linux-kernel - Re: [tip:x86/urgent] x86: Add memory modify constraints to xchg() and cmpxchg()

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Message-ID: <AANLkTikAmaDPji-TVDarmG1yD=fwbffcsmEU=YEuP+8r@mail.gmail.com>
Date:	Wed, 28 Jul 2010 08:45:30 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, glommer@...hat.com,
	alan@...rguk.ukuu.org.uk, zamsden@...hat.com, stable@...nel.org,
	mtosatti@...hat.com, gregkh@...e.de, peter@...frader.org,
	tglx@...utronix.de, avi@...hat.com
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/urgent] x86: Add memory modify constraints to xchg() and 
	cmpxchg()

On Tue, Jul 27, 2010 at 10:33 PM, tip-bot for H. Peter Anvin
<hpa@...or.com> wrote:
>
> x86: Add memory modify constraints to xchg() and cmpxchg()

Ack. I assume this doesn't really change the code generated? At least
not with a gcc that honors the whole memory clobber thing properly?

I also suspect that we can/should get rid of the __xg() thing - it was
there just to make sure gcc didn't see the memory read as a single
word and tried to optimize it. With the "+m" it probably doesn't
matter any more (don't know if it ever did)

               Linus
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