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ΓòÉΓòÉΓòÉ 1. -Preface- ΓòÉΓòÉΓòÉ


ΓòÉΓòÉΓòÉ 2. GNAT User's Guide ΓòÉΓòÉΓòÉ

 GNAT User's Guide

 GNAT, The GNU Ada 95 Compiler

 GNAT Version 3.13p

 Date: 2000/05/16 02:37:19

 Ada Core Technologies, Inc.

 (C) Copyright 1995-2000, Ada Core Technologies, Inc.

 Permission is granted to make and distribute verbatim copies of this manual
 provided the copyright notice and this permission notice are preserved on all
 copies.

 Silicon Graphics and IRIS are registered trademarks and IRIX is a trademark of
 Silicon Graphics, Inc.

 IBM PC is a trademark of International Business Machines Corporation.

 UNIX is a registered trademark of AT&T Bell Laboratories.

 The following are trademarks of Compaq Computers: DEC, DEC Ada, DECthreads,
 DIGITAL, DECset, OpenVMS, and VAX.

 The following are trademarks of Microsoft Corporation: Windows NT, Windows 95,
 Windows 98.

 The following are trademarks of Wind River Systems: VxWorks, Tornado.

 About This Guide              About This Guide
 Getting Started With GNAT     Getting Started With GNAT
 The GNAT Compilation Model    The GNAT Compilation Model
 Compiling Using gcc           Compiling Using gcc
 Binding Using gnatbind        Binding Using gnatbind
 Linking Using gnatlink        Linking Using gnatlink
 The GNAT Make Program gnatmakeThe GNAT Make Program gnatmake
 Renaming Files Using gnatchop Renaming Files Using gnatchop
 Configuration Pragmas         Configuration Pragmas
 Elaboration Order Handling in GNATElaboration Order Handling in GNAT
 The cross-referencing tools gnatxref and gnatfindThe cross-referencing tools
                               gnatxref and gnatfind
 File Name Krunching Using gnatkrFile Name Krunching Using gnatkr
 Preprocessing Using gnatprep  Preprocessing Using gnatprep
 The GNAT library browser gnatlsThe GNAT library browser gnatls
 GNAT and libraries            GNAT and libraries
 Using the GNU make utility    Using the GNU make utility
 Finding memory problems with gnatmemFinding memory problems with gnatmem
 Finding memory problems with GNAT Debug PoolFinding memory problems with GNAT
                               Debug Pool
 Creating Sample Bodies Using gnatstubCreating Sample Bodies Using gnatstub
 Reducing the Size of Ada Executables with gnatelimReducing the Size of Ada
                               Executables with gnatelim
 Other Utility Programs        Other Utility Programs
 Running and Debugging Ada ProgramsRunning and Debugging Ada Programs
 Performance Considerations    Performance Considerations
 Index                         Index  About This Guide
 What This Guide Contains      What This Guide Contains
 What You Should Know Before Reading This GuideWhat You Should Know Before
                               Reading This Guide
 Related Information           Related Information
 Conventions                   Conventions  Getting Started With GNAT
 Running GNAT                  Running GNAT
 Running a Simple Ada Program  Running a Simple Ada Program
 Running a Program With Multiple UnitsRunning a Program With Multiple Units
 Using the gnatmake Utility    Using the gnatmake Utility The GNAT Compilation
                               Model
 Source Representation         Source Representation
 Foreign Language RepresentationForeign Language Representation
 File Naming Rules             File Naming Rules
 Using Other File Names        Using Other File Names
 Generating Object Files       Generating Object Files
 Source Dependencies           Source Dependencies
 The Ada Library Information FilesThe Ada Library Information Files
 Representation of Time Stamps Representation of Time Stamps
 Binding an Ada Program        Binding an Ada Program
 Mixed Language Programming    Mixed Language Programming
 Building mixed Ada & C++ programsBuilding mixed Ada & C++ programs
 Comparison between GNAT and C/C++ Compilation ModelsComparison between GNAT
                               and C/C++ Compilation Models
 Comparison between GNAT and Conventional Ada Library ModelsComparison between
                               GNAT and Conventional Ada Library Models Foreign
                               Language Representation
 Latin-1                       Latin-1
 Other 8-Bit Codes             Other 8-Bit Codes
 Wide Character Encodings      Wide Character Encodings Compiling Ada Programs
                               With gcc
 Compiling Programs            Compiling Programs
 Switches for gcc              Switches for gcc
 Search Paths and the Run-Time Library (RTL)Search Paths and the Run-Time
                               Library (RTL)
 Order of Compilation Issues   Order of Compilation Issues
 Examples                      Examples Switches for gcc
 Output and Error Message ControlOutput and Error Message Control
 Debugging and Assertion ControlDebugging and Assertion Control
 Run-time Checks               Run-time Checks
 Stack Overflow Checking       Stack Overflow Checking
 Run-time Control              Run-time Control
 Style Checking                Style Checking
 Using gcc for Syntax Checking Using gcc for Syntax Checking
 Using gcc for Semantic CheckingUsing gcc for Semantic Checking
 Compiling Ada 83 Programs     Compiling Ada 83 Programs
 Reference Manual Style CheckingReference Manual Style Checking
 Character Set Control         Character Set Control
 File Naming Control           File Naming Control
 Subprogram Inlining Control   Subprogram Inlining Control
 Auxiliary Output Control      Auxiliary Output Control
 Debugging Control             Debugging Control Binding Ada Programs With
                               gnatbind
 Running gnatbind              Running gnatbind
 Generating The Binder Program in CGenerating The Binder Program in C
 Consistency-Checking Modes    Consistency-Checking Modes
 Binder Error Message Control  Binder Error Message Control
 Elaboration Control           Elaboration Control
 Output Control                Output Control
 Binding with Non-Ada Main ProgramsBinding with Non-Ada Main Programs
 Binding Programs with no Main SubprogramBinding Programs with no Main
                               Subprogram
 Summary of Binder Switches    Summary of Binder Switches
 Command-Line Access           Command-Line Access
 Search Paths for gnatbind     Search Paths for gnatbind
 Examples of gnatbind Usage    Examples of gnatbind Usage Linking Using
                               gnatlink
 Running gnatlink              Running gnatlink
 Switches for gnatlink         Switches for gnatlink The GNAT Make Program
                               gnatmake
 Running gnatmake              Running gnatmake
 Switches for gnatmake         Switches for gnatmake
 Mode switches for gnatmake    Mode switches for gnatmake
 Notes on the Command Line     Notes on the Command Line
 How gnatmake Works            How gnatmake Works
 Examples of gnatmake Usage    Examples of gnatmake Usage Renaming Files Using
                               gnatchop
 Handling Files with Multiple UnitsHandling Files with Multiple Units
 Operating gnatchop in Compilation ModeOperating gnatchop in Compilation Mode
 Command Line for gnatchop     Command Line for gnatchop
 Switches for gnatchop         Switches for gnatchop
 Examples of gnatchop Usage    Examples of gnatchop Usage Configuration Pragmas
 Handling of Configuration PragmasHandling of Configuration Pragmas
 The Configuration Pragmas fileThe Configuration Pragmas file Elaboration Order
                               Handling in GNAT
 Elaboration Code in Ada 95    Elaboration Code in Ada 95
 Checking the Elaboration Order in Ada 95Checking the Elaboration Order in Ada
                               95
 Controlling the Elaboration Order in Ada 95Controlling the Elaboration Order
                               in Ada 95
 Controlling Elaboration in GNAT - Internal CallsControlling Elaboration in
                               GNAT - Internal Calls
 Controlling Elaboration in GNAT - External CallsControlling Elaboration in
                               GNAT - External Calls
 Default Behavior in GNAT - Ensuring SafetyDefault Behavior in GNAT - Ensuring
                               Safety
 What to do if the Default Elaboration Behavior FailsWhat to do if the Default
                               Elaboration Behavior Fails
 Elaboration for Access-to-Subprogram ValuesElaboration for
                               Access-to-Subprogram Values
 Summary of Procedures for Elaboration ControlSummary of Procedures for
                               Elaboration Control The cross-referencing tools
                               gnatxref and gnatfind
 Gnatxref switches             Gnatxref switches
 Gnatfind switches             Gnatfind switches
 Project files                 Project files
 Regular expressions in gnatfind and gnatxrefRegular expressions in gnatfind
                               and gnatxref
 Examples of gnatxref usage    Examples of gnatxref usage
 Examples of gnatfind usage    Examples of gnatfind usage File Name Krunching
                               Using gnatkr
 About gnatkr                  About gnatkr
 Using gnatkr                  Using gnatkr
 Krunching Method              Krunching Method
 Examples of gnatkr Usage      Examples of gnatkr Usage Preprocessing Using
                               gnatprep
 Using gnatprep                Using gnatprep
 Switches for gnatprep         Switches for gnatprep
 Form of definitions file      Form of definitions file
 Form of input text for gnatprepForm of input text for gnatprep  The GNAT
                               library browser gnatls
 Running gnatls                Running gnatls
 Switches for gnatls           Switches for gnatls
 Examples of gnatls Usage      Examples of gnatls Usage  GNAT and libraries
 Creating an Ada library       Creating an Ada library
 Installing an Ada library     Installing an Ada library
 Using an Ada library          Using an Ada library
 Rebuilding the GNAT runtime libraryRebuilding the GNAT runtime library Using
                               the GNU make utility
 Using gnatmake in a Makefile  Using gnatmake in a Makefile
 Automatically creating a list of directoriesAutomatically creating a list of
                               directories
 Generating the command line switchesGenerating the command line switches
 Overcoming command line length limitsOvercoming command line length limits
                               Finding memory problems with gnatmem
 Running gnatmem               Running gnatmem
 Switches for gnatmem          Switches for gnatmem
 Examples of gnatmem Usage     Examples of gnatmem Usage
 Implementation note           Implementation note Finding memory problems with
                               GNAT Debug Pool Creating Sample Bodies Using
                               gnatstub
 Running gnatstub              Running gnatstub
 Switches for gnatstub         Switches for gnatstub Reducing the Size of Ada
                               Executables with gnatelim
 About gnatelim                About gnatelim
 Eliminate pragma              Eliminate pragma
 Tree Files                    Tree Files
 Preparing Tree and Bind Files for gnatelimPreparing Tree and Bind Files for
                               gnatelim
 Running gnatelim              Running gnatelim
 Correcting the List of Eliminate PragmasCorrecting the List of Eliminate
                               Pragmas
 Making your Executables smallerMaking your Executables smaller
 Summary of the gnatelim Usage CycleSummary of the gnatelim Usage Cycle Other
                               Utility Programs
 Using Other Utility Programs With GNATUsing Other Utility Programs With GNAT
 The gnatpsys Utility Program  The gnatpsys Utility Program
 The gnatpsta Utility Program  The gnatpsta Utility Program
 The External Symbol Naming Scheme of GNATThe External Symbol Naming Scheme of
                               GNAT
 Ada Mode for emacs            Ada Mode for emacs
 Converting Ada files to html using gnathtmlConverting Ada files to html using
                               gnathtml  Running and Debugging Ada Programs
 The GNAT Debugger GDB         The GNAT Debugger GDB
 Running GDB                   Running GDB
 Introduction to GDB Commands  Introduction to GDB Commands
 Using Ada Expressions         Using Ada Expressions
 Calling User-Defined SubprogramsCalling User-Defined Subprograms
 Ada Exceptions                Ada Exceptions
 Ada Tasks                     Ada Tasks
 Debugging Generic Units       Debugging Generic Units
 GNAT Abnormal Termination     GNAT Abnormal Termination
 Naming Conventions for GNAT Source FilesNaming Conventions for GNAT Source
                               Files
 Getting Internal Debugging InformationGetting Internal Debugging Information
                               Performance Considerations
 Controlling Run-time Checks   Controlling Run-time Checks
 Optimization Levels           Optimization Levels
 Inlining of Subprograms       Inlining of Subprograms
 Index                         Index


ΓòÉΓòÉΓòÉ 3. About This Guide ΓòÉΓòÉΓòÉ


 This guide describes the use of GNAT, a compiler and software development
 toolset for the full Ada 95 programming language. It describes the features of
 the compiler and tools, and details how to use them to build Ada 95
 applications.

 What This Guide Contains      What This Guide Contains
 What You Should Know Before Reading This GuideWhat You Should Know Before
                               Reading This Guide
 Related Information           Related Information
 Conventions                   Conventions


ΓòÉΓòÉΓòÉ 3.1. What This Guide Contains ΓòÉΓòÉΓòÉ


 This guide contains the following chapters:

     Getting Started With GNAT, describes how to get started compiling and
      running Ada programs with the GNAT Ada programming environment.

     The GNAT Compilation Model, describes the compilation model used by GNAT.

     Compiling Using gcc, describes how to compile Ada programs with gcc, the
      Ada compiler.

     Binding Using gnatbind, describes how to perform binding of Ada programs
      with gnatbind, the GNAT binding utility.

     Linking Using gnatlink, describes gnatlink, a program that provides for
      linking using the GNAT run-time library to construct a program. gnatlink
      can also incorporate foreign language object units into the executable.

     The GNAT Make Program gnatmake, describes gnatmake, a utility that
      automatically determines the set of sources needed by an Ada compilation
      unit, and executes the necessary compilations binding and link.

     Renaming Files Using gnatchop, describes gnatchop, a utility that allows
      you to preprocess a file that contains Ada source code, and split it into
      one or more new files, one for each compilation unit.

     The cross-referencing tools gnatxref and gnatfind, discusses gnatxref and
      gnatfind, two tools that provide an easy way to navigate through sources.

     File Name Krunching Using gnatkr, describes the gnatkr file name
      krunching utility, used to handle shortened file names on operating
      systems with a limit on the length of names.

     Preprocessing Using gnatprep, describes gnatprep, a preprocessor utility
      that allows a single source file to be used to generate multiple or
      parameterized source files, by means of macro substitution.

     The GNAT library browser gnatls, describes gnatls, a utility that
      displays information about compiled units, including dependences on the
      corresponding sources files, and consistency of compilations.

     GNAT and libraries, describes the process of creating and using Libraries
      with GNAT. It also describes how to recompile the GNAT runtime library.

     Using the GNU make utility, describes some techniques for using the GNAT
      toolset in Makefiles.

     Finding memory problems with gnatmem, describes gnatmem, a utility that
      monitors dynamic allocation and deallocation activity in a program, and
      displays information about incorrect deallocations and sources of
      possible memory leaks.

     Finding memory problems with GNAT Debug Pool, describes how to use the
      GNAT-specific Debug Pool in order to detect as early as possible the use
      of incorrect memory references.

     Creating Sample Bodies Using gnatstub, discusses gnatstub, a utility that
      generates empty but compilable bodies for library units.

     Reducing the Size of Ada Executables with gnatelim, describes gnatelim, a
      tool which detects unused subprograms and helps the compiler to create a
      smaller executable for the program.

     Other Utility Programs, discusses several other GNAT utilities, including
      gnatpsta and gnatpsys.

     Running and Debugging Ada Programs, describes how to run and debug Ada
      programs.

     Building mixed Ada & C++ programs, gives hints on how to interface with
      c++.

     Performance Considerations, reviews the trade offs between using defaults
      or options in program development.


ΓòÉΓòÉΓòÉ 3.2. What You Should Know Before Reading This Guide ΓòÉΓòÉΓòÉ


 This user's guide assumes that you are familiar with Ada 95 language, as
 described in the International Standard ANSI/ISO/IEC-8652:1995, Jan 1995.


ΓòÉΓòÉΓòÉ 3.3. Related Information ΓòÉΓòÉΓòÉ


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

     GNAT Reference Manual, which contains all reference material for the GNAT
      implementation of Ada 95.

     Ada 95 Language Reference Manual, which contains all reference material
      for the Ada 95 programming language.

     Debugging with GDB contains all details on the use of the GNU
      source-level debugger.

     GNU Emacs Manual contains full information on the extensible editor and
      programming environment Emacs.


ΓòÉΓòÉΓòÉ 3.4. Conventions ΓòÉΓòÉΓòÉ


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

     Functions, utility program names, standard names, and classes.

     'Option flags'

     'File Names', 'button names', and 'field names'.

     Variables.

     Emphasis.

     [optional information or parameters]

     Examples are described by text

                      and then shown this way.


 Commands that are entered by the user are preceded in this manual by the
 characters "$ " (dollar sign followed by space). If your system uses this
 sequence as a prompt, then the commands will appear exactly as you see them in
 the manual. If your system uses some other prompt, then the command will
 appear with the $ replaced by whatever prompt character you are using.


ΓòÉΓòÉΓòÉ 4. Getting Started With GNAT ΓòÉΓòÉΓòÉ


 This chapter describes the simplest ways of using GNAT to compile Ada
 programs.

 Running GNAT                  Running GNAT
 Running a Simple Ada Program  Running a Simple Ada Program
 Running a Program With Multiple UnitsRunning a Program With Multiple Units
 Using the gnatmake Utility    Using the gnatmake Utility


ΓòÉΓòÉΓòÉ 4.1. Running GNAT ΓòÉΓòÉΓòÉ


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

   1. The source file(s) must be compiled.

   2. The file(s) must be bound using the GNAT binder.

   3. All appropriate object files must be linked to produce an executable.

 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.


ΓòÉΓòÉΓòÉ 4.2. Running a Simple Ada Program ΓòÉΓòÉΓòÉ


 Any 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 suppose in our initial example that you have
 used your editor to prepare the following standard format text file:

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

 This file should be named 'hello.adb'. Using the normal default file naming
 conventions, By default, GNAT requires that each file contain a single
 compilation unit whose file name corresponds to the unit name with periods
 replaced by hyphens, and whose extension is '.ads' for a spec and '.adb' for a
 body. This default file naming convention can be overridden by use of the
 special pragma Source_File_Name 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 compilation
 requirements, then the gnatchop utility can be used to perform this renaming
 operation (see Renaming Files Using gnatchop).

 You can compile the program using the following command:

                      $ 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 95 and C. It determines
 you have given it an Ada program by the extension ('.ads' or '.adb'), and will
 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 a file 'hello.ali' which
 contains additional information used to check that an Ada program is
 consistent. To get an executable file, we then use gnatbind to bind the
 program and gnatlink to link it to produce the executable. 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, which is a
 master program which invokes all of 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 a consistent
 compilation is ensured.

                      $ gnatmake hello.adb

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

                      $ ./hello

 and, if all has gone well, you will see

                      Hello WORLD!

 appear in response to this command.


ΓòÉΓòÉΓòÉ 4.3. Running a Program With Multiple Units ΓòÉΓòÉΓòÉ


 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 Text_IO; use 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 a separate
 body, only the body need be compiled. If you want to submit these programs to
 the compiler for semantic checking purposes, then you 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
 capability. All you need to know in this case is the name of the main program
 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.


ΓòÉΓòÉΓòÉ 4.4. Using the gnatmake Utility ΓòÉΓòÉΓòÉ


 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 from which
 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 intricate Ada 95 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.


ΓòÉΓòÉΓòÉ 5. The GNAT Compilation Model ΓòÉΓòÉΓòÉ

 Source Representation         Source Representation
 Foreign Language RepresentationForeign Language Representation
 File Naming Rules             File Naming Rules
 Using Other File Names        Using Other File Names
 Generating Object Files       Generating Object Files
 Source Dependencies           Source Dependencies
 The Ada Library Information FilesThe Ada Library Information Files
 Representation of Time Stamps Representation of Time Stamps
 Binding an Ada Program        Binding an Ada Program
 Mixed Language Programming    Mixed Language Programming
 Building mixed Ada & C++ programsBuilding mixed Ada & C++ programs
 Comparison between GNAT and C/C++ Compilation ModelsComparison between GNAT
                               and C/C++ Compilation Models
 Comparison between GNAT and Conventional Ada Library ModelsComparison between
                               GNAT and Conventional Ada Library Models

 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
 library. The model is initially described without reference to the
 library-based model. If you have not previously used an Ada compiler, you need
 only read the first part of this chapter. The last section describes and
 discusses the differences between the GNAT model and the traditional Ada
 compiler models. If you have used other Ada compilers, this section will help
 you to understand those differences, and the advantages of the GNAT model.


ΓòÉΓòÉΓòÉ 5.1. Source Representation ΓòÉΓòÉΓòÉ


 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:

 VT
           Vertical tab, 16#0B#

 HT
           Horizontal tab, 16#09#

 CR
           Carriage return, 16#0D#

 LF
           Line feed, 16#0A#

 FF
           Form feed, 16#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
 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.


ΓòÉΓòÉΓòÉ 5.2. Foreign Language Representation ΓòÉΓòÉΓòÉ


 GNAT supports the standard character sets defined in Ada 95 as well as several
 other non-standard character sets for use in localized versions of the
 compiler (see Character Set Control).

 Latin-1                       Latin-1
 Other 8-Bit Codes             Other 8-Bit Codes
 Wide Character Encodings      Wide Character Encodings


ΓòÉΓòÉΓòÉ 5.2.1. Latin-1 ΓòÉΓòÉΓòÉ


 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.


ΓòÉΓòÉΓòÉ 5.2.2. Other 8-Bit Codes ΓòÉΓòÉΓòÉ


 GNAT also supports several other 8-bit coding schemes:

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

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

 Latin-4
           Latin-4 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.


ΓòÉΓòÉΓòÉ 5.2.3. Wide Character Encodings ΓòÉΓòÉΓòÉ


 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, but in this implementation, all UTF-8
 sequences of four or more bytes length will be treated as illegal).

 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 the standard ACVC (Ada Compiler
 Validation Capability) test suite distributions.

 Note: Some of these coding schemes do not permit the full use of the Ada 95
 character set. For example, neither Shift JIS, nor EUC allow the use of the
 upper half of the Latin-1 set.


ΓòÉΓòÉΓòÉ 5.3. File Naming Rules ΓòÉΓòÉΓòÉ


 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
 list shows some examples of these rules.

 main.ads
           Main (spec)

 main.adb
           Main (body)

 arith_functions.ads
           Arith_Functions (package spec)

 arith_functions.adb
           Arith_Functions (package body)

 func-spec.ads
           Func.Spec (child package spec)

 func-spec.adb
           Func.Spec (child package body)

 main-sub.adb
           Sub (subunit of Main)

 a~bad.adb
           A.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. See 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 Using gnatchop.)


ΓòÉΓòÉΓòÉ 5.4. Using Other File Names ΓòÉΓòÉΓòÉ


 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.


ΓòÉΓòÉΓòÉ 5.5. Generating Object Files ΓòÉΓòÉΓòÉ


 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:

     If a package spec has no body, compile the package spec to produce the
      object file for the package.

     If a package has both a spec and a body, compile the body to produce the
      object file for the package. The source file for the package spec need
      not be compiled in this case because there is only one object file, which
      contains the code for both the spec and body of the package.

     For a subprogram, compile the subprogram body to produce the object file
      for the subprogram. The spec, if one is present, is as usual in a
      separate file, and need not be compiled.

     In the case of subunits, only compile the parent unit. A single object
      file is generated for the entire subunit tree, which includes all the
      subunits.

     Compile child units independently of their parent units (though, of
      course, the spec of all the ancestor unit must be present in order to
      compile a child unit).

     Compile generic units in the same manner as any other units. The object
      files in this case are small dummy files that contain at most the flag
      used for elaboration checking. This is because GNAT always handles
      generic instantiation by means of macro expansion. However, it is still
      necessary to compile generic units, for dependency checking and
      elaboration purposes.

 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.


ΓòÉΓòÉΓòÉ 5.6. Source Dependencies ΓòÉΓòÉΓòÉ


 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:

     If a file being compiled with's a unit X, the object file depends on the
      file containing the spec of unit X. This includes files that are with'ed
      implicitly either because they are parents of with'ed child units or they
      are run-time units required by the language constructs used in a
      particular unit.

     If a file being compiled instantiates a library level generic unit, the
      object file depends on both the spec and body files for this generic
      unit.

     If a file being compiled instantiates a generic unit defined within a
      package, the object file depends on the body file for the package as well
      as the spec file.

     If a file being compiled contains a call to a subprogram for which pragma
      Inline applies and inlining is activated with the -gnatn switch, the
      object file depends on the file containing the body of this subprogram as
      well as on the file containing the spec.

     If an object file O  depends on the proper body of a subunit through
      inlining or instantiation, it depends on the parent unit of the subunit.
      This means that any modification of the parent unit or one of its
      subunits affects the compilation of O.

     The object file for a parent unit depends on all its subunit body files.

     The previous two rules meant that for purposes of computing dependencies
      and recompilation, a body and all its subunits are treated as an
      indivisible whole.
      These rules are applied transitively: if unit A with's unit B, whose
      elaboration calls an inlined procedure in package C, the object file for
      unit A will depend on the body of C, in file 'c.adb'.

      The set of dependent files described by these rules includes all the
      files on which the unit is semantically dependent, as described in the
      Ada 95 Language Reference Manual. However, it is a superset of what the
      ARM describes, because it includes generic, inline, and subunit
      dependencies.

      An object file must be recreated by recompiling the corresponding source
      file if any of the source files on which it depends are modified. For
      example, if the make utility is used to control compilation, the rule for
      an Ada object file must mention all the source files on which the object
      file depends, according to the above definition. The determination of the
      necessary recompilations is done automatically when one uses gnatmake.


ΓòÉΓòÉΓòÉ 5.7. The Ada Library Information Files ΓòÉΓòÉΓòÉ


 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.

 Normally you need not be concerned with the contents of this file. This
 section is included in case you want to understand how these files are being
 used by the binder and other GNAT utilities. Each ALI file consists of a
 series of lines of the form:

                      Key_Character parameter parameter ┬╖┬╖┬╖

 The first two lines in the file identify the library output version and
 Standard version. These are required to be consistent across the entire set of
 compilation units in your program.

                      V "xxxxxxxxxxxxxxxx"

 This line indicates the library output version, as defined in 'gnatvsn.ads'.
 It ensures that separate object modules of a program are consistent. The
 library output version must be changed if anything in the compiler changes
 that would affect successful binding of modules compiled separately. Examples
 of such changes are modifications in the format of the library information
 described in this package, modifications to calling sequences, or to the way
 data is represented.

                      S "xxxxxxxxxxxxxxxx"

 This line contains information regarding types declared in packages Standard
 as stored in Gnatvsn.Standard_Version. The purpose of this information is to
 ensure that all units in a program are compiled with a consistent set of
 options. This is critical on systems where, for example, the size of Integer
 can be set by command line switches.

                      M type [priority]

 This line is present only for a unit that can be a main program. type is
 either P for a parameterless procedure or F for a function returning a value
 of integral type. The latter is for writing a main program that returns an
 exit status. priority is present only if there was a valid pragma Priority in
 the corresponding unit to set the main task priority. It is an unsigned
 decimal integer.

                      F x

 This line is present if a pragma Float_Representation or Long_Float is used to
 specify other than the default floating-point format. This option applies only
 to implementations of GNAT for the Digital Alpha Systems. The character x is
 'I' for IEEE_Float, 'G' for VAX_Float with Long_Float using G_Float, and 'D'
 for VAX_Float for Long_Float with D_Float.

                      P L=x Q=x T=x

 This line is present if the unit uses tasking directly or indirectly, and has
 one or more valid xxx_Policy pragmas that apply to the unit. The arguments are
 as follows

                      L=x (locking policy)

 This is present if a valid Locking_Policy pragma applies to the unit. The
 single character indicates the policy in effect (e.g. 'C' for
 Ceiling_Locking).

                      Q=x (queuing policy)

 This is present if a valid Queuing_Policy pragma applies to the unit. The
 single character indicates the policy in effect (e.g. 'P' for
 Priority_Queuing).

