v8-internal.h

Go to the documentation of this file.

// 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 INCLUDE_V8_INTERNAL_H_
#define INCLUDE_V8_INTERNAL_H_
 
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include <type_traits>
 
#include "v8-version.h"  // NOLINT(build/include_directory)
#include "v8config.h"    // NOLINT(build/include_directory)
 
namespace v8 {
 
class Context;
class Data;
class Isolate;
 
namespace internal {
 
class Isolate;
 
typedef uintptr_t Address;
static const Address kNullAddress = 0;
 
const int kApiSystemPointerSize = sizeof(void*);
const int kApiDoubleSize = sizeof(double);
const int kApiInt32Size = sizeof(int32_t);
const int kApiInt64Size = sizeof(int64_t);
 
// Tag information for HeapObject.
const int kHeapObjectTag = 1;
const int kWeakHeapObjectTag = 3;
const int kHeapObjectTagSize = 2;
const intptr_t kHeapObjectTagMask = (1 << kHeapObjectTagSize) - 1;
 
// Tag information for Smi.
const int kSmiTag = 0;
const int kSmiTagSize = 1;
const intptr_t kSmiTagMask = (1 << kSmiTagSize) - 1;
 
template <size_t tagged_ptr_size>
struct SmiTagging;
 
constexpr intptr_t kIntptrAllBitsSet = intptr_t{-1};
constexpr uintptr_t kUintptrAllBitsSet =
    static_cast<uintptr_t>(kIntptrAllBitsSet);
 
// Smi constants for systems where tagged pointer is a 32-bit value.
template <>
struct SmiTagging<4> {
  enum { kSmiShiftSize = 0, kSmiValueSize = 31 };
 
  static constexpr intptr_t kSmiMinValue =
      static_cast<intptr_t>(kUintptrAllBitsSet << (kSmiValueSize - 1));
  static constexpr intptr_t kSmiMaxValue = -(kSmiMinValue + 1);
 
  V8_INLINE static int SmiToInt(const internal::Address value) {
    int shift_bits = kSmiTagSize + kSmiShiftSize;
    // Truncate and shift down (requires >> to be sign extending).
    return static_cast<int32_t>(static_cast<uint32_t>(value)) >> shift_bits;
  }
  V8_INLINE static constexpr bool IsValidSmi(intptr_t value) {
    // Is value in range [kSmiMinValue, kSmiMaxValue].
    // Use unsigned operations in order to avoid undefined behaviour in case of
    // signed integer overflow.
    return (static_cast<uintptr_t>(value) -
            static_cast<uintptr_t>(kSmiMinValue)) <=
           (static_cast<uintptr_t>(kSmiMaxValue) -
            static_cast<uintptr_t>(kSmiMinValue));
  }
};
 
// Smi constants for systems where tagged pointer is a 64-bit value.
template <>
struct SmiTagging<8> {
  enum { kSmiShiftSize = 31, kSmiValueSize = 32 };
 
  static constexpr intptr_t kSmiMinValue =
      static_cast<intptr_t>(kUintptrAllBitsSet << (kSmiValueSize - 1));
  static constexpr intptr_t kSmiMaxValue = -(kSmiMinValue + 1);
 
  V8_INLINE static int SmiToInt(const internal::Address value) {
    int shift_bits = kSmiTagSize + kSmiShiftSize;
    // Shift down and throw away top 32 bits.
    return static_cast<int>(static_cast<intptr_t>(value) >> shift_bits);
  }
  V8_INLINE static constexpr bool IsValidSmi(intptr_t value) {
    // To be representable as a long smi, the value must be a 32-bit integer.
    return (value == static_cast<int32_t>(value));
  }
};
 
#ifdef V8_COMPRESS_POINTERS
static_assert(
    kApiSystemPointerSize == kApiInt64Size,
    "Pointer compression can be enabled only for 64-bit architectures");
const int kApiTaggedSize = kApiInt32Size;
#else
const int kApiTaggedSize = kApiSystemPointerSize;
#endif
 
constexpr bool PointerCompressionIsEnabled() {
  return kApiTaggedSize != kApiSystemPointerSize;
}
 
constexpr bool HeapSandboxIsEnabled() {
#ifdef V8_HEAP_SANDBOX
  return true;
#else
  return false;
#endif
}
 
using ExternalPointer_t = Address;
 
