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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 of the GNU compilers.

   Published by the Free Software Foundation
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   Permission is granted to copy, distribute and/or modify this document
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   (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: Disappointments,  Next: C++ Misunderstandings,  Prev: Standard Libraries,  Up: Trouble

Disappointments and Misunderstandings
=====================================

   These problems are perhaps regrettable, but we don't know any
practical way around them.

   * Certain local variables aren't recognized by debuggers when you
     compile with optimization.

     This occurs because sometimes GCC optimizes the variable out of
     existence.  There is no way to tell the debugger how to compute the
     value such a variable "would have had", and it is not clear that
     would be desirable anyway.  So GCC simply does not mention the
     eliminated variable when it writes debugging information.

     You have to expect a certain amount of disagreement between the
     executable and your source code, when you use optimization.

   * Users often think it is a bug when GCC reports an error for code
     like this:

          int foo (struct mumble *);
          
          struct mumble { ... };
          
          int foo (struct mumble *x)
          { ... }

     This code really is erroneous, because the scope of `struct
     mumble' in the prototype is limited to the argument list
     containing it.  It does not refer to the `struct mumble' defined
     with file scope immediately below--they are two unrelated types
     with similar names in different scopes.

     But in the definition of `foo', the file-scope type is used
     because that is available to be inherited.  Thus, the definition
     and the prototype do not match, and you get an error.

     This behavior may seem silly, but it's what the ISO standard
     specifies.  It is easy enough for you to make your code work by
     moving the definition of `struct mumble' above the prototype.
     It's not worth being incompatible with ISO C just to avoid an
     error for the example shown above.

   * Accesses to bit-fields even in volatile objects works by accessing
     larger objects, such as a byte or a word.  You cannot rely on what
     size of object is accessed in order to read or write the
     bit-field; it may even vary for a given bit-field according to the
     precise usage.

     If you care about controlling the amount of memory that is
     accessed, use volatile but do not use bit-fields.

   * GCC comes with shell scripts to fix certain known problems in
     system header files.  They install corrected copies of various
     header files in a special directory where only GCC will normally
     look for them.  The scripts adapt to various systems by searching
     all the system header files for the problem cases that we know
     about.

     If new system header files are installed, nothing automatically
     arranges to update the corrected header files.  You will have to
     reinstall GCC to fix the new header files.  More specifically, go
     to the build directory and delete the files `stmp-fixinc' and
     `stmp-headers', and the subdirectory `include'; then do `make
     install' again.

   * On 68000 and x86 systems, for instance, you can get paradoxical
     results if you test the precise values of floating point numbers.
     For example, you can find that a floating point value which is not
     a NaN is not equal to itself.  This results from the fact that the
     floating point registers hold a few more bits of precision than
     fit in a `double' in memory.  Compiled code moves values between
     memory and floating point registers at its convenience, and moving
     them into memory truncates them.

     You can partially avoid this problem by using the `-ffloat-store'
     option (*note Optimize Options::).

   * On the MIPS, variable argument functions using `varargs.h' cannot
     have a floating point value for the first argument.  The reason
     for this is that in the absence of a prototype in scope, if the
     first argument is a floating point, it is passed in a floating
     point register, rather than an integer register.

     If the code is rewritten to use the ISO standard `stdarg.h' method
     of variable arguments, and the prototype is in scope at the time
     of the call, everything will work fine.

   * On the H8/300 and H8/300H, variable argument functions must be
     implemented using the ISO standard `stdarg.h' method of variable
     arguments.  Furthermore, calls to functions using `stdarg.h'
     variable arguments must have a prototype for the called function
     in scope at the time of the call.

   * On AIX and other platforms without weak symbol support, templates
     need to be instantiated explicitly and symbols for static members
     of templates will not be generated.


File: gcc.info,  Node: C++ Misunderstandings,  Next: Protoize Caveats,  Prev: Disappointments,  Up: Trouble

Common Misunderstandings with GNU C++
=====================================

   C++ is a complex language and an evolving one, and its standard
definition (the ISO C++ standard) was only recently completed.  As a
result, your C++ compiler may occasionally surprise you, even when its
behavior is correct.  This section discusses some areas that frequently
give rise to questions of this sort.

