Re: [RFA] Patch to fix reverse return from subroutine error

[Michael Snyder <msnyder@vmware.com>]

Daniel Jacobowitz wrote:
> On Sat, Jun 27, 2009 at 01:57:22PM -0700, Michael Snyder wrote:
>> The problem is that the second "frame_id_eq" test fails in
>> the case where we've just stepped backward to the RET instruction
>> of a function which, in forward-time, had just returned.
>>
>> It's possible that what we're trying to do here is work around a
>> bug in the i386 implementation of frame_unwind_id.  When I look at
>> the frame_id that it returns at this point, it does not match either
>> the caller or the callee, and its code_addr is particularly wrong.
> 
> I wrote about this problem in my GCC summit paper.  All released
> versions of GCC generate unwind info that is wrong in epilogues.
> I believe it's fixed in trunk GCC, although maybe for specific
> platforms only.
> 
> In order to get this to work for my demo I had an epilogue-specific
> unwinder for ARM.  It detected common epilogue sequences and analyzed
> them to find the frame ID, and was installed at higher priority than
> the DWARF unwinder.
> 
> I think you're going to need the same thing here, or else use the
> existing gdbarch epilogue hook somehow.

Great, I looked up your paper, and found it helpful.
Are your gdb patches available online?  Any head start
would be a boon...

Michael