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/* $OpenBSD: _atomic_lock.c,v 1.1 2017/08/15 06:13:24 guenther Exp $ */
/* David Leonard, <d@csee.uq.edu.au>. Public domain. */
/*
* Atomic lock for amd64 -- taken from i386 code.
*/
#include <machine/spinlock.h>
int
_atomic_lock(volatile _atomic_lock_t *lock)
{
_atomic_lock_t old;
/*
* Use the eXCHanGe instruction to swap the lock value with
* a local variable containing the locked state.
*/
old = _ATOMIC_LOCK_LOCKED;
__asm__("xchg %0,(%2)"
: "=r" (old)
: "0" (old), "r" (lock));
return (old != _ATOMIC_LOCK_UNLOCKED);
}
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