Forking disassembler and simulator for Thumb2 support;...

src/arm/simulator-thumb2.cc

+// Copyright 2010 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 <stdlib.h>
+#include <cstdarg>
+#include "v8.h"
+
+#include "disasm.h"
+#include "assembler.h"
+#include "arm/simulator-thumb2.h"
+
+#if !defined(__arm__)
+
+// Only build the simulator if not compiling for real ARM hardware.
+namespace assembler {
+namespace arm {
+
+using ::v8::internal::Object;
+using ::v8::internal::PrintF;
+using ::v8::internal::OS;
+using ::v8::internal::ReadLine;
+using ::v8::internal::DeleteArray;
+
+// This macro provides a platform independent use of sscanf. The reason for
+// SScanF not being implemented in a platform independent way through
+// ::v8::internal::OS in the same way as SNPrintF is that the
+// Windows C Run-Time Library does not provide vsscanf.
+#define SScanF sscanf  // NOLINT
+
+// The Debugger class is used by the simulator while debugging simulated ARM
+// code.
+class Debugger {
+ public:
+  explicit Debugger(Simulator* sim);
+  ~Debugger();
+
+  void Stop(Instr* instr);
+  void Debug();
+
+ private:
+  static const instr_t kBreakpointInstr =
+      ((AL << 28) | (7 << 25) | (1 << 24) | break_point);
+  static const instr_t kNopInstr =
+      ((AL << 28) | (13 << 21));
+
+  Simulator* sim_;
+
+  int32_t GetRegisterValue(int regnum);
+  bool GetValue(const char* desc, int32_t* value);
+
+  // Set or delete a breakpoint. Returns true if successful.
+  bool SetBreakpoint(Instr* breakpc);
+  bool DeleteBreakpoint(Instr* 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();
+};
+
+
+Debugger::Debugger(Simulator* sim) {
+  sim_ = sim;
+}
+
+
+Debugger::~Debugger() {
+}
+
+
+
+#ifdef GENERATED_CODE_COVERAGE
+static FILE* coverage_log = NULL;
+
+
+static void InitializeCoverage() {
+  char* file_name = getenv("V8_GENERATED_CODE_COVERAGE_LOG");
+  if (file_name != NULL) {
+    coverage_log = fopen(file_name, "aw+");
+  }
+}
+
+
+void Debugger::Stop(Instr* instr) {
+  char* str = reinterpret_cast<char*>(instr->InstructionBits() & 0x0fffffff);
+  if (strlen(str) > 0) {
+    if (coverage_log != NULL) {
+      fprintf(coverage_log, "%s\n", str);
+      fflush(coverage_log);
+    }
+    instr->SetInstructionBits(0xe1a00000);  // Overwrite with nop.
+  }
+  sim_->set_pc(sim_->get_pc() + Instr::kInstrSize);
+}
+
+#else  // ndef GENERATED_CODE_COVERAGE
+
+static void InitializeCoverage() {
+}
+
+
+void Debugger::Stop(Instr* instr) {
+  const char* str = (const char*)(instr->InstructionBits() & 0x0fffffff);
+  PrintF("Simulator hit %s\n", str);
+  sim_->set_pc(sim_->get_pc() + Instr::kInstrSize);
+  Debug();
+}
+#endif
+
+
+int32_t Debugger::GetRegisterValue(int regnum) {
+  if (regnum == kPCRegister) {
+    return sim_->get_pc();
+  } else {
+    return sim_->get_register(regnum);
+  }
+}
+
+
+bool Debugger::GetValue(const char* desc, int32_t* value) {
+  int regnum = Registers::Number(desc);
+  if (regnum != kNoRegister) {
+    *value = GetRegisterValue(regnum);
+    return true;
+  } else {
+    return SScanF(desc, "%i", value) == 1;
+  }
+  return false;
+}
+
+
+bool Debugger::SetBreakpoint(Instr* breakpc) {
+  // Check if a breakpoint can be set. If not return without any side-effects.
+  if (sim_->break_pc_ != NULL) {
+    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 Debugger::DeleteBreakpoint(Instr* breakpc) {
+  if (sim_->break_pc_ != NULL) {
+    sim_->break_pc_->SetInstructionBits(sim_->break_instr_);
+  }
+
+  sim_->break_pc_ = NULL;
+  sim_->break_instr_ = 0;
+  return true;
+}
+
+
+void Debugger::UndoBreakpoints() {
+  if (sim_->break_pc_ != NULL) {
+    sim_->break_pc_->SetInstructionBits(sim_->break_instr_);
+  }
+}
+
+
+void Debugger::RedoBreakpoints() {
+  if (sim_->break_pc_ != NULL) {
+    sim_->break_pc_->SetInstructionBits(kBreakpointInstr);
+  }
+}
+
+
+void Debugger::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];
+
+  // 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();
+
+  while (!done) {
+    if (last_pc != sim_->get_pc()) {
+      disasm::NameConverter converter;
+      disasm::Disassembler dasm(converter);
+      // use a reasonably large buffer
+      v8::internal::EmbeddedVector<char, 256> buffer;
+      dasm.InstructionDecode(buffer,
+                             reinterpret_cast<byte*>(sim_->get_pc()));
+      PrintF("  0x%08x  %s\n", sim_->get_pc(), buffer.start());
+      last_pc = sim_->get_pc();
+    }
+    char* line = ReadLine("sim> ");
+    if (line == NULL) {
+      break;
+    } else {
+      // Use sscanf to parse the individual parts of the command line. At the
+      // moment no command expects more than two parameters.
+      int args = SScanF(line,
+                        "%" XSTR(COMMAND_SIZE) "s "
+                        "%" XSTR(ARG_SIZE) "s "
+                        "%" XSTR(ARG_SIZE) "s",
+                        cmd, arg1, arg2);
+      if ((strcmp(cmd, "si") == 0) || (strcmp(cmd, "stepi") == 0)) {
+        sim_->InstructionDecode(sim_->get_pc());
+      } else if ((strcmp(cmd, "c") == 0) || (strcmp(cmd, "cont") == 0)) {
+        // Execute the one instruction we broke at with breakpoints disabled.
+        sim_->InstructionDecode(sim_->get_pc());
+        // Leave the debugger shell.
