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GNAT User's Guide for Unix Platforms
GNAT, The GNU Ada 95 Compiler
GNAT Version 3.15p
Date: 2002/05/22 04:20:30
Ada Core Technologies, Inc.
Copyright (C) 1995-2001, Free Software Foundation
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being GNU Free Documentation License", with the Front-Cover Texts being GNAT User's Guide for Unix Platforms", and with no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License".
-- The Detailed Node Listing ---
About This Guide
What This Guide Contains What You Should Know before Reading This Guide Related Information Conventions
Getting Started with GNAT
1.1 Running GNAT 1.2 Running a Simple Ada Program 1.3 Running a Program with Multiple Units 1.4 Using the gnatmakeUtility
The GNAT Compilation Model
Foreign Language Representation
2.2.1 Latin-1 2.2.2 Other 8-Bit Codes 2.2.3 Wide Character Encodings
Compiling Ada Programs With gcc
3.1 Compiling Programs 3.2 Switches for gcc3.3 Search Paths and the Run-Time Library (RTL) 3.4 Order of Compilation Issues 3.5 Examples
Switches for gcc
Binding Ada Programs With gnatbind
Linking Using gnatlink
5.1 Running gnatlink5.2 Switches for gnatlink5.3 Setting Stack Size from gnatlink5.4 Setting Heap Size from gnatlink
The GNAT Make Program gnatmake
6.1 Running gnatmake6.2 Switches for gnatmake6.3 Mode Switches for gnatmake6.4 Notes on the Command Line 6.5 How gnatmakeWorks6.6 Examples of gnatmakeUsage
Renaming Files Using gnatchop
7.1 Handling Files with Multiple Units 7.2 Operating gnatchop in Compilation Mode 7.3 Command Line for gnatchop7.4 Switches for gnatchop7.5 Examples of gnatchopUsage
Configuration Pragmas
8.1 Handling of Configuration Pragmas 8.2 The Configuration Pragmas Files
Handling Arbitrary File Naming Conventions Using gnatname
9.1 Arbitrary File Naming Conventions 9.2 Running gnatname9.3 Switches for gnatname9.4 Examples of gnatnameUsage
GNAT Project Manager
Elaboration Order Handling in GNAT
The Cross-Referencing Tools gnatxref and gnatfind
File Name Krunching Using gnatkr
13.1 About gnatkr13.2 Using gnatkr13.3 Krunching Method 13.4 Examples of gnatkrUsage
Preprocessing Using gnatprep
14.1 Using gnatprep14.2 Switches for gnatprep14.3 Form of Definitions File 14.4 Form of Input Text for gnatprep
The GNAT Library Browser gnatls
15.1 Running gnatls15.2 Switches for gnatls15.3 Example of gnatlsUsage
GNAT and Libraries
16.1 Creating an Ada Library 16.2 Installing an Ada Library 16.3 Using an Ada Library 16.4 Creating an Ada Library to be Used in a Non-Ada Context 16.5 Rebuilding the GNAT Run-Time Library
Using the GNU make Utility
17.1 Using gnatmake in a Makefile 17.2 Automatically Creating a List of Directories 17.3 Generating the Command Line Switches 17.4 Overcoming Command Line Length Limits
Finding Memory Problems with gnatmem
18.1 Running gnatmem(GDB Mode)18.2 Running gnatmem(GMEM Mode)18.3 Switches for gnatmem18.4 Example of gnatmemUsage18.5 GDB and GMEM Modes 18.6 Implementation Note
Finding Memory Problems with GNAT Debug Pool
Creating Sample Bodies Using gnatstub
20.1 Running gnatstub20.2 Switches for gnatstub
Reducing the Size of Ada Executables with gnatelim
Other Utility Programs
22.1 Using Other Utility Programs with GNAT 22.2 The gnatpstaUtility Program22.3 The External Symbol Naming Scheme of GNAT 22.4 Ada Mode for Glide22.5 Converting Ada Files to html with gnathtml
Running and Debugging Ada Programs
Inline Assembler
Performance Considerations
25.1 Controlling Run-Time Checks 25.2 Optimization Levels 25.3 Debugging Optimized Code 25.4 Inlining of Subprograms
Index
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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 You Should Know before Reading This Guide Related Information Conventions
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This guide contains the following chapters:
gcc, describes how to compile
Ada programs with gcc, the Ada compiler.
gnatbind, describes how to
perform binding of Ada programs with gnatbind, the GNAT binding
utility.
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.
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.
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.
gnatname, shows how to override
the default GNAT file naming conventions, either for an individual unit or globally.
gnatxref and gnatfind, discusses
gnatxref and gnatfind, two tools that provide an easy
way to navigate through sources.
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.
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.
gnatls, describes gnatls, a
utility that displays information about compiled units, including dependences
on the corresponding sources files, and consistency of compilations.
make Utility, describes some techniques for using
the GNAT toolset in Makefiles.
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.
gnatstub, discusses gnatstub,
a utility that generates empty but compilable bodies for library units.
gnatelim, describes
gnatelim, a tool which detects unused subprograms and helps
the compiler to create a smaller executable for the program.
gnatpsta.
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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.
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For further information about related tools, refer to the following documents:
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Following are examples of the typographical and graphic conventions used in this guide:
Functions, utility program names, standard names,
and classes.
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.
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This chapter describes some simple ways of using GNAT to build executable Ada programs.
1.1 Running GNAT 1.2 Running a Simple Ada Program
1.3 Running a Program with Multiple Units
1.4 Using the gnatmakeUtility1.5 Introduction to Glide and GVD
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Three steps are needed to create an executable file from an Ada source file:
All three steps are most commonly handled by using the gnatmake
utility program that, given the name of the main program, automatically
performs the necessary compilation, binding and linking steps.
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Any text editor may be used to prepare an Ada program. If Glide 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 Ada.Text_IO; use Ada.Text_IO;
procedure Hello is
begin
Put_Line ("Hello WORLD!");
end Hello;
|
This file should be named `hello.adb'.
With the normal default file naming conventions, GNAT requires
that each file
contain a single compilation unit whose file name is the
unit name,
with periods replaced by hyphens; the
extension is `ads' for a
spec and `adb' for a body.
You can override this default file naming convention by use of the
special pragma Source_File_Name (see section 2.4 Using Other File Names).
Alternatively, if you want to rename your files according to this default
convention, which is probably more convenient if you will be using GNAT
for all your compilations, then the gnatchop utility
can be used to generate correctly-named source files
(see section 7. Renaming Files Using gnatchop).
You can compile the program using the following command ($ is used
as the command prompt in the examples in this document):
$ gcc -c hello.adb |
gcc is the command used to run the compiler. This compiler is
capable of compiling programs in several languages, including Ada 95 and
C. It assumes that you have given it an Ada program if the file extension is
either `.ads' or `.adb', and it will then call the GNAT compiler to compile
the specified file.
The `-c' switch is required. It tells gcc to only do a
compilation. (For C programs, gcc can also do linking, but this
capability is not used directly for Ada programs, so the `-c'
switch must always be present.)
This compile command generates a file
`hello.o', which is the object
file corresponding to your Ada program. It also generates an "Ada Library Information" file
`hello.ali',
which contains additional information used to check
that an Ada program is consistent.
To build an executable file,
use gnatbind to bind the program
and gnatlink to link it. The
argument to both gnatbind and gnatlink is the name of the
`ali' file, but the default extension of `.ali' can
be omitted. This means that in the most common case, the argument
is simply the name of the main program:
$ gnatbind hello $ gnatlink hello |
A simpler method of carrying out these steps is to use
gnatmake,
a master program that invokes all the required
compilation, binding and linking tools in the correct order. In particular,
gnatmake automatically recompiles any sources that have been modified
since they were last compiled, or sources that depend
on such modified sources, so that "version skew" is avoided.
$ gnatmake hello.adb |
The result is an executable program called `hello', which can be run by entering:
$ hello |
assuming that the current directory is on the search path for executable programs.
and, if all has gone well, you will see
Hello WORLD! |
appear in response to this command.
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Consider a slightly more complicated example that has three files: a main program, and the spec and body of a package:
package Greetings is
procedure Hello;
procedure Goodbye;
end Greetings;
with Ada.Text_IO; use Ada.Text_IO;
package body Greetings is
procedure Hello is
begin
Put_Line ("Hello WORLD!");
end Hello;
procedure Goodbye is
begin
Put_Line ("Goodbye WORLD!");
end Goodbye;
end Greetings;
with Greetings;
procedure Gmain is
begin
Greetings.Hello;
Greetings.Goodbye;
end Gmain;
|
Following the one-unit-per-file rule, place this program in the following three separate files:
Greetings
Greetings
To build an executable version of this program, we could use four separate steps to compile, bind, and link the program, as follows:
$ gcc -c gmain.adb $ gcc -c greetings.adb $ gnatbind gmain $ gnatlink gmain |
Note that there is no required order of compilation when using GNAT.
In particular it is perfectly fine to compile the main program first.
Also, it is not necessary to compile package specs in the case where
there is an accompanying body; you only need to compile the body. If you want
to submit these files to the compiler for semantic checking and not code generation,
then use the
-gnatc switch:
$ gcc -c greetings.ads -gnatc |
Although the compilation can be done in separate steps as in the
above example, in practice it is almost always more convenient
to use the gnatmake tool. All you need to know in this case
is the name of the main program's source file. The effect of the above four
commands can be achieved with a single one:
$ gnatmake gmain.adb |
In the next section we discuss the advantages of using gnatmake in
more detail.
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gnatmake Utility
If you work on a program by compiling single components at a time using
gcc, you typically keep track of the units you modify. In order to
build a consistent system, you compile not only these units, but also any
units that depend on the units you have modified.
For example, in the preceding case,
if you edit `gmain.adb', you only need to recompile that file. But if
you edit `greetings.ads', you must recompile both
`greetings.adb' and `gmain.adb', because both files contain
units that depend on `greetings.ads'.
gnatbind will warn you if you forget one of these compilation
steps, so that it is impossible to generate an inconsistent program as a
result of forgetting to do a compilation. Nevertheless it is tedious and
error-prone to keep track of dependencies among units.
One approach to handle the dependency-bookkeeping is to use a
makefile. However, makefiles present maintenance problems of their own:
if the dependencies change as you change the program, you must make
sure that the makefile is kept up-to-date manually, which is also an
error-prone process.
The gnatmake utility takes care of these details automatically.
Invoke it using either one of the following forms:
$ gnatmake gmain.adb $ gnatmake gmain |
The argument is the name of the file containing the main program;
you may omit the extension. gnatmake
examines the environment, automatically recompiles any files that need
recompiling, and binds and links the resulting set of object files,
generating the executable file, `gmain'.
In a large program, it
can be extremely helpful to use gnatmake, because working out by hand
what needs to be recompiled can be difficult.
Note that gnatmake
takes into account all the Ada 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.
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gnatmake, etc.) a graphical Interactive Development Environment can make it easier for you to compose, navigate, and debug programs. This section describes the main features of Glide, the GNAT graphical IDE, and also shows how to use the basic commands in GVD, the GNU Visual Debugger. Additional information may be found in the on-line help for these tools.
1.5.1 Building a New Program with Glide 1.5.2 Simple Debugging with GVD 1.5.3 Other Glide Features
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glide at the command prompt. It will generally be useful to issue this as a background command, thus allowing you to continue using your command window for other purposes while Glide is running:
$ glide& |
Glide will start up with an initial screen displaying the top-level menu items as well as some other information. The menu selections are as follows
Buffers
Files
Tools
Edit
Search
Mule
Glide
Help
For this introductory example, you will need to create a new Ada source file. First, select the Files menu. This will pop open a menu with around a dozen or so items. To create a file, select the Open file... choice. Depending on the platform, you may see a pop-up window where you can browse to an appropriate directory and then enter the file name, or else simply see a line at the bottom of the Glide window where you can likewise enter the file name. Note that in Glide, when you attempt to open a non-existent file, the effect is to create a file with that name. For this example enter `hello.adb' as the name of the file.
A new buffer will now appear, occupying the entire Glide window, with the file name at the top. The menu selections are slightly different from the ones you saw on the opening screen; there is an Entities item, and in place of Glide there is now an Ada item. Glide uses the file extension to identify the source language, so `adb' indicates an Ada source file.
You will enter some of the source program lines explicitly, and use the syntax-oriented template mechanism to enter other lines. First, type the following text:
with Ada.Text_IO; use Ada.Text_IO; procedure Hello is begin |
Observe that Glide uses different colors to distinguish reserved words from identifiers. Also, after the procedure Hello is line, the cursor is automatically indented in anticipation of declarations. When you enter begin, Glide recognizes that there are no declarations and thus places begin flush left. But after the begin line the cursor is again indented, where the statement(s) will be placed.
The main part of the program will be a for loop. Instead of entering the text explicitly, however, use a statement template. Select the Ada item on the top menu bar, move the mouse to the Statements item, and you will see a large selection of alternatives. Choose for loop. You will be prompted (at the bottom of the buffer) for a loop name; simply press the Enter key since a loop name is not needed. You should see the beginning of a for loop appear in the source program window. You will now be prompted for the name of the loop variable; enter a line with the identifier ind (lower case). Note that, by default, Glide capitalizes the name (you can override such behavior if you wish, although this is outside the scope of this introduction). Next, Glide prompts you for the loop range; enter a line containing 1..5 and you will see this also appear in the source program, together with the remaining elements of the for loop syntax.
Next enter the statement (with an intentional error, a missing semicolon) that will form the body of the loop:
Put_Line("Hello, World" & Integer'Image(I))
|
Finally, type end Hello; as the last line in the program. Now save the file: choose the File menu item, and then the Save buffer selection. You will see a message at the bottom of the buffer confirming that the file has been saved.
You are now ready to attempt to build the program. Select the Ada item from the top menu bar. Although we could choose simply to compile the file, we will instead attempt to do a build (which invokes gnatmake) since, if the compile is successful, we want to build an executable. Thus select Ada build. This will fail because of the compilation error, and you will notice that the Glide window has been split: the top window contains the source file, and the bottom window contains the output from the GNAT tools. Glide allows you to navigate from a compilation error to the source file position corresponding to the error: click the middle mouse button (or simultaneously press the left and right buttons, on a two-button mouse) on the diagnostic line in the tool window. The focus will shift to the source window, and the cursor will be positioned on the character at which the error was detected.
Correct the error: type in a semicolon to terminate the statement. Although you can again save the file explicitly, you can also simply invoke Ada => Build and you will be prompted to save the file. This time the build will succeed; the tool output window shows you the options that are supplied by default. The GNAT tools' output (e.g., object and ALI files, executable) will go in the directory from which Glide was launched.
To execute the program, choose Ada and then Run. You should see the program's output displayed in the bottom window:
Hello, world 1 Hello, world 2 Hello, world 3 Hello, world 4 Hello, world 5 |
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This section describes how to set breakpoints, examine/modify variables, and step through execution.
In order to enable debugging, you need to pass the `-g' switch to both the compiler and to gnatlink. If you are using the command line, passing `-g' to gnatmake will have this effect. You can then launch GVD, e.g. on the hello program, by issuing the command:
$ gvd hello |
If you are using Glide, then `-g' is passed to the relevant tools by default when you do a build. Start the debugger by selecting the Ada menu item, and then Debug.
GVD comes up in a multi-part window. One pane shows the names of files comprising your executable; another pane shows the source code of the current unit (initially your main subprogram), another pane shows the debugger output and user interactions, and the fourth pane (the data canvas at the top of the window) displays data objects that you have selected.
To the left of the source file pane, you will notice green dots adjacent to some lines. These are lines for which object code exists and where breakpoints can thus be set. You set/reset a breakpoint by clicking the green dot. When a breakpoint is set, the dot is replaced by an X in a red circle. Clicking the circle toggles the breakpoint off, and the red circle is replaced by the green dot.
For this example, set a breakpoint at the statement where Put_Line is invoked.
Start program execution by selecting the Run button on the top menu bar. (The Start button will also start your program, but it will cause program execution to break at the entry to your main subprogram.) Evidence of reaching the breakpoint will appear: the source file line will be highlighted, and the debugger interactions pane will display a relevant message.
You can examine the values of variables in several ways. Move the mouse over an occurrence of Ind in the for loop, and you will see the value (now 1) displayed. Alternatively, right-click on Ind and select Display Ind; a box showing the variable's name and value will appear in the data canvas.
Although a loop index is a constant with respect to Ada semantics, you can change its value in the debugger. Right-click in the box for Ind, and select the Set Value of Ind item. Enter 2 as the new value, and press OK. The box for Ind shows the update.
Press the Step button on the top menu bar; this will step through one line of program text (the invocation of Put_Line), and you can observe the effect of having modified Ind since the value displayed is 2.
Remove the breakpoint, and resume execution by selecting the Cont button. You will see the remaining output lines displayed in the debugger interaction window, along with a message confirming normal program termination.
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You may have observed that some of the menu selections contain abbreviations; e.g., (C-x C-f) for Open file... in the Files menu. These are shortcut keys that you can use instead of selecting menu items. The C stands for Ctrl; thus (C-x C-f) means Ctrl-x followed by Ctrl-f, and this sequence can be used instead of selecting Files and then Open file....
To abort a Glide command, type Ctrl-g.
If you want Glide to start with an existing source file, you can either launch Glide as above and then open the file via Files => Open file..., or else simply pass the name of the source file on the command line:
$ glide hello.adb& |
While you are using Glide, a number of buffers exist. You create some explicitly; e.g., when you open/create a file. Others arise as an effect of the commands that you issue; e.g., the buffer containing the output of the tools invoked during a build. If a buffer is hidden, you can bring it into a visible window by first opening the Buffers menu and then selecting the desired entry.
If a buffer occupies only part of the Glide screen and you want to expand it to fill the entire screen, then click in the buffer and then select Files => One Window.
If a window is occupied by one buffer and you want to split the window to bring up a second buffer, perform the following steps:
Files => Split Window; this will produce two windows each of which holds the original buffer (these are not copies, but rather different views of the same buffer contents)
Buffers menu
To exit from Glide, choose Files => Exit.
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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.
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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 section 2.2 Foreign Language Representation for support of non-USA character sets). The format effector characters are represented using their standard ASCII encodings, as follows:
VT
16#0B#
HT
16#09#
CR
16#0D#
LF
16#0A#
FF
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.
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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 section 3.2.11 Character Set Control).
2.2.1 Latin-1 2.2.2 Other 8-Bit Codes 2.2.3 Wide Character Encodings
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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.
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GNAT also supports several other 8-bit coding schemes:
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.
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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:
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.
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.
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.
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.
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).
[ " 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.
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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.
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 section 13.2 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 section 7. Renaming Files Using gnatchop.)
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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 section 8.1 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.
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In the previous section, we described the use of the Source_File_Name
pragma to allow arbitrary names to be assigned to individual source files.
However, this approach requires one pragma for each file, and especially in
large systems can result in very long `gnat.adc' files, and also create
a maintenance problem.
GNAT also provides a facility for specifying systematic file naming schemes
other than the standard default naming scheme previously described. An
alternative scheme for naming is specified by the use of
Source_File_Name pragmas having the following format:
pragma Source_File_Name ( Spec_File_Name => FILE_NAME_PATTERN [,Casing => CASING_SPEC] [,Dot_Replacement => STRING_LITERAL]); pragma Source_File_Name ( Body_File_Name => FILE_NAME_PATTERN [,Casing => CASING_SPEC] [,Dot_Replacement => STRING_LITERAL]); pragma Source_File_Name ( Subunit_File_Name => FILE_NAME_PATTERN [,Casing => CASING_SPEC] [,Dot_Replacement => STRING_LITERAL]); FILE_NAME_PATTERN ::= STRING_LITERAL CASING_SPEC ::= Lowercase | Uppercase | Mixedcase |
The FILE_NAME_PATTERN string shows how the file name is constructed.
It contains a single asterisk character, and the unit name is substituted
systematically for this asterisk. The optional parameter
Casing indicates
whether the unit name is to be all upper-case letters, all lower-case letters,
or mixed-case. If no
Casing parameter is used, then the default is all
lower-case.
The optional Dot_Replacement string is used to replace any periods
that occur in subunit or child unit names. If no Dot_Replacement
argument is used then separating dots appear unchanged in the resulting
file name.
Although the above syntax indicates that the
Casing argument must appear
before the Dot_Replacement argument, but it
is also permissible to write these arguments in the opposite order.
As indicated, it is possible to specify different naming schemes for
bodies, specs, and subunits. Quite often the rule for subunits is the
same as the rule for bodies, in which case, there is no need to give
a separate Subunit_File_Name rule, and in this case the
Body_File_name rule is used for subunits as well.
The separate rule for subunits can also be used to implement the rather unusual case of a compilation environment (e.g. a single directory) which contains a subunit and a child unit with the same unit name. Although both units cannot appear in the same partition, the Ada Reference Manual allows (but does not require) the possibility of the two units coexisting in the same environment.
The file name translation works in the following steps:
Source_File_Name pragma for the given unit,
then this is always used, and any general pattern rules are ignored.
Source_File_Name pragma that applies to
the unit, then the resulting file name will be used if the file exists. If
more than one pattern matches, the latest one will be tried first, and the
first attempt resulting in a reference to a file that exists will be used.
Source_File_Name pragma that applies to the unit
for which the corresponding file exists, then the standard GNAT default
naming rules are used.
As an example of the use of this mechanism, consider a commonly used scheme in which file names are all lower case, with separating periods copied unchanged to the resulting file name, and specs end with ".1.ada", and bodies end with ".2.ada". GNAT will follow this scheme if the following two pragmas appear:
pragma Source_File_Name (Spec_File_Name => "*.1.ada"); pragma Source_File_Name (Body_File_Name => "*.2.ada"); |
The default GNAT scheme is actually implemented by providing the following default pragmas internally:
pragma Source_File_Name (Spec_File_Name => "*.ads", Dot_Replacement => "-"); pragma Source_File_Name (Body_File_Name => "*.adb", Dot_Replacement => "-"); |
Our final example implements a scheme typically used with one of the Ada 83 compilers, where the separator character for subunits was "__" (two underscores), specs were identified by adding `_.ADA', bodies by adding `.ADA', and subunits by adding `.SEP'. All file names were upper case. Child units were not present of course since this was an Ada 83 compiler, but it seems reasonable to extend this scheme to use the same double underscore separator for child units.
pragma Source_File_Name (Spec_File_Name => "*_.ADA", Dot_Replacement => "__", Casing = Uppercase); pragma Source_File_Name (Body_File_Name => "*.ADA", Dot_Replacement => "__", Casing = Uppercase); pragma Source_File_Name (Subunit_File_Name => "*.SEP", Dot_Replacement => "__", Casing = Uppercase); |
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An Ada program consists of a set of source files, and the first step in compiling the program is to generate the corresponding object files. These are generated by compiling a subset of these source files. The files you need to compile are the following:
The preceding rules describe the set of files that must be compiled to generate the object files for a program. Each object file has the same name as the corresponding source file, except that the extension is `.o' as usual.
You may wish to compile other files for the purpose of checking their syntactic and semantic correctness. For example, in the case where a package has a separate spec and body, you would not normally compile the spec. However, it is convenient in practice to compile the spec to make sure it is error-free before compiling clients of this spec, because such compilations will fail if there is an error in the spec.
GNAT provides an option for compiling such files purely for the
purposes of checking correctness; such compilations are not required as
part of the process of building a program. To compile a file in this
checking mode, use the -gnatc switch.
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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:
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.
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. Note
that for inlining to actually occur as a result of the use of this switch,
it is necessary to compile in optimizing mode.
The use of -gnatN activates a more extensive inlining optimization
that is performed by the front end of the compiler. This inlining does
not require that the code generation be optimized. Like -gnatn,
the use of this switch generates additional dependencies.
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.
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Each compilation actually generates two output files. The first of these is the normal object file that has a `.o' extension. The second is a text file containing full dependency information. It has the same name as the source file, but an `.ali' extension. This file is known as the Ada Library Information (`ali') file. The following information is contained in the `ali' file.
gcc command for the compilation
Pure).
with'ed units, including presence of
Elaborate or Elaborate_All pragmas.
Linker_Options pragmas used in the unit
Body_Version or Version
attributes in the unit.
gnatxref and gnatfind to
provide cross-reference information.
For a full detailed description of the format of the `ali' file,
see the source of the body of unit Lib.Writ, contained in file
`lib-writ.adb' in the GNAT compiler sources.
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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.
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2.10.1 Interfacing to C 2.10.2 Calling Conventions
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gcc -c file1.c gcc -c file2.c |
gnatmake -c my_main.adb |
gnatbind my_main.ali |
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 section 4.7 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:
gcc -c file1.c gcc -c file2.c |
gnatmake -c entry_point1.adb gnatmake -c entry_point2.adb |
gnatbind -n entry_point1.ali entry_point2.ali |
gnatlink entry_point2.ali file1.o file2.o |
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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 run time 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.
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, "/"); |
Program_Error.
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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 run time can be adapted in order to allow inter-language dispatching with a new C++ compiler.
2.11.1 Interfacing to C++ 2.11.2 Linking a Mixed C++ & Ada Program 2.11.3 A Simple Example 2.11.4 Adapting the Run Time to a New C++ Compiler
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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:
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.
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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:
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++ |
$ gnatbind ada_unit $ gnatlink -v -v ada_unit file1.o file2.o --LINK=c++ |
$ gnatlink -v -v ada_unit file1.o file2.o --LINK=./my_script $ cat ./my_script #!/bin/sh unset BINUTILS_ROOT unset GCC_ROOT c++ $* |
$ gnatlink ada_unit file1.o file2.o --LINK=./my_script $ cat ./my_script #!/bin/sh CC $* gcc -print-libgcc-file-name |
Where CC is the name of the non GNU C++ compiler.
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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
|
//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;
|
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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.
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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.
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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:
with'ed, the unit seen by the compiler corresponds
to the version of the unit most recently compiled into 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:
with'ed, the unit seen by the compiler corresponds
to the source version of the unit that is currently accessible to the
compiler.
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.
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gcc
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.
3.1 Compiling Programs 3.2 Switches for gcc3.3 Search Paths and the Run-Time Library (RTL) 3.4 Order of Compilation Issues 3.5 Examples
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The first step in creating an executable program is to compile the units
of the program using the gcc command. You must compile the
following files:
You need not compile the following files
because they are compiled as part of compiling related units. GNAT package specs when the corresponding body is compiled, and subunits when the parent is compiled. If you attempt to compile any of these files, you will get one of the following error messages (where fff is the name of the file you compiled):
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.
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gcc
The gcc command accepts switches that control the
compilation process. These switches are fully described in this section.
First we briefly list all the switches, in alphabetical order, then we
describe the switches in more detail in functionally grouped sections.
-b target
-Bdir
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
Note: for some other languages when using gcc, notably in
the case of C and C++, it is possible to use
use gcc without a -c switch to
compile and link in one step. In the case of GNAT, you
cannot use this approach, because the binder must be run
and gcc cannot be used to run the GNAT binder.
-g
-g switch if you plan on using the debugger.
-Idir
-I-
-o file
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]
-O appears
-O without
an operand.
--RTS=rts-path
gnatmake flag (see 6.2 Switches for gnatmake).
-S
-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
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
gcc
version, not the GNAT version.
-gnata
Pragma Assert and pragma Debug to be
activated.
-gnatA
-gnatb
-gnatc
-gnatC
-gnatD
-gnatecpath
-gnatempath
-gnatE
-gnatf
-gnatF
-gnatg
-gnatG
-gnatic
-gnath
-gnatkn
k = krunch).
-gnatl
-gnatmn
-gnatn
inline is specified.
-gnatN
-fno-inline
-fstack-check
-gnato
-gnatp
-gnatq
-gnatQ
-gnatP
-gnatR[0/1/2/3][s]
-gnats
-gnatt
-gnatT nnn
-gnatu
-gnatU
-gnatv
-gnatV
-gnatwxxxxxx
-gnatWe
-gnatx
-gnaty
-gnatzm
-gnat83
-pass-exit-codes
You may combine a sequence of GNAT switches into a single switch. For example, the combined switch
-gnatofi3 |
is equivalent to specifying the following sequence of switches:
-gnato -gnatf -gnati3 |
The following restrictions apply to the combination of switches in this manner:
-gnatc if combined with other switches must come
first in the string.
-gnats if combined with other switches must come
first in the string.
-gnaty
switch), then all further characters in the switch are interpreted
as style modifiers (see description of -gnaty).
-gnatd
switch), then all further characters in the switch are interpreted
as debug flags (see description of -gnatd).
