simulator-mips64.h

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// Copyright 2011 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_EXECUTION_MIPS64_SIMULATOR_MIPS64_H_
#define V8_EXECUTION_MIPS64_SIMULATOR_MIPS64_H_
 
// Declares a Simulator for MIPS instructions if we are not generating a native
// MIPS binary. This Simulator allows us to run and debug MIPS code generation
// on regular desktop machines.
// V8 calls into generated code via the GeneratedCode wrapper,
// which will start execution in the Simulator or forwards to the real entry
// on a MIPS HW platform.
 
// globals.h defines USE_SIMULATOR.
#include "src/common/globals.h"
 
template <typename T>
int Compare(const T& a, const T& b) {
  if (a == b)
    return 0;
  else if (a < b)
    return -1;
  else
    return 1;
}
 
// Returns the negative absolute value of its argument.
template <typename T,
          typename = typename std::enable_if<std::is_signed<T>::value>::type>
T Nabs(T a) {
  return a < 0 ? a : -a;
}
 
#if defined(USE_SIMULATOR)
// Running with a simulator.
 
#include "src/base/hashmap.h"
#include "src/base/strings.h"
#include "src/codegen/assembler.h"
#include "src/codegen/mips64/constants-mips64.h"
#include "src/execution/simulator-base.h"
#include "src/utils/allocation.h"
 
namespace v8 {
namespace internal {
 
// -----------------------------------------------------------------------------
// Utility functions
 
class CachePage {
 public:
  static const int LINE_VALID = 0;
  static const int LINE_INVALID = 1;
 
  static const int kPageShift = 12;
  static const int kPageSize = 1 << kPageShift;
  static const int kPageMask = kPageSize - 1;
  static const int kLineShift = 2;  // The cache line is only 4 bytes right now.
  static const int kLineLength = 1 << kLineShift;
  static const int kLineMask = kLineLength - 1;
 
  CachePage() { memset(&validity_map_, LINE_INVALID, sizeof(validity_map_)); }
 
  char* ValidityByte(int offset) {
    return &validity_map_[offset >> kLineShift];
  }
 
  char* CachedData(int offset) { return &data_[offset]; }
 
 private:
  char data_[kPageSize];  // The cached data.
  static const int kValidityMapSize = kPageSize >> kLineShift;
  char validity_map_[kValidityMapSize];  // One byte per line.
};
 
class SimInstructionBase : public InstructionBase {
 public:
  Type InstructionType() const { return type_; }
  inline Instruction* instr() const { return instr_; }
  inline int32_t operand() const { return operand_; }
 
 protected:
  SimInstructionBase() : operand_(-1), instr_(nullptr), type_(kUnsupported) {}
  explicit SimInstructionBase(Instruction* instr) {}
 
  int32_t operand_;
  Instruction* instr_;
  Type type_;
 
 private:
  DISALLOW_ASSIGN(SimInstructionBase);
};
 
class SimInstruction : public InstructionGetters<SimInstructionBase> {
 public:
  SimInstruction() {}
 
  explicit SimInstruction(Instruction* instr) { *this = instr; }
 
  SimInstruction& operator=(Instruction* instr) {
    operand_ = *reinterpret_cast<const int32_t*>(instr);
    instr_ = instr;
    type_ = InstructionBase::InstructionType();
    DCHECK(reinterpret_cast<void*>(&operand_) == this);
    return *this;
  }
};
 
class Simulator : public SimulatorBase {
 public:
  friend class MipsDebugger;
 
  // Registers are declared in order. See SMRL chapter 2.
  enum Register {
    no_reg = -1,
    zero_reg = 0,
    at,
    v0,
    v1,
    a0,
    a1,
    a2,
    a3,
    a4,
    a5,
    a6,
    a7,
    t0,
    t1,
    t2,
    t3,
    s0,
    s1,
    s2,
    s3,
    s4,
    s5,
    s6,
    s7,
    t8,
    t9,
    k0,
    k1,
    gp,
    sp,
    s8,
    ra,
    // LO, HI, and pc.
    LO,
    HI,
    pc,  // pc must be the last register.
    kNumSimuRegisters,
    // aliases
    fp = s8
  };
 