+        done = true;
+      } else if ((strcmp(cmd, "p") == 0) || (strcmp(cmd, "print") == 0)) {
+        if (args == 2) {
+          int32_t value;
+          if (strcmp(arg1, "all") == 0) {
+            for (int i = 0; i < kNumRegisters; i++) {
+              value = GetRegisterValue(i);
+              PrintF("%3s: 0x%08x %10d\n", Registers::Name(i), value, value);
+            }
+          } else {
+            if (GetValue(arg1, &value)) {
+              PrintF("%s: 0x%08x %d \n", arg1, value, value);
+            } else {
+              PrintF("%s unrecognized\n", arg1);
+            }
+          }
+        } else {
+          PrintF("print <register>\n");
+        }
+      } else if ((strcmp(cmd, "po") == 0)
+                 || (strcmp(cmd, "printobject") == 0)) {
+        if (args == 2) {
+          int32_t value;
+          if (GetValue(arg1, &value)) {
+            Object* obj = reinterpret_cast<Object*>(value);
+            PrintF("%s: \n", arg1);
+#ifdef DEBUG
+            obj->PrintLn();
+#else
+            obj->ShortPrint();
+            PrintF("\n");
+#endif
+          } else {
+            PrintF("%s unrecognized\n", arg1);
+          }
+        } else {
+          PrintF("printobject <value>\n");
+        }
+      } else if (strcmp(cmd, "disasm") == 0) {
+        disasm::NameConverter converter;
+        disasm::Disassembler dasm(converter);
+        // use a reasonably large buffer
+        v8::internal::EmbeddedVector<char, 256> buffer;
+
+        byte* cur = NULL;
+        byte* end = NULL;
+
+        if (args == 1) {
+          cur = reinterpret_cast<byte*>(sim_->get_pc());
+          end = cur + (10 * Instr::kInstrSize);
+        } else if (args == 2) {
+          int32_t value;
+          if (GetValue(arg1, &value)) {
+            cur = reinterpret_cast<byte*>(value);
+            // no length parameter passed, assume 10 instructions
+            end = cur + (10 * Instr::kInstrSize);
+          }
+        } else {
+          int32_t value1;
+          int32_t value2;
+          if (GetValue(arg1, &value1) && GetValue(arg2, &value2)) {
+            cur = reinterpret_cast<byte*>(value1);
+            end = cur + (value2 * Instr::kInstrSize);
+          }
+        }
+
+        while (cur < end) {
+          dasm.InstructionDecode(buffer, cur);
+          PrintF("  0x%08x  %s\n", cur, buffer.start());
+          cur += Instr::kInstrSize;
+        }
+      } else if (strcmp(cmd, "gdb") == 0) {
+        PrintF("relinquishing control to gdb\n");
+        v8::internal::OS::DebugBreak();
+        PrintF("regaining control from gdb\n");
+      } else if (strcmp(cmd, "break") == 0) {
+        if (args == 2) {
+          int32_t value;
+          if (GetValue(arg1, &value)) {
+            if (!SetBreakpoint(reinterpret_cast<Instr*>(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(NULL)) {
+          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; ", sim_->inexact_vfp_flag_);
+      } else if (strcmp(cmd, "unstop") == 0) {
+        intptr_t stop_pc = sim_->get_pc() - Instr::kInstrSize;
+        Instr* stop_instr = reinterpret_cast<Instr*>(stop_pc);
+        if (stop_instr->ConditionField() == special_condition) {
+          stop_instr->SetInstructionBits(kNopInstr);
+        } else {
+          PrintF("Not at debugger stop.");
+        }
+      } else if ((strcmp(cmd, "t") == 0) || strcmp(cmd, "trace") == 0) {
+        ::v8::internal::FLAG_trace_sim = !::v8::internal::FLAG_trace_sim;
+        PrintF("Trace of executed instructions is %s\n",
+               ::v8::internal::FLAG_trace_sim ? "on" : "off");
+      } else if ((strcmp(cmd, "h") == 0) || (strcmp(cmd, "help") == 0)) {
+        PrintF("cont\n");
+        PrintF("  continue execution (alias 'c')\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("printobject <register>\n");
+        PrintF("  print an object from a register (alias 'po')\n");
+        PrintF("flags\n");
+        PrintF("  print flags\n");
+        PrintF("disasm [<instructions>]\n");
+        PrintF("disasm [[<address>] <instructions>]\n");
+        PrintF("  disassemble code, default is 10 instructions from pc\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("unstop\n");
+        PrintF("  ignore the stop instruction at the current location");
+        PrintF("  from now on\n");
+        PrintF("trace (alias 't')\n");
+        PrintF("  toogle the tracing of all executed statements");
+      } else {
+        PrintF("Unknown command: %s\n", cmd);
+      }
+    }
+    DeleteArray(line);
+  }
+
+  // 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
+}
+
+
+// Create one simulator per thread and keep it in thread local storage.
+static v8::internal::Thread::LocalStorageKey simulator_key;
+
+
+bool Simulator::initialized_ = false;
+
+
+void Simulator::Initialize() {
+  if (initialized_) return;
+  PrintF("This is actually the thumb2 simulator!\n");
+  simulator_key = v8::internal::Thread::CreateThreadLocalKey();
+  initialized_ = true;
+  ::v8::internal::ExternalReference::set_redirector(&RedirectExternalReference);
+}
+
+
+Simulator::Simulator() {
+  Initialize();
+  // Setup simulator support first. Some of this information is needed to
+  // setup the architecture state.
+  size_t stack_size = 1 * 1024*1024;  // allocate 1MB for stack
+  stack_ = reinterpret_cast<char*>(malloc(stack_size));
+  pc_modified_ = false;
+  icount_ = 0;
+  break_pc_ = NULL;
+  break_instr_ = 0;
+
+  // Setup 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;
+
+  // Initializing VFP registers.
+  // All registers are initialized to zero to start with
+  // even though s_registers_ & d_registers_ share the same
+  // physical registers in the target.
+  for (int i = 0; i < num_s_registers; i++) {
+    vfp_register[i] = 0;
+  }
+  n_flag_FPSCR_ = false;
+  z_flag_FPSCR_ = false;
+  c_flag_FPSCR_ = false;
+  v_flag_FPSCR_ = false;
+
+  inv_op_vfp_flag_ = false;
+  div_zero_vfp_flag_ = false;
+  overflow_vfp_flag_ = false;
+  underflow_vfp_flag_ = false;
+  inexact_vfp_flag_ = false;
+
+  // 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_) + stack_size - 64;
+  // 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;
+
+  enter_debug_ = false;
+
+  InitializeCoverage();
+}
+
+
+// When the generated code calls an external reference we need to catch that in
+// the simulator.  The external reference will be a function compiled for the
+// host architecture.  We need to call that function instead of trying to
+// execute it with the simulator.  We do that by redirecting the external
+// reference to a swi (software-interrupt) instruction that is handled by
+// the simulator.  We write the original destination of the jump just at a known
+// offset from the swi instruction so the simulator knows what to call.
+class Redirection {
+ public:
+  Redirection(void* external_function, bool fp_return)
+      : external_function_(external_function),
+        swi_instruction_((AL << 28) | (0xf << 24) | call_rt_redirected),
+        fp_return_(fp_return),
+        next_(list_) {
+    list_ = this;
+  }
+
+  void* address_of_swi_instruction() {
+    return reinterpret_cast<void*>(&swi_instruction_);
+  }
+
+  void* external_function() { return external_function_; }
+  bool fp_return() { return fp_return_; }
+
+  static Redirection* Get(void* external_function, bool fp_return) {
+    Redirection* current;
+    for (current = list_; current != NULL; current = current->next_) {
+      if (current->external_function_ == external_function) return current;
+    }
+    return new Redirection(external_function, fp_return);
+  }
+
+  static Redirection* FromSwiInstruction(Instr* swi_instruction) {
+    char* addr_of_swi = reinterpret_cast<char*>(swi_instruction);
+    char* addr_of_redirection =
+        addr_of_swi - OFFSET_OF(Redirection, swi_instruction_);
+    return reinterpret_cast<Redirection*>(addr_of_redirection);
+  }
+
+ private:
+  void* external_function_;
+  uint32_t swi_instruction_;
+  bool fp_return_;
+  Redirection* next_;
+  static Redirection* list_;
+};
+
+
+Redirection* Redirection::list_ = NULL;
+
+
+void* Simulator::RedirectExternalReference(void* external_function,
+                                           bool fp_return) {
+  Redirection* redirection = Redirection::Get(external_function, fp_return);
+  return redirection->address_of_swi_instruction();
+}
+
+
+// Get the active Simulator for the current thread.
+Simulator* Simulator::current() {
+  Initialize();
+  Simulator* sim = reinterpret_cast<Simulator*>(
+      v8::internal::Thread::GetThreadLocal(simulator_key));
+  if (sim == NULL) {
+    // TODO(146): delete the simulator object when a thread goes away.
+    sim = new Simulator();
+    v8::internal::Thread::SetThreadLocal(simulator_key, sim);
+  }
+  return sim;
+}
+
+
+// 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) {
+  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 {
+  ASSERT((reg >= 0) && (reg < num_registers));
+  if (reg == pc) {
+    int32_t v = registers_[reg];
+    return v + ((v & 1) ? + Instr::kPCReadOffsetThumb : Instr::kPCReadOffset);
+  }
+  return registers_[reg];
+}
+
+
+// Raw access to the PC register.