* Menu:

* Static Definitions::  Static member declarations are not definitions
* Temporaries::         Temporaries may vanish before you expect
* Copy Assignment::     Copy Assignment operators copy virtual bases twice


File: gcc.info,  Node: Static Definitions,  Next: Temporaries,  Up: C++ Misunderstandings

Declare _and_ Define Static Members
-----------------------------------

   When a class has static data members, it is not enough to _declare_
the static member; you must also _define_ it.  For example:

     class Foo
     {
       ...
       void method();
       static int bar;
     };

   This declaration only establishes that the class `Foo' has an `int'
named `Foo::bar', and a member function named `Foo::method'.  But you
still need to define _both_ `method' and `bar' elsewhere.  According to
the ISO standard, you must supply an initializer in one (and only one)
source file, such as:

     int Foo::bar = 0;

   Other C++ compilers may not correctly implement the standard
behavior.  As a result, when you switch to `g++' from one of these
compilers, you may discover that a program that appeared to work
correctly in fact does not conform to the standard: `g++' reports as
undefined symbols any static data members that lack definitions.


File: gcc.info,  Node: Temporaries,  Next: Copy Assignment,  Prev: Static Definitions,  Up: C++ Misunderstandings

Temporaries May Vanish Before You Expect
----------------------------------------

   It is dangerous to use pointers or references to _portions_ of a
temporary object.  The compiler may very well delete the object before
you expect it to, leaving a pointer to garbage.  The most common place
where this problem crops up is in classes like string classes,
especially ones that define a conversion function to type `char *' or
`const char *'--which is one reason why the standard `string' class
requires you to call the `c_str' member function.  However, any class
that returns a pointer to some internal structure is potentially
subject to this problem.

   For example, a program may use a function `strfunc' that returns
`string' objects, and another function `charfunc' that operates on
pointers to `char':

     string strfunc ();
     void charfunc (const char *);
     
     void
     f ()
     {
       const char *p = strfunc().c_str();
       ...
       charfunc (p);
       ...
       charfunc (p);
     }

In this situation, it may seem reasonable to save a pointer to the C
string returned by the `c_str' member function and use that rather than
call `c_str' repeatedly.  However, the temporary string created by the
call to `strfunc' is destroyed after `p' is initialized, at which point
`p' is left pointing to freed memory.

   Code like this may run successfully under some other compilers,
particularly obsolete cfront-based compilers that delete temporaries
along with normal local variables.  However, the GNU C++ behavior is
standard-conforming, so if your program depends on late destruction of
temporaries it is not portable.

   The safe way to write such code is to give the temporary a name,
which forces it to remain until the end of the scope of the name.  For
example:

     string& tmp = strfunc ();
     charfunc (tmp.c_str ());


File: gcc.info,  Node: Copy Assignment,  Prev: Temporaries,  Up: C++ Misunderstandings

Implicit Copy-Assignment for Virtual Bases
------------------------------------------

   When a base class is virtual, only one subobject of the base class
belongs to each full object.  Also, the constructors and destructors are
invoked only once, and called from the most-derived class.  However,
such objects behave unspecified when being assigned.  For example:

     struct Base{
       char *name;
       Base(char *n) : name(strdup(n)){}
       Base& operator= (const Base& other){
        free (name);
        name = strdup (other.name);
       }
     };
     
     struct A:virtual Base{
       int val;
       A():Base("A"){}
     };
     
     struct B:virtual Base{
       int bval;
       B():Base("B"){}
     };
     
     struct Derived:public A, public B{
       Derived():Base("Derived"){}
     };
     
     void func(Derived &d1, Derived &d2)
     {
       d1 = d2;
     }

   The C++ standard specifies that `Base::Base' is only called once
when constructing or copy-constructing a Derived object.  It is
unspecified whether `Base::operator=' is called more than once when the
implicit copy-assignment for Derived objects is invoked (as it is
inside `func' in the example).

   g++ implements the "intuitive" algorithm for copy-assignment: assign
all direct bases, then assign all members.  In that algorithm, the
virtual base subobject can be encountered many times.  In the example,
copying proceeds in the following order: `val', `name' (via `strdup'),
`bval', and `name' again.

