Re: [Qemu-devel] qemu hw/ppc_oldworld.c target-ppc/cpu.h target-...

[Paul Brook <paul@codesourcery.com>]

> > I think what you mean is that they work the way that ppc64 is defined, to
> > remain compatible with ppc32.  IMHO this is entirely irrelevant as we're
> > emulating a ppc32. You could replace the high bits with garbage and
> > nothing would ever be able to tell the difference.
>
> PowerPC is a 64 bits architecture. PowerPC 32 on 32 bits host is
> optimized not to compute the 32 highest bits, the same way it's allowed
> to cut down the GPR when implementing a CPU that would not support the
> 64 bits mode (but this is a tolerance, this is not the architecture is
> defined).

No. PowerPC is defined as a 64-bit archirecure. However there is a subset of 
this architecture (aka ppc32) that is a complete 32-bit architecture in its 
own right.  By your own admission, we can get away with not calculating the 
high 32 bit of the register. If follows that the high bits are completely 
meaningless. 

The qemu ppc32 emulation is implemented in such a way that on 64-bit hosts it 
looks a lot like a ppc64 implementation. However this need not, and should 
not be exposed to the user.

> OK. Those are real bugs to be fixed. I'll take a look.... But I'll try
> not to break the GPR dump. In fact, GPR should always dumped as 64 bits,
> even when runnig on 32 bits hosts. This would be more consistent with
> the specification.

I disagree. qemu is implementing ppc32. Showing more than 32 bits of register 
is completely bogus. Any differences between a 32-bit host and a 64-bit host 
are a qemu bug. If you display 64 bits, then those 64 bits had better be the 
same when run on 32-bit hosts.

Paul