+void Simulator::set_pc(int32_t value) {
+  pc_modified_ = true;
+  registers_[pc] = value;
+}
+
+
+// Raw access to the PC register without the special adjustment when reading.
+int32_t Simulator::get_pc() const {
+  return registers_[pc];
+}
+
+
+// Getting from and setting into VFP registers.
+void Simulator::set_s_register(int sreg, unsigned int value) {
+  ASSERT((sreg >= 0) && (sreg < num_s_registers));
+  vfp_register[sreg] = value;
+}
+
+
+unsigned int Simulator::get_s_register(int sreg) const {
+  ASSERT((sreg >= 0) && (sreg < num_s_registers));
+  return vfp_register[sreg];
+}
+
+
+void Simulator::set_s_register_from_float(int sreg, const float flt) {
+  ASSERT((sreg >= 0) && (sreg < num_s_registers));
+  // Read the bits from the single precision floating point value
+  // into the unsigned integer element of vfp_register[] given by index=sreg.
+  char buffer[sizeof(vfp_register[0])];
+  memcpy(buffer, &flt, sizeof(vfp_register[0]));
+  memcpy(&vfp_register[sreg], buffer, sizeof(vfp_register[0]));
+}
+
+
+void Simulator::set_s_register_from_sinteger(int sreg, const int sint) {
+  ASSERT((sreg >= 0) && (sreg < num_s_registers));
+  // Read the bits from the integer value into the unsigned integer element of
+  // vfp_register[] given by index=sreg.
+  char buffer[sizeof(vfp_register[0])];
+  memcpy(buffer, &sint, sizeof(vfp_register[0]));
+  memcpy(&vfp_register[sreg], buffer, sizeof(vfp_register[0]));
+}
+
+
+void Simulator::set_d_register_from_double(int dreg, const double& dbl) {
+  ASSERT((dreg >= 0) && (dreg < num_d_registers));
+  // Read the bits from the double precision floating point value into the two
+  // consecutive unsigned integer elements of vfp_register[] given by index
+  // 2*sreg and 2*sreg+1.
+  char buffer[2 * sizeof(vfp_register[0])];
+  memcpy(buffer, &dbl, 2 * sizeof(vfp_register[0]));
+#ifndef BIG_ENDIAN_FLOATING_POINT
+  memcpy(&vfp_register[dreg * 2], buffer, 2 * sizeof(vfp_register[0]));
+#else
+  memcpy(&vfp_register[dreg * 2], &buffer[4], sizeof(vfp_register[0]));
+  memcpy(&vfp_register[dreg * 2 + 1], &buffer[0], sizeof(vfp_register[0]));
+#endif
+}
+
+
+float Simulator::get_float_from_s_register(int sreg) {
+  ASSERT((sreg >= 0) && (sreg < num_s_registers));
+
+  float sm_val = 0.0;
+  // Read the bits from the unsigned integer vfp_register[] array
+  // into the single precision floating point value and return it.
+  char buffer[sizeof(vfp_register[0])];
+  memcpy(buffer, &vfp_register[sreg], sizeof(vfp_register[0]));
+  memcpy(&sm_val, buffer, sizeof(vfp_register[0]));
+  return(sm_val);
+}
+
+
+int Simulator::get_sinteger_from_s_register(int sreg) {
+  ASSERT((sreg >= 0) && (sreg < num_s_registers));
+
+  int sm_val = 0;
+  // Read the bits from the unsigned integer vfp_register[] array
+  // into the single precision floating point value and return it.
+  char buffer[sizeof(vfp_register[0])];
+  memcpy(buffer, &vfp_register[sreg], sizeof(vfp_register[0]));
+  memcpy(&sm_val, buffer, sizeof(vfp_register[0]));
+  return(sm_val);
+}
+
+
+double Simulator::get_double_from_d_register(int dreg) {
+  ASSERT((dreg >= 0) && (dreg < num_d_registers));
+
+  double dm_val = 0.0;
+  // Read the bits from the unsigned integer vfp_register[] array
+  // into the double precision floating point value and return it.
+  char buffer[2 * sizeof(vfp_register[0])];
+#ifdef BIG_ENDIAN_FLOATING_POINT
+  memcpy(&buffer[0], &vfp_register[2 * dreg + 1], sizeof(vfp_register[0]));
+  memcpy(&buffer[4], &vfp_register[2 * dreg], sizeof(vfp_register[0]));
+#else
+  memcpy(buffer, &vfp_register[2 * dreg], 2 * sizeof(vfp_register[0]));
+#endif
+  memcpy(&dm_val, buffer, 2 * sizeof(vfp_register[0]));
+  return(dm_val);
+}
+
+
+// For use in calls that take two double values, constructed from r0, r1, r2
+// and r3.
+void Simulator::GetFpArgs(double* x, double* y) {
+  // We use a char buffer to get around the strict-aliasing rules which
+  // otherwise allow the compiler to optimize away the copy.
+  char buffer[2 * sizeof(registers_[0])];
+  // Registers 0 and 1 -> x.
+  memcpy(buffer, registers_, sizeof(buffer));
+  memcpy(x, buffer, sizeof(buffer));
+  // Registers 2 and 3 -> y.
+  memcpy(buffer, registers_ + 2, sizeof(buffer));
+  memcpy(y, buffer, sizeof(buffer));
+}
+
+
+void Simulator::SetFpResult(const double& result) {
+  char buffer[2 * sizeof(registers_[0])];
+  memcpy(buffer, &result, sizeof(buffer));
+  // result -> registers 0 and 1.
+  memcpy(registers_, buffer, sizeof(buffer));
+}
+
+
+void Simulator::TrashCallerSaveRegisters() {
+  // We don't trash the registers with the return value.
+  registers_[2] = 0x50Bad4U;
+  registers_[3] = 0x50Bad4U;
+  registers_[12] = 0x50Bad4U;
+}
+
+
+// The ARM cannot do unaligned reads and writes.  On some ARM platforms an
+// interrupt is caused.  On others it does a funky rotation thing.  For now we
+// simply disallow unaligned reads, but at some point we may want to move to
+// emulating the rotate behaviour.  Note that simulator runs have the runtime
+// system running directly on the host system and only generated code is
+// executed in the simulator.  Since the host is typically IA32 we will not
+// get the correct ARM-like behaviour on unaligned accesses.
