isolate-data.h

// 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_ISOLATE_DATA_H_
#define V8_ISOLATE_DATA_H_

#include "src/builtins/builtins.h"
#include "src/constants-arch.h"
#include "src/external-reference-table.h"
#include "src/roots.h"
#include "src/utils.h"

namespace v8 {
namespace internal {

class Isolate;

// This class contains a collection of data accessible from both C++ runtime
// and compiled code (including assembly stubs, builtins, interpreter bytecode
// handlers and optimized code).
// In particular, it contains pointer to the V8 heap roots table, external
// reference table and builtins array.
// The compiled code accesses the isolate data fields indirectly via the root
// register.
class IsolateData final {
 public:
  IsolateData() = default;

  static constexpr intptr_t kIsolateRootBias = kRootRegisterBias;

  // The value of the kRootRegister.
  Address isolate_root() const {
    return reinterpret_cast<Address>(this) + kIsolateRootBias;
  }

  // Root-register-relative offset of the roots table.
  static constexpr int roots_table_offset() {
    return kRootsTableOffset - kIsolateRootBias;
  }

  // Root-register-relative offset of the given root table entry.
  static constexpr int root_slot_offset(RootIndex root_index) {
    return roots_table_offset() + RootsTable::offset_of(root_index);
  }

  // Root-register-relative offset of the external reference table.
  static constexpr int external_reference_table_offset() {
    return kExternalReferenceTableOffset - kIsolateRootBias;
  }

  // Root-register-relative offset of the builtins table.
  static constexpr int builtins_table_offset() {
    return kBuiltinsTableOffset - kIsolateRootBias;
  }

  // Root-register-relative offset of the given builtin table entry.
  // TODO(ishell): remove in favour of typified id version.
  static int builtin_slot_offset(int builtin_index) {
    DCHECK(Builtins::IsBuiltinId(builtin_index));
    return builtins_table_offset() + builtin_index * kPointerSize;
  }

  // Root-register-relative offset of the builtin table entry.
  static int builtin_slot_offset(Builtins::Name id) {
    return builtins_table_offset() + id * kPointerSize;
  }

  // Root-register-relative offset of the virtual call target register value.
  static constexpr int virtual_call_target_register_offset() {
    return kVirtualCallTargetRegisterOffset - kIsolateRootBias;
  }

  // Returns true if this address points to data stored in this instance.
  // If it's the case then the value can be accessed indirectly through the
  // root register.
  bool contains(Address address) const {
    STATIC_ASSERT(std::is_unsigned<Address>::value);
    Address start = reinterpret_cast<Address>(this);
    return (address - start) < sizeof(*this);
  }

  RootsTable& roots() { return roots_; }
  const RootsTable& roots() const { return roots_; }

  ExternalReferenceTable* external_reference_table() {
    return &external_reference_table_;
  }

  Address* builtins() { return builtins_; }

 private:
// Static layout definition.
#define FIELDS(V)                                                         \
  V(kEmbedderDataOffset, Internals::kNumIsolateDataSlots* kPointerSize)   \
  V(kExternalMemoryOffset, kInt64Size)                                    \
  V(kExternalMemoryLlimitOffset, kInt64Size)                              \
  V(kExternalMemoryAtLastMarkCompactOffset, kInt64Size)                   \
  V(kRootsTableOffset, RootsTable::kEntriesCount* kPointerSize)           \
  V(kExternalReferenceTableOffset, ExternalReferenceTable::SizeInBytes()) \
  V(kBuiltinsTableOffset, Builtins::builtin_count* kPointerSize)          \
  V(kVirtualCallTargetRegisterOffset, kPointerSize)                       \
  /* This padding aligns IsolateData size by 8 bytes. */                  \
  V(kPaddingOffset,                                                       \
    8 + RoundUp<8>(static_cast<int>(kPaddingOffset)) - kPaddingOffset)    \
  /* Total size. */                                                       \
  V(kSize, 0)

  DEFINE_FIELD_OFFSET_CONSTANTS(0, FIELDS)
#undef FIELDS

  // These fields are accessed through the API, offsets must be kept in sync
  // with v8::internal::Internals (in include/v8-internal.h) constants.
  // The layout consitency is verified in Isolate::CheckIsolateLayout() using
  // runtime checks.
  void* embedder_data_[Internals::kNumIsolateDataSlots] = {};

  // TODO(ishell): Move these external memory counters back to Heap once the
  // Node JS bot issue is solved.
  // The amount of external memory registered through the API.
  int64_t external_memory_ = 0;

  // The limit when to trigger memory pressure from the API.
  int64_t external_memory_limit_ = kExternalAllocationSoftLimit;

  // Caches the amount of external memory registered at the last MC.
  int64_t external_memory_at_last_mark_compact_ = 0;

  RootsTable roots_;

  ExternalReferenceTable external_reference_table_;

  // The entries in this array are tagged pointers to Code objects.
  Address builtins_[Builtins::builtin_count] = {};

  // For isolate-independent calls on ia32.
  // TODO(v8:6666): Remove once wasm supports pc-relative jumps to builtins on
  // ia32 (otherwise the arguments adaptor call runs out of registers).
  void* virtual_call_target_register_ = nullptr;

  // Ensure the size is 8-byte aligned in order to make alignment of the field
  // following the IsolateData field predictable. This solves the issue with
  // C++ compilers for 32-bit platforms which are not consistent at aligning
  // int64_t fields.
  // In order to avoid dealing with zero-size arrays the padding size is always
  // in the range [8, 15).
  STATIC_ASSERT(kPaddingOffsetEnd + 1 - kPaddingOffset >= 8);
  char padding_[kPaddingOffsetEnd + 1 - kPaddingOffset];

  V8_INLINE static void AssertPredictableLayout();

  friend class Isolate;
  friend class Heap;
  FRIEND_TEST(HeapTest, ExternalLimitDefault);
  FRIEND_TEST(HeapTest, ExternalLimitStaysAboveDefaultForExplicitHandling);

  DISALLOW_COPY_AND_ASSIGN(IsolateData);
};

// IsolateData object must have "predictable" layout which does not change when
// cross-compiling to another platform. Otherwise there may be compatibility
// issues because of different compilers used for snapshot generator and
// actual V8 code.
void IsolateData::AssertPredictableLayout() {
  STATIC_ASSERT(std::is_standard_layout<RootsTable>::value);
  STATIC_ASSERT(std::is_standard_layout<ExternalReferenceTable>::value);
  STATIC_ASSERT(std::is_standard_layout<IsolateData>::value);
  STATIC_ASSERT(offsetof(IsolateData, roots_) == kRootsTableOffset);
  STATIC_ASSERT(offsetof(IsolateData, external_reference_table_) ==
                kExternalReferenceTableOffset);
  STATIC_ASSERT(offsetof(IsolateData, builtins_) == kBuiltinsTableOffset);
  STATIC_ASSERT(offsetof(IsolateData, virtual_call_target_register_) ==
                kVirtualCallTargetRegisterOffset);
  STATIC_ASSERT(offsetof(IsolateData, external_memory_) ==
                kExternalMemoryOffset);
  STATIC_ASSERT(offsetof(IsolateData, external_memory_limit_) ==
                kExternalMemoryLlimitOffset);
  STATIC_ASSERT(offsetof(IsolateData, external_memory_at_last_mark_compact_) ==
                kExternalMemoryAtLastMarkCompactOffset);
  STATIC_ASSERT(sizeof(IsolateData) == IsolateData::kSize);
}

}  // namespace internal
}  // namespace v8

#endif  // V8_ISOLATE_DATA_H_