// Copyright 2012 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
//       copyright notice, this list of conditions and the following
//       disclaimer in the documentation and/or other materials provided
//       with the distribution.
//     * Neither the name of Google Inc. nor the names of its
//       contributors may be used to endorse or promote products derived
//       from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#include "jit/arm/Simulator-arm.h"

#include "mozilla/Casting.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/EndianUtils.h"
#include "mozilla/Likely.h"

#include <bit>

#include "jit/arm/Assembler-arm.h"
#include "jit/arm/disasm/Constants-arm.h"
#include "jit/AtomicOperations.h"
#include "js/UniquePtr.h"
#include "js/Utility.h"
#include "threading/LockGuard.h"
#include "vm/Float16.h"
#include "vm/JSContext.h"
#include "vm/Runtime.h"
#include "vm/SharedMem.h"
#include "wasm/WasmInstance.h"
#include "wasm/WasmSignalHandlers.h"

extern "C" {

MOZ_EXPORT int64_t __aeabi_idivmod(int x, int y) {
  // Run-time ABI for the ARM architecture specifies that for |INT_MIN / -1|
  // "an implementation is (sic) may return any convenient value, possibly the
  // original numerator."
  //
  // |INT_MIN / -1| traps on x86, which isn't listed as an allowed behavior in
  // the ARM docs, so instead follow LLVM and return the numerator. (And zero
  // for the remainder.)

  if (x == INT32_MIN && y == -1) {
    return uint32_t(x);
  }

  uint32_t lo = uint32_t(x / y);
  uint32_t hi = uint32_t(x % y);
  return (int64_t(hi) << 32) | lo;
}

MOZ_EXPORT int64_t __aeabi_uidivmod(int x, int y) {
  uint32_t lo = uint32_t(x) / uint32_t(y);
  uint32_t hi = uint32_t(x) % uint32_t(y);
  return (int64_t(hi) << 32) | lo;
}
}

namespace js {
namespace jit {

// For decoding load-exclusive and store-exclusive instructions.
namespace excl {

// Bit positions.
enum {
  ExclusiveOpHi = 24,    // Hi bit of opcode field
  ExclusiveOpLo = 23,    // Lo bit of opcode field
  ExclusiveSizeHi = 22,  // Hi bit of operand size field
  ExclusiveSizeLo = 21,  // Lo bit of operand size field
  ExclusiveLoad = 20     // Bit indicating load
};

// Opcode bits for exclusive instructions.
enum { ExclusiveOpcode = 3 };

// Operand size, Bits(ExclusiveSizeHi,ExclusiveSizeLo).
enum {
  ExclusiveWord = 0,
  ExclusiveDouble = 1,
  ExclusiveByte = 2,
  ExclusiveHalf = 3
};

}  // namespace excl

// Load/store multiple addressing mode.
enum BlockAddrMode {
  // Alias modes for comparison when writeback does not matter.
  da_x = (0 | 0 | 0) << 21,  // Decrement after.
  ia_x = (0 | 4 | 0) << 21,  // Increment after.
  db_x = (8 | 0 | 0) << 21,  // Decrement before.
  ib_x = (8 | 4 | 0) << 21,  // Increment before.
};

// Type of VFP register. Determines register encoding.
enum VFPRegPrecision { kSinglePrecision = 0, kDoublePrecision = 1 };

enum NeonListType { nlt_1 = 0x7, nlt_2 = 0xA, nlt_3 = 0x6, nlt_4 = 0x2 };

// Supervisor Call (svc) specific support.

// Special Software Interrupt codes when used in the presence of the ARM
// simulator.
// svc (formerly swi) provides a 24bit immediate value. Use bits 22:0 for
// standard SoftwareInterrupCode. Bit 23 is reserved for the stop feature.
enum SoftwareInterruptCodes {
  kCallRtRedirected = 0x10,  // Transition to C code.
  kBreakpoint = 0x20,        // Breakpoint.
  kStopCode = 1 << 23        // Stop.
};

const uint32_t kStopCodeMask = kStopCode - 1;
const uint32_t kMaxStopCode = kStopCode - 1;

// -----------------------------------------------------------------------------
// Instruction abstraction.

// The class Instruction enables access to individual fields defined in the ARM
// architecture instruction set encoding as described in figure A3-1.
// Note that the Assembler uses using Instr = int32_t.
//
// Example: Test whether the instruction at ptr does set the condition code
// bits.
//
// bool InstructionSetsConditionCodes(byte* ptr) {
//   Instruction* instr = Instruction::At(ptr);
//   int type = instr->TypeValue();
//   return ((type == 0) || (type == 1)) && instr->hasS();
// }
//
class SimInstruction {
 public:
  enum { kInstrSize = 4, kPCReadOffset = 8 };

  // Get the raw instruction bits.
  inline Instr instructionBits() const {
    return *reinterpret_cast<const Instr*>(this);
  }

  // Set the raw instruction bits to value.
  inline void setInstructionBits(Instr value) {
    *reinterpret_cast<Instr*>(this) = value;
  }

  // Read one particular bit out of the instruction bits.
  inline int bit(int nr) const { return (instructionBits() >> nr) & 1; }

  // Read a bit field's value out of the instruction bits.
  inline int bits(int hi, int lo) const {
    return (instructionBits() >> lo) & ((2 << (hi - lo)) - 1);
  }

  // Read a bit field out of the instruction bits.
  inline int bitField(int hi, int lo) const {
    return instructionBits() & (((2 << (hi - lo)) - 1) << lo);
  }

  // Accessors for the different named fields used in the ARM encoding.
  // The naming of these accessor corresponds to figure A3-1.
  //
  // Two kind of accessors are declared:
  // - <Name>Field() will return the raw field, i.e. the field's bits at their
  //   original place in the instruction encoding.
  //   e.g. if instr is the 'addgt r0, r1, r2' instruction, encoded as
  //   0xC0810002 conditionField(instr) will return 0xC0000000.
  // - <Name>Value() will return the field value, shifted back to bit 0.
  //   e.g. if instr is the 'addgt r0, r1, r2' instruction, encoded as
  //   0xC0810002 conditionField(instr) will return 0xC.

  // Generally applicable fields
  inline Assembler::ARMCondition conditionField() const {
    return static_cast<Assembler::ARMCondition>(bitField(31, 28));
  }
  inline int typeValue() const { return bits(27, 25); }
  inline int specialValue() const { return bits(27, 23); }

  inline int rnValue() const { return bits(19, 16); }
  inline int rdValue() const { return bits(15, 12); }

  inline int coprocessorValue() const { return bits(11, 8); }

  // Support for VFP.
  // Vn(19-16) | Vd(15-12) |  Vm(3-0)
  inline int vnValue() const { return bits(19, 16); }
  inline int vmValue() const { return bits(3, 0); }
  inline int vdValue() const { return bits(15, 12); }
  inline int nValue() const { return bit(7); }
  inline int mValue() const { return bit(5); }
  inline int dValue() const { return bit(22); }
  inline int rtValue() const { return bits(15, 12); }
  inline int pValue() const { return bit(24); }
  inline int uValue() const { return bit(23); }
  inline int opc1Value() const { return (bit(23) << 2) | bits(21, 20); }
  inline int opc2Value() const { return bits(19, 16); }
  inline int opc3Value() const { return bits(7, 6); }
  inline int szValue() const { return bit(8); }
  inline int VLValue() const { return bit(20); }
  inline int VCValue() const { return bit(8); }
  inline int VAValue() const { return bits(23, 21); }
  inline int VBValue() const { return bits(6, 5); }
  inline int VFPNRegValue(VFPRegPrecision pre) {
    return VFPGlueRegValue(pre, 16, 7);
  }
  inline int VFPMRegValue(VFPRegPrecision pre) {
    return VFPGlueRegValue(pre, 0, 5);
  }
  inline int VFPDRegValue(VFPRegPrecision pre) {
    return VFPGlueRegValue(pre, 12, 22);
  }

  // Fields used in Data processing instructions.
  inline int opcodeValue() const { return static_cast<ALUOp>(bits(24, 21)); }
  inline ALUOp opcodeField() const {
    return static_cast<ALUOp>(bitField(24, 21));
  }
  inline int sValue() const { return bit(20); }

  // With register.
  inline int rmValue() const { return bits(3, 0); }
  inline ShiftType shifttypeValue() const {
    return static_cast<ShiftType>(bits(6, 5));
  }
  inline int rsValue() const { return bits(11, 8); }
  inline int shiftAmountValue() const { return bits(11, 7); }

  // With immediate.
  inline int rotateValue() const { return bits(11, 8); }
  inline int immed8Value() const { return bits(7, 0); }
  inline int immed4Value() const { return bits(19, 16); }
  inline int immedMovwMovtValue() const {
    return immed4Value() << 12 | offset12Value();
  }

  // Fields used in Load/Store instructions.
  inline int PUValue() const { return bits(24, 23); }
  inline int PUField() const { return bitField(24, 23); }
  inline int bValue() const { return bit(22); }
  inline int wValue() const { return bit(21); }
  inline int lValue() const { return bit(20); }

  // With register uses same fields as Data processing instructions above with
  // immediate.
  inline int offset12Value() const { return bits(11, 0); }

  // Multiple.
  inline int rlistValue() const { return bits(15, 0); }

  // Extra loads and stores.
  inline int signValue() const { return bit(6); }
  inline int hValue() const { return bit(5); }
  inline int immedHValue() const { return bits(11, 8); }
  inline int immedLValue() const { return bits(3, 0); }

  // Fields used in Branch instructions.
  inline int linkValue() const { return bit(24); }
  inline int sImmed24Value() const { return ((instructionBits() << 8) >> 8); }

  // Fields used in Software interrupt instructions.
  inline SoftwareInterruptCodes svcValue() const {
    return static_cast<SoftwareInterruptCodes>(bits(23, 0));
  }

  // Test for special encodings of type 0 instructions (extra loads and
  // stores, as well as multiplications).
  inline bool isSpecialType0() const { return (bit(7) == 1) && (bit(4) == 1); }

  // Test for miscellaneous instructions encodings of type 0 instructions.
  inline bool isMiscType0() const {
    return bit(24) == 1 && bit(23) == 0 && bit(20) == 0 && (bit(7) == 0);
  }

  // Test for a nop instruction, which falls under type 1.
  inline bool isNopType1() const { return bits(24, 0) == 0x0120F000; }

  // Test for a yield instruction, which falls under type 1.
  inline bool isYieldType1() const { return bits(24, 0) == 0x0120F001; }

  // Test for a nop instruction, which falls under type 1.
  inline bool isCsdbType1() const { return bits(24, 0) == 0x0120F014; }

  // Test for a stop instruction.
  inline bool isStop() const {
    return typeValue() == 7 && bit(24) == 1 && svcValue() >= kStopCode;
  }

  // Test for a udf instruction, which falls under type 3.
  inline bool isUDF() const {
    return (instructionBits() & 0xfff000f0) == 0xe7f000f0;
  }

  // Special accessors that test for existence of a value.
  inline bool hasS() const { return sValue() == 1; }
  inline bool hasB() const { return bValue() == 1; }
  inline bool hasW() const { return wValue() == 1; }
  inline bool hasL() const { return lValue() == 1; }
  inline bool hasU() const { return uValue() == 1; }
  inline bool hasSign() const { return signValue() == 1; }
  inline bool hasH() const { return hValue() == 1; }
  inline bool hasLink() const { return linkValue() == 1; }

  // Decoding the double immediate in the vmov instruction.
  double doubleImmedVmov() const;
  // Decoding the float32 immediate in the vmov.f32 instruction.
  float float32ImmedVmov() const;

 private:
  // Join split register codes, depending on single or double precision.
  // four_bit is the position of the least-significant bit of the four
  // bit specifier. one_bit is the position of the additional single bit
  // specifier.
  inline int VFPGlueRegValue(VFPRegPrecision pre, int four_bit, int one_bit) {
    if (pre == kSinglePrecision) {
      return (bits(four_bit + 3, four_bit) << 1) | bit(one_bit);
    }
    return (bit(one_bit) << 4) | bits(four_bit + 3, four_bit);
  }

  SimInstruction() = delete;
  SimInstruction(const SimInstruction& other) = delete;
  void operator=(const SimInstruction& other) = delete;
};

double SimInstruction::doubleImmedVmov() const {
  // Reconstruct a double from the immediate encoded in the vmov instruction.
  //
  //   instruction: [xxxxxxxx,xxxxabcd,xxxxxxxx,xxxxefgh]
  //   double: [aBbbbbbb,bbcdefgh,00000000,00000000,
  //            00000000,00000000,00000000,00000000]
  //
  // where B = ~b. Only the high 16 bits are affected.
  uint64_t high16;
  high16 = (bits(17, 16) << 4) | bits(3, 0);  // xxxxxxxx,xxcdefgh.
  high16 |= (0xff * bit(18)) << 6;            // xxbbbbbb,bbxxxxxx.
  high16 |= (bit(18) ^ 1) << 14;              // xBxxxxxx,xxxxxxxx.
  high16 |= bit(19) << 15;                    // axxxxxxx,xxxxxxxx.

  uint64_t imm = high16 << 48;
  return mozilla::BitwiseCast<double>(imm);
}

float SimInstruction::float32ImmedVmov() const {
  // Reconstruct a float32 from the immediate encoded in the vmov instruction.
  //
  //   instruction: [xxxxxxxx,xxxxabcd,xxxxxxxx,xxxxefgh]
  //   float32: [aBbbbbbc, defgh000, 00000000, 00000000]
  //
  // where B = ~b. Only the high 16 bits are affected.
  uint32_t imm;
  imm = (bits(17, 16) << 23) | (bits(3, 0) << 19);  // xxxxxxxc,defgh000.0.0
  imm |= (0x1f * bit(18)) << 25;                    // xxbbbbbx,xxxxxxxx.0.0
  imm |= (bit(18) ^ 1) << 30;                       // xBxxxxxx,xxxxxxxx.0.0
  imm |= bit(19) << 31;                             // axxxxxxx,xxxxxxxx.0.0

  return mozilla::BitwiseCast<float>(imm);
}

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.
};

// Protects the icache() and redirection() properties of the
// Simulator.
class AutoLockSimulatorCache : public LockGuard<Mutex> {
  using Base = LockGuard<Mutex>;

 public:
  explicit AutoLockSimulatorCache()
      : Base(SimulatorProcess::singleton_->cacheLock_) {}
};

mozilla::Atomic<size_t, mozilla::ReleaseAcquire>
    SimulatorProcess::ICacheCheckingDisableCount(
        1);  // Checking is disabled by default.
SimulatorProcess* SimulatorProcess::singleton_ = nullptr;

int64_t Simulator::StopSimAt = -1L;

Simulator* Simulator::Create() {
  auto sim = MakeUnique<Simulator>();
  if (!sim) {
    return nullptr;
  }

  if (!sim->init()) {
    return nullptr;
  }

  char* stopAtStr = getenv("ARM_SIM_STOP_AT");
  int64_t stopAt;
  if (stopAtStr && sscanf(stopAtStr, "%lld", &stopAt) == 1) {
    fprintf(stderr, "\nStopping simulation at icount %lld\n", stopAt);
    Simulator::StopSimAt = stopAt;
  }

  return sim.release();
}

void Simulator::Destroy(Simulator* sim) { js_delete(sim); }

void Simulator::disassemble(SimInstruction* instr, size_t n) {
#ifdef JS_DISASM_ARM
  disasm::NameConverter converter;
  disasm::Disassembler dasm(converter);
  disasm::EmbeddedVector<char, disasm::ReasonableBufferSize> buffer;
  while (n-- > 0) {
    dasm.InstructionDecode(buffer, reinterpret_cast<uint8_t*>(instr));
    fprintf(stderr, "  0x%08x  %s\n", uint32_t(instr), buffer.start());
    instr = reinterpret_cast<SimInstruction*>(
        reinterpret_cast<uint8_t*>(instr) + 4);
  }
#endif
}

void Simulator::disasm(SimInstruction* instr) { disassemble(instr, 1); }

void Simulator::disasm(SimInstruction* instr, size_t n) {
  disassemble(instr, n);
}

void Simulator::disasm(SimInstruction* instr, size_t m, size_t n) {
  disassemble(reinterpret_cast<SimInstruction*>(
                  reinterpret_cast<uint8_t*>(instr) - m * 4),
              n);
}

// The ArmDebugger class is used by the simulator while debugging simulated ARM
// code.
class ArmDebugger {
 public:
  explicit ArmDebugger(Simulator* sim) : sim_(sim) {}

  void stop(SimInstruction* instr);
  void debug();

 private:
  static const Instr kBreakpointInstr =
      (Assembler::AL | (7 * (1 << 25)) | (1 * (1 << 24)) | kBreakpoint);
  static const Instr kNopInstr = (Assembler::AL | (13 * (1 << 21)));

  Simulator* sim_;

  int32_t getRegisterValue(int regnum);
  double getRegisterPairDoubleValue(int regnum);
  void getVFPDoubleRegisterValue(int regnum, double* value);
  bool getValue(const char* desc, int32_t* value);
  bool getVFPDoubleValue(const char* desc, double* value);

  // Set or delete a breakpoint. Returns true if successful.
  bool setBreakpoint(SimInstruction* breakpc);
  bool deleteBreakpoint(SimInstruction* breakpc);

  // Undo and redo all breakpoints. This is needed to bracket disassembly and
  // execution to skip past breakpoints when run from the debugger.
  void undoBreakpoints();
  void redoBreakpoints();
};

void ArmDebugger::stop(SimInstruction* instr) {
  // Get the stop code.
  uint32_t code = instr->svcValue() & kStopCodeMask;
  // Retrieve the encoded address, which comes just after this stop.
  char* msg =
      *reinterpret_cast<char**>(sim_->get_pc() + SimInstruction::kInstrSize);
  // Update this stop description.
  if (sim_->isWatchedStop(code) && !sim_->watched_stops_[code].desc) {
    sim_->watched_stops_[code].desc = msg;
  }
  // Print the stop message and code if it is not the default code.
  if (code != kMaxStopCode) {
    printf("Simulator hit stop %u: %s\n", code, msg);
  } else {
    printf("Simulator hit %s\n", msg);
  }
  sim_->set_pc(sim_->get_pc() + 2 * SimInstruction::kInstrSize);
  debug();
}

int32_t ArmDebugger::getRegisterValue(int regnum) {
  if (regnum == Registers::pc) {
    return sim_->get_pc();
  }
  return sim_->get_register(regnum);
}

double ArmDebugger::getRegisterPairDoubleValue(int regnum) {
  return sim_->get_double_from_register_pair(regnum);
}

void ArmDebugger::getVFPDoubleRegisterValue(int regnum, double* out) {
  sim_->get_double_from_d_register(regnum, out);
}

bool ArmDebugger::getValue(const char* desc, int32_t* value) {
  Register reg = Register::FromName(desc);
  if (reg != InvalidReg) {
    *value = getRegisterValue(reg.code());
    return true;
  }
  if (strncmp(desc, "0x", 2) == 0) {
    return sscanf(desc + 2, "%x", reinterpret_cast<uint32_t*>(value)) == 1;
  }
  return sscanf(desc, "%u", reinterpret_cast<uint32_t*>(value)) == 1;
}

bool ArmDebugger::getVFPDoubleValue(const char* desc, double* value) {
  FloatRegister reg = FloatRegister::FromCode(FloatRegister::FromName(desc));
  if (reg.isInvalid()) {
    return false;
  }

  if (reg.isSingle()) {
    float fval;
    sim_->get_float_from_s_register(reg.id(), &fval);
    *value = fval;
    return true;
  }

  sim_->get_double_from_d_register(reg.id(), value);
  return true;
}

bool ArmDebugger::setBreakpoint(SimInstruction* breakpc) {
  // Check if a breakpoint can be set. If not return without any side-effects.
  if (sim_->break_pc_) {
    return false;
  }

