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

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Date:	Tue, 03 Jan 2012 18:31:39 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	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}()

Le mardi 03 janvier 2012 à 15:35 +0000, Jan Beulich a écrit :

> And in atomic64_set_cx8 it's the other way around: The comment
> explains why supposedly no LOCK prefix is needed, but that's again
> in conflict with above quoted paragraph from the manual.

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.



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