gcc
gcc
gcc for Syntax Checking
gcc for Semantic Checking
gnatbind
gnatlink
gnatmake
gnatchop
gnatxref and
gnatfind
gnatkr
gnatprep
gnatls
gnatmem
gnatstub
gnatelim
gnatpsys Utility Program
gnatpsta Utility Program
emacs
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.
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.
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.
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, discusses
gnatelim, a tool which detects unused subprograms and produces
information that helps the compiler to create a smaller executable for a
program.
gnatpsta and gnatpsys.
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.
For further information about related tools, refer to the following documents:
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.
This chapter describes the simplest ways of using GNAT to compile Ada programs.
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.
Any editor may be used to prepare an Ada program. If emacs is
used, the optional Ada mode may be helpful in laying out the program. The
program text is a normal text file. We will suppose in our initial example that
you have used your editor to prepare the following standard format text file:
with Text_IO; use Text_IO;
procedure Hello is
begin
Put_Line ("Hello WORLD!");
end Hello;
This file should be named `hello.adb'. Using the normal default file
naming conventions, By default, GNAT requires that each file contain a single
compilation unit whose file name corresponds to the unit name with periods
replaced by hyphens, and whose extension is `.ads' for a spec and
`.adb' for a body. This default file naming convention can be
overridden by use of the special pragma Source_File_Name see
section Using
Other File Names. Alternatively, if you want to rename your files according
to this default convention, which is probably more convenient if you will be
using GNAT for all your compilation requirements, then the gnatchop
utility can be used to perform this renaming operation (see section Renaming
Files Using gnatchop).
You can compile the program using the following command:
$ gcc -c hello.adb
gcc is the command used to run the compiler. This compiler is
capable of compiling programs in several languages including Ada 95 and C. It
determines you have given it an Ada program by the extension (`.ads' or
`.adb'), and will call the GNAT compiler to compile the specified file.
The -c switch is required. It tells gcc to only do
a compilation. (For C programs, gcc can also do linking, but this
capability is not used directly for Ada programs, so the -c switch
must always be present.)
This compile command generates a file `hello.o' which is the object
file corresponding to your Ada program. It also generates a file
`hello.ali' which contains additional information used to check that an
Ada program is consistent. To get an executable file, we then use
gnatbind to bind the program and gnatlink to link it
to produce the executable. The argument to both gnatbind and gnatlink is the
name of the `ali' file, but the default extension of `.ali'
can be omitted. This means that in the most common case, the argument is simply
the name of the main program:
$ gnatbind hello $ gnatlink hello
A simpler method of carrying out these steps is to use gnatmake,
which is a master program which invokes all of the required compilation, binding
and linking tools in the correct order. In particular, gnatmake
automatically recompiles any sources that have been modified since they were
last compiled, or sources that depend on such modified sources, so that a
consistent compilation is ensured.
$ gnatmake hello.adb
The result is an executable program called `hello', which can be run by entering:
$ ./hello
and, if all has gone well, you will see
Hello WORLD!
appear in response to this command.
Consider a slightly more complicated example that has three files: a main program, and the spec and body of a package:
package Greetings is
procedure Hello;
procedure Goodbye;
end Greetings;
with Text_IO; use Text_IO;
package body Greetings is
procedure Hello is
begin
Put_Line ("Hello WORLD!");
end Hello;
procedure Goodbye is
begin
Put_Line ("Goodbye WORLD!");
end Goodbye;
end Greetings;
with Greetings;
procedure Gmain is
begin
Greetings.Hello;
Greetings.Goodbye;
end Gmain;
Following the one-unit-per-file rule, place this program in the following three separate files:
Greetings
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 a separate
body, only the body need be compiled. If you want to submit these programs to
the compiler for semantic checking purposes, then you use the
-gnatc switch:
$ gcc -c greetings.ads -gnatc
Although the compilation can be done in separate steps as in the above
example, in practice it is almost always more convenient to use the
gnatmake capability. All you need to know in this case is the name
of the main program source file. The effect of the above four commands can be
achieved with a single one:
$ gnatmake gmain.adb
In the next section we discuss the advantages of using gnatmake
in more detail.
gnatmake UtilityIf you work on a program by compiling single components at a time using
gcc, you typically keep track of the units you modify. In order to
build a consistent system, you compile not only these units, but also any units
that depend on the units you have modified. For example, in the preceding case,
if you edit `gmain.adb', you only need to recompile that file. But if
you edit `greetings.ads', you must recompile both
`greetings.adb' and `gmain.adb', because both files contain
units that depend on `greetings.ads'.
gnatbind will warn you if you forget one of these compilation
steps, so that it is impossible to generate an inconsistent program as a result
of forgetting to do a compilation. Nevertheless it is tedious and error-prone to
keep track of dependencies among units. One approach to handle the
dependency-bookkeeping is to use a makefile. However, makefiles present
maintenance problems of their own: if the dependencies change as you change the
program, you must make sure that the makefile is kept up-to-date manually, which
is also an error-prone process.
The gnatmake utility takes care of these details automatically.
Invoke it using either one of the following forms:
$ gnatmake gmain.adb $ gnatmake gmain
The argument is the name of the file containing the main program from which
you may omit the extension. gnatmake examines the environment,
automatically recompiles any files that need recompiling, and binds and links
the resulting set of object files, generating the executable file,
`gmain'. In a large program, it can be extremely helpful to use
gnatmake, because working out by hand what needs to be recompiled
can be difficult.
Note that gnatmake takes into account all the intricate Ada 95
rules that establish dependencies among units. These include dependencies that
result from inlining subprogram bodies, and from generic instantiation. Unlike
some other Ada make tools, gnatmake does not rely on the
dependencies that were found by the compiler on a previous compilation, which
may possibly be wrong when sources change. gnatmake determines the
exact set of dependencies from scratch each time it is run.
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.
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 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.
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 Character Set Control).
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.
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.
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 dWhere
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.
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 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 Renaming
Files Using gnatchop.)
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 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.
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.
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. Similarly if the -gnatN switch is used, then
the unit is dependent on all body files.
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.
Each compilation actually generates two output files. The first of these is the normal object file that has a `.o' extension. The second is a text file containing full dependency information. It has the same name as the source file, but an `.ali' extension. This file is known as the Ada Library Information (ALI) file.
Normally you need not be concerned with the contents of this file. This section is included in case you want to understand how these files are being used by the binder and other GNAT utilities. Each ALI file consists of a series of lines of the form:
Key_Character parameter parameter ...
The first two lines in the file identify the library output
version and Standard version. These are required to be consistent
across the entire set of compilation units in your program.
V "xxxxxxxxxxxxxxxx"
This line indicates the library output version, as defined in `gnatvsn.ads'. It ensures that separate object modules of a program are consistent. The library output version must be changed if anything in the compiler changes that would affect successful binding of modules compiled separately. Examples of such changes are modifications in the format of the library information described in this package, modifications to calling sequences, or to the way data is represented.
S "xxxxxxxxxxxxxxxx"
This line contains information regarding
types declared in packages Standard as stored in
Gnatvsn.Standard_Version. The purpose of this information is to
ensure that all units in a program are compiled with a consistent set of
options. This is critical on systems where, for example, the size of
Integer can be set by command line switches.
M type [priority]
This line is present only for a unit that can be a main
program. type is either P for a parameterless procedure
or F for a function returning a value of integral type. The latter
is for writing a main program that returns an exit status. priority
is present only if there was a valid pragma Priority in the
corresponding unit to set the main task priority. It is an unsigned decimal
integer.
F x
This line is present if a pragma Float_Representation or Long_Float is used to specify other than the default floating-point format. This option applies only to implementations of GNAT for the Digital Alpha Systems. The character x is 'I' for IEEE_Float, 'G' for VAX_Float with Long_Float using G_Float, and 'D' for VAX_Float for Long_Float with D_Float.
P L=x Q=x T=x
This line is present if the unit uses tasking directly or indirectly, and has one or more valid xxx_Policy pragmas that apply to the unit. The arguments are as follows
L=x (locking policy)
This is present if a valid Locking_Policy pragma applies to the unit. The single character indicates the policy in effect (e.g. `C' for Ceiling_Locking).
Q=x (queuing policy)
This is present if a valid Queuing_Policy pragma applies to the unit. The single character indicates the policy in effect (e.g. `P' for Priority_Queuing).
T=x (task_dispatching policy)
This is present if a valid Task_Dispatching_Policy pragma applies to the unit. The single character indicates the policy in effect (e.g. `F' for FIFO_Within_Priorities).
Following these header lines is a set of information lines, one per compilation unit. Each line lists a unit in the object file corresponding to this ALI file. In particular, when a package body or subprogram body is compiled there will be two such lines, one for the spec and one for the body, with the entry for the body appearing first. This is the only case in which a single ALI file contains more than one unit. Note that subunits do not count as compilation units for this purpose, and generate no library information, because they are inlined. The lines for each compilation unit have the following form:
U unit-name source-name version [attributes]
This line identifies the unit to which this section of the
library information file applies. unit-name is the unit name in
internal format, as described in package Uname, and
source-name is the name of the source file containing the unit.
version is the version, given by eight hexadecimal characters with lowercase letters. This value is a hash code that includes contributions from the time stamps of this unit and all the units on which it semantically depends.
The optional attributes are a series of two-letter codes indicating information about the unit. They indicate the nature of the unit and they summarize information provided by categorization pragmas.
EB
NE
NE
set, depending on whether or not elaboration code is required.
PK
PU
Pure.
PR
Preelaborate.
RC
Remote_Call_Interface.
RT
Remote_Types.
SP
Shared_Passive.
SU
The attributes may appear in any order, separated by spaces. The next set of lines in the ALI file have the following form:
W unit-name [source-name lib-name [E] [EA] [ED]]
One of these lines is present for each
unit mentioned in an explicit with clause in the current unit.
unit-name is the unit name in internal format. source-name
is the file name of the file that must be compiled to compile that unit (usually
the file for the body, except for packages that have no body).
lib-name is the file name of the library information file that
contains the results of compiling the unit. The E and
EA parameters are present if pragma Elaborate or
pragma Elaborate_All, respectively, apply to this unit.
ED is used to indicate that the compiler has determined that a
pragma Elaborate_All for this unit would be desirable. For details
on the use of the ED parameter see See section Elaboration
Order Handling in GNAT.
