atomic.S (1904B)
1 /* $Id: //depot/blt/lib/libc/atomic.S#1 $ 2 ** 3 ** Copyright 1999 Jeff Bush 4 ** All rights reserved. 5 ** 6 ** Redistribution and use in source and binary forms, with or without 7 ** modification, are permitted provided that the following conditions 8 ** are met: 9 ** 1. Redistributions of source code must retain the above copyright 10 ** notice, this list of conditions, and the following disclaimer. 11 ** 2. Redistributions in binary form must reproduce the above copyright 12 ** notice, this list of conditions, and the following disclaimer in the 13 ** documentation and/or other materials provided with the distribution. 14 ** 3. The name of the author may not be used to endorse or promote products 15 ** derived from this software without specific prior written permission. 16 ** 17 ** THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 18 ** IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 19 ** OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 20 ** IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 21 ** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 22 ** NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 26 ** THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 */ 28 29 .globl atomic_add 30 31 # long atomic_add(long *var, long amount) 32 33 atomic_add: 34 pushl %ebx 35 movl 8(%esp), %ecx # pointer to variable 36 try_add: 37 movl (%ecx), %eax # get original value 38 movl 12(%esp), %ebx # get amount to add 39 addl %eax, %ebx # what result should be 40 lock 41 cmpxchg %ebx, (%ecx) 42 jne try_add # failed, try again 43 popl %ebx 44 ret 45