+
+int Simulator::ReadW(int32_t addr, Instr* instr) {
+  if ((addr & 3) == 0) {
+    intptr_t* ptr = reinterpret_cast<intptr_t*>(addr);
+    return *ptr;
+  }
+  PrintF("Unaligned read at 0x%08x\n", addr);
+  UNIMPLEMENTED();
+  return 0;
+}
+
+
+void Simulator::WriteW(int32_t addr, int value, Instr* instr) {
+  if ((addr & 3) == 0) {
+    intptr_t* ptr = reinterpret_cast<intptr_t*>(addr);
+    *ptr = value;
+    return;
+  }
+  PrintF("Unaligned write at 0x%08x, pc=%p\n", addr, instr);
+  UNIMPLEMENTED();
+}
+
+
+uint16_t Simulator::ReadHU(int32_t addr, Instr* instr) {
+  if ((addr & 1) == 0) {
+    uint16_t* ptr = reinterpret_cast<uint16_t*>(addr);
+    return *ptr;
+  }
+  PrintF("Unaligned unsigned halfword read at 0x%08x, pc=%p\n", addr, instr);
+  UNIMPLEMENTED();
+  return 0;
+}
+
+
+int16_t Simulator::ReadH(int32_t addr, Instr* instr) {
+  if ((addr & 1) == 0) {
+    int16_t* ptr = reinterpret_cast<int16_t*>(addr);
+    return *ptr;
+  }
+  PrintF("Unaligned signed halfword read at 0x%08x\n", addr);
+  UNIMPLEMENTED();
+  return 0;
+}
+
+
+void Simulator::WriteH(int32_t addr, uint16_t value, Instr* instr) {
+  if ((addr & 1) == 0) {
+    uint16_t* ptr = reinterpret_cast<uint16_t*>(addr);
+    *ptr = value;
+    return;
+  }
+  PrintF("Unaligned unsigned halfword write at 0x%08x, pc=%p\n", addr, instr);
+  UNIMPLEMENTED();
+}
+
+
+void Simulator::WriteH(int32_t addr, int16_t value, Instr* instr) {
+  if ((addr & 1) == 0) {
+    int16_t* ptr = reinterpret_cast<int16_t*>(addr);
+    *ptr = value;
+    return;
+  }
+  PrintF("Unaligned halfword write at 0x%08x, pc=%p\n", addr, instr);
+  UNIMPLEMENTED();
+}
+
+
+uint8_t Simulator::ReadBU(int32_t addr) {
+  uint8_t* ptr = reinterpret_cast<uint8_t*>(addr);
+  return *ptr;
+}
+
+
+int8_t Simulator::ReadB(int32_t addr) {
+  int8_t* ptr = reinterpret_cast<int8_t*>(addr);
+  return *ptr;
+}
+
+
+void Simulator::WriteB(int32_t addr, uint8_t value) {
+  uint8_t* ptr = reinterpret_cast<uint8_t*>(addr);
+  *ptr = value;
+}
+
+
+void Simulator::WriteB(int32_t addr, int8_t value) {
+  int8_t* ptr = reinterpret_cast<int8_t*>(addr);
+  *ptr = value;
+}
+
+
+// Returns the limit of the stack area to enable checking for stack overflows.
+uintptr_t Simulator::StackLimit() const {
+  // Leave a safety margin of 256 bytes to prevent overrunning the stack when
+  // pushing values.
+  return reinterpret_cast<uintptr_t>(stack_) + 256;
+}
+
+
+// Unsupported instructions use Format to print an error and stop execution.
+void Simulator::Format(Instr* instr, const char* format) {
+  PrintF("Simulator found unsupported instruction:\n 0x%08x: %s\n",
+         instr, format);
+  UNIMPLEMENTED();
+}
+
+
+// Checks if the current instruction should be executed based on its
+// condition bits.
+bool Simulator::ConditionallyExecute(Instr* instr) {
+  switch (instr->ConditionField()) {
+    case EQ: return z_flag_;
+    case NE: return !z_flag_;
+    case CS: return c_flag_;
+    case CC: return !c_flag_;
+    case MI: return n_flag_;
+    case PL: return !n_flag_;
+    case VS: return v_flag_;
+    case VC: return !v_flag_;
+    case HI: return c_flag_ && !z_flag_;
+    case LS: return !c_flag_ || z_flag_;
+    case GE: return n_flag_ == v_flag_;
+    case LT: return n_flag_ != v_flag_;
+    case GT: return !z_flag_ && (n_flag_ == v_flag_);
+    case LE: return z_flag_ || (n_flag_ != v_flag_);
+    case AL: return true;
+    default: UNREACHABLE();
+  }
+  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) {
+  uint32_t uleft = static_cast<uint32_t>(left);
+  uint32_t uright = static_cast<uint32_t>(right);
+  uint32_t urest  = 0xffffffffU - uleft;
+
+  return (uright > urest);
+}
+
+
+// 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 (isnan(val1) || 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(Instr* instr, bool* carry_out) {
+  Shift shift = instr->ShiftField();
+  int shift_amount = instr->ShiftAmountField();
+  int32_t result = get_register(instr->RmField());
+  if (instr->Bit(4) == 0) {
+    // by immediate
+    if ((shift == ROR) && (shift_amount == 0)) {
+      UNIMPLEMENTED();
+      return result;
+    } else 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: {
+        UNIMPLEMENTED();
+        break;
+      }
+
+      default: {
+        UNREACHABLE();
+        break;
+      }
+    }
+  } else {
+    // by register
+    int rs = instr->RsField();
+    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 {
+          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 {
+          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: {
+        UNIMPLEMENTED();
+        break;
+      }
+
+      default: {
+        UNREACHABLE();
+        break;
+      }
+    }
+  }
+  return result;
+}
+
+
+// Addressing Mode 1 - Data-processing operands:
+// Get the value based on the shifter_operand with immediate.
+int32_t Simulator::GetImm(Instr* instr, bool* carry_out) {
+  int rotate = instr->RotateField() * 2;
+  int immed8 = instr->Immed8Field();
+  int imm = (immed8 >> rotate) | (immed8 << (32 - rotate));
+  *carry_out = (rotate == 0) ? c_flag_ : (imm < 0);
+  return imm;
+}
+
+
+static int count_bits(int bit_vector) {
+  int count = 0;
+  while (bit_vector != 0) {
+    if ((bit_vector & 1) != 0) {
+      count++;
+    }
+    bit_vector >>= 1;
+  }
+  return count;
+}
+
+
+// Addressing Mode 4 - Load and Store Multiple
+void Simulator::HandleRList(Instr* instr, bool load) {
+  int rn = instr->RnField();
+  int32_t rn_val = get_register(rn);
+  int rlist = instr->RlistField();
+  int num_regs = count_bits(rlist);
+
+  intptr_t start_address = 0;
+  intptr_t end_address = 0;
+  switch (instr->PUField()) {
+    case 0: {
+      // Print("da");
+      UNIMPLEMENTED();
+      break;
+    }
+    case 1: {
+      // Print("ia");
+      start_address = rn_val;
+      end_address = rn_val + (num_regs * 4) - 4;
+      rn_val = rn_val + (num_regs * 4);
+      break;
+    }
+    case 2: {
+      // Print("db");
+      start_address = rn_val - (num_regs * 4);
+      end_address = rn_val - 4;
+      rn_val = start_address;
+      break;
+    }
+    case 3: {
+      // Print("ib");
+      UNIMPLEMENTED();
+      break;
+    }
+    default: {
+      UNREACHABLE();
+      break;
+    }
+  }
+  if (instr->HasW()) {
+    set_register(rn, rn_val);
+  }
+  intptr_t* address = reinterpret_cast<intptr_t*>(start_address);
+  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;
+  }
+  ASSERT(end_address == ((intptr_t)address) - 4);
+}
+
+
+// Calls into the V8 runtime are based on this very simple interface.
+// Note: To be able to return two values from some calls the code in runtime.cc
+// uses the ObjectPair which is essentially two 32-bit values stuffed into a
+// 64-bit value. With the code below we assume that all runtime calls return
+// 64 bits of result. If they don't, the r1 result register contains a bogus
+// value, which is fine because it is caller-saved.
+typedef int64_t (*SimulatorRuntimeCall)(int32_t arg0,
+                                        int32_t arg1,
+                                        int32_t arg2,
+                                        int32_t arg3);
+typedef double (*SimulatorRuntimeFPCall)(int32_t arg0,
+                                         int32_t arg1,
+                                         int32_t arg2,
+                                         int32_t arg3);
+
+
+// Software interrupt instructions are used by the simulator to call into the
+// C-based V8 runtime.
+void Simulator::SoftwareInterrupt(Instr* instr) {
+  int swi = instr->SwiField();
+  switch (swi) {
+    case call_rt_redirected: {
+      Redirection* redirection = Redirection::FromSwiInstruction(instr);
+      int32_t arg0 = get_register(r0);
+      int32_t arg1 = get_register(r1);
+      int32_t arg2 = get_register(r2);
+      int32_t arg3 = get_register(r3);
+      // This is dodgy but it works because the C entry stubs are never moved.
