1 // Protocol Buffers - Google's data interchange format
2 // Copyright 2012 Google Inc. All rights reserved.
3 // https://developers.google.com/protocol-buffers/
4 //
5 // Redistribution and use in source and binary forms, with or without
6 // modification, are permitted provided that the following conditions are
7 // met:
8 //
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10 // notice, this list of conditions and the following disclaimer.
11 // * Redistributions in binary form must reproduce the above
12 // copyright notice, this list of conditions and the following disclaimer
13 // in the documentation and/or other materials provided with the
14 // distribution.
15 // * Neither the name of Google Inc. nor the names of its
16 // contributors may be used to endorse or promote products derived from
17 // this software without specific prior written permission.
18 //
19 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
20 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
21 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
22 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
23 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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25 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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28 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
29 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30
31 // This file is an internal atomic implementation, use atomicops.h instead.
32 //
33 // LinuxKernelCmpxchg and Barrier_AtomicIncrement are from Google Gears.
34
35 #ifndef GOOGLE_PROTOBUF_ATOMICOPS_INTERNALS_ARM_GCC_H_
36 #define GOOGLE_PROTOBUF_ATOMICOPS_INTERNALS_ARM_GCC_H_
37
38 namespace google {
39 namespace protobuf {
40 namespace internal {
41
42 // 0xffff0fc0 is the hard coded address of a function provided by
43 // the kernel which implements an atomic compare-exchange. On older
44 // ARM architecture revisions (pre-v6) this may be implemented using
45 // a syscall. This address is stable, and in active use (hard coded)
46 // by at least glibc-2.7 and the Android C library.
47 typedef Atomic32 (*LinuxKernelCmpxchgFunc)(Atomic32 old_value,
48 Atomic32 new_value,
49 volatile Atomic32* ptr);
50 LinuxKernelCmpxchgFunc pLinuxKernelCmpxchg __attribute__((weak)) =
51 (LinuxKernelCmpxchgFunc) 0xffff0fc0;
52
53 typedef void (*LinuxKernelMemoryBarrierFunc)(void);
54 LinuxKernelMemoryBarrierFunc pLinuxKernelMemoryBarrier __attribute__((weak)) =
55 (LinuxKernelMemoryBarrierFunc) 0xffff0fa0;
56
57
NoBarrier_CompareAndSwap(volatile Atomic32 * ptr,Atomic32 old_value,Atomic32 new_value)58 inline Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr,
59 Atomic32 old_value,
60 Atomic32 new_value) {
61 Atomic32 prev_value = *ptr;
62 do {
63 if (!pLinuxKernelCmpxchg(old_value, new_value,
64 const_cast<Atomic32*>(ptr))) {
65 return old_value;
66 }
67 prev_value = *ptr;
68 } while (prev_value == old_value);
69 return prev_value;
70 }
71
NoBarrier_AtomicExchange(volatile Atomic32 * ptr,Atomic32 new_value)72 inline Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr,
73 Atomic32 new_value) {
74 Atomic32 old_value;
75 do {
76 old_value = *ptr;
77 } while (pLinuxKernelCmpxchg(old_value, new_value,
78 const_cast<Atomic32*>(ptr)));
79 return old_value;
80 }
81
NoBarrier_AtomicIncrement(volatile Atomic32 * ptr,Atomic32 increment)82 inline Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr,
83 Atomic32 increment) {
84 return Barrier_AtomicIncrement(ptr, increment);
85 }
86
Barrier_AtomicIncrement(volatile Atomic32 * ptr,Atomic32 increment)87 inline Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
88 Atomic32 increment) {
89 for (;;) {
90 // Atomic exchange the old value with an incremented one.
91 Atomic32 old_value = *ptr;
92 Atomic32 new_value = old_value + increment;
93 if (pLinuxKernelCmpxchg(old_value, new_value,
94 const_cast<Atomic32*>(ptr)) == 0) {
95 // The exchange took place as expected.
96 return new_value;
97 }
98 // Otherwise, *ptr changed mid-loop and we need to retry.
99 }
100 }
101
Acquire_CompareAndSwap(volatile Atomic32 * ptr,Atomic32 old_value,Atomic32 new_value)102 inline Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr,
103 Atomic32 old_value,
104 Atomic32 new_value) {
105 return NoBarrier_CompareAndSwap(ptr, old_value, new_value);
106 }
107
Release_CompareAndSwap(volatile Atomic32 * ptr,Atomic32 old_value,Atomic32 new_value)108 inline Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
109 Atomic32 old_value,
110 Atomic32 new_value) {
111 return NoBarrier_CompareAndSwap(ptr, old_value, new_value);
112 }
113
NoBarrier_Store(volatile Atomic32 * ptr,Atomic32 value)114 inline void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value) {
115 *ptr = value;
116 }
117
MemoryBarrier()118 inline void MemoryBarrier() {
119 pLinuxKernelMemoryBarrier();
120 }
121
Acquire_Store(volatile Atomic32 * ptr,Atomic32 value)122 inline void Acquire_Store(volatile Atomic32* ptr, Atomic32 value) {
123 *ptr = value;
124 MemoryBarrier();
125 }
126
Release_Store(volatile Atomic32 * ptr,Atomic32 value)127 inline void Release_Store(volatile Atomic32* ptr, Atomic32 value) {
128 MemoryBarrier();
129 *ptr = value;
130 }
131
NoBarrier_Load(volatile const Atomic32 * ptr)132 inline Atomic32 NoBarrier_Load(volatile const Atomic32* ptr) {
133 return *ptr;
134 }
135
Acquire_Load(volatile const Atomic32 * ptr)136 inline Atomic32 Acquire_Load(volatile const Atomic32* ptr) {
137 Atomic32 value = *ptr;
138 MemoryBarrier();
139 return value;
140 }
141
Release_Load(volatile const Atomic32 * ptr)142 inline Atomic32 Release_Load(volatile const Atomic32* ptr) {
143 MemoryBarrier();
144 return *ptr;
145 }
146
147 } // namespace internal
148 } // namespace protobuf
149 } // namespace google
150
151 #endif // GOOGLE_PROTOBUF_ATOMICOPS_INTERNALS_ARM_GCC_H_
152