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// Copyright (c) 2009 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// This file is an internal atomic implementation, use base/atomicops.h instead.
//
// LinuxKernelCmpxchg and Barrier_AtomicIncrement are from Google Gears.
#ifndef BASE_ATOMICOPS_INTERNALS_ARM_GCC_H_
#define BASE_ATOMICOPS_INTERNALS_ARM_GCC_H_
#pragma once
namespace base {
namespace subtle {
// 0xffff0fc0 is the hard coded address of a function provided by
// the kernel which implements an atomic compare-exchange. On older
// ARM architecture revisions (pre-v6) this may be implemented using
// a syscall. This address is stable, and in active use (hard coded)
// by at least glibc-2.7 and the Android C library.
typedef Atomic32 (*LinuxKernelCmpxchgFunc)(Atomic32 old_value,
Atomic32 new_value,
volatile Atomic32* ptr);
LinuxKernelCmpxchgFunc pLinuxKernelCmpxchg __attribute__((weak)) =
(LinuxKernelCmpxchgFunc) 0xffff0fc0;
typedef void (*LinuxKernelMemoryBarrierFunc)(void);
LinuxKernelMemoryBarrierFunc pLinuxKernelMemoryBarrier __attribute__((weak)) =
(LinuxKernelMemoryBarrierFunc) 0xffff0fa0;
inline Atomic32 NoBarrier_CompareAndSwap(volatile Atomic32* ptr,
Atomic32 old_value,
Atomic32 new_value) {
Atomic32 prev_value = *ptr;
do {
if (!pLinuxKernelCmpxchg(old_value, new_value,
const_cast<Atomic32*>(ptr))) {
return old_value;
}
prev_value = *ptr;
} while (prev_value == old_value);
return prev_value;
}
inline Atomic32 NoBarrier_AtomicExchange(volatile Atomic32* ptr,
Atomic32 new_value) {
Atomic32 old_value;
do {
old_value = *ptr;
} while (pLinuxKernelCmpxchg(old_value, new_value,
const_cast<Atomic32*>(ptr)));
return old_value;
}
inline Atomic32 NoBarrier_AtomicIncrement(volatile Atomic32* ptr,
Atomic32 increment) {
return Barrier_AtomicIncrement(ptr, increment);
}
inline Atomic32 Barrier_AtomicIncrement(volatile Atomic32* ptr,
Atomic32 increment) {
for (;;) {
// Atomic exchange the old value with an incremented one.
Atomic32 old_value = *ptr;
Atomic32 new_value = old_value + increment;
if (pLinuxKernelCmpxchg(old_value, new_value,
const_cast<Atomic32*>(ptr)) == 0) {
// The exchange took place as expected.
return new_value;
}
// Otherwise, *ptr changed mid-loop and we need to retry.
}
}
inline Atomic32 Acquire_CompareAndSwap(volatile Atomic32* ptr,
Atomic32 old_value,
Atomic32 new_value) {
return NoBarrier_CompareAndSwap(ptr, old_value, new_value);
}
inline Atomic32 Release_CompareAndSwap(volatile Atomic32* ptr,
Atomic32 old_value,
Atomic32 new_value) {
return NoBarrier_CompareAndSwap(ptr, old_value, new_value);
}
inline void NoBarrier_Store(volatile Atomic32* ptr, Atomic32 value) {
*ptr = value;
}
inline void MemoryBarrier() {
pLinuxKernelMemoryBarrier();
}
inline void Acquire_Store(volatile Atomic32* ptr, Atomic32 value) {
*ptr = value;
MemoryBarrier();
}
inline void Release_Store(volatile Atomic32* ptr, Atomic32 value) {
MemoryBarrier();
*ptr = value;
}
inline Atomic32 NoBarrier_Load(volatile const Atomic32* ptr) {
return *ptr;
}
inline Atomic32 Acquire_Load(volatile const Atomic32* ptr) {
Atomic32 value = *ptr;
MemoryBarrier();
return value;
}
inline Atomic32 Release_Load(volatile const Atomic32* ptr) {
MemoryBarrier();
return *ptr;
}
} // namespace base::subtle
} // namespace base
#endif // BASE_ATOMICOPS_INTERNALS_ARM_GCC_H_
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