v8/include/v8-internal.h
Samuel Groß 571eca5ced Implement DetermineAddressSpaceLimit() on x64
This function tries to determine the number of virtual address bits
available on the current CPU and with that the maximum size of the
userspace address space. On x64, it can be implemented through CPUID.

The result of this function is now used in two ways: first, it limits
the maximum size of the virtual memory cage, currently to a quarter of
the address space. Second, it influences the placement of fake cages,
which are attempted to be placed into the lower half of the address
space so that they are followed by large amounts of (hopefully) unused
but addressable virtual memory in which pages can be allocated.

Bug: chromium:1218005
Change-Id: I0edc5d241d899f16dbc47492fa1534b6aaa4aa13
Cq-Include-Trybots: luci.v8.try:v8_linux64_heap_sandbox_dbg_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3220348
Commit-Queue: Samuel Groß <saelo@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77393}
2021-10-14 10:01:57 +00:00

604 lines
23 KiB
C++

// 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 Array;
class Context;
class Data;
class Isolate;
template <typename T>
class Local;
namespace internal {
class Isolate;
typedef uintptr_t Address;
static const Address kNullAddress = 0;
/**
* Configuration of tagging scheme.
*/
const int kApiSystemPointerSize = sizeof(void*);
const int kApiDoubleSize = sizeof(double);
const int kApiInt32Size = sizeof(int32_t);
const int kApiInt64Size = sizeof(int64_t);
const int kApiSizetSize = sizeof(size_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 fowarding pointers stored in object headers.
// 0b00 at the lowest 2 bits in the header indicates that the map word is a
// forwarding pointer.
const int kForwardingTag = 0;
const int kForwardingTagSize = 2;
const intptr_t kForwardingTagMask = (1 << kForwardingTagSize) - 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;
// If the heap sandbox is enabled, these tag values will be ORed with the
// external pointers in the external pointer table to prevent use of pointers of
// the wrong type. When a pointer is loaded, it is ANDed with the inverse of the
// expected type's tag. The tags are constructed in a way that guarantees that a
// failed type check will result in one or more of the top bits of the pointer
// to be set, rendering the pointer inacessible. This construction allows
// performing the type check and removing GC marking bits from the pointer at
// the same time.
enum ExternalPointerTag : uint64_t {
kExternalPointerNullTag = 0x0000000000000000,
kExternalStringResourceTag = 0x00ff000000000000, // 0b000000011111111
kExternalStringResourceDataTag = 0x017f000000000000, // 0b000000101111111
kForeignForeignAddressTag = 0x01bf000000000000, // 0b000000110111111
kNativeContextMicrotaskQueueTag = 0x01df000000000000, // 0b000000111011111
kEmbedderDataSlotPayloadTag = 0x01ef000000000000, // 0b000000111101111
kCodeEntryPointTag = 0x01f7000000000000, // 0b000000111110111
};
constexpr uint64_t kExternalPointerTagMask = 0xffff000000000000;
#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;
}
// Converts encoded external pointer to address.
V8_EXPORT Address DecodeExternalPointerImpl(const Isolate* isolate,
ExternalPointer_t pointer,
ExternalPointerTag tag);
// {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);
V8_EXPORT bool CanHaveInternalField(int instance_type);
/**
* This class exports constants and functionality from within v8 that
* is necessary to implement inline functions in the v8 api. Don't
* depend on functions and constants defined here.
*/
class Internals {
#ifdef V8_MAP_PACKING
V8_INLINE static constexpr internal::Address UnpackMapWord(
internal::Address mapword) {
// TODO(wenyuzhao): Clear header metadata.
return mapword ^ kMapWordXorMask;
}
#endif
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;
#ifdef V8_HEAP_SANDBOX
static const int kEmbedderDataSlotRawPayloadOffset = kApiTaggedSize;
#endif
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;
static const int kStackGuardSize = 7 * kApiSystemPointerSize;
static const int kBuiltinTier0EntryTableSize = 13 * kApiSystemPointerSize;
static const int kBuiltinTier0TableSize = 13 * kApiSystemPointerSize;
// IsolateData layout guarantees.
