[RFA] Patch to fix reverse return from subroutine error

[Daniel Jacobowitz]

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.

-- 
Daniel Jacobowitz
CodeSourcery