| // 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: |
| #ifdef V8_ENABLE_SANDBOX |
| // When the sandbox is enabled, an EmbedderDataSlot always contains a valid |
| // external pointer table index (initially, zero) in it's "raw" part and a |
| // valid tagged value in its 32-bit "tagged" part. |
| // |
| // Layout (sandbox): |
| // +-----------------------------------+-----------------------------------+ |
| // | Tagged (Smi/CompressedPointer) | External Pointer Table Index | |
| // +-----------------------------------+-----------------------------------+ |
| // ^ ^ |
| // kTaggedPayloadOffset kRawPayloadOffset |
| // kExternalPointerOffset |
| static constexpr int kTaggedPayloadOffset = 0; |
| static constexpr int kRawPayloadOffset = kTaggedSize; |
| static constexpr int kExternalPointerOffset = kRawPayloadOffset; |
| #elif defined(V8_COMPRESS_POINTERS) && defined(V8_TARGET_BIG_ENDIAN) |
| // The raw payload is located in the other "tagged" part of the full pointer |
| // and cotains the upper part of an aligned address. The raw part is not |
| // expected to look like a tagged value. |
| // |
| // Layout (big endian pointer compression): |
| // +-----------------------------------+-----------------------------------+ |
| // | External Pointer (high word) | Tagged (Smi/CompressedPointer) | |
| // | | OR External Pointer (low word) | |
| // +-----------------------------------+-----------------------------------+ |
| // ^ ^ |
| // kRawPayloadOffset kTaggedayloadOffset |
| // kExternalPointerOffset |
| static constexpr int kExternalPointerOffset = 0; |
| static constexpr int kRawPayloadOffset = 0; |
| static constexpr int kTaggedPayloadOffset = kTaggedSize; |
| #elif defined(V8_COMPRESS_POINTERS) && defined(V8_TARGET_LITTLE_ENDIAN) |
| // Layout (little endian pointer compression): |
| // +-----------------------------------+-----------------------------------+ |
| // | Tagged (Smi/CompressedPointer) | External Pointer (high word) | |
| // | OR External Pointer (low word) | | |
| // +-----------------------------------+-----------------------------------+ |
| // ^ ^ |
| // kTaggedPayloadOffset kRawPayloadOffset |
| // kExternalPointerOffset |
| static constexpr int kExternalPointerOffset = 0; |
| static constexpr int kTaggedPayloadOffset = 0; |
| static constexpr int kRawPayloadOffset = kTaggedSize; |
| #else |
| // Layout (no pointer compression): |
| // +-----------------------------------------------------------------------+ |
| // | Tagged (Smi/Pointer) OR External Pointer | |
| // +-----------------------------------------------------------------------+ |
| // ^ |
| // kTaggedPayloadOffset |
| // kExternalPointerOffset |
| static constexpr int kTaggedPayloadOffset = 0; |
| static constexpr int kExternalPointerOffset = 0; |
| #endif // V8_ENABLE_SANDBOX |
| |
| static constexpr int kRequiredPtrAlignment = kSmiTagSize; |
| |
| using EmbedderDataSlotSnapshot = Address; |
| V8_INLINE static void PopulateEmbedderDataSnapshot(Tagged<Map> map, |
| Tagged<JSObject> js_object, |
| int entry_index, |
| EmbedderDataSlotSnapshot&); |
| |
| EmbedderDataSlot() : SlotBase(kNullAddress) {} |
| V8_INLINE EmbedderDataSlot(Tagged<EmbedderDataArray> array, int entry_index); |
| V8_INLINE EmbedderDataSlot(Tagged<JSObject> object, int embedder_field_index); |
| V8_INLINE explicit EmbedderDataSlot(const EmbedderDataSlotSnapshot& snapshot); |
| |
| // Opaque type used for storing raw embedder data. |
| using RawData = Address; |
| |
| 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(Isolate* 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, Tagged<HeapObject> host, 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_ |