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// Copyright 2018 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_OBJECTS_EMBEDDER_DATA_SLOT_INL_H_
#define V8_OBJECTS_EMBEDDER_DATA_SLOT_INL_H_
#include "src/base/memory.h"
#include "src/common/globals.h"
#include "src/heap/heap-write-barrier-inl.h"
#include "src/objects/embedder-data-array.h"
#include "src/objects/embedder-data-slot.h"
#include "src/objects/js-objects-inl.h"
#include "src/objects/objects-inl.h"
#include "src/sandbox/external-pointer-inl.h"
// Has to be the last include (doesn't have include guards):
#include "src/objects/object-macros.h"
namespace v8 {
namespace internal {
EmbedderDataSlot::EmbedderDataSlot(EmbedderDataArray array, int entry_index)
: SlotBase(FIELD_ADDR(array,
EmbedderDataArray::OffsetOfElementAt(entry_index))) {}
EmbedderDataSlot::EmbedderDataSlot(JSObject object, int embedder_field_index)
: SlotBase(FIELD_ADDR(
object, object.GetEmbedderFieldOffset(embedder_field_index))) {}
EmbedderDataSlot::EmbedderDataSlot(const EmbedderDataSlotSnapshot& snapshot)
: SlotBase(reinterpret_cast<Address>(&snapshot)) {}
void EmbedderDataSlot::Initialize(Object initial_value) {
// TODO(v8) initialize the slot with Smi::zero() instead. This'll also
// guarantee that we don't need a write barrier.
DCHECK(initial_value.IsSmi() ||
ReadOnlyHeap::Contains(HeapObject::cast(initial_value)));
ObjectSlot(address() + kTaggedPayloadOffset).Relaxed_Store(initial_value);
#ifdef V8_COMPRESS_POINTERS
ObjectSlot(address() + kRawPayloadOffset).Relaxed_Store(Smi::zero());
#endif
}
Object EmbedderDataSlot::load_tagged() const {
return ObjectSlot(address() + kTaggedPayloadOffset).Relaxed_Load();
}
void EmbedderDataSlot::store_smi(Smi value) {
ObjectSlot(address() + kTaggedPayloadOffset).Relaxed_Store(value);
#ifdef V8_COMPRESS_POINTERS
// See gc_safe_store() for the reasons behind two stores.
ObjectSlot(address() + kRawPayloadOffset).Relaxed_Store(Smi::zero());
#endif
}
// static
void EmbedderDataSlot::store_tagged(EmbedderDataArray array, int entry_index,
Object value) {
#ifdef V8_COMPRESS_POINTERS
CHECK(value.IsSmi() ||
V8HeapCompressionScheme::GetPtrComprCageBaseAddress(value.ptr()) ==
V8HeapCompressionScheme::GetPtrComprCageBaseAddress(array.ptr()));
#endif
int slot_offset = EmbedderDataArray::OffsetOfElementAt(entry_index);
ObjectSlot(FIELD_ADDR(array, slot_offset + kTaggedPayloadOffset))
.Relaxed_Store(value);
WRITE_BARRIER(array, slot_offset + kTaggedPayloadOffset, value);
#ifdef V8_COMPRESS_POINTERS
// See gc_safe_store() for the reasons behind two stores.
ObjectSlot(FIELD_ADDR(array, slot_offset + kRawPayloadOffset))
.Relaxed_Store(Smi::zero());
#endif
}
// static
void EmbedderDataSlot::store_tagged(JSObject object, int embedder_field_index,
Object value) {
#ifdef V8_COMPRESS_POINTERS
CHECK(value.IsSmi() ||
V8HeapCompressionScheme::GetPtrComprCageBaseAddress(value.ptr()) ==
V8HeapCompressionScheme::GetPtrComprCageBaseAddress(object.ptr()));
#endif
int slot_offset = object.GetEmbedderFieldOffset(embedder_field_index);
ObjectSlot(FIELD_ADDR(object, slot_offset + kTaggedPayloadOffset))
.Relaxed_Store(value);
WRITE_BARRIER(object, slot_offset + kTaggedPayloadOffset, value);
#ifdef V8_COMPRESS_POINTERS
// See gc_safe_store() for the reasons behind two stores.
ObjectSlot(FIELD_ADDR(object, slot_offset + kRawPayloadOffset))
.Relaxed_Store(Smi::zero());
#endif
}
bool EmbedderDataSlot::ToAlignedPointer(Isolate* isolate,
void** out_pointer) const {
// We don't care about atomicity of access here because embedder slots
// are accessed this way only from the main thread via API during "mutator"
// phase which is propely synched with GC (concurrent marker may still look
// at the tagged part of the embedder slot but read-only access is ok).
#ifdef V8_ENABLE_SANDBOX
// The raw part must always contain a valid external pointer table index.