  // Set the breakpoint.
  sim_->break_pc_ = breakpc;
  sim_->break_instr_ = breakpc->instructionBits();
  // Not setting the breakpoint instruction in the code itself. It will be set
  // when the debugger shell continues.
  return true;
}

bool ArmDebugger::deleteBreakpoint(SimInstruction* breakpc) {
  if (sim_->break_pc_ != nullptr) {
    sim_->break_pc_->setInstructionBits(sim_->break_instr_);
  }

  sim_->break_pc_ = nullptr;
  sim_->break_instr_ = 0;
  return true;
}

void ArmDebugger::undoBreakpoints() {
  if (sim_->break_pc_) {
    sim_->break_pc_->setInstructionBits(sim_->break_instr_);
  }
}

void ArmDebugger::redoBreakpoints() {
  if (sim_->break_pc_) {
    sim_->break_pc_->setInstructionBits(kBreakpointInstr);
  }
}

static char* ReadLine(const char* prompt) {
  UniqueChars result;
  char line_buf[256];
  int offset = 0;
  bool keep_going = true;
  fprintf(stdout, "%s", prompt);
  fflush(stdout);
  while (keep_going) {
    if (fgets(line_buf, sizeof(line_buf), stdin) == nullptr) {
      // fgets got an error. Just give up.
      return nullptr;
    }
    int len = strlen(line_buf);
    if (len > 0 && line_buf[len - 1] == '\n') {
      // Since we read a new line we are done reading the line. This will
      // exit the loop after copying this buffer into the result.
      keep_going = false;
    }
    if (!result) {
      // Allocate the initial result and make room for the terminating
      // '\0'.
      result.reset(js_pod_malloc<char>(len + 1));
      if (!result) {
        return nullptr;
      }
    } else {
      // Allocate a new result with enough room for the new addition.
      int new_len = offset + len + 1;
      char* new_result = js_pod_malloc<char>(new_len);
      if (!new_result) {
        return nullptr;
      }
      // Copy the existing input into the new array and set the new
      // array as the result.
      memcpy(new_result, result.get(), offset * sizeof(char));
      result.reset(new_result);
    }
    // Copy the newly read line into the result.
    memcpy(result.get() + offset, line_buf, len * sizeof(char));
    offset += len;
  }

  MOZ_ASSERT(result);
  result[offset] = '\0';
  return result.release();
}

void ArmDebugger::debug() {
  intptr_t last_pc = -1;
  bool done = false;

#define COMMAND_SIZE 63
#define ARG_SIZE 255

#define STR(a) #a
#define XSTR(a) STR(a)

  char cmd[COMMAND_SIZE + 1];
  char arg1[ARG_SIZE + 1];
  char arg2[ARG_SIZE + 1];
  char* argv[3] = {cmd, arg1, arg2};

  // Make sure to have a proper terminating character if reaching the limit.
  cmd[COMMAND_SIZE] = 0;
  arg1[ARG_SIZE] = 0;
  arg2[ARG_SIZE] = 0;

  // Undo all set breakpoints while running in the debugger shell. This will
  // make them invisible to all commands.
  undoBreakpoints();

#ifndef JS_DISASM_ARM
  static bool disasm_warning_printed = false;
  if (!disasm_warning_printed) {
    printf(
        "  No ARM disassembler present.  Enable JS_DISASM_ARM in "
        "configure.in.");
    disasm_warning_printed = true;
  }
#endif

  while (!done && !sim_->has_bad_pc()) {
    if (last_pc != sim_->get_pc()) {
#ifdef JS_DISASM_ARM
      disasm::NameConverter converter;
      disasm::Disassembler dasm(converter);
      disasm::EmbeddedVector<char, disasm::ReasonableBufferSize> buffer;
      dasm.InstructionDecode(buffer,
                             reinterpret_cast<uint8_t*>(sim_->get_pc()));
      printf("  0x%08x  %s\n", sim_->get_pc(), buffer.start());
#endif
      last_pc = sim_->get_pc();
    }
    char* line = ReadLine("sim> ");
    if (line == nullptr) {
      break;
    } else {
      char* last_input = sim_->lastDebuggerInput();
      if (strcmp(line, "\n") == 0 && last_input != nullptr) {
        line = last_input;
      } else {
        // Ownership is transferred to sim_;
        sim_->setLastDebuggerInput(line);
      }

      // Use sscanf to parse the individual parts of the command line. At the
      // moment no command expects more than two parameters.
      int argc = sscanf(line,
                              "%" XSTR(COMMAND_SIZE) "s "
                              "%" XSTR(ARG_SIZE) "s "
                              "%" XSTR(ARG_SIZE) "s",
                              cmd, arg1, arg2);
      if (argc < 0) {
        continue;
      } else if ((strcmp(cmd, "si") == 0) || (strcmp(cmd, "stepi") == 0)) {
        sim_->instructionDecode(
            reinterpret_cast<SimInstruction*>(sim_->get_pc()));
        sim_->icount_++;
      } else if ((strcmp(cmd, "skip") == 0)) {
        sim_->set_pc(sim_->get_pc() + 4);
        sim_->icount_++;
      } else if ((strcmp(cmd, "c") == 0) || (strcmp(cmd, "cont") == 0)) {
        // Execute the one instruction we broke at with breakpoints
        // disabled.
        sim_->instructionDecode(
            reinterpret_cast<SimInstruction*>(sim_->get_pc()));
        sim_->icount_++;
        // Leave the debugger shell.
        done = true;
      } else if ((strcmp(cmd, "p") == 0) || (strcmp(cmd, "print") == 0)) {
        if (argc == 2 || (argc == 3 && strcmp(arg2, "fp") == 0)) {
          int32_t value;
          double dvalue;
          if (strcmp(arg1, "all") == 0) {
            for (uint32_t i = 0; i < Registers::Total; i++) {
              value = getRegisterValue(i);
              printf("%3s: 0x%08x %10d", Registers::GetName(i), value, value);
              if ((argc == 3 && strcmp(arg2, "fp") == 0) && i < 8 &&
                  (i % 2) == 0) {
                dvalue = getRegisterPairDoubleValue(i);
                printf(" (%.16g)\n", dvalue);
              } else {
                printf("\n");
              }
            }
            for (uint32_t i = 0; i < FloatRegisters::TotalPhys; i++) {
              getVFPDoubleRegisterValue(i, &dvalue);
              uint64_t as_words = mozilla::BitwiseCast<uint64_t>(dvalue);
              printf("%3s: %.16g 0x%08x %08x\n",
                     FloatRegister::FromCode(i).name(), dvalue,
                     static_cast<uint32_t>(as_words >> 32),
                     static_cast<uint32_t>(as_words & 0xffffffff));
            }
          } else {
            if (getValue(arg1, &value)) {
              printf("%s: 0x%08x %d \n", arg1, value, value);
            } else if (getVFPDoubleValue(arg1, &dvalue)) {
              uint64_t as_words = mozilla::BitwiseCast<uint64_t>(dvalue);
              printf("%s: %.16g 0x%08x %08x\n", arg1, dvalue,
                     static_cast<uint32_t>(as_words >> 32),
                     static_cast<uint32_t>(as_words & 0xffffffff));
            } else {
              printf("%s unrecognized\n", arg1);
            }
          }
        } else {
          printf("print <register>\n");
        }
      } else if (strcmp(cmd, "stack") == 0 || strcmp(cmd, "mem") == 0) {
        int32_t* cur = nullptr;
        int32_t* end = nullptr;
        int next_arg = 1;

        if (strcmp(cmd, "stack") == 0) {
          cur = reinterpret_cast<int32_t*>(sim_->get_register(Simulator::sp));
        } else {  // "mem"
          int32_t value;
          if (!getValue(arg1, &value)) {
            printf("%s unrecognized\n", arg1);
            continue;
          }
          cur = reinterpret_cast<int32_t*>(value);
          next_arg++;
        }

        int32_t words;
        if (argc == next_arg) {
          words = 10;
        } else {
          if (!getValue(argv[next_arg], &words)) {
            words = 10;
          }
        }
        end = cur + words;

        while (cur < end) {
          printf("  %p:  0x%08x %10d", cur, *cur, *cur);
          printf("\n");
          cur++;
        }
      } else if (strcmp(cmd, "disasm") == 0 || strcmp(cmd, "di") == 0) {
#ifdef JS_DISASM_ARM
        uint8_t* prev = nullptr;
        uint8_t* cur = nullptr;
        uint8_t* end = nullptr;

        if (argc == 1) {
          cur = reinterpret_cast<uint8_t*>(sim_->get_pc());
          end = cur + (10 * SimInstruction::kInstrSize);
        } else if (argc == 2) {
          Register reg = Register::FromName(arg1);
          if (reg != InvalidReg || strncmp(arg1, "0x", 2) == 0) {
            // The argument is an address or a register name.
            int32_t value;
            if (getValue(arg1, &value)) {
              cur = reinterpret_cast<uint8_t*>(value);
              // Disassemble 10 instructions at <arg1>.
              end = cur + (10 * SimInstruction::kInstrSize);
            }
          } else {
            // The argument is the number of instructions.
            int32_t value;
            if (getValue(arg1, &value)) {
              cur = reinterpret_cast<uint8_t*>(sim_->get_pc());
              // Disassemble <arg1> instructions.
              end = cur + (value * SimInstruction::kInstrSize);
            }
          }
        } else {
          int32_t value1;
          int32_t value2;
          if (getValue(arg1, &value1) && getValue(arg2, &value2)) {
            cur = reinterpret_cast<uint8_t*>(value1);
            end = cur + (value2 * SimInstruction::kInstrSize);
          }
        }
        while (cur < end) {
          disasm::NameConverter converter;
          disasm::Disassembler dasm(converter);
          disasm::EmbeddedVector<char, disasm::ReasonableBufferSize> buffer;

          prev = cur;
          cur += dasm.InstructionDecode(buffer, cur);
          printf("  0x%08x  %s\n", reinterpret_cast<uint32_t>(prev),
                 buffer.start());
        }
#endif
      } else if (strcmp(cmd, "gdb") == 0) {
        printf("relinquishing control to gdb\n");
#ifdef _MSC_VER
        __debugbreak();
#else
        asm("int $3");
#endif
        printf("regaining control from gdb\n");
      } else if (strcmp(cmd, "break") == 0) {
        if (argc == 2) {
          int32_t value;
          if (getValue(arg1, &value)) {
            if (!setBreakpoint(reinterpret_cast<SimInstruction*>(value))) {
              printf("setting breakpoint failed\n");
            }
          } else {
            printf("%s unrecognized\n", arg1);
          }
        } else {
          printf("break <address>\n");
        }
      } else if (strcmp(cmd, "del") == 0) {
        if (!deleteBreakpoint(nullptr)) {
          printf("deleting breakpoint failed\n");
        }
      } else if (strcmp(cmd, "flags") == 0) {
        printf("N flag: %d; ", sim_->n_flag_);
        printf("Z flag: %d; ", sim_->z_flag_);
        printf("C flag: %d; ", sim_->c_flag_);
        printf("V flag: %d\n", sim_->v_flag_);
        printf("INVALID OP flag: %d; ", sim_->inv_op_vfp_flag_);
        printf("DIV BY ZERO flag: %d; ", sim_->div_zero_vfp_flag_);
        printf("OVERFLOW flag: %d; ", sim_->overflow_vfp_flag_);
        printf("UNDERFLOW flag: %d; ", sim_->underflow_vfp_flag_);
        printf("INEXACT flag: %d;\n", sim_->inexact_vfp_flag_);
      } else if (strcmp(cmd, "stop") == 0) {
        int32_t value;
        intptr_t stop_pc = sim_->get_pc() - 2 * SimInstruction::kInstrSize;
        SimInstruction* stop_instr = reinterpret_cast<SimInstruction*>(stop_pc);
        SimInstruction* msg_address = reinterpret_cast<SimInstruction*>(
            stop_pc + SimInstruction::kInstrSize);
        if ((argc == 2) && (strcmp(arg1, "unstop") == 0)) {
          // Remove the current stop.
          if (sim_->isStopInstruction(stop_instr)) {
            stop_instr->setInstructionBits(kNopInstr);
            msg_address->setInstructionBits(kNopInstr);
          } else {
            printf("Not at debugger stop.\n");
          }
        } else if (argc == 3) {
          // Print information about all/the specified breakpoint(s).
          if (strcmp(arg1, "info") == 0) {
            if (strcmp(arg2, "all") == 0) {
              printf("Stop information:\n");
              for (uint32_t i = 0; i < sim_->kNumOfWatchedStops; i++) {
                sim_->printStopInfo(i);
              }
            } else if (getValue(arg2, &value)) {
              sim_->printStopInfo(value);
            } else {
              printf("Unrecognized argument.\n");
            }
          } else if (strcmp(arg1, "enable") == 0) {
            // Enable all/the specified breakpoint(s).
            if (strcmp(arg2, "all") == 0) {
              for (uint32_t i = 0; i < sim_->kNumOfWatchedStops; i++) {
                sim_->enableStop(i);
              }
            } else if (getValue(arg2, &value)) {
              sim_->enableStop(value);
            } else {
              printf("Unrecognized argument.\n");
            }
          } else if (strcmp(arg1, "disable") == 0) {
            // Disable all/the specified breakpoint(s).
            if (strcmp(arg2, "all") == 0) {
              for (uint32_t i = 0; i < sim_->kNumOfWatchedStops; i++) {
                sim_->disableStop(i);
              }
            } else if (getValue(arg2, &value)) {
              sim_->disableStop(value);
            } else {
              printf("Unrecognized argument.\n");
            }
          }
        } else {
          printf("Wrong usage. Use help command for more information.\n");
        }
      } else if ((strcmp(cmd, "h") == 0) || (strcmp(cmd, "help") == 0)) {
        printf("cont\n");
        printf("  continue execution (alias 'c')\n");
        printf("skip\n");
        printf("  skip one instruction (set pc to next instruction)\n");
        printf("stepi\n");
        printf("  step one instruction (alias 'si')\n");
        printf("print <register>\n");
        printf("  print register content (alias 'p')\n");
        printf("  use register name 'all' to print all registers\n");
        printf("  add argument 'fp' to print register pair double values\n");
        printf("flags\n");
        printf("  print flags\n");
        printf("stack [<words>]\n");
        printf("  dump stack content, default dump 10 words)\n");
        printf("mem <address> [<words>]\n");
        printf("  dump memory content, default dump 10 words)\n");
        printf("disasm [<instructions>]\n");
        printf("disasm [<address/register>]\n");
        printf("disasm [[<address/register>] <instructions>]\n");
        printf("  disassemble code, default is 10 instructions\n");
        printf("  from pc (alias 'di')\n");
        printf("gdb\n");
        printf("  enter gdb\n");
        printf("break <address>\n");
        printf("  set a break point on the address\n");
        printf("del\n");
        printf("  delete the breakpoint\n");
        printf("stop feature:\n");
        printf("  Description:\n");
        printf("    Stops are debug instructions inserted by\n");
        printf("    the Assembler::stop() function.\n");
        printf("    When hitting a stop, the Simulator will\n");
        printf("    stop and and give control to the ArmDebugger.\n");
        printf("    The first %d stop codes are watched:\n",
               Simulator::kNumOfWatchedStops);
        printf("    - They can be enabled / disabled: the Simulator\n");
        printf("      will / won't stop when hitting them.\n");
        printf("    - The Simulator keeps track of how many times they \n");
        printf("      are met. (See the info command.) Going over a\n");
        printf("      disabled stop still increases its counter. \n");
        printf("  Commands:\n");
        printf("    stop info all/<code> : print infos about number <code>\n");
        printf("      or all stop(s).\n");
        printf("    stop enable/disable all/<code> : enables / disables\n");
        printf("      all or number <code> stop(s)\n");
        printf("    stop unstop\n");
        printf("      ignore the stop instruction at the current location\n");
        printf("      from now on\n");
      } else {
        printf("Unknown command: %s\n", cmd);
      }
    }
  }

  // Add all the breakpoints back to stop execution and enter the debugger
  // shell when hit.
  redoBreakpoints();

#undef COMMAND_SIZE
#undef ARG_SIZE

#undef STR
#undef XSTR
}

static bool AllOnOnePage(uintptr_t start, int size) {
  intptr_t start_page = (start & ~CachePage::kPageMask);
  intptr_t end_page = ((start + size) & ~CachePage::kPageMask);
  return start_page == end_page;
}

static CachePage* GetCachePageLocked(SimulatorProcess::ICacheMap& i_cache,
                                     void* page) {
  SimulatorProcess::ICacheMap::AddPtr p = i_cache.lookupForAdd(page);
  if (p) {
    return p->value();
  }

  AutoEnterOOMUnsafeRegion oomUnsafe;
  CachePage* new_page = js_new<CachePage>();
  if (!new_page || !i_cache.add(p, page, new_page)) {
    oomUnsafe.crash("Simulator CachePage");
  }

  return new_page;
}

// Flush from start up to and not including start + size.
static void FlushOnePageLocked(SimulatorProcess::ICacheMap& i_cache,
                               intptr_t start, int size) {
  MOZ_ASSERT(size <= CachePage::kPageSize);
  MOZ_ASSERT(AllOnOnePage(start, size - 1));
  MOZ_ASSERT((start & CachePage::kLineMask) == 0);
  MOZ_ASSERT((size & CachePage::kLineMask) == 0);

  void* page = reinterpret_cast<void*>(start & (~CachePage::kPageMask));
  int offset = (start & CachePage::kPageMask);
  CachePage* cache_page = GetCachePageLocked(i_cache, page);
  char* valid_bytemap = cache_page->validityByte(offset);
  memset(valid_bytemap, CachePage::LINE_INVALID, size >> CachePage::kLineShift);
}

static void FlushICacheLocked(SimulatorProcess::ICacheMap& i_cache,
                              void* start_addr, size_t size) {
  intptr_t start = reinterpret_cast<intptr_t>(start_addr);
  int intra_line = (start & CachePage::kLineMask);
  start -= intra_line;
  size += intra_line;
  size = ((size - 1) | CachePage::kLineMask) + 1;
  int offset = (start & CachePage::kPageMask);
  while (!AllOnOnePage(start, size - 1)) {
    int bytes_to_flush = CachePage::kPageSize - offset;
    FlushOnePageLocked(i_cache, start, bytes_to_flush);
    start += bytes_to_flush;
    size -= bytes_to_flush;
    MOZ_ASSERT((start & CachePage::kPageMask) == 0);
    offset = 0;
  }
  if (size != 0) {
    FlushOnePageLocked(i_cache, start, size);
  }
}

/* static */
void SimulatorProcess::checkICacheLocked(SimInstruction* instr) {
  intptr_t address = reinterpret_cast<intptr_t>(instr);
  void* page = reinterpret_cast<void*>(address & (~CachePage::kPageMask));
  void* line = reinterpret_cast<void*>(address & (~CachePage::kLineMask));
  int offset = (address & CachePage::kPageMask);
  CachePage* cache_page = GetCachePageLocked(icache(), page);
  char* cache_valid_byte = cache_page->validityByte(offset);
  bool cache_hit = (*cache_valid_byte == CachePage::LINE_VALID);
  char* cached_line = cache_page->cachedData(offset & ~CachePage::kLineMask);

  if (cache_hit) {
    // Check that the data in memory matches the contents of the I-cache.
    mozilla::DebugOnly<int> cmpret =
        memcmp(reinterpret_cast<void*>(instr), cache_page->cachedData(offset),
               SimInstruction::kInstrSize);
    MOZ_ASSERT(cmpret == 0);
  } else {
    // Cache miss. Load memory into the cache.
    memcpy(cached_line, line, CachePage::kLineLength);
    *cache_valid_byte = CachePage::LINE_VALID;
  }
}

HashNumber SimulatorProcess::ICacheHasher::hash(const Lookup& l) {
  return static_cast<uint32_t>(reinterpret_cast<uintptr_t>(l)) >> 2;
}

bool SimulatorProcess::ICacheHasher::match(const Key& k, const Lookup& l) {
  MOZ_ASSERT((reinterpret_cast<intptr_t>(k) & CachePage::kPageMask) == 0);
  MOZ_ASSERT((reinterpret_cast<intptr_t>(l) & CachePage::kPageMask) == 0);
  return k == l;
}

void Simulator::setLastDebuggerInput(char* input) {
  js_free(lastDebuggerInput_);
  lastDebuggerInput_ = input;
}

/* static */
void SimulatorProcess::FlushICache(void* start_addr, size_t size) {
  JitSpew(JitSpew_CacheFlush, "[%p %zx]", start_addr, size);
  if (!ICacheCheckingDisableCount) {
    AutoLockSimulatorCache als;
    js::jit::FlushICacheLocked(icache(), start_addr, size);
  }
}

Simulator::Simulator() {
  // Set up simulator support first. Some of this information is needed to
  // setup the architecture state.

