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From: Segher Boessenkool <segher@kernel.crashing.org>
Date: Thu, 8 Sep 2005 19:01:18 +0200
To: Kumar Gala <kumar.gala@freescale.com>
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Cc: ppc64-dev <linuxppc64-dev@ozlabs.org>,
	linuxppc-dev list <linuxppc-dev@ozlabs.org>
Subject: Re: r13 is non-volatile?
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> Was looking at merging some code between ppc32 & ppc64 and noticed 
> that in ppc32 we consider r13 to be part of the non-volatile register 
> set.  Is this really correct?

I believe so, yes.

> r13 is suppose to be sdata pointer in ppc32

sdata pointer is non-volatile by definition...

> and system thread id in ppc64.

The 64-bit kernel uses GPR13 as the PACA pointer, so it handles
it specially -- it treats the userland values of the register
as non-volatile, though.

> So I'm wondering should we really be considering it NV on ppc32?

Yeah.  I'm sure there is some way to make the macro's identical
between 32- and 64-bit, though.


Segher