linux-kernel - Re: [PATCH] x86_64 : support atomic ops with 64 bits integer values

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Message-ID: <48A6EC77.8080904@zytor.com>
Date:	Sat, 16 Aug 2008 08:04:23 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Joe Perches <joe@...ches.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86_64 : support atomic ops with 64 bits integer values

Mathieu Desnoyers wrote:
> x86_64 add/sub atomic ops does not seems to accept integer values bigger
> than 32 bits as immediates. Intel's add/sub documentation specifies they
> have to be passed as registers.

This is correct; this is in fact true for all instructions except "mov".

Whether it's sign- or zero-extending is sometimes subtle, but not in 
these cases.

Do you happen to know if this is a manifest bug in the current kernel 
(i.e. if there is anywhere we're using more than ±2 GB as a constant to 
these functions?)

Either way, I'll queue this up to tip:x86/urgent if Ingo hasn't already 
since this is a pure bug fix.

	-hpa
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