Following the unit information is an optional series of lines that indicate
the usage of pragma Linker_Options. For each appearance of pragma
Linker_Options in any of the units for which unit lines are
present, a line of the form
L string
appears. string is the string from the pragma enclosed in quotes. Within the quotes, the following can occur:
For further details, see
Stringt.Write_String_Table_Entry in the file
`stringt.ads'. Note that wide characters of the form {hhhh} cannot be
produced, because pragma Linker_Option accepts only
String, not Wide_String.
Finally, the rest of the ALI file contains a series of lines that indicate the source files on which the compiled units depend. This is used by the binder for consistency checking and looks like:
D source-name time-stamp [comments]
where comments, if present, must be separated from the time stamp by at least one blank. Currently this field is unused.
Blank lines are ignored when the library information is read, and separate sections of the file are separated by blank lines to help readability. Extra blanks between fields are also ignored.
All compiled units are marked with a time stamp, which is derived from the source file. The binder uses these time stamps to ensure consistency of the set of units that constitutes a single program. Time stamps are fourteen-character strings of the form YYYYMMDDHHMMSS. The fields have the following meaning:
YYYY
MM
DD
HH
MM
SS
Time stamps may be compared lexicographically (in other words, the order of Ada comparison operations on strings) to determine which is later or earlier. However, in normal mode, only equality comparisons have any effect on the semantics of the library. Later/earlier comparisons are used only for determining the most informative error messages to be issued by the binder.
The time stamp is the actual stamp stored with the file without any
adjustment resulting from time zone comparisons. This avoids problems in using
libraries across networks with clients spread across multiple time zones, but it
means that the time stamp might differ from that displayed in a directory
listing. For example, in UNIX systems, file time stamps are stored in Greenwich
Mean Time (GMT), but the ls command displays local times.
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.
There are two ways to build a program that contains some Ada files and some other language files depending on whether the main program is in Ada or not. If the main program is in Ada, you should proceed as follows:
gcc -c file1.c gcc -c file2.c
gnatmake -c my_main.adb
gnatbind my_main
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 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 entry_point2
gnatlink entry_point2.ali file1.o file2.o
GNAT follows standard calling sequence conventions and will thus interface to any other language that also follows these conventions. The following Convention identifiers are recognized by GNAT:
Building a mixed application containing both Ada and C++ code may be a challenge for the unaware programmer. As a matter of fact, this interfacing has not been standardized in the Ada 95 reference manual due to the immaturity and lack of standard of C++ at the time. This section gives a few hints that should make this task easier. In particular the first section addresses the differences with interfacing with C. The second section looks into the delicate problem of linking the complete application from its Ada and C++ parts. The last section give some hints on how the GNAT runtime can be adapted in order to allow inter-language dispatching with a new C++ compiler.
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.
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++If there is a problem due to interfering environment variables, it can be workaround by using an intermediate script:
$ gnatlink -v -v ada_unit file1.o file2.o --LINK=./my_script $ cat ./my_script #!/bin/sh unset C_INCLUDE_PATH unset GCC_EXEC_PREFIX c++ $*
$ gnatls -v $ Gdir=<the last directory on the object path> $ gnatlink ada_unit file1.o file2.o -L$Gdir -lgcc --LINK=<cpp_linker>
GNAT offers the capability to derive Ada 95 tagged types directly from
preexisting C++ classes and . See "Interfacing with C++" in the GNAT reference
manual. The mechanism used by GNAT for achieving such a goal has been made user
configurable through a GNAT library unit Interfaces.CPP. The
default version of this file is adapted to the GNU c++ compiler. Internal
knowledge of the virtual table layout used by the new C++ compiler is needed to
configure properly this unit. The Interface of this unit is known by the
compiler and cannot be changed except for the value of the constants defining
the characteristics of the virtual table: CPP_DT_Prologue_Size,
CPP_DT_Entry_Size, CPP_TSD_Prologue_Size, CPP_TSD_Entry_Size. Read comments in
the source of this unit for more details.
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.
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.
gccThis 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.
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.
gccThe gcc command accepts numerous switches to control the
compilation process. These switches are fully described in this section.
-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
gcc without a -c
switch to compile and link in one step. This is because the binder must be
run, and currently gcc cannot be used to run the GNAT binder.
-g
-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.
-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.
-Wuninitialized
-O switch (in other words, This switch works
only if optimization is turned on).
-gnata
Pragma Assert and pragma
Debug to be activated.
-gnatb
stderr even if verbose mode set.
-gnatc
-gnatD
-gnate
-gnatE
-gnatf
-gnatg
-gnatG
-gnatic
-gnath
stdout.
-gnatkn
k =
krunch).
-gnatl
-gnatmn
-gnatn
inline is specified.
-gnatN
inline is specified. This is equivalent to
using -gnatn and adding a pragma inline for every
subprogram in the program.
-fno-inline
-gnato
-gnatp
-gnatq
-gnatP
-gnatR
-gnats
-gnatt
-gnatu
-gnatU
-gnatv
stdout.
-gnatwm
s,e,l for suppress, treat as
error, elaboration warnings).
-gnatWe
-gnatx
-gnatwm
-gnaty
-gnatzm
-gnat83
-gnat95
You may combine a sequence of GNAT switches into a single switch. For example, the combined switch
-gnatcfi3
is equivalent to specifying the following sequence of switches:
-gnatc -gnatf -gnati3
The standard default format for error messages is called "brief format."
Brief format messages are written to stdout (the standard output
file) and have the following form:
e.adb:3:04: Incorrect spelling of keyword "function" e.adb:4:20: ";" should be "is"
The first integer after the file name is the line number in the file, and the
second integer is the column number within the line. emacs can
parse the error messages and point to the referenced character. The following
switches provide control over the error message format:
-gnatv
stdout.
The same program compiled with the -gnatv switch would generate: 3. funcion X (Q : Integer)
|
>>> Incorrect spelling of keyword "function"
4. return Integer;
|
>>> ";" should be "is"
The vertical bar indicates the location of the error, and the
`>>>' prefix can be used to search for error messages.
When this switch is used the only source lines output are those with errors.
-gnatl
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 stdout as
well as the verbose format message or full listing.
-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.
-gnate
-gnate may cause error
messages to be generated out of sequence and also disconnects a number of
useful error message processing circuits. This switch should be used only in
error situations where the compiler terminates with no output at all, or goes
into an infinite loop. In such cases, the -gnate switch may be
used to see if any error situations were detected before the compiler crash
(see section GNAT
Abnormal Termination). In addition to error messages, which correspond to illegalities as defined in the Ada 95 Reference Manual, the compiler detects two kinds of warning situations.
First, the compiler considers some constructs suspicious and generates a warning message to alert you to a possible error. Second, if the compiler detects a situation that is sure to raise an exception at run time, it generates a warning message. The following shows an example of warning messages:
e.adb:4:24: warning: creation of object may raise Storage_Error e.adb:10:17: warning: static value out of range e.adb:10:17: warning: "Constraint_Error" will be raised at run time
GNAT considers a large number of situations as appropriate for the generation
of warning messages. As always, warnings are not definite indications of errors.
For example, if you do an out-of-range assignment with the deliberate intention
of raising a Constraint_Error exception, then the warning that may
be issued does not indicate an error. Some of the situations for which GNAT
issues warnings (at least some of the time) are:
Four switches are available to control the handling of warning messages:
-gnatwe (treat warnings as errors)
-gnatws (suppress warnings)
-gnatwl (warn on elaboration order errors)
-gnatwu (warn 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.
-gnatR
-gnatR causes the
compiler to output a listing showing representation information for declared
array and record types, including record representation clauses.
-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.
-gnata
Assert and Debug
normally have no effect and are ignored. This switch, where `a'
stands for assert, causes Assert and Debug pragmas
to be activated. The pragmas have the form: pragma Assert (Boolean-expression [, static-string-expression]) pragma Debug (procedure call)The
Assert pragma causes Boolean-expression to
be tested. If the result is True, the pragma has no effect (other
than possible side effects from evaluating the expression). If the result is
False, the exception Assert_Error declared in the
package System.Assertions is raised (passing
static-string-expression, if present, as the message associated
with the exception). If no string expression is given the default is a string
giving the file name and line number of the pragma. The Debug
pragma causes procedure to be called. Note that pragma
Debug may appear within a declaration sequence, allowing debugging
procedures to be called between declarations. The -gnatyx switch causes the compiler to enforce specified style rules. A limited set of style rules has been used in writing the GNAT sources themselves. This switch allows user programs to activate all or some of these checks. If the source program fails a specified style check, an appropriate error message is given, preceded by the character sequence "(style)", and the program is considered illegal. The string x is a sequence of letters or digits indicating the particular style checks to be performed. The following checks are defined:
1-9 (specify indentation level)
-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 tool.
--------------------------- -- This is a box comment -- -- with two text lines. -- ---------------------------
e (check end labels)
-gnaty then
optional labels on end statements ending subprograms 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.
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.
The switch -gnaty on its own (that is not followed by any
letters or digits), is equivalent to gnaty3abcefhiklmprst, that is
all checking options are enabled, with an indentation level of 3. This is the
standard checking option that is used for the GNAT sources.
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 Ada semantics). Note that the
-gnato switch does not affect the code generated for any
floating-point operations; it applies only to integer operations. For
floating-point, GNAT has the Machine_Overflows attribute set to
False and the normal mode of operation is to generate IEEE NaN
and infinite values on overflow or invalid operations (such as dividing 0.0 by
0.0).
-gnatE
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.
gcc for Syntax Checking-gnats
s stands for syntax. Run GNAT in
syntax checking only mode. For example, the command $ gcc -c -gnats x.adbcompiles 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 Renaming
Files Using gnatchop). gcc for Semantic Checking-gnatc
c stands for check. Causes the
compiler to operate in semantic check mode, with full checking for all
illegalities specified in the Ada 95 Reference Manual, but without generation
of any source code (no object or ALI file generated). Because dependent files
must be accessed, you must follow the GNAT semantic restrictions on file
structuring to operate in this mode:
-gnat83
-gnat83 switch can be
ported easily to an Ada 83 compiler. This is the main use of the switch. With
few exceptions (most notably the need to use <> on unconstrained generic formal parameters, the use of the new
Ada 95 keywords, and the use of packages with optional bodies), it is not
necessary to use the -gnat83 switch when compiling Ada 83
programs, because, with rare exceptions, Ada 95 is upwardly compatible with
Ada 83. This means that a correct Ada 83 program is usually also a correct Ada
95 program.
-gnat95
-gnatr
else must line up with an if and code in
the then and else parts must be indented. The
compiler treats violations of the layout rules as syntax errors if you specify
this switch.
