1 /* $OpenBSD: _atomic_lock.c,v 1.1 2017/08/15 06:13:24 guenther Exp $ */ 2 /* David Leonard, <d@csee.uq.edu.au>. Public domain. */ 3 4 /* 5 * Atomic lock for sparc64 6 */ 7 8 #include <machine/spinlock.h> 9 10 int 11 _atomic_lock(volatile _atomic_lock_t * lock) 12 { 13 _atomic_lock_t old; 14 15 /* 16 * " ldstub [address], reg_rd 17 * 18 * The atomic load-store instructions copy a byte from memory 19 * into r[rd]m then rewrite the addressed byte in memory to all 20 * ones [_ATOMIC_LOCK_LOCKED]. The operation is performed 21 * atomically, that is, without allowing intervening interrupts 22 * or deferred traps. In a multiprocessor system, two or more 23 * processors executing atomic load-store unsigned byte [...] 24 * addressing the same byte [...] simultaneously are guaranteed 25 * to execute them in an undefined, but serial order." 26 * - p101, The SPARC Architecture Manual (version 8) Prentice-Hall 27 * 28 * "LDSTUB loads a byte value from memory to a register and writes 29 * the value FF_16 into the addressed byte atomically. LDSTUB 30 * is the classic test-and-set instruction. Like SWAP, it has 31 * a consensus number of two and so cannot resolve more than 32 * two contending processes in a wait-free fashion." 33 * - p129, The SPARC Architecture Manual (version 9) Prentice-Hall 34 * (See also section J.6 (spinlocks)) 35 * 36 * (No change to the condition codes are documented.) 37 */ 38 __asm__("ldstub [%1], %0" : "=&r" (old) : "r" (lock) : "memory"); 39 40 return (old == _ATOMIC_LOCK_LOCKED); 41 } 42