/* $OpenBSD: _atomic_lock.c,v 1.8 2003/01/31 22:10:53 deraadt Exp $ */ /* * Atomic lock for sparc */ #include "spinlock.h" int _atomic_lock(volatile _spinlock_lock_t * lock) { _spinlock_lock_t old; /* * " ldstub [address], reg_rd * * The atomic load-store instructions copy a byte from memory * into r[rd]m then rewrite the addressed byte in memory to all * ones [_SPINLOCK_LOCKED]. The operation is performed * atomically, that is, without allowing intervening interrupts * or deferred traps. In a multiprocessor system, two or more * processors executing atomic load-store unsigned byte [...] * addressing the same byte [...] simultaneously are guaranteed * to execute them in an undefined, but serial order." * - p101, The SPARC Architecture Manual (version 8) Prentice-Hall * * "LDSTUB loads a byte value from memory to a register and writes * the value FF_16 into the addressed byte atomically. LDSTUB * is the classic test-and-set instruction. Like SWAP, it has * a consensus number of two and so cannot resolve more than * two contending processes in a wait-free fashion." * - p129, The SPARC Architecture Manual (version 9) Prentice-Hall * (See also section J.6 (spinlocks)) * * (No change to the condition codes are documented.) */ __asm__("ldstub %0,%1" : "=m" (*lock), "=r" (old) : "0" (*lock)); return (old == _SPINLOCK_LOCKED); }