-gnatg
-gnatg switch specified. You can find
the full documentation for the style conventions imposed by
-gnatg in the body of the package Style in the
compiler sources (in the file `style.adb'). You
should not normally use the -gnatg switch. However, you
must use -gnatg for compiling any language-defined unit,
or for adding children to any language-defined unit other than
Standard. -gnatic
1
2
3
4
p
8
f
n
w
-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. -gnatkn
-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 Inlining
of Subprograms.
-gnatN
Inline for every subprogram referenced by the compiled unit.
-gnatt
-gnatu
stdout. The listing includes all units on which the unit being
compiled depends either directly or indirectly. -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:
-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. 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]
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.
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.
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. The following are some typical Ada compilation command line examples:
$ gcc -c xyz.adb
$ gcc -c -O2 -gnata xyz-def.adb
Assert/Debug
statements enabled.
$ gcc -c -gnatc abc-def.adb
gnatbindThis chapter describes the GNAT binder, gnatbind, which is used
to bind compiled GNAT objects. The gnatbind program performs four
separate functions:
gnatlink utility used to link the Ada
application. gnatbindThe form of the gnatbind command is
$ gnatbind [switches] mainprog[.ali] [switches]
where mainprog.adb is the Ada file containing the main program
unit body. If no switches are specified, gnatbind constructs an Ada
package in two files whose names are `b~ada_main.ads', and
`b~ada_main.adb'. For example, if given the parameter
`hello.ali', for a main program contained in file
`hello.adb', the binder output files would be `b~hello.ads'
and `b~hello.adb'.
When doing consistency checking, the binder takes any source files it can
locate into consideration. For example, if the binder determines that the given
main program requires the package Pack, whose ALI file is
`pack.ali' and whose corresponding source spec file is
`pack.ads', it attempts to locate the source file `pack.ads'
(using the same search path conventions as previously described for the
gcc command). If it can locate this source file, it checks that the
time stamps or source checksums of the source and its references to in
`ali' files match. In other words, any `ali' files that
mentions this spec must have resulted from compiling this version of the source
file (or in the case where the source checksums match, a version close enough
that the difference does not matter).
The effect of this consistency checking, which includes source files, is that the binder ensures that the program is consistent with the latest version of the source files that can be located at bind time. Editing a source file without compiling files that depend on the source file cause error messages to be generated by the binder.
For example, suppose you have a main program `hello.adb' and a
package P, from file `p.ads' and you perform the following
steps:
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 (when using -C):
extern int gnat_argc;
extern char **gnat_argv;
extern char **gnat_envp;
extern int gnat_exit_status;
void adafinal ();
void adainit ()
{
__gnat_set_globals (
-1, /* Main_Priority */
-1, /* Time_Slice_Value */
' ', /* Locking_Policy */
' ', /* Queuing_Policy */
' ', /* Tasking_Dispatching_Policy */
adafinal);
system___elabs ();
/* system__standard_library___elabs (); */
/* system__task_specific_data___elabs (); */
/* system__tasking_soft_links___elabs (); */
system__tasking_soft_links___elabb ();
/* system__task_specific_data___elabb (); */
/* system__standard_library___elabb (); */
/* m___elabb (); */
}
void adafinal () {
}
int main (argc, argv, envp)
int argc;
char **argv;
char **envp;
{
gnat_argc = argc;
gnat_argv = argv;
gnat_envp = envp;
__gnat_initialize();
adainit();
_ada_m ();
adafinal();
__gnat_finalize();
exit (gnat_exit_status);
}
unsigned mB = 0x2B0EB17F;
unsigned system__standard_libraryB = 0x0122ED49;
unsigned system__standard_libraryS = 0x79B018CE;
unsigned systemS = 0x08FBDA7E;
unsigned system__task_specific_dataB = 0x6CC7367B;
unsigned system__task_specific_dataS = 0x47178527;
unsigned system__tasking_soft_linksB = 0x5A75A73C;
unsigned system__tasking_soft_linksS = 0x3012AFCB;
/* BEGIN Object file/option list
./system.o
./s-tasoli.o
./s-taspda.o
./s-stalib.o
./m.o
END Object file/option list */
The call to __gnat_set_globals establishes program parameters,
including the priority of the main task, and parameters for tasking control. It
also passes the address of the finalization routine so that it can be called at
the end of program execution.
Next there is code to save the argc and argv values
for later access by the Ada.Command_Line package. The variable
gnat_exit_status saves the exit status set by calls to
Ada.Command_Line.Set_Exit_Status and is used to return an exit
status to the system.
The call to
__gnat_initialize and the corresponding call at the end of
execution to __gnat_finalize allow any specialized initialization
and finalization code to be hooked in. The default versions of these routines do
nothing.
The calls to xxx___elabb and
xxx___elabs perform necessary elaboration of the bodies and specs
respectively of units in the program. These calls are commented out if the unit
in question has no elaboration code.
The call to m is the call to the main program.
The list of unsigned constants gives
the version number information. Version numbers are computed by combining time
stamps of a unit and all units on which it depends. These values are used for
implementation of the Version and Body_Version
attributes.
Finally, a set of comments gives the full names of all the object files that must be linked to provide the Ada component of the program. As seen in the previous example, this list includes the files explicitly supplied and referenced by the user as well as implicitly referenced run-time unit files. The latter are omitted if the corresponding units reside in shared libraries. The directory names for the run-time units depend on the system configuration. See section Output Control.
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). The following switches provide control over the generation of error messages from the binder:
-v
stderr. If this switch is present, a header is
written to stdout and any error messages are directed to
stdout. All that is written to stderr is a brief
summary message.
-b
stderr
even if verbose mode is specified. This is relevant only when used with the
-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
-t should be used only in unusual situations, with extreme
care. The following switches provide additional control over the elaboration order. For full details see See section Elaboration Order Handling in GNAT.
-f
Elaborate_All pragmas, and to use full Ada
95 Reference Manual semantics in an attempt to find a legal elaboration order,
even if it seems likely that this order will cause an elaboration exception.
-p
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. The following switches allow additional control over the output generated by the binder.
-A
-o gnatbind option.
-C
-o gnatbind option.
-e
stdout.
-h
stdout.
-l
stdout.
-O
stdout. This list includes the files explicitly supplied and
referenced by the user as well as implicitly referenced run-time unit files.
The latter are omitted if the corresponding units reside in shared libraries.
The directory names for the run-time units depend on the system configuration.
-o file
-c
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
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.
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.
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
The following are the switches available with gnatbind:
-aO
-aI
-A
-b
stderr even if verbose mode set.
-c
-C
-e
-E
gcc flag -funwind-tables when compiling every
file in your application. See also the packages GNAT.Traceback
and GNAT.Traceback.Symbolic
-f
-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
-Mxyz
-mn
-n
-nostdinc
-nostdlib
-o file
-O
-p
-s
-static
-shared
-t
-Tn
-v
stdout.
-wx
-x
-z
You may obtain this listing by running the program gnatbind with
no arguments.
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.
gnatbindThe 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 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.
-nostdlib is specified. 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.
gnatbind UsageThis 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. gnatlinkThis 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.
gnatlinkThe 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. This list may also include linker
switches.
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.
gnatlinkThe following switches are available with the gnatlink utility:
-A
-C
gnatlink that the binder has generated C code rather
than Ada code.
-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.
--LINK=name
gnatmakeA typical development cycle when working on an Ada program consists of the following steps:
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.
gnatmakeThe form of the gnatmake command is
$ gnatmake [switches] file_name [mode_switches]
The only required argument is file_name, which specifies the
compilation unit that is the main program. If switches are present,
they can be placed before of after file_name. If
mode_switches are present, they must always be placed after
file_name and all switches.
If you are using standard file extensions (.adb and .ads), then the extension
may be omitted from the file_name argument. However, if you are using
non-standard extensions, then it is required that the extension be given. A
relative or absolute directory path can be specified in file_name, in
which case, the input source file will be searched for in the specified
directory only. Otherwise, the input source file will first be searched in the
directory where gnatmake was invoked and if it is not found, it
will be search on the source path of the compiler as described in section Search
Paths and the Run-Time Library (RTL).
All gnatmake output (except when you specify -M) is
to stderr. The output produced by the -M switch is
send to stdout.
gnatmakeYou 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.
--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. -f is also useful in
conjunction with -f if you need to recompile an entire
application, including run-time files, using special configuration pragma
settings, such as a non-standard Float_Representation pragma. By
default gnatmake -a compiles all GNAT internal files with
gcc -c -gnatg rather than gcc -c.
-c
gnatmake will attempt binding and linking
unless all objects are up to date and the executable is more recent than the
objects.
-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 (section 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.
-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
stdout in a form
that can be directly exploited in a `Makefile'. By default, each
source file is prefixed with its (relative or absolute) directory name. This
name is whatever you specified in the various -aI and
-I switches. If you use gnatmake -M -q
(see below), only the source file names, without relative paths, are output.
If you just specify the -M switch, dependencies of the GNAT
internal system files are omitted. This is typically what you want. If you
also specify the -a switch, dependencies of the GNAT internal
files are also listed. Note that dependencies of the objects in external Ada
libraries (see switch -aLdir in the following list)
are never reported.
-n
-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.
-q
gnatmake are displayed.
-v
gnatmake decides are necessary.
-z
gcc switches-g or any uppercase switch (other than
-A, or -L) or any switch that is more than one
character is passed to gcc (e.g. -O,
-gnato, etc.) Source and library search path switches:
-aIdir
-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. 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
gnatmakeThe 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. 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. gnatmake WorksGenerally 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.
gnatmake Usagegnatmake hello.adb
Hello) and bind and link
the resulting object files to generate an executable file `hello'.
gnatmake -q Main_Unit -cargs -O2 -bargs -l
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. Complex project organizations can be handled in a very powerful way by using GNU make combined with gnatmake. Here is for instance a Makefile which allows to build each subsystem of a big project into a separate shared library. Such a makefile allows to significantly reduce the link time of very bug applications while maintaining a complete coherence at each step of the build process.
## 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
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 about the rules below: if your csc are not split into multiple
# directories, but simply by their name, you need to replace *.o and
# *.ali with the appropriate list of files
# Note: In a future version of GNAT, the following commands will be simplified
# by a new tool, gnatmlib
${LIB_DIR}:
mkdir -p ${dir $ }
cd ${dir $ }; gcc -shared -o ${notdir $ } ../*.o -L${GLIB} -lgnat
cd ${dir $ }; cp -f ../*.ali .