  // Note, allocation and anything that depends on allocated memory is
  // deferred until init(), in order to handle OOM properly.

  stack_ = nullptr;
  stackLimit_ = 0;
  pc_modified_ = false;
  icount_ = 0L;
  break_pc_ = nullptr;
  break_instr_ = 0;
  single_stepping_ = false;
  single_step_callback_ = nullptr;
  single_step_callback_arg_ = nullptr;
  skipCalleeSavedRegsCheck = false;

  // Set up architecture state.
  // All registers are initialized to zero to start with.
  for (int i = 0; i < num_registers; i++) {
    registers_[i] = 0;
  }

  n_flag_ = false;
  z_flag_ = false;
  c_flag_ = false;
  v_flag_ = false;

  for (int i = 0; i < num_d_registers * 2; i++) {
    vfp_registers_[i] = 0;
  }

  n_flag_FPSCR_ = false;
  z_flag_FPSCR_ = false;
  c_flag_FPSCR_ = false;
  v_flag_FPSCR_ = false;
  FPSCR_rounding_mode_ = SimRZ;
  FPSCR_default_NaN_mode_ = true;

  inv_op_vfp_flag_ = false;
  div_zero_vfp_flag_ = false;
  overflow_vfp_flag_ = false;
  underflow_vfp_flag_ = false;
  inexact_vfp_flag_ = false;

  // The lr and pc are initialized to a known bad value that will cause an
  // access violation if the simulator ever tries to execute it.
  registers_[pc] = bad_lr;
  registers_[lr] = bad_lr;

  lastDebuggerInput_ = nullptr;

  exclusiveMonitorHeld_ = false;
  exclusiveMonitor_ = 0;
}

bool Simulator::init() {
  // Allocate 2MB for the stack. Note that we will only use 1MB, see below.
  static const size_t stackSize = 2 * 1024 * 1024;
  stack_ = js_pod_malloc<char>(stackSize);
  if (!stack_) {
    return false;
  }

  // Leave a safety margin of 1MB to prevent overrunning the stack when
  // pushing values (total stack size is 2MB).
  stackLimit_ = reinterpret_cast<uintptr_t>(stack_) + 1024 * 1024;

  // The sp is initialized to point to the bottom (high address) of the
  // allocated stack area. To be safe in potential stack underflows we leave
  // some buffer below.
  registers_[sp] = reinterpret_cast<int32_t>(stack_) + stackSize - 64;

  return true;
}

// When the generated code calls a VM function (masm.callWithABI) we need to
// call that function instead of trying to execute it with the simulator
// (because it's x86 code instead of arm code). We do that by redirecting the VM
// call to a svc (Supervisor Call) instruction that is handled by the
// simulator. We write the original destination of the jump just at a known
// offset from the svc instruction so the simulator knows what to call.
class Redirection {
  friend class SimulatorProcess;

  // sim's lock must already be held.
  Redirection(void* nativeFunction, ABIFunctionType type)
      : nativeFunction_(nativeFunction),
        swiInstruction_(Assembler::AL | (0xf * (1 << 24)) | kCallRtRedirected),
        type_(type),
        next_(nullptr) {
    next_ = SimulatorProcess::redirection();
    if (!SimulatorProcess::ICacheCheckingDisableCount) {
      FlushICacheLocked(SimulatorProcess::icache(), addressOfSwiInstruction(),
                        SimInstruction::kInstrSize);
    }
    SimulatorProcess::setRedirection(this);
  }

 public:
  void* addressOfSwiInstruction() { return &swiInstruction_; }
  void* nativeFunction() const { return nativeFunction_; }
  ABIFunctionType type() const { return type_; }

  static Redirection* Get(void* nativeFunction, ABIFunctionType type) {
    AutoLockSimulatorCache als;

    Redirection* current = SimulatorProcess::redirection();
    for (; current != nullptr; current = current->next_) {
      if (current->nativeFunction_ == nativeFunction) {
        MOZ_ASSERT(current->type() == type);
        return current;
      }
    }

    // Note: we can't use js_new here because the constructor is private.
    AutoEnterOOMUnsafeRegion oomUnsafe;
    Redirection* redir = js_pod_malloc<Redirection>(1);
    if (!redir) {
      oomUnsafe.crash("Simulator redirection");
    }
    new (redir) Redirection(nativeFunction, type);
    return redir;
  }

  static Redirection* FromSwiInstruction(SimInstruction* swiInstruction) {
    uint8_t* addrOfSwi = reinterpret_cast<uint8_t*>(swiInstruction);
    uint8_t* addrOfRedirection =
        addrOfSwi - offsetof(Redirection, swiInstruction_);
    return reinterpret_cast<Redirection*>(addrOfRedirection);
  }

 private:
  void* nativeFunction_;
  uint32_t swiInstruction_;
  ABIFunctionType type_;
  Redirection* next_;
};

Simulator::~Simulator() { js_free(stack_); }

SimulatorProcess::SimulatorProcess()
    : cacheLock_(mutexid::SimulatorCacheLock), redirection_(nullptr) {
  if (getenv("ARM_SIM_ICACHE_CHECKS")) {
    ICacheCheckingDisableCount = 0;
  }
}

SimulatorProcess::~SimulatorProcess() {
  Redirection* r = redirection_;
  while (r) {
    Redirection* next = r->next_;
    js_delete(r);
    r = next;
  }
}

/* static */
void* Simulator::RedirectNativeFunction(void* nativeFunction,
                                        ABIFunctionType type) {
  Redirection* redirection = Redirection::Get(nativeFunction, type);
  return redirection->addressOfSwiInstruction();
}

// Sets the register in the architecture state. It will also deal with updating
// Simulator internal state for special registers such as PC.
void Simulator::set_register(int reg, int32_t value) {
  MOZ_ASSERT(reg >= 0 && reg < num_registers);
  if (reg == pc) {
    pc_modified_ = true;
  }
  registers_[reg] = value;
}

// Get the register from the architecture state. This function does handle the
// special case of accessing the PC register.
int32_t Simulator::get_register(int reg) const {
  MOZ_ASSERT(reg >= 0 && reg < num_registers);
  // Work around GCC bug: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43949
  if (reg >= num_registers) return 0;
  return registers_[reg] + ((reg == pc) ? SimInstruction::kPCReadOffset : 0);
}

double Simulator::get_double_from_register_pair(int reg) {
  MOZ_ASSERT(reg >= 0 && reg < num_registers && (reg % 2) == 0);

  // Read the bits from the unsigned integer register_[] array into the double
  // precision floating point value and return it.
  double dm_val = 0.0;
  char buffer[2 * sizeof(vfp_registers_[0])];
  memcpy(buffer, &registers_[reg], 2 * sizeof(registers_[0]));
  memcpy(&dm_val, buffer, 2 * sizeof(registers_[0]));
  return dm_val;
}

void Simulator::set_register_pair_from_double(int reg, double* value) {
  MOZ_ASSERT(reg >= 0 && reg < num_registers && (reg % 2) == 0);
  memcpy(registers_ + reg, value, sizeof(*value));
}

void Simulator::set_dw_register(int dreg, const int* dbl) {
  MOZ_ASSERT(dreg >= 0 && dreg < num_d_registers);
  registers_[dreg] = dbl[0];
  registers_[dreg + 1] = dbl[1];
}

void Simulator::get_d_register(int dreg, uint64_t* value) {
  MOZ_ASSERT(dreg >= 0 && dreg < int(FloatRegisters::TotalPhys));
  memcpy(value, vfp_registers_ + dreg * 2, sizeof(*value));
}

void Simulator::set_d_register(int dreg, const uint64_t* value) {
  MOZ_ASSERT(dreg >= 0 && dreg < int(FloatRegisters::TotalPhys));
  memcpy(vfp_registers_ + dreg * 2, value, sizeof(*value));
}

void Simulator::get_d_register(int dreg, uint32_t* value) {
  MOZ_ASSERT(dreg >= 0 && dreg < int(FloatRegisters::TotalPhys));
  memcpy(value, vfp_registers_ + dreg * 2, sizeof(*value) * 2);
}

void Simulator::set_d_register(int dreg, const uint32_t* value) {
  MOZ_ASSERT(dreg >= 0 && dreg < int(FloatRegisters::TotalPhys));
  memcpy(vfp_registers_ + dreg * 2, value, sizeof(*value) * 2);
}

void Simulator::get_q_register(int qreg, uint64_t* value) {
  MOZ_ASSERT(qreg >= 0 && qreg < num_q_registers);
  memcpy(value, vfp_registers_ + qreg * 4, sizeof(*value) * 2);
}

void Simulator::set_q_register(int qreg, const uint64_t* value) {
  MOZ_ASSERT(qreg >= 0 && qreg < num_q_registers);
  memcpy(vfp_registers_ + qreg * 4, value, sizeof(*value) * 2);
}

void Simulator::get_q_register(int qreg, uint32_t* value) {
  MOZ_ASSERT(qreg >= 0 && qreg < num_q_registers);
  memcpy(value, vfp_registers_ + qreg * 4, sizeof(*value) * 4);
}

void Simulator::set_q_register(int qreg, const uint32_t* value) {
  MOZ_ASSERT((qreg >= 0) && (qreg < num_q_registers));
  memcpy(vfp_registers_ + qreg * 4, value, sizeof(*value) * 4);
}

void Simulator::set_pc(int32_t value) {
  pc_modified_ = true;
  registers_[pc] = value;
}

bool Simulator::has_bad_pc() const {
  return registers_[pc] == bad_lr || registers_[pc] == end_sim_pc;
}

// Raw access to the PC register without the special adjustment when reading.
int32_t Simulator::get_pc() const { return registers_[pc]; }

void Simulator::set_s_register(int sreg, unsigned int value) {
  MOZ_ASSERT(sreg >= 0 && sreg < num_s_registers);
  vfp_registers_[sreg] = value;
}

unsigned Simulator::get_s_register(int sreg) const {
  MOZ_ASSERT(sreg >= 0 && sreg < num_s_registers);
  return vfp_registers_[sreg];
}

template <class InputType, int register_size>
void Simulator::setVFPRegister(int reg_index, const InputType& value) {
  MOZ_ASSERT(reg_index >= 0);
  MOZ_ASSERT_IF(register_size == 1, reg_index < num_s_registers);
  MOZ_ASSERT_IF(register_size == 2, reg_index < int(FloatRegisters::TotalPhys));

  char buffer[register_size * sizeof(vfp_registers_[0])];
  memcpy(buffer, &value, register_size * sizeof(vfp_registers_[0]));
  memcpy(&vfp_registers_[reg_index * register_size], buffer,
         register_size * sizeof(vfp_registers_[0]));
}

template <class ReturnType, int register_size>
void Simulator::getFromVFPRegister(int reg_index, ReturnType* out) {
  MOZ_ASSERT(reg_index >= 0);
  MOZ_ASSERT_IF(register_size == 1, reg_index < num_s_registers);
  MOZ_ASSERT_IF(register_size == 2, reg_index < int(FloatRegisters::TotalPhys));

  char buffer[register_size * sizeof(vfp_registers_[0])];
  memcpy(buffer, &vfp_registers_[register_size * reg_index],
         register_size * sizeof(vfp_registers_[0]));
  memcpy(out, buffer, register_size * sizeof(vfp_registers_[0]));
}

// These forced-instantiations are for jsapi-tests. Evidently, nothing
// requires these to be instantiated.
template void Simulator::getFromVFPRegister<double, 2>(int reg_index,
                                                       double* out);
template void Simulator::getFromVFPRegister<float, 1>(int reg_index,
                                                      float* out);
template void Simulator::setVFPRegister<double, 2>(int reg_index,
                                                   const double& value);
template void Simulator::setVFPRegister<float, 1>(int reg_index,
                                                  const float& value);

void Simulator::getFpArgs(double* x, double* y, int32_t* z) {
  if (ARMFlags::UseHardFpABI()) {
    get_double_from_d_register(0, x);
    get_double_from_d_register(1, y);
    *z = get_register(0);
  } else {
    *x = get_double_from_register_pair(0);
    *y = get_double_from_register_pair(2);
    *z = get_register(2);
  }
}

void Simulator::getFpFromStack(int32_t* stack, double* x) {
  MOZ_ASSERT(stack && x);
  char buffer[2 * sizeof(stack[0])];
  memcpy(buffer, stack, 2 * sizeof(stack[0]));
  memcpy(x, buffer, 2 * sizeof(stack[0]));
}

void Simulator::setCallResultDouble(double result) {
  // The return value is either in r0/r1 or d0.
  if (ARMFlags::UseHardFpABI()) {
    char buffer[2 * sizeof(vfp_registers_[0])];
    memcpy(buffer, &result, sizeof(buffer));
    // Copy result to d0.
    memcpy(vfp_registers_, buffer, sizeof(buffer));
  } else {
    char buffer[2 * sizeof(registers_[0])];
    memcpy(buffer, &result, sizeof(buffer));
    // Copy result to r0 and r1.
    memcpy(registers_, buffer, sizeof(buffer));
  }
}

void Simulator::setCallResultFloat(float result) {
  if (ARMFlags::UseHardFpABI()) {
    char buffer[sizeof(registers_[0])];
    memcpy(buffer, &result, sizeof(buffer));
    // Copy result to s0.
    memcpy(vfp_registers_, buffer, sizeof(buffer));
  } else {
    char buffer[sizeof(registers_[0])];
    memcpy(buffer, &result, sizeof(buffer));
    // Copy result to r0.
    memcpy(registers_, buffer, sizeof(buffer));
  }
}

void Simulator::setCallResult(int64_t res) {
  set_register(r0, static_cast<int32_t>(res));
  set_register(r1, static_cast<int32_t>(res >> 32));
}

void Simulator::exclusiveMonitorSet(uint64_t value) {
  exclusiveMonitor_ = value;
  exclusiveMonitorHeld_ = true;
}

uint64_t Simulator::exclusiveMonitorGetAndClear(bool* held) {
  *held = exclusiveMonitorHeld_;
  exclusiveMonitorHeld_ = false;
  return *held ? exclusiveMonitor_ : 0;
}

void Simulator::exclusiveMonitorClear() { exclusiveMonitorHeld_ = false; }

JS::ProfilingFrameIterator::RegisterState Simulator::registerState() {
  wasm::RegisterState state;
  state.pc = (void*)get_pc();
  state.fp = (void*)get_register(fp);
  state.sp = (void*)get_register(sp);
  state.lr = (void*)get_register(lr);
  return state;
}

uint64_t Simulator::readQ(int32_t addr, SimInstruction* instr,
                          UnalignedPolicy f) {
  if (handleWasmSegFault(addr, 8)) {
    return UINT64_MAX;
  }

  if ((addr & 3) == 0 ||
      (f == AllowUnaligned && !ARMFlags::HasAlignmentFault())) {
    uint64_t* ptr = reinterpret_cast<uint64_t*>(addr);
    return *ptr;
  }

  // See the comments below in readW.
  if (ARMFlags::FixupFault() &&
      wasm::InCompiledCode(reinterpret_cast<void*>(get_pc()))) {
    char* ptr = reinterpret_cast<char*>(addr);
    uint64_t value;
    memcpy(&value, ptr, sizeof(value));
    return value;
  }

  printf("Unaligned read at 0x%08x, pc=%p\n", addr, instr);
  MOZ_CRASH();
}

void Simulator::writeQ(int32_t addr, uint64_t value, SimInstruction* instr,
                       UnalignedPolicy f) {
  if (handleWasmSegFault(addr, 8)) {
    return;
  }

  if ((addr & 3) == 0 ||
      (f == AllowUnaligned && !ARMFlags::HasAlignmentFault())) {
    uint64_t* ptr = reinterpret_cast<uint64_t*>(addr);
    *ptr = value;
    return;
  }

  // See the comments below in readW.
  if (ARMFlags::FixupFault() &&
      wasm::InCompiledCode(reinterpret_cast<void*>(get_pc()))) {
    char* ptr = reinterpret_cast<char*>(addr);
    memcpy(ptr, &value, sizeof(value));
    return;
  }

  printf("Unaligned write at 0x%08x, pc=%p\n", addr, instr);
  MOZ_CRASH();
}

int Simulator::readW(int32_t addr, SimInstruction* instr, UnalignedPolicy f) {
  if (handleWasmSegFault(addr, 4)) {
    return -1;
  }

  if ((addr & 3) == 0 ||
      (f == AllowUnaligned && !ARMFlags::HasAlignmentFault())) {
    intptr_t* ptr = reinterpret_cast<intptr_t*>(addr);
    return *ptr;
  }

  // In WebAssembly, we want unaligned accesses to either raise a signal or
  // do the right thing. Making this simulator properly emulate the behavior
  // of raising a signal is complex, so as a special-case, when in wasm code,
  // we just do the right thing.
  if (ARMFlags::FixupFault() &&
      wasm::InCompiledCode(reinterpret_cast<void*>(get_pc()))) {
    char* ptr = reinterpret_cast<char*>(addr);
    int value;
    memcpy(&value, ptr, sizeof(value));
    return value;
  }

  printf("Unaligned read at 0x%08x, pc=%p\n", addr, instr);
  MOZ_CRASH();
}

void Simulator::writeW(int32_t addr, int value, SimInstruction* instr,
                       UnalignedPolicy f) {
  if (handleWasmSegFault(addr, 4)) {
    return;
  }

  if ((addr & 3) == 0 ||
      (f == AllowUnaligned && !ARMFlags::HasAlignmentFault())) {
    intptr_t* ptr = reinterpret_cast<intptr_t*>(addr);
    *ptr = value;
    return;
  }

  // See the comments above in readW.
  if (ARMFlags::FixupFault() &&
      wasm::InCompiledCode(reinterpret_cast<void*>(get_pc()))) {
    char* ptr = reinterpret_cast<char*>(addr);
    memcpy(ptr, &value, sizeof(value));
    return;
  }

  printf("Unaligned write at 0x%08x, pc=%p\n", addr, instr);
  MOZ_CRASH();
}

// For the time being, define Relaxed operations in terms of SeqCst
// operations - we don't yet need Relaxed operations anywhere else in
// the system, and the distinction is not important to the simulation
// at the level where we're operating.

template <typename T>
static T loadRelaxed(SharedMem<T*> addr) {
  return AtomicOperations::loadSeqCst(addr);
}

template <typename T>
static T compareExchangeRelaxed(SharedMem<T*> addr, T oldval, T newval) {
  return AtomicOperations::compareExchangeSeqCst(addr, oldval, newval);
}

int Simulator::readExW(int32_t addr, SimInstruction* instr) {
  if (addr & 3) {
    MOZ_CRASH("Unaligned exclusive read");
  }

  if (handleWasmSegFault(addr, 4)) {
    return -1;
  }

  SharedMem<int32_t*> ptr =
      SharedMem<int32_t*>::shared(reinterpret_cast<int32_t*>(addr));
  int32_t value = loadRelaxed(ptr);
  exclusiveMonitorSet(value);
  return value;
}

int32_t Simulator::writeExW(int32_t addr, int value, SimInstruction* instr) {
  if (addr & 3) {
    MOZ_CRASH("Unaligned exclusive write");
  }

  if (handleWasmSegFault(addr, 4)) {
    return -1;
  }

  SharedMem<int32_t*> ptr =
      SharedMem<int32_t*>::shared(reinterpret_cast<int32_t*>(addr));
  bool held;
  int32_t expected = int32_t(exclusiveMonitorGetAndClear(&held));
  if (!held) {
    return 1;
  }
  int32_t old = compareExchangeRelaxed(ptr, expected, int32_t(value));
  return old != expected;
}

uint16_t Simulator::readHU(int32_t addr, SimInstruction* instr) {
  if (handleWasmSegFault(addr, 2)) {
    return UINT16_MAX;
  }

  // The regexp engine emits unaligned loads, so we don't check for them here
  // like most of the other methods do.
  if ((addr & 1) == 0 || !ARMFlags::HasAlignmentFault()) {
    uint16_t* ptr = reinterpret_cast<uint16_t*>(addr);
    return *ptr;
  }

  // See comments above in readW.
  if (ARMFlags::FixupFault() &&
      wasm::InCompiledCode(reinterpret_cast<void*>(get_pc()))) {
    char* ptr = reinterpret_cast<char*>(addr);
    uint16_t value;
    memcpy(&value, ptr, sizeof(value));
    return value;
  }

  printf("Unaligned unsigned halfword read at 0x%08x, pc=%p\n", addr, instr);
  MOZ_CRASH();
  return 0;
}

int16_t Simulator::readH(int32_t addr, SimInstruction* instr) {
  if (handleWasmSegFault(addr, 2)) {
    return -1;
  }

  if ((addr & 1) == 0 || !ARMFlags::HasAlignmentFault()) {
    int16_t* ptr = reinterpret_cast<int16_t*>(addr);
    return *ptr;
  }

  // See comments above in readW.
  if (ARMFlags::FixupFault() &&
      wasm::InCompiledCode(reinterpret_cast<void*>(get_pc()))) {
    char* ptr = reinterpret_cast<char*>(addr);
    int16_t value;
    memcpy(&value, ptr, sizeof(value));
    return value;
  }

  printf("Unaligned signed halfword read at 0x%08x\n", addr);
  MOZ_CRASH();
  return 0;
}

void Simulator::writeH(int32_t addr, uint16_t value, SimInstruction* instr) {
  if (handleWasmSegFault(addr, 2)) {
    return;
  }

  if ((addr & 1) == 0 || !ARMFlags::HasAlignmentFault()) {
    uint16_t* ptr = reinterpret_cast<uint16_t*>(addr);
    *ptr = value;
    return;
  }