                      T=x (task_dispatching policy)

 This is present if a valid Task_Dispatching_Policy pragma applies to the unit.
 The single character indicates the policy in effect (e.g. 'F' for
 FIFO_Within_Priorities).
 Following these header lines is a set of information lines, one per
 compilation unit. Each line lists a unit in the object file corresponding to
 this ALI file. In particular, when a package body or subprogram body is
 compiled there will be two such lines, one for the spec and one for the body,
 with the entry for the body appearing first. This is the only case in which a
 single ALI file contains more than one unit. Note that subunits do not count
 as compilation units for this purpose, and generate no library information,
 because they are inlined. The lines for each compilation unit have the
 following form:

                      U unit-name source-name version [attributes]

 This line identifies the unit to which this section of the library information
 file applies. unit-name is the unit name in internal format, as described in
 package Uname, and source-name is the name of the source file containing the
 unit.

 version is the version, given by eight hexadecimal characters with lowercase
 letters. This value is a hash code that includes contributions from the time
 stamps of this unit and all the units on which it semantically depends.

 The optional attributes are a series of two-letter codes indicating
 information about the unit. They indicate the nature of the unit and they
 summarize information provided by categorization pragmas.

 EB
           Unit has pragma Elaborate_Body.

 NE
           Unit has no elaboration routine. All subprogram specs are in this
           category, as are subprogram bodies if access-before-elaboration
           checks are being generated. Package bodies and specs may or may not
           have NE set, depending on whether or not elaboration code is
           required.

 PK
           Unit is a package.

 PU
           Unit has pragma Pure.

 PR
           Unit has pragma Preelaborate.

 RC
           Unit has pragma Remote_Call_Interface.

 RT
           Unit has pragma Remote_Types.

 SP
           Unit has pragma Shared_Passive.

 SU
           Unit is a subprogram.

 The attributes may appear in any order, separated by spaces. The next set of
 lines in the ALI file have the following form:

                      W unit-name [source-name lib-name [E] [EA] [ED]]

 One of these lines is present for each unit mentioned in an explicit with
 clause in the current unit. unit-name is the unit name in internal format.
 source-name is the file name of the file that must be compiled to compile that
 unit (usually the file for the body, except for packages that have no body).
 lib-name is the file name of the library information file that contains the
 results of compiling the unit. The E and EA parameters are present if pragma
 Elaborate or pragma Elaborate_All, respectively, apply to this unit. ED is
 used to indicate that the compiler has determined that a pragma Elaborate_All
 for this unit would be desirable. For details on the use of the ED parameter
 see See Elaboration Order Handling in GNAT.
 Following the unit information is an optional series of lines that indicate
 the usage of pragma Linker_Options. For each appearance of pragma
 Linker_Options in any of the units for which unit lines are present, a line of
 the form

                      L string

 appears. string is the string from the pragma enclosed in quotes. Within the
 quotes, the following can occur:

     7-bit graphic characters other than " or {

     "" (indicating a single " character)

     {hh} indicating a character whose code is hex hh

 For further details, see Stringt.Write_String_Table_Entry in the file
 'stringt.ads'. Note that wide characters of the form {hhhh} cannot be
 produced, because pragma Linker_Option accepts only String, not Wide_String.

 Finally, the rest of the ALI file contains a series of lines that indicate the
 source files on which the compiled units depend. This is used by the binder
 for consistency checking and looks like:

                      D source-name time-stamp [comments]

 where comments, if present, must be separated from the time stamp by at least
 one blank. Currently this field is unused.

 Blank lines are ignored when the library information is read, and separate
 sections of the file are separated by blank lines to help readability. Extra
 blanks between fields are also ignored.


ΓòÉΓòÉΓòÉ 5.8. Representation of Time Stamps ΓòÉΓòÉΓòÉ


 All compiled units are marked with a time stamp, which is derived from the
 source file. The binder uses these time stamps to ensure consistency of the
 set of units that constitutes a single program. Time stamps are
 fourteen-character strings of the form YYYYMMDDHHMMSS. The fields have the
 following meaning:

 YYYY
           year (4 digits)

 MM
           month (2 digits 01-12)

 DD
           day (2 digits 01-31)

 HH
           hour (2 digits 00-23)

 MM
           minutes (2 digits 00-59)

 SS
           seconds (2 digits 00-59)

 Time stamps may be compared lexicographically (in other words, the order of
 Ada comparison operations on strings) to determine which is later or earlier.
 However, in normal mode, only equality comparisons have any effect on the
 semantics of the library. Later/earlier comparisons are used only for
 determining the most informative error messages to be issued by the binder.

 The time stamp is the actual stamp stored with the file without any adjustment
 resulting from time zone comparisons. This avoids problems in using libraries
 across networks with clients spread across multiple time zones, but it means
 that the time stamp might differ from that displayed in a directory listing.
 For example, in UNIX systems, file time stamps are stored in Greenwich Mean
 Time (GMT), but the ls command displays local times.


ΓòÉΓòÉΓòÉ 5.9. Binding an Ada Program ΓòÉΓòÉΓòÉ


 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.


ΓòÉΓòÉΓòÉ 5.10. Mixed Language Programming ΓòÉΓòÉΓòÉ

 Interfacing to C              Interfacing to C
 Calling Conventions           Calling Conventions


ΓòÉΓòÉΓòÉ 5.10.1. Interfacing to C ΓòÉΓòÉΓòÉ


 There are two ways to build a program that contains some Ada files and some
 other language files depending on whether the main program is in Ada or not.
 If the main program is in Ada, you should proceed as follows:

   1. Compile the other language files to generate object files. For instance:

                      gcc -c file1.c
                      gcc -c file2.c

   2. Compile the Ada units to produce a set of object files and ALI files. For
      instance:

                      gnatmake -c my_main.adb

   3. Run the Ada binder on the Ada main program. For instance:

                      gnatbind my_main.ali

   4. Link the Ada main program, the Ada objects and the other language
      objects. For instance:

                      gnatlink my_main.ali file1.o file2.o

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

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

 If the main program is in some language other than Ada, Then you may have more
 than one entry point in the Ada subsystem. You must use a special option of
 the binder to generate callable routines to initialize and finalize the Ada
 units (see 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. You use the same
 procedure for building the program as described previously. In this case,
 however, the binder only places the initialization and finalization
 subprograms into file 'b~xxx.adb' instead of the main program. So, if the main
 program is not in Ada, you should proceed as follows:

   1. Compile the other language files to generate object files. For instance:

                      gcc -c file1.c
                      gcc -c file2.c

   2. Compile the Ada units to produce a set of object files and ALI files. For
      instance:

                      gnatmake -c entry_point1.adb
                      gnatmake -c entry_point2.adb

   3. Run the Ada binder on the Ada main program. For instance:

                      gnatbind -n entry_point1.ali entry_point2.ali

   4. Link the Ada main program, the Ada objects and the other language
      objects. You only need to give the last entry point here. For instance:

                      gnatlink entry_point2.ali file1.o file2.o


ΓòÉΓòÉΓòÉ 5.10.2. Calling Conventions ΓòÉΓòÉΓòÉ

 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 DEC Ada
      83, a higher degree of compatibility can be guaranteed, and in particular
      records are layed 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 runtime of GNAT and DEC
      Ada 83, All the tasking operations must either be entirely within GNAT
      compiled sections of the program, or entirely within DEC Ada 83 compiled
      sections of the program.

     Asm. Equivalent to Ada.

     Assembler. Equivalent to Ada.

     COBOL. Data will be passed according to the conventions described in
      section B.4 of the Ada 95 Reference Manual.

     C. Data will be passed according to the conventions described in section
      B.3 of the Ada 95 Reference Manual.

     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 95 Reference Manual.

     Intrinsic. This applies to an intrinsic operation, as defined in the Ada
      95 Reference Manual. If a 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 can only be applied to the following two sets of
      names, which the GNAT compiler recognizes.

        -  Rotate_Left, Rotate_Right, Shift_Left, Shift_Right, Shift_Right_-
           Arithmetic.  The corresponding subprogram declaration must have two
           formal parameters. The first one must be a signed integer type or a
           modular type with a binary modulus, and the second parameter must be
           of type Natural. The return type must be the same as the type of the
           first argument. The size of this type can only be 8, 16, 32, or 64.

        -  binary arithmetic operators: "+", "-", "*", "/"
           The corresponding operator declaration must have parameters and
           result type that have the same root numeric type (for example, all
           three are long_float types). This simplifies the definition of
           operations that use type checking to perform dimensional checks:

                      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 NT/Win95 implementations of GNAT, and
      specifies that the Stdcall calling sequence will be used, as defined by
      the NT API.

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


ΓòÉΓòÉΓòÉ 5.11. Building mixed Ada & C++ programs ΓòÉΓòÉΓòÉ


 Building a mixed application containing both Ada and C++ code may be a
 challenge for the unaware programmer. As a matter of fact, this interfacing
 has not been standardized in the Ada 95 reference manual due to the immaturity
 and lack of standard of C++ at the time. This section gives a few hints that
 should make this task easier. In particular the first section addresses the
 differences with interfacing with C. The second section looks into the
 delicate problem of linking the complete application from its Ada and C++
 parts. The last section give some hints on how the GNAT runtime can be adapted
 in order to allow inter-language dispatching with a new C++ compiler.

 Interfacing to C++            Interfacing to C++
 Linking a mixed C++ & Ada programLinking a mixed C++ & Ada program
 A simple example              A simple example
 Adapting the runtime to a new C++ compilerAdapting the runtime to a new C++
                               compiler


ΓòÉΓòÉΓòÉ 5.11.1. Interfacing to C++ ΓòÉΓòÉΓòÉ


 GNAT supports interfacing with C++ compilers generating code that is
 compatible with the standard Application Binary Interface of the given
 platform.
 Interfacing can be done at 3 levels: simple data, subprograms and classes. In
 the first 2 cases, GNAT offer a specific Convention CPP that behaves exactly
 like Convention C. Usually C++ mangle names of subprograms and currently GNAT
 does not provide any help to solve the demangling problem. This problem can be
 addressed in 2 ways:

     by modifying the C++ code in order to force a C convention using the
      extern "C" syntax.

     by figuring out the mangled name and use it as the Link_Name argument of
      the pragma import.

 Interfacing at the class level can be achieved by using the GNAT specific
 pragmas such as CPP_Class and  CPP_Virtual. See the GNAT Reference Manual for
 additional information.


ΓòÉΓòÉΓòÉ 5.11.2. Linking a mixed C++ & Ada program ΓòÉΓòÉΓòÉ


 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:

   1. Using GNAT and G++ (GNU C++ compiler) from the same GCC installation. The
      c++ linker can simply be called by using the c++ specific driver called
      c++. Note that this setup is not very common because it may request
      recompiling the whole GCC tree from sources and it does not allow to
      upgrade easily to a new version of one compiler for one of the two
      languages without taking the risk of destabilizing the other.

                      $ c++ -c file1.C
                      $ c++ -c file2.C
                      $ gnatmake ada_unit -largs file1.o file2.o --LINK=c++

   2. Using GNAT and G++ from 2 different GCC installations. If both compilers
      are on the PATH, the same method can be used. It is important to be aware
      that environment variables such as C_INCLUDE_PATH, GCC_EXEC_PREFIX,
      BINUTILS_ROOT or GCC_ROOT will affect both compilers at the same time and
      thus may make one of the 2 compilers operate improperly if they are set
      for the other. In particular it is important that the link command has
      access to the proper gcc library 'libgcc.a', that is to say the one that
      is part of the C++ compiler installation. The implicit link command as
      suggested in the gnatmake command from the former example can be replaced
      by an explicit link command with full verbosity in order to verify which
      library is used:

                      $ gnatbind ada_unit
                      $ gnatlink -v -v ada_unit file1.o file2.o --LINK=c++
 If there is a problem due to interfering environment variables, it can be
 workaround by using an intermediate script. The following example shows the
 proper script to use when GNAT has not been installed at its default location
 and g++ has been installed at its default location:

                      $ gnatlink -v -v ada_unit file1.o file2.o --LINK=./my_script
                      $ cat ./my_script
                      #!/bin/sh
                      unset BINUTILS_ROOT
                      unset GCC_ROOT
                      c++ $*

   3. Using a non GNU C++ compiler. The same set of command as previously
      described can be used to insure that the c++ linker is used. Nonetheless,
      the Ada code may implicitly depend on the gcc library. The latter can be
      located thanks to gnatls: it is to be found on the last directory of the
      object path. It must then be explicitly mentioned in the link command :

                      $ gnatls -v
                      $ Gdir=<the last directory on the object path>
                      $ gnatlink ada_unit file1.o file2.o -L$Gdir -lgcc \
                        --LINK=<cpp_linker>


ΓòÉΓòÉΓòÉ 5.11.3. A simple example ΓòÉΓòÉΓòÉ


 The following example, provided as part of the GNAT examples, show how to
 achieve procedural interfacing between Ada and C++ in both directions. The C++
 class A has 2 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++ calss is modelized by a limited record with a layout
 comparable to the C++ class. The Ada subprogram, in turn, calls the c++
 method. So from the C++ main program the code goes back and forth between the
 2 languages.
 Here are the compilation commands for native configurations:

                      $ gnatmake -c simple_cpp_interface
                      $ c++ -c cpp_main.C
                      $ c++ -c ex7.C
                      $ gnatbind -n simple_cpp_interface
                      $ gnatlink simple_cpp_interface -o cpp_main --LINK=$(CPLUSPLUS) \
                        -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);
                       virtual 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);
                      }
                      -- Ada sources
                      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;
                      package Simple_Cpp_Interface is
                        type A is limited
                         record
                           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;


ΓòÉΓòÉΓòÉ 5.11.4. Adapting the runtime to a new C++ compiler ΓòÉΓòÉΓòÉ


 GNAT offers the capability to derive Ada 95 tagged types directly from
 preexisting C++ classes and . See "Interfacing with C++" in the GNAT reference
 manual. The mechanism used by GNAT for achieving such a goal has been made
 user configurable through a GNAT library unit Interfaces.CPP. The default
 version of this file is adapted to the GNU c++ compiler. Internal knowledge of
 the virtual table layout used by the new C++ compiler is needed to configure
 properly this unit. The Interface of this unit is known by the compiler and
 cannot be changed except for the value of the constants defining the
 characteristics of the virtual table: CPP_DT_Prologue_Size, CPP_DT_Entry_Size,
 CPP_TSD_Prologue_Size, CPP_TSD_Entry_Size. Read comments in the source of this
 unit for more details.


ΓòÉΓòÉΓòÉ 5.12. Comparison between GNAT and C/C++ Compilation Models ΓòÉΓòÉΓòÉ


 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.


ΓòÉΓòÉΓòÉ 5.13. Comparison between GNAT and Conventional Ada Library Models ΓòÉΓòÉΓòÉ


 This section is intended to be useful to Ada programmers who have previously
 used an Ada compiler implementing the traditional Ada library model, as
 described in the Ada 95 Language Reference Manual. If you have not used such a
 system, please go on to the next section.

 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:

     When a unit is with'ed, the unit seen by the compiler corresponds to the
      version of the unit most recently compiled into the library.

     Inlining is effective only if the necessary body has already been
      compiled into the library.

     Compiling a unit may obsolete other units in the library.

 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:

     When a unit is with'ed, the unit seen by the compiler corresponds to the
      source version of the unit that is currently accessible to the compiler.

     Inlining requires the appropriate source files for the package or
      subprogram bodies to be available to the compiler. Inlining is always
      effective, independent of the order in which units are complied.

     Compiling a unit never affects any other compilations. The editing of
      sources may cause previous compilations to be out of date if they
      depended on the source file being modified.

 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.


ΓòÉΓòÉΓòÉ 6. Compiling Using gcc ΓòÉΓòÉΓòÉ


 This chapter 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            Compiling Programs
 Switches for gcc              Switches for gcc
 Search Paths and the Run-Time Library (RTL)Search Paths and the Run-Time
                               Library (RTL)
 Order of Compilation Issues   Order of Compilation Issues
 Examples                      Examples


ΓòÉΓòÉΓòÉ 6.1. Compiling Programs ΓòÉΓòÉΓòÉ


 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:

     the body file ('.adb') for a library level subprogram or generic
      subprogram

     the spec file ('.ads') for a library level package or generic package
      that has no body

     the body file ('.adb') for a library level package or generic package
      that has a body

 You need not compile the following files

     the spec of a library unit which has a body

     subunits

 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):

                      No code generated for file fff (package spec)
                      No code generated for file fff (subunit)

 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.

 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 three separate files to be compiled:

                      $ gcc -c x.adb y.adb z.c

 calls gnat1 (the Ada compiler) twice to compile 'x.adb' and 'y.adb', and cc1
 (the C compiler) once to compile 'z.c'. The compiler generates three object
 files 'x.o', 'y.o' and 'z.o' and the two ALI files 'x.ali' and 'y.ali' from
 the Ada compilations. Any switches apply to all the files listed, except for
 -gnatx switches, which apply only to Ada compilations.


ΓòÉΓòÉΓòÉ 6.2. Switches for gcc ΓòÉΓòÉΓòÉ


 The gcc command accepts numerous switches to control the compilation process.
 These switches are fully described in this section.

 Output and Error Message ControlOutput and Error Message Control
 Debugging and Assertion ControlDebugging and Assertion Control
 Run-time Checks               Run-time Checks
 Stack Overflow Checking       Stack Overflow Checking
 Run-time Control              Run-time Control
 Style Checking                Style Checking
 Using gcc for Syntax Checking Using gcc for Syntax Checking
 Using gcc for Semantic CheckingUsing gcc for Semantic Checking
 Compiling Ada 83 Programs     Compiling Ada 83 Programs
 Reference Manual Style CheckingReference Manual Style Checking
 Character Set Control         Character Set Control
 File Naming Control           File Naming Control
 Subprogram Inlining Control   Subprogram Inlining Control
 Auxiliary Output Control      Auxiliary Output Control
 Debugging Control             Debugging Control

 -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.

 -Bdir
           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 gcc
           manual page for further details. You would normally use the -b or -V
           switch instead.

 -c
           Compile. Always use this switch when compiling Ada programs.

           Note that you may not use gcc without a -c switch to compile and
           link in one step. This is because the binder must be run, and
           currently gcc cannot be used to run the GNAT binder.

 -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.

 -Idir
           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-
           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.

 -O[n]
           n controls the optimization level.

             n = 0
                         No optimization, the default setting if no -O appears

             n = 1
                         Normal optimization, the default if you specify -O
                         without an operand.

             n = 2
                         Extensive optimization

             n = 3
                         Extensive optimization with automatic inlining. This
                         applies only to inlining within a unit. For details on
                         control of inter-unit inlining see See Subprogram
                         Inlining Control.

 -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.

 -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.

 -funwind-tables
           This switch causes the object files to be generated with unwind
           table information. This is required for use of zero cost exception
           handling, of for use of the trace capabilities in the GNAT library.

 -gnata
           Assertions enabled. Pragma Assert and pragma Debug to be activated.

 -gnatb
           Generate brief messages to stderr even if verbose mode set.

 -gnatc
           Check syntax and semantics only (no code generation attempted).

 -gnatD
           Output expanded source files for source level debugging. This switch
           also suppress generation of cross-reference information (see
           -gnatx).

 -gnate
           Force error message generation (for use when compiler crashes).

 -gnatE
           Full dynamic elaboration checks.

 -gnatf
           Full errors. Multiple errors per line, all undefined references.

 -gnatF
           Externals names are folded to all uppercase.

 -gnatg
           GNAT style checks enabled.

 -gnatG
           List generated expanded code in source form.

 -gnatic
           Identifier character set (c=1/2/3/4/8/p/f/n/w).

 -gnath
           Output usage information. The output is written to stdout.

 -gnatkn
           Limit file names to n (1-999) characters (k = krunch).

 -gnatl
           Output full source listing with embedded error messages.

 -gnatmn
           Limit number of detected errors to n (1-999).

 -gnatn
           Activate inlining across unit boundaries for subprograms for which
           pragma inline is specified.

 -fno-inline
           Suppresses all inlining, even if other optimization or inlining
           switches are set.

 -fstack-check
           Activates stack checking. See separate section on stack checking for
           details of the use of this option.

 -gnato
           Enable other checks, not normally enabled by default, including
           numeric overflow checking, and access before elaboration checks.

 -gnatp
           Suppress all checks.

 -gnatq
           Don't quit; try semantics, even if parse errors.

 -gnatP
           Enable polling. This is required on some systems (notably Windows
           NT) to obtain asynchronous abort and asynchronous transfer of
           control capability. See the description of pragma Polling in the
           GNAT Reference Manual for full details.

 -gnatR
           Output representation information for declared array and record
           types.

 -gnats
           Syntax check only.

 -gnatt
           Tree output file to be generated.

 -gnatT nnn
           Set time slice to specified number of microseconds

 -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.

 -gnatwm
           Warning mode (m=s,e,l for suppress, treat as error, elaboration
           warnings).

 -gnatWe
           Wide character encoding method (e=n/h/u/s/e/8).

 -gnatx
           Suppress generation of cross-reference information.

 -gnatwm
           Warning mode

 -gnaty
           Enable built-in style checks. See separate section describing this
           feature.

 -gnatzm
           Distribution stub generation and compilation (m=r/c for
           receiver/caller stubs).

 -gnat83
           Enforce Ada 83 restrictions.

 -gnat95
           Standard Ada 95 mode

 You may combine a sequence of GNAT switches into a single switch. For example,
 the combined switch

                      -gnatcfi3

 is equivalent to specifying the following sequence of switches:

                      -gnatc -gnatf -gnati3


ΓòÉΓòÉΓòÉ 6.2.1. Output and Error Message Control ΓòÉΓòÉΓòÉ


 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. emacs 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. The output might look as follows:

                       1. procedure E is
                       2.   V : Integer;
                       3.   funcion X (Q : Integer)
                          |
                        >>> Incorrect spelling of keyword "function"
                       4.   return Integer;
                                 |
                        >>> ";" should be "is"
                       5.   begin
                       6.    return Q + Q;
                       7.   end;
                       8. begin
                       9.   V := X + X;
                      10.end E;

 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.

 -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).

 -gnatmn
           The m stands for maximum. n is a decimal integer in the range of 1
           to 999 and limits the number of error 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 errors reached
                      compilation abandoned

 -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

 -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.

 -gnate
           Normally, the compiler saves up error messages and generates them at
           the end of compilation in proper sequence. This switch  (the 'e'
           stands for error) causes error messages to be generated as soon as
           they are detected. The use of -gnate may cause error messages to be
           generated out of sequence and also disconnects a number of useful
           error message processing circuits. This switch should be used only
           in error situations where the compiler terminates with no output at
           all, or goes into an infinite loop. In such cases, the -gnate switch
           may be used to see if any error situations were detected before the
           compiler crash (see GNAT Abnormal Termination).

 In addition to error messages, which correspond to illegalities as defined in
 the Ada 95 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:

     Possible infinitely recursive calls

     Out-of-range values being assigned

     Possible order of elaboration problems

     Unreachable code

     Variables that are never assigned a value

     Variables that are referenced before being initialized

     Task entries with no corresponding Accept statement

     Duplicate Accepts for the same task entry in a select

     Objects that take too much storage

     Unchecked conversion between types of differing sizes

     Missing return statements along some execution paths in a function

     Incorrect pragmas

     Incorrect external names

     Allocation from empty storage pool

     Potentially blocking operations in protected types

     Suspicious parenthesization of expressions

     Mismatching bounds in an aggregate

     Attempt to return local value by reference

     Unrecognized pragmas

     Premature instantiation of a generic body

     Attempt to pack aliased components

     Out of bounds array subscripts

     Wrong length on string assignment

 The following switches are available to control the handling of warning
 messages:

 -gnatwa (activate all optional errors)
           This swich activates all optional warning messages, see remaining
           list in this section for details on optional warning messages that
           can be individually controlled.

 -gnatwA (suppress all optional errors)
           This swich suppresses all optional warning messages, see remaining
           list in this section for details on optional warning messages that
           can be individually controlled.

 -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.

 -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.

 -gnatwe (treat warnings as errors)
           This switch causes warning 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.

 -gnatwl (activate warnings on elaboration pragmas)
           This swich activates warnings on missing pragma Elaborate_All
           statements. See the section in this guide on elaboration checking
           for details on when such pragma should be used. The default is that
           such warnings are not generated.

 -gnatwL (suppress warnings on elaboration pragmas)
           This swich suppresses warnings on missing pragma Elaborate_All
           statements. See the section in this guide on elaboration checking
           for details on when such pragma should be used.

 -gnatws (suppress all warnings)
           This switch completely suppresses the output of all warning
           messages.

 -gnatwu (activate warnings on unused entities)
           This switch activates warnings to be generated for entities that are
           defined 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 the
           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.

 -gnatwU (suppress warnings on unused entities)
           This switch suppresses warnings for unused entities and packages.
           A string of warning parameters can be used in the same parameter.
           For example:

                      -gnatwaLe

 Would turn on all optional warnings except for elaboration pragma warnings,
 and also specify that warnings should be treated as errors.

 -gnatR
           Use of the switch -gnatR causes the compiler to output a listing
           showing representation information for declared array and record
           types, including record representation clauses.

 -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.


ΓòÉΓòÉΓòÉ 6.2.2. Debugging and Assertion Control ΓòÉΓòÉΓòÉ

 -gnata

           The pragmas Assert and Debug normally have no effect and are
           ignored. This switch, where 'a' stands for assert, causes Assert and
           Debug pragmas to be activated.

           The pragmas have the form:

                        pragma Assert (Boolean-expression [,
                                 static-string-expression])
                        pragma Debug (procedure call)

 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_Error
 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 giving
 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.


ΓòÉΓòÉΓòÉ 6.2.3. Style Checking ΓòÉΓòÉΓòÉ


 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
 error message is given, preceded by the character sequence "(style)", and the
 program is considered illegal. The string x is a sequence of letters or digits
 indicating the particular style checks to be performed. The following checks
 are defined:

 1-9 (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. 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.

 a (check attribute casing)
           If the letter a appears in the string after -gnaty then 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.

 b (blanks not allowed at statement end)
           If the letter b appears in the string after -gnaty then 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.

 c (check comments)
           If the letter c appears in the string after -gnaty then comments
           must meet the following set of rules:

               1. The "--" that starts the column must either start in column
                  one, or else at least one blank must precede this sequence.

               2. Comments that follow other tokens on a line must have at
                  least one blank following the "--" at the start of the
                  comment.

               3. Full line comments must have two blanks following the "--"
                  that starts the comment, with the following exceptions.

               4. A line consisting only of the "--" characters, possibly
                  preceded by blanks is permitted.

               5. A comment starting with "--!" is permitted. This allows
                  proper processing of the output generated by the gnatprep
                  tool.

               6. A line consisting entirely of minus signs, possibly preceded
                  by blanks, is permitted. This allows the construction of box
                  comments where lines of minus signs are used to form the top
                  and bottom of the box.

               7. If a comment starts and ends with "--" is permitted as long
                  as at least one blank follows the initial "--". Together with
                  the preceding rule, this allows the construction of box
                  comments, as shown in the following example:

                                                        ---------------------------
                                                        -- This is a box comment --
                                                        -- with two text lines.  --
                                                        ---------------------------

 e (check end labels)
           If the letter e appears in the string after -gnaty then optional
           labels on end statements ending subprograms are required to be
           present.

 f (no form feeds or vertical tabs)
           If the letter f appears in the string after -gnaty then neither form
           feeds nor vertical tab characters are not permitted in the source
           text.

 h (no horizontal tabs)
           If the letter h appears in the string after -gnaty then 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.

 i (check if-then layout)
           If the letter i appears in the string after -gnaty, then 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 with at least one non-blank
           line in between containing all or part of the condition to be
           tested.

 k (check keyword casing)
           If the letter k appears in the string after -gnaty then 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).

 l (check layout)
           If the letter l appears in the string after -gnaty then 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. For example,
           either of the following two layouts is acceptable:

                                              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;

 m (check maximum line length)
           If the letter m appears in the string after -gnaty then 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.

 Mnnn (set maximum line length)
           If the sequence Mnnn, where nnn is a decimal number, appears in the
           string after -gnaty then the length of lines must not exceed the
           given value.

 n (check casing of entities in Standard)
           If the letter n appears in the string after -gnaty then any
           identifier from Standard must be cased to match the presentation in
           the Ada Reference Manual (for example, Integer and ASCII.NUL).

 p (check pragma casing)
           If the letter p appears in the string after -gnaty then 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.

 r (check references)
           If the letter r appears in the string after -gnaty then 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.

 s (check separate specs)
           If the letter s appears in the string after -gnaty then 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.

 t (check token spacing)
           If the letter t appears in the string after -gnaty then the
           following token spacing rules are enforced:

               1. The keywords abs and not must be followed by a space.

               2. The token => must be surrounded by spaces.

               3. The token <> must be preceded by a space or a left
                  parenthesis.

               4. Binary operators other than ** must be surrounded by spaces.
                  There is no restriction on the layout of the ** binary
                  operator.

