml): Invoking gnathtml


-T (gnatprep): Switches for gnatprep


-T0 option: Choosing the Scheduling Policy


-u (gnatbind): Switches for gnatbind


-u (gnatls): Switches for gnatls


-u (gnatmake): Switches for gnatmake


-U (gnatmake): Switches for gnatmake


-u (gnatprep): Switches for gnatprep


-v (dlltool): Using gnatdll


-v (gcc): Alphabetical List of All Switches


-V (gcc): Alphabetical List of All Switches


-v (gnatbind): Switches for gnatbind


-V (gnatbind): Switches for gnatbind


-v (gnatbind): Binder Error Message Control


-v (gnatchop): Switches for gnatchop


-v (gnatclean): Switches for gnatclean


-v (gnatdll): Using gnatdll


-v (gnatlink): Switches for gnatlink


-v (gnatls): Switches for gnatls


-v (gnatmake): Switches for gnatmake


-v (gnatname): Switches for gnatname


-v (gnatprep): Switches for gnatprep


-v -v (gnatlink): Switches for gnatlink


-v -v (gnatname): Switches for gnatname


–version (gnatbind): Switches for gnatbind


–version (gnatchop): Switches for gnatchop


–version (gnatclean): Switches for gnatclean


–version (gnatfind): gnatfind Switches


–version (gnatlink): Switches for gnatlink


–version (gnatls): Switches for gnatls


–version (gnatmake): Switches for gnatmake


–version (gnatname): Switches for gnatname


–version (gnatprep): Switches for gnatprep


–version (gnatxref): gnatxref Switches


-vl (gnatmake): Switches for gnatmake


-vm (gnatmake): Switches for gnatmake


-vm (gnatmake): Switches for gnatmake


-vP (gnatclean): Switches for gnatclean


-w (gcc): Alphabetical List of All Switches


-w (gcc): Warning Message Control


-w (gnatbind): Switches for gnatbind


-w (gnatchop): Switches for gnatchop


-Wall (gcc): Warning Message Control


-we (gnatbind): Binder Error Message Control


-Werror (gcc): Warning Message Control


-ws (gnatbind): Binder Error Message Control


-Wstack-usage (gcc): Warning Message Control


-Wuninitialized (gcc): Warning Message Control


-Wunused (gcc): Warning Message Control


-Wx (gnatbind): Switches for gnatbind


-Wx (gnatbind): Consistency-Checking Modes


-x (gnatbind): Switches for gnatbind


-x (gnatbind): Consistency-Checking Modes


-X (gnatclean): Switches for gnatclean


-x (gnatmake): Switches for gnatmake


-x (gnatname): Switches for gnatname


-Xnnn (gnatbind): Switches for gnatbind


-y (gnatbind): Switches for gnatbind


-z (gnatbind): Switches for gnatbind


-z (gnatbind): Binding Programs with No Main Subprogram


-z (gnatmake): Switches for gnatmake


 


_


__gnat_malloc: Switches for gnatbind


 


A


Abnormal Termination or Failure to Terminate: Remote Debugging with gdbserver


Access before elaboration: Run-Time Checks


access before elaboration: Run-Time Checks


activate every optional warning: Warning Message Control


ACVC: Compiling Different Versions of Ada


Ada: Search Paths for gnatbind


Ada 2005 Language Reference Manual: What You Should Know before Reading This Guide