  // Coprocessor registers.
  // Generated code will always use doubles. So we will only use even registers.
  enum FPURegister {
    f0,
    f1,
    f2,
    f3,
    f4,
    f5,
    f6,
    f7,
    f8,
    f9,
    f10,
    f11,
    f12,
    f13,
    f14,
    f15,  // f12 and f14 are arguments FPURegisters.
    f16,
    f17,
    f18,
    f19,
    f20,
    f21,
    f22,
    f23,
    f24,
    f25,
    f26,
    f27,
    f28,
    f29,
    f30,
    f31,
    kNumFPURegisters
  };
 
  // MSA registers
  enum MSARegister {
    w0,
    w1,
    w2,
    w3,
    w4,
    w5,
    w6,
    w7,
    w8,
    w9,
    w10,
    w11,
    w12,
    w13,
    w14,
    w15,
    w16,
    w17,
    w18,
    w19,
    w20,
    w21,
    w22,
    w23,
    w24,
    w25,
    w26,
    w27,
    w28,
    w29,
    w30,
    w31,
    kNumMSARegisters
  };
 
  explicit Simulator(Isolate* isolate);
  ~Simulator();
 
  // The currently executing Simulator instance. Potentially there can be one
  // for each native thread.
  V8_EXPORT_PRIVATE static Simulator* current(v8::internal::Isolate* isolate);
 
  // Accessors for register state. Reading the pc value adheres to the MIPS
  // architecture specification and is off by a 8 from the currently executing
  // instruction.
  void set_register(int reg, int64_t value);
  void set_register_word(int reg, int32_t value);
  void set_dw_register(int dreg, const int* dbl);
  V8_EXPORT_PRIVATE int64_t get_register(int reg) const;
  double get_double_from_register_pair(int reg);
  // Same for FPURegisters.
  void set_fpu_register(int fpureg, int64_t value);
  void set_fpu_register_word(int fpureg, int32_t value);
  void set_fpu_register_hi_word(int fpureg, int32_t value);
  void set_fpu_register_float(int fpureg, float value);
  void set_fpu_register_double(int fpureg, double value);
  void set_fpu_register_invalid_result64(float original, float rounded);
  void set_fpu_register_invalid_result(float original, float rounded);
  void set_fpu_register_word_invalid_result(float original, float rounded);
  void set_fpu_register_invalid_result64(double original, double rounded);
  void set_fpu_register_invalid_result(double original, double rounded);
  void set_fpu_register_word_invalid_result(double original, double rounded);
  int64_t get_fpu_register(int fpureg) const;
  int32_t get_fpu_register_word(int fpureg) const;
  int32_t get_fpu_register_signed_word(int fpureg) const;
  int32_t get_fpu_register_hi_word(int fpureg) const;
  float get_fpu_register_float(int fpureg) const;
  double get_fpu_register_double(int fpureg) const;
  template <typename T>
  void get_msa_register(int wreg, T* value);
  template <typename T>
  void set_msa_register(int wreg, const T* value);
  void set_fcsr_bit(uint32_t cc, bool value);
  bool test_fcsr_bit(uint32_t cc);
  bool set_fcsr_round_error(double original, double rounded);
  bool set_fcsr_round64_error(double original, double rounded);
  bool set_fcsr_round_error(float original, float rounded);
  bool set_fcsr_round64_error(float original, float rounded);
  void round_according_to_fcsr(double toRound, double* rounded,
                               int32_t* rounded_int, double fs);
  void round64_according_to_fcsr(double toRound, double* rounded,
                                 int64_t* rounded_int, double fs);
  void round_according_to_fcsr(float toRound, float* rounded,
                               int32_t* rounded_int, float fs);
  void round64_according_to_fcsr(float toRound, float* rounded,
                                 int64_t* rounded_int, float fs);
  template <typename T_fp, typename T_int>
  void round_according_to_msacsr(T_fp toRound, T_fp* rounded,
                                 T_int* rounded_int);
  void clear_fcsr_cause();
  void set_fcsr_rounding_mode(FPURoundingMode mode);
  void set_msacsr_rounding_mode(FPURoundingMode mode);
  unsigned int get_fcsr_rounding_mode();
  unsigned int get_msacsr_rounding_mode();
  // Special case of set_register and get_register to access the raw PC value.
  void set_pc(int64_t value);
  V8_EXPORT_PRIVATE int64_t get_pc() const;
 
