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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_H_
#define V8_OBJECTS_EMBEDDER_DATA_SLOT_H_
#include <utility>
#include "src/common/assert-scope.h"
#include "src/common/globals.h"
#include "src/objects/slots.h"
// Has to be the last include (doesn't have include guards):
#include "src/objects/object-macros.h"
namespace v8 {
namespace internal {
class EmbedderDataArray;
class JSObject;
class Object;
// An EmbedderDataSlot instance describes a kEmbedderDataSlotSize field ("slot")
// holding an embedder data which may contain raw aligned pointer or a tagged
// pointer (smi or heap object).
// Its address() is the address of the slot.
// The slot's contents can be read and written using respective load_XX() and
// store_XX() methods.
// Storing heap object through this slot may require triggering write barriers
// so this operation must be done via static store_tagged() methods.
class EmbedderDataSlot
: public SlotBase<EmbedderDataSlot, Address, kTaggedSize> {
public:
EmbedderDataSlot() : SlotBase(kNullAddress) {}
V8_INLINE EmbedderDataSlot(EmbedderDataArray array, int entry_index);
V8_INLINE EmbedderDataSlot(JSObject object, int embedder_field_index);
#if defined(V8_TARGET_BIG_ENDIAN) && defined(V8_COMPRESS_POINTERS)
static constexpr int kTaggedPayloadOffset = kTaggedSize;
#else
static constexpr int kTaggedPayloadOffset = 0;
#endif
#ifdef V8_COMPRESS_POINTERS
// The raw payload is located in the other "tagged" part of the full pointer
// and cotains the upper part of aligned address. The raw part is not expected
// to look like a tagged value.
// When V8_HEAP_SANDBOX is defined the raw payload contains an index into the
// external pointer table.
static constexpr int kRawPayloadOffset = kTaggedSize - kTaggedPayloadOffset;
#endif
static constexpr int kRequiredPtrAlignment = kSmiTagSize;
// Opaque type used for storing raw embedder data.
using RawData = Address;
V8_INLINE void AllocateExternalPointerEntry(Isolate* isolate);
V8_INLINE Object load_tagged() const;
V8_INLINE void store_smi(Smi value);
// Setting an arbitrary tagged value requires triggering a write barrier
// which requires separate object and offset values, therefore these static
// functions also has the target object parameter.
static V8_INLINE void store_tagged(EmbedderDataArray array, int entry_index,
Object value);
static V8_INLINE void store_tagged(JSObject object, int embedder_field_index,
Object value);
// Tries reinterpret the value as an aligned pointer and sets *out_result to
// the pointer-like value. Note, that some Smis could still look like an
// aligned pointers.
// Returns true on success.
// When V8 heap sandbox is enabled, calling this method when the raw part of
// the slot does not contain valid external pointer table index is undefined
// behaviour and most likely result in crashes.
V8_INLINE bool ToAlignedPointer(IsolateRoot isolate, void** out_result) const;
// Same as ToAlignedPointer() but with a workaround for V8 heap sandbox.
// When V8 heap sandbox is enabled, this method doesn't crash when the raw
// part of the slot contains "undefined" instead of a correct external table
// entry index (see Factory::InitializeJSObjectBody() for details).
// Returns true when the external pointer table index was pointing to a valid
// entry, otherwise false.
//
// Call this function if you are not sure whether the slot contains valid
// external pointer or not.
V8_INLINE bool ToAlignedPointerSafe(IsolateRoot isolate,
void** out_result) const;
// Returns true if the pointer was successfully stored or false it the pointer
// was improperly aligned.
V8_INLINE V8_WARN_UNUSED_RESULT bool store_aligned_pointer(Isolate* isolate,
void* ptr);
V8_INLINE RawData load_raw(Isolate* isolate,
const DisallowGarbageCollection& no_gc) const;
V8_INLINE void store_raw(Isolate* isolate, RawData data,
const DisallowGarbageCollection& no_gc);
private:
// Stores given value to the embedder data slot in a concurrent-marker
// friendly manner (tagged part of the slot is written atomically).
V8_INLINE void gc_safe_store(Isolate* isolate, Address value);
};
} // namespace internal
} // namespace v8
#include "src/objects/object-macros-undef.h"
#endif // V8_OBJECTS_EMBEDDER_DATA_SLOT_H_
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