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

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Date:	Fri, 14 Mar 2008 08:09:40 +0000
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	<mingo@...e.hu>, <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [RFC] x86: bitops asm constraint fixes

>>> "H. Peter Anvin" <hpa@...or.com> 14.03.08 08:51 >>>
>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.

... which is the case with the patch applied.

So am I taking this as 'yes, a proper re-write of these routines is
worthwhile'? But - you didn't comment on the other issues raised,
so before getting to that I'll have to wait to see what's the reason
(if any) for the other anomalies.

Jan

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