1// Protocol Buffers - Google's data interchange format 2// Copyright 2012 Google Inc. All rights reserved. 3// http://code.google.com/p/protobuf/ 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// 9// * Redistributions of source code must retain the above copyright 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, 24// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 25// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 26// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 27// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 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 38namespace google { 39namespace protobuf { 40namespace 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. 47typedef Atomic32 (*LinuxKernelCmpxchgFunc)(Atomic32 old_value, 48 Atomic32 new_value, 49 volatile Atomic32* ptr); 50LinuxKernelCmpxchgFunc pLinuxKernelCmpxchg __attribute__((weak)) = 51 (LinuxKernelCmpxchgFunc) 0xffff0fc0; 52 53typedef void (*LinuxKernelMemoryBarrierFunc)(void); 54LinuxKernelMemoryBarrierFunc pLinuxKernelMemoryBarrier __attribute__((weak)) = 55 (LinuxKernelMemoryBarrierFunc) 0xffff0fa0; 56 57 58inline 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 72inline 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 82inline Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr, 83 Atomic32 increment) { 84 return Barrier_AtomicIncrement(ptr, increment); 85} 86 87inline 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 102inline 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 108inline 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 114inline void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value) { 115 *ptr = value; 116} 117 118inline void MemoryBarrier() { 119 pLinuxKernelMemoryBarrier(); 120} 121 122inline void Acquire_Store(volatile Atomic32* ptr, Atomic32 value) { 123 *ptr = value; 124 MemoryBarrier(); 125} 126 127inline void Release_Store(volatile Atomic32* ptr, Atomic32 value) { 128 MemoryBarrier(); 129 *ptr = value; 130} 131 132inline Atomic32 NoBarrier_Load(volatile const Atomic32* ptr) { 133 return *ptr; 134} 135 136inline Atomic32 Acquire_Load(volatile const Atomic32* ptr) { 137 Atomic32 value = *ptr; 138 MemoryBarrier(); 139 return value; 140} 141 142inline 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