# The dependencies for the modules
aa/lib/libaa.so: aa/*.o
bb/lib/libbb.so: bb/*.o
bb/lib/libcc.so: cc/*.o
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}
gnatchopThis 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.
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.
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 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.
gnatchopThe 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.
gnatchopgnatchop 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.
-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.
gnatchop Usagegnatchop -w hello_s.ada ichbiah/files
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. 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.
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 Operating
gnatchop in Compilation Mode for details. However, for most purposes, it
will be more convenient to edit the `gnat.adc' file that contains
configuration pragmas directly, as described in the following section.
In GNAT a compilation environment is defined by the current directory at the time that a compile command is given. This current directory is searched for a file whose name is `gnat.adc'. If this file is present, it is expected to contain one or more configuration pragmas that will be applied to the current compilation.
Configuration pragmas may be entered into the `gnat.adc' file either
by running gnatchop on a source file that consists only of
configuration pragmas, or more conveniently by direct editing of the
`gnat.adc' file, which is a standard format source file.
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.
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 numerous
sections of elaboration code, potentially one section for each unit in the
program. It is important that these execute in the correct order. Correctness
here means that, taking the above example of the declaration of
Sqrt_Half, that 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.
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.
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 situation where neither of these three pragmas can be
used. So we also provide methods for clients to control the order of elaboration
of the servers on which they depend:
with statement, and it requires that the body of
the named unit be elaborated before the unit in which the pragma occurs. The
idea is to use this pragma if the current unit calls at elaboration time,
directly or indirectly, some subprogram in the named unit.
Unit ANow if we put a pragmawith's unit B and calls B.Func in elaboration code Unit Bwith's unit C, and B.Func calls C.Func
Elaborate (B) in unit
A, this ensures that the body of B is elaborated
before the call, but not the body of C, so the call to
C.Func could still cause Program_Error to be raised.
The effect of a pragma Elaborate_All is stronger, it requires not
only that the body of the named unit be elaborated before the unit doing the
with, but also the bodies of all units that the named unit uses,
following with links transitively. For example, if we put a
pragma Elaborate_All (B) in unit A, then it requires
not only that the body of B be elaborated before A,
but also the body of C, because B
with's C. We are now in a position to give a usage rule in Ada 95 for avoiding elaboration problems, at least if dynamic dispatching and access to subprogram values are not used. We will handle these cases separately later.
The rule is simple. If a unit has elaboration code that can directly or
indirectly make a call to a subprogram in a with'ed unit, or
instantiate a generic unit in a with'ed unit, then if the
with'ed unit does not have pragma Pure, Preelaborate, or
Elaborate_Body, then the client should have an Elaborate_All for the
with'ed unit. By following this rule a client is assured that calls
can be made without risk of an exception. If this rule is not followed, then a
program may be in one of four states:
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.
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.
The previous section discussed the case in which the execution of a particular thread of elaboration code occurred entirely within a single unit. This is the easy case to handle, because a programmer has direct and total control over the order of elaboration, and furthermore, checks need only be generated in cases which are rare and which the compiler can easily detect. The situation is more complex when separate compilation is taken into account. Consider the following:
package Math is
function Sqrt (Arg : Float) return Float;
end Math;
package body Math is
function Sqrt (Arg : Float) return Float is
begin
...
end Sqrt;
end Math;
with Math;
package Stuff is
X : Float := Math.Sqrt (0.5);
end Stuff;
with Stuff;
procedure Main is
begin
...
end Main;
where Main is the main program. When this program is executed,
the elaboration code must first be executed, and one of the jobs of the binder
is to determine the order in which the units of a program are to be elaborated.
In this case we have four units: the spec and body of Math, the
spec of Stuff and the body of Main). In what order
should the four separate sections of elaboration code be executed?
There are some restrictions in the order of elaboration that the binder can
choose. In particular, if unit U has a with for a package
X, then you are assured that the spec of X is
elaborated before U , but you are not assured that the body of X is
elaborated before U. This means that in the above case, the binder is allowed to
choose the order:
spec of Math spec of Stuff body of Math body of Main
but that's not good, because now the call to Math.Sqrt that
happens during the elaboration of the Stuff spec happens before the
body of Math.Sqrt is elaborated, and hence causes
Program_Error exception to be raised. At first glance, one might
say that the binder is misbehaving, because obviously you want to elaborate the
body of something you with first, but that is not a general rule
that can be followed in all cases. Consider
package X is ... package Y is ... with X; package body Y is ... with Y; package body X is ...
This is a common arrangement, and, apart from the order of elaboration
problems that might arise in connection with elaboration code, this works fine.
A rule that says that you must first elaborate the body of anything you
with cannot work in this case (the body of X
with's Y, which means you would have to elaborate the
body of Y first, but that with's X, which
means you have to elaborate the body of X first, but ... and we
have a loop that cannot be broken.
It is true that the binder can in many cases guess an order of elaboration
that is unlikely to cause a Program_Error exception to be raised,
and it tries to do so (in the above example of Math/Stuff/Spec, the
GNAT binder will in fact always elaborate the body of Math right
after its spec, so all will be well).
However, a program that blindly relies on the binder to be helpful can get into trouble, as we discussed in the previous sections, so GNAT provides a number of facilities for assisting the programmer in developing programs that are robust with respect to elaboration order.
The default behavior in GNAT ensures elaboration safety. In its default mode GNAT implements the rule we previously described as the right approach. Let's restate it:
If a unit has elaboration code that can directly or indirectly make a call to
a subprogram in a with'ed unit, or instantiate a generic unit in a
with'ed unit, then if the with'ed unit does not have
pragma Pure, Preelaborate, or
Elaborate_Body, then the client should have an
Elaborate_All for the with'ed unit. By following this
rule a client is assured that calls and instantiations can be made without risk
of an exception.
In this mode GNAT traces all calls that are potentially made from elaboration
code, and put 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.
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.
-f switch for the gnatbind step, or -bargs
-f if you are using gnatmake. This switch tells the binder
to ignore any implicit Elaborate_All pragmas that were generated
by the compiler, and suppresses any circularity messages that they cause. The
resulting executable will work properly if there are no elaboration problems,
but if there are some order of elaboration problems they will not be detected,
and unexpected results may occur. It is hard to generalize on which of these three approaches should be taken.
Obviously if it is possible to fix the program so that the default treatment
works, this is preferable, but this may not always be practical. It is certainly
simple enough to use -gnatE or -f but the danger in
either case is that, even if the GNAT binder finds a correct elaboration order,
it may not always do so, and certainly a binder from another Ada compiler might
not. A combination of testing and analysis (for which the warnings generated
with the -gnatwl switch can be useful) must be used to ensure that
the program is free of errors. One switch that is useful in this testing is the
-h (horrible elaboration order) switch for gnatbind.
Normally the binder tries to find an order that has the best chance of of
avoiding elaboration problems. With this switch, the binder plays a devil's
advocate role, and tries to choose the order that has the best chance of
failing. If your program works even with this switch, then it has a better
chance of being error free, but this is still not a guarantee.
For an example of this approach in action, consider the C-tests (executable tests) from the ACVC suite. If these are compiled and run with the default treatment, then all but one of them succeed without generating any error diagnostics from the binder. However, there is one test that fails, and this is not surprising, because the whole point of this test is to ensure that the compiler can handle cases where it is impossible to determine a correct order statically, and it checks that an exception is indeed raised at run time.
This one test must be compiled and run using the -gnatE switch,
and then it passes. Alternatively, the entire suite can be run using this
switch. It is never wrong to run with the dynamic elaboration switch if your
code is correct, and we assume that the C-tests are indeed correct (it is less
efficient, but efficiency is not a factor in running the ACVC tests.)
The introduction of access-to-subprogram types in Ada 95 complicates the handling of elaboration. The trouble is that it becomes impossible to tell at compile time which procedure is being called. This means that it is not possible for the binder to analyze the elaboration requirements in this case.
If at the point at which the access value is created, the body of the
subprogram is known to have been elaborated, then the access value is safe, and
its use does not require a check. This may be achieved by appropriate
arrangement of the order of declarations if the subprogram is in the current
unit, or, if the subprogram is in another unit, by using pragma
Pure, Preelaborate, or Elaborate_Body on
the referenced unit.
If the referenced body is not known to have been elaborated at the point the
access value is created, then any use of the access value must do a dynamic
check, and this dynamic check will fail and raise a Program_Error
exception if the body has not been elaborated yet. GNAT will generate the
necessary checks, and in addition, if the -gnatwl switch is set,
will generate warnings that such checks are required.
The use of dynamic dispatching for tagged types similarly generates a
requirement for dynamic checks, and premature calls to any primitive operation
of a tagged type before the body of the operation has been elaborated, will
result in the raising of Program_Error.
First, compile your program with the default options, using none of the
special elaboration control switches. If the binder successfully binds your
program, then you can be confident that, apart from issues raised by the use of
access-to-subprogram types and dynamic dispatching, the program is free of
elaboration errors. If it is important that the program be portable, then use
the -gnatwl switch to generate warnings about missing
Elaborate_All pragmas, and supply the missing pragmas.
If the program fails to bind using the default static elaboration handling,
then you can fix the program to eliminate the binder message, or recompile the
entire program with the -gnatE switch to generate dynamic
elaboration checks, or, if you are sure there really are no elaboration
problems, use the -f switch for the binder to cause it to ignore
implicit Elaborate_All pragmas generated by the compiler.
gnatxref and
gnatfindThe compiler generates cross-referencing information (unless you set the `-gnatx' switch), which are saved in the `.ali' files. This information indicates where in the source each entity is declared and referenced.
Before using any of these two tools, you need to compile successfully your application, so that GNAT gets a chance to generate the cross-referencing information.
The two tools gnatxref and gnatfind take advantage
of this information to provide the user with the capability to easily locate the
declaration and references to an entity. These tools are quite similar, the
difference being that gnatfind is intended for locating definitions
and/or references to a specified entity or entities, whereas
gnatxref is oriented to generating a full report of all
cross-references.
To use these tools, you must not compile your application using the `-gnatx' switch on the `gnatmake' command line (See Info file `gnat_ug', node `The GNAT Make Program gnatmake'). Otherwise, cross-referencing information will not be generated.
The command lines for gnatxref is:
$ gnatxref [switches] sourcefile1 [sourcefile2 ...]
where
sourcefile1, sourcefile2
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
-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 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'.
The command line for gnatfind is:
$ gnatfind [switches] pattern[:sourcefile[:line[:column]]] [file1 file2 ...]
where
pattern
sourcefile
gnatfind will look for references, bodies or declarations of
symbols referenced in `sourcefile', at line `line' and
column `column'. See see section Examples
of gnatfind usage for syntax examples.
line
column
file1 file2 ...
