[Bug c++/56941] New: Thread conflict is reported by helgrind in _Unwind_IteratePhdrCallback

[Bug c++/56941] New: Thread conflict is reported by helgrind in _Unwind_IteratePhdrCallback

[yuri at tsoft dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56941

             Bug #: 56941
           Summary: Thread conflict is reported by helgrind in
                    _Unwind_IteratePhdrCallback
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: yuri@tsoft.com


I get the following error from helgrind on heavily multi-threaded process
throwing a lot of exceptions. gcc in use is 4.7.2 on amd64 architecture.

Line unwind-dw2-fde-dip.c:212:  prev_cache_entry->link = cache_entry->link;

It looks like the error is due to an unprotected cache access.

This should either be fixed, or there should be a good explanation why this
should be considered a non-issue. Data race conditions reported by helgrind
usually correspond to real issues.


---helgrind log---
==83659== Possible data race during write of size 8 at 0x24FECC8 by thread #17
==83659== Locks held: none
==83659==    at 0x22FB1D9: _Unwind_IteratePhdrCallback
(unwind-dw2-fde-dip.c:212)
==83659==    by 0x14D41: dl_iterate_phdr (in /libexec/ld-elf.so.1)
==83659==    by 0x22FB8B1: _Unwind_Find_FDE (unwind-dw2-fde-dip.c:451)
==83659==    by 0x22F8D9A: uw_frame_state_for (unwind-dw2.c:1179)
==83659==    by 0x22F91F6: uw_init_context_1 (unwind-dw2.c:1500)
==83659==    by 0x22F96A6: _Unwind_RaiseException (unwind.inc:88)
==83659==    by 0x1E1FAD0: __cxa_throw (eh_throw.cc:78)
==83659==    <...user stack omitted...>
==83659== 
==83659== This conflicts with a previous write of size 8 by thread #54
==83659== Locks held: none
==83659==    at 0x22FB1D5: _Unwind_IteratePhdrCallback
(unwind-dw2-fde-dip.c:211)
==83659==    by 0x14D41: dl_iterate_phdr (in /libexec/ld-elf.so.1)
==83659==    by 0x22FB8B1: _Unwind_Find_FDE (unwind-dw2-fde-dip.c:451)
==83659==    by 0x22F8D9A: uw_frame_state_for (unwind-dw2.c:1179) 
==83659==    by 0x22F970A: _Unwind_RaiseException (unwind.inc:99)
==83659==    by 0x1E1FAD0: __cxa_throw (eh_throw.cc:78)
==83659==    <...user stack omitted...>