This is doc/gcc.info, produced by makeinfo version 4.0 from
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INFO-DIR-SECTION Programming
START-INFO-DIR-ENTRY
* gcc: (gcc).                  The GNU Compiler Collection.
END-INFO-DIR-ENTRY
   This file documents the use and the internals of the GNU compiler.


   Published by the Free Software Foundation
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   Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
1999, 2000, 2001 Free Software Foundation, Inc.


   Permission is granted to copy, distribute and/or modify this document
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Invariant Sections being "GNU General Public License" and "Funding Free
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Back-Cover Texts being (b) (see below).  A copy of the license is
included in the section entitled "GNU Free Documentation License".

   (a) The FSF's Front-Cover Text is:

   A GNU Manual

   (b) The FSF's Back-Cover Text is:

   You have freedom to copy and modify this GNU Manual, like GNU
software.  Copies published by the Free Software Foundation raise
funds for GNU development.


File: gcc.info,  Node: Bug Reporting,  Next: gccbug,  Prev: Bug Lists,  Up: Bugs

How to Report Bugs
==================

   The fundamental principle of reporting bugs usefully is this:
*report all the facts*.  If you are not sure whether to state a fact or
leave it out, state it!

   Often people omit facts because they think they know what causes the
problem and they conclude that some details don't matter.  Thus, you
might assume that the name of the variable you use in an example does
not matter.  Well, probably it doesn't, but one cannot be sure.
Perhaps the bug is a stray memory reference which happens to fetch from
the location where that name is stored in memory; perhaps, if the name
were different, the contents of that location would fool the compiler
into doing the right thing despite the bug.  Play it safe and give a
specific, complete example.  That is the easiest thing for you to do,
and the most helpful.

   Keep in mind that the purpose of a bug report is to enable someone to
fix the bug if it is not known.  It isn't very important what happens if
the bug is already known.  Therefore, always write your bug reports on
the assumption that the bug is not known.

   Sometimes people give a few sketchy facts and ask, "Does this ring a
bell?"  This cannot help us fix a bug, so it is basically useless.  We
respond by asking for enough details to enable us to investigate.  You
might as well expedite matters by sending them to begin with.

   Try to make your bug report self-contained.  If we have to ask you
for more information, it is best if you include all the previous
information in your response, as well as the information that was
missing.

   Please report each bug in a separate message.  This makes it easier
for us to track which bugs have been fixed and to forward your bugs
reports to the appropriate maintainer.

   To enable someone to investigate the bug, you should include all
these things:

   * The version of GCC.  You can get this by running it with the `-v'
     option.

     Without this, we won't know whether there is any point in looking
     for the bug in the current version of GCC.

   * A complete input file that will reproduce the bug.  If the bug is
     in the C preprocessor, send a source file and any header files
     that it requires.  If the bug is in the compiler proper (`cc1'),
     send the preprocessor output generated by adding `-save-temps' to
     the compilation command (*note Debugging Options::).  When you do
     this, use the same `-I', `-D' or `-U' options that you used in
     actual compilation.  Then send the INPUT.i or INPUT.ii files
     generated.

     A single statement is not enough of an example.  In order to
     compile it, it must be embedded in a complete file of compiler
     input; and the bug might depend on the details of how this is done.

     Without a real example one can compile, all anyone can do about
     your bug report is wish you luck.  It would be futile to try to
     guess how to provoke the bug.  For example, bugs in register
     allocation and reloading frequently depend on every little detail
     of the function they happen in.

     Even if the input file that fails comes from a GNU program, you
     should still send the complete test case.  Don't ask the GCC
     maintainers to do the extra work of obtaining the program in
     question--they are all overworked as it is.  Also, the problem may
     depend on what is in the header files on your system; it is
     unreliable for the GCC maintainers to try the problem with the
     header files available to them.  By sending CPP output, you can
     eliminate this source of uncertainty and save us a certain
     percentage of wild goose chases.

   * The command arguments you gave GCC to compile that example and
     observe the bug.  For example, did you use `-O'?  To guarantee you
     won't omit something important, list all the options.

     If we were to try to guess the arguments, we would probably guess
     wrong and then we would not encounter the bug.

   * The type of machine you are using, and the operating system name
     and version number.

   * The operands you gave to the `configure' command when you installed
     the compiler.