  Address get_sp() const { return static_cast<Address>(get_register(sp)); }
 
  // Accessor to the internal simulator stack area. Adds a safety
  // margin to prevent overflows (kAdditionalStackMargin).
  uintptr_t StackLimit(uintptr_t c_limit) const;
 
  uintptr_t StackBase() const;
 
  // Return central stack view, without additional safety margins.
  // Users, for example wasm::StackMemory, can add their own.
  base::Vector<uint8_t> GetCentralStackView() const;
  static constexpr int JSStackLimitMargin() { return kAdditionalStackMargin; }
 
  void IterateRegistersAndStack(::heap::base::StackVisitor* visitor);
 
  // Executes MIPS instructions until the PC reaches end_sim_pc.
  void Execute();
 
  // Only arguments up to 64 bits in size are supported.
  class CallArgument {
   public:
    template <typename T>
    explicit CallArgument(T argument) {
      bits_ = 0;
      DCHECK(sizeof(argument) <= sizeof(bits_));
      bits_ = ConvertArg(argument);
      type_ = GP_ARG;
    }
 
    explicit CallArgument(double argument) {
      DCHECK(sizeof(argument) == sizeof(bits_));
      memcpy(&bits_, &argument, sizeof(argument));
      type_ = FP_ARG;
    }
 
    explicit CallArgument(float argument) {
      // TODO(all): CallArgument(float) is untested.
      UNIMPLEMENTED();
    }
 
    // This indicates the end of the arguments list, so that CallArgument
    // objects can be passed into varargs functions.
    static CallArgument End() { return CallArgument(); }
 
    int64_t bits() const { return bits_; }
    bool IsEnd() const { return type_ == NO_ARG; }
    bool IsGP() const { return type_ == GP_ARG; }
    bool IsFP() const { return type_ == FP_ARG; }
 
   private:
    enum CallArgumentType { GP_ARG, FP_ARG, NO_ARG };
 
    // All arguments are aligned to at least 64 bits and we don't support
    // passing bigger arguments, so the payload size can be fixed at 64 bits.
    int64_t bits_;
    CallArgumentType type_;
 
    CallArgument() { type_ = NO_ARG; }
  };
 
  template <typename Return, typename... Args>
  Return Call(Address entry, Args... args) {
    // Convert all arguments to CallArgument.
    CallArgument call_args[] = {CallArgument(args)..., CallArgument::End()};
    CallImpl(entry, call_args);
    return ReadReturn<Return>();
  }
 
  // Alternative: call a 2-argument double function.
  double CallFP(Address entry, double d0, double d1);
 
  // Push an address onto the JS stack.
  V8_EXPORT_PRIVATE uintptr_t PushAddress(uintptr_t address);
 
  // Pop an address from the JS stack.
  V8_EXPORT_PRIVATE uintptr_t PopAddress();
 
  // Debugger input.
  void set_last_debugger_input(char* input);
  char* last_debugger_input() { return last_debugger_input_; }
 
  // Redirection support.
  static void SetRedirectInstruction(Instruction* instruction);
 
  // ICache checking.
  static bool ICacheMatch(void* one, void* two);
  static void FlushICache(base::CustomMatcherHashMap* i_cache, void* start,
                          size_t size);
 
  // Returns true if pc register contains one of the 'special_values' defined
  // below (bad_ra, end_sim_pc).
  bool has_bad_pc() const;
 
 private:
  enum special_values {
    // Known bad pc value to ensure that the simulator does not execute
    // without being properly setup.
    bad_ra = -1,
    // A pc value used to signal the simulator to stop execution.  Generally
    // the ra is set to this value on transition from native C code to
    // simulated execution, so that the simulator can "return" to the native
    // C code.
    end_sim_pc = -2,
    // Unpredictable value.
    Unpredictable = 0xbadbeaf
  };
 
