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/* $OpenBSD: _atomic_lock.c,v 1.1 1998/11/20 11:15:37 d Exp $ */
/*
* Atomic lock for mips
*/
#include "pthread_private.h"
#include "spinlock.h"
#include <signal.h>
/*
* uthread atomic lock:
* attempt to acquire a lock (by giving it a non-zero value).
* Return zero on success, or the lock's value on failure
*/
register_t
_atomic_lock(volatile register_t *lock)
{
register_t old;
#if __mips >= 2
register_t temp;
do {
/*
* On a mips2 machine and above, we can use ll/sc.
* Read the lock and tag the cache line with a 'load linked'
* instruction. (Register 17 (LLAddr) will hold the
* physical address of lock for diagnostic purposes);
*/
__asm__("ll %0, %1" : "=r"(old) : "m"(*lock));
if (old)
break; /* already locked */
/*
* Try and store a 1 at the tagged lock address. If
* anyone else has since written it, the tag on the cache
* line will have been wiped, and temp will be set to zero
* by the 'store conditional' instruction.
*/
temp = 1;
__asm__("sc %0, %1" : "=r"(temp), "=m"(*lock)
: "0"(temp));
} while (temp == 0);
#else
/*
* Older MIPS cpus have no way of doing an atomic lock
* without some kind of shift to supervisor mode.
*/
old = _thread_slow_atomic_lock(lock);
#endif
return old;
}
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