   * A complete list of any modifications you have made to the compiler
     source.  (We don't promise to investigate the bug unless it
     happens in an unmodified compiler.  But if you've made
     modifications and don't tell us, then you are sending us on a wild
     goose chase.)

     Be precise about these changes.  A description in English is not
     enough--send a context diff for them.

     Adding files of your own (such as a machine description for a
     machine we don't support) is a modification of the compiler source.

   * Details of any other deviations from the standard procedure for
     installing GCC.

   * A description of what behavior you observe that you believe is
     incorrect.  For example, "The compiler gets a fatal signal," or,
     "The assembler instruction at line 208 in the output is incorrect."

     Of course, if the bug is that the compiler gets a fatal signal,
     then one can't miss it.  But if the bug is incorrect output, the
     maintainer might not notice unless it is glaringly wrong.  None of
     us has time to study all the assembler code from a 50-line C
     program just on the chance that one instruction might be wrong.
     We need _you_ to do this part!

     Even if the problem you experience is a fatal signal, you should
     still say so explicitly.  Suppose something strange is going on,
     such as, your copy of the compiler is out of synch, or you have
     encountered a bug in the C library on your system.  (This has
     happened!)  Your copy might crash and the copy here would not.  If
     you said to expect a crash, then when the compiler here fails to
     crash, we would know that the bug was not happening.  If you don't
     say to expect a crash, then we would not know whether the bug was
     happening.  We would not be able to draw any conclusion from our
     observations.

     If the problem is a diagnostic when compiling GCC with some other
     compiler, say whether it is a warning or an error.

     Often the observed symptom is incorrect output when your program
     is run.  Sad to say, this is not enough information unless the
     program is short and simple.  None of us has time to study a large
     program to figure out how it would work if compiled correctly,
     much less which line of it was compiled wrong.  So you will have
     to do that.  Tell us which source line it is, and what incorrect
     result happens when that line is executed.  A person who
     understands the program can find this as easily as finding a bug
     in the program itself.

   * If you send examples of assembler code output from GCC, please use
     `-g' when you make them.  The debugging information includes
     source line numbers which are essential for correlating the output
     with the input.

   * If you wish to mention something in the GCC source, refer to it by
     context, not by line number.

     The line numbers in the development sources don't match those in
     your sources.  Your line numbers would convey no useful
     information to the maintainers.

   * Additional information from a debugger might enable someone to
     find a problem on a machine which he does not have available.
     However, you need to think when you collect this information if
     you want it to have any chance of being useful.

     For example, many people send just a backtrace, but that is never
     useful by itself.  A simple backtrace with arguments conveys little
     about GCC because the compiler is largely data-driven; the same
     functions are called over and over for different RTL insns, doing
     different things depending on the details of the insn.

     Most of the arguments listed in the backtrace are useless because
     they are pointers to RTL list structure.  The numeric values of the
     pointers, which the debugger prints in the backtrace, have no
     significance whatever; all that matters is the contents of the
     objects they point to (and most of the contents are other such
     pointers).

     In addition, most compiler passes consist of one or more loops that
     scan the RTL insn sequence.  The most vital piece of information
     about such a loop--which insn it has reached--is usually in a
     local variable, not in an argument.

     What you need to provide in addition to a backtrace are the values
     of the local variables for several stack frames up.  When a local
     variable or an argument is an RTX, first print its value and then
     use the GDB command `pr' to print the RTL expression that it points
     to.  (If GDB doesn't run on your machine, use your debugger to call
     the function `debug_rtx' with the RTX as an argument.)  In
     general, whenever a variable is a pointer, its value is no use
     without the data it points to.

   Here are some things that are not necessary:

   * A description of the envelope of the bug.

     Often people who encounter a bug spend a lot of time investigating
     which changes to the input file will make the bug go away and which
     changes will not affect it.

     This is often time consuming and not very useful, because the way
     we will find the bug is by running a single example under the
     debugger with breakpoints, not by pure deduction from a series of
     examples.  You might as well save your time for something else.

     Of course, if you can find a simpler example to report _instead_ of
     the original one, that is a convenience.  Errors in the output
     will be easier to spot, running under the debugger will take less
     time, etc.  Most GCC bugs involve just one function, so the most
     straightforward way to simplify an example is to delete all the
     function definitions except the one where the bug occurs.  Those
     earlier in the file may be replaced by external declarations if
     the crucial function depends on them.  (Exception: inline
     functions may affect compilation of functions defined later in the
     file.)