-gnatw
switch), then all further characters in the switch are interpreted
as warning mode modifiers (see description of -gnatw).
-gnatV
switch), then all further characters in the switch are interpreted
as validity checking options (see description of -gnatV).
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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.
glide can parse the error messages
and point to the referenced character.
The following switches provide control over the error message
format:
-gnatv
-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
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
-gnatb
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
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
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
q stands for quit (really "don't quit").
In normal operation mode, the compiler first parses the program and
determines if there are any syntax errors. If there are, appropriate
error messages are generated and compilation is immediately terminated.
This switch tells
GNAT to continue with semantic analysis even if syntax errors have been
found. This may enable the detection of more errors in a single run. On
the other hand, the semantic analyzer is more likely to encounter some
internal fatal error when given a syntactically invalid tree.
-gnatQ
-gnatQ forces
generation of the `ali' file. This file is marked as being in
error, so it cannot be used for binding purposes, but it does contain
reasonably complete cross-reference information, and thus may be useful
for use by tools (e.g. semantic browsing tools or integrated development
environments) that are driven from the `ali' file.
In addition, if -gnatt is also specified, then the tree file is
generated even if there are illegalities. It may be useful in this case
to also specify -gnatq to ensure that full semantic processing
occurs. The resulting tree file can be processed by ASIS, for the purpose
of providing partial information about illegal units, but if the error
causes the tree to be badly malformed, then ASIS may crash during the
analysis.
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 given in the following
list, which is not necessarily complete.
for loop that is known to be null or might be null
The following switches are available to control the handling of warning messages:
-gnatwa (activate all optional errors)
-gnatwA (suppress all optional errors)
-gnatwb (activate warnings on biased rounding)
-gnatwa does not affect the setting of this warning option.
-gnatwB (suppress warnings on biased rounding)
-gnatwc (activate warnings on conditionals)
-gnatwa.
-gnatwC (suppress warnings on conditionals)
-gnatwe (treat warnings as errors)
-gnatwf (activate warnings on unreferenced formals)
-gnatwa or -gnatwu.
-gnatwF (suppress warnings on unreferenced formals)
-gnatwu followed by -gnatwF has the
effect of warning on unreferenced entities other than subprogram
formals.
-gnatwh (activate warnings on hiding)
-gnatwa does not affect the setting of this warning option.
-gnatwH (suppress warnings on hiding)
-gnatwi (activate warnings on implementation units).
with of an internal GNAT
implementation unit, defined as any unit from the Ada,
Interfaces, GNAT,
or System
hierarchies that is not
documented in either the Ada Reference Manual or the GNAT
Programmer's Reference Manual. Such units are intended only
for internal implementation purposes and should not be with'ed
by user programs. The default is that such warnings are generated
This warning can also be turned on using -gnatwa.
-gnatwI (disable warnings on implementation units).
with of an internal GNAT
implementation unit.
-gnatwl (activate warnings on elaboration pragmas)
-gnatwa.
-gnatwL (suppress warnings on elaboration pragmas)
-gnatwo (activate warnings on address clause overlays)
-gnatwa.
-gnatwO (suppress warnings on address clause overlays)
-gnatwp (activate warnings on ineffective pragma Inlines)
-gnatN) to inline a particular call. There are
many reasons for not being able to inline a call, including most
commonly that the call is too complex to inline.
This warning can also be turned on using -gnatwa.
-gnatwP (suppress warnings on ineffective pragma Inlines)
-gnatwr (activate warnings on redundant constructs)
-gnatwa.
Base where typ'Base is the same
as typ.
Pack when all components are placed by a record
representation clause.
-gnatwR (suppress warnings on redundant constructs)
-gnatws (suppress all warnings)
gcc back end.
To suppress these back end warnings as well, use the switch -w
in addition to -gnatws.
-gnatwu (activate warnings on unused entities)
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.
This switch also activates warnings on unreferenced formals
(it is includes the effect of -gnatwf).
This warning can also be turned on using -gnatwa.
-gnatwU (suppress warnings on unused entities)
-gnatwF).
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.
-w
gcc backend. It may be
used in conjunction with -gnatws to ensure that all warnings
are suppressed during the entire compilation process.
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-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_Failure declared in the package
System.Assertions is
raised (passing static-string-expression, if present, as the
message associated with the exception). If no string expression is
given the default is a string 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.
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The Ada 95 Reference Manual has specific requirements for checking for invalid values. In particular, RM 13.9.1 requires that the evaluation of invalid values (for example from unchecked conversions), not result in erroneous execution. In GNAT, the result of such an evaluation in normal default mode is to either use the value unmodified, or to raise Constraint_Error in those cases where use of the unmodified value would cause erroneous execution. The cases where unmodified values might lead to erroneous execution are case statements (where a wild jump might result from an invalid value), and subscripts on the left hand side (where memory corruption could occur as a result of an invalid value).
The -gnatVx switch allows more control over the validity checking
mode. The x argument here is a string of letters which control which
validity checks are performed in addition to the default checks described
above.
-gnatVc Validity checks for copies
The right hand side of assignments, and the initializing values of object declarations are validity checked.
-gnatVd Default (RM) validity checks
Some validity checks are done by default following normal Ada semantics
(RM 13.9.1 (9-11)).
A check is done in case statements that the expression is within the range
of the subtype. If it is not, Constraint_Error is raised.
For assignments to array components, a check is done that the expression used
as index is within the range. If it is not, Constraint_Error is raised.
Both these validity checks may be turned off using switch -gnatVD.
They are turned on by default. If -gnatVD is specified, a subsequent
switch -gnatVd will leave the checks turned on.
Switch -gnatVD should be used only if you are sure that all such
expressions have valid values. If you use this switch and invalid values
are present, then the program is erroneous, and wild jumps or memory
overwriting may occur.
-gnatVi Validity checks for in mode parameters
Arguments for parameters of mode in are validity checked in function
and procedure calls at the point of call.
-gnatVm Validity checks for in out mode parameters
Arguments for parameters of mode in out are validity checked in
procedure calls at the point of call. The 'm' here stands for
modify, since this concerns parameters that can be modified by the call.
Note that there is no specific option to test out parameters,
but any reference within the subprogram will be tested in the usual
manner, and if an invalid value is copied back, any reference to it
will be subject to validity checking.
-gnatVo Validity checks for operator and attribute operands
Arguments for predefined operators and attributes are validity checked.
This includes all operators in package Standard,
the shift operators defined as intrinsic in package Interfaces
and operands for attributes such as Pos.
-gnatVr Validity checks for function returns
The expression in return statements in functions is validity
checked.
-gnatVs Validity checks for subscripts
All subscripts expressions are checked for validity, whether they appear on the right side or left side (in default mode only left side subscripts are validity checked).
-gnatVt Validity checks for tests
Expressions used as conditions in if, while or exit
statements are checked, as well as guard expressions in entry calls.
-gnatVf Validity checks for floating-point values
In the absence of this switch, validity checking occurs only for discrete
values. If -gnatVf is specified, then validity checking also applies
for floating-point values, and NaN's and infinities are considered invalid,
as well as out of range values for constrained types. Note that this means
that standard IEEE infinity mode is not allowed. The exact contexts
in which floating-point values are checked depends on the setting of other
options. For example -gnatVif or -gnatVfi (the order does
not matter) specifies that floating-point parameters of mode in should
be validity checked.
-gnatVa All validity checks
All the above validity checks are turned on. That is -gnatVa is
equivalent to gnatVcdfimorst.
-gnatVn No validity checks
This switch turns off all validity checking, including the default checking for case statements and left hand side subscripts.
The -gnatV switch may be followed by a string of letters to turn on
a series of validity checking options. For example, -gnatVcr specifies
that in addition to the default validity checking, copies and function
return expressions be validity checked. In order to make it easier to specify
a set of options, the upper case letters CDFIMORST may be used to turn
off the corresponding lower case option, so for example -gnatVaM turns
on all validity checking options except for checking of in out
procedure arguments.
The specification of additional validity checking generates extra code (and
in the case of -gnatva the code expansion can be substantial. However,
these additional checks can be very useful in smoking out cases of
uninitialized variables, incorrect use of unchecked conversion, and other
errors leading to invalid values. The use of pragma Initialize_Scalars
is useful in conjunction with the extra validity checking, since this
ensures that wherever possible uninitialized variables have invalid values.
See also the pragma Validity_Checks which allows modification of
the validity checking mode at the program source level, and also allows for
temporary disabling of validity checks.
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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 warning message is given, preceded by the character sequence "(style)". 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)
-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)
-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)
-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)
-gnaty then
comments must meet the following set of rules:
gnatprep (where --! is used) and the SPARK annnotation
language (where --# is used). For the purposes of this rule, a special
character is defined as being in one of the ASCII ranges
16#21#..16#2F# or 16#3A#..16#3F#.
--------------------------- -- This is a box comment -- -- with two text lines. -- --------------------------- |
e (check end/exit labels)
-gnaty then
optional labels on end statements ending subprograms and on
exit statements exiting named loops, are required to be present.
f (no form feeds or vertical tabs)
-gnaty then
neither form feeds nor vertical tab characters are not permitted
in the source text.
h (no horizontal tabs)
-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)
-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)
-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)
-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)
-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)
-gnaty then the length of lines must not exceed the
given value.
n (check casing of entities in Standard)
-gnaty then any identifier from Standard must be cased
to match the presentation in the Ada Reference Manual (for example,
Integer and ASCII.NUL).
o (check order of subprogram bodies)
-gnaty then all subprogram bodies in a given scope
(e.g. a package body) must be in alphabetical order. The ordering
rule uses normal Ada rules for comparing strings, ignoring casing
of letters, except that if there is a trailing numeric suffix, then
the value of this suffix is used in the ordering (e.g. Junk2 comes
before Junk10).
p (check pragma casing)
-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)
-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)
-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)
-gnaty then
the following token spacing rules are enforced:
abs and not must be followed by a space.
=> must be surrounded by spaces.
<> must be preceded by a space or a left parenthesis.
** must be surrounded by spaces.
There is no restriction on the layout of the ** binary operator.
In the above rules, appearing in column one is always permitted, that is, counts as meeting either a requirement for a required preceding space, or as meeting a requirement for no preceding space.
Appearing at the end of a line is also always permitted, that is, counts as meeting either a requirement for a following space, or as meeting a requirement for no following space.
If any of these style rules is violated, a message is generated giving
details on the violation. The initial characters of such messages are
always "(style)". Note that these messages are treated as warning
messages, so they normally do not prevent the generation of an object
file. The -gnatwe switch can be used to treat warning messages,
including style messages, as fatal errors.
The switch
-gnaty on its own (that is not followed by any letters or digits),
is equivalent to gnaty3abcefhiklmprst, that is all checking
options are enabled with
the exception of -gnatyo,
with an indentation level of 3. This is the standard
checking option that is used for the GNAT sources.
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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
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
Constraint_Error as required by standard Ada
semantics). These overflow checks correspond to situations in which
the true value of the result of an operation may be outside the base
range of the result type. The following example shows the distinction:
X1 : Integer := Integer'Last; X2 : Integer range 1 .. 5 := 5; ... X1 := X1 + 1; -- |
Here the first addition results in a value that is outside the base range
of Integer, and hence requires an overflow check for detection of the
constraint error. The second increment operation results in a violation
of the explicit range constraint, and such range checks are always
performed. Basically the compiler can assume that in the absence of
the -gnato switch that any value of type xxx is
in range of the base type of xxx.
Note that the -gnato switch does not affect the code generated
for any floating-point operations; it applies only to integer
semantics).
For floating-point, GNAT has the Machine_Overflows
attribute set to False and the normal mode of operation is to
generate IEEE NaN and infinite values on overflow or invalid operations
(such as dividing 0.0 by 0.0).
The reason that we distinguish overflow checking from other kinds of range constraint checking is that a failure of an overflow check can generate an incorrect value, but cannot cause erroneous behavior. This is unlike the situation with a constraint check on an array subscript, where failure to perform the check can result in random memory description, or the range check on a case statement, where failure to perform the check can cause a wild jump.
Note again that -gnato is off by default, so overflow checking is
not performed in default mode. This means that out of the box, with the
default settings, GNAT does not do all the checks expected from the
language description in the Ada Reference Manual. If you want all constraint
checks to be performed, as described in this Manual, then you must
explicitly use the -gnato switch either on the gnatmake or
gcc command.
-gnatE
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.
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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. Note that the only purpose of this usage is to limit the amount of stack used by the environment task. If it is necessary to increase the amount of stack for the environment task, then this is an operating systems issue, and must be addressed with the appropriate operating systems commands.
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-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 accommodate 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.
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gcc for Syntax Checking -gnats
The s stands for syntax.
Run GNAT in syntax checking only mode. For example, the command
$ gcc -c -gnats x.adb |
compiles file `x.adb' in syntax-check-only mode. You can check a
series of files in a single command
, and can use 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 section 7. Renaming Files Using gnatchop).
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gcc for Semantic Checking -gnatc
The c stands for check.
Causes the compiler to operate in semantic check mode,
with full checking for all illegalities specified in the
Ada 95 Reference Manual, but without generation of any object code
(no object file is generated).
Because dependent files must be accessed, you must follow the GNAT semantic restrictions on file structuring to operate in this mode:
The output consists of error messages as appropriate. No object file is generated. An `ALI' file is generated for use in the context of cross-reference tools, but this file is marked as not being suitable for binding (since no object file is generated). The checking corresponds exactly to the notion of legality in the Ada 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).
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-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.
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-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
2
3
4
5
9
p
8
f
n
w
See section 2.2 Foreign Language Representation, for full details on the implementation of these character sets.
-gnatWe
h
u
s
e
8
b
-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.
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-gnatkn
For the source file naming rules, See section 2.3 File Naming Rules.
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-gnatn
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 section 25.4 Inlining of Subprograms.
-gnatN
-gnatn inlining mode.
It will also generate additional dependencies.
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-gnatt
-gnatu
-pass-exit-codes
gcc when
compiling multiple files indicates whether all source files have
been successfully used to generate object files or not.
When -pass-exit-codes is used, gcc exits with an extended
exit status and allows an integrated development environment to better
react to a compilation failure. Those exit status are:
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-gnatdx
Debug unit in the compiler source
file `debug.adb'.
-gnatG
-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. The following
is a partial list of these special constructions. See the specification
of package Sprint in file `sprint.ads' for a full list.
new xxx [storage_pool = yyy]
at end procedure-name;
(if expr then expr else expr)
x?y:z construction in C.
target^(source)
target?(source)
target?^(source)
x #/ y
x #mod y
x #* y
x #rem y
free expr [storage_pool = xxx]
free statement.
freeze typename [actions]
reference itype
function-name! (arg, arg, arg)
labelname : label
expr && expr && expr ... && expr
[constraint_error]
Constraint_Error exception.
expression'reference
target-type!(source-expression)
[numerator/denominator]
-gnatD
-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).
-gnatC
-gnatC switch
forces this compression approach to be used on all external names and names
in the debugging information tables. This reduces the size of the generated
executable, at the expense of making the naming scheme more complex. The
compression only affects the qualification of the name. Thus a name in
the source:
Very_Long_Package.Very_Long_Inner_Package.Var |
would normally appear in these tables as:
very_long_package__very_long_inner_package__var |
but if the -gnatC switch is used, then the name appears as
XCb7e0c705__var |
Here b7e0c705 is a compressed encoding of the qualification prefix. The GNAT Ada aware version of GDB understands these encoded prefixes, so if this debugger is used, the encoding is largely hidden from the user of the compiler.
-gnatR[0|1|2|3][s]
-gnatR0, no information is output (equivalent to omitting
the -gnatR switch). For -gnatR1 (which is the default,
so -gnatR with no parameter has the same effect), size and alignment
information is listed for declared array and record types. For
-gnatR2, size and alignment information is listed for all
expression information for values that are computed at run time for
variant records. These symbolic expressions have a mostly obvious
format with #n being used to represent the value of the n'th
discriminant. See source files `repinfo.ads/adb' in the
GNAT sources for full detalis on the format of -gnatR3
output. If the switch is followed by an s (e.g. -gnatR2s), then
the output is to a file with the name `file.rep' where
file is the name of the corresponding source file.
-gnatx
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.
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-gnatempath
A mapping file is a sequence of sets of three lines. In each set, the first line is the unit name, in lower case, with "%s" appended for specifications and "%b" appended for bodies; the second line is the file name; and the third line is the path name.
Example:
main%b main.2.ada /gnat/project1/sources/main.2.ada |
When the switch -gnatem is specified, the compiler will create
in memory the two mappings from the specified file. If there is any problem
(non existent file, truncated file or duplicate entries), no mapping
will be created.
Several -gnatem switches may be specified; however, only the last
one on the command line will be taken into account.
When using a project file, gnatmake create a temporary mapping file
and communicates it to the compiler using this switch.
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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:
-I switch given on the gcc
command line, in the order given.
ADA_INCLUDE_PATH environment variable.
Construct this value
exactly as the PATH environment variable: a list of directory
names separated by colons (semicolons when working with the NT version).
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.
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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:
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.
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The following are some typical Ada compilation command line examples:
$ gcc -c xyz.adb
$ 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
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gnatbind
This chapter describes the GNAT binder, gnatbind, which is used
to bind compiled GNAT objects. The gnatbind program performs
four separate functions:
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.
gnatlink utility used to link the Ada application.
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gnatbind
The form of the gnatbind command is
$ gnatbind [switches] mainprog[.ali] [switches] |
where mainprog.adb is the Ada file containing the main program
unit body. If no switches are specified, gnatbind constructs an Ada
package in two files which 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 into consideration
any source files it can locate. For example, if the binder determines
that the given main program requires the package Pack, whose
`.ali'
file is `pack.ali' and whose corresponding source spec file is
`pack.ads', it attempts to locate the source file `pack.ads'
(using the same search path conventions as previously described for the
gcc command). If it can locate this source file, it checks that
the time stamps
or source checksums of the source and its references to in `ali' files
match. In other words, any `ali' files that mentions this spec must have
resulted from compiling this version of the source file (or in the case
where the source checksums match, a version close enough that the
difference does not matter).
The effect of this consistency checking, which includes source files, is that the binder ensures that the program is consistent with the latest version of the source files that can be located at bind time. Editing a source file without compiling files that depend on the source file cause error messages to be generated by the binder.
For example, suppose you have a main program `hello.adb' and a
package P, from file `p.ads' and you perform the following
steps:
gcc -c hello.adb to compile the main program.
gcc -c p.ads to compile package P.
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 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).
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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:
#ifdef __STDC__
#define PARAMS(paramlist) paramlist
#else
#define PARAMS(paramlist) ()
#endif
extern void __gnat_set_globals
PARAMS ((int, int, int, int, int, int,
void (*) PARAMS ((void)), int, int));
extern void adafinal PARAMS ((void));
extern void adainit PARAMS ((void));
extern void system__standard_library__adafinal PARAMS ((void));
extern int main PARAMS ((int, char **, char **));
extern void exit PARAMS ((int));
extern void __gnat_break_start PARAMS ((void));
extern void _ada_hello PARAMS ((void));
extern void __gnat_initialize PARAMS ((void));
extern void __gnat_finalize PARAMS ((void));
extern void ada__exceptions___elabs PARAMS ((void));
extern void system__exceptions___elabs PARAMS ((void));
extern void interfaces__c_streams___elabs PARAMS ((void));
extern void system__exception_table___elabb PARAMS ((void));
extern void ada__io_exceptions___elabs PARAMS ((void));
extern void system__stack_checking___elabs PARAMS ((void));
extern void system__soft_links___elabb PARAMS ((void));
extern void system__secondary_stack___elabb PARAMS ((void));
extern void ada__tags___elabs PARAMS ((void));
extern void ada__tags___elabb PARAMS ((void));
extern void ada__streams___elabs PARAMS ((void));
extern void system__finalization_root___elabs PARAMS ((void));
extern void ada__exceptions___elabb PARAMS ((void));
extern void system__finalization_implementation___elabs PARAMS ((void));
extern void system__finalization_implementation___elabb PARAMS ((void));
extern void ada__finalization___elabs PARAMS ((void));
extern void ada__finalization__list_controller___elabs PARAMS ((void));
extern void system__file_control_block___elabs PARAMS ((void));
extern void system__file_io___elabb PARAMS ((void));
extern void ada__text_io___elabs PARAMS ((void));
extern void ada__text_io___elabb PARAMS ((void));
extern int __gnat_inside_elab_final_code;
extern int gnat_argc;
extern char **gnat_argv;
extern char **gnat_envp;
extern int gnat_exit_status;
char __gnat_version[] = "GNAT Version: 3.15w (20010315)";
void adafinal () {
system__standard_library__adafinal ();
}
void adainit ()
{
extern char ada__exceptions_E;
extern char system__exceptions_E;
extern char interfaces__c_streams_E;
extern char system__exception_table_E;
extern char ada__io_exceptions_E;
extern char system__secondary_stack_E;
extern char system__stack_checking_E;
extern char system__soft_links_E;
extern char ada__tags_E;
extern char ada__streams_E;
extern char system__finalization_root_E;
extern char system__finalization_implementation_E;
extern char ada__finalization_E;
extern char ada__finalization__list_controller_E;
extern char system__file_control_block_E;
extern char system__file_io_E;
extern char ada__text_io_E;
extern void *__gnat_hello__SDP;
extern void *__gnat_ada__text_io__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__machine_state_operations__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_system__traceback__SDP;
extern void *__gnat_ada__streams__SDP;
extern void *__gnat_ada__tags__SDP;
extern void *__gnat_system__string_ops__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__finalization_implementation__SDP;
extern void *__gnat_system__string_ops_concat_3__SDP;
extern void *__gnat_system__stream_attributes__SDP;
extern void *__gnat_system__file_control_block__SDP;
extern void *__gnat_ada__finalization__list_controller__SDP;
void **st[23] = {
&__gnat_hello__SDP,
&__gnat_ada__text_io__SDP,
&__gnat_ada__exceptions__SDP,
&__gnat_gnat__heap_sort_a__SDP,
&__gnat_system__exception_table__SDP,
&__gnat_system__machine_state_operations__SDP,
&__gnat_system__secondary_stack__SDP,
&__gnat_system__parameters__SDP,
&__gnat_system__soft_links__SDP,
&__gnat_system__stack_checking__SDP,
&__gnat_system__traceback__SDP,
&__gnat_ada__streams__SDP,
&__gnat_ada__tags__SDP,
&__gnat_system__string_ops__SDP,
&__gnat_interfaces__c_streams__SDP,
&__gnat_system__file_io__SDP,
&__gnat_ada__finalization__SDP,
&__gnat_system__finalization_root__SDP,
&__gnat_system__finalization_implementation__SDP,
&__gnat_system__string_ops_concat_3__SDP,
&__gnat_system__stream_attributes__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 system__stack_checking___elabs ();
extern void system__soft_links___elabb ();
extern void system__secondary_stack___elabb ();
extern void ada__tags___elabs ();
extern void ada__tags___elabb ();
extern void ada__streams___elabs ();
extern void system__finalization_root___elabs ();
extern void ada__exceptions___elabb ();
extern void system__finalization_implementation___elabs ();
extern void system__finalization_implementation___elabb ();
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[23]) () = {
adainit,
system__standard_library__adafinal,
ada__exceptions___elabs,
system__exceptions___elabs,
interfaces__c_streams___elabs,
system__exception_table___elabb,
ada__io_exceptions___elabs,
system__stack_checking___elabs,
system__soft_links___elabb,
system__secondary_stack___elabb,
ada__tags___elabs,
ada__tags___elabb,
ada__streams___elabs,
system__finalization_root___elabs,
ada__exceptions___elabb,
system__finalization_implementation___elabs,
system__finalization_implementation___elabb,
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, 23, ea, 23);
__gnat_set_globals (
-1, /* Main_Priority */
-1, /* Time_Slice_Value */
'b', /* WC_Encoding */
' ', /* Locking_Policy */
' ', /* Queuing_Policy */
' ', /* Tasking_Dispatching_Policy */
0, /* Finalization routine address, not used anymore */
0, /* Unreserve_All_Interrupts */
0); /* Exception_Tracebacks */
__gnat_inside_elab_final_code = 1;
if (ada__exceptions_E == 0) {
ada__exceptions___elabs ();
}
if (system__exceptions_E == 0) {
system__exceptions___elabs ();
system__exceptions_E++;
}
if (interfaces__c_streams_E == 0) {
interfaces__c_streams___elabs ();
}
interfaces__c_streams_E = 1;
if (system__exception_table_E == 0) {
system__exception_table___elabb ();
system__exception_table_E++;
}
if (ada__io_exceptions_E == 0) {
ada__io_exceptions___elabs ();
ada__io_exceptions_E++;
}
if (system__stack_checking_E == 0) {
system__stack_checking___elabs ();
}
if (system__soft_links_E == 0) {
system__soft_links___elabb ();
system__soft_links_E++;
}
system__stack_checking_E = 1;
if (system__secondary_stack_E == 0) {
system__secondary_stack___elabb ();
system__secondary_stack_E++;
}
if (ada__tags_E == 0) {
ada__tags___elabs ();
}
if (ada__tags_E == 0) {
ada__tags___elabb ();
ada__tags_E++;
}
if (ada__streams_E == 0) {
ada__streams___elabs ();
ada__streams_E++;
}
if (system__finalization_root_E == 0) {
system__finalization_root___elabs ();
}
system__finalization_root_E = 1;
if (ada__exceptions_E == 0) {
ada__exceptions___elabb ();
ada__exceptions_E++;
}
if (system__finalization_implementation_E == 0) {
system__finalization_implementation___elabs ();
}
if (system__finalization_implementation_E == 0) {
system__finalization_implementation___elabb ();
system__finalization_implementation_E++;
}
if (ada__finalization_E == 0) {
ada__finalization___elabs ();
}
ada__finalization_E = 1;
if (ada__finalization__list_controller_E == 0) {
ada__finalization__list_controller___elabs ();
}
ada__finalization__list_controller_E = 1;
if (system__file_control_block_E == 0) {
system__file_control_block___elabs ();
system__file_control_block_E++;
}
if (system__file_io_E == 0) {
system__file_io___elabb ();
system__file_io_E++;
}
if (ada__text_io_E == 0) {
ada__text_io___elabs ();
}
if (ada__text_io_E == 0) {
ada__text_io___elabb ();
ada__text_io_E++;
}
__gnat_inside_elab_final_code = 0;
}
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 ();
system__standard_library__adafinal ();
__gnat_finalize ();
exit (gnat_exit_status);
}
unsigned helloB = 0x7880BEB3;
unsigned system__standard_libraryB = 0x0D24CBD0;
unsigned system__standard_libraryS = 0x3283DBEB;
unsigned adaS = 0x2359F9ED;
unsigned ada__text_ioB = 0x47C85FC4;
unsigned ada__text_ioS = 0x496FE45C;
unsigned ada__exceptionsB = 0x74F50187;
unsigned ada__exceptionsS = 0x6736945B;
unsigned gnatS = 0x156A40CF;
unsigned gnat__heap_sort_aB = 0x033DABE0;
unsigned gnat__heap_sort_aS = 0x6AB38FEA;
unsigned systemS = 0x0331C6FE;
unsigned system__exceptionsS = 0x20C9ECA4;
unsigned system__exception_tableB = 0x68A22947;
unsigned system__exception_tableS = 0x394BADD5;
unsigned gnat__htableB = 0x08258E1B;
unsigned gnat__htableS = 0x367D5222;
unsigned system__machine_state_operationsB = 0x4F3B7492;
unsigned system__machine_state_operationsS = 0x182F5CF4;
unsigned system__storage_elementsB = 0x2F1EB794;
unsigned system__storage_elementsS = 0x102C83C7;
unsigned system__secondary_stackB = 0x1574B6E9;
unsigned system__secondary_stackS = 0x708E260A;
unsigned system__parametersB = 0x56D770CD;
unsigned system__parametersS = 0x237E39BE;
unsigned system__soft_linksB = 0x08AB6B2C;
unsigned system__soft_linksS = 0x1E2491F3;
unsigned system__stack_checkingB = 0x476457A0;
unsigned system__stack_checkingS = 0x5299FCED;
unsigned system__tracebackB = 0x2971EBDE;
unsigned system__tracebackS = 0x2E9C3122;
unsigned ada__streamsS = 0x7C25DE96;
unsigned ada__tagsB = 0x39ADFFA2;
unsigned ada__tagsS = 0x769A0464;
unsigned system__string_opsB = 0x5EB646AB;
unsigned system__string_opsS = 0x63CED018;
unsigned interfacesS = 0x0357E00A;
unsigned interfaces__c_streamsB = 0x3784FB72;
unsigned interfaces__c_streamsS = 0x2E723019;
unsigned system__file_ioB = 0x623358EA;
unsigned system__file_ioS = 0x31F873E6;
unsigned ada__finalizationB = 0x6843F68A;
unsigned ada__finalizationS = 0x63305874;
unsigned system__finalization_rootB = 0x31E56CE1;
unsigned system__finalization_rootS = 0x23169EF3;
unsigned system__finalization_implementationB = 0x6CCBA70E;
unsigned system__finalization_implementationS = 0x604AA587;
unsigned system__string_ops_concat_3B = 0x572E3F58;
unsigned system__string_ops_concat_3S = 0x01F57876;
unsigned system__stream_attributesB = 0x1D4F93E8;
unsigned system__stream_attributesS = 0x30B2EC3D;
unsigned ada__io_exceptionsS = 0x34054F96;
unsigned system__unsigned_typesS = 0x7B9E7FE3;
unsigned system__file_control_blockS = 0x2FF876A8;
unsigned ada__finalization__list_controllerB = 0x5760634A;
unsigned ada__finalization__list_controllerS = 0x5D851835;
/* BEGIN ELABORATION ORDER
ada (spec)
gnat (spec)
gnat.heap_sort_a (spec)
gnat.htable (spec)
gnat.htable (body)
interfaces (spec)
system (spec)
system.parameters (spec)
system.standard_library (spec)
ada.exceptions (spec)
system.exceptions (spec)
system.parameters (body)
gnat.heap_sort_a (body)
interfaces.c_streams (spec)
interfaces.c_streams (body)
system.exception_table (spec)
system.exception_table (body)
ada.io_exceptions (spec)
system.storage_elements (spec)
system.storage_elements (body)
system.machine_state_operations (spec)
system.machine_state_operations (body)
system.secondary_stack (spec)
system.stack_checking (spec)
system.soft_links (spec)
system.soft_links (body)
system.stack_checking (body)
system.secondary_stack (body)
system.standard_library (body)
system.string_ops (spec)
system.string_ops (body)
ada.tags (spec)
ada.tags (body)
ada.streams (spec)
system.finalization_root (spec)
system.finalization_root (body)
system.string_ops_concat_3 (spec)
system.string_ops_concat_3 (body)
system.traceback (spec)
system.traceback (body)
ada.exceptions (body)
system.unsigned_types (spec)
system.stream_attributes (spec)
system.stream_attributes (body)
system.finalization_implementation (spec)
system.finalization_implementation (body)
ada.finalization (spec)
ada.finalization (body)
ada.finalization.list_controller (spec)
ada.finalization.list_controller (body)
system.file_control_block (spec)
system.file_io (spec)
system.file_io (body)
ada.text_io (spec)
ada.text_io (body)
hello (body)
END ELABORATION ORDER */
/* BEGIN Object file/option list
./hello.o
-L./
-L/usr/local/gnat/lib/gcc-lib/alpha-dec-osf5.1/2.8.1/adalib/
/usr/local/gnat/lib/gcc-lib/alpha-dec-osf5.1/2.8.1/adalib/libgnat.a
-lexc
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.
