1/*
2 * Copyright (C) 2011 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *  * Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 *  * Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in
12 *    the documentation and/or other materials provided with the
13 *    distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29
30/* The purpose of this file is to export a small set of atomic-related
31 * functions from the C library, to ensure binary ABI compatibility for
32 * the NDK.
33 *
34 * These functions were initially exposed by the NDK through <sys/atomics.h>,
35 * which was unfortunate because their implementation didn't provide any
36 * memory barriers at all.
37 *
38 * This wasn't a problem for the platform code that used them, because it
39 * used explicit barrier instructions around them. On the other hand, it means
40 * that any NDK-generated machine code that linked against them would not
41 * perform correctly when running on multi-core devices.
42 *
43 * To fix this, the platform code was first modified to not use any of these
44 * functions (everything is now inlined through assembly statements, see
45 * libc/private/bionic_arm_inline.h and the headers it includes.
46 *
47 * The functions here are thus only for the benefit of NDK applications,
48 * and now includes full memory barriers to prevent any random memory ordering
49 * issue from cropping.
50 *
51 * Note that we also provide an updated <sys/atomics.h> header that defines
52 * always_inlined versions of the functions that use the GCC builtin
53 * intrinsics to perform the same thing.
54 *
55 * NOTE: There is no need for a similar file for non-ARM platforms.
56 */
57
58/* DO NOT INCLUDE <sys/atomics.h> HERE ! */
59
60int
61__atomic_cmpxchg(int old, int _new, volatile int *ptr)
62{
63    /* We must return 0 on success */
64    return __sync_val_compare_and_swap(ptr, old, _new) != old;
65}
66
67int
68__atomic_swap(int _new, volatile int *ptr)
69{
70    int prev;
71    do {
72        prev = *ptr;
73    } while (__sync_val_compare_and_swap(ptr, prev, _new) != prev);
74    return prev;
75}
76
77int
78__atomic_dec(volatile int *ptr)
79{
80  return __sync_fetch_and_sub (ptr, 1);
81}
82
83int
84__atomic_inc(volatile int *ptr)
85{
86  return __sync_fetch_and_add (ptr, 1);
87}
88