     However, simplification is not vital; if you don't want to do this,
     report the bug anyway and send the entire test case you used.

   * In particular, some people insert conditionals `#ifdef BUG' around
     a statement which, if removed, makes the bug not happen.  These
     are just clutter; we won't pay any attention to them anyway.
     Besides, you should send us cpp output, and that can't have
     conditionals.

   * A patch for the bug.

     A patch for the bug is useful if it is a good one.  But don't omit
     the necessary information, such as the test case, on the
     assumption that a patch is all we need.  We might see problems
     with your patch and decide to fix the problem another way, or we
     might not understand it at all.

     Sometimes with a program as complicated as GCC it is very hard to
     construct an example that will make the program follow a certain
     path through the code.  If you don't send the example, we won't be
     able to construct one, so we won't be able to verify that the bug
     is fixed.

     And if we can't understand what bug you are trying to fix, or why
     your patch should be an improvement, we won't install it.  A test
     case will help us to understand.

     See `http://gcc.gnu.org/contribute.html' for guidelines on how to
     make it easy for us to understand and install your patches.

   * A guess about what the bug is or what it depends on.

     Such guesses are usually wrong.  Even I can't guess right about
     such things without first using the debugger to find the facts.

   * A core dump file.

     We have no way of examining a core dump for your type of machine
     unless we have an identical system--and if we do have one, we
     should be able to reproduce the crash ourselves.


File: gcc.info,  Node: gccbug,  Prev: Bug Reporting,  Up: Bugs

The gccbug script
=================

   To simplify creation of bug reports, and to allow better tracking of
reports, we use the GNATS bug tracking system.  Part of that system is
the `gccbug' script.  This is a Unix shell script, so you need a shell
to run it.  It is normally installed in the same directory where `gcc'
is installed.

   The gccbug script is derived from send-pr, *note Creating new
Problem Reports: (send-pr)using send-pr..  When invoked, it starts a
text editor so you can fill out the various fields of the report.  When
the you quit the editor, the report is automatically send to the bug
reporting address.

   A number of fields in this bug report form are specific to GCC, and
are explained at `http://gcc.gnu.org/gnats.html'.


File: gcc.info,  Node: Service,  Next: Contributing,  Prev: Bugs,  Up: Top

How To Get Help with GCC
************************

   If you need help installing, using or changing GCC, there are two
ways to find it:

   * Send a message to a suitable network mailing list.  First try
     <gcc-help@gcc.gnu.org> (for help installing or using GCC), and if
     that brings no response, try <gcc@gcc.gnu.org>.  For help changing
     GCC, ask <gcc@gcc.gnu.org>.  If you think you have found a bug in
     GCC, please report it following the instructions at *note Bug
     Reporting::.

   * Look in the service directory for someone who might help you for a
     fee.  The service directory is found at
     `http://www.gnu.org/prep/service.html'.


File: gcc.info,  Node: Contributing,  Next: VMS,  Prev: Service,  Up: Top

Contributing to GCC Development
*******************************

   If you would like to help pretest GCC releases to assure they work
well, our current development sources are available by CVS (see
`http://gcc.gnu.org/cvs.html').  Source and binary snapshots are also
available for FTP; see `http://gcc.gnu.org/snapshots.html'.

   If you would like to work on improvements to GCC, please read
`http://gcc.gnu.org/contribute.html' and
`http://gcc.gnu.org/contributewhy.html' for information on how to make
useful contributions and avoid duplication of effort.  Suggested
projects are listed at `http://gcc.gnu.org/projects/'.


File: gcc.info,  Node: VMS,  Next: Makefile,  Prev: Contributing,  Up: Top

Using GCC on VMS
****************

   Here is how to use GCC on VMS.

* Menu:

* Include Files and VMS::  Where the preprocessor looks for the include files.
* Global Declarations::    How to do globaldef, globalref and globalvalue with
                           GCC.
* VMS Misc::		   Misc information.