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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
-x
gnatmake because in this
case the checking against sources has already been performed by
gnatmake in the course of compilation (i.e. before binding).
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The following switches provide control over the generation of error messages from the binder:
-v
-b
-v switch.
-mn
-Mxxx
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
-we
-t
GNAT were used for compilation
Normally failure of such checks, in accordance with the consistency requirements of the Ada Reference Manual, causes error messages to be generated which abort the binder and prevent the output of a binder file and subsequent link to obtain an executable.
The -t switch converts these error messages
into warnings, so that
binding and linking can continue to completion even in the presence of such
errors. The result may be a failed link (due to missing symbols), or a
non-functional executable which has undefined semantics.
This means that
-t should be used only in unusual situations,
with extreme care.
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The following switches provide additional control over the elaboration order. For full details see See section 11. Elaboration Order Handling in GNAT.
-p
Program_Error exception. This switch reverses the
action of the binder, and requests that it deliberately choose an order
that is likely to maximize the likelihood of an elaboration error.
This is useful in ensuring portability and avoiding dependence on
accidental fortuitous elaboration ordering.
Normally it only makes sense to use the -p switch if dynamic
elaboration checking is used (-gnatE switch used for compilation).
This is because in the default static elaboration mode, all necessary
Elaborate_All pragmas are implicitly inserted. These implicit
pragmas are still respected by the binder in -p mode, so a
safe elaboration order is assured.
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The following switches allow additional control over the output generated by the binder.
-A
-o gnatbind option.
-c
-C
-o gnatbind
option.
-e
-h
-K
gnatbind.
-l
-O
-o file
-r
pragma Rerstrictions that could be applied to
the current unit. This is useful for code audit purposes, and also may
be used to improve code generation in some cases.
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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 section 2.10 Mixed Language Programming).
The following switch is used in this situation:
-n
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
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
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 the GNAT run time requires a FPU using 80 bits mode precision. Under targets where this is not the default it is required to call GNAT.Float_Control.Reset before using floating point numbers (this include float computation, float input and output) in the Ada code. A side effect is that this could be the wrong mode for the foreign code where floating point computation could be broken after this call.
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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
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The following are the switches available with gnatbind:
-aO
-aI
-A
-b
-c
-C
-e
-E
GNAT.Traceback and
GNAT.Traceback.Symbolic for more information.
Note that on x86 ports, you must not use -fomit-frame-pointer
gcc option.
-h
-I
-I-
gnatbind was
invoked, and do not look for ALI files in the directory containing the
ALI file named in the gnatbind command line.
-l
-Lxxx
-Mxyz
-mn
-n
-nostdinc
-nostdlib
--RTS=rts-path
gnatmake flag (see 6.2 Switches for gnatmake).
-o file
-O
-p
-s
-static
-shared
-t
-Tn
-v
-wx
-x
-z
You may obtain this listing by running the program gnatbind with
no arguments.
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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.
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gnatbind The binder takes the name of an ALI file as its argument and needs to locate source files as well as other ALI files to verify object consistency.
For source files, it follows exactly the same search rules as gcc
(see section 3.3 Search Paths and the Run-Time Library (RTL)). For ALI files the
directories searched are:
-I- is specified.
-I
switches on the gnatbind
command line, in the order given.
ADA_OBJECTS_PATH environment variable.
Construct this value
exactly as the PATH environment variable: a list of directory
names separated by colons (semicolons when working with the NT version
of GNAT).
-nostdlib is
specified.
16.2 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.
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gnatbind Usage
This section contains a number of examples of using the GNAT binding
utility gnatbind.
gnatbind hello
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
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
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
gnatbind -n math dbase -C -o ada-control.c
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.
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gnatlink
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.
5.1 Running gnatlink5.2 Switches for gnatlink5.3 Setting Stack Size from gnatlink5.4 Setting Heap Size from gnatlink
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gnatlink
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 |
Using linker options it is possible to set the program stack and
heap size. See see section 5.3 Setting Stack Size from gnatlink and
see section 5.4 Setting Heap Size from gnatlink.
gnatlink determines the list of objects required by the Ada
program and prepends them to the list of objects passed to the linker.
gnatlink also gathers any arguments set by the use of
pragma Linker_Options and adds them to the list of arguments
presented to the linker.
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gnatlink
The following switches are available with the gnatlink utility:
-A
-C
gnatlink that the binder has generated C code rather than
Ada code.
-f
gnatlink
will generate a separate file for the linker if the list of object files
is too long. The -f flag forces this file to be generated even if
the limit is not exceeded. This is useful in some cases to deal with
special situations where the command line length is exceeded.
-g
-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
-v
-v -v
-o exec-name
gnatlink try.ali creates
an executable called `try'.
-b target
-Bdir
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
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.
If several --GCC=compiler_name are used, only the last
compiler_name is taken into account. However, all the additional
switches are also taken into account. Thus,
--GCC="foo -x -y" --GCC="bar -z -t" is equivalent to
--GCC="bar -x -y -z -t".
--LINK=name
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gnatlink
It is possible to specify the program stack size from gnatlink.
Assuming that the underlying linker is GNU ld there is two ways to do so:
-Xlinker linker option
$ gnatlink hello -Xlinker --stack=0x10000,0x1000 |
This set the stack reserve size to 0x10000 bytes and the stack commit size to 0x1000 bytes.
-Wl linker option
$ gnatlink hello -Wl,--stack=0x1000000 |
This set the stack reserve size to 0x1000000 bytes. Note that with
-Wl option it is not possible to set the stack commit size
because the coma is a separator for this option.
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gnatlink
It is possible to specify the program heap size from gnatlink.
Assuming that the underlying linker is GNU ld there is two ways to do so:
-Xlinker linker option
$ gnatlink hello -Xlinker --heap=0x10000,0x1000 |
This set the heap reserve size to 0x10000 bytes and the heap commit size to 0x1000 bytes.
-Wl linker option
$ gnatlink hello -Wl,--heap=0x1000000 |
This set the heap reserve size to 0x1000000 bytes. Note that with
-Wl option it is not possible to set the heap commit size
because the coma is a separator for this option.
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gnatmake
A typical development cycle when working on an Ada program consists of the following steps:
6.1 Running gnatmake6.2 Switches for gnatmake6.3 Mode Switches for gnatmake6.4 Notes on the Command Line 6.5 How gnatmakeWorks6.6 Examples of gnatmakeUsage
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.
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gnatmake
The usual form of the gnatmake command is
$ gnatmake [switches] file_name [file_names] [mode_switches] |
The only required argument is one file_name, which specifies
a compilation unit that is a main program. Several file_names can be
specified: this will result in several executables being built.
If switches are present, they can be placed before the first
file_name, between file_names or after the last file_name.
If mode_switches are present, they must always be placed after
the last file_name and all switches.
If you are using standard file extensions (.adb and .ads), then the
extension may be omitted from the file_name arguments. However, if
you are using non-standard extensions, then it is required that the
extension be given. A relative or absolute directory path can be
specified in a file_name, in which case, the input source file will
be searched for in the specified directory only. Otherwise, the input
source file will first be searched in the directory where
gnatmake was invoked and if it is not found, it will be search on
the source path of the compiler as described in
3.3 Search Paths and the Run-Time Library (RTL).
When several file_names are specified, if an executable needs to be rebuilt and relinked, all subsequent executables will be rebuilt and relinked, even if this would not be absolutely necessary.
All gnatmake output (except when you specify
-M) is to
`stderr'. The output produced by the
-M switch is send to
`stdout'.
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gnatmake
You may specify any of the following switches to gnatmake:
--GCC=compiler_name
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.
If several --GCC=compiler_name are used, only the last
compiler_name is taken into account. However, all the additional
switches are also taken into account. Thus,
--GCC="foo -x -y" --GCC="bar -z -t" is equivalent to
--GCC="bar -x -y -z -t".
--GNATBIND=binder_name
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
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
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. -a 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 -gnatpg rather than gcc -c.
-b
-c to do compilation
and binding, but no link. Can be combined with -l
to do binding and linking. When not combined with -c
all the units in the closure of the main program must have been previously
compiled and must be up to date. The root unit specified by file_name
may be given without extension, with the source extension or, if no GNAT
Project File is specified, with the ALI file extension.
-c
-b
is also specified. Do not perform linking, except if both
-b and
-l are also specified.
If the root unit specified by file_name is not a main unit, this is the
default. Otherwise gnatmake will attempt binding and linking
unless all objects are up to date and the executable is more recent than
the objects.
-C
gnatmake is invoked with this switch, it will create a mapping
file, initially populated by the project manager, if -P is used,
otherwise initially empty. Each invocation of the compiler will add the newly
accessed sources to the mapping file. This will improve the source search
during the next invocation of the compiler.
-f
-a switch is also specified.
-i
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 (3.3 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
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
gnatmake
terminates.
If gnatmake is invoked with several `file_names' and with this
switch, if there are compilation errors when building an executable,
gnatmake will not attempt to build the following executables.
-l
-b to binding
and linking. Linking will not be performed if combined with
-c
but not with -b.
When not combined with -b
all the units in the closure of the main program must have been previously
compiled and must be up to date, and the main program need to have been bound.
The root unit specified by file_name
may be given without extension, with the source extension or, if no GNAT
Project File is specified, with the ALI file extension.
-m
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
-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
-o exec_name
-o switch is omitted the default
name for the executable will be the name of the input file in appropriate form
for an executable file on the host system.
This switch cannot be used when invoking gnatmake with several
`file_names'.
-q
gnatmake are displayed.
\-s\/SWITCH_CHECK/
-O -O2 is different than -O2 -O, but -g -O is equivalent
to -O -g.
-u
-v
gnatmake
decides are necessary.
-z
gcc switches-g or any uppercase switch (other than -A,
-L or
-S) 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
-aLdir
gnatmake to skip compilation units whose `.ali'
files have been located in directory dir. This allows you to have
missing bodies for the units in dir and to ignore out of date bodies
for the same units. You still need to specify
the location of the specs for these units by using the switches
-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
gnatbind.
-Adir
-aLdir
-aIdir.
-Idir
-aOdir
-aIdir.
-I-
gnatmake was invoked.
-Ldir
-largs -Ldir.
-nostdinc
-nostdlib
--RTS=rts-path
The selected path is handled like a normal RTS path.
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gnatmake
The mode switches (referred to as mode_switches) allow the
inclusion of switches that are to be passed to the compiler itself, the
binder or the linker. The effect of a mode switch is to cause all
subsequent switches up to the end of the switch list, or up to the next
mode switch, to be interpreted as switches to be passed on to the
designated component of GNAT.
-cargs switches
gcc. They will be passed on to
all compile steps performed by gnatmake.
-bargs switches
gcc. They will be passed on to
all bind steps performed by gnatmake.
-largs switches
gcc. They will be passed on to
all link steps performed by gnatmake.
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This section contains some additional useful notes on the operation
of the gnatmake command.
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.
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.
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 |
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.
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gnatmake Works
Generally gnatmake automatically performs all necessary
recompilations and you don't need to worry about how it works. However,
it may be useful to have some basic understanding of the gnatmake
approach and in particular to understand how it uses the results of
previous compilations without incorrectly depending on them.
First a definition: an object file is considered up to date if the corresponding ALI file exists and 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.
When invoking gnatmake with several file_names, if a unit is
imported by several of the executables, it will be recompiled at most once.
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gnatmake Usage
gnatmake hello.adb
Hello) and bind and link the
resulting object files to generate an executable file `hello'.
gnatmake main1 main2 main3
Main1), `main2.adb'
(containing unit Main2) and `main3.adb'
(containing unit Main3) and bind and link the resulting object files
to generate three executable files `main1',
`main2'
and `main3'.
gnatmake -q Main_Unit -cargs -O2 -bargs -l
Compile all files necessary to bind and link the main program unit
Main_Unit (from file `main_unit.adb'). All compilations will
be done with optimization level 2 and the order of elaboration will be
listed by the binder. gnatmake will operate in quiet mode, not
displaying commands it is executing.
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gnatchop
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.
7.1 Handling Files with Multiple Units 7.2 Operating gnatchop in Compilation Mode 7.3 Command Line for gnatchop7.4 Switches for gnatchop7.5 Examples of gnatchopUsage
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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.
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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 section 8.1 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.
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gnatchop
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.
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gnatchop
gnatchop recognizes the following switches:
-c
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
-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
gnatchop to generate a brief help summary to the standard
output file showing usage information.
-kmm
mm
of characters.
This is useful if the
resulting set of files is required to be interoperable with systems
which limit the length of file names.
No space is allowed between the -k and the numeric value. The numeric
value may be omitted in which case a default of -k8,
suitable for use
with DOS-like file systems, is used. If no -k switch
is present then
there is no limit on the length of file names.
-p
gnatchop is used as part of a standard build process.
-q
-r
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
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
gnatchop regards it as a
fatal error if there is already a file with the same name as a
file it would otherwise output, in other words if the files to be
chopped contain duplicated units. This switch bypasses this
check, and causes all but the last instance of such duplicated
units to be skipped.
--GCC=xxxx
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gnatchop Usage
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
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
-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.
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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. The following is a complete list of configuration pragmas
recognized by GNAT:
Ada_83 Ada_95 C_Pass_By_Copy Component_Alignment Discard_Names Elaboration_Checks Eliminate Extend_System Extensions_Allowed External_Name_Casing Float_Representation Initialize_Scalars License Locking_Policy Long_Float No_Run_Time Normalize_Scalars Polling Propagate_Exceptions Queuing_Policy Ravenscar Restricted_Run_Time Restrictions Reviewable Source_File_Name Style_Checks Suppress Task_Dispatching_Policy Unsuppress Use_VADS_Size Warnings Validity_Checks |
8.1 Handling of Configuration Pragmas 8.2 The Configuration Pragmas Files
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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 section 7.2 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.
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In GNAT a compilation environment is defined by the current
directory at the time that a compile command is given. This current
directory is searched for a file whose name is `gnat.adc'. If
this file is present, it is expected to contain one or more
configuration pragmas that will be applied to the current compilation.
However, if the switch -gnatA is used, `gnat.adc' is not
considered.
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.
In addition to `gnat.adc', one additional file containing configuration
pragmas may be applied to the current compilation using the switch
-gnatecpath. path must designate an existing file that
contains only configuration pragmas. These configuration pragmas are
in addition to those found in `gnat.adc' (provided `gnat.adc'
is present and switch -gnatA is not used).
It is allowed to specify several switches -gnatec, however only
the last one on the command line will be taken into account.
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gnatname
9.1 Arbitrary File Naming Conventions 9.2 Running gnatname9.3 Switches for gnatname9.4 Examples of gnatnameUsage
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The GNAT compiler must be able to know the source file name of a compilation unit.
When using the standard GNAT default file naming conventions (.ads for specs,
.adb for bodies), the GNAT compiler does not need additional information.
When the source file names do not follow the standard GNAT default file naming
conventions, the GNAT compiler must be given additional information through
a configuration pragmas file (see 8. Configuration Pragmas) or a project file.
When the non standard file naming conventions are well-defined, a small number of
pragmas Source_File_Name specifying a naming pattern
(see 2.5 Alternative File Naming Schemes) may be sufficient. However,
if the file naming conventions are irregular or arbitrary, a number
of pragma Source_File_Name for individual compilation units must be defined.
To help maintain the correspondence between compilation unit names and
source file names within the compiler,
GNAT provides a tool gnatname to generate the required pragmas for a
set of files.
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gnatname
The usual form of the gnatname command is
$ gnatname [switches] [naming_patterns] |
All of the arguments are optional.
When used with no arguments, gnatname will create a file `gnat.adc'
in the current working directory, that contains configuration pragmas for all
compilation units in the current directory. To find all compilation units,
gnatname will use the GNAT compiler in syntax-check-only mode on all
regular files. For those files that contain an Ada compilation unit,
a pragma Source_File_Name will be generated.
One or several Naming Patterns may be given as arguments to gnatname.
Each Naming Pattern is enclosed between double quotes.
A Naming Pattern is a regular expression similar to the wildcard patterns
used in file names by the Unix shells or the DOS prompt.
Examples of Naming Patterns are
"*.[12].ada" "*.ad[sb]*" "body_*" "spec_*" |
For a more complete description of the syntax of Naming Patterns, see the second kind of regular expressions described in `g-regexp.ads' (the "Glob" regular expressions).
Specifying no Naming Pattern is equivalent to specifying the single Naming Pattern
"*".
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gnatname
Switches for gnatname must precede any specified Naming Pattern.
You may specify any of the following switches to gnatname:
-c`file'
-c and
`file'. `file' may include directory information. `file' must be
writeable. There may be only one switch -c. When a switch -c is
specified, no switch -P may be specified (see below).
-d`dir'
-d and `dir'. When a switch -d is specified,
the current working directory will not be searched for source files, unless it
is explictly
specified with a -d or -D switch. Several switches -d may be
specified. If `dir' is a relative path, it is relative to the directory of
the configuration pragmas file specified with switch -c, or to the directory
of the project file specified with switch -P or, if neither switch -c
nor switch -P are specified, it is relative to the current working
directory. The directory
specified with switch -c must exist and be readable.
-D`file'
-d and `dir'. `file'
must be an existing, readable text file. Each non empty line in `file' must be
a directory. Specifying switch -D is equivalent to specifying as many switches
-d as there are non empty lines in `file'.
-h
-P`proj'
-P and `proj'. `proj' may include directory information.
`proj' must be writeable. There may be only one switch -P.
When a switch -P is specified, no switch -c may be specified.
-v
-v -v
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gnatname Usage
$ gnatname |
equivalent to
$ gnatname -d. "*" |
$ gnatname -c /home/me/names.adc -d sources "[a-z]*.ada*" |
In this example, the directory `/home/me' must already exist and be
writeable. In addition, the directory `/home/me/sources' (specified by
-d sources) must exist and be readable. Note the optional spaces after
-c and -d.
$ gnatname -P/home/me/proj -dsources -dsources/plus -Dcommon_dirs.txt "body_*" "spec_*" |
Note that several switches -d may be used, even in conjunction with one or
several switches -D. Several Naming Patterns are used in this example.
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This chapter describes GNAT's Project Manager, a facility that lets you configure various properties for a collection of source files. In particular, you can specify:
gnatmake,
compiler, binder, linker, gnatls, gnatxref, gnatfind);
you can apply these settings either globally or to individual units
10.1.1 Project Files
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A project is a specific set of values for these properties. You can define a project's settings in a project file, a text file with an Ada-like syntax; a property value is either a string or a list of strings. Properties that are not explicitly set receive default values. A project file may interrogate the values of external variables (user-defined command-line switches or environment variables), and it may specify property settings conditionally, based on the value of such variables.
In simple cases, a project's source files depend only on other source files in the same project, or on the predefined libraries. ("Dependence" is in the technical sense; for example, one Ada unit "with"ing another.) However, the Project Manager also allows much more sophisticated arrangements, with the source files in one project depending on source files in other projects:
More generally, the Project Manager lets you structure large development efforts into hierarchical subsystems, with build decisions deferred to the subsystem level and thus different compilation environments (switch settings) used for different subsystems.
The Project Manager is invoked through the `-Pprojectfile'
switch to gnatmake or to the gnat front driver.
If you want to define (on the command line) an external variable that is
queried by the project file, additionally use the
`-Xvbl=value' switch.
The Project Manager parses and interprets the project file, and drives the
invoked tool based on the project settings.
The Project Manager supports a wide range of development strategies, for systems of all sizes. Some typical practices that are easily handled:
The destination of an executable can be controlled inside a project file
using the `-o' switch. In the absence of such a switch either inside
the project file or on the command line, any executable files generated by
gnatmake will be placed in the directory Exec_Dir specified
in the project file. If no Exec_Dir is specified, they will be placed
in the object directory of the project.
You can use project files to achieve some of the effects of a source versioning system (for example, defining separate projects for the different sets of sources that comprise different releases) but the Project Manager is independent of any source configuration management tools that might be used by the developers.
The next section introduces the main features of GNAT's project facility through a sequence of examples; subsequent sections will present the syntax and semantics in more detail.
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10.2.1 Common Sources with Different Switches and Different Output Directories 10.2.2 Using External Variables 10.2.3 Importing Other Projects 10.2.4 Extending a Project
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Source Files Specifying the Object Directory Specifying the Exec Directory Project File Packages Specifying Switch Settings Main Subprograms Source File Naming Conventions Source Language(s)
Assume that the Ada source files `pack.ads', `pack.adb', and
`proc.adb' are in the `/common' directory. The file
`proc.adb' contains an Ada main subprogram Proc that "with"s
package Pack. We want to compile these source files under two sets
of switches:
gnatmake,
and the `-gnata', `-gnato', and `-gnatE' switches to the
compiler; the compiler's output is to appear in `/common/debug'
The GNAT project files shown below, respectively `debug.gpr' and `release.gpr' in the `/common' directory, achieve these effects.
Diagrammatically:
/common
debug.gpr
release.gpr
pack.ads
pack.adb
proc.adb
/common/debug {-g, -gnata, -gnato, -gnatE}
proc.ali, proc.o
pack.ali, pack.o
/common/release {-O2}
proc.ali, proc.o
pack.ali, pack.o
|
project Debug is
for Object_Dir use "debug";
for Main use ("proc");
package Builder is
for Default_Switches ("Ada") use ("-g");
end Builder;
package Compiler is
for Default_Switches ("Ada")
use ("-fstack-check", "-gnata", "-gnato", "-gnatE");
end Compiler;
end Debug;
|
project Release is
for Object_Dir use "release";
for Exec_Dir use ".";
for Main use ("proc");
package Compiler is
for Default_Switches ("Ada") use ("-O2");
end Compiler;
end Release;
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The name of the project defined by `debug.gpr' is "Debug" (case
insensitive), and analogously the project defined by `release.gpr' is
"Release". For consistency the file should have the same name as the
project, and the project file's extension should be "gpr". These
conventions are not required, but a warning is issued if they are not followed.
If the current directory is `/temp', then the command
gnatmake -P/common/debug.gpr |
generates object and ALI files in `/common/debug', and the proc
executable also in `/common/debug', using the switch settings defined in
the project file.
Likewise, the command
gnatmake -P/common/release.gpr |
generates object and ALI files in `/common/release', and the proc
executable in `/common', using the switch settings from the project file.
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If a project file does not explicitly specify a set of source directories or a set of source files, then by default the project's source files are the Ada source files in the project file directory. Thus `pack.ads', `pack.adb', and `proc.adb' are the source files for both projects.
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Several project properties are modeled by Ada-style attributes;
you define the property by supplying the equivalent of an Ada attribute
definition clause in the project file.
A project's object directory is such a property; the corresponding
attribute is Object_Dir, and its value is a string expression. A
directory may be specified either as absolute or as relative; in the latter
case, it is relative to the project file directory. Thus the compiler's
output is directed to `/common/debug' (for the Debug project)
and to `/common/release' (for the Release project). If
Object_Dir is not specified, then the default is the project file
directory.
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A project's exec directory is another property; the corresponding
attribute is Exec_Dir, and its value is also a string expression,
either specified as relative or absolute. If Exec_Dir is not specified,
then the default is the object directory (which may also be the project file
directory if attribute Object_Dir is not specified). Thus the executable
is placed in `/common/debug' for the Debug project (attribute
Exec_Dir not specified) and in `/common' for the Release
project.
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A GNAT tool integrated with the Project Manager is modeled by a
corresponding package in the project file.
The Debug project defines the packages Builder
(for gnatmake) and Compiler;
the Release project defines only the Compiler package.
The Ada package syntax is not to be taken literally. Although packages in project files bear a surface resemblance to packages in Ada source code, the notation is simply a way to convey a grouping of properties for a named entity. Indeed, the package names permitted in project files are restricted to a predefined set, corresponding to the project-aware tools, and the contents of packages are limited to a small set of constructs. The packages in the example above contain attribute definitions.
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Switch settings for a project-aware tool can be specified through attributes
in the package corresponding to the tool.
The example above illustrates one of the relevant attributes,
Default_Switches, defined in the packages in both project files.
Unlike simple attributes like Source_Dirs, Default_Switches is
known as an associative array. When you define this attribute, you must
supply an "index" (a literal string), and the effect of the attribute
definition is to set the value of the "array" at the specified "index".
For the Default_Switches attribute, the index is a programming
language (in our case, Ada) , and the value specified (after use)
must be a list of string expressions.
The attributes permitted in project files are restricted to a predefined set. Some may appear at project level, others in packages. For any attribute that is an associate array, the index must always be a literal string, but the restrictions on this string (e.g., a file name or a language name) depend on the individual attribute. Also depending on the attribute, its specified value will need to be either a string or a string list.
In the Debug project, we set the switches for two tools,
gnatmake and the compiler, and thus we include corresponding
packages, with each package defining the Default_Switches attribute
with index "Ada".
Note that the package corresponding to
gnatmake is named Builder. The Release project is
similar, but with just the Compiler package.
In project Debug above the switches starting with `-gnat' that
are specified in package Compiler could have been placed in package
Builder, since gnatmake transmits all such switches to the
compiler.
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One of the properties of a project is its list of main subprograms (actually
a list of names of source files containing main subprograms, with the file
extension optional. This property is captured in the Main attribute,
whose value is a list of strings. If a project defines the Main
attribute, then you do not need to identify the main subprogram(s) when
invoking gnatmake (see 10.13.1 gnatmake and Project Files).
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Since the project files do not specify any source file naming conventions,
the GNAT defaults are used. The mechanism for defining source file naming
conventions -- a package named Naming -- will be described below
(see section 10.10 Naming Schemes).