  V8_EXPORT_PRIVATE void CallImpl(Address entry, CallArgument* args);
 
  void CallAnyCTypeFunction(Address target_address,
                            const EncodedCSignature& signature);
 
  // Read floating point return values.
  template <typename T>
  typename std::enable_if<std::is_floating_point<T>::value, T>::type
  ReadReturn() {
    return static_cast<T>(get_fpu_register_double(f0));
  }
  // Read non-float return values.
  template <typename T>
  typename std::enable_if<!std::is_floating_point<T>::value, T>::type
  ReadReturn() {
    return ConvertReturn<T>(get_register(v0));
  }
 
  // Unsupported instructions use Format to print an error and stop execution.
  void Format(Instruction* instr, const char* format);
 
  // Helpers for data value tracing.
  enum TraceType {
    BYTE,
    HALF,
    WORD,
    DWORD,
    FLOAT,
    DOUBLE,
    FLOAT_DOUBLE,
    WORD_DWORD
  };
 
  // MSA Data Format
  enum MSADataFormat { MSA_VECT = 0, MSA_BYTE, MSA_HALF, MSA_WORD, MSA_DWORD };
  union msa_reg_t {
    int8_t b[kMSALanesByte];
    uint8_t ub[kMSALanesByte];
    int16_t h[kMSALanesHalf];
    uint16_t uh[kMSALanesHalf];
    int32_t w[kMSALanesWord];
    uint32_t uw[kMSALanesWord];
    int64_t d[kMSALanesDword];
    uint64_t ud[kMSALanesDword];
  };
 
  // Read and write memory.
  inline uint32_t ReadBU(int64_t addr);
  inline int32_t ReadB(int64_t addr);
  inline void WriteB(int64_t addr, uint8_t value);
  inline void WriteB(int64_t addr, int8_t value);
 
  inline uint16_t ReadHU(int64_t addr, Instruction* instr);
  inline int16_t ReadH(int64_t addr, Instruction* instr);
  // Note: Overloaded on the sign of the value.
  inline void WriteH(int64_t addr, uint16_t value, Instruction* instr);
  inline void WriteH(int64_t addr, int16_t value, Instruction* instr);
 
  inline uint32_t ReadWU(int64_t addr, Instruction* instr);
  inline int32_t ReadW(int64_t addr, Instruction* instr, TraceType t = WORD);
  inline void WriteW(int64_t addr, int32_t value, Instruction* instr);
  void WriteConditionalW(int64_t addr, int32_t value, Instruction* instr,
                         int32_t rt_reg);
  inline int64_t Read2W(int64_t addr, Instruction* instr);
  inline void Write2W(int64_t addr, int64_t value, Instruction* instr);
  inline void WriteConditional2W(int64_t addr, int64_t value,
                                 Instruction* instr, int32_t rt_reg);
 
  inline double ReadD(int64_t addr, Instruction* instr);
  inline void WriteD(int64_t addr, double value, Instruction* instr);
 
  template <typename T>
  T ReadMem(int64_t addr, Instruction* instr);
  template <typename T>
  void WriteMem(int64_t addr, T value, Instruction* instr);
 
  // Helper for debugging memory access.
  inline void DieOrDebug();
 
  void TraceRegWr(int64_t value, TraceType t = DWORD);
  template <typename T>
  void TraceMSARegWr(T* value, TraceType t);
  template <typename T>
  void TraceMSARegWr(T* value);
  void TraceMemWr(int64_t addr, int64_t value, TraceType t);
  void TraceMemRd(int64_t addr, int64_t value, TraceType t = DWORD);
  template <typename T>
  void TraceMemRd(int64_t addr, T value);
  template <typename T>
  void TraceMemWr(int64_t addr, T value);
 
