linux-kernel - Re: [RFC] x86: bitops asm constraint fixes

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Message-ID: <47DA2E6F.5080907@zytor.com>
Date:	Fri, 14 Mar 2008 08:51:11 +0100
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jan Beulich <jbeulich@...ell.com>
CC:	mingo@...e.hu, tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [RFC] x86: bitops asm constraint fixes

Jan Beulich wrote:
> 
> I'd really like understand, though, what the policy of (not) having a
> "memory" clobber in these operations is - currently, this appears to
> be totally inconsistent. Also, many comments of the non-atomic
> functions say those may also be re-ordered - this contradicts the use
> of "asm volatile" in there, which again I'd like to understand.
> 

In general, proper "m" constraints are better than "memory" clobbers, 
since they give gcc more information.  Note that the "m" constraint 
doesn't actually have to be *manifest* in the assembly string.

	-hpa
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