Re: PowerPC prologue analysis

[Aleksandar Ristovski <aristovski at qnx dot com>]

Aleksandar Ristovski wrote:
> Daniel Jacobowitz wrote:
> > On Mon, Jul 28, 2008 at 04:29:18PM -0400, Aleksandar Ristovski wrote:
> > > Thanks for the link! I briefly looked at the patch and it seems to 
> > > address some of the things I am talking about (r30-r31 issue) but the 
> > > comment still reads:
> > >
> > > +     All gpr's from saved_gpr to gpr31 are saved (except during the
> > > +     prologue).  */
> > >
> > > Is that in the ABI? I would think that if it is, then the code I am 
> > > looking at is not according to it (gcc issue or just me not 
> > > understanding powerpc assembly?).
> >
> > Sorry, I don't know which.
>
> There seems to be no such statement in the PowerPC ABI "all gpr's from 
> saved_gpr to gpr31 are saved" - non-volatile registers do not need to be 
> stored in this manner. For example, a function may save r29 but not r30 
> and r31. However PPC prologue analysis in gdb will assume there is r31 
> saved as well which will make unwind_register(r31) fail (fetch bogus 
> value). (Note: I am using gcc 4.2.3).
>
> Another assumption made in gdb code is that if multiple registers are 
> saved by the prologue, they will be saved in the ascending index order - 
> I am not sure this is a requirement stated in the ABI either. (Is it?) I 
> believe there could be cases where registers are saved in different 
> order, e.g. r30, r28, r29, etc... Hopefully this doesn't happen in 
> practise.
>
> I think your patch with gpr_mask covers the first case (not all 
> registers saved) but the second issue (if real issue) is still not handled.


And for the reference: Daniel's patch ( http://sourceware.org/ml/gdb-patches/2007-12/msg00111.html ) does solve the problem with not all registers saved.

Why is the patch not in HEAD gdb?