[Bug libstdc++/64798] [5 regression] g++.old-deja/g++.eh/badalloc1.C FAILs

["rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64798

--- Comment #2 from rguenther at suse dot de <rguenther at suse dot de> ---
On Mon, 26 Jan 2015, Richard Biener wrote:

> On Mon, 26 Jan 2015, ro at gcc dot gnu.org wrote:
> 
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64798
> > 
> >             Bug ID: 64798
> >            Summary: [5 regression] g++.old-deja/g++.eh/badalloc1.C FAILs
> >            Product: gcc
> >            Version: 5.0
> >             Status: UNCONFIRMED
> >           Severity: normal
> >           Priority: P3
> >          Component: libstdc++
> >           Assignee: unassigned at gcc dot gnu.org
> >           Reporter: ro at gcc dot gnu.org
> >                 CC: rguenth at gcc dot gnu.org
> >               Host: sparc*-sun-solaris2.*
> >             Target: sparc*-sun-solaris2.*
> >              Build: sparc*-sun-solaris2.*
> > 
> > Between 20150116 (r219745) and 20150123 (r220039),
> > g++.old-deja/g++.eh/badalloc1.C
> > started to FAIL on 32-bit Solaris/SPARC:
> > 
> > FAIL: g++.old-deja/g++.eh/badalloc1.C  -std=c++11 execution test
> > FAIL: g++.old-deja/g++.eh/badalloc1.C  -std=c++14 execution test
> > FAIL: g++.old-deja/g++.eh/badalloc1.C  -std=c++98 execution test
> > 
> > Program received signal SIGSEGV, Segmentation fault.
> > [Switching to Thread 1 (LWP 1)]
> > __cxxabiv1::__cxa_throw (obj=0x2195c <arena+92>, 
> >     tinfo=0x73908 <typeinfo for int>, dest=0x0)
> >     at /vol/gcc/src/hg/trunk/local/libstdc++-v3/libsupc++/eh_throw.cc:76
> > 76       
> > __GXX_INIT_PRIMARY_EXCEPTION_CLASS(header->exc.unwindHeader.exception_class);
> > 1: x/i $pc
> > => 0xff220314 <__cxxabiv1::__cxa_throw(void*, std::type_info*, void
> > (*)(void*))+96>:    sttw  %g2, [ %i0 + -24 ]
> > (gdb) where
> > #0  __cxxabiv1::__cxa_throw (obj=0x2195c <arena+92>, 
> >     tinfo=0x73908 <typeinfo for int>, dest=0x0)
> >     at /vol/gcc/src/hg/trunk/local/libstdc++-v3/libsupc++/eh_throw.cc:76
> > #1  0x00011114 in fn_throw ()
> >     at
> > /vol/gcc/src/hg/trunk/local/gcc/testsuite/g++.old-deja/g++.eh/badalloc1.C:98
> > #2  0x000112f8 in main ()
> >     at
> > /vol/gcc/src/hg/trunk/local/gcc/testsuite/g++.old-deja/g++.eh/badalloc1.C:129
> > (gdb) p $i0-24
> > $3 = 137540
> > 
> > The SEGV happens because the sttw target needs to be 8-byte aligned, but is
> > not.
> 
> Does malloc return 8-byte aligned memory?  Is __alignof__
> 
>       struct free_entry {
>         std::size_t size;
>         free_entry *next;
>       };
> 
> less than 8?

Ah - the issue might be that g++.old-deja/g++.eh/badalloc1.C does

extern "C" void *malloc (size_t size)
{
  object *p = reinterpret_cast<object *>(&arena[pos]);

  if (fail)
    return 0;

  p->size = size;
  size = (size + __alignof__(object) - 1) & - __alignof__(object);
  pos += size + sizeof(object);

thus it aligns to 'object' but 'object' is

struct object
{
  size_t size __attribute__((aligned));
};

Richard