               5. Colon must be surrounded by spaces.

               6. Colon-equal (assignment) must be surrounded by spaces.

               7. Comma must be the first non-blank character on the line, or
                  be immediately preceded by a non-blank character, and must be
                  followed by a space.

               8. Left parenthesis must be preceded by a space, and must not be
                  followed by a space (it can be at the end of a line).

               9. A right parenthesis must either be the first non-blank
                  character on a line, or it must be preceded by a non-blank
                  character.

               10.A semicolon must not be preceded by a space, and must not be
                  followed by a non-blank character.

               11.A unary plus or minus may not be followed by a space.

               12.A vertical bar must be surrounded by spaces.


             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.

 The switch -gnaty on its own (that is not followed by any letters or digits),
 is equivalent to gnaty3abcefhiklmprst, that is all checking options are
 enabled, with an indentation level of 3. This is the standard checking option
 that is used for the GNAT sources.


ΓòÉΓòÉΓòÉ 6.2.4. Run-time Checks ΓòÉΓòÉΓòÉ


 If you compile with the default options, GNAT will insert many run-time checks
 into the compiled code, including code that performs range checking against
 constraints, but not arithmetic overflow checking for integer operations
 (including division by zero) or checks for access before elaboration on
 subprogram calls. All other run-time checks, as required by the Ada 95
 Reference Manual, are generated by default. The following gcc switches refine
 this default behavior:

 -gnatp
           Suppress all run-time checks as though pragma Suppress (all_checks)
           had been present in the source. Use this switch to improve the
           performance of the code at the expense of safety in the presence of
           invalid data or program bugs.

 -gnato
           Enables overflow checking for integer operations. This causes GNAT
           to generate slower and larger executable programs by adding code to
           check for both overflow and division by zero (resulting in raising
           Constraint_Error as required by Ada semantics). Note that the -gnato
           switch does not affect the code generated for any floating-point
           operations; it applies only to integer operations. 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).

 -gnatE
           Enables dynamic checks for access-before-elaboration on subprogram
           calls and generic instantiations. For full details of the effect and
           use of this switch, See Compiling Using gcc.

 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.


ΓòÉΓòÉΓòÉ 6.2.5. Stack Overflow Checking ΓòÉΓòÉΓòÉ


 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.

 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) do not exceed the available stack space. If the space is
 exceeded, then a Storage_Error exception is raised.

 For declared tasks, the stack size is always controlled by the size given in
 an applicable Storage_Size pragma (or is set to the default size if no pragma
 is used.

 For the environment task, the stack size depends on system defaults and is
 unknown to the compiler. The stack may even dynamically grow on some systems,
 precluding the normal Ada semantics for stack overflow. In the worst case,
 unbounded stack usage, causes unbounded stack expansion resulting in the
 system running out of virtual memory.

 The stack checking may still work correctly if a fixed size stack is
 allocated, but this cannot be guaranteed. To ensure that a clean exception is
 signalled for stack overflow, set the environment variable GNAT_STACK_LIMIT to
 indicate the maximum stack area that can be used, as in:

                      SET GNAT_STACK_LIMIT 1600

 The limit is given in kilobytes, so the above declaration would set the stack
 limit of the environment task to 1.6 megabytes.


ΓòÉΓòÉΓòÉ 6.2.6. Run-time Control ΓòÉΓòÉΓòÉ

 -gnatT nnn

           The gnatT switch can be used to specify the time-slicing value to be
           used for task switching between equal priority tasks. The value nnn
           is given in microseconds as a decimal integer.

           Setting the time-slicing value is only effective if the underlying
           thread control system can accomodate time slicing. Check the
           documentation of your operating system for details. Note that the
           time-slicing value can also be set by use of pragma Time_Slice or by
           use of the t switch in the gnatbind step. The pragma overrides a
           command line argument if both are present, and the t switch for
           gnatbind overrides both the pragma and the gcc command line switch.


ΓòÉΓòÉΓòÉ 6.2.7. Using gcc for Syntax Checking ΓòÉΓòÉΓòÉ

 -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 wild cards 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.

 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 (see Renaming Files Using gnatchop).


ΓòÉΓòÉΓòÉ 6.2.8. Using gcc for Semantic Checking ΓòÉΓòÉΓòÉ

 -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 95 Reference Manual, but without generation of any source code
           (no object or ALI file generated).

           Because dependent files must be accessed, you must follow the GNAT
           semantic restrictions on file structuring to operate in this mode:

               1. The needed source files must be accessible (see Search Paths
                  and the Run-Time Library (RTL)).

               2. Each file must contain only one compilation unit.

               3. The file name and unit name must match (see File Naming
                  Rules).

             The output consists of error messages as appropriate. No object
             file or ALI file is generated. The checking corresponds exactly to
             the notion of legality in the Ada 95 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).


ΓòÉΓòÉΓòÉ 6.2.9. Compiling Ada 83 Programs ΓòÉΓòÉΓòÉ

 -gnat83

           Although GNAT is primarily an Ada 95 compiler, it accepts this
           switch to specify that an Ada 83 program is to be compiled in Ada83
           mode. If you specify this switch, GNAT rejects most Ada 95
           extensions and applies Ada 83 semantics where this can be done
           easily. It is not possible to guarantee this switch does a perfect
           job; for example, some subtle tests, such as are found in earlier
           ACVC tests (that have been removed from the ACVC suite for Ada 95),
           may not compile correctly. However, for most purposes, using this
           switch should help to ensure that programs that compile correctly
           under the -gnat83 switch can be ported easily to an Ada 83 compiler.
           This is the main use of the switch.

           With few exceptions (most notably the need to use <> on
           unconstrained generic formal parameters, the use of the new Ada 95
           keywords, and the use of packages with optional bodies), it is not
           necessary to use the -gnat83 switch when compiling Ada 83 programs,
           because, with rare exceptions, Ada 95 is upwardly compatible with
           Ada 83. This means that a correct Ada 83 program is usually also a
           correct Ada 95 program.

 -gnat95
           This switch specifies normal Ada 95 mode, and cancels the effect of
           any previously given -gnat83 switch.


ΓòÉΓòÉΓòÉ 6.2.10. Reference Manual Style Checking ΓòÉΓòÉΓòÉ

 -gnatr

           Normally, GNAT permits any source layout consistent with the Ada 95
           reference manual requirements. This switch ('r' is for "reference
           manual") enforces the layout conventions suggested by the examples
           and syntax rules of the Ada 95 Language Reference Manual. For
           example, an else must line up with an if and code in the then and
           else parts must be indented. The compiler treats violations of the
           layout rules as syntax errors if you specify this switch.

 -gnatg
           Enforces a set of style conventions that correspond to the style
           used in the GNAT source code. All compiler units are always compiled
           with the -gnatg switch specified.

           You can find the full documentation for the style conventions
           imposed by -gnatg in the body of the package Style in the compiler
           sources (in the file 'style.adb').

           You should not normally use the -gnatg switch. However, you must use
           -gnatg for compiling any language-defined unit, or for adding
           children to any language-defined unit other than Standard.


ΓòÉΓòÉΓòÉ 6.2.11. Character Set Control ΓòÉΓòÉΓòÉ

 -gnatic

           Normally GNAT recognizes the Latin-1 character set in source program
           identifiers, as described in the Ada 95 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
                         Latin-1 identifiers

             2
                         Latin-2 letters allowed in identifiers

             3
                         Latin-3 letters allowed in identifiers

             4
                         Latin-4 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 allowed in identifiers

             See Foreign Language Representation, for full details on the
             implementation of these character sets.

 -gnatWe
           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 the these encoding methods see 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. scheme. If no -gnatW? parameter
             is present, then the default representation is Brackets encoding
             only.

             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.


ΓòÉΓòÉΓòÉ 6.2.12. File Naming Control ΓòÉΓòÉΓòÉ

 -gnatkn
           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, See File Naming Rules.


ΓòÉΓòÉΓòÉ 6.2.13. Subprogram Inlining Control ΓòÉΓòÉΓòÉ

 -gnatn
           The n here is intended to suggest the first syllable of the word
           "inline". GNAT recognizes and processes Inline pragmas. However, for
           the inlining to actually occur, optimization must be enabled. To
           enable inlining across unit boundaries, this is, inlining a call in
           one unit of a subprogram declared in a with'ed unit, you must also
           specify this switch. In the absence of this switch, GNAT does not
           attempt inlining across units and does not need to access the bodies
           of subprograms for which pragma Inline is specified if they are not
           in the current unit.

           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 See Inlining of Subprograms.


ΓòÉΓòÉΓòÉ 6.2.14. Auxiliary Output Control ΓòÉΓòÉΓòÉ

 -gnatt
           Cause GNAT to write the internal tree for a unit to a file (with the
           extension '.atd'. This not normally required, but is used by
           separate analysis tools. Typically these tools do the necessary
           compilations automatically, so you should never have to specify this
           switch in normal operation.

 -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.


ΓòÉΓòÉΓòÉ 6.2.15. Debugging Control ΓòÉΓòÉΓòÉ

 -gnatdx
           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
           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 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:

 -gnatD
           This switch is used in conjunction with -gnatG to cause the expanded
           source, as described above to be written to files with names
           'xxx.dg', where 'xxx' is the normal file name, 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
           suppress generation of cross-reference information (see -gnatx).

 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.

 freeze typename [actions]
           Shows the point at which typename 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.

 labelname : label
           Declaration of label labelname.

 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).


ΓòÉΓòÉΓòÉ 6.3. Search Paths and the Run-Time Library (RTL) ΓòÉΓòÉΓòÉ


 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:

   1. The directory containing the source file of the main unit being compiled
      (the file name on the command line).

   2. Each directory named by an -I switch given on the gcc command line, in
      the order given.

   3. Each of the directories listed in the value of the ADA_INCLUDE_PATH
      environment variable. Construct this value exactly as the PATH
      environment variable: a list of directory names separated by colons.

   4. The content of the "ada_source_path" file which is part of the GNAT
      installation tree and is used to store standard libraries such as the
      GNAT Run Time Library (RTL) source files. Installing an Ada library

 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 routines. 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.


ΓòÉΓòÉΓòÉ 6.4. Order of Compilation Issues ΓòÉΓòÉΓòÉ


 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:

     There is no point in compiling specs (except for package specs with no
      bodies) because these are compiled as needed by clients. If you attempt a
      useless compilation, you will receive an error message. It is also
      useless to compile subunits because they are compiled as needed by the
      parent.

     There are no order of compilation requirements: performing a compilation
      never obsoletes anything. The only way you can obsolete something and
      require recompilations is to modify one of the source files on which it
      depends.

     There is no library as such, apart from the ALI files (see The Ada
      Library Information Files, for information on the format of these files).
      For now we find it convenient to create separate ALI files, but
      eventually the information therein may be incorporated into the object
      file directly.

     When you compile a unit, the source files for the specs of all units that
      it with's, all its subunits, and the bodies of any generics it
      instantiates must be available (reachable by the search-paths mechanism
      described above), or you will receive a fatal error message.


ΓòÉΓòÉΓòÉ 6.5. Examples ΓòÉΓòÉΓòÉ


 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.


ΓòÉΓòÉΓòÉ 7. Binding Using gnatbind ΓòÉΓòÉΓòÉ

 Running gnatbind              Running gnatbind
 Generating The Binder Program in CGenerating The Binder Program in C
 Consistency-Checking Modes    Consistency-Checking Modes
 Binder Error Message Control  Binder Error Message Control
 Elaboration Control           Elaboration Control
 Output Control                Output Control
 Binding with Non-Ada Main ProgramsBinding with Non-Ada Main Programs
 Binding Programs with no Main SubprogramBinding Programs with no Main
                               Subprogram
 Summary of Binder Switches    Summary of Binder Switches
 Command-Line Access           Command-Line Access
 Search Paths for gnatbind     Search Paths for gnatbind
 Examples of gnatbind Usage    Examples of gnatbind Usage

 This chapter describes the GNAT binder, gnatbind, which is used to bind
 compiled GNAT objects. The gnatbind program performs four separate functions:

   1. Checks that a program is consistent, in accordance with the rules in
      Chapter 10 of the Ada 95 Reference Manual. In particular, error messages
      are generated if a program uses inconsistent versions of a given unit.

   2. Checks that an acceptable order of elaboration exists for the program and
      issues an error message if it cannot find an order of elaboration that
      satisfies the rules in Chapter 10 of the Ada 95 Language Manual.

   3. Generates a main program incorporating the given elaboration order. This
      program is a small Ada package (body and spec) that must be subsequently
      compiled using the GNAT compiler. The necessary compilation step is
      usually performed automatically by gnatlink. The two most important
      functions of this program are to call the elaboration routines of units
      in an appropriate order and to call the main program.

   4. Determines the set of object files required by the given main program.
      This information is output in the forms of comments in the generated C
      program, to be read by the gnatlink utility used to link the Ada
      application.


ΓòÉΓòÉΓòÉ 7.1. Running gnatbind ΓòÉΓòÉΓòÉ


 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. If
 no switches are specified, gnatbind constructs an Ada package in two files
 whose names are 'b~ada_main.ads', and 'b~ada_main.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 any source files it can
 locate into consideration. 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:

   1. Enter gcc -c hello.adb to compile the main program.

   2. Enter gcc -c p.ads to compile package P.

   3. Edit file 'p.ads'.

   4. Enter gnatbind hello.

 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 it is similar to the following which is the binder
 file generated for a simple "hello world" program.

                      --  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.
                      with System;
                      package Ada_Main is
                        --  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);
                        --  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);
                        --  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);
                        --  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.
                        procedure Break_Start;
                        pragma Import (C, Break_Start, "__gnat_break_start");
                        --  This is the actual generated main program (it would be
                        --  suppressed if the no main program swich 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.
                        u00001 : constant Integer := 16#425FD0AF#;
                        u00002 : constant Integer := 16#077A2651#;
                        u00003 : constant Integer := 16#08ADDC9E#;
                        u00004 : constant Integer := 16#1D370323#;
                        u00005 : constant Integer := 16#3043D77B#;
                        u00006 : constant Integer := 16#2359F9ED#;
                        u00007 : constant Integer := 16#0CA940CF#;
                        u00008 : constant Integer := 16#69BA6A59#;
                        u00009 : constant Integer := 16#156A40CF#;
                        u00010 : constant Integer := 16#033DABE0#;
                        u00011 : constant Integer := 16#6AB38FEA#;
                        u00012 : constant Integer := 16#7AAA368C#;
                        u00013 : constant Integer := 16#7D13B305#;
                        u00014 : constant Integer := 16#62D2B79D#;
                        u00015 : constant Integer := 16#2E865F1E#;
                        u00016 : constant Integer := 16#6379D875#;
                        u00017 : constant Integer := 16#72D6A51D#;
                        u00018 : constant Integer := 16#6E88E3D7#;
                        u00019 : constant Integer := 16#45C8383C#;
                        u00020 : constant Integer := 16#385E7AC2#;
                        u00021 : constant Integer := 16#08FE4C1F#;
                        u00022 : constant Integer := 16#23B87757#;
                        u00023 : constant Integer := 16#3A4BFD9A#;
                        u00024 : constant Integer := 16#4C9F3930#;
                        u00025 : constant Integer := 16#2F1EB794#;
                        u00026 : constant Integer := 16#0E2A461A#;
                        u00027 : constant Integer := 16#5570D114#;
                        u00028 : constant Integer := 16#501FA6BF#;
                        u00029 : constant Integer := 16#57692181#;
                        u00030 : constant Integer := 16#7C25DE96#;
                        u00031 : constant Integer := 16#521B9399#;
                        u00032 : constant Integer := 16#689CC1B9#;
                        u00033 : constant Integer := 16#0357E00A#;
                        u00034 : constant Integer := 16#1345CFE9#;
                        u00035 : constant Integer := 16#343244DE#;
                        u00036 : constant Integer := 16#6725DC79#;
                        u00037 : constant Integer := 16#2DAF477E#;
                        u00038 : constant Integer := 16#4F0184F2#;
                        u00039 : constant Integer := 16#0A0669D8#;
                        u00040 : constant Integer := 16#26610831#;
                        u00041 : constant Integer := 16#0B5A4DF9#;
                        u00042 : constant Integer := 16#1D4F93E8#;
                        u00043 : constant Integer := 16#30B2EC3D#;
                        u00044 : constant Integer := 16#34054F96#;
                        u00045 : constant Integer := 16#6598BA3E#;
                        u00046 : constant Integer := 16#2C9C021D#;
                        u00047 : constant Integer := 16#177A51F6#;
                        u00048 : constant Integer := 16#1CBC39CD#;
                        u00049 : constant Integer := 16#5461BB3E#;
                        u00050 : constant Integer := 16#03F36D98#;
                        u00051 : constant Integer := 16#208D3EF6#;
                        u00052 : constant Integer := 16#33AF4230#;
                        u00053 : constant Integer := 16#0B97C6BF#;
                        u00054 : constant Integer := 16#34B32999#;
                        --  The following Export pragms 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.
                        pragma Export (C, u00001, "helloB");
                        pragma Export (C, u00002, "system__standard_libraryB");
                        pragma Export (C, u00003, "system__standard_libraryS");
                        pragma Export (C, u00004, "systemS");
                        pragma Export (C, u00005, "system__exceptionsS");
                        pragma Export (C, u00006, "adaS");
                        pragma Export (C, u00007, "ada__exceptionsB");
                        pragma Export (C, u00008, "ada__exceptionsS");
                        pragma Export (C, u00009, "gnatS");
                        pragma Export (C, u00010, "gnat__heap_sort_aB");
                        pragma Export (C, u00011, "gnat__heap_sort_aS");
                        pragma Export (C, u00012, "system__exception_tableB");
                        pragma Export (C, u00013, "system__exception_tableS");
                        pragma Export (C, u00014, "gnat__htableB");
                        pragma Export (C, u00015, "gnat__htableS");
                        pragma Export (C, u00016, "system__machine_codeS");
                        pragma Export (C, u00017, "system__secondary_stackB");
                        pragma Export (C, u00018, "system__secondary_stackS");
                        pragma Export (C, u00019, "system__parametersB");
                        pragma Export (C, u00020, "system__parametersS");
                        pragma Export (C, u00021, "system__soft_linksB");
                        pragma Export (C, u00022, "system__soft_linksS");
                        pragma Export (C, u00023, "system__stack_checkingB");
                        pragma Export (C, u00024, "system__stack_checkingS");
                        pragma Export (C, u00025, "system__storage_elementsB");
                        pragma Export (C, u00026, "system__storage_elementsS");
                        pragma Export (C, u00027, "text_ioS");
                        pragma Export (C, u00028, "ada__text_ioB");
                        pragma Export (C, u00029, "ada__text_ioS");
                        pragma Export (C, u00030, "ada__streamsS");
                        pragma Export (C, u00031, "ada__tagsB");
                        pragma Export (C, u00032, "ada__tagsS");
                        pragma Export (C, u00033, "interfacesS");
                        pragma Export (C, u00034, "interfaces__c_streamsB");
                        pragma Export (C, u00035, "interfaces__c_streamsS");
                        pragma Export (C, u00036, "system__file_ioB");
                        pragma Export (C, u00037, "system__file_ioS");
                        pragma Export (C, u00038, "ada__finalizationB");
                        pragma Export (C, u00039, "ada__finalizationS");
                        pragma Export (C, u00040, "system__finalization_rootB");
                        pragma Export (C, u00041, "system__finalization_rootS");
                        pragma Export (C, u00042, "system__stream_attributesB");
                        pragma Export (C, u00043, "system__stream_attributesS");
                        pragma Export (C, u00044, "ada__io_exceptionsS");
                        pragma Export (C, u00045, "system__unsigned_typesS");
                        pragma Export (C, u00046, "system__finalization_implementationB");
                        pragma Export (C, u00047, "system__finalization_implementationS");
                        pragma Export (C, u00048, "system__string_ops_concat_3B");
                        pragma Export (C, u00049, "system__string_ops_concat_3S");
                        pragma Export (C, u00050, "system__string_opsB");
                        pragma Export (C, u00051, "system__string_opsS");
                        pragma Export (C, u00052, "system__file_control_blockS");
                        pragma Export (C, u00053, "ada__finalization__list_controllerB");
                        pragma Export (C, u00054, "ada__finalization__list_controllerS");
                      end Ada_Main;
                      --  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");
                      package body Ada_Main is
                      --  Generated package body for Ada_Main starts here
                        -------------
                        -- adainit --
                        -------------
                        procedure adainit is
                         --  Set_Globals is a library routine that stores away the
                         --  value of the indicated set of global values in global
                         --  variables within the library.
                         procedure Set_Globals
                          (Main_Priority       : Integer;
                           Time_Slice_Value     : Integer;
                           WC_Encoding        : Character;
                           Locking_Policy      : Character;
                           Queuing_Policy      : Character;
                           Task_Dispatching_Policy  : Character;
                           Adafinal         : System.Address;
                           Unreserve_All_Interrupts : Boolean;
                           Exception_Tracebacks   : Boolean);
                         pragma Import (C, Set_Globals, "__gnat_set_globals");
                         --  SDP_Table_Build is a library routine used to build the
                         --  exception tables. See unit Ada.Exceptions in files
                         --  a-except.ads/adb for full details of how zero cost
                         --  exception handling works. This procedure, the call to
                         --  it, and the two following tables are all omitted if the
                         --  build is in longjmp/setjump exception mode.
                         procedure SDP_Table_Build
                          (SDP_Addresses  : System.Address;
                           SDP_Count    : Natural;
                           Elab_Addresses  : System.Address;
                           Elab_Addr_Count : Natural);
                         pragma Import (C, SDP_Table_Build, "__gnat_SDP_Table_Build");
                         --  Table of Unit_Exception_Table addresses. Used for zero
                         --  cost exception handling to build the top level table.
                         ST : aliased constant array (1 ┬╖┬╖ 21) of System.Address := (
                          Hello'UET_Address,
                          Ada.Exceptions'UET_Address,
                          Gnat.Heap_Sort_A'UET_Address,
                          System.Exception_Table'UET_Address,
                          System.Secondary_Stack'UET_Address,
                          System.Parameters'UET_Address,
                          System.Soft_Links'UET_Address,
                          System.Stack_Checking'UET_Address,
                          Ada.Text_Io'UET_Address,
                          Ada.Streams'UET_Address,
                          Ada.Tags'UET_Address,
                          Interfaces.C_Streams'UET_Address,
                          System.File_Io'UET_Address,
                          Ada.Finalization'UET_Address,
                          System.Finalization_Root'UET_Address,
                          System.Stream_Attributes'UET_Address,
                          System.Finalization_Implementation'UET_Address,
                          System.String_Ops_Concat_3'UET_Address,
                          System.String_Ops'UET_Address,
                          System.File_Control_Block'UET_Address,
                          Ada.Finalization.List_Controller'UET_Address);
                         --  Table of addresses of elaboration routines. Used for
                         --  zero cost exception handling to make sure these
                         --  addresses are included in the top level procedure
                         --  address table.
                         EA : aliased constant array (1 ┬╖┬╖ 22) of System.Address := (
                          adainit'Code_Address,
                          adafinal'Code_Address,
                          Ada.Exceptions'Elab_Spec'Address,
                          System.Exceptions'Elab_Spec'Address,
                          Interfaces.C_Streams'Elab_Spec'Address,
                          System.Exception_Table'Elab_Body'Address,
                          Ada.Io_Exceptions'Elab_Spec'Address,
                          Ada.Tags'Elab_Spec'Address,
                          Ada.Tags'Elab_Body'Address,
                          Ada.Streams'Elab_Spec'Address,
                          System.Stack_Checking'Elab_Spec'Address,
                          System.Soft_Links'Elab_Body'Address,
                          System.Secondary_Stack'Elab_Body'Address,
                          Ada.Exceptions'Elab_Body'Address,
                          System.Finalization_Root'Elab_Spec'Address,
                          System.Finalization_Implementation'Elab_Spec'Address,
                          Ada.Finalization'Elab_Spec'Address,
                          Ada.Finalization.List_Controller'Elab_Spec'Address,
                          System.File_Control_Block'Elab_Spec'Address,
                          System.File_Io'Elab_Body'Address,
                          Ada.Text_Io'Elab_Spec'Address,
                          Ada.Text_Io'Elab_Body'Address);
                        --  Start of processing for adainit
                        begin
                         --  Call SDP_Table_Build to build the top level procedure
                         --  table for zero cost exception handling (omitted in
                         --  longjmp/setjump mode).
                         SDP_Table_Build (ST'Address, 21, EA'Address, 22);
                         --  Call Set_Globals to record various information for
                         --  this partition.  The values are derived by the binder
                         --  from information stored in the ali files by the compiler.
                         Set_Globals
                          (Main_Priority       => -1,
                           --  Priority of main program, -1 if no pragma Priority used
                           Time_Slice_Value     => -1,
                           --  Time slice from Time_Slice pragma, -1 if none used
                           WC_Encoding        => 'b',
                           --  Wide_Character encoding used, default is brackets
                           Locking_Policy      => ' ',
                           --  Locking_Policy used, default of space means not
                           --  specified, otherwise it is the first character of
                           --  the policy name.
                           Queuing_Policy      => ' ',
                           --  Queuing_Policy used, default of space means not
                           --  specified, otherwise it is the first character of
                           --  the policy name.
                           Task_Dispatching_Policy  => ' ',
                           --  Task_Dispatching_Policy used, default of space means
                           --  not specified, otherwise first character of the
                           --  policy name.
                           Adafinal         => adafinal'Address,
                           --  Address of generated ada final routine
                           Unreserve_All_Interrupts => False,
                           --  Set true if pragma Unreserve_All_Interrupts was used
                           Exception_Tracebacks   => False);
                           --  Indicates if exception tracebacks are enabled
                         --  Now we have the elaboration calls for all units in the
                         --  partition. The all is commented out if the given unit
                         --  has no elaboration code. We retain the commented out call
                         --  to indicate the full order chosen. The Elab_Spec and
                         --  Elab_Body attributes generate references to the implicit
                         --  elaboration procedures generated by the compiler for each
                         --  unit that requires elaboration.
                         -- System'Elab_Spec;
                         -- Ada'Elab_Spec;
                         -- Gnat'Elab_Spec;
                         -- Gnat.Heap_Sort_A'Elab_Spec;
                         -- Gnat.Htable'Elab_Spec;
                         -- Gnat.Htable'Elab_Body;
                         -- Interfaces'Elab_Spec;
                         -- System.Machine_Code'Elab_Spec;
                         -- System.Parameters'Elab_Spec;
                         -- System.Standard_Library'Elab_Spec;
                           Ada.Exceptions'Elab_Spec;
                           System.Exceptions'Elab_Spec;
                         -- System.Parameters'Elab_Body;
                         -- Gnat.Heap_Sort_A'Elab_Body;
                           Interfaces.C_Streams'Elab_Spec;
                         -- Interfaces.C_Streams'Elab_Body;
                         -- System.Exception_Table'Elab_Spec;
                           System.Exception_Table'Elab_Body;
                           Ada.Io_Exceptions'Elab_Spec;
                         -- System.Storage_Elements'Elab_Spec;
                         -- System.Storage_Elements'Elab_Body;
                         -- System.Secondary_Stack'Elab_Spec;
                           Ada.Tags'Elab_Spec;
                           Ada.Tags'Elab_Body;
                           Ada.Streams'Elab_Spec;
                           System.Stack_Checking'Elab_Spec;
                         -- System.Soft_Links'Elab_Spec;
                           System.Soft_Links'Elab_Body;
                         -- System.Stack_Checking'Elab_Body;
                           System.Secondary_Stack'Elab_Body;
                           Ada.Exceptions'Elab_Body;
                         -- System.Standard_Library'Elab_Body;
                         -- System.String_Ops'Elab_Spec;
                         -- System.String_Ops'Elab_Body;
                         -- System.String_Ops_Concat_3'Elab_Spec;
                         -- System.String_Ops_Concat_3'Elab_Body;
                         -- System.Unsigned_Types'Elab_Spec;
                         -- System.Stream_Attributes'Elab_Spec;
                         -- System.Stream_Attributes'Elab_Body;
                           System.Finalization_Root'Elab_Spec;
                         -- System.Finalization_Root'Elab_Body;
                           System.Finalization_Implementation'Elab_Spec;
                         -- System.Finalization_Implementation'Elab_Body;
                           Ada.Finalization'Elab_Spec;
                         -- Ada.Finalization'Elab_Body;
                           Ada.Finalization.List_Controller'Elab_Spec;
                         -- Ada.Finalization.List_Controller'Elab_Body;
                           System.File_Control_Block'Elab_Spec;
                         -- System.File_Io'Elab_Spec;
                           System.File_Io'Elab_Body;
                           Ada.Text_Io'Elab_Spec;
                           Ada.Text_Io'Elab_Body;
                         -- Text_Io'Elab_Spec;
                         -- hello'elab_body;
                         null;
                        end adainit;
                        --------------
                        -- adafinal --
                        --------------
                        procedure adafinal is
                         --  The actual finalization is performed by calling the
                         --  library routine in System.Finalization_Implementation.
                         procedure do_finalize;
                         pragma Import
                          (C, do_finalize,
                           "system__finalization_implementation__finalize_global_list");
                        begin
                         do_finalize;
                        end adafinal;
                        ----------
                        -- 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");
                         --  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");
                        --  Start of processing for main
                        begin
                         --  Save global variables
                         gnat_argc := argc;
                         gnat_argv := argv;
                         gnat_envp := envp;
                         --  Call low level system initialization
                         Initialize;
                         --  Call our generated Ada initialization routine
                         adainit;
                         --  This is the point at which we want the debugger to get
                         --  control
                         Break_Start;
                         --  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
                        --  ./system.o
                        --  ./ada.o
                        --  ./gnat.o
                        --  ./g-htable.o
                        --  ./interfac.o
                        --  ./s-maccod.o
                        --  ./s-except.o
                        --  ./s-parame.o
                        --  ./g-hesora.o
                        --  ./i-cstrea.o
                        --  ./s-exctab.o
                        --  ./a-ioexce.o
                        --  ./s-stoele.o
                        --  ./a-tags.o
                        --  ./a-stream.o
                        --  ./s-soflin.o
                        --  ./s-stache.o
                        --  ./s-secsta.o
                        --  ./a-except.o
                        --  ./s-stalib.o
                        --  ./s-strops.o
                        --  ./s-sopco3.o
                        --  ./s-unstyp.o
                        --  ./s-stratt.o
                        --  ./s-finroo.o
                        --  ./s-finimp.o
                        --  ./a-finali.o
                        --  ./a-filico.o
                        --  ./s-ficobl.o
                        --  ./s-fileio.o
                        --  ./a-textio.o
                        --  ./text_io.o
                        --  ./hello.o
                        --  -L./
                      ┬╖┬╖┬╖  Target/System specific library search directives
                        --  -lgnat
                      -- 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 blowing up during elaboration of
 the body of Ada.Text_IO. To chase this bug down, 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).


