Fix atomic ops on ARM to compile in NaCl untrusted targets.

base/atomicops_internals_arm_gcc.h

-// 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_
-
-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_