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Since the project files do not specify a Languages attribute, by
default the GNAT tools assume that the language of the project file is Ada.
More generally, a project can comprise source files
in Ada, C, and/or other languages.
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Instead of supplying different project files for debug and release, we can
define a single project file that queries an external variable (set either
on the command line or via an environment variable) in order to
conditionally define the appropriate settings. Again, assume that the
source files `pack.ads', `pack.adb', and `proc.adb' are
located in directory `/common'. The following project file,
`build.gpr', queries the external variable named STYLE and
defines an object directory and switch settings based on whether the value
is "deb" (debug) or "rel" (release), where the default is
"deb".
project Build is
for Main use ("proc");
type Style_Type is ("deb", "rel");
Style : Style_Type := external ("STYLE", "deb");
case Style is
when "deb" =>
for Object_Dir use "debug";
when "rel" =>
for Object_Dir use "release";
for Exec_Dir use ".";
end case;
package Builder is
case Style is
when "deb" =>
for Default_Switches ("Ada") use ("-g");
end case;
end Builder;
package Compiler is
case Style is
when "deb" =>
for Default_Switches ("Ada") use ("-gnata", "-gnato", "-gnatE");
when "rel" =>
for Default_Switches ("Ada") use ("-O2");
end case;
end Compiler;
end Build;
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Style_Type is an example of a string type, which is the project
file analog of an Ada enumeration type but containing string literals rather
than identifiers. Style is declared as a variable of this type.
The form external("STYLE", "deb") is known as an
external reference; its first argument is the name of an
external variable, and the second argument is a default value to be
used if the external variable doesn't exist. You can define an external
variable on the command line via the `-X' switch, or you can use an
environment variable as an external variable.
Each case construct is expanded by the Project Manager based on the
value of Style. Thus the command
gnatmake -P/common/build.gpr -XSTYLE=deb |
is equivalent to the gnatmake invocation using the project file
`debug.gpr' in the earlier example. So is the command
gnatmake -P/common/build.gpr |
since "deb" is the default for STYLE.
Analogously,
gnatmake -P/common/build.gpr -XSTYLE=rel |
is equivalent to the gnatmake invocation using the project file
`release.gpr' in the earlier example.
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A compilation unit in a source file in one project may depend on compilation
units in source files in other projects. To obtain this behavior, the
dependent project must import the projects containing the needed source
files. This effect is embodied in syntax similar to an Ada with clause,
but the "with"ed entities are strings denoting project files.
As an example, suppose that the two projects GUI_Proj and
Comm_Proj are defined in the project files `gui_proj.gpr' and
`comm_proj.gpr' in directories `/gui' and `/comm',
respectively. Assume that the source files for GUI_Proj are
`gui.ads' and `gui.adb', and that the source files for
Comm_Proj are `comm.ads' and `comm.adb', with each set of
files located in its respective project file directory. Diagrammatically:
/gui gui_proj.gpr gui.ads gui.adb /comm comm_proj.gpr comm.ads comm.adb |
We want to develop an application in directory `/app' that "with"s the
packages GUI and Comm, using the properties of the
corresponding project files (e.g. the switch settings and object directory).
Skeletal code for a main procedure might be something like the following:
with GUI, Comm; procedure App_Main is ... begin ... end App_Main; |
Here is a project file, `app_proj.gpr', that achieves the desired effect:
with "/gui/gui_proj", "/comm/comm_proj";
project App_Proj is
for Main use ("app_main");
end App_Proj;
|
Building an executable is achieved through the command:
gnatmake -P/app/app_proj |
app_main executable in the directory where
`app_proj.gpr' resides.
If an imported project file uses the standard extension (gpr) then
(as illustrated above) the with clause can omit the extension.
Our example specified an absolute path for each imported project file. Alternatively, you can omit the directory if either
ADA_PROJECT_PATH that
includes the directory containing the needed project file.
Thus, if we define ADA_PROJECT_PATH to include `/gui' and
`/comm', then our project file `app_proj.gpr' could be written as
follows:
with "gui_proj", "comm_proj";
project App_Proj is
for Main use ("app_main");
end App_Proj;
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Importing other projects raises the possibility of ambiguities. For example, the same unit might be present in different imported projects, or it might be present in both the importing project and an imported project. Both of these conditions are errors. Note that in the current version of the Project Manager, it is illegal to have an ambiguous unit even if the unit is never referenced by the importing project. This restriction may be relaxed in a future release.
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A common situation in large software systems is to have multiple implementations for a common interface; in Ada terms, multiple versions of a package body for the same specification. For example, one implementation might be safe for use in tasking programs, while another might only be used in sequential applications. This can be modeled in GNAT using the concept of project extension. If one project (the "child") extends another project (the "parent") then by default all source files of the parent project are inherited by the child, but the child project can override any of the parent's source files with new versions, and can also add new files. This facility is the project analog of extension in Object-Oriented Programming. Project hierarchies are permitted (a child project may be the parent of yet another project), and a project that inherits one project can also import other projects.
As an example, suppose that directory `/seq' contains the project file `seq_proj.gpr' and the source files `pack.ads', `pack.adb', and `proc.adb':
/seq pack.ads pack.adb proc.adb seq_proj.gpr |
Note that the project file can simply be empty (that is, no attribute or package is defined):
project Seq_Proj is end Seq_Proj; |
implying that its source files are all the Ada source files in the project directory.
Suppose we want to supply an alternate version of `pack.adb', in
directory `/tasking', but use the existing versions of `pack.ads'
and `proc.adb'. We can define a project Tasking_Proj that
inherits Seq_Proj:
/tasking pack.adb tasking_proj.gpr project Tasking_Proj extends "/seq/seq_proj" is end Tasking_Proj; |
The version of `pack.adb' used in a build depends on which project file is specified.
Note that we could have designed this using project import rather than
project inheritance; a base project would contain the sources for
`pack.ads' and `proc.adb', a sequential project would import
base and add `pack.adb', and likewise a tasking project would
import base and add a different version of `pack.adb'. The
choice depends on whether other sources in the original project need to be
overridden. If they do, then project extension is necessary, otherwise,
importing is sufficient.
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10.3.1 Basic Syntax 10.3.2 Packages 10.3.3 Expressions 10.3.4 String Types 10.3.5 Variables 10.3.6 Attributes 10.3.7 Associative Array Attributes 10.3.8 caseConstructions
This section describes the structure of project files.
A project may be an independent project, entirely defined by a single project file. Any Ada source file in an independent project depends only on the predefined library and other Ada source files in the same project.
A project may also depend on other projects, in either or both of the following ways:
The dependence relation is a directed acyclic graph (the subgraph reflecting the "extends" relation is a tree).
A project's immediate sources are the source files directly defined by that project, either implicitly by residing in the project file's directory, or explicitly through any of the source-related attributes described below. More generally, a project proj's sources are the immediate sources of proj together with the immediate sources (unless overridden) of any project on which proj depends (either directly or indirectly).
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As seen in the earlier examples, project files have an Ada-like syntax. The minimal project file is:
project Empty is end Empty; |
The identifier Empty is the name of the project.
This project name must be present after the reserved
word end at the end of the project file, followed by a semi-colon.
Any name in a project file, such as the project name or a variable name, has the same syntax as an Ada identifier.
The reserved words of project files are the Ada reserved words plus
extends, external, and project. Note that the only Ada
reserved words currently used in project file syntax are:
case
end
for
is
others
package
renames
type
use
when
with
Comments in project files have the same syntax as in Ada, two consecutives hyphens through the end of the line.
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A project file may contain packages. The name of a package must be one of the identifiers (case insensitive) from a predefined list, and a package with a given name may only appear once in a project file. The predefined list includes the following packages:
Naming
Builder
Compiler
Binder
Linker
Finder
Cross_Reference
gnatls
(The complete list of the package names and their attributes can be found in file `prj-attr.adb').
In its simplest form, a package may be empty:
project Simple is package Builder is end Builder; end Simple; |
A package may contain attribute declarations, variable declarations and case constructions, as will be described below.
When there is ambiguity between a project name and a package name,
the name always designates the project. To avoid possible confusion, it is
always a good idea to avoid naming a project with one of the
names allowed for packages or any name that starts with gnat.
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An expression is either a string expression or a string list expression.
A string expression is either a simple string expression or a compound string expression.
A simple string expression is one of the following:
"comm/my_proj.gpr"
A compound string expression is a concatenation of string expressions,
using "&"
Path & "/" & File_Name & ".ads" |
A string list expression is either a simple string list expression or a compound string list expression.
A simple string list expression is one of the following:
File_Names := (File_Name, "gnat.adc", File_Name & ".orig"); Empty_List := (); |
A compound string list expression is the concatenation (using
"&") of a simple string list expression and an expression. Note that
each term in a compound string list expression, except the first, may be
either a string expression or a string list expression.
File_Name_List := () & File_Name; -- One string in this list Extended_File_Name_List := File_Name_List & (File_Name & ".orig"); -- Two strings Big_List := File_Name_List & Extended_File_Name_List; -- Concatenation of two string lists: three strings Illegal_List := "gnat.adc" & Extended_File_Name_List; -- Illegal: must start with a string list |
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The value of a variable may be restricted to a list of string literals. The restricted list of string literals is given in a string type declaration.
Here is an example of a string type declaration:
type OS is ("NT, "nt", "Unix", "Linux", "other OS");
|
Variables of a string type are called typed variables; all other
variables are called untyped variables. Typed variables are
particularly useful in case constructions
(see 10.3.8 case Constructions).
A string type declaration starts with the reserved word type, followed
by the name of the string type (case-insensitive), followed by the reserved
word is, followed by a parenthesized list of one or more string literals
separated by commas, followed by a semicolon.
The string literals in the list are case sensitive and must all be different. They may include any graphic characters allowed in Ada, including spaces.
A string type may only be declared at the project level, not inside a package.
A string type may be referenced by its name if it has been declared in the same project file, or by its project name, followed by a dot, followed by the string type name.
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A variable may be declared at the project file level, or in a package. Here are some examples of variable declarations:
This_OS : OS := external ("OS"); -- a typed variable declaration
That_OS := "Linux"; -- an untyped variable declaration
|
A typed variable declaration includes the variable name, followed by a colon,
followed by the name of a string type, followed by :=, followed by
a simple string expression.
An untyped variable declaration includes the variable name,
followed by :=, followed by an expression. Note that, despite the
terminology, this form of "declaration" resembles more an assignment
than a declaration in Ada. It is a declaration in several senses:
A string variable declaration (typed or untyped) declares a variable whose value is a string. This variable may be used as a string expression.
File_Name := "readme.txt"; Saved_File_Name := File_Name & ".saved"; |
A string list variable declaration declares a variable whose value is a list of strings. The list may contain any number (zero or more) of strings.
Empty_List := ();
List_With_One_Element := ("-gnaty");
List_With_Two_Elements := List_With_One_Element & "-gnatg";
Long_List := ("main.ada", "pack1_.ada", "pack1.ada", "pack2_.ada"
"pack2.ada", "util_.ada", "util.ada");
|
The same typed variable may not be declared more than once at project level, and it may not be declared more than once in any package; it is in effect a constant or a readonly variable.
The same untyped variable may be declared several times. In this case, the new value replaces the old one, and any subsequent reference to the variable uses the new value. However, as noted above, if a variable has been declared as a string, all subsequent declarations must give it a string value. Similarly, if a variable has been declared as a string list, all subsequent declarations must give it a string list value.
A variable reference may take several forms:
A context may be one of the following:
A variable reference may be used in an expression.
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A project (and its packages) may have attributes that define the project's properties. Some attributes have values that are strings; others have values that are string lists.
There are two categories of attributes: simple attributes and associative arrays (see 10.3.7 Associative Array Attributes).
The names of the attributes are restricted; there is a list of project attributes, and a list of package attributes for each package. The names are not case sensitive.
The project attributes are as follows (all are simple attributes):
| Attribute Name | Value |
Source_Files |
string list |
Source_Dirs |
string list |
Source_List_File |
string |
Object_Dir |
string |
Exec_Dir |
string |
Main |
string list |
Languages |
string list |
Library_Dir |
string |
Library_Name |
string |
Library_Kind |
string |
Library_Elaboration |
string |
Library_Version |
string |
The attributes for package Naming are as follows
(see 10.10 Naming Schemes):
| Attribute Name | Category | Index | Value |
Specification_Suffix |
associative array | language name | string |
Implementation_Suffix |
associative array | language name | string |
Separate_Suffix |
simple attribute | n/a | string |
Casing |
simple attribute | n/a | string |
Dot_Replacement |
simple attribute | n/a | string |
Specification |
associative array | Ada unit name | string |
Implementation |
associative array | Ada unit name | string |
Specification_Exceptions |
associative array | language name | string list |
Implementation_Exceptions |
associative array | language name | string list |
The attributes for package Builder, Compiler, Binder,
Linker, Cross_Reference, and Finder
are as follows (see 10.13.1.1 Switches and Project Files).
| Attribute Name | Category | Index | Value |
Default_Switches |
associative array | language name | string list |
Switches |
associative array | file name | string list |
In addition, package Builder has a single string attribute
Local_Configuration_Pragmas and package Builder has a single
string attribute Global_Configuration_Pragmas.
The attribute for package Glide are not documented: they are for
internal use only.
Each simple attribute has a default value: the empty string (for string-valued attributes) and the empty list (for string list-valued attributes).
Similar to variable declarations, an attribute declaration defines a new value for an attribute.
Examples of simple attribute declarations:
for Object_Dir use "objects";
for Source_Dirs use ("units", "test/drivers");
|
A simple attribute declaration starts with the reserved word for,
followed by the name of the attribute, followed by the reserved word
use, followed by an expression (whose kind depends on the attribute),
followed by a semicolon.
Attributes may be referenced in expressions.
The general form for such a reference is <entity>'<attribute>:
the entity for which the attribute is defined,
followed by an apostrophe, followed by the name of the attribute.
For associative array attributes, a litteral string between parentheses
need to be supplied as index.
Examples are:
project'Object_Dir
Naming'Dot_Replacement
Imported_Project'Source_Dirs
Imported_Project.Naming'Casing
Builder'Default_Switches("Ada")
|
The entity may be:
project for an attribute of the current project
Example:
project Prj is
for Source_Dirs use project'Source_Dirs & "units";
for Source_Dirs use project'Source_Dirs & "test/drivers"
end Prj;
|
In the first attribute declaration, initially the attribute Source_Dirs
has the default value: an empty string list. After this declaration,
Source_Dirs is a string list of one element: "units".
After the second attribute declaration Source_Dirs is a string list of
two elements: "units" and "test/drivers".
Note: this example is for illustration only. In practice, the project file would contain only one attribute declaration:
for Source_Dirs use ("units", "test/drivers");
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Some attributes are defined as associative arrays. An associative array may be regarded as a function that takes a string as a parameter and delivers a string or string list value as its result.
Here are some examples of associative array attribute declarations:
for Implementation ("main") use "Main.ada";
for Switches ("main.ada") use ("-v", "-gnatv");
for Switches ("main.ada") use Builder'Switches ("main.ada") & "-g";
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Like untyped variables and simple attributes, associative array attributes may be declared several times. Each declaration supplies a new value for the attribute, replacing the previous setting.
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case Constructions
A case construction is used in a project file to effect conditional
behavior.
Here is a typical example:
project MyProj is
type OS_Type is ("Linux", "Unix", "NT", "VMS");
OS : OS_Type := external ("OS", "Linux");
package Compiler is
case OS is
when "Linux" | "Unix" =>
for Default_Switches ("Ada") use ("-gnath");
when "NT" =>
for Default_Switches ("Ada") use ("-gnatP");
when others =>
end case;
end Compiler;
end MyProj;
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The syntax of a case construction is based on the Ada case statement
(although there is no null construction for empty alternatives).
Following the reserved word case there is the case variable (a typed
string variable), the reserved word is, and then a sequence of one or
more alternatives.
Each alternative comprises the reserved word when, either a list of
literal strings separated by the "|" character or the reserved word
others, and the "=>" token.
Each literal string must belong to the string type that is the type of the
case variable.
An others alternative, if present, must occur last.
The end case; sequence terminates the case construction.
After each =>, there are zero or more constructions. The only
constructions allowed in a case construction are other case constructions and
attribute declarations. String type declarations, variable declarations and
package declarations are not allowed.
The value of the case variable is often given by an external reference (see 10.7 External References in Project Files).
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10.4.1 Object Directory 10.4.2 Exec Directory 10.4.3 Source Directories 10.4.4 Source File Names
Each project has exactly one object directory and one or more source directories. The source directories must contain at least one source file, unless the project file explicitly specifies that no source files are present (see 10.4.4 Source File Names).
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The object directory for a project is the directory containing the compiler's output (such as `ALI' files and object files) for the project's immediate sources. Note that for inherited sources (when extending a parent project) the parent project's object directory is used.
The object directory is given by the value of the attribute Object_Dir
in the project file.
for Object_Dir use "objects"; |
The attribute Object_Dir has a string value, the path name of the object directory. The path name may be absolute or relative to the directory of the project file. This directory must already exist, and be readable and writable.
By default, when the attribute Object_Dir is not given an explicit value
or when its value is the empty string, the object directory is the same as the
directory containing the project file.
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The exec directory for a project is the directory containing the executables for the project's main subprograms.
The exec directory is given by the value of the attribute Exec_Dir
in the project file.
for Exec_Dir use "executables"; |
The attribute Exec_Dir has a string value, the path name of the exec directory. The path name may be absolute or relative to the directory of the project file. This directory must already exist, and be writable.
By default, when the attribute Exec_Dir is not given an explicit value
or when its value is the empty string, the exec directory is the same as the
object directory of the project file.
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The source directories of a project are specified by the project file
attribute Source_Dirs.
This attribute's value is a string list. If the attribute is not given an explicit value, then there is only one source directory, the one where the project file resides.
A Source_Dirs attribute that is explicitly defined to be the empty list,
as in
for Source_Dirs use (); |
indicates that the project contains no source files.
Otherwise, each string in the string list designates one or more source directories.
for Source_Dirs use ("sources", "test/drivers");
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If a string in the list ends with "/**", then the directory whose path
name precedes the two asterisks, as well as all its subdirectories
(recursively), are source directories.
for Source_Dirs use ("/system/sources/**");
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Here the directory /system/sources and all of its subdirectories
(recursively) are source directories.
To specify that the source directories are the directory of the project file
and all of its subdirectories, you can declare Source_Dirs as follows:
for Source_Dirs use ("./**");
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Each of the source directories must exist and be readable.
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In a project that contains source files, their names may be specified by the
attributes Source_Files (a string list) or Source_List_File
(a string). Source file names never include any directory information.
If the attribute Source_Files is given an explicit value, then each
element of the list is a source file name.
for Source_Files use ("main.adb");
for Source_Files use ("main.adb", "pack1.ads", "pack2.adb");
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If the attribute Source_Files is not given an explicit value,
but the attribute Source_List_File is given a string value,
then the source file names are contained in the text file whose path name
(absolute or relative to the directory of the project file) is the
value of the attribute Source_List_File.
Each line in the file that is not empty or is not a comment contains a source file name. A comment line starts with two hyphens.
for Source_List_File use "source_list.txt"; |
By default, if neither the attribute Source_Files nor the attribute
Source_List_File is given an explicit value, then each file in the
source directories that conforms to the project's naming scheme
(see 10.10 Naming Schemes) is an immediate source of the project.
A warning is issued if both attributes Source_Files and
Source_List_File are given explicit values. In this case, the attribute
Source_Files prevails.
Each source file name must be the name of one and only one existing source file in one of the source directories.
A Source_Files attribute defined with an empty list as its value
indicates that there are no source files in the project.
Except for projects that are clearly specified as containing no Ada source
files (Source_Dirs or Source_Files specified as an empty list,
or Languages specified without "Ada" in the list)
for Source_Dirs use ();
for Source_Files use ();
for Languages use ("C", "C++");
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a project must contain at least one immediate source.
Projects with no source files are useful as template packages
(see 10.8 Packages in Project Files) for other projects; in particular to
define a package Naming (see 10.10 Naming Schemes).
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An immediate source of a project P may depend on source files that are neither immediate sources of P nor in the predefined library. To get this effect, P must import the projects that contain the needed source files.
with "project1", "utilities.gpr";
with "/namings/apex.gpr";
project Main is
...
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As can be seen in this example, the syntax for importing projects is similar
to the syntax for importing compilation units in Ada. However, project files
use literal strings instead of names, and the with clause identifies
project files rather than packages.
Each literal string is the file name or path name (absolute or relative) of a project file. If a string is simply a file name, with no path, then its location is determined by the project path:
ADA_PROJECT_PATH exists, then the project
path includes all the directories in this environment variable, plus the
directory of the project file.
ADA_PROJECT_PATH does not exist,
then the project path contains only one directory, namely the one where
the project file is located.
If a relative pathname is used as in
with "tests/proj"; |
then the path is relative to the directory where the importing project file is located. Any symbolic link will be fully resolved in the directory of the importing project file before the imported project file is looked up.
When the with'ed project file name does not have an extension,
the default is `.gpr'. If a file with this extension is not found, then
the file name as specified in the with clause (no extension) will be
used. In the above example, if a file project1.gpr is found, then it
will be used; otherwise, if a file project1 exists then it will be used;
if neither file exists, this is an error.
A warning is issued if the name of the project file does not match the name of the project; this check is case insensitive.
Any source file that is an immediate source of the imported project can be
used by the immediate sources of the importing project, and recursively. Thus
if A imports B, and B imports C, the immediate
sources of A may depend on the immediate sources of C, even if
A does not import C explicitly. However, this is not recommended,
because if and when B ceases to import C, some sources in
A will no longer compile.
A side effect of this capability is that cyclic dependences are not permitted:
if A imports B (directly or indirectly) then B is not
allowed to import A.
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During development of a large system, it is sometimes necessary to use modified versions of some of the source files without changing the original sources. This can be achieved through a facility known as project extension.
project Modified_Utilities extends "/baseline/utilities.gpr" is ... |
The project file for the project being extended (the parent) is
identified by the literal string that follows the reserved word extends,
which itself follows the name of the extending project (the child).
By default, a child project inherits all the sources of its parent. However, inherited sources can be overridden: a unit with the same name as one in the parent will hide the original unit. Inherited sources are considered to be sources (but not immediate sources) of the child project; see 10.3 Project File Syntax.
An inherited source file retains any switches specified in the parent project.
For example if the project Utilities contains the specification and the
body of an Ada package Util_IO, then the project
Modified_Utilities can contain a new body for package Util_IO.
The original body of Util_IO will not be considered in program builds.
However, the package specification will still be found in the project
Utilities.
A child project can have only one parent but it may import any number of other projects.
A project is not allowed to import directly or indirectly at the same time a child project and any of its ancestors.
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A project file may contain references to external variables; such references are called external references.
An external variable is either defined as part of the environment (an environment variable in Unix, for example) or else specified on the command line via the `-Xvbl=value' switch. If both, then the command line value is used.
An external reference is denoted by the built-in function
external, which returns a string value. This function has two forms:
external (external_variable_name)
external (external_variable_name, default_value)
Each parameter must be a string literal. For example:
external ("USER")
external ("OS", "Linux")
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In the form with one parameter, the function returns the value of the external variable given as parameter. If this name is not present in the environment, then the returned value is an empty string.
In the form with two string parameters, the second parameter is
the value returned when the variable given as the first parameter is not
present in the environment. In the example above, if "OS" is not
the name of an environment variable and is not passed on the command line,
then the returned value will be "Linux".
An external reference may be part of a string expression or of a string list expression, to define variables or attributes.
type Mode_Type is ("Debug", "Release");
Mode : Mode_Type := external ("MODE");
case Mode is
when "Debug" =>
...
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The package is the project file feature that defines the settings for project-aware tools. For each such tool you can declare a corresponding package; the names for these packages are preset (see 10.3.2 Packages) but are not case sensitive. A package may contain variable declarations, attribute declarations, and case constructions.
project Proj is
package Builder is -- used by gnatmake
for Default_Switches ("Ada") use ("-v", "-g");
end Builder;
end Proj;
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A package declaration starts with the reserved word package,
followed by the package name (case insensitive), followed by the reserved word
is. It ends with the reserved word end, followed by the package
name, finally followed by a semi-colon.
Most of the packages have an attribute Default_Switches.
This attribute is an associative array, and its value is a string list.
The index of the associative array is the name of a programming language (case
insensitive). This attribute indicates the switch or switches to be used
with the corresponding tool.
Some packages also have another attribute, Switches, an associative
array whose value is a string list. The index is the name of a source file.
This attribute indicates the switch or switches to be used by the corresponding
tool when dealing with this specific file.
Further information on these switch-related attributes is found in 10.13.1.1 Switches and Project Files.
A package may be declared as a renaming of another package; e.g., from the project file for an imported project.
with "/global/apex.gpr";
project Example is
package Naming renames Apex.Naming;
...
end Example;
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Packages that are renamed in other project files often come from project files that have no sources: they are just used as templates. Any modification in the template will be reflected automatically in all the project files that rename a package from the template.
In addition to the tool-oriented packages, you can also declare a package
named Naming to establish specialized source file naming conventions
(see 10.10 Naming Schemes).
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An attribute or variable defined in an imported or parent project can be used in expressions in the importing / extending project. Such an attribute or variable is prefixed with the name of the project and (if relevant) the name of package where it is defined.
with "imported";
project Main extends "base" is
Var1 := Imported.Var;
Var2 := Base.Var & ".new";
package Builder is
for Default_Switches ("Ada") use Imported.Builder.Ada_Switches &
"-gnatg" & "-v";
end Builder;
package Compiler is
for Default_Switches ("Ada") use Base.Compiler.Ada_Switches;
end Compiler;
end Main;
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In this example:
Var1 is a copy of the variable Var defined in the project file
`"imported.gpr"'
Var2 is a copy of the value of variable Var
defined in the project file `base.gpr', concatenated with ".new"
Default_Switches ("Ada") in package Builder
is a string list that includes in its value a copy of variable
Ada_Switches defined in the Builder package in project file
`imported.gpr' plus two new elements: `"-gnatg"' and `"-v"';
Default_Switches ("Ada") in package Compiler
is a copy of the variable Ada_Switches defined in the Compiler
package in project file `base.gpr', the project being extended.
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Sometimes an Ada software system is ported from a foreign compilation
environment to GNAT, with file names that do not use the default GNAT
conventions. Instead of changing all the file names (which for a variety of
reasons might not be possible), you can define the relevant file naming scheme
in the Naming package in your project file. For example, the following
package models the Apex file naming rules:
package Naming is
for Casing use "lowercase";
for Dot_Replacement use ".";
for Specification_Suffix ("Ada") use ".1.ada";
for Implementation_Suffix ("Ada") use ".2.ada";
end Naming;
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You can define the following attributes in package Naming:
Casing
"lowercase",
"uppercase" or "mixedcase"; these strings are case insensitive.
If Casing is not specified, then the default is "lowercase".
Dot_Replacement
'.' except if it the entire string is "."
If Dot_Replacement is not specified, then the default is "-".
Specification_Suffix
Specification_Suffix ("Ada") is not specified, then the default is
".ads".
Implementation_Suffix
Specification_Suffix
Implementation_Suffix ("Ada") is not specified, then the default is
".adb".
Separate_Suffix
Implementation_Suffix.
If Separate_Suffix ("Ada") is not specified, then it defaults to same
value as Implementation_Suffix ("Ada").
Specification
Specification attribute, an associative array, to define
the source file name for an individual Ada compilation unit's spec. The array
index must be a string literal that identifies the Ada unit (case insensitive).
The value of this attribute must be a string that identifies the file that
contains this unit's spec (case sensitive or insensitive depending on the
operating system).
for Specification ("MyPack.MyChild") use "mypack.mychild.spec";
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Implementation
You can use the Implementation attribute, an associative array, to
define the source file name for an individual Ada compilation unit's body
(possibly a subunit). The array index must be a string literal that identifies
the Ada unit (case insensitive). The value of this attribute must be a string
that identifies the file that contains this unit's body or subunit (case
sensitive or insensitive depending on the operating system).
for Implementation ("MyPack.MyChild") use "mypack.mychild.body";
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Library projects are projects whose object code is placed in a library. (Note that this facility is not yet supported on all platforms)
To create a library project, you need to define in its project file
two project-level attributes: Library_Name and Library_Dir.
Additionally, you may define the library-related attributes
Library_Kind, Library_Version and Library_Elaboration.
The Library_Name attribute has a string value that must start with a
letter and include only letters and digits.
The Library_Dir attribute has a string value that designates the path
(absolute or relative) of the directory where the library will reside.