ΓòÉΓòÉΓòÉ 7.2. Generating The Binder Program in C ΓòÉΓòÉΓòÉ


 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.

 However for some purposes it may be convenient to generate the main program in
 C rather than Ada. This may for example be helpful when you are generating a
 mixed language program with the main program in C. The GNAT compiler itself is
 an example. The use of the -C switch for both gnatbind and gnatlink will cause
 the program to be generated in C (and compiled using the gnu C compiler). The
 following shows the C code generated for the same "Hello World" program:

                      extern int gnat_argc;
                      extern char **gnat_argv;
                      extern char **gnat_envp;
                      extern int gnat_exit_status;
                      void adafinal ();
                      void adainit ()
                      {
                        extern void *__gnat_hello__SDP;
                        extern void *__gnat_ada__exceptions__SDP;
                        extern void *__gnat_gnat__heap_sort_a__SDP;
                        extern void *__gnat_system__exception_table__SDP;
                        extern void *__gnat_system__secondary_stack__SDP;
                        extern void *__gnat_system__parameters__SDP;
                        extern void *__gnat_system__soft_links__SDP;
                        extern void *__gnat_system__stack_checking__SDP;
                        extern void *__gnat_ada__text_io__SDP;
                        extern void *__gnat_ada__streams__SDP;
                        extern void *__gnat_ada__tags__SDP;
                        extern void *__gnat_interfaces__c_streams__SDP;
                        extern void *__gnat_system__file_io__SDP;
                        extern void *__gnat_ada__finalization__SDP;
                        extern void *__gnat_system__finalization_root__SDP;
                        extern void *__gnat_system__stream_attributes__SDP;
                        extern void *__gnat_system__finalization_implementation__SDP;
                        extern void *__gnat_system__string_ops_concat_3__SDP;
                        extern void *__gnat_system__string_ops__SDP;
                        extern void *__gnat_system__file_control_block__SDP;
                        extern void *__gnat_ada__finalization__list_controller__SDP;
                        void **st[21] = {
                         &__gnat_hello__SDP,
                         &__gnat_ada__exceptions__SDP,
                         &__gnat_gnat__heap_sort_a__SDP,
                         &__gnat_system__exception_table__SDP,
                         &__gnat_system__secondary_stack__SDP,
                         &__gnat_system__parameters__SDP,
                         &__gnat_system__soft_links__SDP,
                         &__gnat_system__stack_checking__SDP,
                         &__gnat_ada__text_io__SDP,
                         &__gnat_ada__streams__SDP,
                         &__gnat_ada__tags__SDP,
                         &__gnat_interfaces__c_streams__SDP,
                         &__gnat_system__file_io__SDP,
                         &__gnat_ada__finalization__SDP,
                         &__gnat_system__finalization_root__SDP,
                         &__gnat_system__stream_attributes__SDP,
                         &__gnat_system__finalization_implementation__SDP,
                         &__gnat_system__string_ops_concat_3__SDP,
                         &__gnat_system__string_ops__SDP,
                         &__gnat_system__file_control_block__SDP,
                         &__gnat_ada__finalization__list_controller__SDP};
                        extern void ada__exceptions___elabs ();
                        extern void system__exceptions___elabs ();
                        extern void interfaces__c_streams___elabs ();
                        extern void system__exception_table___elabb ();
                        extern void ada__io_exceptions___elabs ();
                        extern void ada__tags___elabs ();
                        extern void ada__tags___elabb ();
                        extern void ada__streams___elabs ();
                        extern void system__stack_checking___elabs ();
                        extern void system__soft_links___elabb ();
                        extern void system__secondary_stack___elabb ();
                        extern void ada__exceptions___elabb ();
                        extern void system__finalization_root___elabs ();
                        extern void system__finalization_implementation___elabs ();
                        extern void ada__finalization___elabs ();
                        extern void ada__finalization__list_controller___elabs ();
                        extern void system__file_control_block___elabs ();
                        extern void system__file_io___elabb ();
                        extern void ada__text_io___elabs ();
                        extern void ada__text_io___elabb ();
                        void (*ea[22]) () = {
                         adainit,
                         adafinal,
                         ada__exceptions___elabs,
                         system__exceptions___elabs,
                         interfaces__c_streams___elabs,
                         system__exception_table___elabb,
                         ada__io_exceptions___elabs,
                         ada__tags___elabs,
                         ada__tags___elabb,
                         ada__streams___elabs,
                         system__stack_checking___elabs,
                         system__soft_links___elabb,
                         system__secondary_stack___elabb,
                         ada__exceptions___elabb,
                         system__finalization_root___elabs,
                         system__finalization_implementation___elabs,
                         ada__finalization___elabs,
                         ada__finalization__list_controller___elabs,
                         system__file_control_block___elabs,
                         system__file_io___elabb,
                         ada__text_io___elabs,
                         ada__text_io___elabb};
                        __gnat_SDP_Table_Build (&st, 21, ea, 22);
                        __gnat_set_globals (
                         -1,    /* Main_Priority        */
                         -1,    /* Time_Slice_Value      */
                         'b',   /* WC_Encoding         */
                         ' ',   /* Locking_Policy       */
                         ' ',   /* Queuing_Policy       */
                         ' ',   /* Tasking_Dispatching_Policy */
                         adafinal,/* Finalization routine address */
                         0,    /* Unreserve_All_Interrupts */
                         0);    /* Exception_Tracebacks */
                      /* system___elabs (); */
                      /* ada___elabs (); */
                      /* gnat___elabs (); */
                      /* gnat__heap_sort_a___elabs (); */
                      /* gnat__htable___elabs (); */
                      /* gnat__htable___elabb (); */
                      /* interfaces___elabs (); */
                      /* system__machine_code___elabs (); */
                      /* system__parameters___elabs (); */
                      /* system__standard_library___elabs (); */
                        ada__exceptions___elabs ();
                        system__exceptions___elabs ();
                      /* system__parameters___elabb (); */
                      /* gnat__heap_sort_a___elabb (); */
                        interfaces__c_streams___elabs ();
                      /* interfaces__c_streams___elabb (); */
                      /* system__exception_table___elabs (); */
                        system__exception_table___elabb ();
                        ada__io_exceptions___elabs ();
                      /* system__storage_elements___elabs (); */
                      /* system__storage_elements___elabb (); */
                      /* system__secondary_stack___elabs (); */
                        ada__tags___elabs ();
                        ada__tags___elabb ();
                        ada__streams___elabs ();
                        system__stack_checking___elabs ();
                      /* system__soft_links___elabs (); */
                        system__soft_links___elabb ();
                      /* system__stack_checking___elabb (); */
                        system__secondary_stack___elabb ();
                        ada__exceptions___elabb ();
                      /* system__standard_library___elabb (); */
                      /* system__string_ops___elabs (); */
                      /* system__string_ops___elabb (); */
                      /* system__string_ops_concat_3___elabs (); */
                      /* system__string_ops_concat_3___elabb (); */
                      /* system__unsigned_types___elabs (); */
                      /* system__stream_attributes___elabs (); */
                      /* system__stream_attributes___elabb (); */
                        system__finalization_root___elabs ();
                      /* system__finalization_root___elabb (); */
                        system__finalization_implementation___elabs ();
                      /* system__finalization_implementation___elabb (); */
                        ada__finalization___elabs ();
                      /* ada__finalization___elabb (); */
                        ada__finalization__list_controller___elabs ();
                      /* ada__finalization__list_controller___elabb (); */
                        system__file_control_block___elabs ();
                      /* system__file_io___elabs (); */
                        system__file_io___elabb ();
                        ada__text_io___elabs ();
                        ada__text_io___elabb ();
                      /* text_io___elabs (); */
                      /* hello___elabb (); */
                      }
                      void adafinal () {
                        system__finalization_implementation__finalize_global_list ();
                      }
                      int main (argc, argv, envp)
                        int argc;
                        char **argv;
                        char **envp;
                      {
                        gnat_argc = argc;
                        gnat_argv = argv;
                        gnat_envp = envp;
                        __gnat_initialize();
                        adainit();
                        __gnat_break_start();
                        _ada_hello ();
                        adafinal();
                        __gnat_finalize();
                        exit (gnat_exit_status);
                      }
                      unsigned helloB = 0x425FD0AF;
                      unsigned system__standard_libraryB = 0x077A2651;
                      unsigned system__standard_libraryS = 0x08ADDC9E;
                      unsigned systemS = 0x1D370323;
                      unsigned system__exceptionsS = 0x3043D77B;
                      unsigned adaS = 0x2359F9ED;
                      unsigned ada__exceptionsB = 0x0CA940CF;
                      unsigned ada__exceptionsS = 0x69BA6A59;
                      unsigned gnatS = 0x156A40CF;
                      unsigned gnat__heap_sort_aB = 0x033DABE0;
                      unsigned gnat__heap_sort_aS = 0x6AB38FEA;
                      unsigned system__exception_tableB = 0x7AAA368C;
                      unsigned system__exception_tableS = 0x7D13B305;
                      unsigned gnat__htableB = 0x62D2B79D;
                      unsigned gnat__htableS = 0x2E865F1E;
                      unsigned system__machine_codeS = 0x6379D875;
                      unsigned system__secondary_stackB = 0x72D6A51D;
                      unsigned system__secondary_stackS = 0x6E88E3D7;
                      unsigned system__parametersB = 0x45C8383C;
                      unsigned system__parametersS = 0x385E7AC2;
                      unsigned system__soft_linksB = 0x08FE4C1F;
                      unsigned system__soft_linksS = 0x23B87757;
                      unsigned system__stack_checkingB = 0x3A4BFD9A;
                      unsigned system__stack_checkingS = 0x4C9F3930;
                      unsigned system__storage_elementsB = 0x2F1EB794;
                      unsigned system__storage_elementsS = 0x0E2A461A;
                      unsigned text_ioS = 0x5570D114;
                      unsigned ada__text_ioB = 0x501FA6BF;
                      unsigned ada__text_ioS = 0x57692181;
                      unsigned ada__streamsS = 0x7C25DE96;
                      unsigned ada__tagsB = 0x521B9399;
                      unsigned ada__tagsS = 0x689CC1B9;
                      unsigned interfacesS = 0x0357E00A;
                      unsigned interfaces__c_streamsB = 0x1345CFE9;
                      unsigned interfaces__c_streamsS = 0x343244DE;
                      unsigned system__file_ioB = 0x6725DC79;
                      unsigned system__file_ioS = 0x2DAF477E;
                      unsigned ada__finalizationB = 0x4F0184F2;
                      unsigned ada__finalizationS = 0x0A0669D8;
                      unsigned system__finalization_rootB = 0x26610831;
                      unsigned system__finalization_rootS = 0x0B5A4DF9;
                      unsigned system__stream_attributesB = 0x1D4F93E8;
                      unsigned system__stream_attributesS = 0x30B2EC3D;
                      unsigned ada__io_exceptionsS = 0x34054F96;
                      unsigned system__unsigned_typesS = 0x6598BA3E;
                      unsigned system__finalization_implementationB = 0x2C9C021D;
                      unsigned system__finalization_implementationS = 0x177A51F6;
                      unsigned system__string_ops_concat_3B = 0x1CBC39CD;
                      unsigned system__string_ops_concat_3S = 0x5461BB3E;
                      unsigned system__string_opsB = 0x03F36D98;
                      unsigned system__string_opsS = 0x208D3EF6;
                      unsigned system__file_control_blockS = 0x33AF4230;
                      unsigned ada__finalization__list_controllerB = 0x0B97C6BF;
                      unsigned ada__finalization__list_controllerS = 0x34B32999;
                      /* BEGIN Object file/option list
                      ┬╖/system.o
                      ┬╖/ada.o
                      ┬╖/gnat.o
                      ┬╖/g-htable.o
                      ┬╖/interfac.o
                      ┬╖/s-maccod.o
                      ┬╖/s-except.o
                      ┬╖/s-parame.o
                      ┬╖/g-hesora.o
                      ┬╖/i-cstrea.o
                      ┬╖/s-exctab.o
                      ┬╖/a-ioexce.o
                      ┬╖/s-stoele.o
                      ┬╖/a-tags.o
                      ┬╖/a-stream.o
                      ┬╖/s-soflin.o
                      ┬╖/s-stache.o
                      ┬╖/s-secsta.o
                      ┬╖/a-except.o
                      ┬╖/s-stalib.o
                      ┬╖/s-strops.o
                      ┬╖/s-sopco3.o
                      ┬╖/s-unstyp.o
                      ┬╖/s-stratt.o
                      ┬╖/s-finroo.o
                      ┬╖/s-finimp.o
                      ┬╖/a-finali.o
                      ┬╖/a-filico.o
                      ┬╖/s-ficobl.o
                      ┬╖/s-fileio.o
                      ┬╖/a-textio.o
                      ┬╖/text_io.o
                      ┬╖/hello.o
                      -L./
                      ┬╖┬╖┬╖  Target/System specific library search directives
                      -lgnat
                        END Object file/option list */

 Here again, the C code is exactly what is generated by the binder. The
 functions of the various parts of this code correspond in an obvious manner
 with the commented Ada code shown in the example in the previous section.


ΓòÉΓòÉΓòÉ 7.3. Consistency-Checking Modes ΓòÉΓòÉΓòÉ


 As described in the previous section, 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.

 -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).


ΓòÉΓòÉΓòÉ 7.4. Binder Error Message Control ΓòÉΓòÉΓòÉ


 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.

 -mn
           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.

 -Mxxx
           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:

               1. Check that time stamps of a given source unit are consistent

               2. Check that checksums of a given source unit are consistent

               3. Check that consistent versions of GNAT were used for
                  compilation

               4. Check consistency of configuration pragmas as required


             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\/NOTIME_STAMP_CHECK 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. This means that -t
             should be used only in unusual situations, with extreme care.


ΓòÉΓòÉΓòÉ 7.5. Elaboration Control ΓòÉΓòÉΓòÉ


 The following switches provide additional control over the elaboration order.
 For full details see See Elaboration Order Handling in GNAT.

 -f
           Instructs the binder to ignore directives from the compiler about
           implied Elaborate_All pragmas, and to use full Ada 95 Reference
           Manual semantics in an attempt to find a legal elaboration order,
           even if it seems likely that this order will cause an elaboration
           exception.

 -p
           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.


ΓòÉΓòÉΓòÉ 7.6. Output Control ΓòÉΓòÉΓòÉ


 The following switches allow additional control over the output generated by
 the binder.

 -A
           Generate binder program in Ada (default). The binder program is
           named 'b~mainprog.adb' by default. This can be changed with -o
           gnatbind option.

 -C
           Generate binder program in C. The binder program is named
           'b_mainprog.c'. This can be changed with -o gnatbind option.

 -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.

 -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. In C mode you would normally give file an
           extension of '.c' because it will be a C source program. 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.

 -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.


ΓòÉΓòÉΓòÉ 7.7. Binding with Non-Ada Main Programs ΓòÉΓòÉΓòÉ


 In our description so far we have 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 (see 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\/OUTPUT=file\. The output is an
 Ada unit in source form that can be compiled with GNAT unless the -C switch is
 used in which case the output is a C source file, which must be compiled using
 the C compiler. This compilation occurs automatically as part of the gnatlink
 processing.

 Currently GNAT runtime 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.


ΓòÉΓòÉΓòÉ 7.8. Binding Programs with no Main Subprogram ΓòÉΓòÉΓòÉ


 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.


ΓòÉΓòÉΓòÉ 7.9. Summary of Binder Switches ΓòÉΓòÉΓòÉ


 The following are the switches available with gnatbind:

 -aO
           Specify directory to be searched for ALI files.

 -aI
           Specify directory to be searched for source file.

 -A
           Generate binder program in Ada (default)

 -b
           Generate brief messages to stderr even if verbose mode set.

 -c
           Check only, no generation of binder output file.

 -C
           Generate binder program in C

 -e
           Output complete list of elaboration-order dependencies.

 -E
           Store tracebacks in exception occurrences when the target supports
           it. This is the default with the zero cost exception mechanism. This
           option is currently only supported on Solaris, Linux and Windows
           ix86. Under Solaris and Linux you need to use explicitly the gcc
           flag -funwind-tables when compiling every file in your application.
           See also the packages GNAT.Traceback and GNAT.Traceback.Symbolic.
           Under Windows there is no specific option to use to enable this
           feature but you must not use -fomit-frame-pointer gcc option.

 -f
           Full elaboration semantics. Follow Ada rules. No attempt to be kind

 -h
           Output usage (help) information

 -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.

 -Mxyz
           Rename generated main program from main to xyz

 -mn
           Limit number of detected errors to n (1-999).

 -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.

 -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
           Output object list.

 -p
           Pessimistic (worst-case) elaboration order

 -s
           Require all source files to be present.

 -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

 -Tn
           Set the time slice value to n microseconds. A value of zero means no
           time slicing and also indicates to the tasking run time to match as
           close as possible to the annex D requirements of the RM.

 -v
           Verbose mode. Write error messages, header, summary output to
           stdout.

 -wx
           Warning mode (x=s/e for suppress/treat as error)

 -x
           Exclude source files (check object consistency only).

 -z
           No main subprogram.

 You may obtain this listing by running the program gnatbind with no arguments.


ΓòÉΓòÉΓòÉ 7.10. Command-Line Access ΓòÉΓòÉΓòÉ


 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.


ΓòÉΓòÉΓòÉ 7.11. Search Paths for gnatbind ΓòÉΓòÉΓòÉ


 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:

   1. The directory containing the ALI file named in the command line, unless
      the switch -I- is specified.

   2. All directories specified by -I switches on the gnatbind command line, in
      the order given.

   3. Each of the directories listed in the value of the ADA_OBJECTS_PATH
      environment variable. Construct this value exactly as the PATH
      environment variable: a list of directory names separated by colons.

   4. The content of the "ada_object_path" file which is part of the GNAT
      installation tree and is used to store standard libraries such as the
      GNAT Run Time Library (RTL) unless the switch -nostdlib is specified.
      Installing an Ada library

 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 -Idir
 is equivalent to -aIdir -aOdir. 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.


ΓòÉΓòÉΓòÉ 7.12. Examples of gnatbind Usage ΓòÉΓòÉΓòÉ


 This section contains a number of examples of using the GNAT binding utility
 gnatbind.

 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, in the case where the
           output is in Ada. Note that if this option is used, then linking
           must be done manually, since gnatlink will not be able to find the
           generated file.

 gnatbind main -C -o mainprog.c -x
           The main program Main (source program in 'main.adb') is bound,
           excluding source files from the consistency checking, generating the
           file 'mainprog.c'.

 gnatbind -x main_program -C -o mainprog.c
           This command is exactly the same as the previous example. Switches
           may appear anywhere in the command line, and single letter switches
           may be combined into a single switch.

 gnatbind -n math dbase -C -o ada-control.c
           The main program is in a language other than Ada, but calls to
           subprograms in packages Math and Dbase appear. This call to gnatbind
           generates the file 'ada-control.c' containing the adainit and
           adafinal routines to be called before and after accessing the Ada
           units.


ΓòÉΓòÉΓòÉ 8. Linking Using gnatlink ΓòÉΓòÉΓòÉ


 This chapter discusses gnatlink, a utility program used to link Ada programs
 and build an executable file. This is a simple program that invokes the UNIX
 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 binder
 to determine this list.

 Running gnatlink              Running gnatlink
 Switches for gnatlink         Switches for gnatlink


ΓòÉΓòÉΓòÉ 8.1. Running gnatlink ΓòÉΓòÉΓòÉ


 The form of the gnatlink command is

                      $ gnatlink [switches] mainprog[.ali] [non-Ada objects] \
                       [linker options]

 '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 UNIX linker command file to create the executable.

 The arguments following 'mainprog.ali' 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 pragma Import statements 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 usually called ld. 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, the gcc switches -Xlinker or -Wl, shall be used. Refer to the GCC
 documentation for details. Here is an example showing how to generate a linker
 map assuming that the underlying linker is GNU ld:

                      $ gnatlink my_prog -Wl,-Map,MAPFILE

 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.


ΓòÉΓòÉΓòÉ 8.2. Switches for gnatlink ΓòÉΓòÉΓòÉ


 The following switches are available with the gnatlink utility:

 -A
           The binder has generated code in Ada. This is the default.

 -C
           If instead of generating a file in Ada, the binder has generated one
           in C, then the linker needs to know about it. Use this switch to
           signal to gnatlink that the binder has generated C code rather than
           Ada code.

 -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. The same procedure apply if a C bind
           file was generated using -C gnatbind option, in this case the
           filenames are 'b_mainprog.c' and 'b_mainprog.o'.

 -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
           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 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.

 -Bdir
           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 gcc
           manual page for further details. You would normally use the -b or -V
           switch instead.

 --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.

 --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').


ΓòÉΓòÉΓòÉ 9. The GNAT Make Program gnatmake ΓòÉΓòÉΓòÉ

 Running gnatmake              Running gnatmake
 Switches for gnatmake         Switches for gnatmake
 Mode switches for gnatmake    Mode switches for gnatmake
 Notes on the Command Line     Notes on the Command Line
 How gnatmake Works            How gnatmake Works
 Examples of gnatmake Usage    Examples of gnatmake Usage

 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.

   5. Test.

 The third step 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.


ΓòÉΓòÉΓòÉ 9.1. Running gnatmake ΓòÉΓòÉΓòÉ


 The form of the gnatmake command is

                      $ gnatmake [switches] file_name [mode_switches]

 The only required argument is file_name, which specifies the compilation unit
 that is the main program. If switches are present, they can be placed before
 of after file_name. If mode_switches are present, they must always be placed
 after 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 argument. 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 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 to stderr. The output
 produced by the -M switch is send to stdout.


ΓòÉΓòÉΓòÉ 9.2. Switches for gnatmake ΓòÉΓòÉΓòÉ


 You may specify any of the following switches to gnatmake:

 --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. 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.

 --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.

 --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
           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. -f is also useful in conjunction with -f if
           you need to recompile an entire application, including run-time
           files, using special configuration pragma settings, such as a
           non-standard Float_Representation pragma. By default gnatmake -a
           compiles all GNAT internal files with gcc -c -gnatg rather than gcc
           -c.

 -c
           Compile only. Do not perform binding and linking. 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.

 -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.

 -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 (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.

 -jn
           Use n processes to carry out the (re)compilations. On a
           multiprocessor machine compilations will occur in parallel. 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.

 -m
           Specifies 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).

 -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 -aLdir 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.

 -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.

 -v
           Verbose. Displays the reason for all recompilations gnatmake decides
           are necessary.

 -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
           The switch -g or any uppercase switch (other than -A, or -L) or any
           switch that is more than one character is passed to gcc (e.g. -O,
           -gnato, etc.)

 Source and library search path switches:

 -aIdir
           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).

 -aLdir
           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. You still need to specify the location of the
           specs for these units by using the switches -aIdir or -Idir. 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.

 -aOdir
           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.

 -Adir
           Equivalent to -aLdir -aIdir.

 -Idir
           Equivalent to -aOdir -aIdir.

 -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.

 -Ldir
           Add directory dir to the list of directories in which the linker
           will search for libraries. This is equivalent to -largs -Ldir.

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

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


ΓòÉΓòÉΓòÉ 9.3. Mode switches for gnatmake ΓòÉΓòÉΓòÉ


 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 gcc. 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 gcc. They will be passed on to all link steps performed
           by gnatmake.


ΓòÉΓòÉΓòÉ 9.4. Notes on the Command Line ΓòÉΓòÉΓòÉ


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

     If gnatmake finds no ALI files, it recompiles the main program and all
      other units required by the main program. This means that gnatmake can be
      used for the initial compile, as well as during subsequent steps of the
      development cycle.

     If you enter gnatmake file.adb, where 'file.adb' is a subunit or body of
      a generic unit, gnatmake recompiles 'file.adb' (because it finds no ALI)
      and stops, issuing a warning.

     In gnatmake the switch -I is used to specify both source and library file
      paths. Use -aI instead if you just want to specify source paths only and
      -aO if you want to specify library paths only.

     gnatmake examines both an ALI file and its corresponding object file for
      consistency. If an ALI is more recent than its corresponding object, or
      if the object file is missing, the corresponding source will be
      recompiled. Note that gnatmake expects an ALI and the corresponding
      object file to be in the same directory.

     gnatmake will ignore any files whose ALI file is write-protected. This
      may conveniently be used to exclude standard libraries from consideration
      and in particular it means that the use of the -f switch will not
      recompile these files unless -a is also specified.

     gnatmake has been designed to make the use of Ada libraries particularly
      convenient. Assume you have an Ada library organized as follows: obj-dir
      contains the objects and ALI files for of your Ada compilation units,
      whereas include-dir contains the specs of these units, but no bodies.
      Then to compile a unit stored in main.adb, which uses this Ada library
      you would just type

                      $ gnatmake -aIinclude-dir  -aLobj-dir  main

     Using gnatmake along with the -m (minimal recompilation) switch provides
      an extremely powerful tool: you can freely update the comments/format of
      your source files without having to recompile everything. Note, however,
      that adding or deleting lines in a source files may render its debugging
      info obsolete. If the file in question is a spec, the impact is rather
      limited, as that debugging info will only be useful during the
      elaboration phase of your program. For bodies the impact can be more
      significant. In all events, your debugger will warn you if a source file
      is more recent than the corresponding object, and therefore obsolescence
      of debugging information will go unnoticed.