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
-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. 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.
The project files allows a programmer to specify how to compile its
application, where to find sources,... These files are used primarily by the
Emacs Ada mode, but they can also be used by the two tools gnatxref
and gnatfind.
A project file name must end with `.adp'. If a single one is present
in the current directory, then gnatxref and gnatfind
will extract the information from it. If multiple project files are found, none
of them is read, and you have to use the `-p' switch to specify the
one you want to use.
The following lines can be included, even though most of them have default values which can be used in most cases. The lines can be entered in any order in the file. Except for `src_dir' and `obj_dir', you can only have one instance of each line. If you have multiple instances, only the last one is taken into account.
gnatxref and gnatfind only take into account the
`src_dir' and `obj_dir' lines, and ignore the others.
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 :
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
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 :
gnatxref usageFor 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.
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.
gnatfind usagegnatfind -f xyz:main.adb
directory/main.ads:106:14: xyz <= declaration directory/main.adb:24:10: xyz <= body directory/foo.ads:45:23: xyz <= declarationthat 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
gnatfind "*":main.adb:123.
gnatfind mydir/main.adb:123:45
gnatkrThis 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.
gnatkrThe 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 reason for this exception is to avoid clashes with the standard names for children of System, Ada, Interfaces, and GNAT, which use the prefixes s- a- i- and g- respectively.
The -gnatknn switch of the compiler activates a
"krunching" circuit that limits file names to nn characters (where nn is a
decimal integer). For example, using OpenVMS, where the maximum file name length
is 39, the value of nn is usually set to 39, but if you want to generate a set
of files that would be usable if ported to a system with some different maximum
file length, then a different value can be specified. The default value of 39
for OpenVMS need not be specified.
The gnatkr utility can be used to determine the krunched name
for a given file, when krunched to a specified maximum length.
gnatkrThe 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.
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:
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
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.
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
gnatprepThe 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.
gnatprepTo call gnatprep use
$ gnatprep [-bcrsu] [-Dsymbol=value] infile outfile [deffile]
where
infile
outfile
deffile
-D switch.
switches
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.
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.
gnatprepThe 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 in column one, but otherwise the format is free
form. Spaces or tabs may appear between the # and the keyword. The
keywords and the symbols are case insensitive as in normal Ada code. Comments
may be used on a preprocessor line, but other than that, no other tokens may
appear on a preprocessor line. Any number of elsif clauses can be
present, including none at all. The else is optional, as in Ada.
The # marking the start of a preprocessor line must be the first
non-blank character on the line, i.e. it must be preceded only by spaces or
horizontal tabs.
Symbol substitution outside of preprocessor lines is obtained by using the sequence
$symbol
anywhere within a source line, except in a comment. The identifier following
the $ must match one of the symbols defined in the symbol
definition file, and the result is to substitute the value of the symbol in
place of $symbol in the output file.
gnatlsgnatls 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.
gnatlsThe gnatls command has the form
$ gnatls switches object_or_ali_file
The main argument is the list of object or `ali' files (see section 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)
gnatlsgnatls recognizes the following switches:
-a
-d.
-d
-h
-o
-s
-u
-aOdir
-aIdir
-Idir
-I-
-nostdinc
gnatmake
-v
Preelaborable
No_Elab_Code
Pure
Elaborate_Body
Remote_Types
Shared_Passive
Predefined
Remote_Call_Interface
gnatls UsageExample 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
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 how the GNAT environment has
been installed and can be located with the command
$ gnatls -v
The last line of the Object Search Path usually contains the gnat library. This Makefile contains its own documentation and in particular the set of instructions needed to rebuild a new library and to use it.
gnatmemgnatmem, 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:
gnatmemThe gnatmem command has the form
$ gnatmem [n] [-o file] user_program [program_arg]* or $ gnatmem [n] -i file
Gnatmem must be supplied with the executable to examine, followed by its run-time inputs. For example, if a program is executed with the command:
$ my_program arg1 arg2
then it can be run under gnatmem control using the command:
$ gnatmem my_program arg1 arg2
The program is transparently executed under the control of the debugger
section 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 section 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.
gnatmemgnatmem recognizes the following switches:
-qn-o file-i filegnatmem processing starting from
file which has been generated by a previous call to
gnatmem with the -o switch. This is useful for post mortem
processing. gnatmem UsageThe 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.
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.
Some of the tools distributed with GNAT are based on the ASIS implementation for GNAT (ASIS-for-GNAT). Binary executables for such tools do not require ASIS-for-GNAT to be around and they have a command-line interface similar to other GNAT tools. The main specific feature of ASIS-based tools is that they process tree output files.
The ASIS implementation for GNAT, called ASIS-for-GNAT, is the implementation if the Ada Semantic Interface Specification (ASIS). It is a separate product which is not included in the standard GNAT distribution. However, the binary executables for tools created on top of ASIS-for-GNAT do not require ASIS-for-GNAT installed on your system and they can be used for a standard GNAT distribution along with other GNAT tools
The ASIS implementation for GNAT is based on tree output files (or, simply, tree files). A tree file stores a snapshot of the compiler internal data structures in the very end of a successful compilation. It contains all the syntactical and semantic information about the unit being compiled and all the units upon which it depends semantically. ASIS-for-GNAT (and, therefore, any tool based on its top) processes tree files, extracts this information from it and converts it into the format prescribing by the ASIS definition.
To use some ASIS-based tools, a user should take care of producing the right set of tree files for the tool, some other ASIS tools produce a needed set of tree files themselves.
GNAT produces a tree file if -gnatt option is set when calling gcc. ASIS needs tree files created in "compile-only" GNAT mode set by -gnatc gcc switch. Names of the tree files are obtained by replacing 'd' with 't' in the extension of the name of the source file being compiled.
Therefore, to produce a tree file for the body of a procedure Foo contained in the source file named 'foo.adb', you can compile it using
$ gcc -c -gnatc -gnatt foo.adb
and you will get the tree file named 'foo.atb' as a result of this compilation.
gnatstubgnatstub creates body samples - that is, empty but compilable
bodies for library unit declarations.
gnatstub is an ASIS-based tool, but it creates a needed tree
file itself, so it can be considered as a usual command-line utility program
when using with GNAT.
To create a body sampler, 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 not only in
the current directory, you have to provide a source search path when calling
gnatstub, see the description of gnatstub switches below.
gnatstubgnatstub has the command-line interface of the form
$ gnatstub [switches] filename [directory]
where
filename
directory
switches
gnatstub-f
-f switch is set or leaves it intact otherwise.
-hs
-hg
-IDIR
-I-
-in
-k
-k prevents deleting the tree file.
-ln
-q
-r
-r also implies -k,
whether or not -k is set explicitly.
-t
-t option is set
-v
gnatelimgnatelimWhen 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 those unused subprograms increases the size of the executable.
gnatelim is a utility tracking unused subprograms in an Ada
program. Its output consists of a list of Eliminate pragmas marking
all the subprograms that are declared, but never called in a given program.
Eliminate is a GNAT-specific pragma, it is described in the next
section. 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 code
for those unused subprograms.
gnatelim is an ASIS-based tool, and it needs as its input data a
set of tree files representing all the components of a program to process. It
also needs a bind file for a main subprogram. (See section Preparing
Tree and Bind Files for gnatelim for full details)
Eliminate pragmaThe syntax of Eliminate pragma is
pragma Eliminate (Library_Unit_Name, Subprogram_Name);
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 having Library_Unit_Name as its defining
program unit name, then the compiler will not generate code for this
subprogram. It applies to all overloaded subprograms denoted by
Subprogram_Name.
Eliminate pragma as unused
is actually used (called) in a program, then the compiler will produce a
diagnosis in place where it is called. gnatelimgnatelim can process only full Ada programs (partitions) and it
needs a set of tree files representing the whole program (partition) to be
presented in the current directory. It also needs a bind file for the main
subprogram of the program (partition) to be presented in the current directory.
Let Main_Prog be the name of a main subprogram, and suppose this
subprogram is in a file named `main_prog.ads' or
`main_prog.adb'.
To create a minimal set of tree files covering the whole program, call
gnatmake for this program as follows:
$ gnatmake -c -f -gnatc -gnatt Main_Prog
The -c gnatmake option turns off the bind and link phases, which
are impossible anyway, because sources are compiled with -gnatc
option, which turns off code generation.
the -f gnatmake option is used to force recompilation of all the
needed sources.
To create a bind file for gnatelim, run gnatbind
for the main subprogram. gnatelim can work with either an Ada or a
C bind file, if both are present, it works with the Ada bind file. To avoid
problems with creating a consistent data for gnatelim, it is
advised to use the following procedure. It creates all the data needed by
gnatelim from scratch and therefore guarantees their consistency:
$ gnatmake -c Main_Prog $ gnatbind main_prog
$ gnatmake -f -c -gnatc -gnatt Main_Prog
Note, that gnatelim needs neither object nor ALI files, so they
can be deleted at this stage.
gnatelimgnatelim 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:
-v
-a
-m
gnatelim directs its output to the standard output, so to
produce a proper GNAT configuration file `gnat.adc', redirection can 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'.
It may happen that gnatelim try to eliminate subprograms which
cannot really be eliminated because they are actually called in the program
although this only happens in very rare cases. In this case, the compiler will
generate an error message of the form:
file.adb:106:07: cannot call eliminated subprogram "My_Prog"
You have to correct the `gnat.adc' file manually by suppressing the faulty Eliminate pragmas. It is advised to recompile your program from scratch after that, because you need a consistent `gnat.adc' file during the complete compilation in order to get an meaningful result.
To get a smaller executable for your program, you have to recompile the
program completely, having the `gnat.adc' file with a set of
Eliminate pragmas 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 got from
gnatelim).
Be aware that a set of Eliminate pragmas is specific to each
program. Therefore, it is not advised to merge sets of Eliminate
pragmas created for different programs in one `gnat.adc' file.
Here is a 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
This chapter discusses some other utility programs available in the Ada environment.
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.
gnatpsys Utility ProgramMany of the definitions in package System are implementation-dependent. Furthermore, although the source of the package System is available for inspection, it uses special attributes for parameterizing many of the critical values, so the source is not informative for the casual user.
The gnatpsys utility is designed to deal with this situation. It
is an Ada program that dynamically determines the values of all the relevant
parameters in System, and prints them out in the form of an Ada source listing
for System, displaying all the values of interest. This output is generated to
`stdout'.