+      // See comment in codegen-arm.cc and bug 1242173.
+      int32_t saved_lr = get_register(lr);
+      if (redirection->fp_return()) {
+        intptr_t external =
+            reinterpret_cast<intptr_t>(redirection->external_function());
+        SimulatorRuntimeFPCall target =
+            reinterpret_cast<SimulatorRuntimeFPCall>(external);
+        if (::v8::internal::FLAG_trace_sim) {
+          double x, y;
+          GetFpArgs(&x, &y);
+          PrintF("Call to host function at %p with args %f, %f\n",
+                 FUNCTION_ADDR(target), x, y);
+        }
+        double result = target(arg0, arg1, arg2, arg3);
+        SetFpResult(result);
+      } else {
+        intptr_t external =
+            reinterpret_cast<int32_t>(redirection->external_function());
+        SimulatorRuntimeCall target =
+            reinterpret_cast<SimulatorRuntimeCall>(external);
+        if (::v8::internal::FLAG_trace_sim) {
+          PrintF(
+              "Call to host function at %p with args %08x, %08x, %08x, %08x\n",
+              FUNCTION_ADDR(target),
+              arg0,
+              arg1,
+              arg2,
+              arg3);
+        }
+        int64_t result = target(arg0, arg1, arg2, arg3);
+        int32_t lo_res = static_cast<int32_t>(result);
+        int32_t hi_res = static_cast<int32_t>(result >> 32);
+        if (::v8::internal::FLAG_trace_sim) {
+          PrintF("Returned %08x\n", lo_res);
+        }
+        set_register(r0, lo_res);
+        set_register(r1, hi_res);
+      }
+      set_register(lr, saved_lr);
+      set_pc(get_register(lr));
+      break;
+    }
+    case break_point: {
+      Debugger dbg(this);
+      dbg.Debug();
+      break;
+    }
+    default: {
+      UNREACHABLE();
+      break;
+    }
+  }
+}
+
+
+// Handle execution based on instruction types.
+
+// 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(Instr* instr) {
+  int type = instr->TypeField();
+  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->RnField();
+        int rm = instr->RmField();
+        int rs = instr->RsField();
+        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.
+            // Format(instr, "mul'cond's 'rn, 'rm, 'rs");
+            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 {
+            // 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.
+            Format(instr, "mla'cond's 'rn, 'rm, 'rs, 'rd");
+          }
+        } 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.)
+          // Format(instr, "'um'al'cond's 'rd, 'rn, 'rs, 'rm");
+          int rd_hi = rn;  // Remap the rn field to the RdHi register.
+          int rd_lo = instr->RdField();
+          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()) {
+            UNIMPLEMENTED();
+          }
+        }
+      } else {
+        UNIMPLEMENTED();  // Not used by V8.
+      }
+    } else {
+      // extra load/store instructions
+      int rd = instr->RdField();
+      int rn = instr->RnField();
+      int32_t rn_val = get_register(rn);
+      int32_t addr = 0;
+      if (instr->Bit(22) == 0) {
+        int rm = instr->RmField();
+        int32_t rm_val = get_register(rm);
+        switch (instr->PUField()) {
+          case 0: {
+            // Format(instr, "'memop'cond'sign'h 'rd, ['rn], -'rm");
+            ASSERT(!instr->HasW());
+            addr = rn_val;
+            rn_val -= rm_val;
+            set_register(rn, rn_val);
+            break;
+          }
+          case 1: {
+            // Format(instr, "'memop'cond'sign'h 'rd, ['rn], +'rm");
+            ASSERT(!instr->HasW());
+            addr = rn_val;
+            rn_val += rm_val;
+            set_register(rn, rn_val);
+            break;
+          }
+          case 2: {
+            // Format(instr, "'memop'cond'sign'h 'rd, ['rn, -'rm]'w");
+            rn_val -= rm_val;
+            addr = rn_val;
+            if (instr->HasW()) {
+              set_register(rn, rn_val);
+            }
+            break;
+          }
+          case 3: {
+            // Format(instr, "'memop'cond'sign'h 'rd, ['rn, +'rm]'w");
+            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.
+            UNREACHABLE();
+            break;
+          }
+        }
+      } else {
+        int32_t imm_val = (instr->ImmedHField() << 4) | instr->ImmedLField();
+        switch (instr->PUField()) {
+          case 0: {
+            // Format(instr, "'memop'cond'sign'h 'rd, ['rn], #-'off8");
+            ASSERT(!instr->HasW());
+            addr = rn_val;
+            rn_val -= imm_val;
+            set_register(rn, rn_val);
+            break;
+          }
+          case 1: {
+            // Format(instr, "'memop'cond'sign'h 'rd, ['rn], #+'off8");
+            ASSERT(!instr->HasW());
+            addr = rn_val;
+            rn_val += imm_val;
+            set_register(rn, rn_val);
+            break;
+          }
+          case 2: {
+            // Format(instr, "'memop'cond'sign'h 'rd, ['rn, #-'off8]'w");
+            rn_val -= imm_val;
+            addr = rn_val;
+            if (instr->HasW()) {
+              set_register(rn, rn_val);
+            }
+            break;
+          }
+          case 3: {
+            // Format(instr, "'memop'cond'sign'h 'rd, ['rn, #+'off8]'w");
+            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.