#ifdef V8_31BIT_SMIS_ON_64BIT_ARCH
using PlatformSmiTagging = SmiTagging<kApiInt32Size>;
#else
using PlatformSmiTagging = SmiTagging<kApiTaggedSize>;
#endif
 
// TODO(ishell): Consinder adding kSmiShiftBits = kSmiShiftSize + kSmiTagSize
// since it's used much more often than the inividual constants.
const int kSmiShiftSize = PlatformSmiTagging::kSmiShiftSize;
const int kSmiValueSize = PlatformSmiTagging::kSmiValueSize;
const int kSmiMinValue = static_cast<int>(PlatformSmiTagging::kSmiMinValue);
const int kSmiMaxValue = static_cast<int>(PlatformSmiTagging::kSmiMaxValue);
constexpr bool SmiValuesAre31Bits() { return kSmiValueSize == 31; }
constexpr bool SmiValuesAre32Bits() { return kSmiValueSize == 32; }
 
V8_INLINE static constexpr internal::Address IntToSmi(int value) {
  return (static_cast<Address>(value) << (kSmiTagSize + kSmiShiftSize)) |
         kSmiTag;
}
 
// {obj} must be the raw tagged pointer representation of a HeapObject
// that's guaranteed to never be in ReadOnlySpace.
V8_EXPORT internal::Isolate* IsolateFromNeverReadOnlySpaceObject(Address obj);
 
// Returns if we need to throw when an error occurs. This infers the language
// mode based on the current context and the closure. This returns true if the
// language mode is strict.
V8_EXPORT bool ShouldThrowOnError(v8::internal::Isolate* isolate);
 
class Internals {
 public:
  // These values match non-compiler-dependent values defined within
  // the implementation of v8.
  static const int kHeapObjectMapOffset = 0;
  static const int kMapInstanceTypeOffset = 1 * kApiTaggedSize + kApiInt32Size;
  static const int kStringResourceOffset =
      1 * kApiTaggedSize + 2 * kApiInt32Size;
 
  static const int kOddballKindOffset = 4 * kApiTaggedSize + kApiDoubleSize;
  static const int kJSObjectHeaderSize = 3 * kApiTaggedSize;
  static const int kFixedArrayHeaderSize = 2 * kApiTaggedSize;
  static const int kEmbedderDataArrayHeaderSize = 2 * kApiTaggedSize;
  static const int kEmbedderDataSlotSize = kApiSystemPointerSize;
  static const int kNativeContextEmbedderDataOffset = 6 * kApiTaggedSize;
  static const int kFullStringRepresentationMask = 0x0f;
  static const int kStringEncodingMask = 0x8;
  static const int kExternalTwoByteRepresentationTag = 0x02;
  static const int kExternalOneByteRepresentationTag = 0x0a;
 
  static const uint32_t kNumIsolateDataSlots = 4;
 
  // IsolateData layout guarantees.
  static const int kIsolateEmbedderDataOffset = 0;
  static const int kExternalMemoryOffset =
      kNumIsolateDataSlots * kApiSystemPointerSize;
  static const int kExternalMemoryLimitOffset =
      kExternalMemoryOffset + kApiInt64Size;
  static const int kExternalMemoryLowSinceMarkCompactOffset =
      kExternalMemoryLimitOffset + kApiInt64Size;
  static const int kIsolateFastCCallCallerFpOffset =
      kExternalMemoryLowSinceMarkCompactOffset + kApiInt64Size;
  static const int kIsolateFastCCallCallerPcOffset =
      kIsolateFastCCallCallerFpOffset + kApiSystemPointerSize;
  static const int kIsolateStackGuardOffset =
      kIsolateFastCCallCallerPcOffset + kApiSystemPointerSize;
  static const int kIsolateRootsOffset =
      kIsolateStackGuardOffset + 7 * kApiSystemPointerSize;
 
  static const int kUndefinedValueRootIndex = 4;
  static const int kTheHoleValueRootIndex = 5;
  static const int kNullValueRootIndex = 6;
  static const int kTrueValueRootIndex = 7;
  static const int kFalseValueRootIndex = 8;
  static const int kEmptyStringRootIndex = 9;
 
  static const int kNodeClassIdOffset = 1 * kApiSystemPointerSize;
  static const int kNodeFlagsOffset = 1 * kApiSystemPointerSize + 3;
  static const int kNodeStateMask = 0x7;
  static const int kNodeStateIsWeakValue = 2;
  static const int kNodeStateIsPendingValue = 3;
 
  static const int kFirstNonstringType = 0x40;
  static const int kOddballType = 0x43;
  static const int kForeignType = 0x46;
  static const int kJSSpecialApiObjectType = 0x410;
  static const int kJSApiObjectType = 0x420;
  static const int kJSObjectType = 0x421;
 
  static const int kUndefinedOddballKind = 5;
  static const int kNullOddballKind = 3;
 