   If application code relies on copy-assignment, a user-defined
copy-assignment operator removes any uncertainties.  With such an
operator, the application can define whether and how the virtual base
subobject is assigned.


File: gcc.info,  Node: Protoize Caveats,  Next: Non-bugs,  Prev: C++ Misunderstandings,  Up: Trouble

Caveats of using `protoize'
===========================

   The conversion programs `protoize' and `unprotoize' can sometimes
change a source file in a way that won't work unless you rearrange it.

   * `protoize' can insert references to a type name or type tag before
     the definition, or in a file where they are not defined.

     If this happens, compiler error messages should show you where the
     new references are, so fixing the file by hand is straightforward.

   * There are some C constructs which `protoize' cannot figure out.
     For example, it can't determine argument types for declaring a
     pointer-to-function variable; this you must do by hand.  `protoize'
     inserts a comment containing `???' each time it finds such a
     variable; so you can find all such variables by searching for this
     string.  ISO C does not require declaring the argument types of
     pointer-to-function types.

   * Using `unprotoize' can easily introduce bugs.  If the program
     relied on prototypes to bring about conversion of arguments, these
     conversions will not take place in the program without prototypes.
     One case in which you can be sure `unprotoize' is safe is when you
     are removing prototypes that were made with `protoize'; if the
     program worked before without any prototypes, it will work again
     without them.

     You can find all the places where this problem might occur by
     compiling the program with the `-Wconversion' option.  It prints a
     warning whenever an argument is converted.

   * Both conversion programs can be confused if there are macro calls
     in and around the text to be converted.  In other words, the
     standard syntax for a declaration or definition must not result
     from expanding a macro.  This problem is inherent in the design of
     C and cannot be fixed.  If only a few functions have confusing
     macro calls, you can easily convert them manually.

   * `protoize' cannot get the argument types for a function whose
     definition was not actually compiled due to preprocessing
     conditionals.  When this happens, `protoize' changes nothing in
     regard to such a function.  `protoize' tries to detect such
     instances and warn about them.

     You can generally work around this problem by using `protoize' step
     by step, each time specifying a different set of `-D' options for
     compilation, until all of the functions have been converted.
     There is no automatic way to verify that you have got them all,
     however.

   * Confusion may result if there is an occasion to convert a function
     declaration or definition in a region of source code where there
     is more than one formal parameter list present.  Thus, attempts to
     convert code containing multiple (conditionally compiled) versions
     of a single function header (in the same vicinity) may not produce
     the desired (or expected) results.

     If you plan on converting source files which contain such code, it
     is recommended that you first make sure that each conditionally
     compiled region of source code which contains an alternative
     function header also contains at least one additional follower
     token (past the final right parenthesis of the function header).
     This should circumvent the problem.

   * `unprotoize' can become confused when trying to convert a function
     definition or declaration which contains a declaration for a
     pointer-to-function formal argument which has the same name as the
     function being defined or declared.  We recommend you avoid such
     choices of formal parameter names.

   * You might also want to correct some of the indentation by hand and
     break long lines.  (The conversion programs don't write lines
     longer than eighty characters in any case.)


File: gcc.info,  Node: Non-bugs,  Next: Warnings and Errors,  Prev: Protoize Caveats,  Up: Trouble

Certain Changes We Don't Want to Make
=====================================

   This section lists changes that people frequently request, but which
we do not make because we think GCC is better without them.

   * Checking the number and type of arguments to a function which has
     an old-fashioned definition and no prototype.

     Such a feature would work only occasionally--only for calls that
     appear in the same file as the called function, following the
     definition.  The only way to check all calls reliably is to add a
     prototype for the function.  But adding a prototype eliminates the
     motivation for this feature.  So the feature is not worthwhile.

   * Warning about using an expression whose type is signed as a shift
     count.

     Shift count operands are probably signed more often than unsigned.
     Warning about this would cause far more annoyance than good.