+            UNREACHABLE();
+            break;
+          }
+        }
+      }
+      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
+        ASSERT(instr->HasSign());
+        ASSERT(instr->HasL());
+        int8_t val = ReadB(addr);
+        set_register(rd, val);
+      }
+      return;
+    }
+  } else {
+    int rd = instr->RdField();
+    int rn = instr->RnField();
+    int32_t rn_val = get_register(rn);
+    int32_t shifter_operand = 0;
+    bool shifter_carry_out = 0;
+    if (type == 0) {
+      shifter_operand = GetShiftRm(instr, &shifter_carry_out);
+    } else {
+      ASSERT(instr->TypeField() == 1);
+      shifter_operand = GetImm(instr, &shifter_carry_out);
+    }
+    int32_t alu_out;
+
+    switch (instr->OpcodeField()) {
+      case AND: {
+        // Format(instr, "and'cond's 'rd, 'rn, 'shift_rm");
+        // Format(instr, "and'cond's 'rd, 'rn, 'imm");
+        alu_out = rn_val & shifter_operand;
+        set_register(rd, alu_out);
+        if (instr->HasS()) {
+          SetNZFlags(alu_out);
+          SetCFlag(shifter_carry_out);
+        }
+        break;
+      }
+
+      case EOR: {
+        // Format(instr, "eor'cond's 'rd, 'rn, 'shift_rm");
+        // Format(instr, "eor'cond's 'rd, 'rn, 'imm");
+        alu_out = rn_val ^ shifter_operand;
+        set_register(rd, alu_out);
+        if (instr->HasS()) {
+          SetNZFlags(alu_out);
+          SetCFlag(shifter_carry_out);
+        }
+        break;
+      }
+
+      case SUB: {
+        // Format(instr, "sub'cond's 'rd, 'rn, 'shift_rm");
+        // Format(instr, "sub'cond's 'rd, 'rn, 'imm");
+        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 RSB: {
+        // Format(instr, "rsb'cond's 'rd, 'rn, 'shift_rm");
+        // Format(instr, "rsb'cond's 'rd, 'rn, 'imm");
+        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 ADD: {
+        // Format(instr, "add'cond's 'rd, 'rn, 'shift_rm");
+        // Format(instr, "add'cond's 'rd, 'rn, 'imm");
+        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 ADC: {
+        Format(instr, "adc'cond's 'rd, 'rn, 'shift_rm");
+        Format(instr, "adc'cond's 'rd, 'rn, 'imm");
+        break;
+      }
+
+      case SBC: {
+        Format(instr, "sbc'cond's 'rd, 'rn, 'shift_rm");
+        Format(instr, "sbc'cond's 'rd, 'rn, 'imm");
+        break;
+      }
+
+      case RSC: {
+        Format(instr, "rsc'cond's 'rd, 'rn, 'shift_rm");
+        Format(instr, "rsc'cond's 'rd, 'rn, 'imm");
+        break;
+      }
+
+      case TST: {
+        if (instr->HasS()) {
+          // Format(instr, "tst'cond 'rn, 'shift_rm");
+          // Format(instr, "tst'cond 'rn, 'imm");
+          alu_out = rn_val & shifter_operand;
+          SetNZFlags(alu_out);
+          SetCFlag(shifter_carry_out);
+        } else {
+          UNIMPLEMENTED();
+        }
+        break;
+      }
+
+      case TEQ: {
+        if (instr->HasS()) {
+          // Format(instr, "teq'cond 'rn, 'shift_rm");
+          // Format(instr, "teq'cond 'rn, 'imm");
+          alu_out = rn_val ^ shifter_operand;
+          SetNZFlags(alu_out);
+          SetCFlag(shifter_carry_out);
+        } else {
+          ASSERT(type == 0);
+          int rm = instr->RmField();
+          switch (instr->Bits(7, 4)) {
+            case BX:
+              set_pc(get_register(rm));
+              break;
+            case BLX: {
+              uint32_t old_pc = get_pc();
+              set_pc(get_register(rm));
+              set_register(lr, old_pc + Instr::kInstrSize);
+              break;
+            }
+            default:
+              UNIMPLEMENTED();
+          }
+        }
+        break;
+      }
+
+      case CMP: {
+        if (instr->HasS()) {
+          // Format(instr, "cmp'cond 'rn, 'shift_rm");
+          // Format(instr, "cmp'cond 'rn, 'imm");
+          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 {
+          UNIMPLEMENTED();
+        }
+        break;
+      }
+
+      case CMN: {
+        if (instr->HasS()) {
+          // Format(instr, "cmn'cond 'rn, 'shift_rm");
+          // Format(instr, "cmn'cond 'rn, 'imm");
+          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 {
+          ASSERT(type == 0);
+          int rm = instr->RmField();
+          int rd = instr->RdField();
+          switch (instr->Bits(7, 4)) {
+            case CLZ: {
+              uint32_t bits = get_register(rm);
+              int leading_zeros = 0;
+              if (bits == 0) {
+                leading_zeros = 32;
+              } else {
+                while ((bits & 0x80000000u) == 0) {
+                  bits <<= 1;
+                  leading_zeros++;
+                }
+              }
+              set_register(rd, leading_zeros);
+              break;
+            }
+            default:
+              UNIMPLEMENTED();
+          }
+        }
+        break;
+      }
+
+      case ORR: {
+        // Format(instr, "orr'cond's 'rd, 'rn, 'shift_rm");
+        // Format(instr, "orr'cond's 'rd, 'rn, 'imm");
+        alu_out = rn_val | shifter_operand;
+        set_register(rd, alu_out);
+        if (instr->HasS()) {
+          SetNZFlags(alu_out);
+          SetCFlag(shifter_carry_out);
+        }
+        break;
+      }
+
+      case MOV: {
+        // Format(instr, "mov'cond's 'rd, 'shift_rm");
+        // Format(instr, "mov'cond's 'rd, 'imm");
+        alu_out = shifter_operand;
+        set_register(rd, alu_out);
+        if (instr->HasS()) {
+          SetNZFlags(alu_out);
+          SetCFlag(shifter_carry_out);
+        }
+        break;
+      }
+
+      case BIC: {
+        // Format(instr, "bic'cond's 'rd, 'rn, 'shift_rm");
+        // Format(instr, "bic'cond's 'rd, 'rn, 'imm");
+        alu_out = rn_val & ~shifter_operand;
+        set_register(rd, alu_out);
+        if (instr->HasS()) {
+          SetNZFlags(alu_out);
+          SetCFlag(shifter_carry_out);
+        }
+        break;
+      }
+
+      case MVN: {
+        // Format(instr, "mvn'cond's 'rd, 'shift_rm");
+        // Format(instr, "mvn'cond's 'rd, 'imm");
+        alu_out = ~shifter_operand;
+        set_register(rd, alu_out);
+        if (instr->HasS()) {
+          SetNZFlags(alu_out);
+          SetCFlag(shifter_carry_out);
+        }
+        break;
+      }
+
+      default: {
+        UNREACHABLE();
+        break;
+      }
+    }
+  }
+}
+
+
+void Simulator::DecodeType2(Instr* instr) {
+  int rd = instr->RdField();
+  int rn = instr->RnField();
+  int32_t rn_val = get_register(rn);
+  int32_t im_val = instr->Offset12Field();
+  int32_t addr = 0;
+  switch (instr->PUField()) {
+    case 0: {
+      // Format(instr, "'memop'cond'b 'rd, ['rn], #-'off12");
+      ASSERT(!instr->HasW());
+      addr = rn_val;
+      rn_val -= im_val;
+      set_register(rn, rn_val);
+      break;
+    }
+    case 1: {
+      // Format(instr, "'memop'cond'b 'rd, ['rn], #+'off12");
+      ASSERT(!instr->HasW());
+      addr = rn_val;
+      rn_val += im_val;
+      set_register(rn, rn_val);
+      break;
+    }
+    case 2: {
+      // Format(instr, "'memop'cond'b 'rd, ['rn, #-'off12]'w");
+      rn_val -= im_val;
+      addr = rn_val;
+      if (instr->HasW()) {
+        set_register(rn, rn_val);
+      }
+      break;
+    }
+    case 3: {
+      // Format(instr, "'memop'cond'b 'rd, ['rn, #+'off12]'w");
+      rn_val += im_val;
+      addr = rn_val;
+      if (instr->HasW()) {
+        set_register(rn, rn_val);
+      }
+      break;
+    }
+    default: {
+      UNREACHABLE();
+      break;
+    }
+  }
+  if (instr->HasB()) {
+    if (instr->HasL()) {
+      byte val = ReadBU(addr);
+      set_register(rd, val);
+    } else {
+      byte val = get_register(rd);
+      WriteB(addr, val);
+    }
+  } else {
+    if (instr->HasL()) {
+      set_register(rd, ReadW(addr, instr));
+    } else {
+      WriteW(addr, get_register(rd), instr);
+    }
+  }
+}
+
+
+void Simulator::DecodeType3(Instr* instr) {
+  ASSERT(instr->Bits(6, 4) == 0x5 || instr->Bit(4) == 0);
+  int rd = instr->RdField();
+  int rn = instr->RnField();
+  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 0: {
+      ASSERT(!instr->HasW());
+      Format(instr, "'memop'cond'b 'rd, ['rn], -'shift_rm");
+      break;
+    }
+    case 1: {
+      ASSERT(!instr->HasW());
+      Format(instr, "'memop'cond'b 'rd, ['rn], +'shift_rm");
+      break;
+    }
+    case 2: {
+      // Format(instr, "'memop'cond'b 'rd, ['rn, -'shift_rm]'w");
+      addr = rn_val - shifter_operand;
+      if (instr->HasW()) {
+        set_register(rn, addr);
+      }
+      break;
+    }
+    case 3: {
+      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->ShiftAmountField());
+        uint32_t msbit = widthminus1 + lsbit;
+        if (msbit <= 31) {
+          uint32_t rm_val =
+              static_cast<uint32_t>(get_register(instr->RmField()));
+          uint32_t extr_val = rm_val << (31 - msbit);
+          extr_val = extr_val >> (31 - widthminus1);
+          set_register(instr->RdField(), extr_val);
+        } else {
+          UNREACHABLE();
+        }
+        return;
+      } else {
+        // Format(instr, "'memop'cond'b 'rd, ['rn, +'shift_rm]'w");
+        addr = rn_val + shifter_operand;
+        if (instr->HasW()) {
+          set_register(rn, addr);
+        }
+      }
+      break;
+    }
+    default: {
+      UNREACHABLE();
+      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));
+    } else {
+      WriteW(addr, get_register(rd), instr);
+    }
+  }
+}
+
+
+void Simulator::DecodeType4(Instr* instr) {
+  ASSERT(instr->Bit(22) == 0);  // only allowed to be set in privileged mode
+  if (instr->HasL()) {
+    // Format(instr, "ldm'cond'pu 'rn'w, 'rlist");
+    HandleRList(instr, true);
+  } else {
+    // Format(instr, "stm'cond'pu 'rn'w, 'rlist");
+    HandleRList(instr, false);
+  }
+}
+
+
+void Simulator::DecodeType5(Instr* instr) {
+  // Format(instr, "b'l'cond 'target");
+  int off = (instr->SImmed24Field() << 2);
+  intptr_t pc_address = get_pc();
+  if (instr->HasLink()) {
+    set_register(lr, pc_address + Instr::kInstrSize);
+  }
+  int pc_reg = get_register(pc);
+  set_pc(pc_reg + off);
+}
+
+
+void Simulator::DecodeType6(Instr* instr) {
+  DecodeType6CoprocessorIns(instr);
+}
+
+
+void Simulator::DecodeType7(Instr* instr) {
+  if (instr->Bit(24) == 1) {
+    SoftwareInterrupt(instr);
+  } else {
+    DecodeTypeVFP(instr);
+  }
+}
+
+
+void Simulator::DecodeUnconditional(Instr* instr) {
+  if (instr->Bits(7, 4) == 0x0B && instr->Bits(27, 25) == 0 && instr->HasL()) {
+    // Load halfword instruction, either register or immediate offset.