  // Operations depending on endianness.
  // Get Double Higher / Lower word.
  inline int32_t GetDoubleHIW(double* addr);
  inline int32_t GetDoubleLOW(double* addr);
  // Set Double Higher / Lower word.
  inline int32_t SetDoubleHIW(double* addr);
  inline int32_t SetDoubleLOW(double* addr);
 
  SimInstruction instr_;
 
  // functions called from DecodeTypeRegister.
  void DecodeTypeRegisterCOP1();
 
  void DecodeTypeRegisterCOP1X();
 
  void DecodeTypeRegisterSPECIAL();
 
  void DecodeTypeRegisterSPECIAL2();
 
  void DecodeTypeRegisterSPECIAL3();
 
  void DecodeTypeRegisterSRsType();
 
  void DecodeTypeRegisterDRsType();
 
  void DecodeTypeRegisterWRsType();
 
  void DecodeTypeRegisterLRsType();
 
  int DecodeMsaDataFormat();
  void DecodeTypeMsaI8();
  void DecodeTypeMsaI5();
  void DecodeTypeMsaI10();
  void DecodeTypeMsaELM();
  void DecodeTypeMsaBIT();
  void DecodeTypeMsaMI10();
  void DecodeTypeMsa3R();
  void DecodeTypeMsa3RF();
  void DecodeTypeMsaVec();
  void DecodeTypeMsa2R();
  void DecodeTypeMsa2RF();
  template <typename T>
  T MsaI5InstrHelper(uint32_t opcode, T ws, int32_t i5);
  template <typename T>
  T MsaBitInstrHelper(uint32_t opcode, T wd, T ws, int32_t m);
  template <typename T>
  T Msa3RInstrHelper(uint32_t opcode, T wd, T ws, T wt);
 
  // Executing is handled based on the instruction type.
  void DecodeTypeRegister();
 
  inline int32_t rs_reg() const { return instr_.RsValue(); }
  inline int64_t rs() const { return get_register(rs_reg()); }
  inline uint64_t rs_u() const {
    return static_cast<uint64_t>(get_register(rs_reg()));
  }
  inline int32_t rt_reg() const { return instr_.RtValue(); }
  inline int64_t rt() const { return get_register(rt_reg()); }
  inline uint64_t rt_u() const {
    return static_cast<uint64_t>(get_register(rt_reg()));
  }
  inline int32_t rd_reg() const { return instr_.RdValue(); }
  inline int32_t fr_reg() const { return instr_.FrValue(); }
  inline int32_t fs_reg() const { return instr_.FsValue(); }
  inline int32_t ft_reg() const { return instr_.FtValue(); }
  inline int32_t fd_reg() const { return instr_.FdValue(); }
  inline int32_t sa() const { return instr_.SaValue(); }
  inline int32_t lsa_sa() const { return instr_.LsaSaValue(); }
  inline int32_t ws_reg() const { return instr_.WsValue(); }
  inline int32_t wt_reg() const { return instr_.WtValue(); }
  inline int32_t wd_reg() const { return instr_.WdValue(); }
 
  inline void SetResult(const int32_t rd_reg, const int64_t alu_out) {
    set_register(rd_reg, alu_out);
    TraceRegWr(alu_out);
  }
 
  inline void SetFPUWordResult(int32_t fd_reg, int32_t alu_out) {
    set_fpu_register_word(fd_reg, alu_out);
    TraceRegWr(get_fpu_register(fd_reg), WORD);
  }
 
  inline void SetFPUWordResult2(int32_t fd_reg, int32_t alu_out) {
    set_fpu_register_word(fd_reg, alu_out);
    TraceRegWr(get_fpu_register(fd_reg));
  }
 
  inline void SetFPUResult(int32_t fd_reg, int64_t alu_out) {
    set_fpu_register(fd_reg, alu_out);
    TraceRegWr(get_fpu_register(fd_reg));
  }
 
  inline void SetFPUResult2(int32_t fd_reg, int64_t alu_out) {
    set_fpu_register(fd_reg, alu_out);
    TraceRegWr(get_fpu_register(fd_reg), DOUBLE);
  }
 
  inline void SetFPUFloatResult(int32_t fd_reg, float alu_out) {
    set_fpu_register_float(fd_reg, alu_out);
    TraceRegWr(get_fpu_register(fd_reg), FLOAT);
  }
 
  inline void SetFPUDoubleResult(int32_t fd_reg, double alu_out) {
    set_fpu_register_double(fd_reg, alu_out);
    TraceRegWr(get_fpu_register(fd_reg), DOUBLE);
  }
 
  void DecodeTypeImmediate();
  void DecodeTypeJump();
 