  // Constants used by PropertyCallbackInfo to check if we should throw when an
  // error occurs.
  static const int kThrowOnError = 0;
  static const int kDontThrow = 1;
  static const int kInferShouldThrowMode = 2;
 
  // Soft limit for AdjustAmountofExternalAllocatedMemory. Trigger an
  // incremental GC once the external memory reaches this limit.
  static constexpr int kExternalAllocationSoftLimit = 64 * 1024 * 1024;
 
  V8_EXPORT static void CheckInitializedImpl(v8::Isolate* isolate);
  V8_INLINE static void CheckInitialized(v8::Isolate* isolate) {
#ifdef V8_ENABLE_CHECKS
    CheckInitializedImpl(isolate);
#endif
  }
 
  V8_INLINE static bool HasHeapObjectTag(const internal::Address value) {
    return (value & kHeapObjectTagMask) == static_cast<Address>(kHeapObjectTag);
  }
 
  V8_INLINE static int SmiValue(const internal::Address value) {
    return PlatformSmiTagging::SmiToInt(value);
  }
 
  V8_INLINE static constexpr internal::Address IntToSmi(int value) {
    return internal::IntToSmi(value);
  }
 
  V8_INLINE static constexpr bool IsValidSmi(intptr_t value) {
    return PlatformSmiTagging::IsValidSmi(value);
  }
 
  V8_INLINE static int GetInstanceType(const internal::Address obj) {
    typedef internal::Address A;
    A map = ReadTaggedPointerField(obj, kHeapObjectMapOffset);
    return ReadRawField<uint16_t>(map, kMapInstanceTypeOffset);
  }
 
  V8_INLINE static int GetOddballKind(const internal::Address obj) {
    return SmiValue(ReadTaggedSignedField(obj, kOddballKindOffset));
  }
 
  V8_INLINE static bool IsExternalTwoByteString(int instance_type) {
    int representation = (instance_type & kFullStringRepresentationMask);
    return representation == kExternalTwoByteRepresentationTag;
  }
 
  V8_INLINE static uint8_t GetNodeFlag(internal::Address* obj, int shift) {
    uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + kNodeFlagsOffset;
    return *addr & static_cast<uint8_t>(1U << shift);
  }
 
  V8_INLINE static void UpdateNodeFlag(internal::Address* obj, bool value,
                                       int shift) {
    uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + kNodeFlagsOffset;
    uint8_t mask = static_cast<uint8_t>(1U << shift);
    *addr = static_cast<uint8_t>((*addr & ~mask) | (value << shift));
  }
 
  V8_INLINE static uint8_t GetNodeState(internal::Address* obj) {
    uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + kNodeFlagsOffset;
    return *addr & kNodeStateMask;
  }
 
  V8_INLINE static void UpdateNodeState(internal::Address* obj, uint8_t value) {
    uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + kNodeFlagsOffset;
    *addr = static_cast<uint8_t>((*addr & ~kNodeStateMask) | value);
  }
 
  V8_INLINE static void SetEmbedderData(v8::Isolate* isolate, uint32_t slot,
                                        void* data) {
    internal::Address addr = reinterpret_cast<internal::Address>(isolate) +
                             kIsolateEmbedderDataOffset +
                             slot * kApiSystemPointerSize;
    *reinterpret_cast<void**>(addr) = data;
  }
 
  V8_INLINE static void* GetEmbedderData(const v8::Isolate* isolate,
                                         uint32_t slot) {
    internal::Address addr = reinterpret_cast<internal::Address>(isolate) +
                             kIsolateEmbedderDataOffset +
                             slot * kApiSystemPointerSize;
    return *reinterpret_cast<void* const*>(addr);
  }
 
