thestig@chromium.org | 569de14 | 2009-05-02 02:57:09 +0900 | [diff] [blame] | 1 | // Copyright (c) 2009 The Chromium Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style license that can be |
| 3 | // found in the LICENSE file. |
| 4 | |
| 5 | // This file is an internal atomic implementation, use base/atomicops.h instead. |
| 6 | // |
| 7 | // LinuxKernelCmpxchg and Barrier_AtomicIncrement are from Google Gears. |
| 8 | |
| 9 | #ifndef BASE_ATOMICOPS_INTERNALS_ARM_GCC_H_ |
| 10 | #define BASE_ATOMICOPS_INTERNALS_ARM_GCC_H_ |
thakis@chromium.org | 01d1452 | 2010-07-27 08:08:24 +0900 | [diff] [blame] | 11 | #pragma once |
thestig@chromium.org | 569de14 | 2009-05-02 02:57:09 +0900 | [diff] [blame] | 12 | |
| 13 | namespace base { |
| 14 | namespace subtle { |
| 15 | |
| 16 | // 0xffff0fc0 is the hard coded address of a function provided by |
| 17 | // the kernel which implements an atomic compare-exchange. On older |
| 18 | // ARM architecture revisions (pre-v6) this may be implemented using |
| 19 | // a syscall. This address is stable, and in active use (hard coded) |
| 20 | // by at least glibc-2.7 and the Android C library. |
| 21 | typedef Atomic32 (*LinuxKernelCmpxchgFunc)(Atomic32 old_value, |
| 22 | Atomic32 new_value, |
| 23 | volatile Atomic32* ptr); |
| 24 | LinuxKernelCmpxchgFunc pLinuxKernelCmpxchg __attribute__((weak)) = |
| 25 | (LinuxKernelCmpxchgFunc) 0xffff0fc0; |
| 26 | |
| 27 | typedef void (*LinuxKernelMemoryBarrierFunc)(void); |
| 28 | LinuxKernelMemoryBarrierFunc pLinuxKernelMemoryBarrier __attribute__((weak)) = |
| 29 | (LinuxKernelMemoryBarrierFunc) 0xffff0fa0; |
| 30 | |
| 31 | |
| 32 | inline Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr, |
| 33 | Atomic32 old_value, |
| 34 | Atomic32 new_value) { |
| 35 | Atomic32 prev_value = *ptr; |
| 36 | do { |
| 37 | if (!pLinuxKernelCmpxchg(old_value, new_value, |
| 38 | const_cast<Atomic32*>(ptr))) { |
| 39 | return old_value; |
| 40 | } |
| 41 | prev_value = *ptr; |
| 42 | } while (prev_value == old_value); |
| 43 | return prev_value; |
| 44 | } |
| 45 | |
| 46 | inline Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr, |
| 47 | Atomic32 new_value) { |
| 48 | Atomic32 old_value; |
| 49 | do { |
| 50 | old_value = *ptr; |
| 51 | } while (pLinuxKernelCmpxchg(old_value, new_value, |
| 52 | const_cast<Atomic32*>(ptr))); |
| 53 | return old_value; |
| 54 | } |
| 55 | |
| 56 | inline Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr, |
| 57 | Atomic32 increment) { |
| 58 | return Barrier_AtomicIncrement(ptr, increment); |
| 59 | } |
| 60 | |
| 61 | inline Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr, |
| 62 | Atomic32 increment) { |
| 63 | for (;;) { |
| 64 | // Atomic exchange the old value with an incremented one. |
| 65 | Atomic32 old_value = *ptr; |
| 66 | Atomic32 new_value = old_value + increment; |
| 67 | if (pLinuxKernelCmpxchg(old_value, new_value, |
| 68 | const_cast<Atomic32*>(ptr)) == 0) { |
| 69 | // The exchange took place as expected. |
| 70 | return new_value; |
| 71 | } |
| 72 | // Otherwise, *ptr changed mid-loop and we need to retry. |
| 73 | } |
| 74 | |
| 75 | } |
| 76 | |
| 77 | inline Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr, |
| 78 | Atomic32 old_value, |
| 79 | Atomic32 new_value) { |
| 80 | return NoBarrier_CompareAndSwap(ptr, old_value, new_value); |
| 81 | } |
| 82 | |
| 83 | inline Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr, |
| 84 | Atomic32 old_value, |
| 85 | Atomic32 new_value) { |
| 86 | return NoBarrier_CompareAndSwap(ptr, old_value, new_value); |
| 87 | } |
| 88 | |
| 89 | inline void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value) { |
| 90 | *ptr = value; |
| 91 | } |
| 92 | |
| 93 | inline void MemoryBarrier() { |
| 94 | pLinuxKernelMemoryBarrier(); |
| 95 | } |
| 96 | |
| 97 | inline void Acquire_Store(volatile Atomic32* ptr, Atomic32 value) { |
| 98 | *ptr = value; |
| 99 | MemoryBarrier(); |
| 100 | } |
| 101 | |
| 102 | inline void Release_Store(volatile Atomic32* ptr, Atomic32 value) { |
| 103 | MemoryBarrier(); |
| 104 | *ptr = value; |
| 105 | } |
| 106 | |
| 107 | inline Atomic32 NoBarrier_Load(volatile const Atomic32* ptr) { |
| 108 | return *ptr; |
| 109 | } |
| 110 | |
| 111 | inline Atomic32 Acquire_Load(volatile const Atomic32* ptr) { |
| 112 | Atomic32 value = *ptr; |
| 113 | MemoryBarrier(); |
| 114 | return value; |
| 115 | } |
| 116 | |
| 117 | inline Atomic32 Release_Load(volatile const Atomic32* ptr) { |
| 118 | MemoryBarrier(); |
| 119 | return *ptr; |
| 120 | } |
| 121 | |
| 122 | } // namespace base::subtle |
| 123 | } // namespace base |
| 124 | |
| 125 | #endif // BASE_ATOMICOPS_INTERNALS_ARM_GCC_H_ |