ΓòÉΓòÉΓòÉ 9.5. How gnatmake Works ΓòÉΓòÉΓòÉ


 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 its time stamp predates that of the object
 file 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.


ΓòÉΓòÉΓòÉ 9.6. Examples of gnatmake Usage ΓòÉΓòÉΓòÉ

 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 -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.


ΓòÉΓòÉΓòÉ 10. Renaming Files Using gnatchop ΓòÉΓòÉΓòÉ


 This chapter 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 UnitsHandling Files with Multiple Units
 Operating gnatchop in Compilation ModeOperating gnatchop in Compilation Mode
 Command Line for gnatchop     Command Line for gnatchop
 Switches for gnatchop         Switches for gnatchop
 Examples of gnatchop Usage    Examples of gnatchop Usage


ΓòÉΓòÉΓòÉ 10.1. Handling Files with Multiple Units ΓòÉΓòÉΓòÉ


 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.


ΓòÉΓòÉΓòÉ 10.2. Operating gnatchop in Compilation Mode ΓòÉΓòÉΓòÉ


 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 the
 section on handling of configuration pragmas 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.


ΓòÉΓòÉΓòÉ 10.3. Command Line for gnatchop ΓòÉΓòÉΓòÉ


 The gnatchop command has the form:

                      $ gnatchop switches file name [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 Text_IO; use 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.


ΓòÉΓòÉΓòÉ 10.4. Switches for gnatchop ΓòÉΓòÉΓòÉ


 gnatchop recognizes the following switches:

 -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.

 -gnatxxx
           This passes the given -gnatxxx 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.

 -kmm
           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.

 -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.


ΓòÉΓòÉΓòÉ 10.5. Examples of gnatchop Usage ΓòÉΓòÉΓòÉ

 gnatchop -w hello_s.ada ichbiah/files
           Chops the source file 'hello_s.ada'. The output files will be placed
           in the directory 'ichbiah/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.


ΓòÉΓòÉΓòÉ 11. Configuration Pragmas ΓòÉΓòÉΓòÉ


 In Ada 95, configuration pragmas include those pragmas described as such in
 the Ada 95 Reference Manual, as well as implementation-dependent pragmas that
 are configuration pragmas. See the individual descriptions of pragmas 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.

 Handling of Configuration PragmasHandling of Configuration Pragmas
 The Configuration Pragmas fileThe Configuration Pragmas file


ΓòÉΓòÉΓòÉ 11.1. Handling of Configuration Pragmas ΓòÉΓòÉΓòÉ

 Configuration pragmas may either appear at the start of a compilation unit, in
 which case they apply only to that unit, or they may 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 section 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.


ΓòÉΓòÉΓòÉ 11.2. The Configuration Pragmas file ΓòÉΓòÉΓòÉ


 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.

 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.


ΓòÉΓòÉΓòÉ 12. Elaboration Order Handling in GNAT ΓòÉΓòÉΓòÉ

 Elaboration Code in Ada 95    Elaboration Code in Ada 95
 Checking the Elaboration Order in Ada 95Checking the Elaboration Order in Ada
                               95
 Controlling the Elaboration Order in Ada 95Controlling the Elaboration Order
                               in Ada 95
 Controlling Elaboration in GNAT - Internal CallsControlling Elaboration in
                               GNAT - Internal Calls
 Controlling Elaboration in GNAT - External CallsControlling Elaboration in
                               GNAT - External Calls
 Default Behavior in GNAT - Ensuring SafetyDefault Behavior in GNAT - Ensuring
                               Safety
 What to do if the Default Elaboration Behavior FailsWhat to do if the Default
                               Elaboration Behavior Fails
 Elaboration for Access-to-Subprogram ValuesElaboration for
                               Access-to-Subprogram Values
 Summary of Procedures for Elaboration ControlSummary of Procedures for
                               Elaboration Control

 This chapter describes the handling of elaboration code in Ada 95 and in GNAT,
 and discusses how the order of elaboration of program units can be controlled
 in GNAT, either automatically or with explicit programming features.


ΓòÉΓòÉΓòÉ 12.1. Elaboration Code in Ada 95 ΓòÉΓòÉΓòÉ


 Ada 95 provides rather general mechanisms for executing code at elaboration
 time, that is to say before the main program starts executing. Such code
 arises in three contexts:

 Initializers for variables.
           Variables declared at the library level, in package specs or bodies,
           can require initialization that is performed at elaboration time, as
           in:

                      Sqrt_Half : Float := Sqrt (0.5);

 Package initialization code
           Code in a BEGIN-END section at the outer level of a package body is
           executed as part of the package body elaboration code.

 Library level task allocators
           Tasks that are declared using task allocators at the library level
           start executing immediately and hence can execute at elaboration
           time.

 Subprogram calls are possible in any of these contexts, which means that any
 arbitrary part of the program may be executed as part of the elaboration code.
 It is even possible to write a program which does all its work at elaboration
 time, with a null main program, although stylistically this would usually be
 considered an inappropriate way to structure a program.

 An important concern arises in the context of elaboration code: we have to be
 sure that it is executed in an appropriate order. What we have is numerous
 sections of elaboration code, potentially one section for each unit in the
 program. It is important that these execute in the correct order. Correctness
 here means that, taking the above example of the declaration of Sqrt_Half, if
 some other piece of elaboration code references Sqrt_Half, then it must run
 after the section of elaboration code that contains the declaration of
 Sqrt_Half.

 There would never be any order of elaboration problem if we made a rule that
 whenever you with a unit, you must elaborate both the spec and body of that
 unit before elaborating the unit doing the with'ing:

                      with Unit_1;
                      package Unit_2 is ┬╖┬╖┬╖

 would require that both the body and spec of Unit_1 be elaborated before the
 spec of Unit_2. However, a rule like that would be far too restrictive. In
 particular, it would make it impossible to have routines in separate packages
 that were mutually recursive.

 You might think that a clever enough compiler could look at the actual
 elaboration code and determine an appropriate correct order of elaboration,
 but in the general case, this is not possible. Consider the following example.

 In the body of Unit_1, we have a procedure Func_1 that references the variable
 Sqrt_1, which is declared in the elaboration code of the body of Unit_1:

                      Sqrt_1 : Float := Sqrt (0.1);

 The elaboration code of the body of Unit_1 also contains:

                      if expression_1 = 1 then
                        Q := Unit_2.Func_2;
                      end if;

 Unit_2 is exactly parallel, it has a procedure Func_2 that references the
 variable Sqrt_2, which is declared in the elaboration code of the body Unit_2:

                      Sqrt_2 : Float := Sqrt (0.1);

 The elaboration code of the body of Unit_2 also contains:

                      if expression_2 = 2 then
                        Q := Unit_1.Func_1;
                      end if;

 Now the question is, which of the following orders of elaboration is
 acceptable:

                      Spec of Unit_1
                      Spec of Unit_2
                      Body of Unit_1
                      Body of Unit_2

 or

                      Spec of Unit_2
                      Spec of Unit_1
                      Body of Unit_2
                      Body of Unit_1

 If you carefully analyze the flow here, you will see that you cannot tell at
 compile time the answer to this question. If expression_1 is not equal to 1,
 and expression_2 is not equal to 2, then either order is acceptable, because
 neither of the function calls is executed. If both tests evaluate to true,
 then neither order is acceptable and in fact there is no correct order.

 If one of the two expressions is true, and the other is false, then one of the
 above orders is correct, and the other is incorrect. For example, if
 expression_1 = 1 and expression_2 /= 2, then the call to Func_2 will occur,
 but not the call to Func_1. This means that it is essential to elaborate the
 body of Unit_1 before the body of Unit_2, so the first order of elaboration is
 correct and the second is wrong.

 By making expression_1 and expression_2 depend on input data, or perhaps the
 time of day, we can make it impossible for the compiler or binder to figure
 out which of these expressions will be true, and hence it is impossible to
 guarantee a safe order of elaboration at run time.


ΓòÉΓòÉΓòÉ 12.2. Checking the Elaboration Order in Ada 95 ΓòÉΓòÉΓòÉ


 In some languages that involve the same kind of elaboration problems, e.g.
 Java and C++, the programmer is expected to worry about these ordering
 problems himself, and it is common to write a program in which an incorrect
 elaboration order  gives surprising results, because it references variables
 before they are initialized. Ada 95 is designed to be a safe language, and a
 programmer-beware approach is clearly not sufficient. Consequently, the
 language provides three lines of defense:

 Standard rules
           Some standard rules restrict the possible choice of elaboration
           order. In particular, if you with a unit, then its spec is always
           elaborated before the unit doing the with. Similarly, a parent spec
           is always elaborated before the child spec, and finally a spec is
           always elaborated before its corresponding body.

 Dynamic elaboration checks
           Dynamic checks are made at run time, so that if some entity is
           accessed before it is elaborated (typically  by means of a
           subprogram call) then the exception (Program_Error) is raised.

 Elaboration control
           Facilities are provided for the programmer to specify the desired
           order of elaboration.

 Let's look at these facilities in more detail. First, the rules for dynamic
 checking. One possible rule would be simply to say that the exception is
 raised if you access a variable which has not yet been elaborated. The trouble
 with this approach is that it could require expensive checks on every variable
 reference. Instead Ada 95 has two rules which are a little more restrictive,
 but easier to check, and easier to state:

 Restrictions on calls
           A subprogram can only be called at elaboration time if its body has
           been elaborated. The rules for elaboration given above guarantee
           that the spec of the subprogram has been elaborated before the call,
           but not the body. If this rule is violated, then the exception
           Program_Error is raised.

 Restrictions on instantiations
           A generic unit can only be instantiated if the body of the generic
           unit has been elaborated. Again, the rules for elaboration given
           above guarantee that the spec of the generic unit has been
           elaborated before the instantiation, but not the body. If this rule
           is violated, then the exception Program_Error is raised.

 The idea is that if the body has been elaborated, then any variables it
 references must have been elaborated; by checking for the body being
 elaborated we guarantee that none of its references causes any trouble. As we
 noted above, this is a little too restrictive, because a subprogram that has
 no non-local references in its body may in fact be safe to call. However, it
 really would be unsafe to rely on this, because it would mean that the caller
 was aware of details of the implementation in the body. This goes against the
 basic tenets of Ada.

 A plausible implementation can be described as follows. A Boolean variable is
 associated with each subprogram and each generic unit. This variable is
 initialized to False, and is set to True at the point body is elaborated.
 Every call or instantiation checks the variable, and raises Program_Error if
 the variable is False.


ΓòÉΓòÉΓòÉ 12.3. Controlling the Elaboration Order in Ada 95 ΓòÉΓòÉΓòÉ


 In the previous section we discussed the rules in Ada 95 which ensure that
 Program_Error is raised if an incorrect elaboration order is chosen. This
 prevents erroneous executions, but we need mechanisms to specify a correct
 execution and avoid the exception altogether. To achieve this, Ada 95 provides
 a number of features for controlling the order of elaboration. We discuss
 these features in this section.

 First, there are several ways of indicating to the compiler that a given unit
 has no elaboration problems:

 packages that do not require a body
           In Ada 95, a library package that does not require a body does not
           permit a body. This means that if we have a such a package, as in:

                      package Definitions is
                        generic
                         type m is new integer;
                        package Subp is
                         type a is array (1 ┬╖┬╖ 10) of m;
                         type b is array (1 ┬╖┬╖ 20) of m;
                        end Subp;
                      end Definitions;

 A package that with's Definitions may safely instantiate Definitions.Subp
 because the compiler can determine that there definitely is no package body to
 worry about in this case

 pragma Pure
           Places sufficient restrictions on a unit to guarantee that no call
           to any subprogram in the unit can result in an elaboration problem.
           This means that the compiler does not need to worry about the point
           of elaboration of such units, and in particular, does not need to
           check any calls to any subprograms in this unit.

 pragma Preelaborate
           This pragma places slightly less stringent restrictions on a unit
           than does pragma Pure, but these restrictions are still sufficient
           to ensure that there are no elaboration problems with any calls to
           the unit.

 pragma Elaborate_Body
           This pragma requires that the body of a unit be elaborated
           immediately after its spec. Suppose a unit A has such a pragma, and
           unit B does a with of unit A. Recall that the standard rules require
           the spec of unit A to be elaborated before the with'ing unit; given
           the pragma in A, we also know that the body of A will be elaborated
           before B, so that calls to A are safe and do not need a check.

 Note that, unlike pragma Pure and pragma Preelaborate, the use of
 Elaborate_Body does not guarantee that the program is free of elaboration
 problems, because it may not be possible to satisfy the requested elaboration
 order. Let's go back to the example with Unit_1 and Unit_2. If a programmer
 marks Unit_1 as Elaborate_Body, and not Unit_2, then the order of elaboration
 will be:

                      Spec of Unit_2
                      Spec of Unit_1
                      Body of Unit_1
                      Body of Unit_2

 Now that means that the call to Func_1 in Unit_2 need not be checked, it must
 be safe. But the call to Func_2 in Unit_1 may still fail if Expression_1 is
 equal to 1, and the programmer must still take responsibility for this not
 being the case.

 If all units carry a pragma Elaborate_Body, then all problems are eliminated,
 except for calls entirely within a body, which are in any case fully under
 programmer control. However, using the pragma everywhere is not always
 possible. In particular, for our Unit_1/Unit_2 example, if we marked both of
 them as having pragma Elaborate_Body, then clearly there would be no possible
 elaboration order.

 The above pragmas allow a server to guarantee safe use by clients, and clearly
 this is the preferable approach. Consequently a good rule in Ada 95 is to mark
 units as Pure or Preelaborate if possible, and if this is not possible, mark
 them as Elaborate_Body if possible. As we have seen, there are situation where
 neither of these three pragmas can be used. So we also provide methods for
 clients to control the order of elaboration of the servers on which they
 depend:

 pragma Elaborate (unit)
           This pragma is placed in the context clause, after a with statement,
           and it requires that the body of the named unit be elaborated before
           the unit in which the pragma occurs. The idea is to use this pragma
           if the current unit calls at elaboration time, directly or
           indirectly, some subprogram in the named unit.

 pragma Elaborate_All (unit)
           This is a stronger version of the Elaborate pragma. Consider the
           following example:

                      Unit A with's unit B and calls B.Func in elab code
                      Unit B with's unit C, and B.Func calls C.Func

 Now if we put a pragma Elaborate (B) in unit A, this ensures that the body of
 B is elaborated before the call, but not the body of C, so the call to C.Func
 could still cause Program_Error to be raised.

 The effect of a pragma Elaborate_All is stronger, it requires not only that
 the body of the named unit be elaborated before the unit doing the with, but
 also the bodies of all units that the named unit uses, following with links
 transitively. For example, if we put a pragma Elaborate_All (B) in unit A,
 then it requires not only that the body of B be elaborated before A, but also
 the body of C, because B with's C.

 We are now in a position to give a usage rule in Ada 95 for avoiding
 elaboration problems, at least if dynamic dispatching and access to subprogram
 values are not used. We will handle these cases separately later.

 The rule is simple. If a unit has elaboration code that can directly or
 indirectly make a call to a subprogram in a with'ed unit, or instantiate a
 generic unit in a with'ed unit, then if the with'ed unit does not have pragma
 Pure, Preelaborate, or Elaborate_Body, then the client should have an
 Elaborate_All for the with'ed unit. By following this rule a client is assured
 that calls can be made without risk of an exception. If this rule is not
 followed, then a program may be in one of four states:

 No order exists
           No order of elaboration exists which follows the rules, taking into
           account any Elaborate, Elaborate_All, or Elaborate_Body pragmas. In
           this case, an Ada 95 compiler must diagnose the situation at bind
           time, and refuse to build an executable program.

 One or more orders exist, all incorrect
           One or more acceptable elaboration orders exists, and all of them
           generate an elaboration order problem. In this case, the binder can
           build an executable program, but Program_Error will be raised when
           the program is run.

 Several orders exist, some right, some incorrect
           One or more acceptable elaboration orders exists, and some of them
           work, and some do not. The programmer has not controlled the order
           of elaboration, so the binder may or may not pick one of the correct
           orders, and the program may or may not raise an exception when it is
           run. This is the worst case, because it means that the program may
           fail when moved to another compiler, or even another version of the
           same compiler.

 One or more orders exists, all correct
           One ore more acceptable elaboration orders exist, and all of them
           work. In this case the program runs successfully. This state of
           affairs can be guaranteed by following the rule we gave above, but
           may be true even if the rule is not followed.

 Note that one additional advantage of following our Elaborate_All rule is that
 the program continues to stay in the ideal (all orders OK) state even if
 maintenance changes some bodies of some subprograms. Conversely, if a program
 that does not follow this rule happens to be safe at some point, this state of
 affairs may deteriorate silently as a result of maintenance changes.


ΓòÉΓòÉΓòÉ 12.4. Controlling Elaboration in GNAT - Internal Calls ΓòÉΓòÉΓòÉ


 In the case of internal calls, i.e. calls within a single package, the
 programmer has full control over the order of elaboration, and it is up to the
 programmer to elaborate declarations in an appropriate order. For example
 writing:

                      function One return Float;
                      Q : Float := One;
                      function One return Float is
                      begin
                         return 1.0;
                      end One;

 will obviously raise Program_Error at run time, because function One will be
 called before its body is elaborated. In this case GNAT will generate a
 warning that the call will raise Program_Error:

                       1. procedure y is
                       2.   function One return Float;
                       3.
                       4.   Q : Float := One;
                                |
                        >>> warning: cannot call "One" before body is elaborated
                        >>> warning: Program_Error will be raised at run time
                       5.
                       6.   function One return Float is
                       7.   begin
                       8.     return 1.0;
                       9.   end One;
                      10.
                      11. begin
                      12.   null;
                      13. end;

 Note that in this particular case, it is likely that the call is safe, because
 the function One does not access any global variables. Nevertheless in Ada 95,
 we do not want the validity of the check to depend on the contents of the body
 (think about the separate compilation case), so this is still wrong, as we
 discussed in the previous sections.

 The error is easily corrected by rearranging the declarations so that the body
 of One appears before the declaration containing the call (note that in Ada
 95, declarations can appear in any order, so there is no restriction that
 would prevent this reordering, and if we write:

                      function One return Float;
                      function One return Float is
                      begin
                         return 1.0;
                      end One;
                      Q : Float := One;

 then all is well, no warning is generated, and no Program_Error exception will
 be raised. Things are more complicated when a chain of subprograms is
 executed:

                      function A return Integer;
                      function B return Integer;
                      function C return Integer;
                      function B return Integer is begin return A; end;
                      function C return Integer is begin return B; end;
                      X : Integer := C;
                      function A return Integer is begin return 1; end;

 Now the call to C at elaboration time in the declaration of X is correct,
 because the body of C is already elaborated, and the call to B within the body
 of C is correct, but the call to A within the body of B is incorrect, because
 the body of A has not been elaborated, so Program_Error will be raised on the
 call to A. In this case GNAT will generate a warning that Program_Error may be
 raised at the point of the call. Let's look at the warning:

                       1. procedure x is
                       2.   function A return Integer;
                       3.   function B return Integer;
                       4.   function C return Integer;
                       5.
                       6.   function B return Integer is begin return A; end;
                                                |
                        >>> warning: call to "A" before body is elaborated may
                               raise Program_Error
                        >>> warning: "B" called at line 7
                        >>> warning: "C" called at line 9
                       7.   function C return Integer is begin return B; end;
                       8.
                       9.   X : Integer := C;
                      10.
                      11.   function A return Integer is begin return 1; end;
                      12.
                      13. begin
                      14.   null;
                      15. end;

 Note that the message here says "may raise", instead of the direct case, where
 the message says "will be raised". That's because whether A is actually called
 depends in general on run-time flow of control. For example, if the body of B
 said

                      function B return Integer is
                      begin
                        if some-condition-depending-on-input-data then
                         return A;
                        else
                         return 1;
                        end if;
                      end B;

 then we could not know until run time whether the incorrect call to A would
 actually occur, so Program_Error might or might not be raised. It is possible
 for a compiler to do a better job of analyzing bodies, to determine whether or
 not Program_Error might be raised, but it certainly couldn't do a perfect job
 (that would require solving the halting problem and is provably impossible),
 and because this is a warning anyway, it does not seem worth the effort to do
 the analysis. Cases in which it would be relevant are rare.

 In practice, warnings of either of the forms given above will usually
 correspond to real errors, and should be examined carefully and eliminated. In
 the rare case where a warning is bogus, it can be suppressed by any of the
 following methods:

     Compile with the -gnatws switch set

     Suppress Elaboration_Checks for the called subprogram

     Use pragma Warnings_Off to turn warnings off for the call

 For the internal elaboration check case, GNAT by default generates the
 necessary run-time checks to ensure that Program_Error is raised if any call
 fails an elaboration check. Of course this can only happen if a warning has
 been issued as described above. The use of pragma Suppress
 (Elaboration_Checks) may (but is not guaranteed) to suppress some of these
 checks, meaning that it may be possible (but is not guaranteed) for a program
 to be able to call a subprogram whose body is not yet elaborated, without
 raising a Program_Error exception.


ΓòÉΓòÉΓòÉ 12.5. Controlling Elaboration in GNAT - External Calls ΓòÉΓòÉΓòÉ


 The previous section discussed the case in which the execution of a particular
 thread of elaboration code occurred entirely within a single unit. This is the
 easy case to handle, because a programmer has direct and total control over
 the order of elaboration, and furthermore, checks need only be generated in
 cases which are rare and which the compiler can easily detect. The situation
 is more complex when separate compilation is taken into account. Consider the
 following:

                      package Math is
                        function Sqrt (Arg : Float) return Float;
                      end Math;
                      package body Math is
                        function Sqrt (Arg : Float) return Float is
                        begin
                           ┬╖┬╖┬╖
                        end Sqrt;
                      end Math;
                      with Math;
                      package Stuff is
                        X : Float := Math.Sqrt (0.5);
                      end Stuff;
                      with Stuff;
                      procedure Main is
                      begin
                        ┬╖┬╖┬╖
                      end Main;

 where Main is the main program. When this program is executed, the elaboration
 code must first be executed, and one of the jobs of the binder is to determine
 the order in which the units of a program are to be elaborated. In this case
 we have four units: the spec and body of Math, the spec of Stuff and the body
 of Main). In what order should the four separate sections of elaboration code
 be executed?

 There are some restrictions in the order of elaboration that the binder can
 choose. In particular, if unit U has a with for a package X, then you are
 assured that the spec of X is elaborated before U , but you are not assured
 that the body of X is elaborated before U. This means that in the above case,
 the binder is allowed to choose the order:

                      spec of Math
                      spec of Stuff
                      body of Math
                      body of Main

 but that's not good, because now the call to Math.Sqrt that happens during the
 elaboration of the Stuff spec happens before the body of Math.Sqrt is
 elaborated, and hence causes Program_Error exception to be raised. At first
 glance, one might say that the binder is misbehaving, because obviously you
 want to elaborate the body of something you with first, but that is not a
 general rule that can be followed in all cases. Consider

                      package X is ┬╖┬╖┬╖
                      package Y is ┬╖┬╖┬╖
                      with X;
                      package body Y is ┬╖┬╖┬╖
                      with Y;
                      package body X is ┬╖┬╖┬╖

 This is a common arrangement, and, apart from the order of elaboration
 problems that might arise in connection with elaboration code, this works
 fine. A rule that says that you must first elaborate the body of anything you
 with cannot work in this case (the body of X with's Y, which means you would
 have to elaborate the body of Y first, but that with's X, which means you have
 to elaborate the body of X first, but ┬╖┬╖┬╖ and we have a loop that cannot be
 broken.

 It is true that the binder can in many cases guess an order of elaboration
 that is unlikely to cause a Program_Error exception to be raised, and it tries
 to do so (in the above example of Math/Stuff/Spec, the GNAT binder will in
 fact always elaborate the body of Math right after its spec, so all will be
 well).

 However, a program that blindly relies on the binder to be helpful can get
 into trouble, as we discussed in the previous sections, so GNAT provides a
 number of facilities for assisting the programmer in developing programs that
 are robust with respect to elaboration order.


ΓòÉΓòÉΓòÉ 12.6. Default Behavior in GNAT - Ensuring Safety ΓòÉΓòÉΓòÉ


 The default behavior in GNAT ensures elaboration safety. In its default mode
 GNAT implements the rule we previously described as the right approach. Let's
 restate it:
 If a unit has elaboration code that can directly or indirectly make a call to
 a subprogram in a with'ed unit, or instantiate a generic unit in a with'ed
 unit, then if the with'ed unit does not have pragma Pure, Preelaborate, or
 Elaborate_Body, then the client should have an Elaborate_All for the with'ed
 unit. By following this rule a client is assured that calls and instantiations
 can be made without risk of an exception.

 In this mode GNAT traces all calls that are potentially made from elaboration
 code, and puts in any missing implicit Elaborate_All pragmas. The advantage of
 this approach is that no elaboration problems are possible if the binder can
 find an elaboration order that is consistent with these implicit Elaborate_All
 pragmas. The disadvantage of this approach is that no such order may exist.

 If the binder does not generate any diagnostics, then it means that it has
 found an elaboration order that is guaranteed to be safe. However, the binder
 may still be relying on implicitly generated Elaborate_All pragmas so
 portability to other compilers than GNAT is not guaranteed.

 If it is important to guarantee portability, then the compilations should use
 the -gnatwl (warn on elaboration problems) switch. This will cause warning
 messages to be generated indicating the missing Elaborate_All pragmas.
 Consider the following source program:

                      with k;
                      package j is
                       m : integer := k.r;
                      end;

 where it is clear that there should be a pragma Elaborate_All for unit k. An
 implicit pragma will be generated, and it is likely that the binder will be
 able to honor it. However, it is safer to include the pragma explicitly in the
 source. If this unit is compiled with the -gnatwl switch, then the compiler
 outputs a warning:

                      1. with k;
                      2. package j is
                      3.  m : integer := k.r;
                                 |
                        >>> warning: call to "r" may raise Program_Error
                        >>> warning: missing pragma Elaborate_All for "k"
                      4. end;

 and these warnings can be used as a guide for supplying manually the missing
 pragmas.


ΓòÉΓòÉΓòÉ 12.7. What to do if the Default Elaboration Behavior Fails ΓòÉΓòÉΓòÉ


 If the binder cannot find an acceptable order, it outputs detailed
 diagnostics. For example:

                      error: elaboration circularity detected
                      info:  "proc (body)" must be elaborated before "pack (body)"
                      info:   reason: Elaborate_All probably needed in unit "pack (body)"
                      info:   recompile "pack (body)" with -gnatwl
                      info:               for full details
                      info:    "proc (body)"
                      info:     is needed by its spec:
                      info:    "proc (spec)"
                      info:     which is withed by:
                      info:    "pack (body)"
                      info:  "pack (body)" must be elaborated before "proc (body)"
                      info:   reason: pragma Elaborate in unit "proc (body)"

 In this case we have a cycle that the binder cannot break. On the one hand,
 there is an explicit pragma Elaborate in proc for pack. This means that the
 body of pack must be elaborated before the body of proc. On the other hand,
 there is elaboration code in pack that calls a subprogram in proc. This means
 that for maximum safety, there should really be a pragma Elaborate_All in pack
 for proc which would require that the body of proc be elaborated before the
 body of pack. Clearly both requirements cannot be satisfied. Faced with a
 circularity of this kind, you have three different options.

 Fix the program
           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 called 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.

 Perform dynamic checks
           If the compilations are done using the -gnatE (dynamic elaboration
           check) switch, then GNAT behaves in a quite different manner.
           Dynamic checks are generated for all calls that could possibly
           result in raising an exception. With this switch, the compiler does
           not generate implicit Elaborate_All pragmas. The behavior then is
           exactly as specified in the Ada 95 Reference Manual. The binder will
           generate an executable program that may or may not raise
           Program_Error, and then it is the programmer's job to ensure that it
           does not raise an exception. Note that it is important to compile
           all units with the switch, it cannot be used selectively.