  V8_INLINE static internal::Address* GetRoot(v8::Isolate* isolate, int index) {
    internal::Address addr = reinterpret_cast<internal::Address>(isolate) +
                             kIsolateRootsOffset +
                             index * kApiSystemPointerSize;
    return reinterpret_cast<internal::Address*>(addr);
  }
 
  template <typename T>
  V8_INLINE static T ReadRawField(internal::Address heap_object_ptr,
                                  int offset) {
    internal::Address addr = heap_object_ptr + offset - kHeapObjectTag;
#ifdef V8_COMPRESS_POINTERS
    if (sizeof(T) > kApiTaggedSize) {
      // 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.
      T r;
      memcpy(&r, reinterpret_cast<void*>(addr), sizeof(T));
      return r;
    }
#endif
    return *reinterpret_cast<const T*>(addr);
  }
 
  V8_INLINE static internal::Address ReadTaggedPointerField(
      internal::Address heap_object_ptr, int offset) {
#ifdef V8_COMPRESS_POINTERS
    uint32_t value = ReadRawField<uint32_t>(heap_object_ptr, offset);
    internal::Address root = GetRootFromOnHeapAddress(heap_object_ptr);
    return root + static_cast<internal::Address>(static_cast<uintptr_t>(value));
#else
    return ReadRawField<internal::Address>(heap_object_ptr, offset);
#endif
  }
 
  V8_INLINE static internal::Address ReadTaggedSignedField(
      internal::Address heap_object_ptr, int offset) {
#ifdef V8_COMPRESS_POINTERS
    uint32_t value = ReadRawField<uint32_t>(heap_object_ptr, offset);
    return static_cast<internal::Address>(static_cast<uintptr_t>(value));
#else
    return ReadRawField<internal::Address>(heap_object_ptr, offset);
#endif
  }
 
  V8_INLINE static internal::Isolate* GetIsolateForHeapSandbox(
      internal::Address obj) {
#ifdef V8_HEAP_SANDBOX
    return internal::IsolateFromNeverReadOnlySpaceObject(obj);
#else
    // Not used in non-sandbox mode.
    return nullptr;
#endif
  }
 
  V8_INLINE static internal::Address ReadExternalPointerField(
      internal::Isolate* isolate, internal::Address heap_object_ptr,
      int offset) {
    internal::Address value = ReadRawField<Address>(heap_object_ptr, offset);
#ifdef V8_HEAP_SANDBOX
    // We currently have to treat zero as nullptr in embedder slots.
    if (value) value = DecodeExternalPointer(isolate, value);
#endif
    return value;
  }
 
#ifdef V8_COMPRESS_POINTERS
  // See v8:7703 or src/ptr-compr.* for details about pointer compression.
  static constexpr size_t kPtrComprHeapReservationSize = size_t{1} << 32;
  static constexpr size_t kPtrComprIsolateRootAlignment = size_t{1} << 32;
 
  // See v8:10391 for details about V8 heap sandbox.
  static constexpr uint32_t kExternalPointerSalt =
      0x7fffffff & ~static_cast<uint32_t>(kHeapObjectTagMask);
 
  V8_INLINE static internal::Address GetRootFromOnHeapAddress(
      internal::Address addr) {
    return addr & -static_cast<intptr_t>(kPtrComprIsolateRootAlignment);
  }
 
  V8_INLINE static internal::Address DecompressTaggedAnyField(
      internal::Address heap_object_ptr, uint32_t value) {
    internal::Address root = GetRootFromOnHeapAddress(heap_object_ptr);
    return root + static_cast<internal::Address>(static_cast<uintptr_t>(value));
  }
 
  V8_INLINE static Address DecodeExternalPointer(
      const Isolate* isolate, ExternalPointer_t encoded_pointer) {
#ifndef V8_HEAP_SANDBOX
    return encoded_pointer;
#else
    return encoded_pointer ^ kExternalPointerSalt;
#endif
  }
#endif  // V8_COMPRESS_POINTERS
};
 
// Only perform cast check for types derived from v8::Data since
// other types do not implement the Cast method.
template <bool PerformCheck>
struct CastCheck {
  template <class T>
  static void Perform(T* data);
};
 
template <>
template <class T>
void CastCheck<true>::Perform(T* data) {
  T::Cast(data);
}
 
template <>
template <class T>
void CastCheck<false>::Perform(T* data) {}
 
template <class T>
V8_INLINE void PerformCastCheck(T* data) {
  CastCheck<std::is_base_of<Data, T>::value>::Perform(data);
}
 
// A base class for backing stores, which is needed due to vagaries of
// how static casts work with std::shared_ptr.
class BackingStoreBase {};
 
}  // namespace internal
}  // namespace v8
 
#endif  // INCLUDE_V8_INTERNAL_H_