linux-kernel - Re: [PATCH 17/39] clobber rbx in putuser

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Message-ID: <4869497B.5040100@redhat.com>
Date:	Mon, 30 Jun 2008 18:00:43 -0300
From:	Glauber Costa <gcosta@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...e.hu,
	x86@...nel.org
Subject: Re: [PATCH 17/39] clobber rbx in putuser_64.S

Andi Kleen wrote:
> Glauber Costa <gcosta@...hat.com> writes:
> 
>> Instead of clobbering r8, clobber rbx, which is the i386 way.
> 
> Note rbx is callee saved on 64bit, so using that one means
> the surrounding function always has to save explicitely.
> Not the case with r8.
> 
> There's a reason it is the way it is.
> 
> -Andi
Right. Thanks for pointing this out.
However, r8 is not available for i386. We could use %ax, but it
holds part of the data for the call itself.

But for this case, I think we can come up with a macro that selects the 
appropriate register for each of them. Should be easy to do now that the 
code is merged.

Many thanks.
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