linux-kernel - Re: [PATCH 1/1] Speedfreq-SMI call clobbers ECX

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Date:	Tue, 11 Mar 2008 00:14:39 +0100
From:	Stephan Diestelhorst <langer_mann@....de>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Ingo Molnar <mingo@...e.hu>, davej@...emonkey.org.uk,
	cpufreq@...ts.linux.org.uk, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] Speedfreq-SMI call clobbers ECX

Stephan Diestelhorst wrote:
> Andi Kleen wrote:
> > Stephan Diestelhorst <langer_mann@....de> writes:
> > > 
> > > New attempt with full clobbers, note that I deliberatly did not change
> > > the order of the output registers. Real output operands still preceede
> > > outputs used for potential clobbering.
> > > 
> > > I'm not too sure about the EBP push/pop frame, but as folks pointed
> > > out already, we should not trust the SMI code too much.
> > 
> > Be careful -- older gcc versions tend to abort for inline asm
> > that clobbers too many registers. Especially when the register
> > is already used (like ebp in a frame pointer enabled kernel) 
> 
> > Make sure it at least works on the oldest supported gcc version 
> > (gcc 3.2) and with frame pointer on.
> 
> As I've said, I do not expect this to be problematic, but will test,
> just to be sure! 

I've tried it on the following GCCs: 3.3, 3.4, 4.0, 4.1, all with and
without frame-pointer ommission.
Result: As expected. Worked w/o problems, warnings anything.

Apologies for not testing gcc-3.2, but compiling it from source did
not work with libtool complaining about tags in libmath. I'd be
grateful if someone with working gcc-3.2 could try this out.

Cheers,
  Stephan
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