gdb crashes when loading core files (in is_ctor_or_dtor)

Created attachment 6531
gdb-fix-crash-when-checking-for-ctor-of-lambda by Thomas Voß

Using GDB to debug this test case: http://pastebin.ubuntu.com/1062024/ causes it to crash in is_ctor_or_dtor.

Attached here patch by Thomas Voß that fixes it.

This is description:
«It turns out that gdb crashes as it tries to determine whether a field of a lambda is a or ctor/dtor, given the fields name. Apparently, the field's name is NULL and I added a check for that, bailing out and returning 0 ("no, this is neither a dtor nor a ctor"). GDB behaves normally when being run on the test program mentioned before. Patch is attached, generated with quilt.»

See launchpad bug http://pad.lv/1006860 for reference.

Please post any patches to gdb-patches at sourceware.org.

I reproduced the bug.

I don't think this is the correct fix.

What seems to be happening here is that we are trying to
compute the physname for a type that is a pointer to a member
function of an unnamed structure type.
Because it is unnamed, c_type_print_base falls through to
printing the body of the structure, instead of its name.
This then crashes.

Maybe NULL checks in is_constructor_name and is_destructor_name
would be ok; though I am not sure. But even if those were there
we would still be seeing very weird results here.

BTW I reproduced using the reported test case:

#include <sigc++/sigc++.h>

#if __cplusplus >= 201100L || defined (__GXX_EXPERIMENTAL_CXX0X__)
#include <type_traits>

namespace sigc
{
    template <typename Functor>
      struct functor_trait<Functor, false>
      {
        typedef decltype (::sigc::mem_fun(std::declval<Functor&>(), &Functor::operator())) _intermediate;
        typedef typename _intermediate::result_type result_type;
        typedef Functor functor_type;
      };
}
#endif

int main()
{
  sigc::slot <bool> slot3 = [] () -> bool { return true; };
  sigc::slot <bool, int> slot4 = [] (int) -> bool { return true; };
  while (1);
}

and building it on Fedora 16 with

g++ -std=c++0x -g -o pr pr.cc $(pkg-config --cflags sigc++-2.0) $(pkg-config --libs sigc++-2.0)

Simplest way to see it is "gdb -readnow pr"

I think Tom is correct. IMO the questionable thing done here is asking c_type_print_base to print details of the type when we have a pointer member/method whose containing class/struct is anonymous (TYPE_NAME (type) == NULL). That just doesn't seem right.

I believe the proper fix is simply for c_type_print_varspec_prefix to honor the SHOW parameter when it is calling other c_type_print_* functions.

In this function, the only cases which do not pass SHOW to the other type printing functions are MEMBERPTR and METHODPTR, exactly where we are seeing problems.

I'm working on a test case for this now, and will submit a patch when it is finished. [It requires hand-written DWARF.]

CVSROOT: /cvs/src
Module name: src
Changes by: <email address hidden> 2012-08-19 19:37:51

Modified files:
 gdb : ChangeLog c-typeprint.c
 gdb/testsuite : ChangeLog
Added files:
 gdb/testsuite/gdb.dwarf2: dw2-anon-mptr.exp dw2-anon-mptr.S

Log message:
 PR c++/14365
 * c-typeprint.c (c_type_print_varspec_prefix): Pass
 -1 for SHOW to c_type_print_base for METHODPTR and MEMBERPTR.

 * gdb.dwarf2/dw2-anon-mptr.exp: New file.
 * gdb.dwarf2/dw2-anon-mptr.S: New file.

Patches:
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/ChangeLog.diff?cvsroot=src&r1=1.14602&r2=1.14603
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/c-typeprint.c.diff?cvsroot=src&r1=1.75&r2=1.76
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/testsuite/ChangeLog.diff?cvsroot=src&r1=1.3343&r2=1.3344
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/testsuite/gdb.dwarf2/dw2-anon-mptr.exp.diff?cvsroot=src&r1=NONE&r2=1.1
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/testsuite/gdb.dwarf2/dw2-anon-mptr.S.diff?cvsroot=src&r1=NONE&r2=1.1

I have committed a patch to fix this. If there are any further problems, please let me know.