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Reporting Bugs | Managing Bugs (GNATS and the test-suite) | Frequently Reported Bugs in GCC 3.0

Reporting Bugs

Our preferred way of receiving bugs is via our GNATS bug reporting system.

Before you report a bug, please check the list of well-known bugs and, if possible in any way, try a current development snapshot or CodeSourcery's Online Test Compilation. If you want to report a bug with egcs 1.x or versions of GCC before 3.0 we strongly recommend upgrading to the current release first.

Before reporting that GCC compiles your code incorrectly, please compile it with gcc -Wall and see whether this shows anything wrong with your code that could be the cause instead of a bug in GCC.

Summarized bug reporting instructions

After this summary, you'll find detailed bug reporting instructions, that explain how to obtain some of the information requested in this summary.

What we need

• The GCC version (not just 3.xx; run gcc -v)
• The system type (the dir name after gcc-lib in the output of gcc -v
• The complete command line that triggers the bug
• The compiler output (error messages, warnings, etc)
• The preprocessed file (*.i*) that triggers the bug, generated by adding -save-temps to the complete compilation command (see below)
• The options given when GCC was configured/built

What we DON'T want

• A source file that #includes header files that are left out of the bug report (see above)
• That source file and a collection of header files (don't waste your time; the preprocessor will collect them for you! :-)
• An attached archive (tar, zip, shar, whatever) containing all (or some :-) of the above, so that we can tell what the bug report is about without having to unarchive it
• A code snippet that won't cause the compiler to produce the exact output mentioned in the bug report (e.g., a snippet with just a few lines around the one that apparently triggers the bug, with some pieces replaced with ellipses or comments for extra obfuscation :-)
• The location (URL) of the package that failed to build (we won't download it, anyway, since you've already given us what we need to duplicate the bug, haven't you? :-)
• An error that occurs only some of the times a certain file is compiled, such that retrying a sufficient number of times results in a successful compilation; this is a symptom of a hardware problem, not of a compiler bug (sorry)
• E-mail messages that complement previous, incomplete bug reports; post a new, self-contained, full bug report instead, if possible as a follow-up (or reply) to the original bug report
• Assembly files (*.s) produced by the compiler, or any binary files, such as object files, executables or core files
• Duplicate bug reports, or reports of bugs already fixed in the development tree, especially those that have already been reported as fixed last week :-)
• Bugs in the assembler, the linker or the C library. These are separate projects, with separate mailing lists and different bug reporting procedures
• Bugs in releases or snapshots of GCC not issued by the GNU Project. Report them to whoever provided you with the release
• Questions about the correctness or the expected behavior of certain constructs that are not GCC extensions. Ask them in forums dedicated to the discussion of the programming language

Where to post it

Please submit your bug report directly to our GNATS bug database. If this is not possible, please mail all information to gcc-bugs@gcc.gnu.org.

Detailed bug reporting instructions

In general, all the information we need can be obtained by collecting the command line below, as well as its output and the preprocessed file it generates.

gcc -v -save-temps all-your-options source-file

Typically the preprocessed file (extension .i for C or .ii for C++) will be large, so please compress the resulting file with one of the popular compression programs such as bzip2, gzip, zip or compress (in decreasing order of preference). Use maximum compression (-9) if available. Please include the compressed preprocessor output in your bug report, even if the source code is freely available elsewhere; it makes the job of our volunteer testers much easier.

The only excuses to not send us the preprocessed sources are (i) if you've found a bug in the preprocessor, or (ii) if you've reduced the testcase to a small file that doesn't include any other file. If you can't post the preprocessed sources because they're proprietary code, then try to create a small file that triggers the same problem.

Since we're supposed to be able to re-create the assembly output (extension .s), you usually should not include it in the bug report, although you may want to post parts of it to point out assembly code you consider to be wrong.

Whether to use MIME attachments or uuencode is up to you. In any case, make sure the compiler command line, version and error output are in plain text, so that we don't have to decode the bug report in order to tell who should take care of it. A meaningful subject indicating language and platform also helps.

Please avoid posting an archive (.tar, .shar or .zip); we generally need just a single file to reproduce the bug (the .i/.ii preprocessed file), and, by storing it in an archive, you're just making our volunteers' jobs harder. Only when your bug report requires multiple source files to be reproduced should you use an archive. In any case, make sure the compiler version, error message, etc, are included in the body of your bug report as plain text, even if needlessly duplicated as part of an archive.

The gcc lists have message size limits (200 kbytes) and bug reports over those limits will currently be bounced. If your bug is larger than that, please post it directly in GNATS.

If you fail to supply enough information for a bug report to be reproduced, someone will probably ask you to post additional information (or just ignore your bug report, if they're in a bad day, so try to get it right on the first posting :-). In this case, please post the additional information to the bug reporting mailing list, not just to the person who requested it, unless explicitly told so. If possible, please include in this follow-up all the information you had supplied in the incomplete bug report (including the preprocessor output), so that the new bug report is self-contained.

Managing Bugs (GNATS and the test-suite)

This section contains information mostly intended for GCC contributors.

If you find a bug, but you are not fixing it (yet):

1. Create a (minimal) test-case.
2. Add the test-case to our test-suite, marking it as XFAIL.
3. Add a bug report referencing the test-case to GNATS.

If you fix a bug for which there is already a GNATS entry:

1. Remove the XFAIL on the test-case.
2. Close the bug report in GNATS.

If you find a bug, and you are fixing it right then:

1. Create a (minimal) test-case.
2. Add the test-case to our test-suite, marking it as PASS.
3. Check in your fixes.

Frequently Reported Bugs in GCC 3.0

General

The following bugs are very frequently reported.

