> If the "next" is for thread 1,
> 
> > That's when we get an event from a different thread (thread 3):
> > 
> >     infrun: target_wait (-1.0.0, status) =
> >     infrun:   28370.28378.0 [Thread 0xb7c5aba0 (LWP 28378)],
> >     infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP
> >     infrun: TARGET_WAITKIND_STOPPED
> >     infrun: stop_pc = 0x80782d0
> >     infrun: context switch
> >     infrun: Switching context from Thread 0xb7ea18c0 (LWP 28370) to Thread 0xb7c5aba0 (LWP 28378)
> > 
> > ... which we find to be at the address where we set a breakpoint
> > on "the unwinder debug hook" (namely "_Unwind_DebugHook"). That's
> > why GDB reports for this event that this is...
> > 
> >     infrun: BPSTAT_WHAT_SET_LONGJMP_RESUME
> 
> Why are we getting this?  longjmp/exception/step-resume breakpoints
> are thread-specific.
> 
> I'd guess that the bug is in bpstat_what:
> 
> struct bpstat_what
> bpstat_what (bpstat bs_head)
> {
> ...
> 	case bp_longjmp:
> 	case bp_longjmp_call_dummy:
> 	case bp_exception:
> 	  this_action = BPSTAT_WHAT_SET_LONGJMP_RESUME;
> 	  retval.is_longjmp = bptype != bp_exception;
> 	  break;
> ...
> 
> This bit is not considering "if (bs->stop)" like e.g.,
> the bp_step_resume case.
> 
> I've seen something like this trigger before, and have a patch
> somewhere to rewrite bpstat_what differently which fixes that.
> I never managed to write a testcase for it so never submitted
> it.  But, could you try the simpler approach?  Try making that:
> 
> 	  if (bs->stop)
> 	    {
> 	       this_action = BPSTAT_WHAT_SET_LONGJMP_RESUME;
> 	       retval.is_longjmp = bptype != bp_exception;
> 	    }
> 	  else
> 	    this_action = BPSTAT_WHAT_SINGLE;
> 	  break;

Ah ha, I missed the fact that the exception breakpoint is thread-
specific. Your fix seems to be working very well; thanks for suggestion,
Pedro! Attached is a patch with a slightly altered analysis as the revision
log. Our SuSE 10 machine is very slow, so I tested it on a more modern
machine with a slightly different distro.

I'm wondering if we shouldn't be doing the same for:

        case bp_longjmp_resume:
        case bp_exception_resume:
          this_action = BPSTAT_WHAT_CLEAR_LONGJMP_RESUME;
          retval.is_longjmp = bptype == bp_longjmp_resume;
          break;

gdb/ChangeLog:

        Pedro Alves  <palves@redhat.com>
        * breakpoint.c (bpstat_what) <bp_longjmp, bp_longjmp_call_dummy>
        <bp_exception>: Correctly handle the case where BS->STOP is not set.

Thanks!
-- 
Joel