text: /* $OpenBSD: _atomic_lock.c,v 1.7 2013/06/01 20:47:40 tedu Exp $ */
  /*
   * Copyright (c) 2005 Marco Peereboom <marco@openbsd.org>
   *
   * Permission to use, copy, modify, and distribute this software for any
   * purpose with or without fee is hereby granted, provided that the above
   * copyright notice and this permission notice appear in all copies.
   *
   * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
   * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
   * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
   * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
   */
  
  #include <machine/spinlock.h>
  #ifdef DIAGNOSTIC
  #include <stdio.h>
  #include <stdlib.h>
  #endif
  
  int
  _atomic_lock(volatile _atomic_lock_t *lock)
  {
  	volatile _atomic_lock_t old;
  
  #ifdef DIAGNOSTIC
  	if ((unsigned long)lock & 0xf) {
  		printf("lock not 16 byte aligned\n");
  		abort();
  	}
  #endif
  
  	asm volatile ("ldcws 0(%2),%0"
  		     : "=&r" (old), "+m" (lock)
  		     : "r" (lock));
  
  	return (old == _ATOMIC_LOCK_LOCKED);
  }
  