File: gcc.info,  Node: Include Files and VMS,  Next: Global Declarations,  Up: VMS

Include Files and VMS
=====================

   Due to the differences between the filesystems of Unix and VMS, GCC
attempts to translate file names in `#include' into names that VMS will
understand.  The basic strategy is to prepend a prefix to the
specification of the include file, convert the whole filename to a VMS
filename, and then try to open the file.  GCC tries various prefixes
one by one until one of them succeeds:

  1. The first prefix is the `GNU_CC_INCLUDE:' logical name: this is
     where GNU C header files are traditionally stored.  If you wish to
     store header files in non-standard locations, then you can assign
     the logical `GNU_CC_INCLUDE' to be a search list, where each
     element of the list is suitable for use with a rooted logical.

  2. The next prefix tried is `SYS$SYSROOT:[SYSLIB.]'.  This is where
     VAX-C header files are traditionally stored.

  3. If the include file specification by itself is a valid VMS
     filename, the preprocessor then uses this name with no prefix in
     an attempt to open the include file.

  4. If the file specification is not a valid VMS filename (i.e. does
     not contain a device or a directory specifier, and contains a `/'
     character), the preprocessor tries to convert it from Unix syntax
     to VMS syntax.

     Conversion works like this: the first directory name becomes a
     device, and the rest of the directories are converted into
     VMS-format directory names.  For example, the name `X11/foobar.h'
     is translated to `X11:[000000]foobar.h' or `X11:foobar.h',
     whichever one can be opened.  This strategy allows you to assign a
     logical name to point to the actual location of the header files.

  5. If none of these strategies succeeds, the `#include' fails.

   Include directives of the form:

     #include foobar

are a common source of incompatibility between VAX-C and GCC.  VAX-C
treats this much like a standard `#include <foobar.h>' directive.  That
is incompatible with the ISO C behavior implemented by GCC: to expand
the name `foobar' as a macro.  Macro expansion should eventually yield
one of the two standard formats for `#include':

     #include "FILE"
     #include <FILE>

   If you have this problem, the best solution is to modify the source
to convert the `#include' directives to one of the two standard forms.
That will work with either compiler.  If you want a quick and dirty fix,
define the file names as macros with the proper expansion, like this:

     #define stdio <stdio.h>

This will work, as long as the name doesn't conflict with anything else
in the program.

   Another source of incompatibility is that VAX-C assumes that:

     #include "foobar"

is actually asking for the file `foobar.h'.  GCC does not make this
assumption, and instead takes what you ask for literally; it tries to
read the file `foobar'.  The best way to avoid this problem is to
always specify the desired file extension in your include directives.

   GCC for VMS is distributed with a set of include files that is
sufficient to compile most general purpose programs.  Even though the
GCC distribution does not contain header files to define constants and
structures for some VMS system-specific functions, there is no reason
why you cannot use GCC with any of these functions.  You first may have
to generate or create header files, either by using the public domain
utility `UNSDL' (which can be found on a DECUS tape), or by extracting
the relevant modules from one of the system macro libraries, and using
an editor to construct a C header file.

   A `#include' file name cannot contain a DECNET node name.  The
preprocessor reports an I/O error if you attempt to use a node name,
whether explicitly, or implicitly via a logical name.


File: gcc.info,  Node: Global Declarations,  Next: VMS Misc,  Prev: Include Files and VMS,  Up: VMS

Global Declarations and VMS
===========================

   GCC does not provide the `globalref', `globaldef' and `globalvalue'
keywords of VAX-C.  You can get the same effect with an obscure feature
of GAS, the GNU assembler.  (This requires GAS version 1.39 or later.)
The following macros allow you to use this feature in a fairly natural
way:

     #ifdef __GNUC__
     #define GLOBALREF(TYPE,NAME)                      \
       TYPE NAME                                       \
       asm ("_$$PsectAttributes_GLOBALSYMBOL$$" #NAME)
     #define GLOBALDEF(TYPE,NAME,VALUE)                \
       TYPE NAME                                       \
       asm ("_$$PsectAttributes_GLOBALSYMBOL$$" #NAME) \
         = VALUE
     #define GLOBALVALUEREF(TYPE,NAME)                 \
       const TYPE NAME[1]                              \
       asm ("_$$PsectAttributes_GLOBALVALUE$$" #NAME)
     #define GLOBALVALUEDEF(TYPE,NAME,VALUE)           \
       const TYPE NAME[1]                              \
       asm ("_$$PsectAttributes_GLOBALVALUE$$" #NAME)  \
         = {VALUE}
     #else
     #define GLOBALREF(TYPE,NAME) \
       globalref TYPE NAME
     #define GLOBALDEF(TYPE,NAME,VALUE) \
       globaldef TYPE NAME = VALUE
     #define GLOBALVALUEDEF(TYPE,NAME,VALUE) \
       globalvalue TYPE NAME = VALUE
     #define GLOBALVALUEREF(TYPE,NAME) \
       globalvalue TYPE NAME
     #endif