  // Used for breakpoints and traps.
  void SoftwareInterrupt();
 
  // Compact branch guard.
  void CheckForbiddenSlot(int64_t current_pc) {
    Instruction* instr_after_compact_branch =
        reinterpret_cast<Instruction*>(current_pc + kInstrSize);
    if (instr_after_compact_branch->IsForbiddenAfterBranch()) {
      FATAL(
          "Error: Unexpected instruction 0x%08x immediately after a "
          "compact branch instruction.",
          *reinterpret_cast<uint32_t*>(instr_after_compact_branch));
    }
  }
 
  // Stop helper functions.
  bool IsWatchpoint(uint64_t code);
  void PrintWatchpoint(uint64_t code);
  void HandleStop(uint64_t code, Instruction* instr);
  bool IsStopInstruction(Instruction* instr);
  bool IsEnabledStop(uint64_t code);
  void EnableStop(uint64_t code);
  void DisableStop(uint64_t code);
  void IncreaseStopCounter(uint64_t code);
  void PrintStopInfo(uint64_t code);
 
  // Executes one instruction.
  void InstructionDecode(Instruction* instr);
  // Execute one instruction placed in a branch delay slot.
  void BranchDelayInstructionDecode(Instruction* instr) {
    if (instr->InstructionBits() == nopInstr) {
      // Short-cut generic nop instructions. They are always valid and they
      // never change the simulator state.
      return;
    }
 
    if (instr->IsForbiddenAfterBranch()) {
      FATAL("Eror:Unexpected %i opcode in a branch delay slot.",
            instr->OpcodeValue());
    }
    InstructionDecode(instr);
    SNPrintF(trace_buf_, " ");
  }
 
  // ICache.
  static void CheckICache(base::CustomMatcherHashMap* i_cache,
                          Instruction* instr);
  static void FlushOnePage(base::CustomMatcherHashMap* i_cache, intptr_t start,
                           size_t size);
  static CachePage* GetCachePage(base::CustomMatcherHashMap* i_cache,
                                 void* page);
 
  enum Exception {
    none,
    kIntegerOverflow,
    kIntegerUnderflow,
    kDivideByZero,
    kNumExceptions
  };
 
  // Exceptions.
  void SignalException(Exception e);
 
  // Handle arguments and return value for runtime FP functions.
  void GetFpArgs(double* x, double* y, int32_t* z);
  void SetFpResult(const double& result);
 
  void CallInternal(Address entry);
 
  // Architecture state.
  // Registers.
  int64_t registers_[kNumSimuRegisters];
  // Coprocessor Registers.
  // Note: FPUregisters_[] array is increased to 64 * 8B = 32 * 16B in
  // order to support MSA registers
  int64_t FPUregisters_[kNumFPURegisters * 2];
  // FPU control register.
  uint32_t FCSR_;
  // MSA control register.
  uint32_t MSACSR_;
 
  // Simulator support.
  uintptr_t stack_;
  static const size_t kStackProtectionSize = KB;
  // This includes a protection margin at each end of the stack area.
  static size_t AllocatedStackSize() {
    return (v8_flags.sim_stack_size * KB) + (2 * kStackProtectionSize);
  }
  static size_t UsableStackSize() { return v8_flags.sim_stack_size * KB; }
  uintptr_t stack_limit_;
  // Added in Simulator::StackLimit()
  static const int kAdditionalStackMargin = 4 * KB;
 
  bool pc_modified_;
  int64_t icount_;
  int break_count_;
  base::EmbeddedVector<char, 128> trace_buf_;
 