Ada 2005 mode: Compiling Different Versions of Ada


Ada 2012 mode: Compiling Different Versions of Ada


Ada 83 mode: Compiling Different Versions of Ada


Ada 83 tests: Compiling Different Versions of Ada


Ada 95 Language Reference Manual: What You Should Know before Reading This Guide


Ada 95 mode: Compiling Different Versions of Ada


Ada compatibility issues warnings: Warning Message Control


Ada compatibility issues warnings: Warning Message Control


Ada expressions (in gdb): Using Ada Expressions


Ada language extensions: Compiling Different Versions of Ada


Ada Library Information files: The Ada Library Information Files


Ada.Characters.Latin_1: Latin-1


adafinal: Binding with Non-Ada Main Programs


adainit: Binding with Non-Ada Main Programs


ADA_INCLUDE_PATH: Using a library


ADA_INCLUDE_PATH: Search Paths and the Run-Time Library RTL


ADA_INCLUDE_PATH: Search Paths and the Run-Time Library RTL


ADA_OBJECTS_PATH: Using a library


ADA_OBJECTS_PATH: Search Paths for gnatbind


ADA_OBJECTS_PATH: Search Paths for gnatbind


ADA_PRJ_INCLUDE_FILE: Search Paths and the Run-Time Library RTL


ADA_PRJ_INCLUDE_FILE: Search Paths and the Run-Time Library RTL


ADA_PRJ_INCLUDE_FILE: Search Paths and the Run-Time Library RTL


ADA_PRJ_OBJECTS_FILE: Search Paths for gnatbind


ADA_PRJ_OBJECTS_FILE: Search Paths for gnatbind


ADA_PRJ_OBJECTS_FILE: Search Paths for gnatbind


ADA_PROJECT_PATH: Installing a library


Address Clauses: Warning Message Control


ALI files: The Ada Library Information Files


Aliasing: Optimization and Strict Aliasing


Aliasing: Aliased Variables and Optimization


alternative: Alternative File Naming Schemes


Annex A (in Ada Reference Manual): Naming Conventions for GNAT Source Files


Annex B (in Ada reference Manual): Naming Conventions for GNAT Source Files


Anonymous allocators: Warning Message Control


Anonymous allocators: Warning Message Control


APIENTRY: Windows Calling Conventions


Asm: Calling Conventions


Assert: Debugging and Assertion Control


Assert failures: Warning Message Control


Assert failures: Warning Message Control


Assertions: Debugging and Assertion Control


Atomic: Atomic Variables and Optimization


Atomic Synchronization: Warning Message Control


Atomic Synchronization: Warning Message Control


attach to process: Program Built with Foreign Tools and DLL Built with GCC/GNAT


 


B


Bad fixed values: Warning Message Control


Biased representation: Warning Message Control


Binder: Binding with Non-Ada Main Programs


Binder consistency checks: Binder Error Message Control


Binder output (example): Example of Binder Output File


Binder output file: Interfacing to C


Binding generation (for Ada specs): Generating C Headers for Ada Specifications


Binding generation (for C and C++ headers): Generating Ada Bindings for C and C++ headers


BINUTILS_ROOT: Linking a Mixed C++ & Ada Program


bit order warnings: Warning Message Control


Breakpoints and tasks: Ada Tasks


building: Building DLLs with GNAT Project files


building: Building DLLs with GNAT


building: Building DLLs with gnatdll


building: Building Resources


Building the GNAT Run-Time Library: Rebuilding the GNAT Run-Time Library


 


