Messages in this thread | | | Date | Wed, 04 Jan 2012 10:54:22 +0000 | From | "Jan Beulich" <> | Subject | RE: [PATCH] x86: fix and improve cmpxchg_double{,_local}() |
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>>> On 04.01.12 at 11:36, "David Laight" <David.Laight@ACULAB.COM> wrote:
>> 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.
Same would be true for atomic64_xchg() and the use of "+c" (v) in subsequent functions (whether unnecessarily strict or too lax varies).
> 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...
Absolutely - "=m" (v->counter) would be the right way to specify this.
Jan
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