To determine the value of any parameter in package System, simply run
gnatpsys with no qualifiers or arguments, and examine the output.
This is preferable to consulting documentation, because you know that the values
you are getting are the actual ones provided by the executing system.
gnatpsta Utility ProgramMany 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.
In order to interpret the output from GNAT, when using tools that are originally intended for use with other languages, it is useful to understand the conventions used to generate link names from the Ada entity names.
All link names are in all lowercase letters. With the exception of library procedure names, the mechanism used is simply to use the full expanded Ada name with dots replaced by double underscores. For example, suppose we have the following package spec:
package QRS is
MN : Integer;
end QRS;
The variable MN has a full expanded Ada name of
QRS.MN, so the corresponding link name is qrs__mn. Of course if a pragma Export is used this may be
overridden:
package Exports is
Var1 : Integer;
pragma Export (Var1, C, External_Name => "var1_name");
Var2 : Integer;
pragma Export (Var2, C, Link_Name => "var2_link_name");
end Exports;
In this case, the link name for Var1 is var1_name, and the link name for Var2 is var2_link_name.
One exception occurs for library level procedures. A
potential ambiguity arises between the required name _main for the
C main program, and the name we would otherwise assign to an Ada library level
procedure called Main (which might well not be the main program).
To avoid this ambiguity, we attach the prefix _ada_ to such
names. So if we have a library level procedure such as
procedure Hello (S : String);
the external name of this procedure will be _ada_hello.
emacsThe Emacs mode for programming in Ada (both, Ada83 and Ada95) helps the user in understanding existing code and facilitates writing new code. It furthermore provides some utility functions for easier integration of standard Emacs features when programming in Ada.
For more information, please see See section Ada
Mode for emacs.
This Perl script allows Ada source files to be browsed using
standard Web browsers. For installation procedure, see the section See section
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 runtime library itself.
-D
gnathtml will also
look for files in the runtime 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
-sc color
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
This chapter discusses how to debug Ada programs. An incorrect Ada program may be handled in three ways by the GNAT compiler:
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.
The debugger can be launched directly and simply from emacs which allows to
browse and modify directly the source code during the debugging session, See
section Ada
Mode for emacs. Here is described the basic use of GDB is text
mode.
The command to run GDB is
$ gdb program
where program is the name of the executable file. This activates
the debugger and results in a prompt for debugger commands. The simplest command
is simply run, which causes the program to run exactly as if the
debugger were not present. The following section describes some of the
additional commands that can be given to GDB.
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
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
continue
step
next
list
backtrace
up
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
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).
GDB supports a fairly large subset of Ada expression syntax, with some extensions. The philosophy behind the design of this subset is
Thus, for brevity, the debugger acts as if there were implicit
with and use clauses in effect for all user-written
packages, thus making it unnecessary to fully qualify most names with their
packages, regardless of context. Where this causes ambiguity, GDB asks the
user's intent.
For details on the supported Ada syntax Debugging with GDB.
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.
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. 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
For more detailed information on the tasking support Debugging with GDB.
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.
When presented with programs that contain serious errors in syntax or semantics, GNAT may on rare occasions experience problems in operation, such as aborting with a segmentation fault or illegal memory access, raising an internal exception, or terminating abnormally. In such cases, you can activate various features of GNAT that can help you pinpoint the construct in your program that is the likely source of the problem.
The following strategies are presented in increasing order of difficulty, corresponding to your programming skills and your familiarity with compiler internals.
gcc with the -gnatf and -gnate
switches. The first switch causes all errors on a given line to be reported.
In its absence, only the first error on a line is displayed. The
-gnate switch causes errors to be displayed as soon as they are
encountered, rather than after compilation is terminated. If GNAT terminates
prematurely, the last error message displayed is likely to pinpoint the
culprit.
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 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. 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. 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.
This chapter describes topics that are specific to the Microsoft Windows platforms (NT, 95 and 98).
One of the strengths of the GNAT technology is that its tool set
(gcc, gnatbind, gnatlink,
gnatmake, the gdb debugger, etc.) is used in the same
way regardless of the platform.
On Windows this tool set is complemented by a number of Microsoft-specific tools that have been provided to facilitate interoperability with Windows when this is required. With these tools:
Developing pure Ada applications on Windows is no different than on other GNAT-supported platforms. However, when developing or porting an application that contains a mix of Ada and C/C++, the choice of your Windows C/C++ development environment conditions your overall interoperability strategy.
If you use gcc to compile the non-Ada part of your application,
there are no Windows-specific restrictions that affect the overall
interoperability with your Ada code. If you plan to use Microsoft tools (e.g.
Microsoft Visual C/C++), you should be aware of the following limitations:
.tls section (Thread Local
Storage section) since the GNAT linker does not yet support this section.
msvcrt.dll. This is because the GNAT runtime uses
the services of msvcrt.dll for its I/Os. Use of other I/O
libraries can cause a conflict with msvcrt.dll services. For
instance Visual C++ I/O stream routines conflict with those in
msvcrt.dll. If you do want to use the Microsoft tools for your non-Ada code and hit one of the above limitations, you have two choices:
When a subprogram F (caller) calls a subprogram G
(callee), there are several ways to push G's parameters on the
stack and there are several possible scenarios to clean up the stack upon
G's return. A calling convention is an agreed upon software
protocol whereby the responsabilities between the caller (F) and
the callee (G) are clearly defined. Several calling conventions are
available for Windows:
C (Microsoft defined)
Stdcall (Microsoft defined)
DLL (GNAT specific) C Calling ConventionThis is the default calling convention used when interfacing to C/C++
routines compiled with either gcc or Microsoft Visual C++.
In the C calling convention subprogram parameters are pushed on
the stack by the caller from right to left. The caller itself is in charge of
cleaning up the stack after the call. In addition, the name of a routine with
C calling convention is mangled by adding a leading underscore.
The name to use on the Ada side when importing (or exporting) a routine with
C calling convention is the name of the routine. For instance the C
function:
int get_val (long);
should be imported from Ada as follows:
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int; pragma Import (C, Get_Val, External_Name => "get_val");
Note that in this particular case the External_Name parameter
could have been omitted since, when missing, this parameter is taken to be the
name of the Ada entity in lower case. When the Link_Name parameter
is missing, as in the above example, this parameter is set to be the
External_Name with a leading underscore.
When importing a variable defined in C, you should always use the
C calling convention unless the object containing the variable is
part of a DLL (in which case you should use the DLL calling
convention, see section DLL
Calling Convention).
Stdcall Calling ConventionThis convention, which was the calling convention used for Pascal programs, is used by Microsoft for all the routines in the Win32 API for efficiency reasons. It must be used to import any routine for which this convention was specified.
In the Stdcall calling convention subprogram parameters are
pushed on the stack by the caller from right to left. The callee (and not the
caller) is in charge of cleaning the stack on routine exit. In addition, the
name of a routine with Stdcall calling convention is mangled by
adding a leading underscore (as for the C calling convention) and a
trailing @nn, where nn is the overall
size (in bytes) of the parameters passed to the routine.
The name to use on the Ada side when importing a C routine with a
Stdcall calling convention is the name of the C routine. The
leading underscore and trailing @nn are added
automatically by the compiler. For instance the Win32 function:
APIENTRY int get_val (long);
should be imported from Ada as follows:
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int; pragma Import (Stdcall, Get_Val); -- On the x86 a long is 4 bytes, so the Link_Name is "_get_val@4"
As for the C calling convention, when the
External_Name parameter is missing, it is taken to be the name of
the Ada entity in lower case. If instead of writing the above import pragma you
write:
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int; pragma Import (Stdcall, Get_Val, External_Name => "retrieve_val");
then the imported routine is _retrieve_val@4. However, if
instead of specifying the External_Name parameter you specify the
Link_Name as in the following example:
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int; pragma Import (Stdcall, Get_Val, Link_Name => "retrieve_val");
then the imported routine is retrieve_val@4, that is, there is
no trailing underscore but the appropriate @nn
is always added at the end of the Link_Name by the compiler.
DLL Calling ConventionThis convention, which is GNAT-specific, must be used when you want to import
in Ada a variables defined in a DLL. For functions and procedures this
convention is equivalent to the Stdcall convention. As an example,
if a DLL contains a variable defined as:
int my_var;
then, to access this variable from Ada you should write:
My_Var : Interfaces.C.int; pragma Import (DLL, My_Var);
The remarks concerning the External_Name and
Link_Name parameters given in the previous sections equally apply
to the DLL calling convention.
A Dynamically Linked Library (DLL) is a library that can be shared by several applications running under Windows. A DLL can contain any number of routines and variables.
One advantage of DLLs is that you can change and enhance them without forcing all the applications that depend on them to be relinked or recompiled. However, you should be aware than all calls to DLL routines are slower since, as you will understand below, such calls are indirect.
To illustrate the remainder of this section, suppose that an application wants to use the services of a DLL `API.dll'. To use the services provided by `API.dll' you must statically link against an import library which contains a jump table with an entry for each routine and variable exported by the DLL. In the Microsoft world this import library is called `API.lib'. When using GNAT this import library is called either `libAPI.a' or `libapi.a' (names are case insensitive).
After you have statically linked your application with the import library and you run your application, here is what happens:
DllMain or
DllMainCRTStartup are invoked. These routines typically contain
the initialization code needed for the well-being of the routines and
variables exported by the DLL. There is an additional point which is worth mentioning. In the Windows world there are two kind of DLLs: relocatable and non-relocatable DLLs. Non-relocatable DLLs can only be loaded at a very specific address in the target application address space. If the addresses of two non-relocatable DLLs overlap and these happen to be used by the same application, a conflict will occur and the application will run incorrectly. Hence, when possible, it is always preferable to use and build relocatable DLLs. Both relocatable and non-relocatable DLLs are supported by GNAT.
As a side note, an interesting difference between Microsoft DLLs and Unix shared libraries, is the fact that on most Unix systems all public routines are exported by default in a Unix shared library, while under Windows the exported routines must be listed explicitly in a definition file (see section The Definition File).
To use the services of a DLL, say `API.dll', in your Ada application you must have:
Once you have all the above, to compile an Ada application that uses the
services of `API.dll' and whose main subprogram is
My_Ada_App, you simply issue the command
$ gnatmake my_ada_app -largs -lAPI
The argument -largs -lAPI at the end of the
gnatmake command tells the GNAT linker to look first for a library
named `API.lib' (Microsoft-style name) and if not found for a library
named `libAPI.a' (GNAT-style name). Note that if the Ada package spec
for `API.dll' contains the following pragma
pragma Linker_Options ("-lAPI");
you do not have to add -largs -lAPI at the end of the
gnatmake command.