static const int kIsolateCageBaseOffset = 0;
static const int kIsolateStackGuardOffset =
kIsolateCageBaseOffset + kApiSystemPointerSize;
static const int kBuiltinTier0EntryTableOffset =
kIsolateStackGuardOffset + kStackGuardSize;
static const int kBuiltinTier0TableOffset =
kBuiltinTier0EntryTableOffset + kBuiltinTier0EntryTableSize;
static const int kIsolateEmbedderDataOffset =
kBuiltinTier0TableOffset + kBuiltinTier0TableSize;
static const int kIsolateFastCCallCallerFpOffset =
kIsolateEmbedderDataOffset + kNumIsolateDataSlots * kApiSystemPointerSize;
static const int kIsolateFastCCallCallerPcOffset =
kIsolateFastCCallCallerFpOffset + kApiSystemPointerSize;
static const int kIsolateFastApiCallTargetOffset =
kIsolateFastCCallCallerPcOffset + kApiSystemPointerSize;
static const int kIsolateLongTaskStatsCounterOffset =
kIsolateFastApiCallTargetOffset + kApiSystemPointerSize;
static const int kIsolateRootsOffset =
kIsolateLongTaskStatsCounterOffset + kApiSizetSize;
static const int kExternalPointerTableBufferOffset = 0;
static const int kExternalPointerTableLengthOffset =
kExternalPointerTableBufferOffset + kApiSystemPointerSize;
static const int kExternalPointerTableCapacityOffset =
kExternalPointerTableLengthOffset + kApiInt32Size;
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 kJSObjectType = 0x421;
static const int kFirstJSApiObjectType = 0x422;
static const int kLastJSApiObjectType = 0x80A;
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;
#ifdef V8_MAP_PACKING
static const uintptr_t kMapWordMetadataMask = 0xffffULL << 48;
// The lowest two bits of mapwords are always `0b10`
static const uintptr_t kMapWordSignature = 0b10;
// XORing a (non-compressed) map with this mask ensures that the two
// low-order bits are 0b10. The 0 at the end makes this look like a Smi,
// although real Smis have all lower 32 bits unset. We only rely on these
// values passing as Smis in very few places.
static const int kMapWordXorMask = 0b11;
#endif
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);
#ifdef V8_MAP_PACKING
map = UnpackMapWord(map);
#endif
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 void IncrementLongTasksStatsCounter(v8::Isolate* isolate) {
internal::Address addr = reinterpret_cast<internal::Address>(isolate) +
kIsolateLongTaskStatsCounterOffset;
++(*reinterpret_cast<size_t*>(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 base =
GetPtrComprCageBaseFromOnHeapAddress(heap_object_ptr);
return base + 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 Address DecodeExternalPointer(
const Isolate* isolate, ExternalPointer_t encoded_pointer,
ExternalPointerTag tag) {
#ifdef V8_HEAP_SANDBOX
return internal::DecodeExternalPointerImpl(isolate, encoded_pointer, tag);
#else
return encoded_pointer;
#endif
}
V8_INLINE static internal::Address ReadExternalPointerField(
internal::Isolate* isolate, internal::Address heap_object_ptr, int offset,
ExternalPointerTag tag) {
#ifdef V8_HEAP_SANDBOX
internal::ExternalPointer_t encoded_value =
ReadRawField<uint32_t>(heap_object_ptr, offset);
// We currently have to treat zero as nullptr in embedder slots.
return encoded_value ? DecodeExternalPointer(isolate, encoded_value, tag)
: 0;
#else
return ReadRawField<Address>(heap_object_ptr, offset);
#endif
}
#ifdef V8_COMPRESS_POINTERS
// See v8:7703 or src/ptr-compr.* for details about pointer compression.