 Suppress checks
           The drawback of dynamic checks is that they generate a significant
           overhead at run time, both in space and time. If you are absolutely
           sure that your program cannot raise any elaboration exceptions, then
           you can use the -f switch for the gnatbind step, or -bargs -f if you
           are using gnatmake. This switch tells the binder to ignore any
           implicit Elaborate_All pragmas that were generated by the compiler,
           and suppresses any circularity messages that they cause. The
           resulting executable will work properly if there are no elaboration
           problems, but if there are some order of elaboration problems they
           will not be detected, and unexpected results may occur.

 It is hard to generalize on which of these three approaches should be taken.
 Obviously if it is possible to fix the program so that the default treatment
 works, this is preferable, but this may not always be practical. It is
 certainly simple enough to use -gnatE or -f but the danger in either case is
 that, even if the GNAT binder finds a correct elaboration order, it may not
 always do so, and certainly a binder from another Ada compiler might not. A
 combination of testing and analysis (for which the warnings generated with the
 -gnatwl switch can be useful) must be used to ensure that the program is free
 of errors. One switch that is useful in this testing is the -h (horrible
 elaboration order) switch for gnatbind. Normally the binder tries to find an
 order that has the best chance of of avoiding elaboration problems. With this
 switch, the binder plays a devil's advocate role, and tries to choose the
 order that has the best chance of failing. If your program works even with
 this switch, then it has a better chance of being error free, but this is
 still not a guarantee.

 For an example of this approach in action, consider the C-tests (executable
 tests) from the ACVC suite. If these are compiled and run with the default
 treatment, then all but one of them succeed without generating any error
 diagnostics from the binder. However, there is one test that fails, and this
 is not surprising, because the whole point of this test is to ensure that the
 compiler can handle cases where it is impossible to determine a correct order
 statically, and it checks that an exception is indeed raised at run time.

 This one test must be compiled and run using the -gnatE switch, and then it
 passes. Alternatively, the entire suite can be run using this switch. It is
 never wrong to run with the dynamic elaboration switch if your code is
 correct, and we assume that the C-tests are indeed correct (it is less
 efficient, but efficiency is not a factor in running the ACVC tests.)


ΓòÉΓòÉΓòÉ 12.8. Elaboration for Access-to-Subprogram Values ΓòÉΓòÉΓòÉ


 The introduction of access-to-subprogram types in Ada 95 complicates the
 handling of elaboration. The trouble is that it becomes impossible to tell at
 compile time which procedure is being called. This means that it is not
 possible for the binder to analyze the elaboration requirements in this case.

 If at the point at which  the access value is created, the body of the
 subprogram is known to have been elaborated, then the access value is safe,
 and its use does not require a check. This may be achieved by appropriate
 arrangement of the order of declarations if the subprogram is in the current
 unit, or, if the subprogram is in another unit, by using pragma Pure,
 Preelaborate, or Elaborate_Body on the referenced unit.

 If the referenced body is not known to have been elaborated at the point the
 access value is created, then any use of the access value must do a dynamic
 check, and this dynamic check will fail and raise a Program_Error exception if
 the body has not been elaborated yet. GNAT will generate the necessary checks,
 and in addition, if the -gnatwl switch is set, will generate warnings that
 such checks are required.

 The use of dynamic dispatching for tagged types similarly generates a
 requirement for dynamic checks, and premature calls to any primitive operation
 of a tagged type before the body of the operation has been elaborated, will
 result in the raising of Program_Error.


ΓòÉΓòÉΓòÉ 12.9. Summary of Procedures for Elaboration Control ΓòÉΓòÉΓòÉ


 First, compile your program with the default options, using none of the
 special elaboration control switches. If the binder successfully binds your
 program, then you can be confident that, apart from issues raised by the use
 of access-to-subprogram types and dynamic dispatching, the program is free of
 elaboration errors. If it is important that the program be portable, then use
 the -gnatwl switch to generate warnings about missing Elaborate_All pragmas,
 and supply the missing pragmas.

 If the program fails to bind using the default static elaboration handling,
 then you can fix the program to eliminate the binder message, or recompile the
 entire program with the -gnatE switch to generate dynamic elaboration checks,
 or, if you are sure there really are no elaboration problems, use the -f
 switch for the binder to cause it to ignore implicit Elaborate_All pragmas
 generated by the compiler.


ΓòÉΓòÉΓòÉ 13. The cross-referencing tools gnatxref and gnatfind ΓòÉΓòÉΓòÉ


 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.

 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 (information will not be generated.

 Gnatxref switches             Gnatxref switches
 Gnatfind switches             Gnatfind switches
 Project files                 Project files
 Regular expressions in gnatfind and gnatxrefRegular expressions in gnatfind
                               and gnatxref
 Examples of gnatxref usage    Examples of gnatxref usage
 Examples of gnatfind usage    Examples of gnatfind usage


ΓòÉΓòÉΓòÉ 13.1. Gnatxref switches ΓòÉΓòÉΓòÉ


 The command lines for gnatxref is:

                      $ gnatxref [switches] sourcefile1 [sourcefile2 ┬╖┬╖┬╖]

 where

 sourcefile1, sourcefile2
           identifies the source files for which a report is to be generated.
           The 'with'ed 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'.

 The switches can be :

 -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.

 -aIDIR
           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'.

 -aODIR
           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'.

 -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.

 -IDIR
           Equivalent to '-aODIR -aIDIR'.

 -pFILE
           Specify a project file to use See Project files. By default,
           gnatxref and gnatfind will try to locate a project file in the
           current directory.

           If a project file is either specified or found by the tools, then
           the content of the source directory and object directory lines are
           added as if they had been specified respectively by '-aI' and '-aO'.

 -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 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'.


ΓòÉΓòÉΓòÉ 13.2. Gnatfind switches ΓòÉΓòÉΓòÉ


 The command line for gnatfind is:

                      $ gnatfind [switches] pattern[:sourcefile[:line[:column]]] \
                       [file1 file2 ┬╖┬╖┬╖]

 where

 pattern
           An entity will be output only if it matches the regular expression
           found in 'pattern', see 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
           see Examples of gnatfind usage for syntax examples.

 line
           is a decimal integer identifying the line number containing the
           reference to the entity (or entities) to be located.

 column
           is 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 files. If none are given,
           then the search will be done for every library file in the search
           path. These file 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'.

           Not 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:

 -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.

 -aIDIR
           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'.

 -aODIR
           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'.

 -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.

 -IDIR
           Equivalent to '-aODIR -aIDIR'.

 -pFILE
           Specify a project file (see Project files) to use. By default,
           gnatxref and gnatfind will try to locate a project file in the
           current directory.

           If a project file is either specified or found by the tools, then
           the content of the source directory and object directory lines are
           added as if they had been specified respectively by '-aI' and '-aO'.

 -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.


ΓòÉΓòÉΓòÉ 13.3. Project files ΓòÉΓòÉΓòÉ


 The project files allows a programmer to specify how to compile its
 application, where to find sources,┬╖┬╖┬╖ These files are used primarily by the
 Emacs Ada mode, but they can also be used by the two tools gnatxref and
 gnatfind.

 A project file name must end with '.adp'. If a single one is present in the
 current directory, then gnatxref and gnatfind will extract the information
 from it. If multiple project files are found, none of them is read, and you
 have to use the '-p' switch to specify the one you want to use.

 The following lines can be included, even though most of them have default
 values which can be used in most cases. The lines can be entered in any order
 in the file. Except for 'src_dir' and 'obj_dir', you can only have one
 instance of each line. If you have multiple instances, only the last one is
 taken into account.

 'src_dir=DIR     [default: "./"]'
           specifies a directory where to look for source files. Multiple
           src_dir lines can be specified and they will be searched in the
           order they are specified.

 'obj_dir=DIR     [default: "./"]'
           specifies a directory where to look for object and library files.
           Multiple obj_dir lines can be specified and they will be searched in
           the order they are specified

 'comp_opt=SWITCHES  [default: ""]'
           creates a variable which can be referred to subsequently by using
           the '${comp_opt}' notation. This is intended to store the default
           switches given to 'gnatmake' and 'gcc'.

 'bind_opt=SWITCHES  [default: ""]'
           creates a variable which can be referred to subsequently by using
           the '${bind_opt}' notation. This is intended to store the default
           switches given to 'gnatbind'.

 'link_opt=SWITCHES  [default: ""]'
           creates a variable which can be referred to subsequently by using
           the '${link_opt}' notation. This is intended to store the default
           switches given to 'gnatlink'.

 'main=EXECUTABLE   [default: ""]'
           specifies the name of the executable for the application. This
           variable can be referred to in the following lines by using the
           '${main}' notation.

 'comp_cmd=COMMAND   [default: "gcc -c -I${src_dir} -g -gnatq"]'
           specifies the command used to compile a single file in the
           application.

 'make_cmd=COMMAND   [default: "gnatmake ${main} -aI${src_dir} -aO${obj_dir} -g
 -gnatq -cargs ${comp_opt} -bargs ${bind_opt} -largs ${link_opt}"]'
           specifies the command used to recompile the whole application.

 'run_cmd=COMMAND   [default: "${main}"]'
           specifies the command used to run the application.

 'debug_cmd=COMMAND  [default: "gdb ${main}"]'
           specifies the command used to debug the application

 gnatxref and gnatfind only take into account the 'src_dir' and 'obj_dir'
 lines, and ignore the others.


ΓòÉΓòÉΓòÉ 13.4. Regular expressions in gnatfind and gnatxref ΓòÉΓòÉΓòÉ


 As specified in the section about gnatfind, the pattern can be a regular
 expression. Actually, there are to set of regular expressions which are
 recognized by the program :

 'globbing patterns'
           These are the most usual regular expression. They are the same that
           you generally used in a Unix shell command line, or in a DOS
           session.

           Here is a more formal grammar :

                      regexp ::= term
                      term  ::= elmt       -- matches elmt
                      term  ::= elmt elmt    -- concatenation (elmt then elmt)
                      term  ::= *        -- any string of 0 or more characters
                      term  ::= ?        -- matches any character
                      term  ::= [char {char}] -- matches any character listed
                      term  ::= [char - char]  -- matches any character in range

 'full regular expression'
           The second set of regular expressions is much more powerful. This is
           the type of regular expressions recognized by utilities such a
           'grep'.

           The following is the form of a regular expression, expressed in Ada
           reference manual style BNF is as follows

                      regexp ::= term {| term} -- alternation (term or term ┬╖┬╖┬╖)
                      term ::= item {item}   -- concatenation (item then item)
                      item ::= elmt        -- match elmt
                      item ::= elmt *       -- zero or more elmt's
                      item ::= elmt +       -- one or more elmt's
                      item ::= elmt ?       -- matches elmt or nothing
                      elmt ::= nschar       -- matches given character
                      elmt ::= [nschar {nschar}]  -- matches any character listed
                      elmt ::= [^ nschar {nschar}] -- matches any character not listed
                      elmt ::= [char - char]   -- matches chars in given range
                      elmt ::= \ char       -- matches given character
                      elmt ::= .         -- matches any single character
                      elmt ::= ( regexp )     -- parens used for grouping
                      char ::= any character, including special characters
                      nschar ::= any character except ()[].*+?^

 Following are a few examples :

             'abcde|fghi'
                         will match any of the two strings 'abcde' and 'fghi'.

             'abc*d'
                         will match any string like 'abd', 'abcd', 'abccd',
                         'abcccd', and so on

             '[a-z]+'
                         will match any string which has only lowercase
                         characters in it (and at least one character


ΓòÉΓòÉΓòÉ 13.5. Examples of gnatxref usage ΓòÉΓòÉΓòÉ


ΓòÉΓòÉΓòÉ 13.5.1. General usage ΓòÉΓòÉΓòÉ


 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:

 gnatxref main.adb
           gnatxref generates cross-reference information for main.adb and
           every unit 'with'ed by main.adb.

           The output would be:

                      B                            Type: Integer
                       Decl: bar.ads      2:22
                      B                            Type: Integer
                       Decl: main.ads      3:20
                       Body: main.adb      2:20
                       Ref:  main.adb      4:13   5:13   6:19
                      Bar                           Type: Unit
                       Decl: bar.ads      1:9
                       Ref:  main.adb      6:8    7:8
                          main.ads      1:6
                      C                            Type: Integer
                       Decl: main.ads      4:5
                       Modi: main.adb      4:8
                       Ref:  main.adb      7:19
                      D                            Type: Integer
                       Decl: main.ads      6:5
                       Modi: main.adb      5:8
                      Foo                           Type: Unit
                       Decl: main.ads      3:15
                       Body: main.adb      2:15
                      Main                           Type: Unit
                       Decl: main.ads      2:9
                       Body: main.adb      1:14
                      Print                          Type: Unit
                       Decl: bar.ads      2:15
                       Ref:  main.adb      6:12   7:12

 that is the entity Main is declared in main.ads, line 2, column 9, its body is
 in main.adb, line 1, column 14 and is not referenced any where.

 The entity Print is declared in bar.ads, line 2, column 15 and it it
 referenced in main.adb, line 6 column 12 and line 7 column 12.

 gnatxref package1.adb package2.ads
           gnatxref will generates cross-reference information for
           package1.adb, package2.ads and any other package 'with'ed by any of
           these.


ΓòÉΓòÉΓòÉ 13.5.2. Using gnatxref with vi ΓòÉΓòÉΓòÉ

 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

 will generate the tags file for gnatfind itself (if the sources are in the
 search path!).

 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.


ΓòÉΓòÉΓòÉ 13.6. Examples of gnatfind usage ΓòÉΓòÉΓòÉ

 gnatfind -f xyz:main.adb
           Find declarations for all entities xyz referenced at least once in
           main.adb. The references are search in every library file in the
           search path.

           The directories will be printed as well (as the '-f' switch is set)

           The output will look like:

                      directory/main.ads:106:14: xyz <= declaration
                      directory/main.adb:24:10: xyz <= body
                      directory/foo.ads:45:23: xyz <= declaration

 that is to say, one of the entities xyz found in main.adb is declared at line
 12 of main.ads (and its body is in main.adb), and another one is declared at
 line 45 of foo.ads

 gnatfind -fs xyz:main.adb
           This is the same command as the previous one, instead gnatfind will
           display the content of the Ada source file lines.

           The output will look like:

                      directory/main.ads:106:14: xyz <= declaration
                        procedure xyz;
                      directory/main.adb:24:10: xyz <= body
                        procedure xyz is
                      directory/foo.ads:45:23: xyz <= declaration
                        xyz : Integer;

 This can make it easier to find exactly the location your are looking for.

 gnatfind -r "*x*":main.ads:123 foo.adb
           Find references to all entities containing an x that are referenced
           on line 123 of main.ads. The references will be searched only in
           main.adb and foo.adb.

 gnatfind main.ads:123
           Find declarations and bodies for all entities that are referenced on
           line 123 of main.ads.

           This is the same as gnatfind "*":main.adb:123.

 gnatfind mydir/main.adb:123:45
           Find the declaration for the entity referenced at column 45 in line
           123 of file main.adb in directory mydir. Note that it is usual to
           omit the identifier name when the column is given, since the column
           position identifies a unique reference.

           The column has to be the beginning of the identifier, and should not
           point to any character in the middle of the identifier.


ΓòÉΓòÉΓòÉ 14. File Name Krunching Using gnatkr ΓòÉΓòÉΓòÉ


 This chapter 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                  About gnatkr
 Using gnatkr                  Using gnatkr
 Krunching Method              Krunching Method
 Examples of gnatkr Usage      Examples of gnatkr Usage


ΓòÉΓòÉΓòÉ 14.1. About gnatkr ΓòÉΓòÉΓòÉ


 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:

     Take the unit name and replace all dots by hyphens.

     If such a replacement occurs in the second character position of a name,
      and the first character is a, g, s, or i then replace the dot by the
      character ~ (tilde) instead of a minus.
 The reason for this exception is to avoid clashes with the standard names for
 children of System, Ada, Interfaces, and GNAT, which use the prefixes s- a- i-
 and g- respectively.

 The -gnatknn switch of the compiler activates a "krunching" circuit that
 limits file names to nn characters (where nn is a decimal integer). For
 example, using OpenVMS, where the maximum file name length is 39, the value of
 nn is usually set to 39, but if you want to generate a set of files that would
 be usable if ported to a system with some different maximum file length, then
 a different value can be specified. The default value of 39 for OpenVMS need
 not be specified.

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


ΓòÉΓòÉΓòÉ 14.2. Using gnatkr ΓòÉΓòÉΓòÉ


 The gnatkr command has the form

                      $ gnatkr name [length]

 name can be an Ada name with dots or the GNAT name of the unit, where the dots
 representing child units or subunit are replaced by hyphens. The only
 confusion arises if a name ends in .ads or .adb. gnatkr takes this to be an
 extension if there are no other dots in the name and the whole name is in
 lowercase.

 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 which are always 8.
 The output is the krunched name. The output has an extension only if the
 original argument was a file name with an extension.


ΓòÉΓòÉΓòÉ 14.3. Krunching Method ΓòÉΓòÉΓòÉ


 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
 specification 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:

     The name is divided into segments separated by hyphens, tildes or
      underscores and all hyphens, tildes, and underscores are eliminated. If
      this leaves the name short enough, we are done.

     If the name is too long, the longest segment is located (left-most if
      there are two of equal length), and shortened by dropping its last
      character. This is repeated until the name is short enough.

      As an example, consider the krunching of
      'our-strings-wide_fixed.adb' to fit the name into 8 characters as
      required by some operating systems.

                      our-strings-wide_fixed 22
                      our strings wide fixed 19
                      our string  wide fixed 18
                      our strin  wide fixed 17
                      our stri   wide fixed 16
                      our stri   wide fixe  15
                      our str   wide fixe  14
                      our str   wid  fixe  13
                      our str   wid  fix  12
                      ou  str   wid  fix  11
                      ou  st    wid  fix  10
                      ou  st    wi  fix  9
                      ou  st    wi  fi   8
                      Final file name: oustwifi.adb

     The file names for all predefined units are always krunched to eight
      characters. The krunching of these predefined units uses the following
      special prefix replacements:

      ada-
                     replaced by 'a-'

      gnat-
                     replaced by 'g-'

      interfaces-
                     replaced by 'i-'

      system-
                     replaced by 's-'

      These system files have a hyphen in the second character position. That
      is why normal user files replace such a character with a tilde, to avoid
      confusion with system file names.

      As an example of this special rule, consider
      'ada-strings-wide_fixed.adb', which gets krunched as follows:

                                ada-strings-wide_fixed 22
                                a-  strings wide fixed 18
                                a-  string  wide fixed 17
                                a-  strin  wide fixed 16
                                a-  stri   wide fixed 15
                                a-  stri   wide fixe  14
                                a-  str   wide fixe  13
                                a-  str   wid  fixe  12
                                a-  str   wid  fix  11
                                a-  st    wid  fix  10
                                a-  st    wi  fix  9
                                a-  st    wi  fi   8
                                Final file name: a-stwifi.adb

 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.


ΓòÉΓòÉΓòÉ 14.4. Examples of gnatkr Usage ΓòÉΓòÉΓòÉ

                      $ gnatkr very_long_unit_name.ads    --> velounna.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


ΓòÉΓòÉΓòÉ 15. Preprocessing Using gnatprep ΓòÉΓòÉΓòÉ


 The gnatprep utility provides a simple preprocessing capability for Ada
 programs. It is designed for use with GNAT, but is not dependent on any
 special features of GNAT.

 Using gnatprep                Using gnatprep
 Switches for gnatprep         Switches for gnatprep
 Form of definitions file      Form of definitions file
 Form of input text for gnatprepForm of input text for gnatprep


ΓòÉΓòÉΓòÉ 15.1. Using gnatprep ΓòÉΓòÉΓòÉ


 To call gnatprep use

                      $ gnatprep [-bcrsu] [-Dsymbol=value] infile outfile [deffile]

 where

 infile
           is the full name of the input file, which is an Ada source file
           containing preprocessor directives.

 outfile
           is the full name of the output file, which is an Ada source in
           standard Ada form. When used with GNAT, this file name will normally
           have an ads or adb suffix.

 deffile
           is the full name of a text file containing definitions of symbols to
           be referenced by the preprocessor. This argument is optional, and
           can be replaced by the use of the -D switch.

 switches
           is an optional sequence of switches as described in the next
           section.


ΓòÉΓòÉΓòÉ 15.2. Switches for gnatprep ΓòÉΓòÉΓòÉ

 -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.

 -Dsymbol=value
           Defines a new symbol, associated with 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.

 -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.

 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.


ΓòÉΓòÉΓòÉ 15.3. Form of definitions file ΓòÉΓòÉΓòÉ


 The definitions file contains lines of the form

                      symbol := value

 where symbol is an identifier, following normal Ada (case-insensitive) rules
 for its syntax, and value is one of the following:

     Empty, corresponding to a null substitution

     A string literal using normal Ada syntax

     Any sequence of characters from the set (letters, digits, period,
      underline).

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


ΓòÉΓòÉΓòÉ 15.4. Form of input text for gnatprep ΓòÉΓòÉΓòÉ


 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> 'Defined
                      expression ::=  not expression
                      expression ::=  expression and expression
                      expression ::=  expression or expression
                      expression ::=  expression and then expression
                      expression ::=  expression or else expression
                      expression ::=  ( expression )

 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.

 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, so that
 the lines are included only if the symbol is not defined. 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. 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.


ΓòÉΓòÉΓòÉ 16. The GNAT library browser gnatls ΓòÉΓòÉΓòÉ


 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                Running gnatls
 Switches for gnatls           Switches for gnatls
 Examples of gnatls Usage      Examples of gnatls Usage


ΓòÉΓòÉΓòÉ 16.1. Running gnatls ΓòÉΓòÉΓòÉ


 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 qualifier -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.


ΓòÉΓòÉΓòÉ 16.2. Switches for gnatls ΓòÉΓòÉΓòÉ


 gnatls recognizes the following switches:

 -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.

 -aOdir

 -aIdir

 -Idir

 -I-

 -nostdinc
           Source and Object path manipulation. Same meaning as the equivalent
           $ gnatmake flags Switches for gnatmake

 -v
           Verbose mode. Output the complete source and object 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:

             Preelaborable
                         The unit is preelaborable in the Ada 95 sense.

             No_Elab_Code
                         No elaboration code has been produced by the compiler
                         for this unit.

             Pure
                         The unit is pure in the Ada 95 sense.

             Elaborate_Body
                         The unit contains a pragma Elaborate_Body.

             Remote_Types
                         The unit contains a pragma Remote_Types.

             Shared_Passive
                         The unit contains a pragma Shared_Passive.

             Predefined
                         This unit is part of the predefined environment and
                         cannot be modified by the user.

             Remote_Call_Interface
                         The unit contains a pragma Remote_Call_Interface.


ΓòÉΓòÉΓòÉ 16.3. Example of gnatls Usage ΓòÉΓòÉΓòÉ


 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 3.10w (970212) Copyright 1999 Free Software Foundation, Inc.
                      Source Search Path:
                        <Current_Directory>
                        ┬╖┬╖/
                        /home/comar/local/adainclude/
                      Object Search Path:
                        <Current_Directory>
                        ┬╖┬╖/
                        /home/comar/local/lib/gcc-lib/mips-sni-sysv4/2.7.2/adalib/
                      ┬╖/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


ΓòÉΓòÉΓòÉ 17. GNAT and libraries ΓòÉΓòÉΓòÉ


 This chapter addresses some of the issues related to building and using a
 library with GNAT. It also shows how the GNAT runtime library can be
 recompiled.

 Creating an Ada library       Creating an Ada library
 Installing an Ada library     Installing an Ada library
 Using an Ada library          Using an Ada library
 Rebuilding the GNAT runtime libraryRebuilding the GNAT runtime library


ΓòÉΓòÉΓòÉ 17.1. Creating an Ada library ΓòÉΓòÉΓòÉ


 In the GNAT environment, a library has two components:

     Source files.

     Compiled code and Ali files. See The Ada Library Information Files.

 In order to use other packages The GNAT Compilation Model requires a certain
 number of sources to be available to the compiler. The minimal set of sources
 required includes the specs of all the packages that make up the visible part
 of the library as well as all the sources upon which they depend. The bodies
 of all visible generic units must also be provided.
 Although it is not strictly mandatory, it is recommended that all sources
 needed to recompile the library be provided, so that the user can make full
 use of interunit inlining and source-level debugging. This can also make the
 situation easier for users that need to upgrade their compilation toolchain
 and thus need to recompile the library from sources.
 The compiled code can be provided in different ways. The simplest way is to
 provide directly the set of objects produced by the compiler during the
 compilation of the library. It is also possible to group the objects into an
 archive using whatever commands are provided by the operating system. Finally,
 it is also possible to create a shared library (see option -shared in the GCC
 manual).
 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, in order to build all the necessary objects. Here is an example of
 such a dummy program and the generic commands used to build an archive or a
 shared library.

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

 When the objects are grouped in an archive or a shared library, the user needs
 to specify the desired library at link time, unless a pragma linker_options
 has been used in one of the sources:

                      pragma Linker_Options ("-lmy_lib");


ΓòÉΓòÉΓòÉ 17.2. Installing an Ada library ΓòÉΓòÉΓòÉ


 In the GNAT model, installing a library consists in copying into a specific
 location the files that make up this library. It is possible to install the
 sources in a different directory from the other files (ALI, objects, archives)
 since the source path and the object path can easily be specified separately.
 For general purpose libraries, it is possible for the system administrator to
 put those libraries in the default compiler paths. To achieve this, he must
 specify their location in the configuration files "ada_source_path" and
 "ada_object_path" that 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 simple format: each line in them
 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.
 "ada_source_path" and "ada_object_path" might actually not be present in a
 GNAT installation, in which case, GNAT will look for its runtime 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" at all, and thus the "ada_source_path" file must contain the
 location for the GNAT runtime sources (which can simply be "adainclude"). In
 the same way, the "ada_object_path" file must contain the location for the
 GNAT runtime objects (which can simply be "adalib").
 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.


ΓòÉΓòÉΓòÉ 17.3. Using an Ada library ΓòÉΓòÉΓòÉ


 In order to use a Ada library, you need to make sure that this library is on
 both your source and object path Search Paths and the Run-Time Library (RTL)
 and Search Paths for gnatbind. For instance, 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 simplified down to the following:

                      $ gnatmake my_appl
 when the following conditions are met:

     "/dir/my_lib_src" has been added by the user to the environment variable
      "ADA_INCLUDE_PATH", or by the administrator to the file "ada_source_path"

     "/dir/my_lib_obj" has been added by the user to the environment variable
      "ADA_OBJECTS_PATH", or by the administrator to the file "ada_object_path"

     a pragma linker_options, as mentioned in Creating an Ada library as been
      added to the sources.


ΓòÉΓòÉΓòÉ 17.4. Rebuilding the GNAT runtime library ΓòÉΓòÉΓòÉ


 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_Scalar. 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 line of 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.


ΓòÉΓòÉΓòÉ 18. Using the GNU make utility ΓòÉΓòÉΓòÉ


 This chapter offers some examples of makefiles that solve specific problems.
 It does not explain how to write a makefile (see the GNU make documentation),
 nor does it try to replace the gnatmake utility (see The GNAT Make Program
 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  Using gnatmake in a Makefile
 Automatically creating a list of directoriesAutomatically creating a list of
                               directories
 Generating the command line switchesGenerating the command line switches
 Overcoming command line length limitsOvercoming command line length limits


ΓòÉΓòÉΓòÉ 18.1. Using gnatmake in a Makefile ΓòÉΓòÉΓòÉ


 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 (see 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 $@ }; cp -f ┬╖┬╖/*.ali .
                      # The dependencies for the modules
                      aa/lib/libaa.so: aa/*.o
                      bb/lib/libbb.so: bb/*.o
                      bb/lib/libcc.so: cc/*.o
                      # Make sure all of the shared libraries are in the path before starting the
                      # program
                      run::
                          LD_LIBRARY_PATH=pwd/aa/lib:pwd/bb/lib:pwd/cc/lib ./${MAIN}
                      clean::
                          ${RM} -rf ${CSC_LIST:%=%/lib}
                          ${RM} ${CSC_LIST:%=%/*.ali}
                          ${RM} ${CSC_LIST:%=%/*.o}
                          ${RM} *.o *.ali ${MAIN}


ΓòÉΓòÉΓòÉ 18.2. Automatically creating a list of directories ΓòÉΓòÉΓòÉ


 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, altough 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,┬╖┬╖┬╖

 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}


ΓòÉΓòÉΓòÉ 18.3. Generating the command line switches ΓòÉΓòÉΓòÉ


 Once you have created the list of directories as explained in the previous
 section (see Automatically creating a list of directories), you can easily
 generate the command line arguments to pass to gnatmake.