It must designate an existing directory, and this directory needs to be
different from the project's object directory. It also needs to be writable.
If both Library_Name and Library_Dir are specified and
are legal, then the project file defines a library project. The optional
library-related attributes are checked only for such project files.
The Library_Kind attribute has a string value that must be one of the
following (case insensitive): "static", "dynamic" or
"relocatable". If this attribute is not specified, the library is a
static library. Otherwise, the library may be dynamic or relocatable.
Depending on the operating system, there may or may not be a distinction
between dynamic and relocatable libraries. For example, on Unix there is no
such distinction.
The Library_Version attribute has a string value whose interpretation
is platform dependent. On Unix, it is used only for dynamic/relocatable
libraries as the internal name of the library (the "soname"). If the
library file name (built from the Library_Name) is different from the
Library_Version, then the library file will be a symbolic link to the
actual file whose name will be Library_Version.
Example (on Unix):
project Plib is Version := "1"; for Library_Dir use "lib_dir"; for Library_Name use "dummy"; for Library_Kind use "relocatable"; for Library_Version use "libdummy.so." & Version; end Plib; |
Directory `lib_dir' will contain the internal library file whose name will be `libdummy.so.1', and `libdummy.so' will be a symbolic link to `libdummy.so.1'.
When gnatmake detects that a project file (not the main project file)
is a library project file, it will check all immediate sources of the project
and rebuild the library if any of the sources have been recompiled.
All `ALI' files will also be copied from the object directory to the
library directory. To build executables, gnatmake will use the
library rather than the individual object files.
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The following switches are used by GNAT tools that support project files:
`-Pproject'
There must be only one `-P' switch on the command line.
Since the Project Manager parses the project file only after all the switches on the command line are checked, the order of the switches `-P', `-Vpx' or `-X' is not significant.
`-Xname=value'
external(name) when parsing the project file.
If name or value includes a space, then name=value should be put between quotes.
-XOS=NT -X"user=John Doe" |
Several `-X' switches can be used simultaneously. If several `-X' switches specify the same name, only the last one is used.
An external variable specified with a `-X' switch takes precedence over the value of the same name in the environment.
`-vPx'
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10.13.1 gnatmake and Project Files 10.13.2 The GNAT Driver and Project Files 10.13.3 Glide and Project Files
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This section covers two topics related to gnatmake and project files:
defining switches for gnatmake and for the tools that it invokes;
and the use of the Main attribute.
10.13.1.1 Switches and Project Files 10.13.1.2 Project Files and Main Subprograms
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For each of the packages Builder, Compiler, Binder, and
Linker, you can specify a Default_Switches attribute, a
Switches attribute, or both; as their names imply, these switch-related
attributes affect which switches are used for which files when
gnatmake is invoked. As will be explained below, these
package-contributed switches precede the switches passed on the
gnatmake command line.
The Default_Switches attribute is an associative array indexed by
language name (case insensitive) and returning a string list. For example:
package Compiler is
for Default_Switches ("Ada") use ("-gnaty", "-v");
end Compiler;
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The Switches attribute is also an associative array, indexed by a file
name (which may or may not be case sensitive, depending on the operating
system) and returning a string list. For example:
package Builder is
for Switches ("main1.adb") use ("-O2");
for Switches ("main2.adb") use ("-g");
end Builder;
|
For the Builder package, the file names should designate source files
for main subprograms. For the Binder and Linker packages, the
file names should designate `ALI' or source files for main subprograms.
In each case just the file name (without explicit extension) is acceptable.
For each tool used in a program build (gnatmake, the compiler, the
binder, and the linker), its corresponding package contributes a set of
switches for each file on which the tool is invoked, based on the
switch-related attributes defined in the package. In particular, the switches
that each of these packages contributes for a given file f comprise:
Switches (f), if it is specified in the
package for the given file,
Default_Switches ("Ada"), if it is specified in
the package.
If neither of these attributes is defined in the package, then the package does not contribute any switches for the given file.
When gnatmake is invoked on a file, the switches comprise two sets,
in the following order: those contributed for the file by the Builder
package; and the switches passed on the command line.
When gnatmake invokes a tool (compiler, binder, linker) on a file,
the switches passed to the tool comprise three sets, in the following order:
Builder package
in the project file supplied on the command line;
The term applicable switches reflects the fact that gnatmake
switches may or may not be passed to individual tools, depending on the
individual switch.
gnatmake may invoke the compiler on source files from different
projects. The Project Manager will use the appropriate project file to
determine the Compiler package for each source file being compiled.
Likewise for the Binder and Linker packages.
As an example, consider the following package in a project file:
project Proj1 is
package Compiler is
for Default_Switches ("Ada") use ("-g");
for Switches ("a.adb") use ("-O1");
for Switches ("b.adb") use ("-O2", "-gnaty");
end Compiler;
end Proj1;
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If gnatmake is invoked with this project file, and it needs to
compile, say, the files `a.adb', `b.adb', and `c.adb', then
`a.adb' will be compiled with the switch `-O1', `b.adb'
with switches `-O2' and `-gnaty', and `c.adb' with
`-g'.
Another example illustrates the ordering of the switches contributed by different packages:
project Proj2 is
package Builder is
for Switches ("main.adb") use ("-g", "-O1", "-f");
end Builder;
package Compiler is
for Switches ("main.adb") use ("-O2");
end Compiler;
end Proj2;
|
If you issue the command:
gnatmake -PProj2 -O0 main |
then the compiler will be invoked on `main.adb' with the following sequence of switches
-g -O1 -O2 -O0 |
with the last `-O' switch having precedence over the earlier ones; several other switches (such as `-c') are added implicitly.
The switches `-g' and `-O1' are contributed by package
Builder, `-O2' is contributed by the package Compiler
and `-O0' comes from the command line.
The `-g' switch will also be passed in the invocation of
gnatlink.
A final example illustrates switch contributions from packages in different project files:
project Proj3 is
for Source_Files use ("pack.ads", "pack.adb");
package Compiler is
for Default_Switches ("Ada") use ("-gnata");
end Compiler;
end Proj3;
with "Proj3";
project Proj4 is
for Source_Files use ("foo_main.adb", "bar_main.adb");
package Builder is
for Switches ("foo_main.adb") use ("-s", "-g");
end Builder;
end Proj4;
-- Ada source file:
with Pack;
procedure Foo_Main is
...
end Foo_Main;
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If the command is
gnatmake -PProj4 foo_main.adb -cargs -gnato |
then the switches passed to the compiler for `foo_main.adb' are
`-g' (contributed by the package Proj4.Builder) and
`-gnato' (passed on the command line).
When the imported package Pack is compiled, the switches used are
`-g' from Proj4.Builder, `-gnata' (contributed from
package Proj3.Compiler, and `-gnato' from the command line.
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When using a project file, you can invoke gnatmake
with several main subprograms, by specifying their source files on the command
line. Each of these needs to be an immediate source file of the project.
gnatmake -Pprj main1 main2 main3 |
When using a project file, you can also invoke gnatmake without
explicitly specifying any main, and the effect depends on whether you have
defined the Main attribute. This attribute has a string list value,
where each element in the list is the name of a source file (the file
extension is optional) containing a main subprogram.
If the Main attribute is defined in a project file as a non-empty
string list and the switch `-u' is not used on the command line, then
invoking gnatmake with this project file but without any main on the
command line is equivalent to invoking gnatmake with all the file
names in the Main attribute on the command line.
Example:
project Prj is
for Main use ("main1", "main2", "main3");
end Prj;
|
With this project file, "gnatmake -Pprj" is equivalent to
"gnatmake -Pprj main1 main2 main3".
When the project attribute Main is not specified, or is specified
as an empty string list, or when the switch `-u' is used on the command
line, then invoking gnatmake with no main on the command line will
result in all immediate sources of the project file being checked, and
potentially recompiled. Depending on the presence of the switch `-u',
sources from other project files on which the immediate sources of the main
project file depend are also checked and potentially recompiled. In other
words, the `-u' switch is applied to all of the immediate sources of themain project file.
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A number of GNAT tools, other than gnatmake are project-aware:
gnatbind, gnatfind, gnatlink, gnatls
and gnatxref. However, none of these tools can be invoked directly
with a project file switch (-P). They need to be invoke through the
gnat driver.
The gnat driver is a front-end that accepts a number of commands and
call the corresponding tool. It has been designed initially for VMS to convert
VMS style qualifiers to Unix style switches, but it is now available to all
the GNAT supported platforms.
On non VMS platforms, the gnat driver accepts the following commands
(case insensitive):
gnatbind
gnatchop
gnatelim
gnatfind
gnatkr
gnatlink
gnatls
gnatmake
gnatname
gnatprep
gnatpsta
gnatstub
gnatxref
Note that the compiler is invoked using the command gnatmake -f -u.
Following the command, you may put switches and arguments for the invoked tool.
gnat bind -C main.ali gnat ls -a main gnat chop foo.txt |
In addition, for command BIND, FIND, LS or LIST, LINK and XREF, the project
file related switches (-P, -X and -vPx) may be used in
addition to the switches of the invoking tool.
For each of these command, there is possibly a package in the main project that corresponds to the invoked tool.
Binder for command BIND (invoking gnatbind)
Finder for command FIND (invoking gnatfind)
Gnatls for command LS or LIST (invoking gnatls)
Linker for command LINK (invoking gnatlink)
Cross_Reference for command XREF (invoking gnatlink)
Package Gnatls has a unique attribute Switches, a simple variable
with a string list value. It contains switches for the invocation of
gnatls.
project Proj1 is
package gnatls is
for Switches use ("-a", "-v");
end gnatls;
end Proj1;
|
All other packages contains a switch Default_Switches, an associative
array, indexed by the programming language (case insensitive) and having a
string list value. Default_Switches ("Ada") contains the switches for
the invocation of the tool corresponding to the package.
project Proj is
for Source_Dirs use ("./**");
package gnatls is
for Switches use ("-a", "-v");
end gnatls;
package Binder is
for Default_Switches ("Ada") use ("-C", "-e");
end Binder;
package Linker is
for Default_Switches ("Ada") use ("-C");
end Linker;
package Finder is
for Default_Switches ("Ada") use ("-a", "-f");
end Finder;
package Cross_Reference is
for Default_Switches ("Ada") use ("-a", "-f", "-d", "-u");
end Cross_Reference;
end Proj;
|
With the above project file, commands such as
gnat ls -Pproj main gnat xref -Pproj main gnat bind -Pproj main.ali |
will set up the environment properly and invoke the tool with the switches found in the package corresponding to the tool.
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Glide will automatically recognize the `.gpr' extension for
project files, and will
convert them to its own internal format automatically. However, it
doesn't provide a syntax-oriented editor for modifying these
files.
The project file will be loaded as text when you select the menu item
Ada => Project => Edit.
You can edit this text and save the `gpr' file;
when you next select this project file in Glide it
will be automatically reloaded.
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Suppose that we have two programs, prog1 and prog2, with the sources
in the respective directories. We would like to build them with a single
gnatmake command, and we would like to place their object files into
`.build' subdirectories of the source directories. Furthermore, we would
like to have to have two separate subdirectories in `.build' --
`release' and `debug' -- which will contain the object files compiled with
different set of compilation flags.
In other words, we have the following structure:
main
|- prog1
| |- .build
| | debug
| | release
|- prog2
|- .build
| debug
| release
|
Here are the project files that we need to create in a directory `main' to maintain this structure:
Common project with a package Compiler that
specifies the compilation switches:
File "common.gpr":
project Common is
for Source_Dirs use (); -- No source files
type Build_Type is ("release", "debug");
Build : Build_Type := External ("BUILD", "debug");
package Compiler is
case Build is
when "release" =>
for Default_Switches ("Ada") use ("-O2");
when "debug" =>
for Default_Switches ("Ada") use ("-g");
end case;
end Compiler;
end Common;
|
File "prog1.gpr":
with "common";
project Prog1 is
for Source_Dirs use ("prog1");
for Object_Dir use "prog1/.build/" & Common.Build;
package Compiler renames Common.Compiler;
end Prog1;
|
File "prog2.gpr":
with "common";
project Prog2 is
for Source_Dirs use ("prog2");
for Object_Dir use "prog2/.build/" & Common.Build;
package Compiler renames Common.Compiler;
end Prog2;
|
File "main.gpr": with "common"; with "prog1"; with "prog2"; project Main is package Compiler renames Common.Compiler; end Main; |
withs (either
explicitly or implicitly) all the sources of our two programs.
Now we can build the programs using the command
gnatmake -Pmain dummy |
for the Debug mode, or
gnatmake -Pmain -XBUILD=release |
for the Release mode.
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project ::=
context_clause project_declaration
context_clause ::=
{with_clause}
with_clause ::=
with literal_string { , literal_string } ;
project_declaration ::=
project <project_>simple_name [ extends literal_string ] is
{declarative_item}
end <project_>simple_name;
declarative_item ::=
package_declaration |
typed_string_declaration |
other_declarative_item
package_declaration ::=
package <package_>simple_name package_completion
package_completion ::=
package_body | package_renaming
package body ::=
is
{other_declarative_item}
end <package_>simple_name ;
package_renaming ::==
renames <project_>simple_name.<package_>simple_name ;
typed_string_declaration ::=
type <typed_string_>_simple_name is
( literal_string {, literal_string} );
other_declarative_item ::=
attribute_declaration |
typed_variable_declaration |
variable_declaration |
case_construction
attribute_declaration ::=
for attribute use expression ;
attribute ::=
<simple_attribute_>simple_name |
<associative_array_attribute_>simple_name ( literal_string )
typed_variable_declaration ::=
<typed_variable_>simple_name : <typed_string_>name := string_expression ;
variable_declaration ::=
<variable_>simple_name := expression;
expression ::=
term {& term}
term ::=
literal_string |
string_list |
<variable_>name |
external_value |
attribute_reference
literal_string ::=
(same as Ada)
string_list ::=
( <string_>expression { , <string_>expression } )
external_value ::=
external ( literal_string [, literal_string] )
attribute_reference ::=
attribute_parent ' <simple_attribute_>simple_name [ ( literal_string ) ]
attribute_parent ::=
project |
<project_or_package>simple_name |
<project_>simple_name . <package_>simple_name
case_construction ::=
case <typed_variable_>name is
{case_item}
end case ;
case_item ::=
when discrete_choice_list => {case_construction | attribute_declaration}
discrete_choice_list ::=
literal_string {| literal_string}
name ::=
simple_name {. simple_name}
simple_name ::=
identifier (same as Ada)
|
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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.
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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:
Sqrt_Half : Float := Sqrt (0.5); |
BEGIN-END section at the outer level of a package body is
executed as part of the package body elaboration code.
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 a series of elaboration code sections, 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.
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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:
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.
Program_Error) is raised.
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:
Program_Error is raised.
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.
Note that one might think that it would be good enough to have one Boolean
variable for each package, but that would not deal with cases of trying
to call a body in the same package as the call
that has not been elaborated yet.
Of course a compiler may be able to do enough analysis to optimize away
some of the Boolean variables as unnecessary, and GNAT indeed
does such optimizations, but still the easiest conceptual model is to
think of there being one variable per subprogram.
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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:
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
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 situations 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:
with clause,
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.
Unit A |
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 or Preelaborate, then the client should have
a pragma 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:
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.
Program_Error will be raised
when the program is run.
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.
You may have noticed that the above discussion did not mention
the use of Elaborate_Body. This was a deliberate omission. If you
with an Elaborate_Body unit, it still may be the case that
code in the body makes calls to some other unit, so it is still necessary
to use Elaborate_All on such units.
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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:
-gnatws switch set
Elaboration_Checks for the called subprogram
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.
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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
by default
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.
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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:
with'ed unit, or instantiate a generic unit
in a with'ed unit, then if the with'ed unit
does not have pragma Pure or
Preelaborate, 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.
This default mode is more restrictive than the Ada Reference Manual, and it is possible to construct programs which will compile using the dynamic model described there, but will run into a circularity using the safer static model we have described.
Of course any Ada compiler must be able to operate in a mode consistent with the requirements of the Ada Reference Manual, and in particular must have the capability of implementing the standard dynamic model of elaboration with run-time checks.
In GNAT, this standard mode can be achieved either by the use of
the -gnatE switch on the compiler (gcc or gnatmake)
command, or by the use of the configuration pragma:
pragma Elaboration_Checks (RM); |
Either approach will cause the unit affected to be compiled using the standard dynamic run-time elaboration checks described in the Ada Reference Manual. The static model is generally preferable, since it is clearly safer to rely on compile and link time checks rather than run-time checks. However, in the case of legacy code, it may be difficult to meet the requirements of the static model. This issue is further discussed in 11.9 What to Do If the Default Elaboration Behavior Fails.
Note that the static model provides a strict subset of the allowed behavior and programs of the Ada Reference Manual, so if you do adhere to the static model and no circularities exist, then you are assured that your program will work using the dynamic model.
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In this section we examine special elaboration issues that arise for programs that declare library level tasks.
Generally the model of execution of an Ada program is that all units are elaborated, and then execution of the program starts. However, the declaration of library tasks definitely does not fit this model. The reason for this is that library tasks start as soon as they are declared (more precisely, as soon as the statement part of the enclosing package body is reached), that is to say before elaboration of the program is complete. This means that if such a task calls a subprogram, or an entry in another task, the callee may or may not be elaborated yet, and in the standard Reference Manual model of dynamic elaboration checks, you can even get timing dependent Program_Error exceptions, since there can be a race between the elaboration code and the task code.
The static model of elaboration in GNAT seeks to avoid all such dynamic behavior, by being conservative, and the conservative approach in this particular case is to assume that all the code in a task body is potentially executed at elaboration time if a task is declared at the library level.
This can definitely result in unexpected circularities. Consider the following example
package Decls is
task Lib_Task is
entry Start;
end Lib_Task;
type My_Int is new Integer;
function Ident (M : My_Int) return My_Int;
end Decls;
with Utils;
package body Decls is
task body Lib_Task is
begin
accept Start;
Utils.Put_Val (2);
end Lib_Task;
function Ident (M : My_Int) return My_Int is
begin
return M;
end Ident;
end Decls;
with Decls;
package Utils is
procedure Put_Val (Arg : Decls.My_Int);
end Utils;
with Text_IO;
package body Utils is
procedure Put_Val (Arg : Decls.My_Int) is
begin
Text_IO.Put_Line (Decls.My_Int'Image (Decls.Ident (Arg)));
end Put_Val;
end Utils;
with Decls;
procedure Main is
begin
Decls.Lib_Task.Start;
end;
|
If the above example is compiled in the default static elaboration
mode, then a circularity occurs. The circularity comes from the call
Utils.Put_Val in the task body of Decls.Lib_Task. Since
this call occurs in elaboration code, we need an implicit pragma
Elaborate_All for Utils. This means that not only must
the spec and body of Utils be elaborated before the body
of Decls, but also the spec and body of any unit that is
with'ed by the body of Utils must also be elaborated before
the body of Decls. This is the transitive implication of
pragma Elaborate_All and it makes sense, because in general
the body of Put_Val might have a call to something in a
with'ed unit.
In this case, the body of Utils (actually its spec) with's
Decls. Unfortunately this means that the body of Decls
must be elaborated before itself, in case there is a call from the
body of Utils.
Here is the exact chain of events we are worrying about:
Decls a call is made from within the body of a library
task to a subprogram in the package Utils. Since this call may
occur at elaboration time (given that the task is activated at elaboration
time), we have to assume the worst, i.e. that the
call does happen at elaboration time.
Util must be elaborated before
the body of Decls so that this call does not cause an access before
elaboration.
Util, specifically within the body of
Util.Put_Val there may be calls to any unit with'ed
by this package.
with'ed package is package Decls, so there
might be a call to a subprogram in Decls in Put_Val.
In fact there is such a call in this example, but we would have to
assume that there was such a call even if it were not there, since
we are not supposed to write the body of Decls knowing what
is in the body of Utils; certainly in the case of the
static elaboration model, the compiler does not know what is in
other bodies and must assume the worst.
Decls must also be
elaborated before we elaborate the unit containing the call, but
that unit is Decls! This means that the body of Decls
must be elaborated before itself, and that's a circularity.
Indeed, if you add an explicit pragma Elaborate_All for Utils in
the body of Decls you will get a true Ada Reference Manual
circularity that makes the program illegal.
In practice, we have found that problems with the static model of elaboration in existing code often arise from library tasks, so we must address this particular situation.
Note that if we compile and run the program above, using the dynamic model of
elaboration (that is to say use the -gnatE switch),
then it compiles, binds,
links, and runs, printing the expected result of 2. Therefore in some sense
the circularity here is only apparent, and we need to capture
the properties of this program that distinguish it from other library-level
tasks that have real elaboration problems.
We have four possible answers to this question:
If we use the -gnatE switch, then as noted above, the program works.
Why is this? If we examine the task body, it is apparent that the task cannot
proceed past the
accept statement until after elaboration has been completed, because
the corresponding entry call comes from the main program, not earlier.
This is why the dynamic model works here. But that's really giving
up on a precise analysis, and we prefer to take this approach only if we cannot
solve the
problem in any other manner. So let us examine two ways to reorganize
the program to avoid the potential elaboration problem.
Write separate packages, so that library tasks are isolated from other declarations as much as possible. Let us look at a variation on the above program.
package Decls1 is
task Lib_Task is
entry Start;
end Lib_Task;
end Decls1;
with Utils;
package body Decls1 is
task body Lib_Task is
begin
accept Start;
Utils.Put_Val (2);
end Lib_Task;
end Decls1;
package Decls2 is
type My_Int is new Integer;
function Ident (M : My_Int) return My_Int;
end Decls2;
with Utils;
package body Decls2 is
function Ident (M : My_Int) return My_Int is
begin
return M;
end Ident;
end Decls2;
with Decls2;
package Utils is
procedure Put_Val (Arg : Decls2.My_Int);
end Utils;
with Text_IO;
package body Utils is
procedure Put_Val (Arg : Decls2.My_Int) is
begin
Text_IO.Put_Line (Decls2.My_Int'Image (Decls2.Ident (Arg)));
end Put_Val;
end Utils;
with Decls1;
procedure Main is
begin
Decls1.Lib_Task.Start;
end;
|
All we have done is to split Decls into two packages, one
containing the library task, and one containing everything else. Now
there is no cycle, and the program compiles, binds, links and executes
using the default static model of elaboration.
A significant part of the problem arises because of the use of the single task declaration form. This means that the elaboration of the task type, and the elaboration of the task itself (i.e. the creation of the task) happen at the same time. A good rule of style in Ada 95 is to always create explicit task types. By following the additional step of placing task objects in separate packages from the task type declaration, many elaboration problems are avoided. Here is another modified example of the example program:
package Decls is
task type Lib_Task_Type is
entry Start;
end Lib_Task_Type;
type My_Int is new Integer;
function Ident (M : My_Int) return My_Int;
end Decls;
with Utils;
package body Decls is
task body Lib_Task_Type is
begin
accept Start;
Utils.Put_Val (2);
end Lib_Task_Type;
function Ident (M : My_Int) return My_Int is
begin
return M;
end Ident;
end Decls;
with Decls;
package Utils is
procedure Put_Val (Arg : Decls.My_Int);
end Utils;
with Text_IO;
package body Utils is
procedure Put_Val (Arg : Decls.My_Int) is
begin
Text_IO.Put_Line (Decls.My_Int'Image (Decls.Ident (Arg)));
end Put_Val;
end Utils;
with Decls;
package Declst is
Lib_Task : Decls.Lib_Task_Type;
end Declst;
with Declst;
procedure Main is
begin
Declst.Lib_Task.Start;
end;
|
What we have done here is to replace the task declaration in
package Decls with a task type declaration. Then we
introduce a separate package Declst to contain the actual
task object. This separates the elaboration issues for
the task type
declaration, which causes no trouble, from the elaboration issues
of the task object, which is also unproblematic, since it is now independent
of the elaboration of Utils.
This separation of concerns also corresponds to
a generally sound engineering principle of separating declarations
from instances. This version of the program also compiles, binds, links,
and executes, generating the expected output.
The previous two approaches described how a program can be restructured to avoid the special problems caused by library task bodies. in practice, however, such restructuring may be difficult to apply to existing legacy code, so we must consider solutions that do not require massive rewriting.
Let us consider more carefully why our original sample program works
under the dynamic model of elaboration. The reason is that the code
in the task body blocks immediately on the accept
statement. Now of course there is nothing to prohibit elaboration
code from making entry calls (for example from another library level task),
so we cannot tell in isolation that
the task will not execute the accept statement during elaboration.
However, in practice it is very unusual to see elaboration code
make any entry calls, and the pattern of tasks starting
at elaboration time and then immediately blocking on accept or
select statements is very common. What this means is that
the compiler is being too pessimistic when it analyzes the
whole package body as though it might be executed at elaboration
time.
If we know that the elaboration code contains no entry calls, (a very safe assumption most of the time, that could almost be made the default behavior), then we can compile all units of the program under control of the following configuration pragma:
pragma Restrictions (No_Entry_Calls_In_Elaboration_Code); |
This pragma can be placed in the `gnat.adc' file in the usual
manner. If we take our original unmodified program and compile it
in the presence of a `gnat.adc' containing the above pragma,
then once again, we can compile, bind, link, and execute, obtaining
the expected result. In the presence of this pragma, the compiler does
not trace calls in a task body, that appear after the first accept
or select statement, and therefore does not report a potential
circularity in the original program.
The compiler will check to the extent it can that the above restriction is not violated, but it is not always possible to do a complete check at compile time, so it is important to use this pragma only if the stated restriction is in fact met, that is to say no task receives an entry call before elaboration of all units is completed.
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The basic rule is that a unit compiled with the static model cannot
be with'ed by a unit compiled with the dynamic model. The
reason for this is that in the static model, a unit assumes that
its clients guarantee to use (the equivalent of) pragma
Elaborate_All so that no elaboration checks are required
in inner subprograms, and this assumption is violated if the
client is compiled with dynamic checks.
The precise rule is as follows. A unit that is compiled with dynamic
checks can only with a unit that meets at least one of the
following criteria:
with'ed unit is itself compiled with dynamic elaboration
checks (that is with the -gnatE switch.
with'ed unit is an internal GNAT implementation unit from
the System, Interfaces, Ada, or GNAT hierarchies.
with'ed unit has pragma Preelaborate or pragma Pure.
with'ing unit (that is the client) has an explicit pragma
Elaborate_All for the with'ed unit.
If this rule is violated, that is if a unit with dynamic elaboration
checks with's a unit that does not meet one of the above four
criteria, then the binder (gnatbind) will issue a warning
similar to that in the following example:
warning: "x.ads" has dynamic elaboration checks and with's warning: "y.ads" which has static elaboration checks |
These warnings indicate that the rule has been violated, and that as a result
elaboration checks may be missed in the resulting executable file.
This warning may be suppressed using the -ws binder switch
in the usual manner.
One useful application of this mixing rule is in the case of a subsystem
which does not itself with units from the remainder of the
application. In this case, the entire subsystem can be compiled with
dynamic checks to resolve a circularity in the subsystem, while
allowing the main application that uses this subsystem to be compiled
using the more reliable default static model.
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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.
-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 (Elaboration_Checks) to suppress all such checks. For
example this pragma could be placed in the `gnat.adc' file.
Suppress (Elaboration_Check) can
be used with different granularity to suppress warnings and break
elaboration circularities:
These four cases are listed in order of decreasing safety, and therefore require increasing programmer care in their application. Consider the following program:
package Pack1 is
function F1 return Integer;
X1 : Integer;
end Pack1;
package Pack2 is
function F2 return Integer;
function Pure (x : integer) return integer;
-- pragma Suppress (Elaboration_Check, On => Pure); -- (3)
-- pragma Suppress (Elaboration_Check); -- (4)
end Pack2;
with Pack2;
package body Pack1 is
function F1 return Integer is
begin
return 100;
end F1;
Val : integer := Pack2.Pure (11); -- Elab. call (1)
begin
declare
-- pragma Suppress(Elaboration_Check, Pack2.F2); -- (1)
-- pragma Suppress(Elaboration_Check); -- (2)
begin
X1 := Pack2.F2 + 1; -- Elab. call (2)
end;
end Pack1;
with Pack1;
package body Pack2 is
function F2 return Integer is
begin
return Pack1.F1;
end F2;
function Pure (x : integer) return integer is
begin
return x ** 3 - 3 * x;
end;
end Pack2;
with Pack1, Ada.Text_IO;
procedure Proc3 is
begin
Ada.Text_IO.Put_Line(Pack1.X1'Img); -- 101
end Proc3;
|
error: elaboration circularity detected info: "pack1 (body)" must be elaborated before "pack1 (body)" info: reason: Elaborate_All probably needed in unit "pack1 (body)" info: recompile "pack1 (body)" with -gnatwl for full details info: "pack1 (body)" info: must be elaborated along with its spec: info: "pack1 (spec)" info: which is withed by: info: "pack2 (body)" info: which must be elaborated along with its spec: info: "pack2 (spec)" info: which is withed by: info: "pack1 (body)" |
Pack2.Pure and
Pack2.F2 in the body of Pack1. We can see that the call to
F2 is safe, even though F2 calls F1, because the call appears after the
elaboration of the body of F1. Therefore the pragma (1) is safe, and will
remove the warning on the call. It is also possible to use pragma (2)
because there are no other potentially unsafe calls in the block.
