[patch] Fix oddity in personality routine

Tue Nov 17 16:18:00 GMT 2009

On Tue, Nov 17, 2009 at 02:54:53PM +0000, Andrew Haley wrote:
> Jack Howarth wrote:
>> > In the unwinder walk, are there any particular places where I could
> > get additional debug information in gdb that would be helpful to diagnose this
> > issue?
>> Sure. The trace you provided is very incomplete, and in particular
> I can't see any stepping into _Unwind_RaiseException.
>> The main loop looks like this:
>> while (1)
> {
> _Unwind_FrameState fs;
>> /* Set up fs to describe the FDE for the caller of cur_context. The
> 	 first time through the loop, that means __cxa_throw. */
> code = uw_frame_state_for (&cur_context, &fs);
>> if (code == _URC_END_OF_STACK)
> 	/* Hit end of stack with no handler found. */
> 	return _URC_END_OF_STACK;
>> if (code != _URC_NO_REASON)
> 	/* Some error encountered. Usually the unwinder doesn't
> 	 diagnose these and merely crashes. */
> 	return _URC_FATAL_PHASE1_ERROR;
>> /* Unwind successful. Run the personality routine, if any. */
> if (fs.personality)
> 	{
> 	 code = (*fs.personality) (1, _UA_SEARCH_PHASE, exc->exception_class,
> 				 exc, &cur_context);
> 	 if (code == _URC_HANDLER_FOUND)
> 	 break;
> 	 else if (code != _URC_CONTINUE_UNWIND)
> 	 return _URC_FATAL_PHASE1_ERROR;
> 	}
>> /* Update cur_context to describe the same frame as fs. */
> uw_update_context (&cur_context, &fs);
> }
>> So, for each stack frame, we read the unwinder data and then call the
> appropriate personality routine (in this case, in libgcj.)
>> cur_context.ra is the program counter for the current stack frame.
> So,
>> (gdb) x cur_context.ra
> 0x7ffff659ca7f <_ZN4java3net14URLClassLoader9findClassEJPNS_4lang5ClassEPNS2_6StringE+255>:	0x41c58949
>> tells you which frame is being inspected. So, you can see where the
> exception handler should be, and you can step into the personality
> routine to see why it's not recognized.
>Andrew,
 At which points should I be sampling with 'x cur_context.ra'? Is there a particular
breakpoint that would be useful to set in order to do this? Also, would it help if I
recompiled libgcj with -O0 as well?
 Jack
>> Andrew.