linux-kernel - RE: [PATCH] x86: fix and improve cmpxchg_double{,

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Date:	Wed, 4 Jan 2012 10:36:34 -0000
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Eric Dumazet" <eric.dumazet@...il.com>,
	"Jan Beulich" <JBeulich@...e.com>
Cc:	<mingo@...e.hu>, <tglx@...utronix.de>,
	"Christoph Lameter" <cl@...ux.com>, <linux-kernel@...r.kernel.org>,
	"netdev" <netdev@...r.kernel.org>, <hpa@...or.com>
Subject: RE: [PATCH] x86: fix and improve cmpxchg_double{,_local}()

 
> BTW atomic64_set() asm() contraints are wrong :
> 
> static inline void atomic64_set(atomic64_t *v, long long i)
> {
>         unsigned high = (unsigned)(i >> 32);
>         unsigned low = (unsigned)i;
>         asm volatile(ATOMIC64_ALTERNATIVE(set)
>                      : "+b" (low), "+c" (high)
>                      : "S" (v)
>                      : "eax", "edx", "memory"
>                      );
> }
> 
> 
> ebx/ecx registers are not modified by cmpxchg8b (or the 
> atomic64_set_386 emulation). Only eax/edx can be modified.

Isn't it also possible to constrain the "memory"
constraint to only apply to '*v' not all of memory?
I can't remember the syntax off hand though...

	David


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