The call to Pure is safe because this function does not depend on the
state of Pack2. Therefore any call to this function is safe, and it
is correct to place pragma (3) in the corresponding package spec.
Finally, we could place pragma (4) in the spec of Pack2 to disable
warnings on all calls to functions declared therein. Note that this is not
necessarily safe, and requires more detailed examination of the subprogram
bodies involved. In particular, a call to F2 requires that F1
be already elaborated.
It is hard to generalize on which of these four 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
but the danger in this 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
-p (pessimistic 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.)
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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
(i.e., the evaluation of P'Access for a subprogram P),
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.
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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,
and, if you are sure there really are no elaboration problems,
use a global pragma Suppress (Elaboration_Checks).
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The purpose of the elaboration rules in the Ada Reference Manual is to make sure that no entity is accessed before it has been elaborated. For a subprogram, this means that the spec and body must have been elaborated before the subprogram is called. For an object, this means that the object must have been elaborated before its value is read or written. A violation of either of these two requirements is an access before elaboration order, and this section has been all about avoiding such errors.
In the case where more than one order of elaboration is possible, in the sense that access before elaboration errors are avoided, then any one of the orders is "correct" in the sense that it meets the requirements of the Ada Reference Manual, and no such error occurs.
However, it may be the case for a given program, that there are constraints on the order of elaboration that come not from consideration of avoiding elaboration errors, but rather from extra-lingual logic requirements. Consider this example:
with Init_Constants; package Constants is X : Integer := 0; Y : Integer := 0; end Constants; package Init_Constants is procedure Calc; end Init_Constants; with Constants; package body Init_Constants is procedure Calc is begin null; end; begin Constants.X := 3; Constants.Y := 4; end Init_Constants; with Constants; package Calc is Z : Integer := Constants.X + Constants.Y; end Calc; with Calc; with Text_IO; use Text_IO; procedure Main is begin Put_Line (Calc.Z'Img); end Main; |
In this example, there is more than one valid order of elaboration. For example both the following are correct orders:
Init_Constants spec Constants spec Calc spec Main body Init_Constants body and Init_Constants spec Init_Constants body Constants spec Calc spec Main body |
There is no language rule to prefer one or the other, both are correct
from an order of elaboration point of view. But the programmatic effects
of the two orders are very different. In the first, the elaboration routine
of Calc initializes Z to zero, and then the main program
runs with this value of zero. But in the second order, the elaboration
routine of Calc runs after the body of Init_Constants has set
X and Y and thus Z is set to 7 before Main
runs.
One could perhaps by applying pretty clever non-artificial intelligence to the situation guess that it is more likely that the second order of elaboration is the one desired, but there is no formal linguistic reason to prefer one over the other. In fact in this particular case, GNAT will prefer the second order, because of the rule that bodies are elaborated as soon as possible, but it's just luck that this is what was wanted (if indeed the second order was preferred).
If the program cares about the order of elaboration routines in a case like this, it is important to specify the order required. In this particular case, that could have been achieved by adding to the spec of Calc:
pragma Elaborate_All (Constants); |
which requires that the body (if any) and spec of Constants,
as well as the body and spec of any unit with'ed by
Constants be elaborated before Calc is elaborated.
Clearly no automatic method can always guess which alternative you require,
and if you are working with legacy code that had constraints of this kind
which were not properly specified by adding Elaborate or
Elaborate_All pragmas, then indeed it is possible that two different
compilers can choose different orders.
The gnatbind
-p switch may be useful in smoking
out problems. This switch causes bodies to be elaborated as late as possible
instead of as early as possible. In the example above, it would have forced
the choice of the first elaboration order. If you get different results
when using this switch, and particularly if one set of results is right,
and one is wrong as far as you are concerned, it shows that you have some
missing Elaborate pragmas. For the example above, we have the
following output:
gnatmake -f -q main main 7 gnatmake -f -q main -bargs -p main 0 |
It is of course quite unlikely that both these results are correct, so
it is up to you in a case like this to investigate the source of the
difference, by looking at the two elaboration orders that are chosen,
and figuring out which is correct, and then adding the necessary
Elaborate_All pragmas to ensure the desired order.
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gnatxref and gnatfind The compiler generates cross-referencing information (unless you set the `-gnatx' switch), which are saved in the `.ali' files. This information indicates where in the source each entity is declared and referenced. Note that entities in package Standard are not included, but entities in all other predefined units are included in the output.
Before using any of these two tools, you need to compile successfully your application, so that GNAT gets a chance to generate the cross-referencing information.
The two tools gnatxref and gnatfind take advantage of this
information to provide the user with the capability to easily locate the
declaration and references to an entity. These tools are quite similar,
the difference being that gnatfind is intended for locating
definitions and/or references to a specified entity or entities, whereas
gnatxref is oriented to generating a full report of all
cross-references.
To use these tools, you must not compile your application using the `-gnatx' switch on the `gnatmake' command line (See Info file `gnat_ug', node `The GNAT Make Program gnatmake'). Otherwise, cross-referencing information will not be generated.
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gnatxref Switches
The command lines for gnatxref is:
$ gnatxref [switches] sourcefile1 [sourcefile2 ...] |
where
sourcefile1, sourcefile2
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
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
-aODIR
-nostdinc
-nostdlib
--RTS=rts-path
gnatmake flag (see 6.2 Switches for gnatmake).
-d
gnatxref will output the parent type
reference for each matching derived types.
-f
-g
gnatfind and gnatxref.
-IDIR
-pFILE
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
gnatxref will then
display every unused entity and 'with'ed package.
-v
gnatxref will generate a
`tags' file that can be used by vi. For examples how to use this
feature, see See section 12.5 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'.
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gnatfind Switches
The command line for gnatfind is:
$ gnatfind [switches] pattern[:sourcefile[:line[:column]]]
[file1 file2 ...]
|
where
pattern
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 section 12.6 Examples of gnatfind Usage
for syntax examples.
line
column
file1 file2 ...
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
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
-aODIR
-nostdinc
-nostdlib
--RTS=rts-path
gnatmake flag (see 6.2 Switches for gnatmake).
-d
gnatfind will output the parent type
reference for each matching derived types.
-e
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
-g
gnatfind and gnatxref.
-IDIR
-pFILE
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
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
gnatfind will output the content
of the Ada source file lines were the entity was found.
-t
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.
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gnatxref and gnatfind
Project files allow a programmer to specify how to compile its
application, where to find sources,... These files are used primarily by
the Glide 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: "./"]
obj_dir=DIR [default: "./"]
comp_opt=SWITCHES [default: ""]
bind_opt=SWITCHES [default: ""]
link_opt=SWITCHES [default: ""]
main=EXECUTABLE [default: ""]
comp_cmd=COMMAND [default: "gcc -c -I${src_dir} -g -gnatq"]
make_cmd=COMMAND [default: "gnatmake ${main} -aI${src_dir} -aO${obj_dir} -g -gnatq -cargs ${comp_opt} -bargs ${bind_opt} -largs ${link_opt}"]
run_cmd=COMMAND [default: "${main}"]
debug_cmd=COMMAND [default: "gdb ${main}"]
gnatxref and gnatfind only take into account the `src_dir'
and `obj_dir' lines, and ignore the others.
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gnatfind and gnatxref
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
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 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 :
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gnatxref Usage
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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; |
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.
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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.
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gnatfind Usage
gnatfind -f xyz:main.adb
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
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
gnatfind main.ads:123
This is the same as gnatfind "*":main.adb:123.
gnatfind mydir/main.adb:123:45
The column has to be the beginning of the identifier, and should not point to any character in the middle of the identifier.
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gnatkr
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.
13.1 About gnatkr13.2 Using gnatkr13.3 Krunching Method 13.4 Examples of gnatkrUsage
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gnatkr The default file naming rule in GNAT is that the file name must be derived from the unit name. The exact default rule is as follows:
The -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.
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gnatkr
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.
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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:
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 |
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.
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gnatkr Usage
$ 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 |
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gnatprep
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.
14.1 Using gnatprep14.2 Switches for gnatprep14.3 Form of Definitions File 14.4 Form of Input Text for gnatprep
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gnatprep
To call gnatprep use
$ gnatprep [-bcrsu] [-Dsymbol=value] infile outfile [deffile] |
where
infile
outfile
deffile
-D switch.
switches
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gnatprep
-b
-c
-Dsymbol=value
True. This switch
can be used in place of a definition file.
-r
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
-u
#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.
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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:
Comment lines may also appear in the definitions file, starting with
the usual --,
and comments may be added to the definitions lines.
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gnatprep The input text may contain preprocessor conditional inclusion lines, as well as general symbol substitution sequences. The preprocessor conditional inclusion commands have the form
#if expression [then] lines #elsif expression [then] lines #elsif expression [then] lines ... #else lines #end if; |
In this example, expression is defined by the following grammar:
expression ::= <symbol> expression ::= <symbol> = "<value>" expression ::= <symbol> = <symbol> expression ::= <symbol> '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 or within a
string literal. The identifier
following the $ must match one of the symbols defined in the symbol
definition file, and the result is to substitute the value of the
symbol in place of $symbol in the output file.
Note that although the substitution of strings within a string literal
is not possible, it is possible to have a symbol whose defined value is
a string literal. So instead of setting XYZ to hello and writing:
Header : String := "$XYZ"; |
you should set XYZ to "hello" and write:
Header : String := $XYZ; |
and then the substitution will occur as desired.
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gnatls
gnatls is a tool that outputs information about compiled
units. It gives the relationship between objects, unit names and source
files. It can also be used to check the source dependencies of a unit
as well as various characteristics.
15.1 Running gnatls15.2 Switches for gnatls15.3 Example of gnatlsUsage
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gnatls
The gnatls command has the form
$ gnatls switches object_or_ali_file |
The main argument is the list of object or `ali' files (see section 2.8 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)
MOK (slightly modified)
-m (minimal recompilation), a file marked
MOK will not be recompiled.
DIF (modified)
??? (file not found)
HID (hidden, unchanged version not first on PATH)
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gnatls
gnatls recognizes the following switches:
-a
-d.
-d
-h
-o
-s
-u
-aOdir
-aIdir
-Idir
-I-
-nostdinc
gnatmake flags
(see 6.2 Switches for gnatmake).
--RTS=rts-path
gnatmake flag (see 6.2 Switches for gnatmake).
-v
Preelaborable
No_Elab_Code
Pure
Elaborate_Body
Remote_Types
Shared_Passive
Predefined
Remote_Call_Interface
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gnatls Usage Example of using the verbose switch. Note how the source and object paths are affected by the -I switch.
$ gnatls -v -I.. demo1.o
GNATLS 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
|
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This chapter addresses some of the issues related to building and using a library with GNAT. It also shows how the GNAT run-time library can be recompiled.
16.1 Creating an Ada Library 16.2 Installing an Ada Library 16.3 Using an Ada Library 16.4 Creating an Ada Library to be Used in a Non-Ada Context 16.5 Rebuilding the GNAT Run-Time Library
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In the GNAT environment, a library has two components:
In order to use other packages 2. 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 inter-unit 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 17. 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");
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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 run-time library in the directories "adainclude" for the sources and "adalib" for the objects and ALI files. When the files exist, the compiler does not look in "adainclude" and "adalib" at all, and thus the "ada_source_path" file must contain the location for the GNAT run-time sources (which can simply be "adainclude"). In the same way, the "ada_object_path" file must contain the location for the GNAT run-time objects (which can simply be "adalib").
You can also specify a new default path to the runtime library at compilation time with the switch "--RTS=rts-path". You can easily choose and change the runtime you want your program to be compiled with. This switch is recognized by gcc, gnatmake, gnatbind, gnatls, gnatfind and gnatxref.
It is possible to install a library before or after the standard GNAT library, by reordering the lines in the configuration files. In general, a library must be installed before the GNAT library if it redefines any part of it.
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In order to use a Ada library, you need to make sure that this
library is on both your source and object path
3.3 Search Paths and the Run-Time Library (RTL)
and 4.11 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 |
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The previous sections detailed how to create and install a library that was usable from an Ada main program. Using this library in a non-Ada context is not possible, because the elaboration of the library is automatically done as part of the main program elaboration.
GNAT also provides the ability to build libraries that can be used both in an Ada and non-Ada context. This section describes how to build such a library, and then how to use it from a C program. The method for interfacing with the library from other languages such as Fortran for instance remains the same.
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Here is an example of simple library interface:
package Interface is procedure Do_Something; procedure Do_Something_Else; end Interface; |
pragma Export or pragma Convention for the
exported entities.
Our package Interface is then updated as follow:
package Interface is procedure Do_Something; pragma Export (C, Do_Something, "do_something"); procedure Do_Something_Else; pragma Export (C, Do_Something_Else, "do_something_else"); end Interface; |
This step is performed by invoking gnatbind with the -L<prefix>
switch. gnatbind will then generate the library elaboration
procedure (named <prefix>init) and the run-time finalization
procedure (named <prefix>final).
# generate the binder file in Ada $ gnatbind -Lmylib interface # generate the binder file in C $ gnatbind -C -Lmylib interface |
$ gcc -c b~interface.adb |
The procedure is identical to the procedure explained in 16.1 Creating an Ada Library, except that `b~interface.o' needs to be added to the list of objects.
# create an archive file $ ar cr libmylib.a b~interface.o <other object files> # create a shared library $ gcc -shared -o libmylib.so b~interface.o <other object files> |
The example below shows the content of mylib_interface.h (note
that there is no rule for the naming of this file, any name can be used)
/* the library elaboration procedure */ extern void mylibinit (void); /* the library finalization procedure */ extern void mylibfinal (void); /* the interface exported by the library */ extern void do_something (void); extern void do_something_else (void); |
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Libraries built as explained above can be used from any program, provided
that the elaboration procedures (named mylibinit in the previous
example) are called before the library services are used. Any number of
libraries can be used simultaneously, as long as the elaboration
procedure of each library is called.
Below is an example of C program that uses our mylib library.
#include "mylib_interface.h"
int
main (void)
{
/* First, elaborate the library before using it */
mylibinit ();
/* Main program, using the library exported entities */
do_something ();
do_something_else ();
/* Library finalization at the end of the program */
mylibfinal ();
return 0;
}
|
Note that this same library can be used from an equivalent Ada main program. In addition, if the libraries are installed as detailed in 16.2 Installing an Ada Library, it is not necessary to invoke the library elaboration and finalization routines. The binder will ensure that this is done as part of the main program elaboration and finalization phases.
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Invoking any library finalization procedure generated by gnatbind
shuts down the Ada run time permanently. Consequently, the finalization
of all Ada libraries must be performed at the end of the program. No
call to these libraries nor the Ada run time should be made past the
finalization phase.
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The pragmas listed below should be used with caution inside libraries, as they can create incompatibilities with other Ada libraries:
Locking_Policy
Queuing_Policy
Task_Dispatching_Policy
Unreserve_All_Interrupts
Program_Error will
be raised during the elaboration of the conflicting
libraries. The usage of these pragmas and its consequences for the user
should therefore be well documented.
Similarly, the traceback in exception occurrences mechanism should be enabled or disabled in a consistent manner across all libraries. Otherwise, a Program_Error will be raised during the elaboration of the conflicting libraries.
If the 'Version and 'Body_Version
attributes are used inside a library, then it is necessary to
perform a gnatbind step that mentions all ali files in all
libraries, so that version identifiers can be properly computed.
In practice these attributes are rarely used, so this is unlikely
to be a consideration.
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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 entry in the object search path usually contains the gnat library. This Makefile contains its own documentation and in particular the set of instructions needed to rebuild a new library and to use it.
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make Utility
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 section 6. 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.
17.1 Using gnatmake in a Makefile 17.2 Automatically Creating a List of Directories 17.3 Generating the Command Line Switches 17.4 Overcoming Command Line Length Limits
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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 section 17.2 Automatically Creating a List of Directories) which might help you in case your project has a lot of subdirectories.
## This Makefile is intended to be used with the following directory
## configuration:
## - The sources are split into a series of csc (computer software components)
## Each of these csc is put in its own directory.
## Their name are referenced by the directory names.
## They will be compiled into shared library (although this would also work
## with static libraries
## - The main program (and possibly other packages that do not belong to any
## csc is put in the top level directory (where the Makefile is).
## toplevel_dir __ first_csc (sources) __ lib (will contain the library)
## \_ second_csc (sources) __ lib (will contain the library)
## \_ ...
## Although this Makefile is build for shared library, it is easy to modify
## to build partial link objects instead (modify the lines with -shared and
## gnatlink below)
##
## With this makefile, you can change any file in the system or add any new
## file, and everything will be recompiled correctly (only the relevant shared
## objects will be recompiled, and the main program will be re-linked).
# The list of computer software component for your project. This might be
# generated automatically.
CSC_LIST=aa bb cc
# Name of the main program (no extension)
MAIN=main
# If we need to build objects with -fPIC, uncomment the following line
#NEED_FPIC=-fPIC
# The following variable should give the directory containing libgnat.so
# You can get this directory through 'gnatls -v'. This is usually the last
# directory in the Object_Path.
GLIB=...
# The directories for the libraries
# (This macro expands the list of CSC to the list of shared libraries, you
# could simply use the expanded form :
# LIB_DIR=aa/lib/libaa.so bb/lib/libbb.so cc/lib/libcc.so
LIB_DIR=${foreach dir,${CSC_LIST},${dir}/lib/lib${dir}.so}
${MAIN}: objects ${LIB_DIR}
gnatbind ${MAIN} ${CSC_LIST:%=-aO%/lib} -shared
gnatlink ${MAIN} ${CSC_LIST:%=-l%}
objects::
# recompile the sources
gnatmake -c -i ${MAIN}.adb ${NEED_FPIC} ${CSC_LIST:%=-I%}
# Note: In a future version of GNAT, the following commands will be simplified
# by a new tool, gnatmlib
${LIB_DIR}:
mkdir -p ${dir $@ }
cd ${dir $@ }; gcc -shared -o ${notdir $@ } ../*.o -L${GLIB} -lgnat
cd ${dir $@ }; cp -f ../*.ali .
# The dependencies for the modules
# Note that we have to force the expansion of *.o, since in some cases make won't
# be able to do it itself.
aa/lib/libaa.so: ${wildcard aa/*.o}
bb/lib/libbb.so: ${wildcard bb/*.o}
cc/lib/libcc.so: ${wildcard cc/*.o}
# Make sure all of the shared libraries are in the path before starting the
# program
run::
LD_LIBRARY_PATH=pwd/aa/lib:pwd/bb/lib:pwd/cc/lib ./${MAIN}
clean::
${RM} -rf ${CSC_LIST:%=%/lib}
${RM} ${CSC_LIST:%=%/*.ali}
${RM} ${CSC_LIST:%=%/*.o}
${RM} *.o *.ali ${MAIN}
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In most makefiles, you will have to specify a list of directories, and store it in a variable. For small projects, it is often easier to specify each of them by hand, since you then have full control over what is the proper order for these directories, which ones should be included...
However, in larger projects, which might involve hundreds of subdirectories, it might be more convenient to generate this list automatically.
The example below presents two methods. The first one, although less
general, gives you more control over the list. It involves wildcard
characters, that are automatically expanded by make. Its
shortcoming is that you need to explicitly specify some of the
organization of your project, such as for instance the directory tree
depth, whether some directories are found in a separate tree,...
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 |
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Once you have created the list of directories as explained in the previous section (see section 17.2 Automatically Creating a List of Directories), you can easily generate the command line arguments to pass to gnatmake.
For the sake of completeness, this example assumes that the source path is not the same as the object path, and that you have two separate lists of directories.
# see "Automatically creating a list of directories" to create
# these variables
SOURCE_DIRS=
OBJECT_DIRS=
GNATMAKE_SWITCHES := ${patsubst %,-aI%,${SOURCE_DIRS}}
GNATMAKE_SWITCHES += ${patsubst %,-aO%,${OBJECT_DIRS}}
all:
gnatmake ${GNATMAKE_SWITCHES} main_unit
|
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One problem that might be encountered on big projects is that many operating systems limit the length of the command line. It is thus hard to give gnatmake the list of source and object directories.
This example shows how you can set up environment variables, which will
make gnatmake behave exactly as if the directories had been
specified on the command line, but have a much higher length limit (or
even none on most systems).
It assumes that you have created a list of directories in your Makefile, using one of the methods presented in 17.2 Automatically Creating a List of Directories. For the sake of completeness, we assume that the object path (where the ALI files are found) is different from the sources patch.
Note a small trick in the Makefile below: for efficiency reasons, we
create two temporary variables (SOURCE_LIST and OBJECT_LIST), that are
expanded immediately by make. This way we overcome the standard
make behavior which is to expand the variables only when they are
actually used.
# In this example, we create both ADA_INCLUDE_PATH and ADA_OBJECT_PATH.
# This is the same thing as putting the -I arguments on the command line.
# (the equivalent of using -aI on the command line would be to define
# only ADA_INCLUDE_PATH, the equivalent of -aO is ADA_OBJECT_PATH).
# You can of course have different values for these variables.
#
# Note also that we need to keep the previous values of these variables, since
# they might have been set before running 'make' to specify where the GNAT
# library is installed.
# see "Automatically creating a list of directories" to create these
# variables
SOURCE_DIRS=
OBJECT_DIRS=
empty:=
space:=${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
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gnatmem
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:
The gnatmem command has two modes. It can be used with gdb
or with instrumented allocation and deallocation routines. The later
mode is called the GMEM mode. Both modes produce the very same
output.
18.1 Running gnatmem(GDB Mode)18.2 Running gnatmem(GMEM Mode)18.3 Switches for gnatmem18.4 Example of gnatmemUsage18.5 GDB and GMEM Modes 18.6 Implementation Note
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gnatmem (GDB Mode)
The gnatmem command has the form
$ gnatmem [-q] [n] [-o file] user_program [program_arg]* or $ gnatmem [-q] [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 |
gnatmem control using the command:
$ gnatmem my_program arg1 arg2 |
The program is transparently executed under the control of the debugger
23.1 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 3.2 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.
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gnatmem (GMEM Mode)
The gnatmem command has the form
$ gnatmem [-q] [n] -i gmem.out user_program [program_arg]* |
The program must have been linked with the instrumented version of the
allocation and deallocation routines. This is done with linking with the
`libgmem.a' library. For better results, the user program should be
compiled with debugging options 3.2 Switches for gcc. For example to
build `my_program':
$ gnatmake -g my_program -largs -lgmem |
When running `my_program' the file `gmem.out' is produced. This file
contains information about all allocations and deallocations done by the
program. It is produced by the instrumented allocations and
deallocations routines and will be used by gnatmem.
Gnatmem must be supplied with the `gmem.out' file and the executable to examine followed by its run-time inputs. For example, if a program is executed with the command:
$ my_program arg1 arg2 |
gnatmem using the command:
$ gnatmem -i gmem.out my_program arg1 arg2 |
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gnatmem
gnatmem recognizes the following switches:
-q
n
-o filegdb script used
to generate this output is also saved in the file `gnatmem.tmp'.
-i filegnatmem processing starting from `file' which has
been generated by a previous call to gnatmem with the -o
switch or `gmem.out' produced by GMEM mode. This is useful
for post mortem processing.
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gnatmem Usage
This section is based on the GDB mode of gnatmem. The same
results can be achieved using GMEM mode. See section
18.2 Running gnatmem (GMEM Mode).
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.
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The main advantage of the GMEM mode is that it is a lot faster than the
GDB mode where the application must be monitored by a GDB script.
But the GMEM mode is available only for DEC Unix, Linux x86,
Solaris (sparc and x86) and Windows 95/98/NT/2000 (x86).
The main advantage of the GDB mode is that it is available on all
supported platforms. But it can be very slow if the application does a
lot of allocations and deallocations.
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18.6.1 gnatmemUsingGDBMode18.6.2 gnatmemUsingGMEMMode
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gnatmem Using GDB Mode
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.
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gnatmem Using GMEM Mode
This mode use the same algorithm to detect memory leak as the GDB
mode of gnatmem, the only difference is in the way data are
gathered. In GMEM mode the program is linked with instrumented
version of __gnat_malloc and __gnat_free
routines. Information needed to find memory leak are recorded by these
routines in file `gmem.out'. This mode also require that the stack
traceback be available, this is only implemented on some platforms
18.5 GDB and GMEM Modes.
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The use of unchecked deallocation and unchecked conversion can easily
lead to incorrect memory references. The problems generated by such
references are usually difficult to tackle because the symptoms can be
very remote from the origin of the problem. In such cases, it is
very helpful to detect the problem as early as possible. This is the
purpose of the Storage Pool provided by GNAT.Debug_Pools.
In order to use the GNAT specific debugging pool, the user must associate a debug pool object with each of the access types that may be related to suspected memory problems. See Ada Reference Manual 13.11.
type Ptr is access Some_Type; Pool : GNAT.Debug_Pools.Debug_Pool; for Ptr'Storage_Pool use Pool; |
GNAT.Debug_Pools is derived from 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;
|
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 |
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gnatstub
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.
20.1 Running gnatstub20.2 Switches for gnatstub
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gnatstub
gnatstub has the command-line interface of the form
$ gnatstub [switches] filename [directory] |
where
filename
directory
switches
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gnatstub
-f
-hs
-hg
-IDIR
-I-
gnatstub to compile an argument source file.
-in
-k
gnatstub) after creating the body stub.
-ln
-q
-r
-r
also implies -k, whether or not
-k is set explicitly.
-t
-t option is set
-v
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gnatelim
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gnatelim 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 21.3 Tree Files) representing all the components of a program to
process and a bind file for a main subprogram (see
21.4 Preparing Tree and Bind Files for gnatelim).
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Eliminate Pragma
The simplified syntax of the Eliminate pragma used by gnatelim is:
pragma Eliminate (Library_Unit_Name, Subprogram_Name); |
where
Library_Unit_Name
Subprogram_Name
The effect of an Eliminate pragma placed in the GNAT configuration
file `gnat.adc' is:
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.
Eliminate is used (called)
in a program, the compiler will produce an error message in the place where
it is called.
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A tree file stores a snapshot of the compiler internal data structures at the very end of a successful compilation. It contains all the syntactic and semantic information for the compiled unit and all the units upon which it depends semantically. To use tools that make use of tree files, you need to first produce the right set of tree files.
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'. compilation.
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gnatelim
A set of tree files covering the program to be analyzed with
gnatelim and
the bind file for the main subprogram does not have to
be in the current directory.
'-T' gnatelim option may be used to provide
the search path for tree files, and '-b'
option may be used to point to the bind
file to process (see 21.5 Running gnatelim)
If you do not have the appropriate set of tree files and the right bind file, you may create them in the current directory using the following procedure.
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
steps, that are useless 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.
This sequence of actions will create all the data needed by gnatelim
from scratch and therefore guarantee its consistency. If you would like to
use some existing set of files as gnatelim output, you must make
sure that the set of files is complete and consistent. You can use the
-m switch to check if there are missed tree files
Note, that gnatelim needs neither object nor ALI files.
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gnatelim
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
gnatelim generates to the standard error
stream a trace of the source file names of the compilation units being
processed. This option turns this trace off.
-v
gnatelim version information is printed as Ada
comments to the standard output stream.
-a
-m
\-T\dir
\-b\bind_file
-dx
Gnatelim.Options unit in the compiler
source file `gnatelim-options.adb'.
gnatelim sends its output to the standard output stream, and all the
tracing and debug information is sent to the standard error stream.
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'.
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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.
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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.
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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.
$ gnatmake -c Main_Prog $ gnatbind main_prog $ gnatmake -f -c -gnatc -gnatt Main_Prog |
Eliminate pragmas
$ gnatelim Main_Prog >[>] gnat.adc |
$ gnatmake -f Main_Prog |
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This chapter discusses some other utility programs available in the Ada environment.