C


C: Calling Conventions


C headers (binding generation): Generating Ada Bindings for C and C++ headers


C headers (binding generation): Generating C Headers for Ada Specifications


C varargs function: Calling Conventions


C++: Calling Conventions


C++ headers (binding generation): Generating Ada Bindings for C and C++ headers


Calling Conventions: Calling Conventions


cannot generate code: Compiling Programs


Check: Run-Time Checks


Check: Run-Time Checks


Checks: Run-Time Checks


Checks: Run-Time Checks


Checks: Run-Time Checks


Checks: Run-Time Checks


Checks: Run-Time Checks


Checks: Run-Time Checks


Checks: Controlling Run-Time Checks


Checks (overflow): Example of unused subprogram/data elimination


COBOL: Calling Conventions


code page 437 (IBM PC): Other 8-Bit Codes


code page 850 (IBM PC): Other 8-Bit Codes


Combining GNAT switches: Alphabetical List of All Switches


Command Line Argument Expansion: Disabling Command Line Argument Expansion


Command line length: Switches for gnatlink


Compatibility with Ada 83: Compiling Different Versions of Ada


compilation (definition): Source Representation


Compilation model: The GNAT Compilation Model


Compile_Time_Error: Warning Message Control


Compile_Time_Warning: Warning Message Control


compiling: Compiling Resources


Component clause: Warning Message Control


Conditional compilation: Rebuilding the GNAT Run-Time Library


Conditional compilation: Conditional Compilation


Conditionals: Warning Message Control


configuration: Configuration Pragmas


Configuration pragmas: Configuration Pragmas


Consistency checks: Binder Error Message Control


CONSOLE Subsystem: CONSOLE and WINDOWS subsystems


constant: Warning Message Control


Convention Ada: Calling Conventions


Convention Asm: Calling Conventions


Convention Assembler: Calling Conventions


Convention C: Calling Conventions


Convention C++: Calling Conventions


Convention COBOL: Calling Conventions


Convention Default: Calling Conventions


Convention DLL: Calling Conventions


Convention External: Calling Conventions


Convention Fortran: Calling Conventions


Convention Stdcall: Calling Conventions


Convention Stubbed: Calling Conventions


Convention Win32: Calling Conventions


Conventions: Conventions


CR: Source Representation


Cyrillic: Other 8-Bit Codes


C_INCLUDE_PATH: Linking a Mixed C++ & Ada Program


 


D


Deactivated code: Warning Message Control


Debug: Debugging and Assertion Control


Debug Pool: The GNAT Debug Pool Facility


Debugger: Running and Debugging Ada Programs


Debugging: Running and Debugging Ada Programs


Debugging Generic Units: Ada Tasks


Debugging information: Switches for gnatlink


Debugging optimized code: Debugging Optimized Code


Debugging options: Debugging Control


Default: Calling Conventions


Definition file: Creating an Import Library


Deleted code: Warning Message Control


Dependencies: Switches for gnatmake


Dependency rules (compilation): Building with gnatmake


Dereferencing: Warning Message Control


Dimension aspect: Performing Dimensionality Analysis in GNAT


Dimension aspect: Performing Dimensionality Analysis in GNAT


Dimension Vector (for a dimensioned subtype): Performing Dimensionality Analysis in GNAT


Dimensionable type: Performing Dimensionality Analysis in GNAT


Dimensionality analysis: Performing Dimensionality Analysis in GNAT


Dimensioned subtype: Performing Dimensionality Analysis in GNAT


Dimension_System aspect: Performing Dimensionality Analysis in GNAT


Dimension_System aspect: Performing Dimensionality Analysis in GNAT


Division by zero: Run-Time Checks


division by zero: Run-Time Checks


DLL: Calling Conventions


DLL: Introduction to Dynamic Link Libraries DLLs


DLL debugging: Debugging a DLL


DLL debugging: Program Built with Foreign Tools and DLL Built with GCC/GNAT


DLLs: Building DLLs with GNAT Project files


DLLs: Building DLLs with GNAT


DLLs: Building DLLs with gnatdll


DLLs and elaboration: Ada DLLs and Elaboration


DLLs and finalization: Ada DLLs and Finalization


Dynamic elaboration model: Controlling the Elaboration Order in GNAT


 


