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/* $OpenBSD: _atomic_lock.S,v 1.1 2017/08/15 06:13:24 guenther Exp $ */
/* David Leonard, <d@csee.uq.edu.au>. Public domain. */
#include <machine/asm.h>
LEAF(_atomic_lock,1)
LDGP(pv)
/* NOTE: using ldl_l/stl_c instead of
ldq_l and stq_c as machine/spinlock.h
defines _atomic_lock_t as int */
0: ldl_l v0, 0(a0) /* read existing lock value */
mov 1, t0 /* locked value to store */
stl_c t0, 0(a0) /* attempt to store, status in t0 */
beq t0, 1f /* branch forward to optimise prediction */
mb /* sync with other processors */
RET /* return with v0==0 if lock obtained */
1: br 0b /* loop to try again */
END(_atomic_lock)
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