(The `_$$PsectAttributes_GLOBALSYMBOL' prefix at the start of the name
is removed by the assembler, after it has modified the attributes of
the symbol).  These macros are provided in the VMS binaries
distribution in a header file `GNU_HACKS.H'.  An example of the usage
is:

     GLOBALREF (int, ijk);
     GLOBALDEF (int, jkl, 0);

   The macros `GLOBALREF' and `GLOBALDEF' cannot be used
straightforwardly for arrays, since there is no way to insert the array
dimension into the declaration at the right place.  However, you can
declare an array with these macros if you first define a typedef for the
array type, like this:

     typedef int intvector[10];
     GLOBALREF (intvector, foo);

   Array and structure initializers will also break the macros; you can
define the initializer to be a macro of its own, or you can expand the
`GLOBALDEF' macro by hand.  You may find a case where you wish to use
the `GLOBALDEF' macro with a large array, but you are not interested in
explicitly initializing each element of the array.  In such cases you
can use an initializer like: `{0,}', which will initialize the entire
array to `0'.

   A shortcoming of this implementation is that a variable declared with
`GLOBALVALUEREF' or `GLOBALVALUEDEF' is always an array.  For example,
the declaration:

     GLOBALVALUEREF(int, ijk);

declares the variable `ijk' as an array of type `int [1]'.  This is
done because a globalvalue is actually a constant; its "value" is what
the linker would normally consider an address.  That is not how an
integer value works in C, but it is how an array works.  So treating
the symbol as an array name gives consistent results--with the
exception that the value seems to have the wrong type.  *Don't try to
access an element of the array.*  It doesn't have any elements.  The
array "address" may not be the address of actual storage.

   The fact that the symbol is an array may lead to warnings where the
variable is used.  Insert type casts to avoid the warnings.  Here is an
example; it takes advantage of the ISO C feature allowing macros that
expand to use the same name as the macro itself.

     GLOBALVALUEREF (int, ss$_normal);
     GLOBALVALUEDEF (int, xyzzy,123);
     #ifdef __GNUC__
     #define ss$_normal ((int) ss$_normal)
     #define xyzzy ((int) xyzzy)
     #endif

   Don't use `globaldef' or `globalref' with a variable whose type is
an enumeration type; this is not implemented.  Instead, make the
variable an integer, and use a `globalvaluedef' for each of the
enumeration values.  An example of this would be:

     #ifdef __GNUC__
     GLOBALDEF (int, color, 0);
     GLOBALVALUEDEF (int, RED, 0);
     GLOBALVALUEDEF (int, BLUE, 1);
     GLOBALVALUEDEF (int, GREEN, 3);
     #else
     enum globaldef color {RED, BLUE, GREEN = 3};
     #endif


File: gcc.info,  Node: VMS Misc,  Prev: Global Declarations,  Up: VMS

Other VMS Issues
================

   GCC automatically arranges for `main' to return 1 by default if you
fail to specify an explicit return value.  This will be interpreted by
VMS as a status code indicating a normal successful completion.
Version 1 of GCC did not provide this default.

   GCC on VMS works only with the GNU assembler, GAS.  You need version
1.37 or later of GAS in order to produce value debugging information for
the VMS debugger.  Use the ordinary VMS linker with the object files
produced by GAS.

   Under previous versions of GCC, the generated code would occasionally
give strange results when linked to the sharable `VAXCRTL' library.
Now this should work.

   A caveat for use of `const' global variables: the `const' modifier
must be specified in every external declaration of the variable in all
of the source files that use that variable.  Otherwise the linker will
issue warnings about conflicting attributes for the variable.  Your
program will still work despite the warnings, but the variable will be
placed in writable storage.