*out_pointer = reinterpret_cast<void*>(
ReadExternalPointerField<kEmbedderDataSlotPayloadTag>(
address() + kExternalPointerOffset, isolate));
return true;
#else
Address raw_value;
if (COMPRESS_POINTERS_BOOL) {
// TODO(ishell, v8:8875): When pointer compression is enabled 8-byte size
// fields (external pointers, doubles and BigInt data) are only kTaggedSize
// aligned so we have to use unaligned pointer friendly way of accessing
// them in order to avoid undefined behavior in C++ code.
raw_value = base::ReadUnalignedValue<Address>(address());
} else {
raw_value = *location();
}
*out_pointer = reinterpret_cast<void*>(raw_value);
return HAS_SMI_TAG(raw_value);
#endif // V8_ENABLE_SANDBOX
}
bool EmbedderDataSlot::store_aligned_pointer(Isolate* isolate, void* ptr) {
Address value = reinterpret_cast<Address>(ptr);
if (!HAS_SMI_TAG(value)) return false;
#ifdef V8_ENABLE_SANDBOX
DCHECK_EQ(0, value & kExternalPointerTagMask);
// When the sandbox is enabled, the external pointer handles in
// EmbedderDataSlots are lazily initialized: initially they contain the null
// external pointer handle (see EmbedderDataSlot::Initialize), and only once
// an external pointer is stored in them are they properly initialized.
WriteLazilyInitializedExternalPointerField<kEmbedderDataSlotPayloadTag>(
address() + kExternalPointerOffset, isolate, value);
ObjectSlot(address() + kTaggedPayloadOffset).Relaxed_Store(Smi::zero());
return true;
#else
gc_safe_store(isolate, value);
return true;
#endif // V8_ENABLE_SANDBOX
}
EmbedderDataSlot::RawData EmbedderDataSlot::load_raw(
Isolate* isolate, const DisallowGarbageCollection& no_gc) const {
// We don't care about atomicity of access here because embedder slots
// are accessed this way only by serializer from the main thread when
// GC is not active (concurrent marker may still look at the tagged part
// of the embedder slot but read-only access is ok).
#ifdef V8_COMPRESS_POINTERS
// TODO(ishell, v8:8875): When pointer compression is enabled 8-byte size
// fields (external pointers, doubles and BigInt data) are only kTaggedSize
// aligned so we have to use unaligned pointer friendly way of accessing them
// in order to avoid undefined behavior in C++ code.
return base::ReadUnalignedValue<EmbedderDataSlot::RawData>(address());
#else
return *location();
#endif
}
void EmbedderDataSlot::store_raw(Isolate* isolate,
EmbedderDataSlot::RawData data,
const DisallowGarbageCollection& no_gc) {
gc_safe_store(isolate, data);
}
void EmbedderDataSlot::gc_safe_store(Isolate* isolate, Address value) {
#ifdef V8_COMPRESS_POINTERS
static_assert(kSmiShiftSize == 0);
static_assert(SmiValuesAre31Bits());
static_assert(kTaggedSize == kInt32Size);
// We have to do two 32-bit stores here because
// 1) tagged part modifications must be atomic to be properly synchronized
// with the concurrent marker.
// 2) atomicity of full pointer store is not guaranteed for embedder slots
// since the address of the slot may not be kSystemPointerSize aligned
// (only kTaggedSize alignment is guaranteed).
// TODO(ishell, v8:8875): revisit this once the allocation alignment
// inconsistency is fixed.
Address lo = static_cast<intptr_t>(static_cast<int32_t>(value));
ObjectSlot(address() + kTaggedPayloadOffset).Relaxed_Store(Smi(lo));
Address hi = value >> 32;
// Here we use MaybeObjectSlot because ObjectSlot expects a valid `Object`.
// This allows us to store a non-smi, that is not a valid `HeapObject`.
MaybeObjectSlot(address() + kRawPayloadOffset).Relaxed_Store(MaybeObject(hi));
#else
ObjectSlot(address() + kTaggedPayloadOffset).Relaxed_Store(Smi(value));
#endif
}
// static
void EmbedderDataSlot::PopulateEmbedderDataSnapshot(
Map map, JSObject js_object, int entry_index,
EmbedderDataSlotSnapshot& snapshot) {
#ifdef V8_COMPRESS_POINTERS
static_assert(sizeof(EmbedderDataSlotSnapshot) == sizeof(AtomicTagged_t) * 2);
#else // !V8_COMPRESS_POINTERS
static_assert(sizeof(EmbedderDataSlotSnapshot) == sizeof(AtomicTagged_t));
#endif // !V8_COMPRESS_POINTERS
static_assert(sizeof(EmbedderDataSlotSnapshot) == kEmbedderDataSlotSize);
const Address field_base =
FIELD_ADDR(js_object, js_object.GetEmbedderFieldOffset(entry_index));
#if defined(V8_TARGET_BIG_ENDIAN) && defined(V8_COMPRESS_POINTERS)
const int index = 1;
#else
const int index = 0;
#endif
reinterpret_cast<AtomicTagged_t*>(&snapshot)[index] =
AsAtomicTagged::Relaxed_Load(
reinterpret_cast<AtomicTagged_t*>(field_base + kTaggedPayloadOffset));
#ifdef V8_COMPRESS_POINTERS
reinterpret_cast<AtomicTagged_t*>(&snapshot)[1 - index] =
AsAtomicTagged::Relaxed_Load(
reinterpret_cast<AtomicTagged_t*>(field_base + kRawPayloadOffset));
#endif // V8_COMPRESS_POINTERS
}
} // namespace internal
} // namespace v8
#include "src/objects/object-macros-undef.h"
#endif // V8_OBJECTS_EMBEDDER_DATA_SLOT_INL_H_
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