Mark Kettenis wrote:
>> Date: Fri, 03 Jul 2009 17:34:59 -0700
>> From: Michael Snyder <msnyder@vmware.com>
>>
>> Michael Snyder wrote:
>>> This comes out of a discussion with Daniel, about how gcc
>>> does not generate the right dwarf info to allow correct
>>> frame unwinding in function epilogues, causing frame_unwind
>>> to return bad results.
>>>
>>> It's necessary for reverse-step, which will frequently step
>>> backward to the return instruction of a function.  But it also
>>> provides an improvement for forward debugging, in that now,
>>> without this change, if you STEPI until you are at the return
>>> instruction, you will get a bad backtrace.
>>>
>>> The infrun changes that take advantage of this patch will follow
>>> separately.
>>>
>>> Michael
>> Oops, the patch wasn't meant to have that "#if 0" in it...
>> corrected patch below.
> 
> Still has the #if 0 in there.

Sorry.  ;-(
> 
> I also think you should add a comment about the specific ordering of
> this unwinder.  It has to come before the dwarf2 unwinder because GCC
> doesn't provide proper CFI for the epilogue, right?

Right.  Since the others are similarly order-dependent, I will
expand on their comments as well.


>> +  if (target_read_memory (pc, &insn, 1) != 0)
>> +    return 0;	/* Can't read memory at pc.  */
> 
> For consistency's sake, can you drop the != 0 here?

OK.

>> +  if (insn != 0xc3)	/* RET */
>> +    return 0;
> 
> Please use lowercase for instruction mnemonics.

OK.  Revised patch attached.