E


Elaboration: Warning Message Control


elaboration: Run-Time Checks


Elaboration checks: Run-Time Checks


Elaboration control: Elaboration Order Handling in GNAT


Elaboration order control: Comparison between GNAT and C/C++ Compilation Models


End of source file; Source file, end: Source Representation


environment variable; ADA_INCLUDE_PATH: Using a library


environment variable; ADA_INCLUDE_PATH: Search Paths and the Run-Time Library RTL


environment variable; ADA_OBJECTS_PATH: Using a library


environment variable; ADA_OBJECTS_PATH: Search Paths for gnatbind


environment variable; ADA_PRJ_INCLUDE_FILE: Search Paths and the Run-Time Library RTL


environment variable; ADA_PRJ_INCLUDE_FILE: Search Paths and the Run-Time Library RTL


environment variable; ADA_PRJ_OBJECTS_FILE: Search Paths for gnatbind


environment variable; ADA_PRJ_OBJECTS_FILE: Search Paths for gnatbind


environment variable; BINUTILS_ROOT: Linking a Mixed C++ & Ada Program


environment variable; C_INCLUDE_PATH: Linking a Mixed C++ & Ada Program


environment variable; GCC_EXEC_PREFIX: Linking a Mixed C++ & Ada Program


environment variable; GCC_ROOT: Linking a Mixed C++ & Ada Program


environment variable; PATH: Search Paths and the Run-Time Library RTL


environment variable; PATH: Search Paths for gnatbind


environment variable; TMP: Temporary Files


environment variable; TMP: Temporary Files


environment variable; TMP: Temporary Files


Error messages: Output and Error Message Control


EUC Coding: Wide_Character Encodings


Exceptions (in gdb): Stopping When Ada Exceptions Are Raised


Export table: Exporting Ada Entities


Export/Import pragma warnings: Warning Message Control


External: Calling Conventions


 


F


Features: Warning Message Control


FF: Source Representation


File cleanup tool: The File Cleanup Utility gnatclean


File names: Using Other File Names


File names: Alternative File Naming Schemes


File Naming Conventions: Handling Arbitrary File Naming Conventions with gnatname


File naming schemes: Alternative File Naming Schemes


Fixed-point Small value: Warning Message Control


Floating-Point Operations: Floating_Point_Operations


for gnatmake: Switches for gnatmake


for profiling: Compilation for profiling


for profiling: Compilation for profiling


Foreign Languages: Calling Conventions


Formals: Warning Message Control


Fortran: Calling Conventions


 


G


GCC_EXEC_PREFIX: Linking a Mixed C++ & Ada Program


GCC_ROOT: Linking a Mixed C++ & Ada Program


gdb: Running and Debugging Ada Programs


Generic formal parameters: Compiling Different Versions of Ada


Generics: Generating Object Files


Generics: Ada Tasks


GNAT: Search Paths for gnatbind


GNAT (package): Naming Conventions for GNAT Source Files


GNAT compilation model: The GNAT Compilation Model


GNAT extensions: Compiling Different Versions of Ada


GNAT library: Comparison between GNAT and Conventional Ada Library Models


GNAT Run-Time Library: Rebuilding the GNAT Run-Time Library


gnat.adc: Using Other File Names


gnat.adc: The Configuration Pragmas Files


gnat1: Compiling Programs


gnatbind: Binding with gnatbind


gnatchop: Renaming Files with gnatchop


gnatclean: The File Cleanup Utility gnatclean


gnatdll: Using gnatdll


gnatfind: The Cross-Referencing Tools gnatxref and gnatfind


gnathtml: The Ada to HTML Converter gnathtml


gnatkr: File Name Krunching with gnatkr


gnatlink: Linking with gnatlink


gnatls: The GNAT Library Browser gnatls


gnatmake: Building with gnatmake


gnatname: Alternative File Naming Schemes


gnatprep: Preprocessing


gnatprep: Preprocessing with gnatprep


gnatxref: The Cross-Referencing Tools gnatxref and gnatfind


gnat_argc: Command-Line Access


gnat_argv: Command-Line Access


GNAT_INIT_SCALARS: Switches for gnatbind


GNU make: Using the GNU make Utility


GNU/Linux: Choosing the Scheduling Policy


gprof: Profiling


GPR_PROJECT_PATH: Installing a library


 


H


Hiding of Declarations: Warning Message Control


HT: Source Representation


 