   Although the VMS linker does distinguish between upper and lower case
letters in global symbols, most VMS compilers convert all such symbols
into upper case and most run-time library routines also have upper case
names.  To be able to reliably call such routines, GCC (by means of the
assembler GAS) converts global symbols into upper case like other VMS
compilers.  However, since the usual practice in C is to distinguish
case, GCC (via GAS) tries to preserve usual C behavior by augmenting
each name that is not all lower case.  This means truncating the name
to at most 23 characters and then adding more characters at the end
which encode the case pattern of those 23.   Names which contain at
least one dollar sign are an exception; they are converted directly into
upper case without augmentation.

   Name augmentation yields bad results for programs that use
precompiled libraries (such as Xlib) which were generated by another
compiler.  You can use the compiler option `/NOCASE_HACK' to inhibit
augmentation; it makes external C functions and variables
case-independent as is usual on VMS.  Alternatively, you could write
all references to the functions and variables in such libraries using
lower case; this will work on VMS, but is not portable to other
systems.  The compiler option `/NAMES' also provides control over
global name handling.

   Function and variable names are handled somewhat differently with
G++.  The GNU C++ compiler performs "name mangling" on function names,
which means that it adds information to the function name to describe
the data types of the arguments that the function takes.  One result of
this is that the name of a function can become very long.  Since the
VMS linker only recognizes the first 31 characters in a name, special
action is taken to ensure that each function and variable has a unique
name that can be represented in 31 characters.

   If the name (plus a name augmentation, if required) is less than 32
characters in length, then no special action is performed.  If the name
is longer than 31 characters, the assembler (GAS) will generate a hash
string based upon the function name, truncate the function name to 23
characters, and append the hash string to the truncated name.  If the
`/VERBOSE' compiler option is used, the assembler will print both the
full and truncated names of each symbol that is truncated.

   The `/NOCASE_HACK' compiler option should not be used when you are
compiling programs that use libg++.  libg++ has several instances of
objects (i.e.  `Filebuf' and `filebuf') which become indistinguishable
in a case-insensitive environment.  This leads to cases where you need
to inhibit augmentation selectively (if you were using libg++ and Xlib
in the same program, for example).  There is no special feature for
doing this, but you can get the result by defining a macro for each
mixed case symbol for which you wish to inhibit augmentation.  The
macro should expand into the lower case equivalent of itself.  For
example:

     #define StuDlyCapS studlycaps

   These macro definitions can be placed in a header file to minimize
the number of changes to your source code.


File: gcc.info,  Node: Makefile,  Next: Portability,  Prev: VMS,  Up: Top

Additional Makefile and configure information.
**********************************************

Makefile Targets
================

`all'
     This is the default target.  Depending on what your
     build/host/target configuration is, it coordinates all the things
     that need to be built.

`doc'
     Produce info-formatted documentation.  Also, `make dvi' is
     available for DVI-formatted documentation, and `make
     generated-manpages' to generate man pages.

`mostlyclean'
     Delete the files made while building the compiler.

`clean'
     That, and all the other files built by `make all'.

`distclean'
     That, and all the files created by `configure'.

`extraclean'
     That, and any temporary or intermediate files, like emacs backup
     files.

`maintainer-clean'
     Distclean plus any file that can be generated from other files.
     Note that additional tools may be required beyond what is normally
     needed to build gcc.

`install'
     Installs gcc.

`uninstall'
     Deletes installed files.

`check'
     Run the testsuite.  This creates a `testsuite' subdirectory that
     has various `.sum' and `.log' files containing the results of the
     testing.  You can run subsets with, for example, `make check-gcc'.
     You can specify specific tests by setting RUNTESTFLAGS to be the
     name of the `.exp' file, optionally followed by (for some tests)
     an equals and a file wildcard, like:

          make check-gcc RUNTESTFLAGS="execute.exp=19980413-*"

     Note that running the testsuite may require additional tools be
     installed, such as TCL or dejagnu.

`bootstrap'
     Builds gcc three times--once with the native compiler, once with
     the native-built compiler it just built, and once with the
     compiler it built the second time.  In theory, the last two should
     produce the same results, which `make compare' can check.  Each
     step of this process is called a "stage", and the results of each
     stage N (N = 1...3) are copied to a subdirectory `stageN/'.