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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.
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gnatpsta Utility Program 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.
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In order to interpret the output from GNAT, when using tools that are originally intended for use with other languages, it is useful to understand the conventions used to generate link names from the Ada entity names.
All link names are in all lowercase letters. With the exception of library procedure names, the mechanism used is simply to use the full expanded Ada name with dots replaced by double underscores. For example, suppose we have the following package spec:
package QRS is MN : Integer; end QRS; |
The variable MN has a full expanded Ada name of QRS.MN, so
the corresponding link name is qrs__mn.
Of course if a pragma Export is used this may be overridden:
package Exports is Var1 : Integer; pragma Export (Var1, C, External_Name => "var1_name"); Var2 : Integer; pragma Export (Var2, C, Link_Name => "var2_link_name"); end Exports; |
In this case, the link name for Var1 is whatever link name the C compiler would assign for the C function var1_name. This typically would be either var1_name or _var1_name, depending on operating system conventions, but other possibilities exist. The link name for Var2 is var2_link_name, and this is not operating system dependent.
One exception occurs for library level procedures. A potential ambiguity
arises between the required name _main for the C main program,
and the name we would otherwise assign to an Ada library level procedure
called Main (which might well not be the main program).
To avoid this ambiguity, we attach the prefix _ada_ to such
names. So if we have a library level procedure such as
procedure Hello (S : String); |
the external name of this procedure will be _ada_hello.
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Glide The Glide 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.
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For more information, please refer to the online Glide documentation available in the Glide --> Help Menu.
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gnathtml
This Perl script allows Ada source files to be browsed using
standard Web browsers. For installation procedure, see the section
See section 22.6 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
-cc color
-d
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 run-time library itself.
-D
gnathtml will also look
for files in the run-time library, and generate html files for them.
-f
-f on the command line, then links will be generated for local
entities too.
-l number
gnathtml
will number the html files every number line.
-I dir
-o dir
-p file
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
-t file
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gnathtml
Perl needs to be installed on your machine to run this script.
Perl is freely available for almost every architecture and
Operating System via the Internet.
On Unix systems, you may want to modify the first line of the script
gnathtml, to explicitly 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 |
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This chapter discusses how to debug Ada programs. An incorrect Ada program may be handled in three ways by the GNAT compiler:
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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.
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The debugger can be launched directly and simply from glide or
through its graphical interface: gvd. It can also be used
directly in text mode. Here is described the basic use of GDB
in text mode. All the commands described below can be used in the
gvd console window eventhough there is usually other more
graphical ways to achieve the same goals.
The command to run de graphical interface of the debugger is
$ gvd program |
The command to run GDB in text mode 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.
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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
set args
command is not needed if the program does not require arguments.
run
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
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
print expression
GDB, so the expression
can contain function calls, variables, operators, and attribute references.
continue
step
next
list
backtrace
up
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
GDB down from the frame currently being
examined to the frame of its callee (the reverse of the previous command),
frame n
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).
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GDB supports a fairly large subset of Ada expression syntax, with some
extensions. The philosophy behind the design of this subset is
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).
GDB user.
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, see Debugging with GDB.
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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.
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When you use the next command in a function, the current source
location will advance to the next statement as usual. A special case
arises in the case of a return statement.
Part of the code for a return statement is the "epilog" of the function. This is the code that returns to the caller. There is only one copy of this epilog code, and it is typically associated with the last return statement in the function if there is more than one return. In some implementations, this epilog is associated with the first statement of the function.
The result is that if you use the next command from a return
statement that is not the last return statement of the function you
may see a strange apparent jump to the last return statement or to
the start of the function. You should simply ignore this odd jump.
The value returned is always that from the first return statement
that was stepped through.
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You can set breakpoints that trip when your program raises selected exceptions.
break exception
break exception name
break exception unhandled
info exceptions
info exceptions regexp
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.
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GDB allows the following task-related commands:
info tasks
(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 ...
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, see Debugging with GDB.
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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.
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When presented with programs that contain serious errors in syntax or semantics, GNAT may on rare occasions experience problems in operation, such as aborting with a segmentation fault or illegal memory access, raising an internal exception, terminating abnormally, or failing to terminate at all. In such cases, you can activate various features of GNAT that can help you pinpoint the construct in your program that is the likely source of the problem.
The following strategies are presented in increasing order of difficulty, corresponding to your experience in using GNAT and your familiarity with compiler internals.
gcc with the -gnatf. This 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 -gnatdO switch causes errors to be displayed as soon as they
are encountered, rather than after compilation is terminated. If GNAT
terminates prematurely or goes into an infinite loop, the last error
message displayed may help to pinpoint the culprit.
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.
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.
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 section 23.1 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.
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In order to examine the workings of the GNAT system, the following brief description of its organization may be helpful:
Ada, as
defined in Annex A.
Interfaces, as
defined in Annex B.
System. This includes
both language-defined children and GNAT run-time routines.
GNAT. These are useful
general-purpose packages, fully documented in their specifications. All
the other `.c' files are modifications of common gcc files.
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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.
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Traceback is a mechanism to display the sequence of subprogram calls that leads to a specified execution point in a program. Often (but not always) the execution point is an instruction at which an exception has been raised. This mechanism is also known as stack unwinding because it obtains its information by scanning the run-time stack and recovering the activation records of all active subprograms. Stack unwinding is one of the most important tools for program debugging.
The first entry stored in traceback corresponds to the deepest calling level, that is to say the subprogram currently executing the instruction from which we want to obtain the traceback.
Note that there is no runtime performance penalty when stack traceback is enabled and no exception are raised during program execution.
23.13.1 Non-Symbolic Traceback 23.13.2 Symbolic Traceback
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Note: this feature is not supported on all platforms. See `GNAT.Traceback spec in g-traceb.ads' for a complete list of supported platforms.
23.13.1.1 Tracebacks From an Unhandled Exception 23.13.1.2 Tracebacks From Exception Occurrences 23.13.1.3 Tracebacks From Anywhere in a Program
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A runtime non-symbolic traceback is a list of addresses of call instructions.
To enable this feature you must use the -E
gnatbind's option. With this option a stack traceback is stored as part
of exception information. It is possible to retrieve this information using the
standard Ada.Exception.Exception_Information routine.
Let's have a look at a simple example:
procedure STB is
procedure P1 is
begin
raise Constraint_Error;
end P1;
procedure P2 is
begin
P1;
end P2;
begin
P2;
end STB;
|
$ gnatmake stb -bargs -E $ stb Execution terminated by unhandled exception Exception name: CONSTRAINT_ERROR Message: stb.adb:5 Call stack traceback locations: 0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4 |
As we see the traceback lists a sequence of addresses for the unhandled
exception CONSTAINT_ERROR raised in procedure P1. It is easy to
guess that this exception come from procedure P1. To translate these
addresses into the source lines where the calls appear, the
addr2line tool, described below, is invaluable. The use of this tool
requires the program to be compiled with debug information.
$ gnatmake -g stb -bargs -E $ stb Execution terminated by unhandled exception Exception name: CONSTRAINT_ERROR Message: stb.adb:5 Call stack traceback locations: 0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4 $ addr2line --exe=stb 0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4 00401373 at d:/stb/stb.adb:5 0040138B at d:/stb/stb.adb:10 0040139C at d:/stb/stb.adb:14 00401335 at d:/stb/b~stb.adb:104 004011C4 at /build/.../crt1.c:200 004011F1 at /build/.../crt1.c:222 77E892A4 in ?? at ??:0 |
addr2line has a number of other useful options:
--functions
--demangle=gnat
--demangle.
$ addr2line --exe=stb --functions --demangle=gnat 0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 00401373 in stb.p1 at d:/stb/stb.adb:5 0040138B in stb.p2 at d:/stb/stb.adb:10 0040139C in stb at d:/stb/stb.adb:14 00401335 in main at d:/stb/b~stb.adb:104 004011C4 in <__mingw_CRTStartup> at /build/.../crt1.c:200 004011F1 in <mainCRTStartup> at /build/.../crt1.c:222 |
From this traceback we can see that the exception was raised in
`stb.adb' at line 5, which was reached from a procedure call in
`stb.adb' at line 10, and so on. The `b~std.adb' is the binder file,
which contains the call to the main program.
see section 4.1 Running gnatbind. The remaining entries are assorted runtime routines,
and the output will vary from platform to platform.
It is also possible to use GDB with these traceback addresses to debug
the program. For example, we can break at a given code location, as reported
in the stack traceback:
$ gdb -nw stb (gdb) break *0x401373 Breakpoint 1 at 0x401373: file stb.adb, line 5. |
It is important to note that the stack traceback addresses do not change when debug information is included. This is particularly useful because it makes it possible to release software without debug information (to minimize object size), get a field report that includes a stack traceback whenever an internal bug occurs, and then be able to retrieve the sequence of calls with the same program compiled with debug information.
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Non-symbolic tracebacks are obtained by using the -E binder argument.
The stack traceback is attached to the exception information string, and can
be retrieved in an exception handler within the Ada program, by means of the
Ada95 facilities defined in Ada.Exceptions. Here is a simple example:
with Ada.Text_IO;
with Ada.Exceptions;
procedure STB is
use Ada;
use Ada.Exceptions;
procedure P1 is
K : Positive := 1;
begin
K := K - 1;
exception
when E : others =>
Text_IO.Put_Line (Exception_Information (E));
end P1;
procedure P2 is
begin
P1;
end P2;
begin
P2;
end STB;
|
This program will output:
$ stb Exception name: CONSTRAINT_ERROR Message: stb.adb:12 Call stack traceback locations: 0x4015e4 0x401633 0x401644 0x401461 0x4011c4 0x4011f1 0x77e892a4 |
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It is also possible to retrieve a stack traceback from anywhere in a
program. For this you need to
use the GNAT.Traceback API. This package includes a procedure called
Call_Chain that computes a complete stack traceback, as well as useful
display procedures described below. It is not necessary to use the
-E gnatbind option in this case, because the stack traceback mechanism
is invoked explicitly.
In the following example we compute a traceback at a specific location in
the program, and we display it using GNAT.Debug_Utilities.Image to
convert addresses to strings:
with Ada.Text_IO;
with GNAT.Traceback;
with GNAT.Debug_Utilities;
procedure STB is
use Ada;
use GNAT;
use GNAT.Traceback;
procedure P1 is
TB : Tracebacks_Array (1 .. 10);
-- We are asking for a maximum of 10 stack frames.
Len : Natural;
-- Len will receive the actual number of stack frames returned.
begin
Call_Chain (TB, Len);
Text_IO.Put ("In STB.P1 : ");
for K in 1 .. Len loop
Text_IO.Put (Debug_Utilities.Image (TB (K)));
Text_IO.Put (' ');
end loop;
Text_IO.New_Line;
end P1;
procedure P2 is
begin
P1;
end P2;
begin
P2;
end STB;
|
$ gnatmake stb $ stb In STB.P1 : 16#0040_F1E4# 16#0040_14F2# 16#0040_170B# 16#0040_171C# 16#0040_1461# 16#0040_11C4# 16#0040_11F1# 16#77E8_92A4# |
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A symbolic traceback is a stack traceback in which procedure names are associated with each code location.
Note that this feature is not supported on all platforms. See `GNAT.Traceback.Symbolic spec in g-trasym.ads' for a complete list of currently supported platforms.
Note that the symbolic traceback requires that the program be compiled with debug information. If it is not compiled with debug information only the non-symbolic information will be valid.
23.13.2.1 Tracebacks From Exception Occurrences 23.13.2.2 Tracebacks From Anywhere in a Program
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with Ada.Text_IO;
with GNAT.Traceback.Symbolic;
procedure STB is
procedure P1 is
begin
raise Constraint_Error;
end P1;
procedure P2 is
begin
P1;
end P2;
procedure P3 is
begin
P2;
end P3;
begin
P3;
exception
when E : others =>
Ada.Text_IO.Put_Line (GNAT.Traceback.Symbolic.Symbolic_Traceback (E));
end STB;
|
$ gnatmake -g stb -bargs -E -largs -lgnat -laddr2line -lintl $ stb 0040149F in stb.p1 at stb.adb:8 004014B7 in stb.p2 at stb.adb:13 004014CF in stb.p3 at stb.adb:18 004015DD in ada.stb at stb.adb:22 00401461 in main at b~stb.adb:168 004011C4 in __mingw_CRTStartup at crt1.c:200 004011F1 in mainCRTStartup at crt1.c:222 77E892A4 in ?? at ??:0 |
The exact sequence of linker options may vary from platform to platform.
The above -largs section is for Windows platforms. By contrast,
under Unix there is no need for the -largs section.
Differences across platforms are due to details of linker implementation.
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It is possible to get a symbolic stack traceback
from anywhere in a program, just as for non-symbolic tracebacks.
The first step is to obtain a non-symbolic
traceback, and then call Symbolic_Traceback to compute the symbolic
information. Here is an example:
with Ada.Text_IO;
with GNAT.Traceback;
with GNAT.Traceback.Symbolic;
procedure STB is
use Ada;
use GNAT.Traceback;
use GNAT.Traceback.Symbolic;
procedure P1 is
TB : Tracebacks_Array (1 .. 10);
-- We are asking for a maximum of 10 stack frames.
Len : Natural;
-- Len will receive the actual number of stack frames returned.
begin
Call_Chain (TB, Len);
Text_IO.Put_Line (Symbolic_Traceback (TB (1 .. Len)));
end P1;
procedure P2 is
begin
P1;
end P2;
begin
P2;
end STB;
|
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If you need to write low-level software that interacts directly with the hardware, Ada provides two ways to incorporate assembly language code into your program. First, you can import and invoke external routines written in assembly language, an Ada feature fully supported by GNAT. However, for small sections of code it may be simpler or more efficient to include assembly language statements directly in your Ada source program, using the facilities of the implementation-defined package System.Machine_Code, which incorporates the gcc Inline Assembler. The Inline Assembler approach offers a number of advantages, including the following:
This chapter presents a series of examples to show you how to use the Inline Assembler. Although it focuses on the Intel x86, the general approach applies also to other processors. It is assumed that you are familiar with Ada and with assembly language programming.
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The assembler used by GNAT and gcc is based not on the Intel assembly language, but rather on a language that descends from the AT&T Unix assembler as (and which is often referred to as AT&T syntax"). The following table summarizes the main features of as syntax and points out the differences from the Intel conventions. See the gcc as and gas (an as macro pre-processor) documentation for further information.
%eax
eax
$4
4
$loc
loc
loc
[loc]
(%eax)
[eax]
0xA0
A0h
movw to move a 16-bit word
mov
rep
stosl
rep stosl
movw $4, %eax
mov eax, 4
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The following example will generate a single assembly language statement, nop, which does nothing. Despite its lack of run-time effect, the example will be useful in illustrating the basics of the Inline Assembler facility.
with System.Machine_Code; use System.Machine_Code;
procedure Nothing is
begin
Asm ("nop");
end Nothing;
|
Asm is a procedure declared in package System.Machine_Code; here it takes one parameter, a template string that must be a static expression and that will form the generated instruction.
Asm may be regarded as a compile-time procedure that parses the template string and additional parameters (none here), from which it generates a sequence of assembly language instructions.
The examples in this chapter will illustrate several of the forms for invoking Asm; a complete specification of the syntax is found in the GNAT Reference Manual.
Under the standard GNAT conventions, the Nothing procedure should be in a file named `nothing.adb'. You can build the executable in the usual way:
gnatmake nothing |
gcc -c -S -fomit-frame-pointer -gnatp `nothing.adb' |
-c
-S
-fomit-frame-pointer
-gnatp
This gives a human-readable assembler version of the code. The resulting
file will have the same name as the Ada source file, but with a .s extension.
In our example, the file `nothing.s' has the following contents:
.file "nothing.adb" gcc2_compiled.: ___gnu_compiled_ada: .text .align 4 .globl __ada_nothing __ada_nothing: #APP nop #NO_APP jmp L1 .align 2,0x90 L1: ret |
The assembly code you included is clearly indicated by
the compiler, between the #APP and #NO_APP
delimiters. The character before the 'APP' and 'NOAPP'
can differ on different targets. For example, Linux uses '#APP' while
on NT you will see '/APP'.
If you make a mistake in your assembler code (such as using the wrong size modifier, or using a wrong operand for the instruction) GNAT will report this error in a temporary file, which will be deleted when the compilation is finished. Generating an assembler file will help in such cases, since you can assemble this file separately using the as assembler that comes with gcc.
Assembling the file using the command
as `nothing.s' |
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The examples in this section, showing how to access the processor flags, illustrate how to specify the destination operands for assembly language statements.
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Get_Flags is
Flags : Unsigned_32;
use ASCII;
begin
Asm ("pushfl" & LF & HT & -- push flags on stack
"popl %%eax" & LF & HT & -- load eax with flags
"movl %%eax, %0", -- store flags in variable
Outputs => Unsigned_32'Asm_Output ("=g", Flags));
Put_Line ("Flags register:" & Flags'Img);
end Get_Flags;
|
In order to have a nicely aligned assembly listing, we have separated multiple assembler statements in the Asm template string with linefeed (ASCII.LF) and horizontal tab (ASCII.HT) characters. The resulting section of the assembly output file is:
#APP pushfl popl %eax movl %eax, -40(%ebp) #NO_APP |
It would have been legal to write the Asm invocation as:
Asm ("pushfl popl %%eax movl %%eax, %0")
|
but in the generated assembler file, this would come out as:
#APP pushfl popl %eax movl %eax, -40(%ebp) #NO_APP |
which is not so convenient for the human reader.
We use Ada comments at the end of each line to explain what the assembler instructions actually do. This is a useful convention.
When writing Inline Assembler instructions, you need to precede each register and variable name with a percent sign. Since the assembler already requires a percent sign at the beginning of a register name, you need two consecutive percent signs for such names in the Asm template string, thus %%eax. In the generated assembly code, one of the percent signs will be stripped off.
Names such as %0, %1, %2, etc., denote input or output variables: operands you later define using Input or Output parameters to Asm.
An output variable is illustrated in
the third statement in the Asm template string:
movl %%eax, %0 |
movl %%eax, Flags would not necessarily work, since the compiler might optimize by using a register to hold Flags, and the expansion of the movl instruction would not be aware of this optimization. The solution is not to store the result directly but rather to advise the compiler to choose the correct operand form; that is the purpose of the %0 output variable.
Information about the output variable is supplied in the Outputs parameter to Asm:
Outputs => Unsigned_32'Asm_Output ("=g", Flags));
|
The output is defined by the Asm_Output attribute of the target type; the general format is
Type'Asm_Output (constraint_string, variable_name) |
The constraint string directs the compiler how to store/access the associated variable. In the example
Unsigned_32'Asm_Output ("=m", Flags);
|
"m" (memory) constraint tells the compiler that the variable
Flags should be stored in a memory variable, thus preventing
the optimizer from keeping it in a register. In contrast,
Unsigned_32'Asm_Output ("=r", Flags);
|
"r" (register) constraint, telling the compiler to
store the variable in a register.
If the constraint is preceded by the equal character (=), it tells the compiler that the variable will be used to store data into it.
In the Get_Flags example, we used the "g" (global) constraint, allowing the optimizer
to choose whatever it deems best.
There are a fairly large number of constraints, but the ones that are most useful (for the Intel x86 processor) are the following:
=
g
m
I
a
b
c
d
S
D
r
q
The full set of constraints is described in the gcc and as documentation; note that it is possible to combine certain constraints in one constraint string.
You specify the association of an output variable with an assembler operand through the %n notation, where n is a non-negative integer. Thus in
Asm ("pushfl" & LF & HT & -- push flags on stack
"popl %%eax" & LF & HT & -- load eax with flags
"movl %%eax, %0", -- store flags in variable
Outputs => Unsigned_32'Asm_Output ("=g", Flags));
|
%0 will be replaced in the expanded code by the appropriate operand,
whatever
the compiler decided for the Flags variable.
In general, you may have any number of output variables:
%0, %1, etc.
Outputs parameter as a parenthesized comma-separated list of Asm_Output attributes
For example:
Asm ("movl %%eax, %0" & LF & HT &
"movl %%ebx, %1" & LF & HT &
"movl %%ecx, %2",
Outputs => (Unsigned_32'Asm_Output ("=g", Var_A), -- %0 = Var_A
Unsigned_32'Asm_Output ("=g", Var_B), -- %1 = Var_B
Unsigned_32'Asm_Output ("=g", Var_C))); -- %2 = Var_C
|
Var_A, Var_B, and Var_C are variables in the Ada program.
As a variation on the Get_Flags example, we can use the constraints string to direct the compiler to store the eax register into the Flags variable, instead of including the store instruction explicitly in the Asm template string:
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Get_Flags_2 is
Flags : Unsigned_32;
use ASCII;
begin
Asm ("pushfl" & LF & HT & -- push flags on stack
"popl %%eax", -- save flags in eax
Outputs => Unsigned_32'Asm_Output ("=a", Flags));
Put_Line ("Flags register:" & Flags'Img);
end Get_Flags_2;
|
The "a" constraint tells the compiler that the Flags
variable will come from the eax register. Here is the resulting code:
#APP pushfl popl %eax #NO_APP movl %eax,-40(%ebp) |
The compiler generated the store of eax into Flags after expanding the assembler code.
Actually, there was no need to pop the flags into the eax register; more simply, we could just pop the flags directly into the program variable:
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Get_Flags_3 is
Flags : Unsigned_32;
use ASCII;
begin
Asm ("pushfl" & LF & HT & -- push flags on stack
"pop %0", -- save flags in Flags
Outputs => Unsigned_32'Asm_Output ("=g", Flags));
Put_Line ("Flags register:" & Flags'Img);
end Get_Flags_3;
|
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The example in this section illustrates how to specify the source operands for assembly language statements. The program simply increments its input value by 1:
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Increment is
function Incr (Value : Unsigned_32) return Unsigned_32 is
Result : Unsigned_32;
begin
Asm ("incl %0",
Inputs => Unsigned_32'Asm_Input ("a", Value),
Outputs => Unsigned_32'Asm_Output ("=a", Result));
return Result;
end Incr;
Value : Unsigned_32;
begin
Value := 5;
Put_Line ("Value before is" & Value'Img);
Value := Incr (Value);
Put_Line ("Value after is" & Value'Img);
end Increment;
|
The Outputs parameter to Asm specifies
that the result will be in the eax register and that it is to be stored in the Result
variable.
The Inputs parameter looks much like the Outputs parameter, but with an
Asm_Input attribute. The
"=" constraint, indicating an output value, is not present.
You can have multiple input variables, in the same way that you can have more than one output variable.
The parameter count (%0, %1) etc, now starts at the first input statement, and continues with the output statements. When both parameters use the same variable, the compiler will treat them as the same %n operand, which is the case here.
Just as the Outputs parameter causes the register to be stored into the
target variable after execution of the assembler statements, so does the
Inputs parameter cause its variable to be loaded into the register before execution
of the
assembler statements.
Thus the effect of the Asm invocation is:
Value into eax
incl %eax instruction
Result variable
The resulting assembler file (with -O2 optimization) contains:
_increment__incr.1: subl $4,%esp movl 8(%esp),%eax #APP incl %eax #NO_APP movl %eax,%edx movl %ecx,(%esp) addl $4,%esp ret |
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For a short subprogram such as the Incr function in the previous section, the overhead of the call and return (creating / deleting the stack frame)
can be significant, compared to the amount of code in the subprogram body.
A solution is to apply Ada's Inline pragma to the subprogram,
which directs the compiler to expand invocations of the subprogram at the point(s)
of call, instead of setting up a stack frame for out-of-line calls.
Here is the resulting program:
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Increment_2 is
function Incr (Value : Unsigned_32) return Unsigned_32 is
Result : Unsigned_32;
begin
Asm ("incl %0",
Inputs => Unsigned_32'Asm_Input ("a", Value),
Outputs => Unsigned_32'Asm_Output ("=a", Result));
return Result;
end Incr;
pragma Inline (Increment);
Value : Unsigned_32;
begin
Value := 5;
Put_Line ("Value before is" & Value'Img);
Value := Increment (Value);
Put_Line ("Value after is" & Value'Img);
end Increment_2;
|
Compile the program with both optimization (-O2) and inlining
enabled (-gnatpn instead of -gnatp).
The Incr function is still compiled as usual, but at the
point in Increment where our function used to be called:
pushl %edi call _increment__incr.1 |
the code for the function body directly appears:
movl %esi,%eax #APP incl %eax #NO_APP movl %eax,%edx |
thus saving the overhead of stack frame setup and an out-of-line call.
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Asm Functionality
This section describes two important parameters to the Asm procedure: Clobber, which identifies register usage; and Volatile, which inhibits unwanted optimizations.
24.6.1 The ClobberParameter24.6.2 The VolatileParameter
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Clobber Parameter One of the dangers of intermixing assembly language and a compiled language such as Ada is that the compiler needs to be aware of which registers are being used by the assembly code. In some cases, such as the earlier examples, the constraint string is sufficient to indicate register usage (e.g. "a" for the eax register). But more generally, the compiler needs an explicit identification of the registers that are used by the Inline Assembly statements.
Using a register that the compiler doesn't know about
could be a side effect of an instruction (like mull
storing its result in both eax and edx).
It can also arise from explicit register usage in your
assembly code; for example:
Asm ("movl %0, %%ebx" & LF & HT &
"movl %%ebx, %1",
Inputs => Unsigned_32'Asm_Input ("g", Var_In),
Outputs => Unsigned_32'Asm_Output ("=g", Var_Out));
|
Asm template string)
does not know you are using the ebx register.
In such cases you need to supply the Clobber parameter to Asm,
to identify the registers that will be used by your assembly code:
Asm ("movl %0, %%ebx" & LF & HT &
"movl %%ebx, %1",
Inputs => Unsigned_32'Asm_Input ("g", Var_In),
Outputs => Unsigned_32'Asm_Output ("=g", Var_Out),
Clobber => "ebx");
|
The Clobber parameter is a static string expression specifying the
register(s) you are using. Note that register names are not prefixed by a percent sign.
Also, if more than one register is used then their names are separated by commas; e.g., "eax, ebx"
The Clobber parameter has several additional uses:
cc to indicate that flags might have changed
memory if you changed a memory location
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Volatile Parameter
Compiler optimizations in the presence of Inline Assembler may sometimes have unwanted effects.
For example, when
an Asm invocation with an input variable is inside a loop, the compiler might move
the loading of the input variable outside the loop, regarding it as a
one-time initialization.
If this effect is not desired, you can disable such optimizations by setting the
Volatile parameter to True; for example:
Asm ("movl %0, %%ebx" & LF & HT &
"movl %%ebx, %1",
Inputs => Unsigned_32'Asm_Input ("g", Var_In),
Outputs => Unsigned_32'Asm_Output ("=g", Var_Out),
Clobber => "ebx",
Volatile => True);
|
By default, Volatile is set to False unless there is no Outputs
parameter.
Although setting Volatile to True prevents unwanted optimizations,
it will also disable other optimizations that might be important for efficiency.
In general, you should set Volatile to True only if the compiler's
optimizations have created problems.
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This section contains a complete program illustrating a realistic usage of GNAT's Inline Assembler
capabilities. It comprises a main procedure Check_CPU and a package Intel_CPU.
The package declares a collection of functions that detect the properties of the 32-bit
x86 processor that is running the program. The main procedure invokes these functions
and displays the information.
The Intel_CPU package could be enhanced by adding functions to detect the type of x386 co-processor, the processor caching options and special operations such as the SIMD extensions.
Although the Intel_CPU package has been written for 32-bit Intel compatible CPUs, it is OS neutral. It has been tested on DOS, Windows/NT and Linux.
