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From: Kumar Gala <galak@kernel.crashing.org>
Subject: Re: Saving to 32 bits of GPRs in signal context
Date: Tue, 29 May 2007 09:17:48 -0500
To: Ulrich Weigand <Ulrich.Weigand@de.ibm.com>
Cc: linuxppc-dev list <linuxppc-dev@ozlabs.org>,
	Paul Mackerras <paulus@samba.org>, Steve Munroe <sjmunroe@us.ibm.com>,
	Anton Blanchard <anton@samba.org>
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On May 29, 2007, at 9:08 AM, Ulrich Weigand wrote:

>
> Steve Munroe <sjmunroe@us.ibm.com> wrote on 05/29/2007 04:00:42 PM:
>
> > Yes exactly why make an incompatible ABI change to the powerp32  
> ABI, when
> > you can just use the existing 64-bit ABI.
> >
> > Especially as you can only run what is proposed on 64-bit hardware!
> >
> > We don't need another ABI change to powerpc32 (still recovering  
> from the
> > -msecure-plt ABI change) and WE DONT NEED a 3rd ABI.
> >
> > ABI changes ripple everywhere (not just GCC/GLIBC) including all  
> debuggers
> > and performance tools. Believe me you really don't want this.
>
> Fully agreed.  This may have gotten lost in the discussion thread,  
> but what
> Ben originally proposed was *not* an ABI change, for exactly that  
> reason.
> We simply want to allow strictly local use of 64-bit registers for
> performance optimization purposes, while still fully complying with
> the 32-bit ABI.

But we can't do that any more since the architecture specifically  
allows for the 'upper bits' not to have valid data in them.

- k