`bootstrap-lean'
     Like `bootstrap', except that the various stages are removed once
     they're no longer needed.  This saves disk space.

`bubblestrap'
     Once bootstrapped, this incrementally rebuilds each of the three
     stages, one at a time.  It does this by "bubbling" the stages up
     from their subdirectories, rebuilding them, and copying them back
     to their subdirectories.  This will allow you to, for example,
     quickly rebuild a bootstrapped compiler after changing the
     sources, without having to do a full bootstrap.

`quickstrap'
     Rebuilds the most recently built stage.  Since each stage requires
     special invocation, using this target means you don't have to keep
     track of which stage you're on or what invocation that stage needs.

`cleanstrap'
     Removed everything (`make clean') and rebuilds (`make bootstrap').

`stageN (N = 1...4)'
     For each stage, moves the appropriate files to the `stageN'
     subdirectory.

`unstageN (N = 1...4)'
     Undoes the corresponding `stageN'.

`restageN (N = 1...4)'
     Undoes the corresponding `stageN' and rebuilds it with the
     appropriate flags.

`compare'
     Compares the results of stages 2 and 3.  This ensures that the
     compiler is running properly, since it should produce the same
     object files regardless of how it itself was compiled.

Configure Terms and History
===========================

   This section is not instructions for building GCC.  If you are
trying to do a build, you should first read
`http://gcc.gnu.org/install/' or whatever installation instructions
came with your source package.

   The configure and build process has a long and colorful history, and
can be confusing to anyone who doesn't know why things are the way they
are.  While there are other documents which describe the configuration
process in detail, here are a few things that everyone working on GCC
should know.

   There are three system names that the build knows about: the machine
you are building on ("build"), the machine that you are building for
("host"), and the machine that GCC will produce code for ("target").
When you configure GCC, you specify these with `--build=', `--host=',
and `--target='.

   Specifying the host without specifying the build should be avoided,
as `configure' may (and once did) assume that the host you specify is
also the build, which may not be true.

   If build, host, and target are all the same, this is called a
"native".  If build and host are the same but target is different, this
is called a "cross".  If build, host, and target are all different this
is called a "canadian" (for obscure reasons dealing with Canada's
political party and the background of the person working on the build
at that time).  If host and target are the same, but build is
different, you are using a cross-compiler to build a native for a
different system.  Some people call this a "host-x-host", "crossed
native", or "cross-built native".  If build and target are the same,
but host is different, you are using a cross compiler to build a cross
compiler that produces code for the machine you're building on.  This
is rare, so there is no common say of describing it (although I propose
calling it a "crossback").

   If build and host are the same, the GCC you are building will also be
used to build the target libraries (like `libstdc++').  If build and
host are different, you must have already build and installed a cross
compiler that will be used to build the target libraries (if you
configured with `--target=foo-bar', this compiler will be called
`foo-bar-gcc').

   In the case of target libraries, the machine you're building for is
the machine you specified with `--target'.  So, build is the machine
you're building on (no change there), host is the machine you're
building for (the target libraries are built for the target, so host is
the target you specified), and target doesn't apply (because you're not
building a compiler, you're building libraries).  The configure/make
process will adjust these variables as needed.  It also sets
`$with_cross_host' to the original `--host' value in case you need it.

   Libiberty, for example, is built twice.  The first time, host comes
from `--host' and the second time host comes from `--target'.
Historically, libiberty has not been built for the build machine,
though, which causes some interesting issues with programs used to
generate sources for the build.  Fixing this, so that libiberty is built
three times, has long been on the to-do list.


File: gcc.info,  Node: Portability,  Next: Interface,  Prev: Makefile,  Up: Top

GCC and Portability
*******************

   The main goal of GCC was to make a good, fast compiler for machines
in the class that the GNU system aims to run on: 32-bit machines that
address 8-bit bytes and have several general registers.  Elegance,
theoretical power and simplicity are only secondary.

   GCC gets most of the information about the target machine from a
machine description which gives an algebraic formula for each of the
machine's instructions.  This is a very clean way to describe the
target.  But when the compiler needs information that is difficult to
express in this fashion, I have not hesitated to define an ad-hoc
parameter to the machine description.  The purpose of portability is to
reduce the total work needed on the compiler; it was not of interest
for its own sake.

