Re: c++/8511: (hopefully) reproducible cc1plus SIGSEGV.

[Zack Weinberg <zack@codesourcery.com>]

The following reply was made to PR c++/8511; it has been noted by GNATS.

From: Zack Weinberg <zack@codesourcery.com>
To: wwieser@gmx.de
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: c++/8511: (hopefully) reproducible cc1plus SIGSEGV.
Date: Sun, 10 Nov 2002 12:43:03 -0800

 On Sat, Nov 09, 2002 at 12:33:14PM -0000, wwieser@gmx.de wrote:
 > Compiling the attached code, I am able to reproducible 
 > SIGSEGV the GNU C++ compiler. 
 > 
 > I am sorry for not reducing code size very much but after spending more 
 > than an hour on stripping it down, gcc-3.2.1 crashed while 3.3 did not.
 > Also, removing lines which I think have little to do with the problem 
 > also turns the crash into "just" an internal compiler error.
 
 That is an expected effect for the sort of bug you have found.
 
 > First of all, I patched toplev.c to not call signal(SIGSEGV,crash_signal) 
 > but die of SIGSEGV instead. This makes it possible to find the crash 
 > with gdb. [BTW, to ease debugging, I suggest you do not _exit(1) on 
 > SIGSEGV/ILL/... and ICE but terminate the program by killing itself via 
 > SIGABRT. This way, it gets much easier to debug internal errors.]
 
 I do not understand why you need this.  When I run cc1(plus) under
 GDB and it takes a fatal signal, GDB recovers control at the point of
 the signal, before signal handlers have a chance to run.
 
 For debugging 'plain' ICEs, the thing to do is set a breakpoint on
 internal_error() before running the program.
 
 >       if (type == 0 || TREE_CODE (type) != REFERENCE_TYPE)
 >         {
 > ==>       if (TREE_CODE (TREE_TYPE (val)) == ARRAY_TYPE
 >               || TREE_CODE (TREE_TYPE (val)) == FUNCTION_TYPE
 >               || TREE_CODE (TREE_TYPE (val)) == METHOD_TYPE)
 >             val = default_conversion (val);
 >         }
 >     
 >       if (val == error_mark_node)
 >         return error_mark_node;
 >     
 > ...
 > 
 > (Neither type nor val are NULL.)
 
 There's not enough information here to know what went wrong.  Probably
 TREE_TYPE (val) was an invalid pointer.
 
 > ==>   switch (TREE_CODE (t))
 >         {
 >         case IDENTIFIER_NODE:
 >           return do_identifier (t, 0, NULL_TREE);
 > 
 > Crash with t=0xa5a5a5a5 (uh, looks suspicious...)
 
 Yeah.  That means the garbage collector ate a piece of live data.
 These are a pain to debug -- even slight changes in the input will
 make the problem vanish.  Unfortunately, using the code you posted, I
 cannot reproduce the crash; I see same the ICE in c_expand_expr that
 Volker Reichelt did.  This is very likely to be because the libstdc++
 headers have changed just enough to perturb the bug into going away; I
 don't see any logged changes that could plausibly have fixed the bug.
 
 We need you to give us a preprocessed source file.  Using your
 installation, issue this command:
 
 g++ -V3.3 -v -save-temps -I. -Wno-non-template-friend -Wno-unused \
         -ftemplate-depth-30 -c -o spline.o spline.cpp 
 
 That should provoke the same crash, but it will produce a file named
 spline.i as a side effect.  Send us that file (compressed! it will be
 huge) and the complete output of the command.
 
 zw