  // See the comments above in readW.
  if (ARMFlags::FixupFault() &&
      wasm::InCompiledCode(reinterpret_cast<void*>(get_pc()))) {
    char* ptr = reinterpret_cast<char*>(addr);
    memcpy(ptr, &value, sizeof(value));
    return;
  }

  printf("Unaligned unsigned halfword write at 0x%08x, pc=%p\n", addr, instr);
  MOZ_CRASH();
}

void Simulator::writeH(int32_t addr, int16_t value, SimInstruction* instr) {
  if (handleWasmSegFault(addr, 2)) {
    return;
  }

  if ((addr & 1) == 0 || !ARMFlags::HasAlignmentFault()) {
    int16_t* ptr = reinterpret_cast<int16_t*>(addr);
    *ptr = value;
    return;
  }

  // See the comments above in readW.
  if (ARMFlags::FixupFault() &&
      wasm::InCompiledCode(reinterpret_cast<void*>(get_pc()))) {
    char* ptr = reinterpret_cast<char*>(addr);
    memcpy(ptr, &value, sizeof(value));
    return;
  }

  printf("Unaligned halfword write at 0x%08x, pc=%p\n", addr, instr);
  MOZ_CRASH();
}

uint16_t Simulator::readExHU(int32_t addr, SimInstruction* instr) {
  if (addr & 1) {
    MOZ_CRASH("Unaligned exclusive read");
  }

  if (handleWasmSegFault(addr, 2)) {
    return UINT16_MAX;
  }

  SharedMem<uint16_t*> ptr =
      SharedMem<uint16_t*>::shared(reinterpret_cast<uint16_t*>(addr));
  uint16_t value = loadRelaxed(ptr);
  exclusiveMonitorSet(value);
  return value;
}

int32_t Simulator::writeExH(int32_t addr, uint16_t value,
                            SimInstruction* instr) {
  if (addr & 1) {
    MOZ_CRASH("Unaligned exclusive write");
  }

  if (handleWasmSegFault(addr, 2)) {
    return -1;
  }

  SharedMem<uint16_t*> ptr =
      SharedMem<uint16_t*>::shared(reinterpret_cast<uint16_t*>(addr));
  bool held;
  uint16_t expected = uint16_t(exclusiveMonitorGetAndClear(&held));
  if (!held) {
    return 1;
  }
  uint16_t old = compareExchangeRelaxed(ptr, expected, value);
  return old != expected;
}

uint8_t Simulator::readBU(int32_t addr) {
  if (handleWasmSegFault(addr, 1)) {
    return UINT8_MAX;
  }

  uint8_t* ptr = reinterpret_cast<uint8_t*>(addr);
  return *ptr;
}

uint8_t Simulator::readExBU(int32_t addr) {
  if (handleWasmSegFault(addr, 1)) {
    return UINT8_MAX;
  }

  SharedMem<uint8_t*> ptr =
      SharedMem<uint8_t*>::shared(reinterpret_cast<uint8_t*>(addr));
  uint8_t value = loadRelaxed(ptr);
  exclusiveMonitorSet(value);
  return value;
}

int32_t Simulator::writeExB(int32_t addr, uint8_t value) {
  if (handleWasmSegFault(addr, 1)) {
    return -1;
  }

  SharedMem<uint8_t*> ptr =
      SharedMem<uint8_t*>::shared(reinterpret_cast<uint8_t*>(addr));
  bool held;
  uint8_t expected = uint8_t(exclusiveMonitorGetAndClear(&held));
  if (!held) {
    return 1;
  }
  uint8_t old = compareExchangeRelaxed(ptr, expected, value);
  return old != expected;
}

int8_t Simulator::readB(int32_t addr) {
  if (handleWasmSegFault(addr, 1)) {
    return -1;
  }

  int8_t* ptr = reinterpret_cast<int8_t*>(addr);
  return *ptr;
}

void Simulator::writeB(int32_t addr, uint8_t value) {
  if (handleWasmSegFault(addr, 1)) {
    return;
  }

  uint8_t* ptr = reinterpret_cast<uint8_t*>(addr);
  *ptr = value;
}

void Simulator::writeB(int32_t addr, int8_t value) {
  if (handleWasmSegFault(addr, 1)) {
    return;
  }

  int8_t* ptr = reinterpret_cast<int8_t*>(addr);
  *ptr = value;
}

int32_t* Simulator::readDW(int32_t addr) {
  if (handleWasmSegFault(addr, 8)) {
    return nullptr;
  }

  if ((addr & 3) == 0) {
    int32_t* ptr = reinterpret_cast<int32_t*>(addr);
    return ptr;
  }

  printf("Unaligned read at 0x%08x\n", addr);
  MOZ_CRASH();
}

void Simulator::writeDW(int32_t addr, int32_t value1, int32_t value2) {
  if (handleWasmSegFault(addr, 8)) {
    return;
  }

  if ((addr & 3) == 0) {
    int32_t* ptr = reinterpret_cast<int32_t*>(addr);
    *ptr++ = value1;
    *ptr = value2;
    return;
  }

  printf("Unaligned write at 0x%08x\n", addr);
  MOZ_CRASH();
}

int32_t Simulator::readExDW(int32_t addr, int32_t* hibits) {
  if (addr & 3) {
    MOZ_CRASH("Unaligned exclusive read");
  }

  if (handleWasmSegFault(addr, 8)) {
    return -1;
  }

  SharedMem<uint64_t*> ptr =
      SharedMem<uint64_t*>::shared(reinterpret_cast<uint64_t*>(addr));
  // The spec says that the low part of value shall be read from addr and
  // the high part shall be read from addr+4.  On a little-endian system
  // where we read a 64-bit quadword the low part of the value will be in
  // the low part of the quadword, and the high part of the value in the
  // high part of the quadword.
  uint64_t value = loadRelaxed(ptr);
  exclusiveMonitorSet(value);
  *hibits = int32_t(value >> 32);
  return int32_t(value);
}

int32_t Simulator::writeExDW(int32_t addr, int32_t value1, int32_t value2) {
  if (addr & 3) {
    MOZ_CRASH("Unaligned exclusive write");
  }

  if (handleWasmSegFault(addr, 8)) {
    return -1;
  }

  SharedMem<uint64_t*> ptr =
      SharedMem<uint64_t*>::shared(reinterpret_cast<uint64_t*>(addr));
  // The spec says that value1 shall be stored at addr and value2 at
  // addr+4.  On a little-endian system that means constructing a 64-bit
  // value where value1 is in the low half of a 64-bit quadword and value2
  // is in the high half of the quadword.
  uint64_t value = (uint64_t(value2) << 32) | uint32_t(value1);
  bool held;
  uint64_t expected = exclusiveMonitorGetAndClear(&held);
  if (!held) {
    return 1;
  }
  uint64_t old = compareExchangeRelaxed(ptr, expected, value);
  return old != expected;
}

uintptr_t Simulator::stackLimit() const { return stackLimit_; }

uintptr_t* Simulator::addressOfStackLimit() { return &stackLimit_; }

bool Simulator::overRecursed(uintptr_t newsp) const {
  if (newsp == 0) {
    newsp = get_register(sp);
  }
  return newsp <= stackLimit();
}

bool Simulator::overRecursedWithExtra(uint32_t extra) const {
  uintptr_t newsp = get_register(sp) - extra;
  return newsp <= stackLimit();
}

// Checks if the current instruction should be executed based on its condition
// bits.
bool Simulator::conditionallyExecute(SimInstruction* instr) {
  switch (instr->conditionField()) {
    case Assembler::EQ:
      return z_flag_;
    case Assembler::NE:
      return !z_flag_;
    case Assembler::CS:
      return c_flag_;
    case Assembler::CC:
      return !c_flag_;
    case Assembler::MI:
      return n_flag_;
    case Assembler::PL:
      return !n_flag_;
    case Assembler::VS:
      return v_flag_;
    case Assembler::VC:
      return !v_flag_;
    case Assembler::HI:
      return c_flag_ && !z_flag_;
    case Assembler::LS:
      return !c_flag_ || z_flag_;
    case Assembler::GE:
      return n_flag_ == v_flag_;
    case Assembler::LT:
      return n_flag_ != v_flag_;
    case Assembler::GT:
      return !z_flag_ && (n_flag_ == v_flag_);
    case Assembler::LE:
      return z_flag_ || (n_flag_ != v_flag_);
    case Assembler::AL:
      return true;
    default:
      MOZ_CRASH();
  }
  return false;
}

// Calculate and set the Negative and Zero flags.
void Simulator::setNZFlags(int32_t val) {
  n_flag_ = (val < 0);
  z_flag_ = (val == 0);
}

// Set the Carry flag.
void Simulator::setCFlag(bool val) { c_flag_ = val; }

// Set the oVerflow flag.
void Simulator::setVFlag(bool val) { v_flag_ = val; }

// Calculate C flag value for additions.
bool Simulator::carryFrom(int32_t left, int32_t right, int32_t carry) {
  uint32_t uleft = static_cast<uint32_t>(left);
  uint32_t uright = static_cast<uint32_t>(right);
  uint32_t urest = 0xffffffffU - uleft;
  return (uright > urest) ||
         (carry && (((uright + 1) > urest) || (uright > (urest - 1))));
}

// Calculate C flag value for subtractions.
bool Simulator::borrowFrom(int32_t left, int32_t right) {
  uint32_t uleft = static_cast<uint32_t>(left);
  uint32_t uright = static_cast<uint32_t>(right);
  return (uright > uleft);
}

// Calculate V flag value for additions and subtractions.
bool Simulator::overflowFrom(int32_t alu_out, int32_t left, int32_t right,
                             bool addition) {
  bool overflow;
  if (addition) {
    // Operands have the same sign.
    overflow = ((left >= 0 && right >= 0) || (left < 0 && right < 0))
               // And operands and result have different sign.
               && ((left < 0 && alu_out >= 0) || (left >= 0 && alu_out < 0));
  } else {
    // Operands have different signs.
    overflow = ((left < 0 && right >= 0) || (left >= 0 && right < 0))
               // And first operand and result have different signs.
               && ((left < 0 && alu_out >= 0) || (left >= 0 && alu_out < 0));
  }
  return overflow;
}

// Support for VFP comparisons.
void Simulator::compute_FPSCR_Flags(double val1, double val2) {
  if (std::isnan(val1) || std::isnan(val2)) {
    n_flag_FPSCR_ = false;
    z_flag_FPSCR_ = false;
    c_flag_FPSCR_ = true;
    v_flag_FPSCR_ = true;
    // All non-NaN cases.
  } else if (val1 == val2) {
    n_flag_FPSCR_ = false;
    z_flag_FPSCR_ = true;
    c_flag_FPSCR_ = true;
    v_flag_FPSCR_ = false;
  } else if (val1 < val2) {
    n_flag_FPSCR_ = true;
    z_flag_FPSCR_ = false;
    c_flag_FPSCR_ = false;
    v_flag_FPSCR_ = false;
  } else {
    // Case when (val1 > val2).
    n_flag_FPSCR_ = false;
    z_flag_FPSCR_ = false;
    c_flag_FPSCR_ = true;
    v_flag_FPSCR_ = false;
  }
}

void Simulator::copy_FPSCR_to_APSR() {
  n_flag_ = n_flag_FPSCR_;
  z_flag_ = z_flag_FPSCR_;
  c_flag_ = c_flag_FPSCR_;
  v_flag_ = v_flag_FPSCR_;
}

// Addressing Mode 1 - Data-processing operands:
// Get the value based on the shifter_operand with register.
int32_t Simulator::getShiftRm(SimInstruction* instr, bool* carry_out) {
  ShiftType shift = instr->shifttypeValue();
  int shift_amount = instr->shiftAmountValue();
  int32_t result = get_register(instr->rmValue());
  if (instr->bit(4) == 0) {
    // By immediate.
    if (shift == ROR && shift_amount == 0) {
      MOZ_CRASH("NYI");
      return result;
    }
    if ((shift == LSR || shift == ASR) && shift_amount == 0) {
      shift_amount = 32;
    }
    switch (shift) {
      case ASR: {
        if (shift_amount == 0) {
          if (result < 0) {
            result = 0xffffffff;
            *carry_out = true;
          } else {
            result = 0;
            *carry_out = false;
          }
        } else {
          result >>= (shift_amount - 1);
          *carry_out = (result & 1) == 1;
          result >>= 1;
        }
        break;
      }

      case LSL: {
        if (shift_amount == 0) {
          *carry_out = c_flag_;
        } else {
          result <<= (shift_amount - 1);
          *carry_out = (result < 0);
          result <<= 1;
        }
        break;
      }

      case LSR: {
        if (shift_amount == 0) {
          result = 0;
          *carry_out = c_flag_;
        } else {
          uint32_t uresult = static_cast<uint32_t>(result);
          uresult >>= (shift_amount - 1);
          *carry_out = (uresult & 1) == 1;
          uresult >>= 1;
          result = static_cast<int32_t>(uresult);
        }
        break;
      }

      case ROR: {
        if (shift_amount == 0) {
          *carry_out = c_flag_;
        } else {
          uint32_t left = static_cast<uint32_t>(result) >> shift_amount;
          uint32_t right = static_cast<uint32_t>(result) << (32 - shift_amount);
          result = right | left;
          *carry_out = (static_cast<uint32_t>(result) >> 31) != 0;
        }
        break;
      }

      default:
        MOZ_CRASH();
    }
  } else {
    // By register.
    int rs = instr->rsValue();
    shift_amount = get_register(rs) & 0xff;
    switch (shift) {
      case ASR: {
        if (shift_amount == 0) {
          *carry_out = c_flag_;
        } else if (shift_amount < 32) {
          result >>= (shift_amount - 1);
          *carry_out = (result & 1) == 1;
          result >>= 1;
        } else {
          MOZ_ASSERT(shift_amount >= 32);
          if (result < 0) {
            *carry_out = true;
            result = 0xffffffff;
          } else {
            *carry_out = false;
            result = 0;
          }
        }
        break;
      }

      case LSL: {
        if (shift_amount == 0) {
          *carry_out = c_flag_;
        } else if (shift_amount < 32) {
          result <<= (shift_amount - 1);
          *carry_out = (result < 0);
          result <<= 1;
        } else if (shift_amount == 32) {
          *carry_out = (result & 1) == 1;
          result = 0;
        } else {
          MOZ_ASSERT(shift_amount > 32);
          *carry_out = false;
          result = 0;
        }
        break;
      }

      case LSR: {
        if (shift_amount == 0) {
          *carry_out = c_flag_;
        } else if (shift_amount < 32) {
          uint32_t uresult = static_cast<uint32_t>(result);
          uresult >>= (shift_amount - 1);
          *carry_out = (uresult & 1) == 1;
          uresult >>= 1;
          result = static_cast<int32_t>(uresult);
        } else if (shift_amount == 32) {
          *carry_out = (result < 0);
          result = 0;
        } else {
          *carry_out = false;
          result = 0;
        }
        break;
      }

      case ROR: {
        if (shift_amount == 0) {
          *carry_out = c_flag_;
        } else {
          uint32_t left = static_cast<uint32_t>(result) >> shift_amount;
          uint32_t right = static_cast<uint32_t>(result) << (32 - shift_amount);
          result = right | left;
          *carry_out = (static_cast<uint32_t>(result) >> 31) != 0;
        }
        break;
      }

      default:
        MOZ_CRASH();
    }
  }
  return result;
}

// Addressing Mode 1 - Data-processing operands:
// Get the value based on the shifter_operand with immediate.
int32_t Simulator::getImm(SimInstruction* instr, bool* carry_out) {
  int rotate = instr->rotateValue() * 2;
  int immed8 = instr->immed8Value();
  int imm = (immed8 >> rotate) | (immed8 << (32 - rotate));
  *carry_out = (rotate == 0) ? c_flag_ : (imm < 0);
  return imm;
}

int32_t Simulator::processPU(SimInstruction* instr, int num_regs, int reg_size,
                             intptr_t* start_address, intptr_t* end_address) {
  int rn = instr->rnValue();
  int32_t rn_val = get_register(rn);
  switch (instr->PUField()) {
    case da_x:
      MOZ_CRASH();
      break;
    case ia_x:
      *start_address = rn_val;
      *end_address = rn_val + (num_regs * reg_size) - reg_size;
      rn_val = rn_val + (num_regs * reg_size);
      break;
    case db_x:
      *start_address = rn_val - (num_regs * reg_size);
      *end_address = rn_val - reg_size;
      rn_val = *start_address;
      break;
    case ib_x:
      *start_address = rn_val + reg_size;
      *end_address = rn_val + (num_regs * reg_size);
      rn_val = *end_address;
      break;
    default:
      MOZ_CRASH();
  }
  return rn_val;
}

// Addressing Mode 4 - Load and Store Multiple
void Simulator::handleRList(SimInstruction* instr, bool load) {
  int rlist = instr->rlistValue();
  int num_regs = std::popcount(unsigned(rlist));

  intptr_t start_address = 0;
  intptr_t end_address = 0;
  int32_t rn_val =
      processPU(instr, num_regs, sizeof(void*), &start_address, &end_address);
  intptr_t* address = reinterpret_cast<intptr_t*>(start_address);

  // Catch null pointers a little earlier.
  MOZ_ASSERT(start_address > 8191 || start_address < 0);

  int reg = 0;
  while (rlist != 0) {
    if ((rlist & 1) != 0) {
      if (load) {
        set_register(reg, *address);
      } else {
        *address = get_register(reg);
      }
      address += 1;
    }
    reg++;
    rlist >>= 1;
  }
  MOZ_ASSERT(end_address == ((intptr_t)address) - 4);
  if (instr->hasW()) {
    set_register(instr->rnValue(), rn_val);
  }
}

// Addressing Mode 6 - Load and Store Multiple Coprocessor registers.
void Simulator::handleVList(SimInstruction* instr) {
  VFPRegPrecision precision =
      (instr->szValue() == 0) ? kSinglePrecision : kDoublePrecision;
  int operand_size = (precision == kSinglePrecision) ? 4 : 8;
  bool load = (instr->VLValue() == 0x1);

  int vd;
  int num_regs;
  vd = instr->VFPDRegValue(precision);
  if (precision == kSinglePrecision) {
    num_regs = instr->immed8Value();
  } else {
    num_regs = instr->immed8Value() / 2;
  }

  intptr_t start_address = 0;
  intptr_t end_address = 0;
  int32_t rn_val =
      processPU(instr, num_regs, operand_size, &start_address, &end_address);

  intptr_t* address = reinterpret_cast<intptr_t*>(start_address);
  for (int reg = vd; reg < vd + num_regs; reg++) {
    if (precision == kSinglePrecision) {
      if (load) {
        set_s_register_from_sinteger(
            reg, readW(reinterpret_cast<int32_t>(address), instr));
      } else {
        writeW(reinterpret_cast<int32_t>(address),
               get_sinteger_from_s_register(reg), instr);
      }
      address += 1;
    } else {
      if (load) {
        int32_t data[] = {readW(reinterpret_cast<int32_t>(address), instr),
                          readW(reinterpret_cast<int32_t>(address + 1), instr)};
        double d;
        memcpy(&d, data, 8);
        set_d_register_from_double(reg, d);
      } else {
        int32_t data[2];
        double d;
        get_double_from_d_register(reg, &d);
        memcpy(data, &d, 8);
        writeW(reinterpret_cast<int32_t>(address), data[0], instr);
        writeW(reinterpret_cast<int32_t>(address + 1), data[1], instr);
      }
      address += 2;
    }
  }
  MOZ_ASSERT(reinterpret_cast<intptr_t>(address) - operand_size == end_address);
  if (instr->hasW()) {
    set_register(instr->rnValue(), rn_val);
  }
}

ABI_FUNCTION_TYPE_SIM_PROTOTYPES

// Fill the volatile registers with scratch values.
//
// Some of the ABI calls assume that the float registers are not scratched,
// even though the ABI defines them as volatile - a performance
// optimization. These are all calls passing operands in integer registers,
// so for now the simulator does not scratch any float registers for these
// calls. Should try to narrow it further in future.
//
void Simulator::scratchVolatileRegisters(void* target) {
  // The ARM backend makes calls to __aeabi_idivmod and
  // __aeabi_uidivmod assuming that the float registers are
  // non-volatile as a performance optimization, so the float
  // registers must not be scratch when calling these.
  bool scratchFloat = target != __aeabi_idivmod && target != __aeabi_uidivmod;
  int32_t scratch_value = 0xa5a5a5a5 ^ uint32_t(icount_);
  set_register(r0, scratch_value);
  set_register(r1, scratch_value);
  set_register(r2, scratch_value);
  set_register(r3, scratch_value);
  set_register(r12, scratch_value);  // Intra-Procedure-call scratch register.
  set_register(r14, scratch_value);  // Link register.