static constexpr size_t kPtrComprCageReservationSize = size_t{1} << 32;
static constexpr size_t kPtrComprCageBaseAlignment = size_t{1} << 32;
V8_INLINE static internal::Address GetPtrComprCageBaseFromOnHeapAddress(
internal::Address addr) {
return addr & -static_cast<intptr_t>(kPtrComprCageBaseAlignment);
}
V8_INLINE static internal::Address DecompressTaggedAnyField(
internal::Address heap_object_ptr, uint32_t value) {
internal::Address base =
GetPtrComprCageBaseFromOnHeapAddress(heap_object_ptr);
return base + static_cast<internal::Address>(static_cast<uintptr_t>(value));
}
#endif // V8_COMPRESS_POINTERS
};
constexpr bool VirtualMemoryCageIsEnabled() {
#ifdef V8_VIRTUAL_MEMORY_CAGE
return true;
#else
return false;
#endif
}
#ifdef V8_VIRTUAL_MEMORY_CAGE_IS_AVAILABLE
#define GB (1ULL << 30)
#define TB (1ULL << 40)
// Size of the virtual memory cage, excluding the guard regions surrounding it.
constexpr size_t kVirtualMemoryCageSize = 1ULL * TB;
// Required alignment of the virtual memory cage. For simplicity, we require the
// size of the guard regions to be a multiple of this, so that this specifies
// the alignment of the cage including and excluding surrounding guard regions.
// The alignment requirement is due to the pointer compression cage being
// located at the start of the virtual memory cage.
constexpr size_t kVirtualMemoryCageAlignment =
Internals::kPtrComprCageBaseAlignment;
// Size of the guard regions surrounding the virtual memory cage. This assumes a
// worst-case scenario of a 32-bit unsigned index being used to access an array
// of 64-bit values.
constexpr size_t kVirtualMemoryCageGuardRegionSize = 32ULL * GB;
static_assert((kVirtualMemoryCageGuardRegionSize %
kVirtualMemoryCageAlignment) == 0,
"The size of the virtual memory cage guard region must be a "
"multiple of its required alignment.");
// Minimum size of the virtual memory cage, excluding the guard regions
// surrounding it. If the cage reservation fails, its size is currently halved
// until either the reservation succeeds or the minimum size is reached. A
// minimum of 32GB allows the 4GB pointer compression region as well as the
// ArrayBuffer partition and two 10GB WASM memory cages to fit into the cage.
// 32GB should also be the minimum possible size of the userspace address space
// as there are some machine configurations with only 36 virtual address bits.
constexpr size_t kVirtualMemoryCageMinimumSize = 32ULL * GB;
static_assert(kVirtualMemoryCageMinimumSize <= kVirtualMemoryCageSize,
"The minimal size of the virtual memory cage must be smaller or "
"equal to the regular size.");
// On OSes where reservation virtual memory is too expensive to create a real
// cage, notably Windows pre 8.1, we create a fake cage that doesn't actually
// reserve most of the memory, and so doesn't have the desired security
// properties, but still ensures that objects that should be located inside the
// cage are allocated within kVirtualMemoryCageSize bytes from the start of the
// cage, and so appear to be inside the cage. The minimum size of the virtual
// memory range that is actually reserved for a fake cage is specified by this
// constant and should be big enough to contain the pointer compression region
// as well as the ArrayBuffer partition.
constexpr size_t kFakeVirtualMemoryCageMinReservationSize = 8ULL * GB;
static_assert(kVirtualMemoryCageMinimumSize >
Internals::kPtrComprCageReservationSize,
"The virtual memory cage must be larger than the pointer "
"compression cage contained within it.");
static_assert(kFakeVirtualMemoryCageMinReservationSize >
Internals::kPtrComprCageReservationSize,
"The reservation for a fake virtual memory cage must be larger "
"than the pointer compression cage contained within it.");
// For now, even if the virtual memory cage is enabled, we still allow backing
// stores to be allocated outside of it as fallback. This will simplify the
// initial rollout. However, if the heap sandbox is also enabled, we already use
// the "enforcing mode" of the virtual memory cage. This is useful for testing.
#ifdef V8_HEAP_SANDBOX
constexpr bool kAllowBackingStoresOutsideCage = false;
#else
constexpr bool kAllowBackingStoresOutsideCage = true;
#endif // V8_HEAP_SANDBOX
#undef GB
#undef TB
#endif // V8_VIRTUAL_MEMORY_CAGE_IS_AVAILABLE
// 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 &&
!std::is_same<Data, std::remove_cv_t<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_