If any one of the items above is missing you will have to create it yourself. The following sections explain how to do so using as an example a fictitious DLL called `API.dll'.
A DLL typically comes with a C/C++ header file which provides the definitions of the routines and variables exported by the DLL. The Ada equivalent of this header file is a package spec that contains definitions for the imported entities. If the DLL you intend to use does not come with an Ada spec you have to generate one such spec yourself. For example if the header file of `API.dll' is a file `api.h' containing the following two definitions:
int some_var; int get (char *);
then the equivalent Ada spec could be:
with Interfaces.C.Strings;
package API is
use Interfaces;
Some_Var : C.int;
function Get (Str : C.Strings.Chars_Ptr) return C.int;
private
pragma Import (C, Get);
pragma Import (DLL, Some_Var);
end API;
Note that a variable is always imported with a DLL
convention. A function can have C, Stdcall or
DLL convention. For subprograms, the DLL convention is
a synonym of Stdcall (see section Windows
Calling Conventions).
If a Microsoft-style import library `API.lib' or a GNAT-style import library `libAPI.a' is available with `API.dll' you can skip this section. Otherwise read on.
As previously mentioned, and unlike Unix systems, the list of symbols that
are exported from a DLL must be provided explicitly in Windows. The main goal of
a definition file is precisely that: list the symbols exported by a DLL. A
definition file (usually a file with a .def suffix) has the
following structure:
[LIBRARY name]
[DESCRIPTION string]
EXPORTS
symbol1
symbol2
...
LIBRARY name
DESCRIPTION string
EXPORTS
EXPORTS section of `API.def' looks like: EXPORTS
some_var
get
Note that you must specify the correct suffix
(@nn) (see section Windows
Calling Conventions) for a Stdcall calling convention function in the
exported symbols list.
There can actually be other sections in a definition file, but these sections are not relevant to the discussion at hand.
To create a static import library from `API.dll' with the GNAT tools you should proceed as follows:
dll2def tool as follows: $ dll2def API.dll > API.def
dll2def is a very simple tool: it takes as input a DLL and
prints to standard output the list of entry points in the DLL. Note that if
some routines in the DLL have the Stdcall convention (see section
Windows
Calling Conventions) then you'll have to edit `api.def' to add
the needed @nn suffix.
libAPI.a, using gnatdll
(see section Using
gnatdll) as follows: $ gnatdll -e API.def -d API.dll
gnatdll takes as input a definition file `API.def'
and the name of the DLL containing the services listed in the definition file
`API.dll'. The name of the static import library generated is
computed from the name of the definition file as follows: if the definition
file name is xyz.def, the import library name will be
libxyz.a. Note that in the previous example
option -e could have been removed because the name of the
definition file (before the ".def" suffix) is the same as the
name of the DLL (see section Using
gnatdll for more information about gnatdll).
With GNAT you can either use a GNAT-style or Microsoft-style import library. A Microsoft import library is needed only if you plan to make an Ada DLL available to applications developed with Microsoft tools (see section Mixed-Language Programming on Windows).
To create a Microsoft-style import library for `API.dll' you should proceed as follows:
dll2def tool as described above or the Microsoft
dumpbin tool (see the corresponding Microsoft documentation for
further details).
lib
utility: $ lib -machine:IX86 -def:API.def -out:API.libIf you use the above command the definition file `API.def' must contain a line giving the name of the DLL:
LIBRARY "API"See the Microsoft documentation for further details about the usage of
lib. This section explains how to build DLLs containing Ada code. These DLLs will be referred to as Ada DLLs in the remainder of this section.
The steps required to build an Ada DLL that is to be used by Ada as well as non-Ada applications are as follows:
C or Stdcall calling convention to avoid any Ada
name mangling for the entities exported by the DLL (see section Exporting
Ada Entities). You can skip this step if you plan to use the Ada DLL only
from Ada applications.
adainit generated by gnatbind to perform the
elaboration of the Ada code in the DLL (see section Ada
DLLs and Elaboration). The initialization routine exported by the Ada DLL
must be invoked by the clients of the DLL to initialize the DLL.
adafinal generated by gnatbind to perform
the finalization of the Ada code in the DLL (see section Ada
DLLs and Finalization). The finalization routine exported by the Ada DLL
must be invoked by the clients of the DLL when the DLL services are no further
needed.
gnatdll to produce the DLL and the
import library (see section Using
gnatdll). When using Ada DLLs from Ada applications there is a limitation users should be aware of. Because on Windows the GNAT runtime is not in a DLL of its own, each Ada DLL includes a part of the GNAT runtime. Specifically, each Ada DLL includes the services of the GNAT runtime that are necessary to the Ada code inside the DLL. As a result, when an Ada program uses an Ada DLL there are two independent GNAT runtimes: one in the Ada DLL and one in the main program.
It is therefore not possible to exchange GNAT runtime objects between the Ada
DLL and the main Ada program. Example of GNAT runtime objects are file handles
(e.g. Text_IO.File_Type), tasks types, protected objects types,
etc.
It is completely safe to exchange plain elementary, array or record types, Windows object handles, etc.
Building a DLL is a way to encapsulate a set of services usable from any
application. As a result, the Ada entities exported by a DLL should be exported
with the C or Stdcall calling conventions to avoid any
Ada name mangling. Please note that the Stdcall convention should
only be used for subprograms, not for variables. As an example here is an Ada
package API, spec and body, exporting two procedures, a function,
and a variable:
with Interfaces.C; use Interfaces;
package API is
Count : C.int := 0;
function Factorial (Val : C.int) return C.int;
procedure Initialize_API;
procedure Finalize_API;
-- Initialization & Finalization routines. More in the next section.
private
pragma Export (C, Initialize_API);
pragma Export (C, Finalize_API);
pragma Export (C, Count);
pragma Export (C, Factorial);
end API;
package body API is
function Factorial (Val : C.int) return C.int is
Fact : C.int := 1;
begin
Count := Count + 1;
for K in 1 .. Val loop
Fact := Fact * K;
end loop;
return Fact;
end Factorial;
procedure Initialize_API is
procedure Adainit;
pragma Import (C, Adainit);
begin
Adainit;
end Initialize_API;
procedure Finalize_API is
procedure Adafinal;
pragma Import (C, Adafinal);
begin
Adafinal;
end Finalize_API;
end API;
If the Ada DLL you are building will only be used by Ada applications you do
not have to export Ada entities with a C or Stdcall
convention. As an example, the previous package could be written as follows:
package API is
Count : Integer := 0;
function Factorial (Val : Integer) return Integer;
procedure Initialize_API;
procedure Finalize_API;
-- Initialization and Finalization routines.
end API;
package body API is
function Factorial (Val : Integer) return Integer is
Fact : Integer := 1;
begin
Count := Count + 1;
for K in 1 .. Val loop
Fact := Fact * K;
end loop;
return Fact;
end Factorial;
...
-- The remainder of this package body is unchanged.
end API;
Note that if you do not export the Ada entities with a C or
Stdcall convention you will have to provide the mangled Ada names
in the definition file of the Ada DLL (see section Creating
the Definition File).
The DLL that you are building contains your Ada code as well as all the routines in the Ada library that are needed by it. The first thing a user of your DLL must do is elaborate the Ada code (see section Elaboration Order Handling in GNAT).
To achieve this you must export an initialization routine
(Initialize_API in the previous example), which must be invoked
before using any of the DLL services. This elaboration routine must call the Ada
elaboration routine adainit generated by the GNAT binder (see
section Binding
with Non-Ada Main Programs). See the body of Initialize_Api for
an example. Note that the GNAT binder is automatically invoked during the DLL
build process by the gnatdll tool (see section Using
gnatdll).
When a DLL is loaded, Windows systematically invokes a routine called
DllMain. It would therefore be possible to call
adainit directly from DllMain without having to
provide an explicit initialization routine. Unfortunately, it is not possible to
call adainit from the DllMain if your program has
library level tasks because access to the DllMain entry point is
serialized by the system (that is, only a single thread can execute "through" it
at a time), which means that the GNAT runtime will deadlock waiting for the
newly created task to complete its initialization.
When the services of an Ada DLL are no longer needed, the client code should
invoke the DLL finalization routine, if available. The DLL finalization routine
is in charge of releasing all resources acquired by the DLL. In the case of the
Ada code contained in the DLL, this is achieved by calling routine
adafinal generated by the GNAT binder (see section Binding
with Non-Ada Main Programs). See the body of Finalize_Api for
an example. As already pointed out the GNAT binder is automatically invoked
during the DLL build process by the gnatdll tool (see section Using
gnatdll).
To use the services exported by the Ada DLL from another programming language
(e.g. C), you have to translate the specs of the exported Ada entities in that
language. For instance in the case of API.dll, the corresponding C
header file could look like:
extern int *__imp__count; #define count (*__imp__count) int factorial (int);
It is important to understand that when building an Ada DLL to be used by
other Ada applications, you need two different specs for the packages contained
in the DLL: one for building the DLL and the other for using the DLL. This is
because the DLL calling convention is needed to use a variable
defined in a DLL, but when building the DLL, the variable must have either the
Ada or C calling convention. As an example consider a
DLL comprising the following package API:
package API is
Count : Integer := 0;
...
-- Remainder of the package omitted.
end API;
After producing a DLL containing package API, the spec that must
be used to import API.Count from Ada code outside of the DLL is:
package API is
Count : Integer;
pragma Import (DLL, Count);
end API;
The definition file is the last file needed to build the DLL. It lists the
exported symbols. As an example, the definition file for a DLL containing only
package API (where all the entities are exported with a
C calling convention) is:
EXPORTS
count
factorial
finalize_api
initialize_api
If the C calling convention is missing from package
API, then the definition file contains the mangled Ada names of the
above entities, which in this case are:
EXPORTS
api__count
api__factorial
api__finalize_api
api__initialize_api
gnatdllgnatdll is a tool to automate the DLL build process once all the
Ada and non-Ada sources that make up your DLL have been compiled.
gnatdll is actually in charge of two distinct tasks: build the
static import library for the DLL and the actual DLL. The form of the
gnatdll command is
$ gnatdll [switches] list-of-files [-largs opts]
where list-of-files is a list of ALI and object files. The object file list must be the exact list of objects corresponding to the non-Ada sources whose services are to be included in the DLL. The ALI file list must be the exact list of ALI files for the corresponding Ada sources whose services are to be included in the DLL. If list-of-files is missing, only the static import library is generated.