I


implicit: Warning Message Control


Implicit dereferencing: Warning Message Control


Import library: Creating an Import Library


Improving performance: Improving Performance


in binder: Binder Error Message Control


in binder: Binder Error Message Control


including: Switches for gnatlink


Inline: Source Dependencies


Inline: Inlining of Subprograms


Inline Assembler: Inline Assembler


Inlining: Comparison between GNAT and Conventional Ada Library Models


Inlining: Warning Message Control


Interfaces: Search Paths for gnatbind


Interfacing to Ada: Calling Conventions


Interfacing to Assembly: Calling Conventions


Interfacing to C: Calling Conventions


Interfacing to C varargs function: Calling Conventions


Interfacing to C++: Calling Conventions


Interfacing to COBOL: Calling Conventions


Interfacing to Fortran: Calling Conventions


Internal trees: Auxiliary Output Control


ISO 8859-15: Other 8-Bit Codes


ISO 8859-2: Other 8-Bit Codes


ISO 8859-3: Other 8-Bit Codes


ISO 8859-4: Other 8-Bit Codes


ISO 8859-5: Other 8-Bit Codes


 


L


Latin-1: Source Representation


Latin-1: Latin-1


Latin-2: Other 8-Bit Codes


Latin-3: Other 8-Bit Codes


Latin-4: Other 8-Bit Codes


Latin-9: Other 8-Bit Codes


Layout: Warning Message Control


Legacy elaboration models: Controlling the Elaboration Order in GNAT


LF: Source Representation


Library browser: The GNAT Library Browser gnatls


Library building and using: GNAT and Libraries


Linker libraries: Switches for gnatmake


Linux: Choosing the Scheduling Policy


 


M


Machine_Overflows: Run-Time Checks


make (GNU): Using the GNU make Utility


memory corruption: The GNAT Debug Pool Facility


Memory Pool: Some Useful Memory Pools


Microsoft Visual Studio: Using GNAT DLLs from Microsoft Visual Studio Applications


missing: Warning Message Control


Mixed Language Programming: Mixed Language Programming


MKS_Type type: Performing Dimensionality Analysis in GNAT


multiple input files: Binding with Non-Ada Main Programs


Multiple units: Using gcc for Syntax Checking


 


N


naming scheme: Switches for gnatmake


No information messages for why package spec needs body: Warning Message Control


non-symbolic: Stack Traceback


No_Strict_Aliasing: Optimization and Strict Aliasing


 


O


obsolescent: Warning Message Control


Obsolescent features: Warning Message Control


Optimization and debugging: Debugging Optimized Code


Optimization Switches: Vectorization of loops


Optimization Switches: Other Optimization Switches


Order of elaboration: Elaboration Order Handling in GNAT


OS X: Mac OS Topics


Other Ada compilers: Calling Conventions


overflow: Run-Time Checks


overflow: Controlling Run-Time Checks


Overflow checks: Run-Time Checks


Overflow checks: Controlling Run-Time Checks


Overflow checks: Example of unused subprogram/data elimination


Overflow mode: Run-Time Checks


 


