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