You may specify any of the following switches to gnatdll:
-a[address]
gnatdll
builds relocatable DLL. We advise the reader to build relocatable DLL.
-d dllfile
gnatdll to do anything. The name of the
generated import library is obtained algorithmically from dllfile
as shown in the following example: if dllfile is
xyz.dll, the import library name is libxyz.a. The
name of the definition file to use (if not specified by option
-e) is obtained algorithmically from dllfile as shown
in the following example: if dllfile is xyz.dll, the
definition file used is xyz.def.
-e deffile
-h
gnatdll switch usage
information.
-l file
-n
-q
-v
-largs opts
gnatdll ExampleAs an example the command to build a relocatable DLL from `api.adb' once `api.adb' has been compiled and `api.def' created is
$ gnatdll -d api.dll api.ali
The above command creates two files: `libapi.a' (the import library) and `api.dll' (the actual DLL). If you want to create only the DLL, just type:
$ gnatdll -d api.dll -n api.ali
Alternatively if you want to create just the import library, type:
$ gnatdll -d api.dll
gnatdll Behind the ScenesThis section details the steps involved in creating a DLL.
gnatdll does these steps for you. Unless you are interested in
understanding what goes on behind the scenes, you should skip this section.
We use the previous example of a DLL containing the Ada package
API, to illustrate the steps necessary to build a DLL. The starting
point is a set of objects that will make up the DLL and the corresponding ALI
files. In the case of this example this means that `api.o' and
`api.ali' are available. To build a relocatable DLL,
gnatdll does the following:
gnatdll builds the base file (`api.base'). A base
file gives the information necessary to generate relocation information for
the DLL. $ gnatbind -n api $ gnatlink api -o api.jnk -mdll -Wl,--base-file,api.baseIn addition to the base file, the
gnatlink command
generates an output file `api.jnk' which can be discarded. The
-mdll switch asks gnatlink to generate the routines
DllMain and DllMainCRTStartup that are called by the
Windows loader when the DLL is loaded into memory.
gnatdll uses dlltool (see section Using
dlltool) to build the export table (`api.exp'). The
export table contains the relocation information in a form which can be used
during the final link to ensure that the Windows loader is able to place the
DLL anywhere in memory. $ dlltool --dllname api.dll --def api.def --base-file api.base \
--output-exp api.exp
gnatdll builds the base file using the new export table. Note
that gnatbind must be called once again since the binder
generated file has been deleted during the previous call to
gnatlink. $ gnatbind -n api
$ gnatlink api -o api.jnk api.exp -mdll \
-Wl,--base-file,api.base
gnatdll builds the new export table using the new base file
and generates the DLL import library `libAPI.a'. $ dlltool --dllname api.dll --def api.def --base-file api.base \
--output-exp api.exp --output-lib libAPI.a
gnatdll builds the relocatable DLL using the final
export table. $ gnatbind -n api $ gnatlink api api.exp -o api.dll -mdll
dlltooldlltool is the low-level tool used by gnatdll to
build DLLs and static import libraries. This section summarizes the most common
dlltool switches. The form of the dlltool command is
$ dlltool [switches]
dlltool switches include:
--base-file basefile
--def deffile
--dllname name
dlltool with switch
--output-lib.
-k
@nn from exported names (see section Windows
Calling Conventions for a discussion about Stdcall-style
symbols.
--help
dlltool switches with a concise description.
--output-exp exportfile
--output-lib libfile
-v
--as assembler-name
as. Resources are an easy way to add Windows specific objects to your application. The objects that can be added as resources include:
This section explains how to build, compile and use resources.
A resource file is an ASCII file. By convention resource files have an
`.rc' extension. The easiest way to build a resource file is to use
Microsoft tools such as imagedit.exe to build bitmaps, icons and
cursors and dlgedit.exe to build dialogs. It is always possible to
build an `.rc' file yourself by writing a resource script.
It is not our objective to explain how to write a resource file. A complete description of the resource script language can be found in the Microsoft documentation.
This section describes how to build a GNAT-compatible (COFF) object file
containing the resources. This is done using the Resource Compiler
rcl as follows:
$ rcl -i myres.rc -o myres.o
By default rcl will run gcc to preprocess the
`.rc' file. You can specify an alternate preprocessor (usually named
`cpp.exe') using the rcl -cpp parameter. A
list of all possible options may be obtained by entering the command
rcl with no parameters.
It is also possible to use the Microsoft resource compiler
rc.exe to produce a `.res' file (binary resource file).
See the corresponding Microsoft documentation for further details. In this case
you need to use res2coff to translate the `.res' file to a
GNAT-compatible object file as follows:
$ res2coff -i myres.res -o myres.o
To include the resource file in your program just add the GNAT-compatible
object file for the resource(s) to the linker arguments. With
gnatmake this is done by using the -largs option:
$ gnatmake myprog -largs myres.o
In this section we describe the current limitations together with suggestions for workarounds.
rcl does not handle the RCINCLUDE directive.
RCINCLUDE by an #include
directive.
rcl does not handle the brackets as block delimiters.
BEGIN and '}' by
END. Note that Microsoft's rc handles both forms of
block delimiters.
rcl does not handle TypeLib resources. This type
of resource is used to build COM, DCOM or ActiveX objects. rc, the Microsoft resource compiler.
strip to remove the debugging
symbols from a program with resources. -s to strip debugging symbols from the final executable. This section is temporarily left blank.
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.
By default, GNAT produces all run-time checks, except arithmetic overflow
checking for integer operations (that includes division by zero) and checks for
access before elaboration on subprogram calls. Two gnat switches, -gnatp and -gnato
allow this default to be modified. See section Run-time
Checks.
Our experience is that the default is suitable for most development purposes.
We treat integer overflow specially because these are quite expensive and in our experience are not as important as other run-time checks in the development process.
Elaboration checks are off by default, and also not needed by default, since GNAT uses a static elaboration analysis approach that avoids the need for run-time checking. This manual contains a full chapter discussing the issue of elaboration checks, and if the default is not satisfactory for your use, you should read this chapter.
Note that the setting of the switches
controls the default setting of the checks. They may be modified using either
pragma Suppress (to remove checks) or pragma
Unsuppress (to add back suppressed checks) in the program source.
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.
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.
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.
--GCC=compiler_name
(gnatlink)
--GCC=compiler_name
(gnatmake)
--GNATBIND=binder_name
(gnatmake)
--GNATLINK=linker_name
(gnatmake)
--LINK=
(gnatlink)
-83
(gnathtml)
-A
(gnatbind)
-a
(gnatdll)
-A
(gnatlink)
-a
(gnatls)
-A
(gnatmake)
-a
(gnatmake)
-aI
(gnatmake)
-aL
(gnatmake)
-aO
(gnatmake)
-B
(gcc)
-b
(gcc)
-b
(gnatbind)
-B
(gnatlink)
-b
(gnatlink)
-bargs
(gnatmake)
-c
(gcc)
-C
(gnatbind)
-c
(gnatbind)
-c
(gnatchop)
-C
(gnatlink)
-c
(gnatmake)
-cargs
(gnatmake)
-d
(gnatdll)
-d
(gnathtml)
-d
(gnatls)
-e
(gnatbind)
-e
(gnatdll)
-f
(gnatbind)
-f
(gnathtml)
-f
(gnatmake)
-fno-inline
(gcc)
-g
(gcc)
-g
(gnatlink)
-gnat83
(gcc)
-gnat95
(gcc)
-gnata
(gcc)
-gnatb
(gcc)
-gnatc
(gcc)
-gnatD
(gcc)
-gnatdc
switch
-gnate
(gcc)
-gnatE
(gcc)
-gnatf
(gcc)
-gnatG
(gcc)
-gnatg
(gcc)
-gnati
(gcc)
-gnatk
(gcc)
-gnatl
(gcc)
-gnatm
(gcc)
-gnatn
switch
-gnatn
(gcc), -gnatn
(gcc)
-gnato
(gcc), -gnato
(gcc)
-gnatp
(gcc), -gnatp
(gcc)
-gnatq
(gcc)
-gnatr
(gcc)
-gnatR
(gcc)
-gnats
(gcc)
-gnatt
(gcc)
-gnatU
(gcc)
-gnatu
(gcc)
-gnatv
(gcc)
-gnatW
(gcc)
-gnatwe
(gcc)
-gnatwl
(gcc)
-gnatws
(gcc)
-gnatwu
(gcc)
-gnatx
(gcc)
-h
(gnatbind), -h
(gnatbind)
-h
(gnatdll)
-h
(gnatls)
-I-
(gcc)
-I-
(gnatmake)
-I
(gcc)
-I
(gnathtml)
-I
(gnatmake)
-i
(gnatmake)
-i
(gnatmem)
-j
(gnatmake)
-k
(gnatchop)
-k
(gnatmake)
-l
(gnatbind)
-l
(gnatdll)
-l
(gnathtml)
-L
(gnatmake)
-largs
(gnatdll)
-largs
(gnatmake)
-M
(gnatbind)
-m
(gnatbind)
-m
(gnatmake)
-M
(gnatmake)
-n
(gnatbind)
-n
(gnatdll)
-n
(gnatlink)
-n
(gnatmake)
-nostdinc
(gnatmake)
-nostdlib
(gnatmake)
-O
(gcc), -O
(gcc)
-o
(gcc)
-o
(gnatbind)
-O
(gnatbind)
-o
(gnathtml)
-o
(gnatlink)
-o
(gnatls)
-o
(gnatmake)
-o
(gnatmem)
-p
(gnathtml)
-q
(gnatchop)
-q
(gnatdll)
-q
(gnatmake)
-q
(gnatmem)
-r
(gnatchop)
-S
(gcc)
-s
(gnatbind)
-s
(gnatls), -s
(gnatls)
-t
(gnatbind)
-u
(gnatls)
-v
-v (gnatlink)
-V
(gcc)
-v
(gcc)
-v
(gnatbind)
-v
(gnatchop)
-v
(gnatdll)
-v
(gnatlink)
-v
(gnatmake)
-w
(gnatchop)
-we
(gnatbind)
-ws
(gnatbind)
-Wuninitialized
(gcc)
-x
(gnatbind)
-z
(gnatbind)
-z
(gnatmake) n
(gnatmem)
gnatmake
gnatmake
This document was generated on 6 September 1999 using the texi2html translator version 1.51a (and posted "as is" to the ERAU environment by M.S. Jaffe)