/*      $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 i386
 */

#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);
}