24.7.1 Check_CPUProcedure24.7.2 Intel_CPUPackage Specification24.7.3 Intel_CPUPackage Body
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Check_CPU Procedure
---------------------------------------------------------------------
-- --
-- Uses the Intel_CPU package to identify the CPU the program is --
-- running on, and some of the features it supports. --
-- --
---------------------------------------------------------------------
with Intel_CPU; -- Intel CPU detection functions
with Ada.Text_IO; -- Standard text I/O
with Ada.Command_Line; -- To set the exit status
procedure Check_CPU is
Type_Found : Boolean := False;
-- Flag to indicate that processor was identified
Features : Intel_CPU.Processor_Features;
-- The processor features
Signature : Intel_CPU.Processor_Signature;
-- The processor type signature
begin
-----------------------------------
-- Display the program banner. --
-----------------------------------
Ada.Text_IO.Put_Line (Ada.Command_Line.Command_Name &
": check Intel CPU version and features, v1.0");
Ada.Text_IO.Put_Line ("distribute freely, but no warranty whatsoever");
Ada.Text_IO.New_Line;
-----------------------------------------------------------------------
-- We can safely start with the assumption that we are on at least --
-- a x386 processor. If the CPUID instruction is present, then we --
-- have a later processor type. --
-----------------------------------------------------------------------
if Intel_CPU.Has_CPUID = False then
-- No CPUID instruction, so we assume this is indeed a x386
-- processor. We can still check if it has a FP co-processor.
if Intel_CPU.Has_FPU then
Ada.Text_IO.Put_Line
("x386-type processor with a FP co-processor");
else
Ada.Text_IO.Put_Line
("x386-type processor without a FP co-processor");
end if; -- check for FPU
-- Program done
Ada.Command_Line.Set_Exit_Status (Ada.Command_Line.Success);
return;
end if; -- check for CPUID
-----------------------------------------------------------------------
-- If CPUID is supported, check if this is a true Intel processor, --
-- if it is not, display a warning. --
-----------------------------------------------------------------------
if Intel_CPU.Vendor_ID /= Intel_CPU.Intel_Processor then
Ada.Text_IO.Put_Line ("*** This is a Intel compatible processor");
Ada.Text_IO.Put_Line ("*** Some information may be incorrect");
end if; -- check if Intel
----------------------------------------------------------------------
-- With the CPUID instruction present, we can assume at least a --
-- x486 processor. If the CPUID support level is < 1 then we have --
-- to leave it at that. --
----------------------------------------------------------------------
if Intel_CPU.CPUID_Level < 1 then
-- Ok, this is a x486 processor. we still can get the Vendor ID
Ada.Text_IO.Put_Line ("x486-type processor");
Ada.Text_IO.Put_Line ("Vendor ID is " & Intel_CPU.Vendor_ID);
-- We can also check if there is a FPU present
if Intel_CPU.Has_FPU then
Ada.Text_IO.Put_Line ("Floating-Point support");
else
Ada.Text_IO.Put_Line ("No Floating-Point support");
end if; -- check for FPU
-- Program done
Ada.Command_Line.Set_Exit_Status (Ada.Command_Line.Success);
return;
end if; -- check CPUID level
---------------------------------------------------------------------
-- With a CPUID level of 1 we can use the processor signature to --
-- determine it's exact type. --
---------------------------------------------------------------------
Signature := Intel_CPU.Signature;
----------------------------------------------------------------------
-- Ok, now we go into a lot of messy comparisons to get the --
-- processor type. For clarity, no attememt to try to optimize the --
-- comparisons has been made. Note that since Intel_CPU does not --
-- support getting cache info, we cannot distinguish between P5 --
-- and Celeron types yet. --
----------------------------------------------------------------------
-- x486SL
if Signature.Processor_Type = 2#00# and
Signature.Family = 2#0100# and
Signature.Model = 2#0100# then
Type_Found := True;
Ada.Text_IO.Put_Line ("x486SL processor");
end if;
-- x486DX2 Write-Back
if Signature.Processor_Type = 2#00# and
Signature.Family = 2#0100# and
Signature.Model = 2#0111# then
Type_Found := True;
Ada.Text_IO.Put_Line ("Write-Back Enhanced x486DX2 processor");
end if;
-- x486DX4
if Signature.Processor_Type = 2#00# and
Signature.Family = 2#0100# and
Signature.Model = 2#1000# then
Type_Found := True;
Ada.Text_IO.Put_Line ("x486DX4 processor");
end if;
-- x486DX4 Overdrive
if Signature.Processor_Type = 2#01# and
Signature.Family = 2#0100# and
Signature.Model = 2#1000# then
Type_Found := True;
Ada.Text_IO.Put_Line ("x486DX4 OverDrive processor");
end if;
-- Pentium (60, 66)
if Signature.Processor_Type = 2#00# and
Signature.Family = 2#0101# and
Signature.Model = 2#0001# then
Type_Found := True;
Ada.Text_IO.Put_Line ("Pentium processor (60, 66)");
end if;
-- Pentium (75, 90, 100, 120, 133, 150, 166, 200)
if Signature.Processor_Type = 2#00# and
Signature.Family = 2#0101# and
Signature.Model = 2#0010# then
Type_Found := True;
Ada.Text_IO.Put_Line
("Pentium processor (75, 90, 100, 120, 133, 150, 166, 200)");
end if;
-- Pentium OverDrive (60, 66)
if Signature.Processor_Type = 2#01# and
Signature.Family = 2#0101# and
Signature.Model = 2#0001# then
Type_Found := True;
Ada.Text_IO.Put_Line ("Pentium OverDrive processor (60, 66)");
end if;
-- Pentium OverDrive (75, 90, 100, 120, 133, 150, 166, 200)
if Signature.Processor_Type = 2#01# and
Signature.Family = 2#0101# and
Signature.Model = 2#0010# then
Type_Found := True;
Ada.Text_IO.Put_Line
("Pentium OverDrive cpu (75, 90, 100, 120, 133, 150, 166, 200)");
end if;
-- Pentium OverDrive processor for x486 processor-based systems
if Signature.Processor_Type = 2#01# and
Signature.Family = 2#0101# and
Signature.Model = 2#0011# then
Type_Found := True;
Ada.Text_IO.Put_Line
("Pentium OverDrive processor for x486 processor-based systems");
end if;
-- Pentium processor with MMX technology (166, 200)
if Signature.Processor_Type = 2#00# and
Signature.Family = 2#0101# and
Signature.Model = 2#0100# then
Type_Found := True;
Ada.Text_IO.Put_Line
("Pentium processor with MMX technology (166, 200)");
end if;
-- Pentium OverDrive with MMX for Pentium (75, 90, 100, 120, 133)
if Signature.Processor_Type = 2#01# and
Signature.Family = 2#0101# and
Signature.Model = 2#0100# then
Type_Found := True;
Ada.Text_IO.Put_Line
("Pentium OverDrive processor with MMX " &
"technology for Pentium processor (75, 90, 100, 120, 133)");
end if;
-- Pentium Pro processor
if Signature.Processor_Type = 2#00# and
Signature.Family = 2#0110# and
Signature.Model = 2#0001# then
Type_Found := True;
Ada.Text_IO.Put_Line ("Pentium Pro processor");
end if;
-- Pentium II processor, model 3
if Signature.Processor_Type = 2#00# and
Signature.Family = 2#0110# and
Signature.Model = 2#0011# then
Type_Found := True;
Ada.Text_IO.Put_Line ("Pentium II processor, model 3");
end if;
-- Pentium II processor, model 5 or Celeron processor
if Signature.Processor_Type = 2#00# and
Signature.Family = 2#0110# and
Signature.Model = 2#0101# then
Type_Found := True;
Ada.Text_IO.Put_Line
("Pentium II processor, model 5 or Celeron processor");
end if;
-- Pentium Pro OverDrive processor
if Signature.Processor_Type = 2#01# and
Signature.Family = 2#0110# and
Signature.Model = 2#0011# then
Type_Found := True;
Ada.Text_IO.Put_Line ("Pentium Pro OverDrive processor");
end if;
-- If no type recognized, we have an unknown. Display what
-- we _do_ know
if Type_Found = False then
Ada.Text_IO.Put_Line ("Unknown processor");
end if;
-----------------------------------------
-- Display processor stepping level. --
-----------------------------------------
Ada.Text_IO.Put_Line ("Stepping level:" & Signature.Stepping'Img);
---------------------------------
-- Display vendor ID string. --
---------------------------------
Ada.Text_IO.Put_Line ("Vendor ID: " & Intel_CPU.Vendor_ID);
------------------------------------
-- Get the processors features. --
------------------------------------
Features := Intel_CPU.Features;
-----------------------------
-- Check for a FPU unit. --
-----------------------------
if Features.FPU = True then
Ada.Text_IO.Put_Line ("Floating-Point unit available");
else
Ada.Text_IO.Put_Line ("no Floating-Point unit");
end if; -- check for FPU
--------------------------------
-- List processor features. --
--------------------------------
Ada.Text_IO.Put_Line ("Supported features: ");
-- Virtual Mode Extension
if Features.VME = True then
Ada.Text_IO.Put_Line (" VME - Virtual Mode Extension");
end if;
-- Debugging Extension
if Features.DE = True then
Ada.Text_IO.Put_Line (" DE - Debugging Extension");
end if;
-- Page Size Extension
if Features.PSE = True then
Ada.Text_IO.Put_Line (" PSE - Page Size Extension");
end if;
-- Time Stamp Counter
if Features.TSC = True then
Ada.Text_IO.Put_Line (" TSC - Time Stamp Counter");
end if;
-- Model Specific Registers
if Features.MSR = True then
Ada.Text_IO.Put_Line (" MSR - Model Specific Registers");
end if;
-- Physical Address Extension
if Features.PAE = True then
Ada.Text_IO.Put_Line (" PAE - Physical Address Extension");
end if;
-- Machine Check Extension
if Features.MCE = True then
Ada.Text_IO.Put_Line (" MCE - Machine Check Extension");
end if;
-- CMPXCHG8 instruction supported
if Features.CX8 = True then
Ada.Text_IO.Put_Line (" CX8 - CMPXCHG8 instruction");
end if;
-- on-chip APIC hardware support
if Features.APIC = True then
Ada.Text_IO.Put_Line (" APIC - on-chip APIC hardware support");
end if;
-- Fast System Call
if Features.SEP = True then
Ada.Text_IO.Put_Line (" SEP - Fast System Call");
end if;
-- Memory Type Range Registers
if Features.MTRR = True then
Ada.Text_IO.Put_Line (" MTTR - Memory Type Range Registers");
end if;
-- Page Global Enable
if Features.PGE = True then
Ada.Text_IO.Put_Line (" PGE - Page Global Enable");
end if;
-- Machine Check Architecture
if Features.MCA = True then
Ada.Text_IO.Put_Line (" MCA - Machine Check Architecture");
end if;
-- Conditional Move Instruction Supported
if Features.CMOV = True then
Ada.Text_IO.Put_Line
(" CMOV - Conditional Move Instruction Supported");
end if;
-- Page Attribute Table
if Features.PAT = True then
Ada.Text_IO.Put_Line (" PAT - Page Attribute Table");
end if;
-- 36-bit Page Size Extension
if Features.PSE_36 = True then
Ada.Text_IO.Put_Line (" PSE_36 - 36-bit Page Size Extension");
end if;
-- MMX technology supported
if Features.MMX = True then
Ada.Text_IO.Put_Line (" MMX - MMX technology supported");
end if;
-- Fast FP Save and Restore
if Features.FXSR = True then
Ada.Text_IO.Put_Line (" FXSR - Fast FP Save and Restore");
end if;
---------------------
-- Program done. --
---------------------
Ada.Command_Line.Set_Exit_Status (Ada.Command_Line.Success);
exception
when others =>
Ada.Command_Line.Set_Exit_Status (Ada.Command_Line.Failure);
raise;
end Check_CPU;
|
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Intel_CPU Package Specification
-------------------------------------------------------------------------
-- --
-- file: intel_cpu.ads --
-- --
-- ********************************************* --
-- * WARNING: for 32-bit Intel processors only * --
-- ********************************************* --
-- --
-- This package contains a number of subprograms that are useful in --
-- determining the Intel x86 CPU (and the features it supports) on --
-- which the program is running. --
-- --
-- The package is based upon the information given in the Intel --
-- Application Note AP-485: "Intel Processor Identification and the --
-- CPUID Instruction" as of April 1998. This application note can be --
-- found on www.intel.com. --
-- --
-- It currently deals with 32-bit processors only, will not detect --
-- features added after april 1998, and does not guarantee proper --
-- results on Intel-compatible processors. --
-- --
-- Cache info and x386 fpu type detection are not supported. --
-- --
-- This package does not use any privileged instructions, so should --
-- work on any OS running on a 32-bit Intel processor. --
-- --
-------------------------------------------------------------------------
with Interfaces; use Interfaces;
-- for using unsigned types
with System.Machine_Code; use System.Machine_Code;
-- for using inline assembler code
with Ada.Characters.Latin_1; use Ada.Characters.Latin_1;
-- for inserting control characters
package Intel_CPU is
----------------------
-- Processor bits --
----------------------
subtype Num_Bits is Natural range 0 .. 31;
-- the number of processor bits (32)
--------------------------
-- Processor register --
--------------------------
-- define a processor register type for easy access to
-- the individual bits
type Processor_Register is array (Num_Bits) of Boolean;
pragma Pack (Processor_Register);
for Processor_Register'Size use 32;
-------------------------
-- Unsigned register --
-------------------------
-- define a processor register type for easy access to
-- the individual bytes
type Unsigned_Register is
record
L1 : Unsigned_8;
H1 : Unsigned_8;
L2 : Unsigned_8;
H2 : Unsigned_8;
end record;
for Unsigned_Register use
record
L1 at 0 range 0 .. 7;
H1 at 0 range 8 .. 15;
L2 at 0 range 16 .. 23;
H2 at 0 range 24 .. 31;
end record;
for Unsigned_Register'Size use 32;
---------------------------------
-- Intel processor vendor ID --
---------------------------------
Intel_Processor : constant String (1 .. 12) := "GenuineIntel";
-- indicates an Intel manufactured processor
------------------------------------
-- Processor signature register --
------------------------------------
-- a register type to hold the processor signature
type Processor_Signature is
record
Stepping : Natural range 0 .. 15;
Model : Natural range 0 .. 15;
Family : Natural range 0 .. 15;
Processor_Type : Natural range 0 .. 3;
Reserved : Natural range 0 .. 262143;
end record;
for Processor_Signature use
record
Stepping at 0 range 0 .. 3;
Model at 0 range 4 .. 7;
Family at 0 range 8 .. 11;
Processor_Type at 0 range 12 .. 13;
Reserved at 0 range 14 .. 31;
end record;
for Processor_Signature'Size use 32;
-----------------------------------
-- Processor features register --
-----------------------------------
-- a processor register to hold the processor feature flags
type Processor_Features is
record
FPU : Boolean; -- floating point unit on chip
VME : Boolean; -- virtual mode extension
DE : Boolean; -- debugging extension
PSE : Boolean; -- page size extension
TSC : Boolean; -- time stamp counter
MSR : Boolean; -- model specific registers
PAE : Boolean; -- physical address extension
MCE : Boolean; -- machine check extension
CX8 : Boolean; -- cmpxchg8 instruction
APIC : Boolean; -- on-chip apic hardware
Res_1 : Boolean; -- reserved for extensions
SEP : Boolean; -- fast system call
MTRR : Boolean; -- memory type range registers
PGE : Boolean; -- page global enable
MCA : Boolean; -- machine check architecture
CMOV : Boolean; -- conditional move supported
PAT : Boolean; -- page attribute table
PSE_36 : Boolean; -- 36-bit page size extension
Res_2 : Natural range 0 .. 31; -- reserved for extensions
MMX : Boolean; -- MMX technology supported
FXSR : Boolean; -- fast FP save and restore
Res_3 : Natural range 0 .. 127; -- reserved for extensions
end record;
for Processor_Features use
record
FPU at 0 range 0 .. 0;
VME at 0 range 1 .. 1;
DE at 0 range 2 .. 2;
PSE at 0 range 3 .. 3;
TSC at 0 range 4 .. 4;
MSR at 0 range 5 .. 5;
PAE at 0 range 6 .. 6;
MCE at 0 range 7 .. 7;
CX8 at 0 range 8 .. 8;
APIC at 0 range 9 .. 9;
Res_1 at 0 range 10 .. 10;
SEP at 0 range 11 .. 11;
MTRR at 0 range 12 .. 12;
PGE at 0 range 13 .. 13;
MCA at 0 range 14 .. 14;
CMOV at 0 range 15 .. 15;
PAT at 0 range 16 .. 16;
PSE_36 at 0 range 17 .. 17;
Res_2 at 0 range 18 .. 22;
MMX at 0 range 23 .. 23;
FXSR at 0 range 24 .. 24;
Res_3 at 0 range 25 .. 31;
end record;
for Processor_Features'Size use 32;
-------------------
-- Subprograms --
-------------------
function Has_FPU return Boolean;
-- return True if a FPU is found
-- use only if CPUID is not supported
function Has_CPUID return Boolean;
-- return True if the processor supports the CPUID instruction
function CPUID_Level return Natural;
-- return the CPUID support level (0, 1 or 2)
-- can only be called if the CPUID instruction is supported
function Vendor_ID return String;
-- return the processor vendor identification string
-- can only be called if the CPUID instruction is supported
function Signature return Processor_Signature;
-- return the processor signature
-- can only be called if the CPUID instruction is supported
function Features return Processor_Features;
-- return the processors features
-- can only be called if the CPUID instruction is supported
private
------------------------
-- EFLAGS bit names --
------------------------
ID_Flag : constant Num_Bits := 21;
-- ID flag bit
end Intel_CPU;
|
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Intel_CPU Package Body
package body Intel_CPU is
---------------------------
-- Detect FPU presence --
---------------------------
-- There is a FPU present if we can set values to the FPU Status
-- and Control Words.
function Has_FPU return Boolean is
Register : Unsigned_16;
-- processor register to store a word
begin
-- check if we can change the status word
Asm (
-- the assembler code
"finit" & LF & HT & -- reset status word
"movw $0x5A5A, %%ax" & LF & HT & -- set value status word
"fnstsw %0" & LF & HT & -- save status word
"movw %%ax, %0", -- store status word
-- output stored in Register
-- register must be a memory location
Outputs => Unsigned_16'Asm_output ("=m", Register),
-- tell compiler that we used eax
Clobber => "eax");
-- if the status word is zero, there is no FPU
if Register = 0 then
return False; -- no status word
end if; -- check status word value
-- check if we can get the control word
Asm (
-- the assembler code
"fnstcw %0", -- save the control word
-- output into Register
-- register must be a memory location
Outputs => Unsigned_16'Asm_output ("=m", Register));
-- check the relevant bits
if (Register and 16#103F#) /= 16#003F# then
return False; -- no control word
end if; -- check control word value
-- FPU found
return True;
end Has_FPU;
--------------------------------
-- Detect CPUID instruction --
--------------------------------
-- The processor supports the CPUID instruction if it is possible
-- to change the value of ID flag bit in the EFLAGS register.
function Has_CPUID return Boolean is
Original_Flags, Modified_Flags : Processor_Register;
-- EFLAG contents before and after changing the ID flag
begin
-- try flipping the ID flag in the EFLAGS register
Asm (
-- the assembler code
"pushfl" & LF & HT & -- push EFLAGS on stack
"pop %%eax" & LF & HT & -- pop EFLAGS into eax
"movl %%eax, %0" & LF & HT & -- save EFLAGS content
"xor $0x200000, %%eax" & LF & HT & -- flip ID flag
"push %%eax" & LF & HT & -- push EFLAGS on stack
"popfl" & LF & HT & -- load EFLAGS register
"pushfl" & LF & HT & -- push EFLAGS on stack
"pop %1", -- save EFLAGS content
-- output values, may be anything
-- Original_Flags is %0
-- Modified_Flags is %1
Outputs =>
(Processor_Register'Asm_output ("=g", Original_Flags),
Processor_Register'Asm_output ("=g", Modified_Flags)),
-- tell compiler eax is destroyed
Clobber => "eax");
-- check if CPUID is supported
if Original_Flags(ID_Flag) /= Modified_Flags(ID_Flag) then
return True; -- ID flag was modified
else
return False; -- ID flag unchanged
end if; -- check for CPUID
end Has_CPUID;
-------------------------------
-- Get CPUID support level --
-------------------------------
function CPUID_Level return Natural is
Level : Unsigned_32;
-- returned support level
begin
-- execute CPUID, storing the results in the Level register
Asm (
-- the assembler code
"cpuid", -- execute CPUID
-- zero is stored in eax
-- returning the support level in eax
Inputs => Unsigned_32'Asm_input ("a", 0),
-- eax is stored in Level
Outputs => Unsigned_32'Asm_output ("=a", Level),
-- tell compiler ebx, ecx and edx registers are destroyed
Clobber => "ebx, ecx, edx");
-- return the support level
return Natural (Level);
end CPUID_Level;
--------------------------------
-- Get CPU Vendor ID String --
--------------------------------
-- The vendor ID string is returned in the ebx, ecx and edx register
-- after executing the CPUID instruction with eax set to zero.
-- In case of a true Intel processor the string returned is
-- "GenuineIntel"
function Vendor_ID return String is
Ebx, Ecx, Edx : Unsigned_Register;
-- registers containing the vendor ID string
Vendor_ID : String (1 .. 12);
-- the vendor ID string
begin
-- execute CPUID, storing the results in the processor registers
Asm (
-- the assembler code
"cpuid", -- execute CPUID
-- zero stored in eax
-- vendor ID string returned in ebx, ecx and edx
Inputs => Unsigned_32'Asm_input ("a", 0),
-- ebx is stored in Ebx
-- ecx is stored in Ecx
-- edx is stored in Edx
Outputs => (Unsigned_Register'Asm_output ("=b", Ebx),
Unsigned_Register'Asm_output ("=c", Ecx),
Unsigned_Register'Asm_output ("=d", Edx)));
-- now build the vendor ID string
Vendor_ID( 1) := Character'Val (Ebx.L1);
Vendor_ID( 2) := Character'Val (Ebx.H1);
Vendor_ID( 3) := Character'Val (Ebx.L2);
Vendor_ID( 4) := Character'Val (Ebx.H2);
Vendor_ID( 5) := Character'Val (Edx.L1);
Vendor_ID( 6) := Character'Val (Edx.H1);
Vendor_ID( 7) := Character'Val (Edx.L2);
Vendor_ID( 8) := Character'Val (Edx.H2);
Vendor_ID( 9) := Character'Val (Ecx.L1);
Vendor_ID(10) := Character'Val (Ecx.H1);
Vendor_ID(11) := Character'Val (Ecx.L2);
Vendor_ID(12) := Character'Val (Ecx.H2);
-- return string
return Vendor_ID;
end Vendor_ID;
-------------------------------
-- Get processor signature --
-------------------------------
function Signature return Processor_Signature is
Result : Processor_Signature;
-- processor signature returned
begin
-- execute CPUID, storing the results in the Result variable
Asm (
-- the assembler code
"cpuid", -- execute CPUID
-- one is stored in eax
-- processor signature returned in eax
Inputs => Unsigned_32'Asm_input ("a", 1),
-- eax is stored in Result
Outputs => Processor_Signature'Asm_output ("=a", Result),
-- tell compiler that ebx, ecx and edx are also destroyed
Clobber => "ebx, ecx, edx");
-- return processor signature
return Result;
end Signature;
------------------------------
-- Get processor features --
------------------------------
function Features return Processor_Features is
Result : Processor_Features;
-- processor features returned
begin
-- execute CPUID, storing the results in the Result variable
Asm (
-- the assembler code
"cpuid", -- execute CPUID
-- one stored in eax
-- processor features returned in edx
Inputs => Unsigned_32'Asm_input ("a", 1),
-- edx is stored in Result
Outputs => Processor_Features'Asm_output ("=d", Result),
-- tell compiler that ebx and ecx are also destroyed
Clobber => "ebx, ecx");
-- return processor signature
return Result;
end Features;
end Intel_CPU;
|
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The GNAT system provides a number of options that allow a trade-off between
The defaults (if no options are selected) aim at improving the speed of compilation and minimizing dependences, at the expense of performance of the generated code:
These options are suitable for most program development purposes. This chapter describes how you can modify these choices, and also provides some guidelines on debugging optimized code.
25.1 Controlling Run-Time Checks 25.2 Optimization Levels 25.3 Debugging Optimized Code 25.4 Inlining of Subprograms
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By default, GNAT generates all run-time checks, except arithmetic overflow
checking for integer operations and checks for access before elaboration on
subprogram calls. The latter are not required in default mode, because all
necessary checking is done at compile time.
Two gnat switches, -gnatp and -gnato allow this default to
be modified. See section 3.2.5 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. Note that division by zero is not considered an overflow check, and divide by zero checks are generated where required by default.
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.
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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
-O1
-O2
-O3
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.
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Since the compiler generates debugging tables for a compilation unit before it performs optimizations, the optimizing transformations may invalidate some of the debugging data. You therefore need to anticipate certain anomalous situations that may arise while debugging optimized code. This section describes the most common cases.
goto, a return, or
a break in a C switch statement.
In general, when an unexpected value appears for a local variable or parameter you should first ascertain if that value was actually computed by your program, as opposed to being incorrectly reported by the debugger. Record fields or array elements in an object designated by an access value are generally less of a problem, once you have ascertained that the access value is sensible. Typically, this means checking variables in the preceding code and in the calling subprogram to verify that the value observed is explainable from other values (one must apply the procedure recursively to those other values); or re-running the code and stopping a little earlier (perhaps before the call) and stepping to better see how the variable obtained the value in question; or continuing to step from the point of the strange value to see if code motion had simply moved the variable's assignments later.
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A call to a subprogram in the current unit is inlined if all the following conditions are met:
-O1.
gcc
cannot support in inlined subprograms.
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:
-O1.
gcc cannot
support in inlined subprograms.
pragma Inline for the subprogram.
-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.
The use of front end inlining with -gnatN generates similar
additional dependencies.
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.
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Version 1.1, March 2000
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| Jump to: | -
\
_
A B C D E F G H I L M N O P R S T U V W Z |
|---|
| Jump to: | -
\
_
A B C D E F G H I L M N O P R S T U V W Z |
|---|
| [Top] | [Contents] | [Index] | [ ? ] |
gnatmake Utility
gcc
gcc
gcc for Syntax Checking
gcc for Semantic Checking
gnatbind
gnatbind
gnatbind
gnatbind Usage
gnatlink
gnatlink
gnatlink
gnatlink
gnatlink
gnatmake
gnatmake
gnatmake
gnatmake
gnatmake Works
gnatmake Usage
gnatchop
gnatchop
gnatchop
gnatchop Usage
gnatname
gnatname
gnatname
gnatname Usage
case Constructions
gnatxref and gnatfind
gnatxref Switches
gnatfind Switches
gnatxref and gnatfind
gnatfind and gnatxref
gnatxref Usage
gnatfind Usage
gnatkr
gnatkr
gnatkr
gnatkr Usage
gnatprep
gnatprep
gnatprep
gnatprep
gnatls
gnatls
gnatls
gnatls Usage
make Utility
gnatmem
gnatmem (GDB Mode)
gnatmem (GMEM Mode)
gnatmem
gnatmem Usage
gnatmem Using GDB Mode
gnatmem Using GMEM Mode
gnatstub
gnatstub
gnatstub
gnatelim
gnatelim
Eliminate Pragma
gnatelim
gnatelim
gnatpsta Utility Program
Glide
gnathtml
gnathtml
Asm Functionality
Clobber Parameter
Volatile Parameter
Check_CPU Procedure
Intel_CPU Package Specification
Intel_CPU Package Body
| [Top] | [Contents] | [Index] | [ ? ] |
About This Guide
1. Getting Started with GNAT
2. The GNAT Compilation Model
3. Compiling Usinggcc
4. Binding Usinggnatbind
5. Linking Usinggnatlink
6. The GNAT Make Programgnatmake
7. Renaming Files Usinggnatchop
8. Configuration Pragmas
9. Handling Arbitrary File Naming Conventions Usinggnatname
10. GNAT Project Manager
11. Elaboration Order Handling in GNAT
12. The Cross-Referencing Toolsgnatxrefandgnatfind
13. File Name Krunching Usinggnatkr
14. Preprocessing Usinggnatprep
15. The GNAT Library Browsergnatls
16. GNAT and Libraries
17. Using the GNUmakeUtility
18. Finding Memory Problems withgnatmem
19. Finding Memory Problems with GNAT Debug Pool
20. Creating Sample Bodies Usinggnatstub
21. Reducing the Size of Ada Executables withgnatelim
22. Other Utility Programs
23. Running and Debugging Ada Programs
24. Inline Assembler
25. Performance Considerations
A. GNU Free Documentation License
Index
| [Top] | [Contents] | [Index] | [ ? ] |
| Button | Name | Go to | From 1.2.3 go to |
|---|---|---|---|
| [ < ] | Back | previous section in reading order | 1.2.2 |
| [ > ] | Forward | next section in reading order | 1.2.4 |
| [ << ] | FastBack | previous or up-and-previous section | 1.1 |
| [ Up ] | Up | up section | 1.2 |
| [ >> ] | FastForward | next or up-and-next section | 1.3 |
| [Top] | Top | cover (top) of document | |
| [Contents] | Contents | table of contents | |
| [Index] | Index | concept index | |
| [ ? ] | About | this page |