PowerPC prologue analysis

Aleksandar Ristovski aristovski@qnx.com
Tue Jul 29 15:42:00 GMT 2008

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?

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