1 /* $OpenBSD: _atomic_lock.c,v 1.2 2020/06/25 02:22:31 drahn Exp $ */ 2 /* 3 * Copyright (c) 1998 Dale Rahn <drahn@openbsd.org> 4 * 5 * Permission to use, copy, modify, and distribute this software for any 6 * purpose with or without fee is hereby granted, provided that the above 7 * copyright notice and this permission notice appear in all copies. 8 * 9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16 */ 17 18 /* 19 * Atomic lock for powerpc 20 */ 21 22 #include <machine/spinlock.h> 23 24 int 25 _atomic_lock(volatile _atomic_lock_t *lock) 26 { 27 _atomic_lock_t old; 28 29 __asm__("1: lwarx 0,0,%1 \n" 30 " stwcx. %2,0,%1 \n" 31 " bne- 1b \n" 32 " mr %0, 0 \n" 33 : "=r" (old), "=r" (lock) 34 : "r" (_ATOMIC_LOCK_LOCKED), "1" (lock) : "0" 35 ); 36 37 return (old != _ATOMIC_LOCK_UNLOCKED); 38 39 /* 40 * Dale <drahn@openbsd.org> says: 41 * Side note. to prevent two processes from accessing 42 * the same address with the lwarx in one instruction 43 * and the stwcx in another process, the current powerpc 44 * kernel uses a stwcx instruction without the corresponding 45 * lwarx which causes any reservation of a process 46 * to be removed. if a context switch occurs 47 * between the two accesses the store will not occur 48 * and the condition code will cause it to loop. If on 49 * a dual processor machine, the reserve will cause 50 * appropriate bus cycle accesses to notify other 51 * processors. 52 */ 53 } 54