   * Warning about assigning a signed value to an unsigned variable.

     Such assignments must be very common; warning about them would
     cause more annoyance than good.

   * Warning when a non-void function value is ignored.

     Coming as I do from a Lisp background, I balk at the idea that
     there is something dangerous about discarding a value.  There are
     functions that return values which some callers may find useful;
     it makes no sense to clutter the program with a cast to `void'
     whenever the value isn't useful.

   * Making `-fshort-enums' the default.

     This would cause storage layout to be incompatible with most other
     C compilers.  And it doesn't seem very important, given that you
     can get the same result in other ways.  The case where it matters
     most is when the enumeration-valued object is inside a structure,
     and in that case you can specify a field width explicitly.

   * Making bit-fields unsigned by default on particular machines where
     "the ABI standard" says to do so.

     The ISO C standard leaves it up to the implementation whether a
     bit-field declared plain `int' is signed or not.  This in effect
     creates two alternative dialects of C.

     The GNU C compiler supports both dialects; you can specify the
     signed dialect with `-fsigned-bitfields' and the unsigned dialect
     with `-funsigned-bitfields'.  However, this leaves open the
     question of which dialect to use by default.

     Currently, the preferred dialect makes plain bit-fields signed,
     because this is simplest.  Since `int' is the same as `signed int'
     in every other context, it is cleanest for them to be the same in
     bit-fields as well.

     Some computer manufacturers have published Application Binary
     Interface standards which specify that plain bit-fields should be
     unsigned.  It is a mistake, however, to say anything about this
     issue in an ABI.  This is because the handling of plain bit-fields
     distinguishes two dialects of C.  Both dialects are meaningful on
     every type of machine.  Whether a particular object file was
     compiled using signed bit-fields or unsigned is of no concern to
     other object files, even if they access the same bit-fields in the
     same data structures.

     A given program is written in one or the other of these two
     dialects.  The program stands a chance to work on most any machine
     if it is compiled with the proper dialect.  It is unlikely to work
     at all if compiled with the wrong dialect.

     Many users appreciate the GNU C compiler because it provides an
     environment that is uniform across machines.  These users would be
     inconvenienced if the compiler treated plain bit-fields
     differently on certain machines.

     Occasionally users write programs intended only for a particular
     machine type.  On these occasions, the users would benefit if the
     GNU C compiler were to support by default the same dialect as the
     other compilers on that machine.  But such applications are rare.
     And users writing a program to run on more than one type of
     machine cannot possibly benefit from this kind of compatibility.

     This is why GCC does and will treat plain bit-fields in the same
     fashion on all types of machines (by default).

     There are some arguments for making bit-fields unsigned by default
     on all machines.  If, for example, this becomes a universal de
     facto standard, it would make sense for GCC to go along with it.
     This is something to be considered in the future.

     (Of course, users strongly concerned about portability should
     indicate explicitly in each bit-field whether it is signed or not.
     In this way, they write programs which have the same meaning in
     both C dialects.)

   * Undefining `__STDC__' when `-ansi' is not used.

     Currently, GCC defines `__STDC__' as long as you don't use
     `-traditional'.  This provides good results in practice.

     Programmers normally use conditionals on `__STDC__' to ask whether
     it is safe to use certain features of ISO C, such as function
     prototypes or ISO token concatenation.  Since plain `gcc' supports
     all the features of ISO C, the correct answer to these questions is
     "yes".

     Some users try to use `__STDC__' to check for the availability of
     certain library facilities.  This is actually incorrect usage in
     an ISO C program, because the ISO C standard says that a conforming
     freestanding implementation should define `__STDC__' even though it
     does not have the library facilities.  `gcc -ansi -pedantic' is a
     conforming freestanding implementation, and it is therefore
     required to define `__STDC__', even though it does not come with
     an ISO C library.

     Sometimes people say that defining `__STDC__' in a compiler that
     does not completely conform to the ISO C standard somehow violates
     the standard.  This is illogical.  The standard is a standard for
     compilers that claim to support ISO C, such as `gcc -ansi'--not
     for other compilers such as plain `gcc'.  Whatever the ISO C
     standard says is relevant to the design of plain `gcc' without
     `-ansi' only for pragmatic reasons, not as a requirement.