  if (scratchFloat) {
    uint64_t scratch_value_d =
        0x5a5a5a5a5a5a5a5aLU ^ uint64_t(icount_) ^ (uint64_t(icount_) << 30);
    for (uint32_t i = d0; i < d8; i++) {
      set_d_register(i, &scratch_value_d);
    }
    for (uint32_t i = d16; i < FloatRegisters::TotalPhys; i++) {
      set_d_register(i, &scratch_value_d);
    }
  }
}

static int64_t MakeInt64(int32_t first, int32_t second) {
  // Little-endian order.
  return ((int64_t)second << 32) | (uint32_t)first;
}

// Software interrupt instructions are used by the simulator to call into C++.
void Simulator::softwareInterrupt(SimInstruction* instr) {
  int svc = instr->svcValue();
  switch (svc) {
    case kCallRtRedirected: {
      Redirection* redirection = Redirection::FromSwiInstruction(instr);
      int32_t* stack_pointer = reinterpret_cast<int32_t*>(get_register(sp));
      int32_t a0 = get_register(r0);
      int32_t a1 = get_register(r1);
      int32_t a2 = get_register(r2);
      int32_t a3 = get_register(r3);
      float s0, s1, s2, s3, s4;
      get_float_from_s_register(0, &s0);
      get_float_from_s_register(0, &s1);
      get_float_from_s_register(0, &s2);
      get_float_from_s_register(0, &s3);
      get_float_from_s_register(0, &s4);
      double d0, d1, d2, d3, d4;
      get_double_from_d_register(0, &d0);
      get_double_from_d_register(1, &d1);
      get_double_from_d_register(2, &d2);
      get_double_from_d_register(3, &d3);
      get_double_from_d_register(4, &d4);

      int32_t saved_lr = get_register(lr);
      intptr_t external =
          reinterpret_cast<intptr_t>(redirection->nativeFunction());

      bool stack_aligned = (get_register(sp) & (ABIStackAlignment - 1)) == 0;
      if (!stack_aligned) {
        fprintf(stderr, "Runtime call with unaligned stack!\n");
        MOZ_CRASH();
      }

      if (single_stepping_) {
        single_step_callback_(single_step_callback_arg_, this, nullptr);
      }

      switch (redirection->type()) {
        ABI_FUNCTION_TYPE_ARM32_SIM_DISPATCH
        default:
          MOZ_CRASH("call");
      }

      if (single_stepping_) {
        single_step_callback_(single_step_callback_arg_, this, nullptr);
      }

      set_register(lr, saved_lr);
      set_pc(get_register(lr));
      break;
    }
    case kBreakpoint: {
      ArmDebugger dbg(this);
      dbg.debug();
      break;
    }
    default: {  // Stop uses all codes greater than 1 << 23.
      if (svc >= (1 << 23)) {
        uint32_t code = svc & kStopCodeMask;
        if (isWatchedStop(code)) {
          increaseStopCounter(code);
        }

        // Stop if it is enabled, otherwise go on jumping over the stop and
        // the message address.
        if (isEnabledStop(code)) {
          ArmDebugger dbg(this);
          dbg.stop(instr);
        } else {
          set_pc(get_pc() + 2 * SimInstruction::kInstrSize);
        }
      } else {
        // This is not a valid svc code.
        MOZ_CRASH();
        break;
      }
    }
  }
}

void Simulator::canonicalizeNaN(double* value) {
  if (!wasm::CodeExists && !wasm::LookupCodeBlock(get_pc_as<void*>()) &&
      FPSCR_default_NaN_mode_) {
    *value = JS::CanonicalizeNaN(*value);
  }
}

void Simulator::canonicalizeNaN(float* value) {
  if (!wasm::CodeExists && !wasm::LookupCodeBlock(get_pc_as<void*>()) &&
      FPSCR_default_NaN_mode_) {
    *value = JS::CanonicalizeNaN(*value);
  }
}

// Stop helper functions.
bool Simulator::isStopInstruction(SimInstruction* instr) {
  return (instr->bits(27, 24) == 0xF) && (instr->svcValue() >= kStopCode);
}

bool Simulator::isWatchedStop(uint32_t code) {
  MOZ_ASSERT(code <= kMaxStopCode);
  return code < kNumOfWatchedStops;
}

bool Simulator::isEnabledStop(uint32_t code) {
  MOZ_ASSERT(code <= kMaxStopCode);
  // Unwatched stops are always enabled.
  return !isWatchedStop(code) ||
         !(watched_stops_[code].count & kStopDisabledBit);
}

void Simulator::enableStop(uint32_t code) {
  MOZ_ASSERT(isWatchedStop(code));
  if (!isEnabledStop(code)) {
    watched_stops_[code].count &= ~kStopDisabledBit;
  }
}

void Simulator::disableStop(uint32_t code) {
  MOZ_ASSERT(isWatchedStop(code));
  if (isEnabledStop(code)) {
    watched_stops_[code].count |= kStopDisabledBit;
  }
}

void Simulator::increaseStopCounter(uint32_t code) {
  MOZ_ASSERT(code <= kMaxStopCode);
  MOZ_ASSERT(isWatchedStop(code));
  if ((watched_stops_[code].count & ~(1 << 31)) == 0x7fffffff) {
    printf(
        "Stop counter for code %i has overflowed.\n"
        "Enabling this code and reseting the counter to 0.\n",
        code);
    watched_stops_[code].count = 0;
    enableStop(code);
  } else {
    watched_stops_[code].count++;
  }
}

// Print a stop status.
void Simulator::printStopInfo(uint32_t code) {
  MOZ_ASSERT(code <= kMaxStopCode);
  if (!isWatchedStop(code)) {
    printf("Stop not watched.");
  } else {
    const char* state = isEnabledStop(code) ? "Enabled" : "Disabled";
    int32_t count = watched_stops_[code].count & ~kStopDisabledBit;
    // Don't print the state of unused breakpoints.
    if (count != 0) {
      if (watched_stops_[code].desc) {
        printf("stop %i - 0x%x: \t%s, \tcounter = %i, \t%s\n", code, code,
               state, count, watched_stops_[code].desc);
      } else {
        printf("stop %i - 0x%x: \t%s, \tcounter = %i\n", code, code, state,
               count);
      }
    }
  }
}

// Instruction types 0 and 1 are both rolled into one function because they only
// differ in the handling of the shifter_operand.
void Simulator::decodeType01(SimInstruction* instr) {
  int type = instr->typeValue();
  if (type == 0 && instr->isSpecialType0()) {
    // Multiply instruction or extra loads and stores.
    if (instr->bits(7, 4) == 9) {
      if (instr->bit(24) == 0) {
        // Raw field decoding here. Multiply instructions have their Rd
        // in funny places.
        int rn = instr->rnValue();
        int rm = instr->rmValue();
        int rs = instr->rsValue();
        int32_t rs_val = get_register(rs);
        int32_t rm_val = get_register(rm);
        if (instr->bit(23) == 0) {
          if (instr->bit(21) == 0) {
            // The MUL instruction description (A 4.1.33) refers to
            // Rd as being the destination for the operation, but it
            // confusingly uses the Rn field to encode it.
            int rd = rn;  // Remap the rn field to the Rd register.
            int32_t alu_out = rm_val * rs_val;
            set_register(rd, alu_out);
            if (instr->hasS()) {
              setNZFlags(alu_out);
            }
          } else {
            int rd = instr->rdValue();
            int32_t acc_value = get_register(rd);
            if (instr->bit(22) == 0) {
              // The MLA instruction description (A 4.1.28) refers
              // to the order of registers as "Rd, Rm, Rs,
              // Rn". But confusingly it uses the Rn field to
              // encode the Rd register and the Rd field to encode
              // the Rn register.
              int32_t mul_out = rm_val * rs_val;
              int32_t result = acc_value + mul_out;
              set_register(rn, result);
            } else {
              int32_t mul_out = rm_val * rs_val;
              int32_t result = acc_value - mul_out;
              set_register(rn, result);
            }
          }
        } else {
          // The signed/long multiply instructions use the terms RdHi
          // and RdLo when referring to the target registers. They are
          // mapped to the Rn and Rd fields as follows:
          // RdLo == Rd
          // RdHi == Rn (This is confusingly stored in variable rd here
          //             because the mul instruction from above uses the
          //             Rn field to encode the Rd register. Good luck figuring
          //             this out without reading the ARM instruction manual
          //             at a very detailed level.)
          int rd_hi = rn;  // Remap the rn field to the RdHi register.
          int rd_lo = instr->rdValue();
          int32_t hi_res = 0;
          int32_t lo_res = 0;
          if (instr->bit(22) == 1) {
            int64_t left_op = static_cast<int32_t>(rm_val);
            int64_t right_op = static_cast<int32_t>(rs_val);
            uint64_t result = left_op * right_op;
            hi_res = static_cast<int32_t>(result >> 32);
            lo_res = static_cast<int32_t>(result & 0xffffffff);
          } else {
            // Unsigned multiply.
            uint64_t left_op = static_cast<uint32_t>(rm_val);
            uint64_t right_op = static_cast<uint32_t>(rs_val);
            uint64_t result = left_op * right_op;
            hi_res = static_cast<int32_t>(result >> 32);
            lo_res = static_cast<int32_t>(result & 0xffffffff);
          }
          set_register(rd_lo, lo_res);
          set_register(rd_hi, hi_res);
          if (instr->hasS()) {
            MOZ_CRASH();
          }
        }
      } else {
        if (instr->bits(excl::ExclusiveOpHi, excl::ExclusiveOpLo) ==
            excl::ExclusiveOpcode) {
          // Load-exclusive / store-exclusive.
          if (instr->bit(excl::ExclusiveLoad)) {
            int rn = instr->rnValue();
            int rt = instr->rtValue();
            int32_t address = get_register(rn);
            switch (instr->bits(excl::ExclusiveSizeHi, excl::ExclusiveSizeLo)) {
              case excl::ExclusiveWord:
                set_register(rt, readExW(address, instr));
                break;
              case excl::ExclusiveDouble: {
                MOZ_ASSERT((rt % 2) == 0);
                int32_t hibits;
                int32_t lobits = readExDW(address, &hibits);
                set_register(rt, lobits);
                set_register(rt + 1, hibits);
                break;
              }
              case excl::ExclusiveByte:
                set_register(rt, readExBU(address));
                break;
              case excl::ExclusiveHalf:
                set_register(rt, readExHU(address, instr));
                break;
            }
          } else {
            int rn = instr->rnValue();
            int rd = instr->rdValue();
            int rt = instr->bits(3, 0);
            int32_t address = get_register(rn);
            int32_t value = get_register(rt);
            int32_t result = 0;
            switch (instr->bits(excl::ExclusiveSizeHi, excl::ExclusiveSizeLo)) {
              case excl::ExclusiveWord:
                result = writeExW(address, value, instr);
                break;
              case excl::ExclusiveDouble: {
                MOZ_ASSERT((rt % 2) == 0);
                int32_t value2 = get_register(rt + 1);
                result = writeExDW(address, value, value2);
                break;
              }
              case excl::ExclusiveByte:
                result = writeExB(address, (uint8_t)value);
                break;
              case excl::ExclusiveHalf:
                result = writeExH(address, (uint16_t)value, instr);
                break;
            }
            set_register(rd, result);
          }
        } else {
          MOZ_CRASH();  // Not used atm
        }
      }
    } else {
      // Extra load/store instructions.
      int rd = instr->rdValue();
      int rn = instr->rnValue();
      int32_t rn_val = get_register(rn);
      int32_t addr = 0;
      if (instr->bit(22) == 0) {
        int rm = instr->rmValue();
        int32_t rm_val = get_register(rm);
        switch (instr->PUField()) {
          case da_x:
            MOZ_ASSERT(!instr->hasW());
            addr = rn_val;
            rn_val -= rm_val;
            set_register(rn, rn_val);
            break;
          case ia_x:
            MOZ_ASSERT(!instr->hasW());
            addr = rn_val;
            rn_val += rm_val;
            set_register(rn, rn_val);
            break;
          case db_x:
            rn_val -= rm_val;
            addr = rn_val;
            if (instr->hasW()) {
              set_register(rn, rn_val);
            }
            break;
          case ib_x:
            rn_val += rm_val;
            addr = rn_val;
            if (instr->hasW()) {
              set_register(rn, rn_val);
            }
            break;
          default:
            // The PU field is a 2-bit field.
            MOZ_CRASH();
            break;
        }
      } else {
        int32_t imm_val = (instr->immedHValue() << 4) | instr->immedLValue();
        switch (instr->PUField()) {
          case da_x:
            MOZ_ASSERT(!instr->hasW());
            addr = rn_val;
            rn_val -= imm_val;
            set_register(rn, rn_val);
            break;
          case ia_x:
            MOZ_ASSERT(!instr->hasW());
            addr = rn_val;
            rn_val += imm_val;
            set_register(rn, rn_val);
            break;
          case db_x:
            rn_val -= imm_val;
            addr = rn_val;
            if (instr->hasW()) {
              set_register(rn, rn_val);
            }
            break;
          case ib_x:
            rn_val += imm_val;
            addr = rn_val;
            if (instr->hasW()) {
              set_register(rn, rn_val);
            }
            break;
          default:
            // The PU field is a 2-bit field.
            MOZ_CRASH();
            break;
        }
      }
      if ((instr->bits(7, 4) & 0xd) == 0xd && instr->bit(20) == 0) {
        MOZ_ASSERT((rd % 2) == 0);
        if (instr->hasH()) {
          // The strd instruction.
          int32_t value1 = get_register(rd);
          int32_t value2 = get_register(rd + 1);
          writeDW(addr, value1, value2);
        } else {
          // The ldrd instruction.
          int* rn_data = readDW(addr);
          if (rn_data) {
            set_dw_register(rd, rn_data);
          }
        }
      } else if (instr->hasH()) {
        if (instr->hasSign()) {
          if (instr->hasL()) {
            int16_t val = readH(addr, instr);
            set_register(rd, val);
          } else {
            int16_t val = get_register(rd);
            writeH(addr, val, instr);
          }
        } else {
          if (instr->hasL()) {
            uint16_t val = readHU(addr, instr);
            set_register(rd, val);
          } else {
            uint16_t val = get_register(rd);
            writeH(addr, val, instr);
          }
        }
      } else {
        // Signed byte loads.
        MOZ_ASSERT(instr->hasSign());
        MOZ_ASSERT(instr->hasL());
        int8_t val = readB(addr);
        set_register(rd, val);
      }
      return;
    }
  } else if ((type == 0) && instr->isMiscType0()) {
    if (instr->bits(7, 4) == 0) {
      if (instr->bit(21) == 0) {
        // mrs
        int rd = instr->rdValue();
        uint32_t flags;
        if (instr->bit(22) == 0) {
          // CPSR. Note: The Q flag is not yet implemented!
          flags = (n_flag_ << 31) | (z_flag_ << 30) | (c_flag_ << 29) |
                  (v_flag_ << 28);
        } else {
          // SPSR
          MOZ_CRASH();
        }
        set_register(rd, flags);
      } else {
        // msr
        if (instr->bits(27, 23) == 2) {
          // Register operand. For now we only emit mask 0b1100.
          int rm = instr->rmValue();
          mozilla::DebugOnly<uint32_t> mask = instr->bits(19, 16);
          MOZ_ASSERT(mask == (3 << 2));

          uint32_t flags = get_register(rm);
          n_flag_ = (flags >> 31) & 1;
          z_flag_ = (flags >> 30) & 1;
          c_flag_ = (flags >> 29) & 1;
          v_flag_ = (flags >> 28) & 1;
        } else {
          MOZ_CRASH();
        }
      }
    } else if (instr->bits(22, 21) == 1) {
      int rm = instr->rmValue();
      switch (instr->bits(7, 4)) {
        case 1:  // BX
          set_pc(get_register(rm));
          break;
        case 3: {  // BLX
          uint32_t old_pc = get_pc();
          set_pc(get_register(rm));
          set_register(lr, old_pc + SimInstruction::kInstrSize);
          break;
        }
        case 7: {  // BKPT
          fprintf(stderr, "Simulator hit BKPT.\n");
          if (getenv("ARM_SIM_DEBUGGER")) {
            ArmDebugger dbg(this);
            dbg.debug();
          } else {
            fprintf(stderr,
                    "Use ARM_SIM_DEBUGGER=1 to enter the builtin debugger.\n");
            MOZ_CRASH("ARM simulator breakpoint");
          }
          break;
        }
        default:
          MOZ_CRASH();
      }
    } else if (instr->bits(22, 21) == 3) {
      int rm = instr->rmValue();
      int rd = instr->rdValue();
      switch (instr->bits(7, 4)) {
        case 1: {  // CLZ
          uint32_t bits = get_register(rm);
          int leading_zeros = std::countl_zero(bits);
          set_register(rd, leading_zeros);
          break;
        }
        default:
          MOZ_CRASH();
          break;
      }
    } else {
      printf("%08x\n", instr->instructionBits());
      MOZ_CRASH();
    }
  } else if ((type == 1) && instr->isNopType1()) {
    // NOP.
  } else if ((type == 1) && instr->isYieldType1()) {
    AtomicOperations::pause();
  } else if ((type == 1) && instr->isCsdbType1()) {
    // Speculation barrier. (No-op for the simulator)
  } else {
    int rd = instr->rdValue();
    int rn = instr->rnValue();
    // Use uint32_t here for integer overflow in operations below not to be
    // undefined behavior, leading to our own calculations of overflow being
    // messed up by the compiler.
    uint32_t rn_val = get_register(rn);
    uint32_t shifter_operand = 0;
    bool shifter_carry_out = 0;
    if (type == 0) {
      shifter_operand = getShiftRm(instr, &shifter_carry_out);
    } else {
      MOZ_ASSERT(instr->typeValue() == 1);
      shifter_operand = getImm(instr, &shifter_carry_out);
    }
    int32_t alu_out;
    switch (instr->opcodeField()) {
      case OpAnd:
        alu_out = rn_val & shifter_operand;
        set_register(rd, alu_out);
        if (instr->hasS()) {
          setNZFlags(alu_out);
          setCFlag(shifter_carry_out);
        }
        break;
      case OpEor:
        alu_out = rn_val ^ shifter_operand;
        set_register(rd, alu_out);
        if (instr->hasS()) {
          setNZFlags(alu_out);
          setCFlag(shifter_carry_out);
        }
        break;
      case OpSub:
        alu_out = rn_val - shifter_operand;
        set_register(rd, alu_out);
        if (instr->hasS()) {
          setNZFlags(alu_out);
          setCFlag(!borrowFrom(rn_val, shifter_operand));
          setVFlag(overflowFrom(alu_out, rn_val, shifter_operand, false));
        }
        break;
      case OpRsb:
        alu_out = shifter_operand - rn_val;
        set_register(rd, alu_out);
        if (instr->hasS()) {
          setNZFlags(alu_out);
          setCFlag(!borrowFrom(shifter_operand, rn_val));
          setVFlag(overflowFrom(alu_out, shifter_operand, rn_val, false));
        }
        break;
      case OpAdd:
        alu_out = rn_val + shifter_operand;
        set_register(rd, alu_out);
        if (instr->hasS()) {
          setNZFlags(alu_out);
          setCFlag(carryFrom(rn_val, shifter_operand));
          setVFlag(overflowFrom(alu_out, rn_val, shifter_operand, true));
        }
        break;
      case OpAdc:
        alu_out = rn_val + shifter_operand + getCarry();
        set_register(rd, alu_out);
        if (instr->hasS()) {
          setNZFlags(alu_out);
          setCFlag(carryFrom(rn_val, shifter_operand, getCarry()));
          setVFlag(overflowFrom(alu_out, rn_val, shifter_operand, true));
        }
        break;
      case OpSbc:
        alu_out = rn_val - shifter_operand - (getCarry() == 0 ? 1 : 0);
        set_register(rd, alu_out);
        if (instr->hasS()) {
          MOZ_CRASH();
        }
        break;
      case OpRsc:
        alu_out = shifter_operand - rn_val - (getCarry() == 0 ? 1 : 0);
        set_register(rd, alu_out);
        if (instr->hasS()) {
          MOZ_CRASH();
        }
        break;
      case OpTst:
        if (instr->hasS()) {
          alu_out = rn_val & shifter_operand;
          setNZFlags(alu_out);
          setCFlag(shifter_carry_out);
        } else {
          alu_out = instr->immedMovwMovtValue();
          set_register(rd, alu_out);
        }
        break;
      case OpTeq:
        if (instr->hasS()) {
          alu_out = rn_val ^ shifter_operand;
          setNZFlags(alu_out);
          setCFlag(shifter_carry_out);
        } else {
          // Other instructions matching this pattern are handled in the
          // miscellaneous instructions part above.
          MOZ_CRASH();
        }
        break;
      case OpCmp:
        if (instr->hasS()) {
          alu_out = rn_val - shifter_operand;
          setNZFlags(alu_out);
          setCFlag(!borrowFrom(rn_val, shifter_operand));
          setVFlag(overflowFrom(alu_out, rn_val, shifter_operand, false));
        } else {
          alu_out =
              (get_register(rd) & 0xffff) | (instr->immedMovwMovtValue() << 16);
          set_register(rd, alu_out);
        }
        break;
      case OpCmn:
        if (instr->hasS()) {
          alu_out = rn_val + shifter_operand;
          setNZFlags(alu_out);
          setCFlag(carryFrom(rn_val, shifter_operand));
          setVFlag(overflowFrom(alu_out, rn_val, shifter_operand, true));
        } else {
          // Other instructions matching this pattern are handled in the
          // miscellaneous instructions part above.
          MOZ_CRASH();
        }
        break;
      case OpOrr:
        alu_out = rn_val | shifter_operand;
        set_register(rd, alu_out);
        if (instr->hasS()) {
          setNZFlags(alu_out);
          setCFlag(shifter_carry_out);
        }
        break;
      case OpMov:
        alu_out = shifter_operand;
        set_register(rd, alu_out);
        if (instr->hasS()) {
          setNZFlags(alu_out);
          setCFlag(shifter_carry_out);
        }
        break;
      case OpBic:
        alu_out = rn_val & ~shifter_operand;
        set_register(rd, alu_out);
        if (instr->hasS()) {
          setNZFlags(alu_out);
          setCFlag(shifter_carry_out);
        }
        break;
      case OpMvn:
        alu_out = ~shifter_operand;
        set_register(rd, alu_out);
        if (instr->hasS()) {
          setNZFlags(alu_out);
          setCFlag(shifter_carry_out);
        }
        break;
      default:
        MOZ_CRASH();
        break;
    }
  }
}