+    int rd = instr->RdField();
+    int rn = instr->RnField();
+    int32_t rn_val = get_register(rn);
+    int32_t addr = 0;
+    int32_t offset;
+    if (instr->Bit(22) == 0) {
+      // Register offset.
+      int rm = instr->RmField();
+      offset = get_register(rm);
+    } else {
+      // Immediate offset
+      offset = instr->Bits(3, 0) + (instr->Bits(11, 8) << 4);
+    }
+    switch (instr->PUField()) {
+      case 0: {
+        // Post index, negative.
+        ASSERT(!instr->HasW());
+        addr = rn_val;
+        rn_val -= offset;
+        set_register(rn, rn_val);
+        break;
+      }
+      case 1: {
+        // Post index, positive.
+        ASSERT(!instr->HasW());
+        addr = rn_val;
+        rn_val += offset;
+        set_register(rn, rn_val);
+        break;
+      }
+      case 2: {
+        // Pre index or offset, negative.
+        rn_val -= offset;
+        addr = rn_val;
+        if (instr->HasW()) {
+          set_register(rn, rn_val);
+        }
+        break;
+      }
+      case 3: {
+        // Pre index or offset, positive.
+        rn_val += offset;
+        addr = rn_val;
+        if (instr->HasW()) {
+          set_register(rn, rn_val);
+        }
+        break;
+      }
+      default: {
+        // The PU field is a 2-bit field.
+        UNREACHABLE();
+        break;
+      }
+    }
+    // Not sign extending, so load as unsigned.
+    uint16_t halfword = ReadH(addr, instr);
+    set_register(rd, halfword);
+  } else {
+    Debugger dbg(this);
+    dbg.Stop(instr);
+  }
+}
+
+
+// void Simulator::DecodeTypeVFP(Instr* instr)
+// The Following ARMv7 VFPv instructions are currently supported.
+// vmov :Sn = Rt
+// vmov :Rt = Sn
+// vcvt: Dd = Sm
+// vcvt: Sd = Dm
+// Dd = vadd(Dn, Dm)
+// Dd = vsub(Dn, Dm)
+// Dd = vmul(Dn, Dm)
+// Dd = vdiv(Dn, Dm)
+// vcmp(Dd, Dm)
+// VMRS
+void Simulator::DecodeTypeVFP(Instr* instr) {
+  ASSERT((instr->TypeField() == 7) && (instr->Bit(24) == 0x0) );
+
+  int rt = instr->RtField();
+  int vm = instr->VmField();
+  int vn = instr->VnField();
+  int vd = instr->VdField();
+
+  if (instr->Bit(23) == 1) {
+    if ((instr->Bits(21, 19) == 0x7) &&
+        (instr->Bits(18, 16) == 0x5) &&
+        (instr->Bits(11, 9) == 0x5) &&
+        (instr->Bit(8) == 1) &&
+        (instr->Bit(6) == 1) &&
+        (instr->Bit(4) == 0)) {
+      double dm_val = get_double_from_d_register(vm);
+      int32_t int_value = static_cast<int32_t>(dm_val);
+      set_s_register_from_sinteger(((vd<<1) | instr->DField()), int_value);
+    } else if ((instr->Bits(21, 19) == 0x7) &&
+               (instr->Bits(18, 16) == 0x0) &&
+               (instr->Bits(11, 9) == 0x5) &&
+               (instr->Bit(8) == 1) &&
+               (instr->Bit(7) == 1) &&
+               (instr->Bit(6) == 1) &&
+               (instr->Bit(4) == 0)) {
+      int32_t int_value = get_sinteger_from_s_register(((vm<<1) |
+                                                       instr->MField()));
+      double dbl_value = static_cast<double>(int_value);
+      set_d_register_from_double(vd, dbl_value);
+    } else if ((instr->Bit(21) == 0x0) &&
+               (instr->Bit(20) == 0x0) &&
+               (instr->Bits(11, 9) == 0x5) &&
+               (instr->Bit(8) == 1) &&
+               (instr->Bit(6) == 0) &&
+               (instr->Bit(4) == 0)) {
+      double dn_value = get_double_from_d_register(vn);
+      double dm_value = get_double_from_d_register(vm);
+      double dd_value = dn_value / dm_value;
+      set_d_register_from_double(vd, dd_value);
+    } else if ((instr->Bits(21, 20) == 0x3) &&
+               (instr->Bits(19, 16) == 0x4) &&
+               (instr->Bits(11, 9) == 0x5) &&
+               (instr->Bit(8) == 0x1) &&
+               (instr->Bit(6) == 0x1) &&
+               (instr->Bit(4) == 0x0)) {
+      double dd_value = get_double_from_d_register(vd);
+      double dm_value = get_double_from_d_register(vm);
+      Compute_FPSCR_Flags(dd_value, dm_value);
+    } else if ((instr->Bits(23, 20) == 0xF) &&
+               (instr->Bits(19, 16) == 0x1) &&
+               (instr->Bits(11, 8) == 0xA) &&
+               (instr->Bits(7, 5) == 0x0) &&
+               (instr->Bit(4) == 0x1)    &&
+               (instr->Bits(3, 0) == 0x0)) {
+      if (instr->Bits(15, 12) == 0xF)
+        Copy_FPSCR_to_APSR();
+      else
+        UNIMPLEMENTED();  // Not used by V8.
+    } else {
+      UNIMPLEMENTED();  // Not used by V8.