P


Package spec needing body: Warning Message Control


Parallel make: Switches for gnatmake


Parameter order: Warning Message Control


Parentheses: Warning Message Control


Passive Task: Passive Task Optimization


PATH: Search Paths and the Run-Time Library RTL


PATH: Search Paths for gnatbind


pool: Some Useful Memory Pools


pool: The GNAT Debug Pool Facility


Postcondition: Debugging and Assertion Control


pragma Assert: Debugging - A Special Case


pragma Assertion_Policy: Debugging - A Special Case


pragma Debug: Debugging - A Special Case


pragma Debug_Policy: Debugging - A Special Case


pragma Elaborate (Unit): Controlling the Elaboration Order in Ada


pragma Elaborate_All (Unit): Controlling the Elaboration Order in Ada


pragma Elaborate_Body: Controlling the Elaboration Order in Ada


pragma Export: The External Symbol Naming Scheme of GNAT


pragma Inline: Inlining of Subprograms


pragma Overflow_Mode: Specifying the Desired Mode


pragma Preelaborate: Controlling the Elaboration Order in Ada


pragma Pure: Controlling the Elaboration Order in Ada


pragma Restrictions: Debugging Control


pragma Suppress: Controlling Run-Time Checks


pragma Task_Dispatching_Policy: Choosing the Scheduling Policy


pragma Time_Slice: Choosing the Scheduling Policy


pragma Unsuppress: Controlling Run-Time Checks


Pragmas: Configuration Pragmas


Pragmas: Warning Message Control


Precondition: Debugging and Assertion Control


Preprocessing: Preprocessing


Preprocessing (gnatprep): Preprocessing with gnatprep


Preprocessors (contrasted with conditional compilation): Use of Boolean Constants


producing list: Switches for gnatmake


Profiling: Pretty-Printers for the GNAT runtime


Profiling: Profiling


 


R


rc: Compiling Resources


rebuilding: Rebuilding the GNAT Run-Time Library


rebuilding: Rebuilding the GNAT Run-Time Library


Rebuilding the GNAT Run-Time Library: Rebuilding the GNAT Run-Time Library


Recompilation (by gnatmake): Notes on the Command Line


Record Representation (component sizes): Warning Message Control


Record Representation (gaps): Warning Message Control


Relaxed elaboration mode: Controlling the Elaboration Order in GNAT


Remote Debugging with gdbserver: Debugging Generic Units


Resources: GNAT and Windows Resources


Resources: Building Resources


Resources: Compiling Resources


Resources: Using Resources


RTL: Alphabetical List of All Switches


RTL: Alphabetical List of All Switches


Run-time libraries (platform-specific information): Run-Time Libraries


Run-Time Library: Rebuilding the GNAT Run-Time Library


 