     GCC normally defines `__STDC__' to be 1, and in addition defines
     `__STRICT_ANSI__' if you specify the `-ansi' option, or a `-std'
     option for strict conformance to some version of ISO C.  On some
     hosts, system include files use a different convention, where
     `__STDC__' is normally 0, but is 1 if the user specifies strict
     conformance to the C Standard.  GCC follows the host convention
     when processing system include files, but when processing user
     files it follows the usual GNU C convention.

   * Undefining `__STDC__' in C++.

     Programs written to compile with C++-to-C translators get the
     value of `__STDC__' that goes with the C compiler that is
     subsequently used.  These programs must test `__STDC__' to
     determine what kind of C preprocessor that compiler uses: whether
     they should concatenate tokens in the ISO C fashion or in the
     traditional fashion.

     These programs work properly with GNU C++ if `__STDC__' is defined.
     They would not work otherwise.

     In addition, many header files are written to provide prototypes
     in ISO C but not in traditional C.  Many of these header files can
     work without change in C++ provided `__STDC__' is defined.  If
     `__STDC__' is not defined, they will all fail, and will all need
     to be changed to test explicitly for C++ as well.

   * Deleting "empty" loops.

     Historically, GCC has not deleted "empty" loops under the
     assumption that the most likely reason you would put one in a
     program is to have a delay, so deleting them will not make real
     programs run any faster.

     However, the rationale here is that optimization of a nonempty loop
     cannot produce an empty one, which holds for C but is not always
     the case for C++.

     Moreover, with `-funroll-loops' small "empty" loops are already
     removed, so the current behavior is both sub-optimal and
     inconsistent and will change in the future.

   * Making side effects happen in the same order as in some other
     compiler.

     It is never safe to depend on the order of evaluation of side
     effects.  For example, a function call like this may very well
     behave differently from one compiler to another:

          void func (int, int);
          
          int i = 2;
          func (i++, i++);

     There is no guarantee (in either the C or the C++ standard language
     definitions) that the increments will be evaluated in any
     particular order.  Either increment might happen first.  `func'
     might get the arguments `2, 3', or it might get `3, 2', or even
     `2, 2'.

   * Not allowing structures with volatile fields in registers.

     Strictly speaking, there is no prohibition in the ISO C standard
     against allowing structures with volatile fields in registers, but
     it does not seem to make any sense and is probably not what you
     wanted to do.  So the compiler will give an error message in this
     case.

   * Making certain warnings into errors by default.

     Some ISO C testsuites report failure when the compiler does not
     produce an error message for a certain program.

     ISO C requires a "diagnostic" message for certain kinds of invalid
     programs, but a warning is defined by GCC to count as a
     diagnostic.  If GCC produces a warning but not an error, that is
     correct ISO C support.  If test suites call this "failure", they
     should be run with the GCC option `-pedantic-errors', which will
     turn these warnings into errors.



File: gcc.info,  Node: Warnings and Errors,  Prev: Non-bugs,  Up: Trouble

Warning Messages and Error Messages
===================================

   The GNU compiler can produce two kinds of diagnostics: errors and
warnings.  Each kind has a different purpose:

     "Errors" report problems that make it impossible to compile your
     program.  GCC reports errors with the source file name and line
     number where the problem is apparent.

     "Warnings" report other unusual conditions in your code that _may_
     indicate a problem, although compilation can (and does) proceed.
     Warning messages also report the source file name and line number,
     but include the text `warning:' to distinguish them from error
     messages.

   Warnings may indicate danger points where you should check to make
sure that your program really does what you intend; or the use of
obsolete features; or the use of nonstandard features of GNU C or C++.
Many warnings are issued only if you ask for them, with one of the `-W'
options (for instance, `-Wall' requests a variety of useful warnings).