• GCC 2.95.2 does not build on GNU/Linux systems using glibc 2.2, such as Red Hat 7.0. A patch is available. This will be fixed in GCC 2.95.3 and GCC 3.0.
• GCC 2.95.2 crashes when compiling mbx.c from the PINE 4.30 or IMAP2000 distribution on Sparc systems running Solaris.

Fortran

Fortran bugs are documented in the G77 manual rather than explicitly listed here. Please see "Known Causes of Trouble with GNU Fortran" in the G77 manual.

C++

This is the list of bugs (and non-bugs) in g++ (aka GNU C++) that are reported very often, but not yet fixed. While it is certainly better to fix bugs instead of documenting them, this document might save people the effort of writing a bug report when the bug is already well-known. How to report bugs tells you how to report a bug.

There are many reasons why reported bugs don't get fixed. It might be difficult to fix, or fixing it might break compatibility. Often, reports get a low priority when there is a simple work-around. In particular, bugs caused by invalid C++ code have a simple work-around, fix the code. Now that there is an agreed ISO/ANSI standard for C++, the compiler has a definitive document to adhere to. Earlier versions might have accepted source code that is no longer C++. This means that code which might have `worked' in a previous version, is now rejected. You should update your code to be C++.

You should try to use the latest stable release of the GNU C++ compiler. This is currently 3.0. Many commonly reported bugs in earlier releases are fixed in that version.

Common problems updating from g++ 2.95 to g++ 3.0

g++ 3.0 conforms much closer to the ISO C++ standard (available at http://www.ncits.org/cplusplus.htm). We have also implemented some of the core and library defect reports (available at http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/cwg_defects.html & http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-defects.html respectively).

• The ABI has changed. This means that both class layout and name mangling is different. You must recompile all c++ libraries (if you don't you will get link errors).
• The standard library is much more conformant, and uses the std:: namespace.
• std:: is now a real namespace, not an alias for ::.
• The standard header files for the c library don't end with .h, but begin with c (i.e. <cstdlib> rather than <stdlib.h>). The .h names are still available, but are deprecated.
• <strstream> is deprecated, use <stringstream> instead.
• streambuf::seekoff & streambuf::seekpos are private, instead use streambuf::pubseekoff & streambuf::pubseekpos respectively.
• If std::operator << (std::ostream &, long long) doesn't exist, you need to recompile libstdc++ with --enable-long-long.

• Say, std::strcmp at the call. This is the most explicit way of saying what you mean.
• Say, using std::strcmp; somewhere before the call. You will need to do this for each function or type you wish to use from the standard library.
• Say, using namespace std; somewhere before the call. This is the quick-but-dirty fix. This brings the whole of the std:: namespace into scope. Never do this in a header file, as you will be forcing users of your header file to do the same.

Non-bugs

Nested classes can access private types of the containing class.

G++ now implements type access control on member types. Defect report 45 clarifies that nested classes are members of the class they are nested in, and so are granted access to private members of that class.

Classes in exception specifiers must be complete types.

[15.4]/1 tells you that you cannot have an incomplete type, or pointer to incomplete (other than cv void *) in an exception specification.

G++ emits two copies of constructors and destructors.

In general there are three types of constructor (and destructor).

1. The complete object constructor/destructor.
2. The base object constructor/destructor.
3. The allocating destructor/deallocating destructor.

The first two are different, when virtual base classes are involved. In some cases we can do better, and this is logged in GNATS.

Exceptions don't work in multithreaded applications

You need to rebuild g++ and libstdc++ with --enable-threads. Remember, c++ exceptions are not like hardware interrupts. You cannot throw an exception in one thread and catch it in another. You cannot throw an exception from a signal handler, and catch it in the main thread.

Global destructors are not run in the correct order

Global destructors should be run in the reverse order of their constructors completing. In most cases this is the same as the reverse order of constructors starting, but sometimes it is different, and that is important. You need to compile and link your programs with --use-cxa-atexit. We have not turned this switch on by default, as it requires a cxa aware runtime library (libc, glibc, or equivalent).

Missing features

export is not implemented.

The keyword will be parsed correctly, but has no effect.

Two stage lookup in templates is not implemented.

[14.6] specifies how names are looked up inside a template. G++ does not do this correctly, but for most templates this will not be noticeable.

Parse errors for "simple" code

Up to and including GCC 3.0, the compiler will give "parse error" for seemingly simple code, such as

struct A{
  A();
  A(int);
  void func();
};

struct B{
  B(A);
  B(A,A);
  void func();
};

void foo(){
  B b(A(),A(1));     //Variable b, initialized with two temporaries
  B(A(2)).func();    //B temporary, initialized with A temporary
}

The problem is that GCC starts to parse the declaration of b as a function b returning B, taking a function returning A as an argument. When it sees the 1, it is too late. The work-around in these cases is to add additional parentheses around the expressions that are mistaken as declarations:

  (B(A(2))).func();

Sometimes, even that is not enough; to show the compiler that this should be really an expression, a comma operator with a dummy argument can be used:

  B b((0,A()),A(1));

Another example is the parse error for the return statement in

struct A{};

struct B{
  A a;
  A f1(bool);
};

A B::f1(bool b)
{
  if (b)
    return (A()); 
  return a;
}

The problem is that the compiler interprets A() as a function (taking no arguments, returning A), and (A()) as a cast - with a missing expression, hence the parse error. The work-around is to omit the parentheses:

  if (b)
    return A(); 

This problem occurs in a number of variants; in throw statements, people also frequently put the object in parentheses. The exact error also somewhat varies with the compiler version. The work-arounds proposed do not change the semantics of the program at all; they make them perhaps less readable.

Optimization at -O3 takes a very long time

At -O3, all functions are candidates for inlining. The heuristic used has some deficiencies which show up when allowed such freedom. This is g++ specific, as it has an earlier inliner than gcc.