 For the sake of completness, 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


ΓòÉΓòÉΓòÉ 18.4. Overcoming command line length limits ΓòÉΓòÉΓòÉ


 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 completness, 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
 immediatly by make. This way we overcome the standard make behavior which is
 to expand the variables only when they are actually used.

                      # In this example, we create both ADA_INCLUDE_PATH and ADA_OBJECT_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_OBJECT_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_OBJECT_PATH += ${OBJECT_LIST}
                      export ADA_INCLUDE_PATH
                      export ADA_OBJECT_PATH
                      all:
                          gnatmake main_unit


ΓòÉΓòÉΓòÉ 19. Finding memory problems with gnatmem ΓòÉΓòÉΓòÉ


 gnatmem, is a tool that monitors dynamic allocation and deallocation activity
 in a program, and displays information about incorrect deallocations and
 possible sources of memory leaks. Gnatmem provides three type of information:

     General information concerning memory management, such as the total
      number of allocations and deallocations, the amount of allocated memory
      and the high water mark, i.e. the largest amount of allocated memory in
      the course of program execution.

     Backtraces for all incorrect deallocations, that is to say deallocations
      which do not correspond to a valid allocation.

     Information on each allocation that is potentially the origin of a memory
      leak.

 Running gnatmem               Running gnatmem
 Switches for gnatmem          Switches for gnatmem
 Examples of gnatmem Usage     Examples of gnatmem Usage
 Implementation note           Implementation note


ΓòÉΓòÉΓòÉ 19.1. Running gnatmem ΓòÉΓòÉΓòÉ


 The gnatmem command has the form

                        $ gnatmem [n] [-o file] user_program [program_arg]*
                      or
                        $ gnatmem [n] -i file

 Gnatmem must be supplied with the executable to examine, followed by its
 run-time inputs. For example, if a program is executed with the command:

                      $ my_program arg1 arg2
 then it can be run under gnatmem control using the command:

                      $ gnatmem my_program arg1 arg2

 The program is transparently executed under the control of the debugger The
 GNAT Debugger GDB. This does not affect the behavior of the program, except
 for sensitive real-time programs. When the program has completed execution,
 gnatmem outputs a report containing general allocation/deallocation
 information and potential memory leak. For better results, the user program
 should be compiled with debugging options Switches for gcc.

 Here is a simple example of use:

 *************** debut cc

                      $ gnatmem test_gm
                      Global information
                      ------------------
                        Total number of allocations     :  45
                        Total number of deallocations    :  6
                        Final Water Mark (non freed mem)  :  11.29 Kilobytes
                        High Water Mark           :  11.40 Kilobytes
                      ┬╖
                      ┬╖
                      ┬╖
                      Allocation Root # 2
                      -------------------
                       Number of non freed allocations   :  11
                       Final Water Mark (non freed mem)  :  1.16 Kilobytes
                       High Water Mark           :  1.27 Kilobytes
                       Backtrace              :
                        test_gm.adb:23 test_gm.alloc
                      ┬╖
                      ┬╖
                      ┬╖

 The first block of output give general information. In this case, the Ada
 construct "new" was executed 45 times, and only 6 calls to an unchecked
 deallocation routine occurred.

 Subsequent paragraphs display  information on all allocation roots. An
 allocation root is a specific point in the execution of the program that
 generates some dynamic allocation, such as a "new" construct. This root is
 represented by an execution backtrace (or subprogram call stack). By default
 the backtrace depth for allocations roots is 1, so that a root corresponds
 exactly to a source location. The backtrace can be made deeper, to make the
 root more specific.


ΓòÉΓòÉΓòÉ 19.2. Switches for gnatmem ΓòÉΓòÉΓòÉ


 gnatmem recognizes the following switches:

 -q
           Quiet. Gives the minimum output needed to identify the origin of the
           memory leaks. Omit statistical information.

 n
           N is an integer literal (usually between 1 and 10) which controls
           the depth of the backtraces defining allocation root. The default
           value for N is 1. The deeper the backtrace, the more precise the
           localization of the root. Note that the total number of roots can
           depend on this parameter.

 -o file
           Direct the gdb output to the specified file. The gdb script used to
           generate this output is also saved in the file 'gnatmem.tmp'.

 -i file
           Do the gnatmem processing starting from file which has been
           generated by a previous call to gnatmem with the -o switch. This is
           useful for post mortem processing.


ΓòÉΓòÉΓòÉ 19.3. Example of gnatmem Usage ΓòÉΓòÉΓòÉ


 The first example shows the use of gnatmem on a simple leaking program.
 Suppose that we have the following Ada program:

                      with Unchecked_Deallocation;
                      procedure Test_Gm is
                        type T is array (1┬╖┬╖1000) of Integer;
                        type Ptr is access T;
                        procedure Free is new Unchecked_Deallocation (T, Ptr);
                        A : Ptr;
                        procedure My_Alloc is
                        begin
                         A := new T;
                        end My_Alloc;
                        procedure My_DeAlloc is
                         B : Ptr := A;
                        begin
                         Free (B);
                        end My_DeAlloc;
                      begin
                        My_Alloc;
                        for I in 1 ┬╖┬╖ 5 loop
                         for J in I ┬╖┬╖ 5 loop
                           My_Alloc;
                         end loop;
                         My_Dealloc;
                        end loop;
                      end;

 The program needs to be compiled with debugging option:

                      $ gnatmake -g test_gm

 gnatmem is invoked simply with

                      $ gnatmem test_gm

 which produces the following output:

                      Global information
                      ------------------
                        Total number of allocations     :  18
                        Total number of deallocations    :  5
                        Final Water Mark (non freed mem)  :  53.00 Kilobytes
                        High Water Mark           :  56.90 Kilobytes
                      Allocation Root # 1
                      -------------------
                       Number of non freed allocations   :  11
                       Final Water Mark (non freed mem)  :  42.97 Kilobytes
                       High Water Mark           :  46.88 Kilobytes
                       Backtrace              :
                        test_gm.adb:11 test_gm.my_alloc
                      Allocation Root # 2
                      -------------------
                       Number of non freed allocations   :  1
                       Final Water Mark (non freed mem)  :  10.02 Kilobytes
                       High Water Mark           :  10.02 Kilobytes
                       Backtrace              :
                        s-secsta.adb:81 system.secondary_stack.ss_init
                      Allocation Root # 3
                      -------------------
                       Number of non freed allocations   :  1
                       Final Water Mark (non freed mem)  :  12 Bytes
                       High Water Mark           :  12 Bytes
                       Backtrace              :
                        s-secsta.adb:181 system.secondary_stack.ss_init

 Note that the GNAT run time contains itself a certain number of allocations
 that have no  corresponding deallocation, as shown here for root #2 and root
 #1. This is a normal behavior when the number of non freed allocations is one,
 it locates dynamic data structures that the run time needs for the complete
 lifetime of the program. Note also that there is only one allocation root in
 the user program with a single line back trace: test_gm.adb:11
 test_gm.my_alloc, whereas a careful analysis of the program shows that
 'My_Alloc' is called at 2 different points in the source (line 21 and line
 24). If those two allocation roots need to be distinguished, the backtrace
 depth parameter can be used:

                      $ gnatmem 3 test_gm

 which will give the following output:

                      Global information
                      ------------------
                        Total number of allocations     :  18
                        Total number of deallocations    :  5
                        Final Water Mark (non freed mem)  :  53.00 Kilobytes
                        High Water Mark           :  56.90 Kilobytes
                      Allocation Root # 1
                      -------------------
                       Number of non freed allocations   :  10
                       Final Water Mark (non freed mem)  :  39.06 Kilobytes
                       High Water Mark           :  42.97 Kilobytes
                       Backtrace              :
                        test_gm.adb:11 test_gm.my_alloc
                        test_gm.adb:24 test_gm
                        b_test_gm.c:52 main
                      Allocation Root # 2
                      -------------------
                       Number of non freed allocations   :  1
                       Final Water Mark (non freed mem)  :  10.02 Kilobytes
                       High Water Mark           :  10.02 Kilobytes
                       Backtrace              :
                        s-secsta.adb:81  system.secondary_stack.ss_init
                        s-secsta.adb:283 <system__secondary_stack___elabb>
                        b_test_gm.c:33  adainit
                      Allocation Root # 3
                      -------------------
                       Number of non freed allocations   :  1
                       Final Water Mark (non freed mem)  :  3.91 Kilobytes
                       High Water Mark           :  3.91 Kilobytes
                       Backtrace              :
                        test_gm.adb:11 test_gm.my_alloc
                        test_gm.adb:21 test_gm
                        b_test_gm.c:52 main
                      Allocation Root # 4
                      -------------------
                       Number of non freed allocations   :  1
                       Final Water Mark (non freed mem)  :  12 Bytes
                       High Water Mark           :  12 Bytes
                       Backtrace              :
                        s-secsta.adb:181 system.secondary_stack.ss_init
                        s-secsta.adb:283 <system__secondary_stack___elabb>
                        b_test_gm.c:33  adainit

 The allocation root #1 of the first example has been split in 2 roots #1 and
 #3 thanks to the more precise associated backtrace.


ΓòÉΓòÉΓòÉ 19.4. Implementation note ΓòÉΓòÉΓòÉ


 gnatmem executes the user program under the control of gdb using a script that
 sets breakpoints and gathers information on each dynamic allocation and
 deallocation. The output of the script is then analyzed by gnatmem in order to
 locate memory leaks and their origin in the program. Gnatmem works by
 recording each address returned by the allocation procedure (__gnat_malloc)
 along with the backtrace at the allocation point. On each deallocation, the
 deallocated address is matched with the corresponding allocation. At the end
 of the processing, the unmatched allocations are considered potential leaks.
 All the allocations associated with the same backtrace are grouped together
 and form an allocation root. The allocation roots are then sorted so that
 those with the biggest number of unmatched allocation are printed first. A
 delicate aspect of this technique is to distinguish between the data produced
 by the user program and the data produced by the gdb script. Currently, on
 systems that allow probing the terminal, the gdb command "tty" is used to
 force the program output to be redirected to the current terminal while the
 gdb output is directed to a file or to a pipe in order to be processed
 subsequently by gnatmem.


ΓòÉΓòÉΓòÉ 20. Finding memory problems with GNAT Debug Pool ΓòÉΓòÉΓòÉ


 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 specifc 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 of 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:

     GNAT.Debug_Pools.Accessing_Not_Allocated_Storage

     GNAT.Debug_Pools.Accessing_Deallocated_Storage

     GNAT.Debug_Pools.Freeing_Not_Allocated_Storage

     GNAT.Debug_Pools.Freeing_Deallocated_Storage

 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. The deallocation strategy consists
 in not releasing the memory to the underlying system but rather to fill it
 with a memory pattern easily recognizable during debugging sessions: The
 memory pattern is the old IBM hexadecimal convention: 16#DEADBEEF#. 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


ΓòÉΓòÉΓòÉ 21. Creating Sample Bodies Using gnatstub ΓòÉΓòÉΓòÉ


 gnatstub creates body stubs, that is, empty but compilable bodies for library
 unit declarations.

 To create a body stub, gnatstub has to compile the library unit declaration.
 Therefore, bodies can be created only for legal library units. Moreover, if a
 library unit depends semantically upon units located outside the current
 directory, you have to provide the source search path when calling gnatstub,
 see the description of gnatstub switches below.

 Running gnatstub              Running gnatstub
 Switches for gnatstub         Switches for gnatstub


ΓòÉΓòÉΓòÉ 21.1. Running gnatstub ΓòÉΓòÉΓòÉ


 gnatstub has the command-line interface of the form

                      $ gnatstub [switches] filename [directory]

 where

 filename
           is the name of the source file that contains a library unit
           declaration for which a body must be created. This name should
           follow the GNAT file name conventions. No crunching is allowed for
           this file name. The file name may contain the path information.

 directory
           indicates the directory to place a body stub (default is the current
           directory)

 switches
           is an optional sequence of switches as described in the next section


ΓòÉΓòÉΓòÉ 21.2. Switches for gnatstub ΓòÉΓòÉΓòÉ

 -f
           If the destination directory already contains a file with a name of
           the body file for the argument spec file, replace it with the
           generated body stub.

 -hs
           Put the comment header (i.e. all the comments preceding the
           compilation unit) from the source of the library unit declaration
           into the body stub.

 -hg
           Put a sample comment header into the body stub.

 -IDIR

 -I-
           These switches have the same meaning as in calls to gcc. They define
           the source search path in the call to gcc issued by gnatstub to
           compile an argument source file.

 -in
           (n is a decimal natural number). Set the indentation level in the
           generated body sample to n, '-i0' means "no indentation", the
           default indentation is 3.

 -k
           Do not remove the tree file (i.e. the snapshot of the compiler
           internal structures used by gnatstub) after creating the body stub.

 -ln
           (n is a decimal positive number) Set the maximum line length in the
           body stub to n, the default is 78.

 -q
           Quiet mode: do not generate a confirmation when a body is
           successfully created or a message when a body is not required for an
           argument unit.

 -r
           Reuse the tree file (if it exists) instead of creating it: instead
           of creating the tree file for the library unit declaration, gnatstub
           tries to find it in the current directory and use it for creating a
           body. If the tree file is not found, no body is created. -r also
           implies -k, whether or not -k is set explicitly.

 -t
           Overwrite the existing tree file: if the current directory already
           contains the file which, according to the GNAT file name rules
           should be considered as a tree file for the argument source file,
           gnatstub will refuse to create the tree file needed to create a body
           sampler, unless -t option is set

 -v
           Verbose mode: generate version information.


ΓòÉΓòÉΓòÉ 22. Reducing the Size of Ada Executables with gnatelim ΓòÉΓòÉΓòÉ

 About gnatelim                About gnatelim
 Eliminate pragma              Eliminate pragma
 Tree Files                    Tree Files
 Preparing Tree and Bind Files for gnatelimPreparing Tree and Bind Files for
                               gnatelim
 Running gnatelim              Running gnatelim
 Correcting the List of Eliminate PragmasCorrecting the List of Eliminate
                               Pragmas
 Making your Executables smallerMaking your Executables smaller
 Summary of the gnatelim Usage CycleSummary of the gnatelim Usage Cycle


ΓòÉΓòÉΓòÉ 22.1. About gnatelim ΓòÉΓòÉΓòÉ


 When a program shares a set of Ada packages with other programs, it may happen
 that this program uses only a fraction of the subprograms defined in these
 packages. The code created for these unused subprograms increases the size of
 the executable.

 gnatelim tracks unused subprograms in an Ada program and outputs a list of
 GNAT-specific Eliminate pragmas (see next section) marking all the subprograms
 that are declared but never called. By placing the list of Eliminate pragmas
 in the GNAT configuration file 'gnat.adc' and recompiling your program, you
 may decrease the size of its executable, because the compiler will not
 generate the code for 'eliminated' subprograms.

 gnatelim needs as its input data a set of tree files (see Tree Files)
 representing all the components of a program to process and a bind file for a
 main subprogram (see Preparing Tree and Bind Files for gnatelim). Both of
 these must be present in the current directory.


ΓòÉΓòÉΓòÉ 22.2. Eliminate pragma ΓòÉΓòÉΓòÉ


 The simplified syntax of Eliminate pragma that gnatelim makes use of is

                      pragma Eliminate (Library_Unit_Name, Subprogram_Name);

 where

 Library_Unit_Name
           full expanded Ada name of a library unit

 Subprogram_Name
           a simple or expanded name of a subprogram declared within this
           compilation unit

 The effect of an Eliminate pragma placed in the GNAT configuration file
 'gnat.adc' is:

     If the subprogram Subprogram_Name is declared within the library unit
      Library_Unit_Name, the compiler will not generate code for this
      subprogram. This applies to all overloaded subprograms denoted by
      Subprogram_Name.

     If a subprogram marked by the pragma Eliminate is used (called) in a
      program, the compiler will produce an error message in the place where it
      is called.


ΓòÉΓòÉΓòÉ 22.3. Tree Files ΓòÉΓòÉΓòÉ


 A tree file stores a snapshot of the compiler internal data structures in the
 very end of a successful compilation. It contains all the syntactical and
 semantic information about the unit being compiled and all the units upon
 which it depends semantically. Some tools need tree files to obtain this
 information.

 To use some of these tools, a user should take care of producing the right set
 of tree files for them.

 GNAT produces correct tree files when -gnatt -gnatc options are set in a gcc
 call. The tree files have an .adt extension.

 Therefore, to produce a tree file for the compilation unit contained in a file
 named 'foo.adb', you must use the command

                      $ gcc -c -gnatc -gnatt foo.adb

 and you will get the tree file 'foo.adt' as a result of this compilation.


ΓòÉΓòÉΓòÉ 22.4. Preparing Tree and Bind Files for gnatelim ΓòÉΓòÉΓòÉ


 Let Main_Prog be the name of a main subprogram, and suppose this subprogram is
 in a file named 'main_prog.adb'.

 To create a bind file for gnatelim, run gnatbind for the main subprogram.
 gnatelim can work with both Ada and C bind files; when both are present, it
 uses the Ada bind file. The following commands will build the program and
 create the bind file:

                      $ gnatmake -c Main_Prog
                      $ gnatbind main_prog

 To create a minimal set of tree files covering the whole program, call
 gnatmake for this program as follows:

                      $ gnatmake -f -c -gnatc -gnatt Main_Prog

 The -c gnatmake option turns off the bind and link phases, that are impossible
 anyway because the sources are compiled with -gnatc option which turns off
 code generation.

  the -f gnatmake option forces recompilation of all the needed sources.

 Such sequence of actions will create all the data needed by gnatelim from
 scratch and therefore guarantee its consistency.

 Note, that gnatelim needs neither object nor ALI files, so they can be deleted
 at this stage.


ΓòÉΓòÉΓòÉ 22.5. Running gnatelim ΓòÉΓòÉΓòÉ


 gnatelim has the following command-line interface:

                      $ gnatelim [options] name

 name should be a full expanded Ada name of a main subprogram of a program
 (partition).

 gnatelim options:

 -q
           Quiet mode: by default gnatelim version information is printed as
           Ada comments to the standard output stream. Various debugging
           information and information reflecting some details of the analysis
           done by gnatelim is output to the standard error stream.

 -a
           Also look for subprograms from the GNAT runtime that can be
           eliminated.

 -m
           Check if any tree files are missing for an accurate result.

 -dx
           Activate internal debugging switches.  x is a letter or digit, or
           string of letters or digits, which specifies the type of debugging
           mode 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 Gnatelim.Options unit in the
           compiler source file 'gnatelim-options.adb'.

 gnatelim sends its output to the standard output stream, so in order to
 produce a proper GNAT configuration file 'gnat.adc', redirection must be used:

                      $ gnatelim Main_Prog > gnat.adc

 or

                      $ gnatelim Main_Prog >> gnat.adc

 In order to append the gnatelim output to the existing contents of 'gnat.adc'.


ΓòÉΓòÉΓòÉ 22.6. Correcting the List of Eliminate Pragmas ΓòÉΓòÉΓòÉ


 In some rare cases it may happen that gnatelim will try to eliminate
 subprograms which are actually called in the program. In this case, the
 compiler will generate an error message of the form:

                      file.adb:106:07: cannot call eliminated subprogram "My_Prog"

 You will need to manually remove the wrong Eliminate pragmas from the
 'gnat.adc' file. It is advised that you recompile your program from scratch
 after that because you need a consistent 'gnat.adc' file during the entire
 compilation.


ΓòÉΓòÉΓòÉ 22.7. Making your Executables smaller ΓòÉΓòÉΓòÉ


 In order to get a smaller executable for your program you now have to
 recompile the program completely with the new 'gnat.adc' file created by
 gnatelim in your current directory:

                      $ gnatmake -f Main_Prog

 (you will need -f option for gnatmake to recompile everything with the set of
 pragmas Eliminate you have obtained with gnatelim).

 Be aware that the set of Eliminate pragmas is specific to each program. It is
 not recommended to merge sets of Eliminate pragmas created for different
 programs in one 'gnat.adc' file.


ΓòÉΓòÉΓòÉ 22.8. Summary of the gnatelim Usage Cycle ΓòÉΓòÉΓòÉ


 Here is a quick summary of the steps to be taken in order to reduce the size
 of your executables with gnatelim. You may use other GNAT options to control
 the optimization level, to produce the debugging information, to set search
 path, etc.

   1. Produce a bind file and a set of tree files

                      $ gnatmake -c Main_Prog
                      $ gnatbind main_prog
                      $ gnatmake -f -c -gnatc -gnatt Main_Prog

   2. Generate a list of Eliminate pragmas

                      $ gnatelim Main_Prog >[>] gnat.adc

   3. Recompile the application

                      $ gnatmake -f Main_Prog


ΓòÉΓòÉΓòÉ 23. Other Utility Programs ΓòÉΓòÉΓòÉ


 This chapter discusses some other utility programs available in the Ada
 environment.

 Using Other Utility Programs With GNATUsing Other Utility Programs With GNAT
 The gnatpsys Utility Program  The gnatpsys Utility Program
 The gnatpsta Utility Program  The gnatpsta Utility Program
 The External Symbol Naming Scheme of GNATThe External Symbol Naming Scheme of
                               GNAT
 Ada Mode for emacs            Ada Mode for emacs
 Converting Ada files to html using gnathtmlConverting Ada files to html using
                               gnathtml
 Installing gnathtml           Installing gnathtml


ΓòÉΓòÉΓòÉ 23.1. Using Other Utility Programs With GNAT ΓòÉΓòÉΓòÉ


 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.


ΓòÉΓòÉΓòÉ 23.2. The gnatpsys Utility Program ΓòÉΓòÉΓòÉ


 Many of the definitions in package System are implementation-dependent.
 Furthermore, although the source of the package System is available for
 inspection, it uses special attributes for parameterizing many of the critical
 values, so the source is not informative for the casual user.

 The gnatpsys utility is designed to deal with this situation. It is an Ada
 program that dynamically determines the values of all the relevant parameters
 in System, and prints them out in the form of an Ada source listing for
 System, displaying all the values of interest. This output is generated to
 'stdout'.

 To determine the value of any parameter in package System, simply run gnatpsys
 with no qualifiers or arguments, and examine the output. This is preferable to
 consulting documentation, because you know that the values you are getting are
 the actual ones provided by the executing system.


ΓòÉΓòÉΓòÉ 23.3. The gnatpsta Utility Program ΓòÉΓòÉΓòÉ


 Many of the definitions in package Standard are implementation-dependent.
 However, the source of this package does not exist as an Ada source file, so
 these values cannot be determined by inspecting the source. They can be
 determined by examining in detail the coding of 'cstand.adb' which creates the
 image of Standard in the compiler, but this is awkward and requires a great
 deal of internal knowledge about the system.

 The gnatpsta utility is designed to deal with this situation. It is an Ada
 program that dynamically determines the values of all the relevant parameters
 in Standard, and prints them out in the form of an Ada source listing for
 Standard, displaying all the values of interest. This output is generated to
 'stdout'.

 To determine the value of any parameter in package Standard, simply run
 gnatpsta with no qualifiers or arguments, and examine the output. This is
 preferable to consulting documentation, because you know that the values you
 are getting are the actual ones provided by the executing system.


ΓòÉΓòÉΓòÉ 23.4. The External Symbol Naming Scheme of GNAT ΓòÉΓòÉΓòÉ


 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 var1_name, and the link name for Var2
 is var2_link_name.

 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.


ΓòÉΓòÉΓòÉ 23.5. Ada Mode for emacs ΓòÉΓòÉΓòÉ


 The Emacs mode for programming in Ada (both, Ada83 and Ada95) helps the user
 in understanding existing code and facilitates writing new code. It
 furthermore provides some utility functions for easier integration of standard
 Emacs features when programming in Ada.


ΓòÉΓòÉΓòÉ 23.6. General features: ΓòÉΓòÉΓòÉ

     Full Integrated Development Environment :

        -  support of 'project files' for the configuration (directories,
           compilation options,┬╖┬╖┬╖)

        -  compiling and stepping through error messages.

        -  running and debugging your applications within Emacs.

     easy to use for beginners by pull-down menus,

     user configurable by many user-option variables.


ΓòÉΓòÉΓòÉ 23.7. Ada mode features that help understanding code: ΓòÉΓòÉΓòÉ

     functions for easy and quick stepping through Ada code,

     getting cross reference information for identifiers (e.g. find the
      defining place by a keystroke),

     displaying an index menu of types and subprograms and move point to the
      chosen one,

     automatic color highlighting of the various entities in Ada code.


ΓòÉΓòÉΓòÉ 23.8. Emacs support for writing Ada code: ΓòÉΓòÉΓòÉ

     switching between spec and body files with possible autogeneration of
      body files,

     automatic formating of subprograms parameter lists.

     automatic smart indentation according to Ada syntax,

     automatic completion of identifiers,

     automatic casing of identifiers, keywords, and attributes,

     insertion of statement templates,

     filling comment paragraphs like filling normal text,

 For more information, please see See Ada Mode for emacs.


ΓòÉΓòÉΓòÉ 23.9. Converting Ada files to html using gnathtml ΓòÉΓòÉΓòÉ


 This Perl script allows Ada source files to be browsed using standard Web
 browsers. For installation procedure, see the section 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.

 The command line is as follow:

                      $ perl gnathtml.pl [switches] ada-files

 You can pass it 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 available switches are the following ones :

 -83
           Only the subset on the Ada 83 keywords will be highlighted, not the
           full Ada 95 keywords set.

 -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 (using for instance the
           with command, the latter will also be converted to html. Only the
           files in the user project will be converted to html, not the files
           in the runtime library itself.

 -D
           This command is the same as -d above, but gnathtml will also look
           for files in the runtime library, and generate html files for them.

 -f
           By default, gnathtml will generate html links only for global
           entities ('with'ed units, global variables and types,┬╖┬╖┬╖). If you
           specify the -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 be using
           '.adp' 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 option 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.


ΓòÉΓòÉΓòÉ 23.10. Installing gnathtml ΓòÉΓòÉΓòÉ


 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  tell  the Operating  system  where Perl is. 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


ΓòÉΓòÉΓòÉ 24. Running and Debugging Ada Programs ΓòÉΓòÉΓòÉ


 This chapter discusses how to debug Ada programs. An incorrect Ada program may
 be handled in three ways by the GNAT compiler:

   1. The illegality may be a violation of the static semantics of Ada. In that
      case GNAT diagnoses the constructs in the program that are illegal. It is
      then a straightforward matter for the user to modify those parts of the
      program.

   2. The illegality may be a violation of the dynamic semantics of Ada. In
      that case the program compiles and executes, but may generate incorrect
      results, or may terminate abnormally with some exception.

   3. When presented with a program that contains convoluted errors, GNAT
      itself may terminate abnormally without providing full diagnostics on the
      incorrect user program.

 The GNAT Debugger GDB         The GNAT Debugger GDB
 Running GDB                   Running GDB
 Introduction to GDB Commands  Introduction to GDB Commands
 Using Ada Expressions         Using Ada Expressions
 Calling User-Defined SubprogramsCalling User-Defined Subprograms
 Ada Exceptions                Ada Exceptions
 Ada Tasks                     Ada Tasks
 Debugging Generic Units       Debugging Generic Units
 GNAT Abnormal Termination     GNAT Abnormal Termination
 Naming Conventions for GNAT Source FilesNaming Conventions for GNAT Source
                               Files
 Getting Internal Debugging InformationGetting Internal Debugging Information


ΓòÉΓòÉΓòÉ 24.1. The GNAT Debugger GDB ΓòÉΓòÉΓòÉ


 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. The manual Debugging
 with GDB contains 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.