void Simulator::decodeType2(SimInstruction* instr) {
  int rd = instr->rdValue();
  int rn = instr->rnValue();
  int32_t rn_val = get_register(rn);
  int32_t im_val = instr->offset12Value();
  int32_t addr = 0;
  switch (instr->PUField()) {
    case da_x:
      MOZ_ASSERT(!instr->hasW());
      addr = rn_val;
      rn_val -= im_val;
      set_register(rn, rn_val);
      break;
    case ia_x:
      MOZ_ASSERT(!instr->hasW());
      addr = rn_val;
      rn_val += im_val;
      set_register(rn, rn_val);
      break;
    case db_x:
      rn_val -= im_val;
      addr = rn_val;
      if (instr->hasW()) {
        set_register(rn, rn_val);
      }
      break;
    case ib_x:
      rn_val += im_val;
      addr = rn_val;
      if (instr->hasW()) {
        set_register(rn, rn_val);
      }
      break;
    default:
      MOZ_CRASH();
      break;
  }
  if (instr->hasB()) {
    if (instr->hasL()) {
      uint8_t val = readBU(addr);
      set_register(rd, val);
    } else {
      uint8_t val = get_register(rd);
      writeB(addr, val);
    }
  } else {
    if (instr->hasL()) {
      set_register(rd, readW(addr, instr, AllowUnaligned));
    } else {
      writeW(addr, get_register(rd), instr, AllowUnaligned);
    }
  }
}

static uint32_t rotateBytes(uint32_t val, int32_t rotate) {
  switch (rotate) {
    default:
      return val;
    case 1:
      return (val >> 8) | (val << 24);
    case 2:
      return (val >> 16) | (val << 16);
    case 3:
      return (val >> 24) | (val << 8);
  }
}

void Simulator::decodeType3(SimInstruction* instr) {
  if (MOZ_UNLIKELY(instr->isUDF())) {
    uint8_t* newPC;
    if (wasm::HandleIllegalInstruction(registerState(), &newPC)) {
      set_pc((int32_t)newPC);
      return;
    }
    MOZ_CRASH("illegal instruction encountered");
  }

  int rd = instr->rdValue();
  int rn = instr->rnValue();
  int32_t rn_val = get_register(rn);
  bool shifter_carry_out = 0;
  int32_t shifter_operand = getShiftRm(instr, &shifter_carry_out);
  int32_t addr = 0;
  switch (instr->PUField()) {
    case da_x:
      MOZ_ASSERT(!instr->hasW());
      MOZ_CRASH();
      break;
    case ia_x: {
      if (instr->bit(4) == 0) {
        // Memop.
      } else {
        if (instr->bit(5) == 0) {
          switch (instr->bits(22, 21)) {
            case 0:
              if (instr->bit(20) == 0) {
                if (instr->bit(6) == 0) {
                  // Pkhbt.
                  uint32_t rn_val = get_register(rn);
                  uint32_t rm_val = get_register(instr->rmValue());
                  int32_t shift = instr->bits(11, 7);
                  rm_val <<= shift;
                  set_register(rd, (rn_val & 0xFFFF) | (rm_val & 0xFFFF0000U));
                } else {
                  // Pkhtb.
                  uint32_t rn_val = get_register(rn);
                  int32_t rm_val = get_register(instr->rmValue());
                  int32_t shift = instr->bits(11, 7);
                  if (shift == 0) {
                    shift = 32;
                  }
                  rm_val >>= shift;
                  set_register(rd, (rn_val & 0xFFFF0000U) | (rm_val & 0xFFFF));
                }
              } else {
                MOZ_CRASH();
              }
              break;
            case 1:
              MOZ_CRASH();
              break;
            case 2:
              MOZ_CRASH();
              break;
            case 3: {
              // Usat.
              int32_t sat_pos = instr->bits(20, 16);
              int32_t sat_val = (1 << sat_pos) - 1;
              int32_t shift = instr->bits(11, 7);
              int32_t shift_type = instr->bit(6);
              int32_t rm_val = get_register(instr->rmValue());
              if (shift_type == 0) {  // LSL
                rm_val <<= shift;
              } else {  // ASR
                rm_val >>= shift;
              }

              // If saturation occurs, the Q flag should be set in the
              // CPSR. There is no Q flag yet, and no instruction (MRS)
              // to read the CPSR directly.
              if (rm_val > sat_val) {
                rm_val = sat_val;
              } else if (rm_val < 0) {
                rm_val = 0;
              }
              set_register(rd, rm_val);
              break;
            }
          }
        } else {
          switch (instr->bits(22, 21)) {
            case 0:
              MOZ_CRASH();
              break;
            case 1:
              if (instr->bits(7, 4) == 7 && instr->bits(19, 16) == 15) {
                uint32_t rm_val = rotateBytes(get_register(instr->rmValue()),
                                              instr->bits(11, 10));
                if (instr->bit(20)) {
                  // Sxth.
                  set_register(rd, (int32_t)(int16_t)(rm_val & 0xFFFF));
                } else {
                  // Sxtb.
                  set_register(rd, (int32_t)(int8_t)(rm_val & 0xFF));
                }
              } else if (instr->bits(20, 16) == 0b1'1111 &&
                         instr->bits(11, 4) == 0b1111'0011) {
                // Rev
                uint32_t rm_val = get_register(instr->rmValue());

                static_assert(std::endian::native == std::endian::little);
                set_register(rd,
                             mozilla::NativeEndian::swapToBigEndian(rm_val));
              } else if (instr->bits(20, 16) == 0b1'1111 &&
                         instr->bits(11, 4) == 0b1111'1011) {
                // Rev16
                uint32_t rm_val = get_register(instr->rmValue());

                static_assert(std::endian::native == std::endian::little);
                uint32_t hi = mozilla::NativeEndian::swapToBigEndian(
                    uint16_t(rm_val >> 16));
                uint32_t lo =
                    mozilla::NativeEndian::swapToBigEndian(uint16_t(rm_val));
                set_register(rd, (hi << 16) | lo);
              } else {
                MOZ_CRASH();
              }
              break;
            case 2:
              if ((instr->bit(20) == 0) && (instr->bits(9, 6) == 1)) {
                if (instr->bits(19, 16) == 0xF) {
                  // Uxtb16.
                  uint32_t rm_val = rotateBytes(get_register(instr->rmValue()),
                                                instr->bits(11, 10));
                  set_register(rd, (rm_val & 0xFF) | (rm_val & 0xFF0000));
                } else {
                  MOZ_CRASH();
                }
              } else {
                MOZ_CRASH();
              }
              break;
            case 3:
              if ((instr->bit(20) == 0) && (instr->bits(9, 6) == 1)) {
                if (instr->bits(19, 16) == 0xF) {
                  // Uxtb.
                  uint32_t rm_val = rotateBytes(get_register(instr->rmValue()),
                                                instr->bits(11, 10));
                  set_register(rd, (rm_val & 0xFF));
                } else {
                  // Uxtab.
                  uint32_t rn_val = get_register(rn);
                  uint32_t rm_val = rotateBytes(get_register(instr->rmValue()),
                                                instr->bits(11, 10));
                  set_register(rd, rn_val + (rm_val & 0xFF));
                }
              } else if ((instr->bit(20) == 1) && (instr->bits(9, 6) == 1)) {
                if (instr->bits(19, 16) == 0xF) {
                  // Uxth.
                  uint32_t rm_val = rotateBytes(get_register(instr->rmValue()),
                                                instr->bits(11, 10));
                  set_register(rd, (rm_val & 0xFFFF));
                } else {
                  // Uxtah.
                  uint32_t rn_val = get_register(rn);
                  uint32_t rm_val = rotateBytes(get_register(instr->rmValue()),
                                                instr->bits(11, 10));
                  set_register(rd, rn_val + (rm_val & 0xFFFF));
                }
              } else if (instr->bits(20, 16) == 0b1'1111 &&
                         instr->bits(11, 4) == 0b1111'1011) {
                // Revsh
                uint32_t rm_val = get_register(instr->rmValue());

                static_assert(std::endian::native == std::endian::little);
                set_register(
                    rd, int32_t(int16_t(mozilla::NativeEndian::swapToBigEndian(
                            uint16_t(rm_val)))));
              } else {
                MOZ_CRASH();
              }
              break;
          }
        }
        return;
      }
      break;
    }
    case db_x: {  // sudiv
      if (instr->bit(22) == 0x0 && instr->bit(20) == 0x1 &&
          instr->bits(15, 12) == 0x0f && instr->bits(7, 4) == 0x1) {
        if (!instr->hasW()) {
          // sdiv (in V8 notation matching ARM ISA format) rn = rm/rs.
          int rm = instr->rmValue();
          int32_t rm_val = get_register(rm);
          int rs = instr->rsValue();
          int32_t rs_val = get_register(rs);
          int32_t ret_val = 0;
          MOZ_ASSERT(rs_val != 0);
          if ((rm_val == INT32_MIN) && (rs_val == -1)) {
            ret_val = INT32_MIN;
          } else {
            ret_val = rm_val / rs_val;
          }
          set_register(rn, ret_val);
          return;
        } else {
          // udiv (in V8 notation matching ARM ISA format) rn = rm/rs.
          int rm = instr->rmValue();
          uint32_t rm_val = get_register(rm);
          int rs = instr->rsValue();
          uint32_t rs_val = get_register(rs);
          uint32_t ret_val = 0;
          MOZ_ASSERT(rs_val != 0);
          ret_val = rm_val / rs_val;
          set_register(rn, ret_val);
          return;
        }
      }

      addr = rn_val - shifter_operand;
      if (instr->hasW()) {
        set_register(rn, addr);
      }
      break;
    }
    case ib_x: {
      if (instr->hasW() && (instr->bits(6, 4) == 0x5)) {
        uint32_t widthminus1 = static_cast<uint32_t>(instr->bits(20, 16));
        uint32_t lsbit = static_cast<uint32_t>(instr->bits(11, 7));
        uint32_t msbit = widthminus1 + lsbit;
        if (msbit <= 31) {
          if (instr->bit(22)) {
            // ubfx - unsigned bitfield extract.
            uint32_t rm_val =
                static_cast<uint32_t>(get_register(instr->rmValue()));
            uint32_t extr_val = rm_val << (31 - msbit);
            extr_val = extr_val >> (31 - widthminus1);
            set_register(instr->rdValue(), extr_val);
          } else {
            // sbfx - signed bitfield extract.
            int32_t rm_val = get_register(instr->rmValue());
            int32_t extr_val = rm_val << (31 - msbit);
            extr_val = extr_val >> (31 - widthminus1);
            set_register(instr->rdValue(), extr_val);
          }
        } else {
          MOZ_CRASH();
        }
        return;
      } else if (!instr->hasW() && (instr->bits(6, 4) == 0x1)) {
        uint32_t lsbit = static_cast<uint32_t>(instr->bits(11, 7));
        uint32_t msbit = static_cast<uint32_t>(instr->bits(20, 16));
        if (msbit >= lsbit) {
          // bfc or bfi - bitfield clear/insert.
          uint32_t rd_val =
              static_cast<uint32_t>(get_register(instr->rdValue()));
          uint32_t bitcount = msbit - lsbit + 1;
          uint32_t mask = (1 << bitcount) - 1;
          rd_val &= ~(mask << lsbit);
          if (instr->rmValue() != 15) {
            // bfi - bitfield insert.
            uint32_t rm_val =
                static_cast<uint32_t>(get_register(instr->rmValue()));
            rm_val &= mask;
            rd_val |= rm_val << lsbit;
          }
          set_register(instr->rdValue(), rd_val);
        } else {
          MOZ_CRASH();
        }
        return;
      } else {
        addr = rn_val + shifter_operand;
        if (instr->hasW()) {
          set_register(rn, addr);
        }
      }
      break;
    }
    default:
      MOZ_CRASH();
      break;
  }
  if (instr->hasB()) {
    if (instr->hasL()) {
      uint8_t byte = readB(addr);
      set_register(rd, byte);
    } else {
      uint8_t byte = get_register(rd);
      writeB(addr, byte);
    }
  } else {
    if (instr->hasL()) {
      set_register(rd, readW(addr, instr, AllowUnaligned));
    } else {
      writeW(addr, get_register(rd), instr, AllowUnaligned);
    }
  }
}

void Simulator::decodeType4(SimInstruction* instr) {
  // Only allowed to be set in privileged mode.
  MOZ_ASSERT(instr->bit(22) == 0);
  bool load = instr->hasL();
  handleRList(instr, load);
}

void Simulator::decodeType5(SimInstruction* instr) {
  int off = instr->sImmed24Value() << 2;
  intptr_t pc_address = get_pc();
  if (instr->hasLink()) {
    set_register(lr, pc_address + SimInstruction::kInstrSize);
  }
  int pc_reg = get_register(pc);
  set_pc(pc_reg + off);
}

void Simulator::decodeType6(SimInstruction* instr) {
  decodeType6CoprocessorIns(instr);
}

void Simulator::decodeType7(SimInstruction* instr) {
  if (instr->bit(24) == 1) {
    softwareInterrupt(instr);
  } else if (instr->bit(4) == 1 && instr->bits(11, 9) != 5) {
    decodeType7CoprocessorIns(instr);
  } else {
    decodeTypeVFP(instr);
  }
}

void Simulator::decodeType7CoprocessorIns(SimInstruction* instr) {
  if (instr->bit(20) == 0) {
    // MCR, MCR2
    if (instr->coprocessorValue() == 15) {
      int opc1 = instr->bits(23, 21);
      int opc2 = instr->bits(7, 5);
      int CRn = instr->bits(19, 16);
      int CRm = instr->bits(3, 0);
      if (opc1 == 0 && opc2 == 4 && CRn == 7 && CRm == 10) {
        // ARMv6 DSB instruction.  We do not use DSB.
        MOZ_CRASH("DSB not implemented");
      } else if (opc1 == 0 && opc2 == 5 && CRn == 7 && CRm == 10) {
        // ARMv6 DMB instruction.
        AtomicOperations::fenceSeqCst();
      } else if (opc1 == 0 && opc2 == 4 && CRn == 7 && CRm == 5) {
        // ARMv6 ISB instruction.  We do not use ISB.
        MOZ_CRASH("ISB not implemented");
      } else {
        MOZ_CRASH();
      }
    } else {
      MOZ_CRASH();
    }
  } else {
    // MRC, MRC2
    MOZ_CRASH();
  }
}

void Simulator::decodeTypeVFP(SimInstruction* instr) {
  MOZ_ASSERT(instr->typeValue() == 7 && instr->bit(24) == 0);
  MOZ_ASSERT(instr->bits(11, 9) == 0x5);

  // Obtain double precision register codes.
  VFPRegPrecision precision =
      (instr->szValue() == 1) ? kDoublePrecision : kSinglePrecision;
  int vm = instr->VFPMRegValue(precision);
  int vd = instr->VFPDRegValue(precision);
  int vn = instr->VFPNRegValue(precision);