   GCC does not contain machine dependent code, but it does contain code
that depends on machine parameters such as endianness (whether the most
significant byte has the highest or lowest address of the bytes in a
word) and the availability of autoincrement addressing.  In the
RTL-generation pass, it is often necessary to have multiple strategies
for generating code for a particular kind of syntax tree, strategies
that are usable for different combinations of parameters.  Often I have
not tried to address all possible cases, but only the common ones or
only the ones that I have encountered.  As a result, a new target may
require additional strategies.  You will know if this happens because
the compiler will call `abort'.  Fortunately, the new strategies can be
added in a machine-independent fashion, and will affect only the target
machines that need them.


File: gcc.info,  Node: Interface,  Next: Passes,  Prev: Portability,  Up: Top

Interfacing to GCC Output
*************************

   GCC is normally configured to use the same function calling
convention normally in use on the target system.  This is done with the
machine-description macros described (*note Target Macros::).

   However, returning of structure and union values is done differently
on some target machines.  As a result, functions compiled with PCC
returning such types cannot be called from code compiled with GCC, and
vice versa.  This does not cause trouble often because few Unix library
routines return structures or unions.

   GCC code returns structures and unions that are 1, 2, 4 or 8 bytes
long in the same registers used for `int' or `double' return values.
(GCC typically allocates variables of such types in registers also.)
Structures and unions of other sizes are returned by storing them into
an address passed by the caller (usually in a register).  The
machine-description macros `STRUCT_VALUE' and `STRUCT_INCOMING_VALUE'
tell GCC where to pass this address.

   By contrast, PCC on most target machines returns structures and
unions of any size by copying the data into an area of static storage,
and then returning the address of that storage as if it were a pointer
value.  The caller must copy the data from that memory area to the
place where the value is wanted.  This is slower than the method used
by GCC, and fails to be reentrant.

   On some target machines, such as RISC machines and the 80386, the
standard system convention is to pass to the subroutine the address of
where to return the value.  On these machines, GCC has been configured
to be compatible with the standard compiler, when this method is used.
It may not be compatible for structures of 1, 2, 4 or 8 bytes.

   GCC uses the system's standard convention for passing arguments.  On
some machines, the first few arguments are passed in registers; in
others, all are passed on the stack.  It would be possible to use
registers for argument passing on any machine, and this would probably
result in a significant speedup.  But the result would be complete
incompatibility with code that follows the standard convention.  So this
change is practical only if you are switching to GCC as the sole C
compiler for the system.  We may implement register argument passing on
certain machines once we have a complete GNU system so that we can
compile the libraries with GCC.

   On some machines (particularly the Sparc), certain types of arguments
are passed "by invisible reference".  This means that the value is
stored in memory, and the address of the memory location is passed to
the subroutine.

   If you use `longjmp', beware of automatic variables.  ISO C says that
automatic variables that are not declared `volatile' have undefined
values after a `longjmp'.  And this is all GCC promises to do, because
it is very difficult to restore register variables correctly, and one
of GCC's features is that it can put variables in registers without
your asking it to.

   If you want a variable to be unaltered by `longjmp', and you don't
want to write `volatile' because old C compilers don't accept it, just
take the address of the variable.  If a variable's address is ever
taken, even if just to compute it and ignore it, then the variable
cannot go in a register:

     {
       int careful;
       &careful;
       ...
     }

   Code compiled with GCC may call certain library routines.  Most of
them handle arithmetic for which there are no instructions.  This
includes multiply and divide on some machines, and floating point
operations on any machine for which floating point support is disabled
with `-msoft-float'.  Some standard parts of the C library, such as
`bcopy' or `memcpy', are also called automatically.  The usual function
call interface is used for calling the library routines.

   These library routines should be defined in the library `libgcc.a',
which GCC automatically searches whenever it links a program.  On
machines that have multiply and divide instructions, if hardware
floating point is in use, normally `libgcc.a' is not needed, but it is
searched just in case.

   Each arithmetic function is defined in `libgcc1.c' to use the
corresponding C arithmetic operator.  As long as the file is compiled
with another C compiler, which supports all the C arithmetic operators,
this file will work portably.  However, `libgcc1.c' does not work if
compiled with GCC, because each arithmetic function would compile into
a call to itself!