  // Debugger input.
  char* last_debugger_input_;
 
  v8::internal::Isolate* isolate_;
 
  // Registered breakpoints.
  Instruction* break_pc_;
  Instr break_instr_;
 
  // Stop is disabled if bit 31 is set.
  static const uint32_t kStopDisabledBit = 1 << 31;
 
  // A stop is enabled, meaning the simulator will stop when meeting the
  // instruction, if bit 31 of watched_stops_[code].count is unset.
  // The value watched_stops_[code].count & ~(1 << 31) indicates how many times
  // the breakpoint was hit or gone through.
  struct StopCountAndDesc {
    uint32_t count;
    char* desc;
  };
  StopCountAndDesc watched_stops_[kMaxStopCode + 1];
 
  // Synchronization primitives.
  enum class MonitorAccess {
    Open,
    RMW,
  };
 
  enum class TransactionSize {
    None = 0,
    Word = 4,
    DoubleWord = 8,
  };
 
  // The least-significant bits of the address are ignored. The number of bits
  // is implementation-defined, between 3 and minimum page size.
  static const uintptr_t kExclusiveTaggedAddrMask = ~((1 << 3) - 1);
 
  class LocalMonitor {
   public:
    LocalMonitor();
 
    // These functions manage the state machine for the local monitor, but do
    // not actually perform loads and stores. NotifyStoreConditional only
    // returns true if the store conditional is allowed; the global monitor will
    // still have to be checked to see whether the memory should be updated.
    void NotifyLoad();
    void NotifyLoadLinked(uintptr_t addr, TransactionSize size);
    void NotifyStore();
    bool NotifyStoreConditional(uintptr_t addr, TransactionSize size);
 
   private:
    void Clear();
 
    MonitorAccess access_state_;
    uintptr_t tagged_addr_;
    TransactionSize size_;
  };
 
  class GlobalMonitor {
   public:
    class LinkedAddress {
     public:
      LinkedAddress();
 
     private:
      friend class GlobalMonitor;
      // These functions manage the state machine for the global monitor, but do
      // not actually perform loads and stores.
      void Clear_Locked();
      void NotifyLoadLinked_Locked(uintptr_t addr);
      void NotifyStore_Locked();
      bool NotifyStoreConditional_Locked(uintptr_t addr,
                                         bool is_requesting_thread);
 
      MonitorAccess access_state_;
      uintptr_t tagged_addr_;
      LinkedAddress* next_;
      LinkedAddress* prev_;
      // A scd can fail due to background cache evictions. Rather than
      // simulating this, we'll just occasionally introduce cases where an
      // store conditional fails. This will happen once after every
      // kMaxFailureCounter exclusive stores.
      static const int kMaxFailureCounter = 5;
      int failure_counter_;
    };
 
    // Exposed so it can be accessed by Simulator::{Read,Write}Ex*.
    base::Mutex mutex;
 
    void NotifyLoadLinked_Locked(uintptr_t addr, LinkedAddress* linked_address);
    void NotifyStore_Locked(LinkedAddress* linked_address);
    bool NotifyStoreConditional_Locked(uintptr_t addr,
                                       LinkedAddress* linked_address);
 
    // Called when the simulator is destroyed.
    void RemoveLinkedAddress(LinkedAddress* linked_address);
 
    static GlobalMonitor* Get();
 
   private:
    // Private constructor. Call {GlobalMonitor::Get()} to get the singleton.
    GlobalMonitor() = default;
    friend class base::LeakyObject<GlobalMonitor>;
 
    bool IsProcessorInLinkedList_Locked(LinkedAddress* linked_address) const;
    void PrependProcessor_Locked(LinkedAddress* linked_address);
 
    LinkedAddress* head_ = nullptr;
  };
 
  LocalMonitor local_monitor_;
  GlobalMonitor::LinkedAddress global_monitor_thread_;
};
 
}  // namespace internal
}  // namespace v8
 
#endif  // defined(USE_SIMULATOR)
#endif  // V8_EXECUTION_MIPS64_SIMULATOR_MIPS64_H_