ΓòÉΓòÉΓòÉ 24.2. Running GDB ΓòÉΓòÉΓòÉ


 The debugger can be launched directly and simply from emacs which allows to
 browse and modify directly the source code during the debugging session, See
 Ada Mode for emacs. Here is described the basic use of GDB is text mode.
 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.


ΓòÉΓòÉΓòÉ 24.3. Introduction to GDB Commands ΓòÉΓòÉΓòÉ


 GDB contains a large repertoire of commands. The manual Debugging with GDB
 includes 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.

 set args arguments
           The arguments list above is a list of arguments to be passed to the
           program on a subsequent run command, just as though the arguments
           had been entered on a normal invocation of the program. The set args
           command is not needed if the program does not require arguments.

 run
           The run command causes execution of the program to start from the
           beginning. If the program is already running, that is to say if you
           are currently positioned  at a breakpoint, then a prompt will ask
           for confirmation that you want to abandon the current execution and
           restart.

 breakpoint location
           The breakpoint command sets a breakpoint, that is to say a point at
           which execution will halt and GDB will await further commands.
           location is either a line number within a file, given in the format
           file:linenumber, or it is the name of a subprogram. If you request
           that a breakpoint be set on a subprogram that is overloaded, a
           prompt will ask you to specify on which of those subprograms you
           want to breakpoint. You can also specify that all of them should be
           breakpointed. If the program is run and execution encounters the
           breakpoint, then the program stops and GDB signals that the
           breakpoint was encountered by printing the line of code before which
           the program is halted.

 breakpoint exception name
           A special form of the breakpoint command which breakpoints whenever
           exception name is raised. If name is omitted, then a breakpoint will
           occur when any exception is raised.

 print expression
           This will print the value of the given expression. Most simple Ada
           expression formats are properly handled by GDB, so the expression
           can contain function calls, variables, operators, and attribute
           references.

 continue
           Continues execution following a breakpoint, until the next
           breakpoint or the termination of the program.

 step
           Executes a single line after a breakpoint. If the next statement is
           a subprogram call, execution continues into (the first statement of)
           the called subprogram.

 next
           Executes a single line. If this line is a subprogram call, executes
           and returns from the call.

 list
           Lists a few lines around the current source location. In practice,
           it is usually more convenient to have a separate edit window open
           with the relevant source file displayed. Successive applications of
           this command print subsequent lines. The command can be given an
           argument which is a line number, in which case it displays a few
           lines around the specified one.

 backtrace
           Displays a backtrace of the call chain. This command is typically
           used after a breakpoint has occurred, to examine the sequence of
           calls that leads to the current breakpoint. The display includes one
           line for each activation record (frame) corresponding to an active
           subprogram.

 up
           At a breakpoint, GDB can display the values of variables local to
           the current frame. The command up can be used to examine the
           contents of other active frames, by moving the focus up the stack,
           that is to say from callee to caller, one frame at a time.

 down
           Moves the focus of GDB down from the frame currently being examined
           to the frame of its callee (the reverse of the previous command),

 frame n
           Inspect the frame with the given number. The value 0 denotes the
           frame of the current breakpoint, that is to say the top of the call
           stack.

 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).


ΓòÉΓòÉΓòÉ 24.4. Using Ada Expressions ΓòÉΓòÉΓòÉ


 GDB supports a fairly large subset of Ada expression syntax, with some
 extensions. The philosophy behind the design of this subset is

     That GDB should provide basic literals and access to operations for
      arithmetic, dereferencing, field selection, indexing, and subprogram
      calls, leaving more sophisticated computations to subprograms written
      into the program (which therefore may be called from GDB).

     That type safety and strict adherence to Ada language restrictions are
      not particularly important to the GDB user.

     That brevity is important to the GDB user.

 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 Debugging with GDB.


ΓòÉΓòÉΓòÉ 24.5. Calling User-Defined Subprograms ΓòÉΓòÉΓòÉ


 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.


ΓòÉΓòÉΓòÉ 24.6. Breaking on Ada Exceptions ΓòÉΓòÉΓòÉ


 You can set breakpoints that trip when your program raises selected
 exceptions.

 break exception
           Set a breakpoint that trips whenever (any task in the) program
           raises any exception.

 break exception name
           Set a breakpoint that trips whenever (any task in the) program
           raises the exception name.

 break exception unhandled
           Set a breakpoint that trips whenever (any task in the) program
           raises an exception for which there is no handler.

 info exceptions

 info exceptions regexp
           The info exceptions command permits the user to examine all defined
           exceptions within Ada programs. With a regular expression, regexp,
           as argument, prints out only those exceptions whose name matches
           regexp.


ΓòÉΓòÉΓòÉ 24.7. Ada Tasks ΓòÉΓòÉΓòÉ


 GDB allows the following task-related commands:

 info tasks
           This command shows a list of current Ada tasks, as in the following
           example:

                      (gdb) info tasks
                       ID    TID P-ID  Thread Pri State         Name
                        1  8088000  0  807e000  15 Child Activation Wait main_task
                        2  80a4000  1  80ae000  15 Accept/Select Wait   b
                        3  809a800  1  80a4800  15 Child Activation Wait a
                      *  4  80ae800  3  80b8000  15 Running        c

 In this listing, the asterisk before the first task indicates it to be the
 currently running task. The first column lists the task ID that is used to
 refer to tasks in the following commands.

 break linespec task taskid

 break linespec task taskid if ┬╖┬╖┬╖
           These commands are like the break ┬╖┬╖┬╖ thread ┬╖┬╖┬╖. linespec specifies
           source lines.

           Use the qualifier 'task taskid' with a breakpoint command to specify
           that you only want GDB to stop the program when a particular Ada
           task reaches this breakpoint. taskid is one of the numeric task
           identifiers assigned by GDB, shown in the first column of the 'info
           tasks' display.

           If you do not specify 'task taskid' when you set a breakpoint, the
           breakpoint applies to all tasks of your program.

           You can use the task qualifier on conditional breakpoints as well;
           in this case, place 'task taskid' before the breakpoint condition
           (before the if).

 task taskno
           This command allows to switch to the task referred by taskno. In
           particular, This allows to browse the backtrace of the specified
           task. It is advised to switch back to the original task before
           continuing execution otherwise the scheduling of the program may be
           perturbated.

 For more detailed information on the tasking support Debugging with GDB.


ΓòÉΓòÉΓòÉ 24.8. Debugging Generic Units ΓòÉΓòÉΓòÉ


 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.


ΓòÉΓòÉΓòÉ 24.9. GNAT Abnormal Termination ΓòÉΓòÉΓòÉ


 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, or terminating abnormally. 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 programming skills and your familiarity with compiler
 internals.

   1. Run gcc with the -gnatf and -gnate switches. The first switch causes all
      errors on a given line to be reported. In its absence, only the first
      error on a line is displayed.

      The -gnate switch causes errors to be displayed as soon as they are
      encountered, rather than after compilation is terminated. If GNAT
      terminates prematurely, the last error message displayed is likely to
      pinpoint the culprit.

   2. Run gcc with the -v (verbose) switch. In this mode, gcc produces ongoing
      information about the progress of the compilation and provides the name
      of each procedure as code is generated. This switch allows you to find
      which Ada procedure was being compiled when it encountered a code
      generation problem.

   3. Run gcc with the -gnatdc switch. This is a GNAT specific switch that does
      for the front-end what -v does for the back end. The system prints the
      name of each unit, either a compilation unit or nested unit, as it is
      being analyzed.

   4. Finally, you can start gdb directly on the gnat1 executable. gnat1 is the
      front-end of GNAT, and can be run independently (normally it is just
      called from gcc). You can use gdb on gnat1 as you would on a C program
      (but see The GNAT Debugger GDB for caveats). The where command is the
      first line of attack; the variable lineno (seen by print lineno), used by
      the second phase of gnat1 and by the gcc backend, indicates the source
      line at which the execution stopped, and input_file name indicates the
      name of the source file.


ΓòÉΓòÉΓòÉ 24.10. Naming Conventions for GNAT Source Files ΓòÉΓòÉΓòÉ


 In order to examine the workings of the GNAT system, the following brief
 description of its organization may be helpful:

     Files with prefix 'sc' contain the lexical scanner.

     All files prefixed with 'par' are components of the parser. The numbers
      correspond to chapters of the Ada 95 Reference Manual. For example,
      parsing of select statements can be found in 'par-ch9.adb'.

     All files prefixed with 'sem' perform semantic analysis. The numbers
      correspond to chapters of the Ada standard. For example, all issues
      involving context clauses can be found in 'sem_ch10.adb'. In addition,
      some features of the language require sufficient special processing to
      justify their own semantic files: sem_aggr for aggregates, sem_disp for
      dynamic dispatching, etc.

     All files prefixed with 'exp' perform normalization and expansion of the
      intermediate representation (abstract syntax tree, or AST). these files
      use the same numbering scheme as the parser and semantics files. For
      example, the construction of record initialization procedures is done in
      'exp_ch3.adb'.

     The files prefixed with 'bind' implement the binder, which verifies the
      consistency of the compilation, determines an order of elaboration, and
      generates the bind file.

     The files 'atree.ads' and 'atree.adb' detail the low-level data
      structures used by the front-end.

     The files 'sinfo.ads' and 'sinfo.adb' detail the structure of the
      abstract syntax tree as produced by the parser.

     The files 'einfo.ads' and 'einfo.adb' detail the attributes of all
      entities, computed during semantic analysis.

     Library management issues are dealt with in files with prefix 'lib'.

     Ada files with the prefix 'a-' are children of Ada, as defined in Annex
      A.

     Files with prefix 'i-' are children of Interfaces, as defined in Annex B.

     Files with prefix 's-' are children of System. This includes both
      language-defined children and GNAT run-time routines.

     Files with prefix 'g-' are children of GNAT. These are useful
      general-purpose packages, fully documented in their specifications. All
      the other '.c' files are modifications of common gcc files.


ΓòÉΓòÉΓòÉ 24.11. Getting Internal Debugging Information ΓòÉΓòÉΓòÉ


 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.


ΓòÉΓòÉΓòÉ 25. Performance Considerations ΓòÉΓòÉΓòÉ


 The GNAT system provides a number of options that allow a trade-off between

     performance of the generated code

     speed of compilation

     minimization of dependences and recompilation

     the degree of run-time checking.

 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:

     no optimization

     no inlining of subprogram calls

     all run-time checks enabled except overflow and elaboration checks

 These options are suitable for most program development purposes. This chapter
 describes how you can modify these choices.

 Controlling Run-time Checks   Controlling Run-time Checks
 Optimization Levels           Optimization Levels
 Inlining of Subprograms       Inlining of Subprograms


ΓòÉΓòÉΓòÉ 25.1. Controlling Run-time Checks ΓòÉΓòÉΓòÉ


 By default, GNAT produces all run-time checks, except arithmetic overflow
 checking for integer operations (that includes division by zero) and checks
 for access before elaboration on subprogram calls. Two gnat switches, -gnatp
 and -gnato allow this default to be modified. See Run-time Checks.

 Our experience is that the default is suitable for most development purposes.

 We treat integer overflow specially because these are quite expensive and in
 our experience are not as important as other run-time checks in the
 development process.

 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.

 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.


ΓòÉΓòÉΓòÉ 25.2. Optimization Levels ΓòÉΓòÉΓòÉ


 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 -On switch, where n is an integer from 0 to 3, on the gcc command line
 to control the optimization level:

 -O0
           no optimization (the default)

 -O1
           medium level optimization

 -O2
           full optimization

 -O3
           full optimization, and also attempt automatic inlining of small
           subprograms within a unit (see Inlining of Subprograms).

 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.

 Note: 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.


ΓòÉΓòÉΓòÉ 25.3. Inlining of Subprograms ΓòÉΓòÉΓòÉ


 A call to a subprogram in the current unit is inlined if all the following
 conditions are met:

     The optimization level is at least -O1.

     The called subprogram is suitable for inlining: It must be small enough
      and not contain nested subprograms or anything else that gcc cannot
      support in inlined subprograms.

     The call occurs after the definition of the body of the subprogram.

     Either pragma Inline applies to the subprogram or it is small and
      automatic inlining (optimization level -O3) is specified.

 Calls to subprograms in with'ed units are normally not inlined. To achieve
 this level of inlining, the following conditions must all be true:

     The optimization level is at least -O1.

     The called subprogram is suitable for inlining: It must be small enough
      and not contain nested subprograms or anything else gcc cannot support in
      inlined subprograms.

     The call appears in a body (not in a package spec).

     There is a pragma Inline for the subprogram.

     The -gnatn switch is used in the gcc command line

 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.

 Note: The -fno-inline switch can be used to prevent all inlining. This switch
 overrides all other conditions and ensures that no inlining occurs. The extra
 dependences resulting from -gnatn will still be active, even if this switch is
 used to suppress the resulting inlining actions.


ΓòÉΓòÉΓòÉ 26. Index ΓòÉΓòÉΓòÉ

 'gnat.adc'                                        Using Other File Names
                                                   The Configuration Pragmas
                                                   file
 --GCC=compiler_name (gnatlink)                    Switches for gnatlink
 --GCC=compiler_name (gnatmake)                    Switches for gnatmake
 --GNATBIND=binder_name (gnatmake)                 Switches for gnatmake
 --GNATLINK=linker_name (gnatmake)                 Switches for gnatmake
 --LINK= (gnatlink)                                Switches for gnatlink
 -83 (gnathtml)                                    Converting Ada files to html
                                                   using gnathtml
 -A (gnatbind)                                     Output Control
 -A (gnatlink)                                     Switches for gnatlink
 -a (gnatls)                                       Switches for gnatls
 -a (gnatmake)                                     Switches for gnatmake
                                                   Switches for gnatmake
 -aI (gnatmake)                                    Switches for gnatmake
 -aL (gnatmake)                                    Switches for gnatmake
 -aO (gnatmake)                                    Switches for gnatmake
 -b (gcc)                                          Switches for gcc
                                                   Switches for gcc
 -b (gnatbind)                                     Binder Error Message Control
 -b (gnatlink)                                     Switches for gnatlink
                                                   Switches for gnatlink
 -bargs (gnatmake)                                 Mode switches for gnatmake
 -c (gcc)                                          Switches for gcc
 -C (gnatbind)                                     Output Control
                                                   Output Control
 -c (gnatchop)                                     Switches for gnatchop
 -C (gnatlink)                                     Switches for gnatlink
 -c (gnatmake)                                     Switches for gnatmake
 -cargs (gnatmake)                                 Mode switches for gnatmake
 -d (gnathtml)                                     Converting Ada files to html
                                                   using gnathtml
 -d (gnatls)                                       Switches for gnatls
 -e (gnatbind)                                     Output Control
 -f (gnatbind)                                     Elaboration Control
 -f (gnathtml)                                     Converting Ada files to html
                                                   using gnathtml
 -f (gnatmake)                                     Switches for gnatmake
 -fno-inline (gcc)                                 Inlining of Subprograms
 -fstack-check                                     Stack Overflow Checking
 -g (gcc)                                          Switches for gcc
 -g (gnatlink)                                     Switches for gnatlink
 -gnat83 (gcc)                                     Compiling Ada 83 Programs
 -gnat95 (gcc)                                     Compiling Ada 83 Programs
 -gnata (gcc)                                      Debugging and Assertion
                                                   Control
 -gnatb (gcc)                                      Output and Error Message
                                                   Control
 -gnatc (gcc)                                      Using gcc for Semantic
                                                   Checking
 -gnatD (gcc)                                      Debugging Control
 -gnatdc switch                                    GNAT Abnormal Termination
 -gnate (gcc)                                      Output and Error Message
                                                   Control
                                                   Run-time Checks
 -gnatf (gcc)                                      Output and Error Message
                                                   Control
 -gnatg (gcc)                                      Reference Manual Style
                                                   Checking
                                                   Debugging Control
 -gnati (gcc)                                      Character Set Control
 -gnatk (gcc)                                      File Naming Control
 -gnatl (gcc)                                      Output and Error Message
                                                   Control
 -gnatm (gcc)                                      Output and Error Message
                                                   Control
 -gnatn (gcc)                                      Subprogram Inlining Control
                                                   Inlining of Subprograms
 -gnatn switch                                     Source Dependencies
 -gnato (gcc)                                      Run-time Checks
                                                   Controlling Run-time Checks
 -gnatp (gcc)                                      Run-time Checks
                                                   Controlling Run-time Checks
 -gnatq (gcc)                                      Output and Error Message
                                                   Control
 -gnatR (gcc)                                      Output and Error Message
                                                   Control
                                                   Reference Manual Style
                                                   Checking
 -gnats (gcc)                                      Using gcc for Syntax
                                                   Checking
 -gnatT (gcc)                                      Run-time Control
                                                   Auxiliary Output Control
 -gnatU (gcc)                                      Output and Error Message
                                                   Control
                                                   Auxiliary Output Control
 -gnatv (gcc)                                      Output and Error Message
                                                   Control
 -gnatW (gcc)                                      Character Set Control
 -gnatwa (gcc)                                     Output and Error Message
                                                   Control
                                                   Output and Error Message
                                                   Control
 -gnatwc (gcc)                                     Output and Error Message
                                                   Control
                                                   Output and Error Message
                                                   Control
 -gnatwe (gcc)                                     Output and Error Message
                                                   Control
 -gnatwl (gcc)                                     Output and Error Message
                                                   Control
                                                   Output and Error Message
                                                   Control
 -gnatws (gcc)                                     Output and Error Message
                                                   Control
 -gnatwu (gcc)                                     Output and Error Message
                                                   Control
                                                   Output and Error Message
                                                   Control
 -gnatx (gcc)                                      Output and Error Message
                                                   Control
 -h (gnatbind)                                     Elaboration Control
                                                   Output Control
 -h (gnatls)                                       Switches for gnatls
 -I (gcc)                                          Switches for gcc
 -I (gnathtml)                                     Converting Ada files to html
                                                   using gnathtml
 -i (gnatmake)                                     Switches for gnatmake
                                                   Switches for gnatmake
 -i (gnatmem)                                      Switches for gnatmem
 -I- (gcc)                                         Switches for gcc
 -I- (gnatmake)                                    Switches for gnatmake
 -j (gnatmake)                                     Switches for gnatmake
 -k (gnatchop)                                     Switches for gnatchop
 -k (gnatmake)                                     Switches for gnatmake
 -l (gnatbind)                                     Output Control
 -l (gnathtml)                                     Converting Ada files to html
                                                   using gnathtml
 -L (gnatmake)                                     Switches for gnatmake
 -largs (gnatmake)                                 Mode switches for gnatmake
 -m (gnatbind)                                     Binder Error Message Control
                                                   Binder Error Message Control
 -m (gnatmake)                                     Switches for gnatmake
                                                   Switches for gnatmake
 -n (gnatbind)                                     Binding with Non-Ada Main
                                                   Programs
 -n (gnatlink)                                     Switches for gnatlink
 -n (gnatmake)                                     Switches for gnatmake
 -nostdinc (gnatmake)                              Switches for gnatmake
 -nostdlib (gnatmake)                              Switches for gnatmake
 -o (gcc)                                          Switches for gcc
                                                   Switches for gcc
                                                   Optimization Levels
 -O (gnatbind)                                     Output Control
                                                   Output Control
 -o (gnathtml)                                     Converting Ada files to html
                                                   using gnathtml
 -o (gnatlink)                                     Switches for gnatlink
 -o (gnatls)                                       Switches for gnatls
 -o (gnatmake)                                     Switches for gnatmake
 -o (gnatmem)                                      Switches for gnatmem
 -p (gnathtml)                                     Converting Ada files to html
                                                   using gnathtml
 -q (gnatchop)                                     Switches for gnatchop
 -q (gnatmake)                                     Switches for gnatmake
 -q (gnatmem)                                      Switches for gnatmem
 -r (gnatchop)                                     Switches for gnatchop
 -S (gcc)                                          Switches for gcc
 -s (gnatbind)                                     Consistency-Checking Modes
 -s (gnatls)                                       Switches for gnatls
                                                   Switches for gnatls
 -s (gnatmake)                                     Switches for gnatmake
 -sc (gnathtml)                                    Converting Ada files to html
                                                   using gnathtml
 -t (gnatbind)                                     Binder Error Message Control
 -t (gnathtml)                                     Converting Ada files to html
                                                   using gnathtml
 -u (gnatls)                                       Switches for gnatls
 -v (gcc)                                          Switches for gcc
                                                   Switches for gcc
 -v (gnatbind)                                     Binder Error Message Control
 -v (gnatchop)                                     Switches for gnatchop
 -v (gnatlink)                                     Switches for gnatlink
 -v (gnatmake)                                     Switches for gnatmake
 -v -v (gnatlink)                                  Switches for gnatlink
 -w (gnatchop)                                     Switches for gnatchop
 -we (gnatbind)                                    Binder Error Message Control
 -ws (gnatbind)                                    Binder Error Message Control
 -x (gnatbind)                                     Consistency-Checking Modes
 -z (gnatbind)                                     Binding Programs with no
                                                   Main Subprogram
 -z (gnatmake)                                     Switches for gnatmake
 Access before elaboration                         Run-time Checks
 Access-to-subprogram                              Elaboration for
                                                   Access-to-Subprogram Values
 ACVC, Ada 83 tests                                Compiling Ada 83 Programs
 Ada 83 compatibility                              Compiling Ada 83 Programs
 Ada 95 Language Reference Manual                  What You Should Know Before
                                                   Reading This Guide
 Ada expressions                                   Using Ada Expressions
 Annex A                                           Naming Conventions for GNAT
                                                   Source Files
 Annex B                                           Naming Conventions for GNAT
                                                   Source Files
 Assertions                                        Debugging and Assertion
                                                   Control
 Binder consistency checks                         Binder Error Message Control
 Binder output file                                Interfacing to C
 Binder, multiple input files                      Binding with Non-Ada Main
                                                   Programs
 Breakpoints and tasks                             Ada Tasks
 Calling Conventions                               Calling Conventions
 Check, elaboration                                Run-time Checks
 Check, overflow                                   Run-time Checks
 Checks, access before elaboration                 Run-time Checks
 Checks, division by zero                          Run-time Checks
 Checks, elaboration                               Checking the Elaboration
                                                   Order in Ada 95
 Checks, overflow                                  Controlling Run-time Checks
 Checks, suppressing                               Run-time Checks
 code page 437                                     Other 8-Bit Codes
 code page 850                                     Other 8-Bit Codes
 Combining GNAT switches                           Switches for gcc
 Compilation model                                 The GNAT Compilation Model
 Configuration pragmas                             Configuration Pragmas
 Consistency checks, in binder                     Binder Error 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 Fortran                                Calling Conventions
 Convention Stdcall                                Calling Conventions
 Convention Stubbed                                Calling Conventions
 Conventions                                       Conventions
 Debugger                                          Running and Debugging Ada
                                                   Programs
 Debugging                                         Running and Debugging Ada
                                                   Programs
 Debugging Generic Units                           Debugging Generic Units
 Debugging information, including                  Switches for gnatlink
 Debugging options                                 Debugging Control
 Dependencies, producing list                      Switches for gnatmake
 Dependency rules                                  The GNAT Make Program
                                                   gnatmake
 Division by zero                                  Run-time Checks
 Elaboration checks                                Run-time Checks
                                                   Checking the Elaboration
                                                   Order in Ada 95
 Elaboration control                               Elaboration Order Handling
                                                   in GNAT
                                                   Summary of Procedures for
                                                   Elaboration Control
 Elaboration order control                         Comparison between GNAT and
                                                   C/C++ Compilation Models
 End of source file                                Source Representation
 Error messages, suppressing                       Output and Error Message
                                                   Control
 EUC Coding                                        Wide Character Encodings
 Exceptions                                        Breaking on Ada Exceptions
 File names                                        Using Other File Names
 Foreign Languages                                 Calling Conventions
 Generic formal parameters                         Compiling Ada 83 Programs
 Generics                                          Generating Object Files
                                                   Debugging Generic Units
 GNAT Abnormal Termination                         GNAT Abnormal Termination
 GNAT compilation model                            The GNAT Compilation Model
 GNAT library                                      Comparison between GNAT and
                                                   Conventional Ada Library
                                                   Models
 GNAT_STACK_LIMIT                                  Stack Overflow Checking
 GNU make                                          Using gnatmake in a Makefile
 Inlining                                          Comparison between GNAT and
                                                   Conventional Ada Library
                                                   Models
 Interfacing to Ada                                Calling Conventions
 Interfacing to Assembler                          Calling Conventions
 Interfacing to C                                  Calling Conventions
 Interfacing to C++                                Calling Conventions
 Interfacing to COBOL                              Calling Conventions
 Interfacing to Fortran                            Calling Conventions
 Internal trees, writing to file                   Auxiliary Output Control
 Latin-1                                           Source Representation
                                                   Latin-1
 Latin-2                                           Other 8-Bit Codes
 Latin-3                                           Other 8-Bit Codes
 Latin-4                                           Other 8-Bit Codes
 Library browser                                   The GNAT library browser
                                                   gnatls
 Library, building, installing                     GNAT and libraries
 Linker libraries                                  Switches for gnatmake
 Mixed Language Programming                        Mixed Language Programming
 Multiple units, syntax checking                   Using gcc for Syntax
                                                   Checking
 n (gnatmem)                                       Switches for gnatmem
 No code generated                                 Compiling Programs
 Order of elaboration                              Elaboration Order Handling
                                                   in GNAT
 Other Ada compilers                               Calling Conventions
 Overflow checks                                   Run-time Checks
                                                   Controlling Run-time Checks
 Parallel make                                     Switches for gnatmake
 Performance                                       Performance Considerations
 pragma Elaborate                                  The Ada Library Information
                                                   Files
                                                   Controlling the Elaboration
                                                   Order in Ada 95
 pragma Elaborate_All                              The Ada Library Information
                                                   Files
                                                   Controlling the Elaboration
                                                   Order in Ada 95
 pragma Elaborate_Body                             The Ada Library Information
                                                   Files
                                                   Controlling the Elaboration
                                                   Order in Ada 95
 pragma Inline                                     Inlining of Subprograms
 pragma Preelaborate                               The Ada Library Information
                                                   Files
                                                   Controlling the Elaboration
                                                   Order in Ada 95
 pragma Pure                                       The Ada Library Information
                                                   Files
                                                   Controlling the Elaboration
                                                   Order in Ada 95
 pragma Remote_Call_Interface                      The Ada Library Information
                                                   Files
 pragma Remote_Types                               The Ada Library Information
                                                   Files
 pragma Shared_Passive                             The Ada Library Information
                                                   Files
 pragma Suppress                                   Controlling Run-time Checks
 pragma Unsuppress                                 Controlling Run-time Checks
 Pragmas, configuration                            Configuration Pragmas
 Recompilation, by gnatmake                        Notes on the Command Line
 RTL                                               Switches for gcc
                                                   Switches for gcc
 Search paths, for gnatmake                        Switches for gnatmake
 Shift JIS Coding                                  Wide Character Encodings
 Source file, end                                  Source Representation
 Source files, suppressing search                  Switches for gnatmake
 Source files, use by binder                       Running gnatbind
 Source_File_Name pragma                           Using Other File Names
 Stack Overflow Checking                           Stack Overflow Checking
 storage, pool, memory corruption                  Finding memory problems with
                                                   GNAT Debug Pool
 Subunits                                          Generating Object Files
 Suppressing checks                                Run-time Checks
 Task switching                                    Ada Tasks
 Tasks                                             Ada Tasks
 Time Slicing                                      Run-time Control
 Time stamp checks, in binder                      Binder Error Message Control
 Tree file                                         Tree Files
 Typographical conventions                         Conventions
 Upper-Half Coding                                 Wide Character Encodings
 Warning messages                                  Output and Error Message
                                                   Control
 Warnings                                          Binder Error Message Control
 Writing internal trees                            Auxiliary Output Control