Re: [offbyone RFC] Merge i386newframe

[Andrew Cagney <ac131313 at redhat dot com>]

>    If the previous frame's direction flag should have been reset then the    register unwind code should have done that (wonder if dwarf2cfi is    powerful enough to specify this).
>
> I felt that it is somehow different from a "saved" registers.  But
> your phrasing makes me believe it's more correct to reset from the
> register unwind code.
>
> I don't think it is any different.  For:
>
>     (gdb) up
>     Frame #1 foo()
>     (gdb) info register psw
>
> to work correctly, the register unwind code will need to zap that bit. Otherwize GDB will mis-represent the value of the PSW in the calling frame.
>
> I think there is still going to be a problem in the CFI unwinder.  The CFI spec as the `architectural' register unwind rule as a loop-hole. Something related to that may need to be added.  Wonder if GCC even thought to generate it.  Hmm, the throw/catch code must have done something .... 

Thinking about this some more, a generic pop function won't work.

Consider the frames:

- sentinel
- normal
- sigtramp
- dummy

It's only when unwinding a normal frame that that PSW bit should be 
zapped.  For all the others the PSW value of the callee was hopefully 
completly saved by the caller.

Andrew