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/* $OpenBSD: _atomic_lock.c,v 1.4 2002/10/11 19:08:41 marc Exp $ */
/*
* Atomic lock for powerpc
*/
#include "spinlock.h"
int
_atomic_lock(volatile _spinlock_lock_t *lock)
{
_spinlock_lock_t old;
__asm__("1: lwarx %0,0,%1 \n"
" stwcx. %2,0,%1 \n"
" bne- 1b \n"
: "=r" (old), "=r" (lock)
: "r" (_SPINLOCK_LOCKED), "1" (lock)
);
return (old != _SPINLOCK_UNLOCKED);
/*
* Dale <rahnds@openbsd.org> says:
* Side note. to prevent two processes from accessing
* the same address with the lwarx in one instrution
* and the stwcx in another process, the current powerpc
* kernel uses a stwcx instruction without the corresponding
* lwarx which causes any reservation of a process
* to be removed. if a context switch occurs
* between the two accesses the store will not occur
* and the condition code will cause it to loop. If on
* a dual processor machine, the reserve will cause
* appropriate bus cycle accesses to notify other
* processors.
*/
}
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