  if (instr->bit(4) == 0) {
    if (instr->opc1Value() == 0x7) {
      // Other data processing instructions.
      if ((instr->opc2Value() == 0x0) && (instr->opc3Value() == 0x1)) {
        // vmov register to register.
        if (instr->szValue() == 0x1) {
          int m = instr->VFPMRegValue(kDoublePrecision);
          int d = instr->VFPDRegValue(kDoublePrecision);
          double temp;
          get_double_from_d_register(m, &temp);
          set_d_register_from_double(d, temp);
        } else {
          int m = instr->VFPMRegValue(kSinglePrecision);
          int d = instr->VFPDRegValue(kSinglePrecision);
          float temp;
          get_float_from_s_register(m, &temp);
          set_s_register_from_float(d, temp);
        }
      } else if ((instr->opc2Value() == 0x0) && (instr->opc3Value() == 0x3)) {
        // vabs
        if (instr->szValue() == 0x1) {
          union {
            double f64;
            uint64_t u64;
          } u;
          get_double_from_d_register(vm, &u.f64);
          u.u64 &= 0x7fffffffffffffffu;
          double dd_value = u.f64;
          canonicalizeNaN(&dd_value);
          set_d_register_from_double(vd, dd_value);
        } else {
          union {
            float f32;
            uint32_t u32;
          } u;
          get_float_from_s_register(vm, &u.f32);
          u.u32 &= 0x7fffffffu;
          float fd_value = u.f32;
          canonicalizeNaN(&fd_value);
          set_s_register_from_float(vd, fd_value);
        }
      } else if ((instr->opc2Value() == 0x1) && (instr->opc3Value() == 0x1)) {
        // vneg
        if (instr->szValue() == 0x1) {
          double dm_value;
          get_double_from_d_register(vm, &dm_value);
          double dd_value = -dm_value;
          canonicalizeNaN(&dd_value);
          set_d_register_from_double(vd, dd_value);
        } else {
          float fm_value;
          get_float_from_s_register(vm, &fm_value);
          float fd_value = -fm_value;
          canonicalizeNaN(&fd_value);
          set_s_register_from_float(vd, fd_value);
        }
      } else if ((instr->opc2Value() == 0x7) && (instr->opc3Value() == 0x3)) {
        decodeVCVTBetweenDoubleAndSingle(instr);
      } else if ((instr->opc2Value() == 0x8) && (instr->opc3Value() & 0x1)) {
        decodeVCVTBetweenFloatingPointAndInteger(instr);
      } else if ((instr->opc2Value() == 0xA) && (instr->opc3Value() == 0x3) &&
                 (instr->bit(8) == 1)) {
        // vcvt.f64.s32 Dd, Dd, #<fbits>.
        int fraction_bits = 32 - ((instr->bits(3, 0) << 1) | instr->bit(5));
        int fixed_value = get_sinteger_from_s_register(vd * 2);
        double divide = 1 << fraction_bits;
        set_d_register_from_double(vd, fixed_value / divide);
      } else if (((instr->opc2Value() >> 1) == 0x6) &&
                 (instr->opc3Value() & 0x1)) {
        decodeVCVTBetweenFloatingPointAndInteger(instr);
      } else if (((instr->opc2Value() == 0x4) || (instr->opc2Value() == 0x5)) &&
                 (instr->opc3Value() & 0x1)) {
        decodeVCMP(instr);
      } else if (((instr->opc2Value() == 0x1)) && (instr->opc3Value() == 0x3)) {
        // vsqrt
        if (instr->szValue() == 0x1) {
          double dm_value;
          get_double_from_d_register(vm, &dm_value);
          double dd_value = std::sqrt(dm_value);
          canonicalizeNaN(&dd_value);
          set_d_register_from_double(vd, dd_value);
        } else {
          float fm_value;
          get_float_from_s_register(vm, &fm_value);
          float fd_value = std::sqrt(fm_value);
          canonicalizeNaN(&fd_value);
          set_s_register_from_float(vd, fd_value);
        }
      } else if (instr->opc3Value() == 0x0) {
        // vmov immediate.
        if (instr->szValue() == 0x1) {
          set_d_register_from_double(vd, instr->doubleImmedVmov());
        } else {
          // vmov.f32 immediate.
          set_s_register_from_float(vd, instr->float32ImmedVmov());
        }
      } else if ((instr->opc2Value() & ~0x1) == 0x2 &&
                 (instr->opc3Value() & 0x1)) {
        decodeVCVTBetweenFloatingPointAndHalf(instr);
      } else {
        decodeVCVTBetweenFloatingPointAndIntegerFrac(instr);
      }
    } else if (instr->opc1Value() == 0x3) {
      if (instr->szValue() != 0x1) {
        if (instr->opc3Value() & 0x1) {
          // vsub
          float fn_value;
          get_float_from_s_register(vn, &fn_value);
          float fm_value;
          get_float_from_s_register(vm, &fm_value);
          float fd_value = fn_value - fm_value;
          canonicalizeNaN(&fd_value);
          set_s_register_from_float(vd, fd_value);
        } else {
          // vadd
          float fn_value;
          get_float_from_s_register(vn, &fn_value);
          float fm_value;
          get_float_from_s_register(vm, &fm_value);
          float fd_value = fn_value + fm_value;
          canonicalizeNaN(&fd_value);
          set_s_register_from_float(vd, fd_value);
        }
      } else {
        if (instr->opc3Value() & 0x1) {
          // vsub
          double dn_value;
          get_double_from_d_register(vn, &dn_value);
          double dm_value;
          get_double_from_d_register(vm, &dm_value);
          double dd_value = dn_value - dm_value;
          canonicalizeNaN(&dd_value);
          set_d_register_from_double(vd, dd_value);
        } else {
          // vadd
          double dn_value;
          get_double_from_d_register(vn, &dn_value);
          double dm_value;
          get_double_from_d_register(vm, &dm_value);
          double dd_value = dn_value + dm_value;
          canonicalizeNaN(&dd_value);
          set_d_register_from_double(vd, dd_value);
        }
      }
    } else if ((instr->opc1Value() == 0x2) && !(instr->opc3Value() & 0x1)) {
      // vmul
      if (instr->szValue() != 0x1) {
        float fn_value;
        get_float_from_s_register(vn, &fn_value);
        float fm_value;
        get_float_from_s_register(vm, &fm_value);
        float fd_value = fn_value * fm_value;
        canonicalizeNaN(&fd_value);
        set_s_register_from_float(vd, fd_value);
      } else {
        double dn_value;
        get_double_from_d_register(vn, &dn_value);
        double dm_value;
        get_double_from_d_register(vm, &dm_value);
        double dd_value = dn_value * dm_value;
        canonicalizeNaN(&dd_value);
        set_d_register_from_double(vd, dd_value);
      }
    } else if ((instr->opc1Value() == 0x0)) {
      // vmla, vmls
      const bool is_vmls = (instr->opc3Value() & 0x1);

      if (instr->szValue() != 0x1) {
        MOZ_CRASH("Not used by V8.");
      }

      double dd_val;
      get_double_from_d_register(vd, &dd_val);
      double dn_val;
      get_double_from_d_register(vn, &dn_val);
      double dm_val;
      get_double_from_d_register(vm, &dm_val);

      // Note: we do the mul and add/sub in separate steps to avoid
      // getting a result with too high precision.
      set_d_register_from_double(vd, dn_val * dm_val);
      double temp;
      get_double_from_d_register(vd, &temp);
      if (is_vmls) {
        temp = dd_val - temp;
      } else {
        temp = dd_val + temp;
      }
      canonicalizeNaN(&temp);
      set_d_register_from_double(vd, temp);
    } else if ((instr->opc1Value() == 0x4) && !(instr->opc3Value() & 0x1)) {
      // vdiv
      if (instr->szValue() != 0x1) {
        float fn_value;
        get_float_from_s_register(vn, &fn_value);
        float fm_value;
        get_float_from_s_register(vm, &fm_value);
        float fd_value = fn_value / fm_value;
        div_zero_vfp_flag_ = (fm_value == 0);
        canonicalizeNaN(&fd_value);
        set_s_register_from_float(vd, fd_value);
      } else {
        double dn_value;
        get_double_from_d_register(vn, &dn_value);
        double dm_value;
        get_double_from_d_register(vm, &dm_value);
        double dd_value = dn_value / dm_value;
        div_zero_vfp_flag_ = (dm_value == 0);
        canonicalizeNaN(&dd_value);
        set_d_register_from_double(vd, dd_value);
      }
    } else {
      MOZ_CRASH();
    }
  } else {
    if (instr->VCValue() == 0x0 && instr->VAValue() == 0x0) {
      decodeVMOVBetweenCoreAndSinglePrecisionRegisters(instr);
    } else if ((instr->VLValue() == 0x0) && (instr->VCValue() == 0x1) &&
               (instr->bit(23) == 0x0)) {
      // vmov (ARM core register to scalar).
      int vd = instr->bits(19, 16) | (instr->bit(7) << 4);
      double dd_value;
      get_double_from_d_register(vd, &dd_value);
      int32_t data[2];
      memcpy(data, &dd_value, 8);
      data[instr->bit(21)] = get_register(instr->rtValue());
      memcpy(&dd_value, data, 8);
      set_d_register_from_double(vd, dd_value);
    } else if ((instr->VLValue() == 0x1) && (instr->VCValue() == 0x1) &&
               (instr->bit(23) == 0x0)) {
      // vmov (scalar to ARM core register).
      int vn = instr->bits(19, 16) | (instr->bit(7) << 4);
      double dn_value;
      get_double_from_d_register(vn, &dn_value);
      int32_t data[2];
      memcpy(data, &dn_value, 8);
      set_register(instr->rtValue(), data[instr->bit(21)]);
    } else if ((instr->VLValue() == 0x1) && (instr->VCValue() == 0x0) &&
               (instr->VAValue() == 0x7) && (instr->bits(19, 16) == 0x1)) {
      // vmrs
      uint32_t rt = instr->rtValue();
      if (rt == 0xF) {
        copy_FPSCR_to_APSR();
      } else {
        // Emulate FPSCR from the Simulator flags.
        uint32_t fpscr = (n_flag_FPSCR_ << 31) | (z_flag_FPSCR_ << 30) |
                         (c_flag_FPSCR_ << 29) | (v_flag_FPSCR_ << 28) |
                         (FPSCR_default_NaN_mode_ << 25) |
                         (inexact_vfp_flag_ << 4) | (underflow_vfp_flag_ << 3) |
                         (overflow_vfp_flag_ << 2) | (div_zero_vfp_flag_ << 1) |
                         (inv_op_vfp_flag_ << 0) | (FPSCR_rounding_mode_);
        set_register(rt, fpscr);
      }
    } else if ((instr->VLValue() == 0x0) && (instr->VCValue() == 0x0) &&
               (instr->VAValue() == 0x7) && (instr->bits(19, 16) == 0x1)) {
      // vmsr
      uint32_t rt = instr->rtValue();
      if (rt == pc) {
        MOZ_CRASH();
      } else {
        uint32_t rt_value = get_register(rt);
        n_flag_FPSCR_ = (rt_value >> 31) & 1;
        z_flag_FPSCR_ = (rt_value >> 30) & 1;
        c_flag_FPSCR_ = (rt_value >> 29) & 1;
        v_flag_FPSCR_ = (rt_value >> 28) & 1;
        FPSCR_default_NaN_mode_ = (rt_value >> 25) & 1;
        inexact_vfp_flag_ = (rt_value >> 4) & 1;
        underflow_vfp_flag_ = (rt_value >> 3) & 1;
        overflow_vfp_flag_ = (rt_value >> 2) & 1;
        div_zero_vfp_flag_ = (rt_value >> 1) & 1;
        inv_op_vfp_flag_ = (rt_value >> 0) & 1;
        FPSCR_rounding_mode_ =
            static_cast<VFPRoundingMode>((rt_value)&kVFPRoundingModeMask);
      }
    } else {
      MOZ_CRASH();
    }
  }
}

void Simulator::decodeVMOVBetweenCoreAndSinglePrecisionRegisters(
    SimInstruction* instr) {
  MOZ_ASSERT(instr->bit(4) == 1 && instr->VCValue() == 0x0 &&
             instr->VAValue() == 0x0);

  int t = instr->rtValue();
  int n = instr->VFPNRegValue(kSinglePrecision);
  bool to_arm_register = (instr->VLValue() == 0x1);
  if (to_arm_register) {
    int32_t int_value = get_sinteger_from_s_register(n);
    set_register(t, int_value);
  } else {
    int32_t rs_val = get_register(t);
    set_s_register_from_sinteger(n, rs_val);
  }
}

void Simulator::decodeVCMP(SimInstruction* instr) {
  MOZ_ASSERT((instr->bit(4) == 0) && (instr->opc1Value() == 0x7));
  MOZ_ASSERT(((instr->opc2Value() == 0x4) || (instr->opc2Value() == 0x5)) &&
             (instr->opc3Value() & 0x1));
  // Comparison.

  VFPRegPrecision precision = kSinglePrecision;
  if (instr->szValue() == 1) {
    precision = kDoublePrecision;
  }

  int d = instr->VFPDRegValue(precision);
  int m = 0;
  if (instr->opc2Value() == 0x4) {
    m = instr->VFPMRegValue(precision);
  }

  if (precision == kDoublePrecision) {
    double dd_value;
    get_double_from_d_register(d, &dd_value);
    double dm_value = 0.0;
    if (instr->opc2Value() == 0x4) {
      get_double_from_d_register(m, &dm_value);
    }

    // Raise exceptions for quiet NaNs if necessary.
    if (instr->bit(7) == 1) {
      if (std::isnan(dd_value)) {
        inv_op_vfp_flag_ = true;
      }
    }
    compute_FPSCR_Flags(dd_value, dm_value);
  } else {
    float fd_value;
    get_float_from_s_register(d, &fd_value);
    float fm_value = 0.0;
    if (instr->opc2Value() == 0x4) {
      get_float_from_s_register(m, &fm_value);
    }

    // Raise exceptions for quiet NaNs if necessary.
    if (instr->bit(7) == 1) {
      if (std::isnan(fd_value)) {
        inv_op_vfp_flag_ = true;
      }
    }
    compute_FPSCR_Flags(fd_value, fm_value);
  }
}

void Simulator::decodeVCVTBetweenDoubleAndSingle(SimInstruction* instr) {
  MOZ_ASSERT(instr->bit(4) == 0 && instr->opc1Value() == 0x7);
  MOZ_ASSERT(instr->opc2Value() == 0x7 && instr->opc3Value() == 0x3);

  VFPRegPrecision dst_precision = kDoublePrecision;
  VFPRegPrecision src_precision = kSinglePrecision;
  if (instr->szValue() == 1) {
    dst_precision = kSinglePrecision;
    src_precision = kDoublePrecision;
  }

  int dst = instr->VFPDRegValue(dst_precision);
  int src = instr->VFPMRegValue(src_precision);

  if (dst_precision == kSinglePrecision) {
    double val;
    get_double_from_d_register(src, &val);
    set_s_register_from_float(dst, static_cast<float>(val));
  } else {
    float val;
    get_float_from_s_register(src, &val);
    set_d_register_from_double(dst, static_cast<double>(val));
  }
}

static bool get_inv_op_vfp_flag(VFPRoundingMode mode, double val,
                                bool unsigned_) {
  MOZ_ASSERT(mode == SimRN || mode == SimRM || mode == SimRZ);
  double max_uint = static_cast<double>(0xffffffffu);
  double max_int = static_cast<double>(INT32_MAX);
  double min_int = static_cast<double>(INT32_MIN);

  // Check for NaN.
  if (val != val) {
    return true;
  }

  // Check for overflow. This code works because 32bit integers can be exactly
  // represented by ieee-754 64bit floating-point values.
  switch (mode) {
    case SimRN:
      return unsigned_ ? (val >= (max_uint + 0.5)) || (val < -0.5)
                       : (val >= (max_int + 0.5)) || (val < (min_int - 0.5));
    case SimRM:
      return unsigned_ ? (val >= (max_uint + 1.0)) || (val < 0)
                       : (val >= (max_int + 1.0)) || (val < min_int);
    case SimRZ:
      return unsigned_ ? (val >= (max_uint + 1.0)) || (val <= -1)
                       : (val >= (max_int + 1.0)) || (val <= (min_int - 1.0));
    default:
      MOZ_CRASH();
      return true;
  }
}

// We call this function only if we had a vfp invalid exception.
// It returns the correct saturated value.
static int VFPConversionSaturate(double val, bool unsigned_res) {
  if (val != val) {  // NaN.
    return 0;
  }
  if (unsigned_res) {
    return (val < 0) ? 0 : 0xffffffffu;
  }
  return (val < 0) ? INT32_MIN : INT32_MAX;
}

void Simulator::decodeVCVTBetweenFloatingPointAndInteger(
    SimInstruction* instr) {
  MOZ_ASSERT((instr->bit(4) == 0) && (instr->opc1Value() == 0x7) &&
             (instr->bits(27, 23) == 0x1D));
  MOZ_ASSERT(
      ((instr->opc2Value() == 0x8) && (instr->opc3Value() & 0x1)) ||
      (((instr->opc2Value() >> 1) == 0x6) && (instr->opc3Value() & 0x1)));

  // Conversion between floating-point and integer.
  bool to_integer = (instr->bit(18) == 1);

  VFPRegPrecision src_precision =
      (instr->szValue() == 1) ? kDoublePrecision : kSinglePrecision;

  if (to_integer) {
    // We are playing with code close to the C++ standard's limits below,
    // hence the very simple code and heavy checks.
    //
    // Note: C++ defines default type casting from floating point to integer
    // as (close to) rounding toward zero ("fractional part discarded").

    int dst = instr->VFPDRegValue(kSinglePrecision);
    int src = instr->VFPMRegValue(src_precision);

    // Bit 7 in vcvt instructions indicates if we should use the FPSCR
    // rounding mode or the default Round to Zero mode.
    VFPRoundingMode mode = (instr->bit(7) != 1) ? FPSCR_rounding_mode_ : SimRZ;
    MOZ_ASSERT(mode == SimRM || mode == SimRZ || mode == SimRN);

    bool unsigned_integer = (instr->bit(16) == 0);
    bool double_precision = (src_precision == kDoublePrecision);

    double val;
    if (double_precision) {
      get_double_from_d_register(src, &val);
    } else {
      float fval;
      get_float_from_s_register(src, &fval);
      val = double(fval);
    }

    int temp = unsigned_integer ? static_cast<uint32_t>(val)
                                : static_cast<int32_t>(val);

    inv_op_vfp_flag_ = get_inv_op_vfp_flag(mode, val, unsigned_integer);

    double abs_diff = unsigned_integer
                          ? std::fabs(val - static_cast<uint32_t>(temp))
                          : std::fabs(val - temp);

    inexact_vfp_flag_ = (abs_diff != 0);

    if (inv_op_vfp_flag_) {
      temp = VFPConversionSaturate(val, unsigned_integer);
    } else {
      switch (mode) {
        case SimRN: {
          int val_sign = (val > 0) ? 1 : -1;
          if (abs_diff > 0.5) {
            temp += val_sign;
          } else if (abs_diff == 0.5) {
            // Round to even if exactly halfway.
            temp = ((temp % 2) == 0) ? temp : temp + val_sign;
          }
          break;
        }

        case SimRM:
          temp = temp > val ? temp - 1 : temp;
          break;

        case SimRZ:
          // Nothing to do.
          break;

        default:
          MOZ_CRASH();
      }
    }

    // Update the destination register.
    set_s_register_from_sinteger(dst, temp);
  } else {
    bool unsigned_integer = (instr->bit(7) == 0);
    int dst = instr->VFPDRegValue(src_precision);
    int src = instr->VFPMRegValue(kSinglePrecision);

    int val = get_sinteger_from_s_register(src);

    if (src_precision == kDoublePrecision) {
      if (unsigned_integer) {
        set_d_register_from_double(
            dst, static_cast<double>(static_cast<uint32_t>(val)));
      } else {
        set_d_register_from_double(dst, static_cast<double>(val));
      }
    } else {
      if (unsigned_integer) {
        set_s_register_from_float(
            dst, static_cast<float>(static_cast<uint32_t>(val)));
      } else {
        set_s_register_from_float(dst, static_cast<float>(val));
      }
    }
  }
}

// A VFPv3 specific instruction.
void Simulator::decodeVCVTBetweenFloatingPointAndIntegerFrac(
    SimInstruction* instr) {
  MOZ_ASSERT(instr->bits(27, 24) == 0xE && instr->opc1Value() == 0x7 &&
             instr->bit(19) == 1 && instr->bit(17) == 1 &&
             instr->bits(11, 9) == 0x5 && instr->bit(6) == 1 &&
             instr->bit(4) == 0);

  int size = (instr->bit(7) == 1) ? 32 : 16;

  int fraction_bits = size - ((instr->bits(3, 0) << 1) | instr->bit(5));
  double mult = 1 << fraction_bits;

  MOZ_ASSERT(size == 32);  // Only handling size == 32 for now.

