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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/objects/embedder-data-slot.h"
#include "src/base/memory.h"
#include "src/heap/heap-write-barrier-inl.h"
#include "src/objects/embedder-data-array.h"
#include "src/objects/js-objects-inl.h"
#include "src/objects/objects-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))) {}
void EmbedderDataSlot::AllocateExternalPointerEntry(Isolate* isolate) {
#ifdef V8_HEAP_SANDBOX
// TODO(v8:10391, saelo): Use InitExternalPointerField() once
// ExternalPointer_t is 4-bytes.
uint32_t index = isolate->external_pointer_table().allocate();
// Object slots don't support storing raw values, so we just "reinterpret
// cast" the index value to Object.
Object index_as_object(index);
ObjectSlot(address() + kRawPayloadOffset).Relaxed_Store(index_as_object);
ObjectSlot(address() + kTaggedPayloadOffset).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) {
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) {
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 and why the second is
// only done if !V8_HEAP_SANDBOX_BOOL
ObjectSlot(FIELD_ADDR(object, slot_offset + kRawPayloadOffset))
.Relaxed_Store(Smi::zero());
#endif
}
bool EmbedderDataSlot::ToAlignedPointer(PtrComprCageBase isolate_root,
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).
Address raw_value;
#ifdef V8_HEAP_SANDBOX
// TODO(syg): V8_HEAP_SANDBOX doesn't work with pointer cage
#ifdef V8_COMPRESS_POINTERS_IN_SHARED_CAGE
#error "V8_HEAP_SANDBOX requires per-Isolate pointer compression cage"
#endif
uint32_t index = base::Memory<uint32_t>(address() + kRawPayloadOffset);
const Isolate* isolate = Isolate::FromRootAddress(isolate_root.address());
raw_value = isolate->external_pointer_table().get(index) ^
kEmbedderDataSlotPayloadTag;
#else
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();
}
#endif
*out_pointer = reinterpret_cast<void*>(raw_value);
return HAS_SMI_TAG(raw_value);
}
bool EmbedderDataSlot::ToAlignedPointerSafe(PtrComprCageBase isolate_root,
void** out_pointer) const {
#ifdef V8_HEAP_SANDBOX
// TODO(syg): V8_HEAP_SANDBOX doesn't work with pointer cage
#ifdef V8_COMPRESS_POINTERS_IN_SHARED_CAGE
#error "V8_HEAP_SANDBOX requires per-Isolate pointer compression cage"
#endif
uint32_t index = base::Memory<uint32_t>(address() + kRawPayloadOffset);
Address raw_value;
const Isolate* isolate = Isolate::FromRootAddress(isolate_root.address());
if (isolate->external_pointer_table().is_valid_index(index)) {
raw_value = isolate->external_pointer_table().get(index) ^
kEmbedderDataSlotPayloadTag;
*out_pointer = reinterpret_cast<void*>(raw_value);
return true;
}
return false;
#else
return ToAlignedPointer(isolate_root, out_pointer);
#endif // V8_HEAP_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_HEAP_SANDBOX
if (V8_HEAP_SANDBOX_BOOL) {
AllocateExternalPointerEntry(isolate);
// Raw payload contains the table index. Object slots don't support loading
// of raw values, so we just "reinterpret cast" Object value to index.
Object index_as_object =
ObjectSlot(address() + kRawPayloadOffset).Relaxed_Load();
uint32_t index = static_cast<uint32_t>(index_as_object.ptr());
isolate->external_pointer_table().set(index,
value ^ kEmbedderDataSlotPayloadTag);
return true;
}
#endif
gc_safe_store(isolate, value);
return true;
}
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;
ObjectSlot(address() + kRawPayloadOffset).Relaxed_Store(Object(hi));
#else
ObjectSlot(address() + kTaggedPayloadOffset).Relaxed_Store(Smi(value));
#endif
}
} // namespace internal
} // namespace v8
#include "src/objects/object-macros-undef.h"
#endif // V8_OBJECTS_EMBEDDER_DATA_SLOT_INL_H_
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