S


s-digemk.ads file: Performing Dimensionality Analysis in GNAT


SCHED_FIFO scheduling policy: Specifying a Run-Time Library


SCHED_OTHER scheduling policy: Specifying a Run-Time Library


SCHED_RR scheduling policy: Specifying a Run-Time Library


Search paths: Switches for gnatmake


setjmp/longjmp Exception Model: Run-Time Libraries


Shift JIS Coding: Wide_Character Encodings


Size/Alignment warnings: Warning Message Control


Size/Alignment warnings: Warning Message Control


SJLJ (setjmp/longjmp Exception Model): Run-Time Libraries


Small value: Warning Message Control


Source files: Switches for gnatmake


Source files: Running gnatbind


Source files: Switches for gnatclean


Source_File_Name pragma: Using Other File Names


Source_File_Name pragma: Alternative File Naming Schemes


Source_Reference pragmas: Switches for gnatchop


SPARK elaboration model: Controlling the Elaboration Order in GNAT


spec (definition): Source Representation


stack overflow checking: Run-Time Checks


Stack Overflow Checking: Run-Time Checks


stack overflow checking: Run-Time Checks


Stack Overflow Checking: Stack Overflow Checking


stack traceback: Getting Internal Debugging Information


stack unwinding: Getting Internal Debugging Information


Stand-alone libraries: Stand-alone Ada Libraries


Static elaboration model: Controlling the Elaboration Order in GNAT


Static Stack Usage Analysis: Static Stack Usage Analysis


Stdcall: Calling Conventions


Stdcall: Windows Calling Conventions


stderr: Output and Error Message Control


storage: Some Useful Memory Pools


storage: The GNAT Debug Pool Facility


Strict Aliasing: Optimization and Strict Aliasing


String indexing warnings: Warning Message Control


Stubbed: Calling Conventions


Style checking: Style Checking


SUB (control character): Source Representation


Subtype predicates: Debugging and Assertion Control


Subunits: Generating Object Files


Subunits (and conditional compilation): Use of Alternative Implementations


Suppress: Run-Time Checks


Suppress: Controlling Run-Time Checks


suppressing: Output and Error Message Control


suppressing: Run-Time Checks


suppressing: Run-Time Checks


Suppressing checks: Run-Time Checks


Suppressing checks: Run-Time Checks


suppressing search: Switches for gnatmake


suppressing search: Switches for gnatclean


symbolic: Non-Symbolic Traceback


symbolic links: Switches for gnatmake


syntax checking: Using gcc for Syntax Checking


System: Search Paths for gnatbind


System (package in Ada Reference Manual): Naming Conventions for GNAT Source Files


System.Dim.Mks package (GNAT library): Performing Dimensionality Analysis in GNAT


System.IO: Search Paths and the Run-Time Library RTL


 


T


Task switching (in gdb): Ada Tasks


Tasking and threads libraries: Run-Time Libraries


Tasks (in gdb): Stopping When Ada Exceptions Are Raised


Temporary files: Temporary Files


Text_IO and performance: Text_IO Suggestions


Threads libraries and tasking: Run-Time Libraries


Time stamp checks: Binder Error Message Control


TMP: Temporary Files


TMP: Temporary Files


TMP: Temporary Files


traceback: Getting Internal Debugging Information


traceback: Stack Traceback


traceback: Non-Symbolic Traceback


treat as error: Warning Message Control


treat as error: Warning Message Control


Type invariants: Debugging and Assertion Control


typographical: Conventions


Typographical conventions: Conventions


 


U


Unassigned variable warnings: Warning Message Control


Unchecked_Conversion warnings: Warning Message Control


unrecognized: Warning Message Control


unreferenced: Warning Message Control


Unsuppress: Run-Time Checks


Unsuppress: Controlling Run-Time Checks


Upper-Half Coding: Wide_Character Encodings


use by binder: Running gnatbind


use with GNAT DLLs: Using GNAT DLLs from Microsoft Visual Studio Applications


using: Using Resources


Uunused subprogram/data elimination: Reducing Size of Executables with Unused Subprogram/Data Elimination


 


V


Validity Checking: Validity Checking


varargs function interfaces: Calling Conventions


Version skew (avoided by ‘‘gnatmake‘‘): Running a Simple Ada Program


Volatile parameter: The Volatile Parameter


VT: Source Representation


 


W


Warning messages: Warning Message Control


Warnings: Warning Message Control


Warnings: Warning Message Control


Warnings: Warning Message Control


warnings: Warning Message Control


warnings: Warning Message Control


warnings: Warning Message Control


warnings: Warning Message Control


warnings: Warning Message Control


warnings: Warning Message Control


warnings: Warning Message Control


warnings: Warning Message Control


warnings: Warning Message Control


warnings: Warning Message Control


Warnings: Binder Error Message Control


Warnings Off control: Warning Message Control


Win32: Calling Conventions


Windows: Required Packages on GNU/Linux


windows: GNAT and Windows Resources


WINDOWS Subsystem: CONSOLE and WINDOWS subsystems


windres: Compiling Resources


Writing internal trees: Auxiliary Output Control


writing to file: Auxiliary Output Control


 


Z


ZCX (Zero-Cost Exceptions): Run-Time Libraries


Zero Cost Exceptions: Exception Handling Control


Zero-Cost Exceptions: Run-Time Libraries


 




Jump to:   -
   
_
   


A
   
B
   
C
   
D
   
E
   
F
   
G
   
H
   
I
   
L
   
M
   
N
   
O
   
P
   
R
   
S
   
T
   
U
   
V
   
W
   
Z
   




                              
                              







Footnotes



(1)


http://docs.adacore.com/gdb-docs/html/gdb.html#Pretty_002dPrinter-Introduction


(2)


http://docs.adacore.com/gdb-docs/html/gdb.html#Pretty_002dPrinter-Commands