linux-kernel - Re: [PATCH 1 of 4] mm: add a ptep_modify

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Message-ID: <alpine.LFD.1.10.0806201211560.3167@woody.linux-foundation.org>
Date:	Fri, 20 Jun 2008 12:15:24 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
cc:	Ingo Molnar <mingo@...e.hu>, benh@...nel.crashing.org,
	xen-devel <xen-devel@...ts.xensource.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	kvm-devel <kvm-devel@...ts.sourceforge.net>, x86@...nel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	Hugh Dickins <hugh@...itas.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1 of 4] mm: add a ptep_modify_prot transaction
 abstraction

On Fri, 20 Jun 2008, Jeremy Fitzhardinge wrote:
> 
> Blows up on "gcc version 3.4.4 20050314 (prerelease) (Debian 3.4.3-13)":

Yeah, I was a bit worried about that. Gcc sometimes does insane things.

We literally just tested that the asm should only _ever_ be generated with 
a constant value, but if some gcc dead-code removal thing doesn't work, it 
will then screw up and try to generate the asm even for a non-constant 
thing.

The fairly trivial fix is probably to just change the "i" to "ir", safe in 
the knowledge that any _sane_ case will never use the "r" possibility. I 
suspect even your insane case will end up then killing the bad choice 
later.

		Linus
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