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
60 int
__atomic_cmpxchg(int old,int _new,volatile int * ptr)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
67 int
__atomic_swap(int _new,volatile int * ptr)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
77 int
__atomic_dec(volatile int * ptr)78 __atomic_dec(volatile int *ptr)
79 {
80 return __sync_fetch_and_sub (ptr, 1);
81 }
82
83 int
__atomic_inc(volatile int * ptr)84 __atomic_inc(volatile int *ptr)
85 {
86 return __sync_fetch_and_add (ptr, 1);
87 }
88