   GCC always tries to compile your program if possible; it never
gratuitously rejects a program whose meaning is clear merely because
(for instance) it fails to conform to a standard.  In some cases,
however, the C and C++ standards specify that certain extensions are
forbidden, and a diagnostic _must_ be issued by a conforming compiler.
The `-pedantic' option tells GCC to issue warnings in such cases;
`-pedantic-errors' says to make them errors instead.  This does not
mean that _all_ non-ISO constructs get warnings or errors.

   *Note Options to Request or Suppress Warnings: Warning Options, for
more detail on these and related command-line options.


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

Reporting Bugs
**************

   Your bug reports play an essential role in making GCC reliable.

   When you encounter a problem, the first thing to do is to see if it
is already known.  *Note Trouble::.  If it isn't known, then you should
report the problem.

   Reporting a bug may help you by bringing a solution to your problem,
or it may not.  (If it does not, look in the service directory; see
*Note Service::.)  In any case, the principal function of a bug report
is to help the entire community by making the next version of GCC work
better.  Bug reports are your contribution to the maintenance of GCC.

   Since the maintainers are very overloaded, we cannot respond to every
bug report.  However, if the bug has not been fixed, we are likely to
send you a patch and ask you to tell us whether it works.

   In order for a bug report to serve its purpose, you must include the
information that makes for fixing the bug.

* Menu:

* Criteria:  Bug Criteria.   Have you really found a bug?
* Where: Bug Lists.	     Where to send your bug report.
* Reporting: Bug Reporting.  How to report a bug effectively.
* GNATS: gccbug.             You can use a bug reporting tool.
* Known: Trouble.            Known problems.
* Help: Service.             Where to ask for help.


File: gcc.info,  Node: Bug Criteria,  Next: Bug Lists,  Up: Bugs

Have You Found a Bug?
=====================

   If you are not sure whether you have found a bug, here are some
guidelines:

   * If the compiler gets a fatal signal, for any input whatever, that
     is a compiler bug.  Reliable compilers never crash.

   * If the compiler produces invalid assembly code, for any input
     whatever (except an `asm' statement), that is a compiler bug,
     unless the compiler reports errors (not just warnings) which would
     ordinarily prevent the assembler from being run.

   * If the compiler produces valid assembly code that does not
     correctly execute the input source code, that is a compiler bug.

     However, you must double-check to make sure, because you may have
     run into an incompatibility between GNU C and traditional C (*note
     Incompatibilities::).  These incompatibilities might be considered
     bugs, but they are inescapable consequences of valuable features.

     Or you may have a program whose behavior is undefined, which
     happened by chance to give the desired results with another C or
     C++ compiler.

     For example, in many nonoptimizing compilers, you can write `x;'
     at the end of a function instead of `return x;', with the same
     results.  But the value of the function is undefined if `return'
     is omitted; it is not a bug when GCC produces different results.

     Problems often result from expressions with two increment
     operators, as in `f (*p++, *p++)'.  Your previous compiler might
     have interpreted that expression the way you intended; GCC might
     interpret it another way.  Neither compiler is wrong.  The bug is
     in your code.

     After you have localized the error to a single source line, it
     should be easy to check for these things.  If your program is
     correct and well defined, you have found a compiler bug.

   * If the compiler produces an error message for valid input, that is
     a compiler bug.

   * If the compiler does not produce an error message for invalid
     input, that is a compiler bug.  However, you should note that your
     idea of "invalid input" might be my idea of "an extension" or
     "support for traditional practice".

   * If you are an experienced user of one of the languages GCC
     supports, your suggestions for improvement of GCC are welcome in
     any case.


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

Where to Report Bugs
====================

   Send bug reports for the GNU Compiler Collection to
<gcc-bugs@gcc.gnu.org>.  In accordance with the GNU-wide convention, in
which bug reports for tool "foo" are sent to `bug-foo@gnu.org', the
address <bug-gcc@gnu.org> may also be used; it will forward to the
address given above.

   Please read `http://gcc.gnu.org/bugs.html' for additional and/or
more up-to-date bug reporting instructions before you post a bug report.


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 the
advice at these URLs:

     `http://gcc.gnu.org/contribute.html'
     `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: Funding,  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.

