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/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef ART_RUNTIME_MIRROR_OBJECT_READBARRIER_INL_H_
#define ART_RUNTIME_MIRROR_OBJECT_READBARRIER_INL_H_
#include "object.h"
#include "base/atomic.h"
#include "heap_poisoning.h"
#include "lock_word-inl.h"
#include "object_reference-inl.h"
#include "read_barrier.h"
#include "runtime.h"
namespace art {
namespace mirror {
template<VerifyObjectFlags kVerifyFlags>
inline LockWord Object::GetLockWord(bool as_volatile) {
if (as_volatile) {
return LockWord(GetField32Volatile<kVerifyFlags>(MonitorOffset()));
}
return LockWord(GetField32<kVerifyFlags>(MonitorOffset()));
}
template<bool kTransactionActive, bool kCheckTransaction, VerifyObjectFlags kVerifyFlags>
inline bool Object::CasField32(MemberOffset field_offset,
int32_t old_value,
int32_t new_value,
CASMode mode,
std::memory_order memory_order) {
if (kCheckTransaction) {
DCHECK_EQ(kTransactionActive, Runtime::Current()->IsActiveTransaction());
}
if (kTransactionActive) {
Runtime::Current()->RecordWriteField32(this, field_offset, old_value, true);
}
if (kVerifyFlags & kVerifyThis) {
VerifyObject(this);
}
uint8_t* raw_addr = reinterpret_cast<uint8_t*>(this) + field_offset.Int32Value();
AtomicInteger* atomic_addr = reinterpret_cast<AtomicInteger*>(raw_addr);
return atomic_addr->CompareAndSet(old_value, new_value, mode, memory_order);
}
inline bool Object::CasLockWord(LockWord old_val,
LockWord new_val,
CASMode mode,
std::memory_order memory_order) {
// Force use of non-transactional mode and do not check.
return CasField32<false, false>(MonitorOffset(),
old_val.GetValue(),
new_val.GetValue(),
mode,
memory_order);
}
inline uint32_t Object::GetReadBarrierState(uintptr_t* fake_address_dependency) {
if (!kUseBakerReadBarrier) {
LOG(FATAL) << "Unreachable";
UNREACHABLE();
}
#if defined(__arm__)
uintptr_t obj = reinterpret_cast<uintptr_t>(this);
uintptr_t result;
DCHECK_EQ(OFFSETOF_MEMBER(Object, monitor_), 4U);
// Use inline assembly to prevent the compiler from optimizing away the false dependency.
__asm__ __volatile__(
"ldr %[result], [%[obj], #4]\n\t"
// This instruction is enough to "fool the compiler and the CPU" by having `fad` always be
// null, without them being able to assume that fact.
"eor %[fad], %[result], %[result]\n\t"
: [result] "+r" (result), [fad] "=r" (*fake_address_dependency)
: [obj] "r" (obj));
DCHECK_EQ(*fake_address_dependency, 0U);
LockWord lw(static_cast<uint32_t>(result));
uint32_t rb_state = lw.ReadBarrierState();
return rb_state;
#elif defined(__aarch64__)
uintptr_t obj = reinterpret_cast<uintptr_t>(this);
uintptr_t result;
DCHECK_EQ(OFFSETOF_MEMBER(Object, monitor_), 4U);
// Use inline assembly to prevent the compiler from optimizing away the false dependency.
__asm__ __volatile__(
"ldr %w[result], [%[obj], #4]\n\t"
// This instruction is enough to "fool the compiler and the CPU" by having `fad` always be
// null, without them being able to assume that fact.
"eor %[fad], %[result], %[result]\n\t"
: [result] "+r" (result), [fad] "=r" (*fake_address_dependency)
: [obj] "r" (obj));
DCHECK_EQ(*fake_address_dependency, 0U);
LockWord lw(static_cast<uint32_t>(result));
uint32_t rb_state = lw.ReadBarrierState();
return rb_state;
#elif defined(__i386__) || defined(__x86_64__)
LockWord lw = GetLockWord(false);
// i386/x86_64 don't need fake address dependency. Use a compiler fence to avoid compiler
// reordering.
*fake_address_dependency = 0;
std::atomic_signal_fence(std::memory_order_acquire);
uint32_t rb_state = lw.ReadBarrierState();
return rb_state;
#else
UNUSED(fake_address_dependency);
LOG(FATAL) << "Unsupported architecture.";
UNREACHABLE();
#endif
}
inline uint32_t Object::GetReadBarrierState() {
if (!kUseBakerReadBarrier) {
LOG(FATAL) << "Unreachable";
UNREACHABLE();
}
DCHECK(kUseBakerReadBarrier);
LockWord lw(GetFieldPrimitive<uint32_t, /*kIsVolatile=*/false>(MonitorOffset()));
uint32_t rb_state = lw.ReadBarrierState();
DCHECK(ReadBarrier::IsValidReadBarrierState(rb_state)) << rb_state;
return rb_state;
}
inline uint32_t Object::GetReadBarrierStateAcquire() {
if (!kUseBakerReadBarrier) {
LOG(FATAL) << "Unreachable";
UNREACHABLE();
}
LockWord lw(GetFieldAcquire<uint32_t>(MonitorOffset()));
uint32_t rb_state = lw.ReadBarrierState();
DCHECK(ReadBarrier::IsValidReadBarrierState(rb_state)) << rb_state;
return rb_state;
}
template<std::memory_order kMemoryOrder>
inline bool Object::AtomicSetReadBarrierState(uint32_t expected_rb_state, uint32_t rb_state) {
if (!kUseBakerReadBarrier) {
LOG(FATAL) << "Unreachable";
UNREACHABLE();
}
DCHECK(ReadBarrier::IsValidReadBarrierState(expected_rb_state)) << expected_rb_state;
DCHECK(ReadBarrier::IsValidReadBarrierState(rb_state)) << rb_state;
LockWord expected_lw;
LockWord new_lw;
do {
LockWord lw = GetLockWord(false);
if (UNLIKELY(lw.ReadBarrierState() != expected_rb_state)) {
// Lost the race.
return false;
}
expected_lw = lw;
expected_lw.SetReadBarrierState(expected_rb_state);
new_lw = lw;
new_lw.SetReadBarrierState(rb_state);
// ConcurrentCopying::ProcessMarkStackRef uses this with
// `kMemoryOrder` == `std::memory_order_release`.
// If `kMemoryOrder` == `std::memory_order_release`, use a CAS release so that when GC updates
// all the fields of an object and then changes the object from gray to black (non-gray), the
// field updates (stores) will be visible (won't be reordered after this CAS.)
} while (!CasLockWord(expected_lw, new_lw, CASMode::kWeak, kMemoryOrder));
return true;
}
inline bool Object::AtomicSetMarkBit(uint32_t expected_mark_bit, uint32_t mark_bit) {
LockWord expected_lw;
LockWord new_lw;
do {
LockWord lw = GetLockWord(false);
if (UNLIKELY(lw.MarkBitState() != expected_mark_bit)) {
// Lost the race.
return false;
}
expected_lw = lw;
new_lw = lw;
new_lw.SetMarkBitState(mark_bit);
// Since this is only set from the mutator, we can use the non-release CAS.
} while (!CasLockWord(expected_lw, new_lw, CASMode::kWeak, std::memory_order_relaxed));
return true;
}
} // namespace mirror
} // namespace art
#endif // ART_RUNTIME_MIRROR_OBJECT_READBARRIER_INL_H_
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