  // Conversion between floating-point and integer.
  bool to_fixed = (instr->bit(18) == 1);

  VFPRegPrecision precision =
      (instr->szValue() == 1) ? kDoublePrecision : kSinglePrecision;

  if (to_fixed) {
    // We are playing with code close to the C++ standard's limits below,
    // hence the very simple code and heavy checks.
    //
    // Note: C++ defines default type casting from floating point to integer
    // as (close to) rounding toward zero ("fractional part discarded").

    int dst = instr->VFPDRegValue(precision);

    bool unsigned_integer = (instr->bit(16) == 1);
    bool double_precision = (precision == kDoublePrecision);

    double val;
    if (double_precision) {
      get_double_from_d_register(dst, &val);
    } else {
      float fval;
      get_float_from_s_register(dst, &fval);
      val = double(fval);
    }

    // Scale value by specified number of fraction bits.
    val *= mult;

    // Rounding down towards zero. No need to account for the rounding error
    // as this instruction always rounds down towards zero. See SimRZ below.
    int temp = unsigned_integer ? static_cast<uint32_t>(val)
                                : static_cast<int32_t>(val);

    inv_op_vfp_flag_ = get_inv_op_vfp_flag(SimRZ, val, unsigned_integer);

    double abs_diff = unsigned_integer
                          ? std::fabs(val - static_cast<uint32_t>(temp))
                          : std::fabs(val - temp);

    inexact_vfp_flag_ = (abs_diff != 0);

    if (inv_op_vfp_flag_) {
      temp = VFPConversionSaturate(val, unsigned_integer);
    }

    // Update the destination register.
    if (double_precision) {
      uint32_t dbl[2];
      dbl[0] = temp;
      dbl[1] = 0;
      set_d_register(dst, dbl);
    } else {
      set_s_register_from_sinteger(dst, temp);
    }
  } else {
    MOZ_CRASH();  // Not implemented, fixed to float.
  }
}

void Simulator::decodeVCVTBetweenFloatingPointAndHalf(SimInstruction* instr) {
  MOZ_ASSERT(instr->bit(4) == 0 && instr->opc1Value() == 0x7);
  MOZ_ASSERT((instr->opc2Value() & ~0x1) == 0x2 && (instr->opc3Value() & 0x1));

  bool top_half = (instr->bit(7) == 1);
  bool to_half = (instr->bit(16) == 1);

  VFPRegPrecision dst_precision = kSinglePrecision;
  VFPRegPrecision src_precision = kSinglePrecision;
  if (instr->szValue() == 1) {
    if (to_half) {
      src_precision = kDoublePrecision;
    } else {
      dst_precision = kDoublePrecision;
    }
  }

  int dst = instr->VFPDRegValue(dst_precision);
  int src = instr->VFPMRegValue(src_precision);

  if (to_half) {
    uint32_t f16bits;
    if (src_precision == kSinglePrecision) {
      float val;
      get_float_from_s_register(src, &val);
      f16bits = js::float16{val}.toRawBits();
    } else {
      double val;
      get_double_from_d_register(src, &val);
      f16bits = js::float16{val}.toRawBits();
    }

    float val;
    get_float_from_s_register(dst, &val);
    uint32_t f32bits = mozilla::BitwiseCast<uint32_t>(val);

    if (top_half) {
      f32bits = (f16bits << 16) | (f32bits & 0xffff);
    } else {
      f32bits = (f32bits & 0xffff'0000) | f16bits;
    }

    float rval;
    mozilla::BitwiseCast(f32bits, &rval);

    set_s_register_from_float(dst, rval);
  } else {
    float val;
    get_float_from_s_register(src, &val);
    uint32_t f32bits = mozilla::BitwiseCast<uint32_t>(val);

    if (top_half) {
      f32bits >>= 16;
    }

    auto rval = js::float16::fromRawBits(uint16_t(f32bits));

    if (dst_precision == kSinglePrecision) {
      set_s_register_from_float(dst, static_cast<float>(rval));
    } else {
      set_d_register_from_double(dst, static_cast<double>(rval));
    }
  }
}

void Simulator::decodeType6CoprocessorIns(SimInstruction* instr) {
  MOZ_ASSERT(instr->typeValue() == 6);

  if (instr->coprocessorValue() == 0xA) {
    switch (instr->opcodeValue()) {
      case 0x8:
      case 0xA:
      case 0xC:
      case 0xE: {  // Load and store single precision float to memory.
        int rn = instr->rnValue();
        int vd = instr->VFPDRegValue(kSinglePrecision);
        int offset = instr->immed8Value();
        if (!instr->hasU()) {
          offset = -offset;
        }

        int32_t address = get_register(rn) + 4 * offset;
        if (instr->hasL()) {
          // Load double from memory: vldr.
          set_s_register_from_sinteger(vd, readW(address, instr));
        } else {
          // Store double to memory: vstr.
          writeW(address, get_sinteger_from_s_register(vd), instr);
        }
        break;
      }
      case 0x4:
      case 0x5:
      case 0x6:
      case 0x7:
      case 0x9:
      case 0xB:
        // Load/store multiple single from memory: vldm/vstm.
        handleVList(instr);
        break;
      default:
        MOZ_CRASH();
    }
  } else if (instr->coprocessorValue() == 0xB) {
    switch (instr->opcodeValue()) {
      case 0x2:
        // Load and store double to two GP registers
        if (instr->bits(7, 6) != 0 || instr->bit(4) != 1) {
          MOZ_CRASH();  // Not used atm.
        } else {
          int rt = instr->rtValue();
          int rn = instr->rnValue();
          int vm = instr->VFPMRegValue(kDoublePrecision);
          if (instr->hasL()) {
            int32_t data[2];
            double d;
            get_double_from_d_register(vm, &d);
            memcpy(data, &d, 8);
            set_register(rt, data[0]);
            set_register(rn, data[1]);
          } else {
            int32_t data[] = {get_register(rt), get_register(rn)};
            double d;
            memcpy(&d, data, 8);
            set_d_register_from_double(vm, d);
          }
        }
        break;
      case 0x8:
      case 0xA:
      case 0xC:
      case 0xE: {  // Load and store double to memory.
        int rn = instr->rnValue();
        int vd = instr->VFPDRegValue(kDoublePrecision);
        int offset = instr->immed8Value();
        if (!instr->hasU()) {
          offset = -offset;
        }
        int32_t address = get_register(rn) + 4 * offset;
        if (instr->hasL()) {
          // Load double from memory: vldr.
          uint64_t data = readQ(address, instr);
          double val;
          memcpy(&val, &data, 8);
          set_d_register_from_double(vd, val);
        } else {
          // Store double to memory: vstr.
          uint64_t data;
          double val;
          get_double_from_d_register(vd, &val);
          memcpy(&data, &val, 8);
          writeQ(address, data, instr);
        }
        break;
      }
      case 0x4:
      case 0x5:
      case 0x6:
      case 0x7:
      case 0x9:
      case 0xB:
        // Load/store multiple double from memory: vldm/vstm.
        handleVList(instr);
        break;
      default:
        MOZ_CRASH();
    }
  } else {
    MOZ_CRASH();
  }
}

void Simulator::decodeSpecialCondition(SimInstruction* instr) {
  switch (instr->specialValue()) {
    case 5:
      if (instr->bits(18, 16) == 0 && instr->bits(11, 6) == 0x28 &&
          instr->bit(4) == 1) {
        // vmovl signed
        if ((instr->vdValue() & 1) != 0) {
          MOZ_CRASH("Undefined behavior");
        }
        int Vd = (instr->bit(22) << 3) | (instr->vdValue() >> 1);
        int Vm = (instr->bit(5) << 4) | instr->vmValue();
        int imm3 = instr->bits(21, 19);
        if (imm3 != 1 && imm3 != 2 && imm3 != 4) {
          MOZ_CRASH();
        }
        int esize = 8 * imm3;
        int elements = 64 / esize;
        int8_t from[8];
        get_d_register(Vm, reinterpret_cast<uint64_t*>(from));
        int16_t to[8];
        int e = 0;
        while (e < elements) {
          to[e] = from[e];
          e++;
        }
        set_q_register(Vd, reinterpret_cast<uint64_t*>(to));
      } else {
        MOZ_CRASH();
      }
      break;
    case 7:
      if (instr->bits(18, 16) == 0 && instr->bits(11, 6) == 0x28 &&
          instr->bit(4) == 1) {
        // vmovl unsigned.
        if ((instr->vdValue() & 1) != 0) {
          MOZ_CRASH("Undefined behavior");
        }
        int Vd = (instr->bit(22) << 3) | (instr->vdValue() >> 1);
        int Vm = (instr->bit(5) << 4) | instr->vmValue();
        int imm3 = instr->bits(21, 19);
        if (imm3 != 1 && imm3 != 2 && imm3 != 4) {
          MOZ_CRASH();
        }
        int esize = 8 * imm3;
        int elements = 64 / esize;
        uint8_t from[8];
        get_d_register(Vm, reinterpret_cast<uint64_t*>(from));
        uint16_t to[8];
        int e = 0;
        while (e < elements) {
          to[e] = from[e];
          e++;
        }
        set_q_register(Vd, reinterpret_cast<uint64_t*>(to));
      } else {
        MOZ_CRASH();
      }
      break;
    case 8:
      if (instr->bits(21, 20) == 0) {
        // vst1
        int Vd = (instr->bit(22) << 4) | instr->vdValue();
        int Rn = instr->vnValue();
        int type = instr->bits(11, 8);
        int Rm = instr->vmValue();
        int32_t address = get_register(Rn);
        int regs = 0;
        switch (type) {
          case nlt_1:
            regs = 1;
            break;
          case nlt_2:
            regs = 2;
            break;
          case nlt_3:
            regs = 3;
            break;
          case nlt_4:
            regs = 4;
            break;
          default:
            MOZ_CRASH();
            break;
        }
        int r = 0;
        while (r < regs) {
          uint32_t data[2];
          get_d_register(Vd + r, data);
          // TODO: We should AllowUnaligned here only if the alignment attribute
          // of the instruction calls for default alignment.
          //
          // Use writeQ to get handling of traps right.  (The spec says to
          // perform two individual word writes, but let's not worry about
          // that.)
          writeQ(address, (uint64_t(data[1]) << 32) | uint64_t(data[0]), instr,
                 AllowUnaligned);
          address += 8;
          r++;
        }
        if (Rm != 15) {
          if (Rm == 13) {
            set_register(Rn, address);
          } else {
            set_register(Rn, get_register(Rn) + get_register(Rm));
          }
        }
      } else if (instr->bits(21, 20) == 2) {
        // vld1
        int Vd = (instr->bit(22) << 4) | instr->vdValue();
        int Rn = instr->vnValue();
        int type = instr->bits(11, 8);
        int Rm = instr->vmValue();
        int32_t address = get_register(Rn);
        int regs = 0;
        switch (type) {
          case nlt_1:
            regs = 1;
            break;
          case nlt_2:
            regs = 2;
            break;
          case nlt_3:
            regs = 3;
            break;
          case nlt_4:
            regs = 4;
            break;
          default:
            MOZ_CRASH();
            break;
        }
        int r = 0;
        while (r < regs) {
          uint32_t data[2];
          // TODO: We should AllowUnaligned here only if the alignment attribute
          // of the instruction calls for default alignment.
          //
          // Use readQ to get handling of traps right.  (The spec says to
          // perform two individual word reads, but let's not worry about that.)
          uint64_t tmp = readQ(address, instr, AllowUnaligned);
          data[0] = tmp;
          data[1] = tmp >> 32;
          set_d_register(Vd + r, data);
          address += 8;
          r++;
        }
        if (Rm != 15) {
          if (Rm == 13) {
            set_register(Rn, address);
          } else {
            set_register(Rn, get_register(Rn) + get_register(Rm));
          }
        }
      } else {
        MOZ_CRASH();
      }
      break;
    case 9:
      if (instr->bits(9, 8) == 0) {
        int Vd = (instr->bit(22) << 4) | instr->vdValue();
        int Rn = instr->vnValue();
        int size = instr->bits(11, 10);
        int Rm = instr->vmValue();
        int index = instr->bits(7, 5);
        int align = instr->bit(4);
        int32_t address = get_register(Rn);
        if (size != 2 || align) {
          MOZ_CRASH("NYI");
        }
        int a = instr->bits(5, 4);
        if (a != 0 && a != 3) {
          MOZ_CRASH("Unspecified");
        }
        if (index > 1) {
          Vd++;
          index -= 2;
        }
        uint32_t data[2];
        get_d_register(Vd, data);
        switch (instr->bits(21, 20)) {
          case 0:
            // vst1 single element from one lane
            writeW(address, data[index], instr, AllowUnaligned);
            break;
          case 2:
            // vld1 single element to one lane
            data[index] = readW(address, instr, AllowUnaligned);
            set_d_register(Vd, data);
            break;
          default:
            MOZ_CRASH("NYI");
        }
        address += 4;
        if (Rm != 15) {
          if (Rm == 13) {
            set_register(Rn, address);
          } else {
            set_register(Rn, get_register(Rn) + get_register(Rm));
          }
        }
      } else {
        MOZ_CRASH();
      }
      break;
    case 0xA:
      if (instr->bits(31, 20) == 0xf57) {
        switch (instr->bits(7, 4)) {
          case 1:  // CLREX
            exclusiveMonitorClear();
            break;
          case 5:  // DMB
            AtomicOperations::fenceSeqCst();
            break;
          case 4:  // DSB
            // We do not use DSB.
            MOZ_CRASH("DSB unimplemented");
          case 6:  // ISB
            // We do not use ISB.
            MOZ_CRASH("ISB unimplemented");
          default:
            MOZ_CRASH();
        }
      } else {
        MOZ_CRASH();
      }
      break;
    case 0xB:
      if (instr->bits(22, 20) == 5 && instr->bits(15, 12) == 0xf) {
        // pld: ignore instruction.
      } else {
        MOZ_CRASH();
      }
      break;
    case 0x1C:
    case 0x1D:
      if (instr->bit(4) == 1 && instr->bits(11, 9) != 5) {
        // MCR, MCR2, MRC, MRC2 with cond == 15
        decodeType7CoprocessorIns(instr);
      } else {
        MOZ_CRASH();
      }
      break;
    default:
      MOZ_CRASH();
  }
}

// Executes the current instruction.
void Simulator::instructionDecode(SimInstruction* instr) {
  if (!SimulatorProcess::ICacheCheckingDisableCount) {
    AutoLockSimulatorCache als;
    SimulatorProcess::checkICacheLocked(instr);
  }

  pc_modified_ = false;

  static const uint32_t kSpecialCondition = 15 << 28;
  if (instr->conditionField() == kSpecialCondition) {
    decodeSpecialCondition(instr);
  } else if (conditionallyExecute(instr)) {
    switch (instr->typeValue()) {
      case 0:
      case 1:
        decodeType01(instr);
        break;
      case 2:
        decodeType2(instr);
        break;
      case 3:
        decodeType3(instr);
        break;
      case 4:
        decodeType4(instr);
        break;
      case 5:
        decodeType5(instr);
        break;
      case 6:
        decodeType6(instr);
        break;
      case 7:
        decodeType7(instr);
        break;
      default:
        MOZ_CRASH();
        break;
    }
    // If the instruction is a non taken conditional stop, we need to skip
    // the inlined message address.
  } else if (instr->isStop()) {
    set_pc(get_pc() + 2 * SimInstruction::kInstrSize);
  }
  if (!pc_modified_) {
    set_register(pc,
                 reinterpret_cast<int32_t>(instr) + SimInstruction::kInstrSize);
  }
}

void Simulator::enable_single_stepping(SingleStepCallback cb, void* arg) {
  single_stepping_ = true;
  single_step_callback_ = cb;
  single_step_callback_arg_ = arg;
  single_step_callback_(single_step_callback_arg_, this, (void*)get_pc());
}

void Simulator::disable_single_stepping() {
  if (!single_stepping_) {
    return;
  }
  single_step_callback_(single_step_callback_arg_, this, (void*)get_pc());
  single_stepping_ = false;
  single_step_callback_ = nullptr;
  single_step_callback_arg_ = nullptr;
}

template <bool EnableStopSimAt>
void Simulator::execute() {
  if (single_stepping_) {
    single_step_callback_(single_step_callback_arg_, this, nullptr);
  }

  // Get the PC to simulate. Cannot use the accessor here as we need the raw
  // PC value and not the one used as input to arithmetic instructions.
  int program_counter = get_pc();

  while (program_counter != end_sim_pc) {
    if (EnableStopSimAt && (icount_ == Simulator::StopSimAt)) {
      fprintf(stderr, "\nStopped simulation at icount %lld\n", icount_);
      ArmDebugger dbg(this);
      dbg.debug();
    } else {
      if (single_stepping_) {
        single_step_callback_(single_step_callback_arg_, this,
                              (void*)program_counter);
      }
      SimInstruction* instr =
          reinterpret_cast<SimInstruction*>(program_counter);
      instructionDecode(instr);
      icount_++;
    }
    program_counter = get_pc();
  }

  if (single_stepping_) {
    single_step_callback_(single_step_callback_arg_, this, nullptr);
  }
}

void Simulator::callInternal(uint8_t* entry) {
  // Prepare to execute the code at entry.
  set_register(pc, reinterpret_cast<int32_t>(entry));

  // Put down marker for end of simulation. The simulator will stop simulation
  // when the PC reaches this value. By saving the "end simulation" value into
  // the LR the simulation stops when returning to this call point.
  set_register(lr, end_sim_pc);

  // Remember the values of callee-saved registers. The code below assumes
  // that r9 is not used as sb (static base) in simulator code and therefore
  // is regarded as a callee-saved register.
  int32_t r4_val = get_register(r4);
  int32_t r5_val = get_register(r5);
  int32_t r6_val = get_register(r6);
  int32_t r7_val = get_register(r7);
  int32_t r8_val = get_register(r8);
  int32_t r9_val = get_register(r9);
  int32_t r10_val = get_register(r10);
  int32_t r11_val = get_register(r11);

  // Remember d8 to d15 which are callee-saved.
  uint64_t d8_val;
  get_d_register(d8, &d8_val);
  uint64_t d9_val;
  get_d_register(d9, &d9_val);
  uint64_t d10_val;
  get_d_register(d10, &d10_val);
  uint64_t d11_val;
  get_d_register(d11, &d11_val);
  uint64_t d12_val;
  get_d_register(d12, &d12_val);
  uint64_t d13_val;
  get_d_register(d13, &d13_val);
  uint64_t d14_val;
  get_d_register(d14, &d14_val);
  uint64_t d15_val;
  get_d_register(d15, &d15_val);

  // Set up the callee-saved registers with a known value. To be able to check
  // that they are preserved properly across JS execution.
  int32_t callee_saved_value = uint32_t(icount_);
  uint64_t callee_saved_value_d = uint64_t(icount_);

  if (!skipCalleeSavedRegsCheck) {
    set_register(r4, callee_saved_value);
    set_register(r5, callee_saved_value);
    set_register(r6, callee_saved_value);
    set_register(r7, callee_saved_value);
    set_register(r8, callee_saved_value);
    set_register(r9, callee_saved_value);
    set_register(r10, callee_saved_value);
    set_register(r11, callee_saved_value);

    set_d_register(d8, &callee_saved_value_d);
    set_d_register(d9, &callee_saved_value_d);
    set_d_register(d10, &callee_saved_value_d);
    set_d_register(d11, &callee_saved_value_d);
    set_d_register(d12, &callee_saved_value_d);
    set_d_register(d13, &callee_saved_value_d);
    set_d_register(d14, &callee_saved_value_d);
    set_d_register(d15, &callee_saved_value_d);
  }
  // Start the simulation.
  if (Simulator::StopSimAt != -1L) {
    execute<true>();
  } else {
    execute<false>();
  }

  if (!skipCalleeSavedRegsCheck) {
    // Check that the callee-saved registers have been preserved.
    MOZ_ASSERT(callee_saved_value == get_register(r4));
    MOZ_ASSERT(callee_saved_value == get_register(r5));
    MOZ_ASSERT(callee_saved_value == get_register(r6));
    MOZ_ASSERT(callee_saved_value == get_register(r7));
    MOZ_ASSERT(callee_saved_value == get_register(r8));
    MOZ_ASSERT(callee_saved_value == get_register(r9));
    MOZ_ASSERT(callee_saved_value == get_register(r10));
    MOZ_ASSERT(callee_saved_value == get_register(r11));

    uint64_t value;
    get_d_register(d8, &value);
    MOZ_ASSERT(callee_saved_value_d == value);
    get_d_register(d9, &value);
    MOZ_ASSERT(callee_saved_value_d == value);
    get_d_register(d10, &value);
    MOZ_ASSERT(callee_saved_value_d == value);
    get_d_register(d11, &value);
    MOZ_ASSERT(callee_saved_value_d == value);
    get_d_register(d12, &value);
    MOZ_ASSERT(callee_saved_value_d == value);
    get_d_register(d13, &value);
    MOZ_ASSERT(callee_saved_value_d == value);
    get_d_register(d14, &value);
    MOZ_ASSERT(callee_saved_value_d == value);
    get_d_register(d15, &value);
    MOZ_ASSERT(callee_saved_value_d == value);

    // Restore callee-saved registers with the original value.
    set_register(r4, r4_val);
    set_register(r5, r5_val);
    set_register(r6, r6_val);
    set_register(r7, r7_val);
    set_register(r8, r8_val);
    set_register(r9, r9_val);
    set_register(r10, r10_val);
    set_register(r11, r11_val);

    set_d_register(d8, &d8_val);
    set_d_register(d9, &d9_val);
    set_d_register(d10, &d10_val);
    set_d_register(d11, &d11_val);
    set_d_register(d12, &d12_val);
    set_d_register(d13, &d13_val);
    set_d_register(d14, &d14_val);
    set_d_register(d15, &d15_val);
  }
}

int32_t Simulator::call(uint8_t* entry, int argument_count, ...) {
  va_list parameters;
  va_start(parameters, argument_count);

  // First four arguments passed in registers.
  if (argument_count >= 1) {
    set_register(r0, va_arg(parameters, int32_t));
  }
  if (argument_count >= 2) {
    set_register(r1, va_arg(parameters, int32_t));
  }
  if (argument_count >= 3) {
    set_register(r2, va_arg(parameters, int32_t));
  }
  if (argument_count >= 4) {
    set_register(r3, va_arg(parameters, int32_t));
  }

  // Remaining arguments passed on stack.
  int original_stack = get_register(sp);
  int entry_stack = original_stack;
  if (argument_count >= 4) {
    entry_stack -= (argument_count - 4) * sizeof(int32_t);
  }

  entry_stack &= ~ABIStackAlignment;

  // Store remaining arguments on stack, from low to high memory.
  intptr_t* stack_argument = reinterpret_cast<intptr_t*>(entry_stack);
  for (int i = 4; i < argument_count; i++) {
    stack_argument[i - 4] = va_arg(parameters, int32_t);
  }
  va_end(parameters);
  set_register(sp, entry_stack);

  callInternal(entry);

  // Pop stack passed arguments.
  MOZ_ASSERT(entry_stack == get_register(sp));
  set_register(sp, original_stack);

  int32_t result = get_register(r0);
  return result;
}

Simulator* Simulator::Current() {
  JSContext* cx = TlsContext.get();
  MOZ_ASSERT(CurrentThreadCanAccessRuntime(cx->runtime()));
  return cx->simulator();
}

}  // namespace jit
}  // namespace js

js::jit::Simulator* JSContext::simulator() const { return simulator_; }