// 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 <type_traits>
#include <utility>
#include "include/cppgc/allocation.h"
#include "include/cppgc/garbage-collected.h"
#include "include/cppgc/visitor.h"
#include "src/common/assert-scope.h"
#include "src/common/globals.h"
#include "src/objects/slots.h"
#include "src/sandbox/isolate.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;
// A wrapper CppGC object referenced by the CppHeapPointerTable for entries in
// EmbedderDataSlot that store arbitrary C++ pointers.
class EmbedderDataSlotWrapper final
: public cppgc::GarbageCollected<EmbedderDataSlotWrapper> {
public:
EmbedderDataSlotWrapper(void* pointer, ExternalPointerTag tag)
: pointer_(pointer), tag_(tag) {}
void* pointer() const { return pointer_; }
ExternalPointerTag tag() const { return tag_; }
void Trace(cppgc::Visitor*) const {}
private:
void* const pointer_;
const ExternalPointerTag tag_;
};
// 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:
// When the sandbox is enabled, an EmbedderDataSlot always contains a valid
// CppHeap pointer table index (initially, zero) in its "raw" part and a
// valid tagged value in its 32-bit "tagged" part.
// When pointer compression is disabled, an EmbedderDataSlot similarly
// contains two separate fields: a tagged value in its "tagged" part and a
// raw external pointer in its "raw" part.
//
// Layout (sandbox or no pointer compression):
// +-----------------------------------+-----------------------------------+
// | Tagged (Smi/Pointer) | CppHeap Pointer Table Index / |
// | | CppHeap Pointer |
// +-----------------------------------+-----------------------------------+
// ^ ^
// kTaggedPayloadOffset kCppHeapPointerOffset
static constexpr int kTaggedPayloadOffset = 0;
static constexpr int kCppHeapPointerOffset = kTaggedSize;
static constexpr int kRequiredPtrAlignment = kSmiTagSize;
EmbedderDataSlot() : SlotBase(kNullAddress) {}
V8_INLINE EmbedderDataSlot(Tagged<EmbedderDataArray> array, int entry_index);
V8_INLINE EmbedderDataSlot(Tagged<JSObject> object, int embedder_field_index);
// Opaque type used for storing raw embedder data.
#ifdef V8_COMPRESS_POINTERS
using RawData = uint64_t;
#else
struct RawData {
Address pointer;
Address tagged;
constexpr RawData() : pointer(0), tagged(0) {}
constexpr RawData(Address pointer, Address tagged)
: pointer(pointer), tagged(tagged) {}
constexpr RawData(Address addr) : pointer(addr), tagged(0) {}
};
#endif
V8_INLINE void Initialize(Tagged<Object> initial_value);
V8_INLINE Tagged<Object> load_tagged() const;
V8_INLINE void store_smi(Tagged<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(Tagged<EmbedderDataArray> array,
int entry_index, Tagged<Object> value);
static V8_INLINE void store_tagged(Tagged<JSObject> object,
int embedder_field_index,
Tagged<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 the 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(IsolateForPointerCompression isolate,
void** out_result,
ExternalPointerTagRange tag_range) const;
V8_INLINE bool ToAlignedPointer(IsolateForPointerCompression isolate,
void** out_result,
CppHeapPointerTagRange tag_range) const;
V8_INLINE bool ToGenericAlignedPointer(IsolateForPointerCompression isolate,
void** out_result) const;
// Deprecated, either use ToAlignedPointer with a `tag_range`, or use
// `ToGenericAlignedPointer to indicate that the read pointer will not be
// dereferenced.
V8_INLINE bool DeprecatedToAlignedPointer(
IsolateForPointerCompression isolate, void** out_result) const;
// Returns true if the pointer was successfully stored or false if the pointer
// was improperly aligned.
V8_INLINE V8_WARN_UNUSED_RESULT bool store_aligned_pointer(
Isolate* isolate, Tagged<HeapObject> host, void* ptr,
CppHeapPointerTag tag);
template <typename T>
requires std::is_same_v<EmbedderDataArray, T> || std::is_same_v<JSObject, T>
static V8_INLINE V8_WARN_UNUSED_RESULT bool store_aligned_pointer(
Isolate* isolate, DirectHandle<T> host, int entry_or_embedder_field_index,
void* ptr, ExternalPointerTag tag);
#ifdef V8_COMPRESS_POINTERS
V8_INLINE void store_tagged_without_barrier(Tagged<Object> value);
V8_INLINE V8_WARN_UNUSED_RESULT bool store_handle_without_barrier(
IsolateForPointerCompression isolate, CppHeapPointerHandle handle);
#endif // V8_COMPRESS_POINTERS
V8_INLINE bool MustClearDuringSerialization(
const DisallowGarbageCollection& no_gc);
// IMPORTANT: load_raw and store_raw are strictly intended for temporary
// in-place save-and-restore of an object's embedder slots during snapshot
// serialization (see ContextSerializer::SerializeObjectWithEmbedderFields).
// They must NEVER be used to copy or duplicate embedder slot contents across
// different objects or slots, as doing so would duplicate raw
// CppHeapPointerHandles without updating the CppHeapPointerTable.
V8_INLINE RawData load_raw(IsolateForPointerCompression isolate,
const DisallowGarbageCollection& no_gc) const;
// IMPORTANT: load_raw and store_raw are strictly intended for temporary
// in-place save-and-restore of an object's embedder slots during snapshot
// serialization (see ContextSerializer::SerializeObjectWithEmbedderFields).
// They must NEVER be used to copy or duplicate embedder slot contents across
// different objects or slots, as doing so would duplicate raw
// CppHeapPointerHandles without updating the CppHeapPointerTable.
V8_INLINE void store_raw(IsolateForPointerCompression isolate, RawData data,
const DisallowGarbageCollection& no_gc);
private:
static V8_INLINE void clear_cpp_heap_pointer_field(Address slot_address);
};
} // namespace internal
} // namespace v8
#include "src/objects/object-macros-undef.h"
#endif // V8_OBJECTS_EMBEDDER_DATA_SLOT_H_