linux-kernel - Re: [PATCH] mark %esi as clobbered in E820 BIOS call

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Date:	Sat, 28 Mar 2009 12:18:15 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	"Michael K. Johnson" <johnsonm@...th.com>, jmforbes@...uxtx.org,
	Jordan_Hargrave@...l.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mark %esi as clobbered in E820 BIOS call

Ingo Molnar wrote:
> * Michael K. Johnson <johnsonm@...th.com> wrote:
> 
>> Justin and Peter, please review this for stable .y trees.  Peter,
>> please review this for trunk unless you decide to do a more 
>> extensive workaround for BIOS register clobbering.
>>
>> Thanks!
>>
>> $ cat e820-esi-clobber-workaround.patch
>> Jordan Hargrave diagnosed a BIOS clobbering %esi in the E820 call.
>> That particular BIOS has been fixed, but there is a possibility that
>> this is responsible for other occasional reports of early boot
>> failure, and it does not hurt to add %esi to the clobbers.
> 
> nice fix! Would you mind to update the clobber list to include _all_ 
> registers? I dont see why any of the other registers couldnt be 
> clobbered by a BIOS, and this is boot-only code so micro-performance 
> is not an issue.

%esi and %ebp are the only registers that aren't already clobbered.  gcc
doesn't like %ebp clobbers, so it has to be done via push..pop.  I have
been thinking about doing a generic register-save wrapper for *all* BIOS
calls; this plus the recent patch to do a bunch of similar hacks for
VESA calls kind of tells me it's time to do this.  However, I'm going to
clean up this for the trunk and Cc: stable for now.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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