+    }
+  } else if (instr->Bit(21) == 1) {
+    if ((instr->Bit(20) == 0x1) &&
+        (instr->Bits(11, 9) == 0x5) &&
+        (instr->Bit(8) == 0x1) &&
+        (instr->Bit(6) == 0) &&
+        (instr->Bit(4) == 0)) {
+      double dn_value = get_double_from_d_register(vn);
+      double dm_value = get_double_from_d_register(vm);
+      double dd_value = dn_value + dm_value;
+      set_d_register_from_double(vd, dd_value);
+    } else if ((instr->Bit(20) == 0x1) &&
+               (instr->Bits(11, 9) == 0x5) &&
+               (instr->Bit(8) == 0x1) &&
+               (instr->Bit(6) == 1) &&
+               (instr->Bit(4) == 0)) {
+      double dn_value = get_double_from_d_register(vn);
+      double dm_value = get_double_from_d_register(vm);
+      double dd_value = dn_value - dm_value;
+      set_d_register_from_double(vd, dd_value);
+    } else if ((instr->Bit(20) == 0x0) &&
+               (instr->Bits(11, 9) == 0x5) &&
+               (instr->Bit(8) == 0x1) &&
+               (instr->Bit(6) == 0) &&
+               (instr->Bit(4) == 0)) {
+      double dn_value = get_double_from_d_register(vn);
+      double dm_value = get_double_from_d_register(vm);
+      double dd_value = dn_value * dm_value;
+      set_d_register_from_double(vd, dd_value);
+    } else {
+      UNIMPLEMENTED();  // Not used by V8.
+    }
+  } else {
+    if ((instr->Bit(20) == 0x0) &&
+        (instr->Bits(11, 8) == 0xA) &&
+        (instr->Bits(6, 5) == 0x0) &&
+        (instr->Bit(4) == 1) &&
+        (instr->Bits(3, 0) == 0x0)) {
+      int32_t rs_val = get_register(rt);
+      set_s_register_from_sinteger(((vn<<1) | instr->NField()), rs_val);
+    } else if ((instr->Bit(20) == 0x1) &&
+               (instr->Bits(11, 8) == 0xA) &&
+               (instr->Bits(6, 5) == 0x0) &&
+               (instr->Bit(4) == 1) &&
+               (instr->Bits(3, 0) == 0x0)) {
+      int32_t int_value = get_sinteger_from_s_register(((vn<<1) |
+                                                       instr->NField()));
+      set_register(rt, int_value);
+    } else {
+      UNIMPLEMENTED();  // Not used by V8.
+    }
+  }
+}
+
+
+// void Simulator::DecodeType6CoprocessorIns(Instr* instr)
+// Decode Type 6 coprocessor instructions.
+// Dm = vmov(Rt, Rt2)
+// <Rt, Rt2> = vmov(Dm)
+// Ddst = MEM(Rbase + 4*offset).
+// MEM(Rbase + 4*offset) = Dsrc.
+void Simulator::DecodeType6CoprocessorIns(Instr* instr) {
+  ASSERT((instr->TypeField() == 6));
+
+  if (instr->CoprocessorField() != 0xB) {
+    UNIMPLEMENTED();  // Not used by V8.
+  } else {
+    switch (instr->OpcodeField()) {
+      case 0x2:
+        // Load and store double to two GP registers
+        if (instr->Bits(7, 4) != 0x1) {
+          UNIMPLEMENTED();  // Not used by V8.
+        } else {
+          int rt = instr->RtField();
+          int rn = instr->RnField();
+          int vm = instr->VmField();
+          if (instr->HasL()) {
+            int32_t rt_int_value = get_sinteger_from_s_register(2*vm);
+            int32_t rn_int_value = get_sinteger_from_s_register(2*vm+1);
+
+            set_register(rt, rt_int_value);
+            set_register(rn, rn_int_value);
+          } else {
+            int32_t rs_val = get_register(rt);
+            int32_t rn_val = get_register(rn);
+
+            set_s_register_from_sinteger(2*vm, rs_val);
+            set_s_register_from_sinteger((2*vm+1), rn_val);
+          }
+        }
+        break;
+      case 0x8:
+      case 0xC: {  // Load and store double to memory.
+        int rn = instr->RnField();
+        int vd = instr->VdField();
+        int offset = instr->Immed8Field();
+        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(2*vd, ReadW(address, instr));
+          set_s_register_from_sinteger(2*vd + 1, ReadW(address + 4, instr));
+        } else {
+          // Store double to memory: vstr.
+          WriteW(address, get_sinteger_from_s_register(2*vd), instr);
+          WriteW(address + 4, get_sinteger_from_s_register(2*vd + 1), instr);
+        }
+        break;
+      }
+      default:
+        UNIMPLEMENTED();  // Not used by V8.
+        break;
+    }
+  }
+}
+
+void Simulator::InstructionDecode(int32_t adr) {
+  if (::v8::internal::FLAG_trace_sim) {
+    disasm::NameConverter converter;
+    disasm::Disassembler dasm(converter);
+    // use a reasonably large buffer
+    v8::internal::EmbeddedVector<char, 256> buffer;
+    dasm.InstructionDecode(buffer,
+                           reinterpret_cast<byte*>(adr));
+    PrintF("  0x%08x  %s\n", adr, buffer.start());
+  }
+  if (adr & 1) {
+    InstructionDecodeThumb2(reinterpret_cast<byte*>(adr));
+  } else {
+    InstructionDecodeArm(reinterpret_cast<Instr*>(adr));
+  }
+}
+
+int32_t Simulator::GetOperand2(const InstrThumb2& instr, bool* carry_out) {
+  switch (instr.Variant()) {
+    case VARIANT_IMMEDIATE:
+      return instr.Imm();
+
+    case VARIANT_REGISTER:
+      return GetRmShiftImm(instr, carry_out);
+
+    default:
+      UNIMPLEMENTED();
+      return -1;
+  }
+}
+
+int32_t Simulator::GetRmShiftImm(const InstrThumb2& instr, bool* carry_out) {
+  Shift shift = (Shift) instr.Type();
+  int shift_amount = instr.Imm();
+  int32_t result = get_register(instr.Rm());
+
+  switch (shift) {
+    case no_shift:
+      break;
+
+    case ASR: {
+      result >>= (shift_amount - 1);
+      *carry_out = (result & 1) == 1;
+      result >>= 1;
+      break;
+    }
+
+    case LSL: {
+      result <<= (shift_amount - 1);
+      *carry_out = (result < 0);
+      result <<= 1;
+      break;
+    }
+
+    case LSR: {
+      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 RRX:
+    case ROR: {
+      UNIMPLEMENTED();
+      break;
+    }
+
+    default: {
+      UNREACHABLE();
+      break;
+    }
+  }
+  return result;
+}
+
+
+
+void Simulator::InstructionDecodeThumb2(byte* adr) {
+  pc_modified_ = false;
+  InstrThumb2 instr(adr);
+  bool shifter_carry_out = 0;
+  int32_t alu_out;
+  int32_t operand2;
+
+//  enter_debug_ = true;
+
+
+//  PrintF("executing OP: %i size: %i rn: %i rm: %i rd: %i\n",
+//         instr.Op(), instr.Size(), instr.Rn(), instr.Rm(), instr.Rd());
+
+  int32_t rn_val = get_register(instr.Rn());
+  switch (instr.Op()) {
+    case OP_AND:
+      alu_out = rn_val & GetOperand2(instr, &shifter_carry_out);
+      set_register(instr.Rd(), alu_out);
+      if (instr.HasS()) {
+        SetNZFlags(alu_out);
+        SetCFlag(shifter_carry_out);
+      }
+      break;
+    case OP_ADD:
+      operand2 = GetOperand2(instr, &shifter_carry_out);
+      alu_out = rn_val + operand2;
+      set_register(instr.Rd(), alu_out);
+      if (instr.HasS()) {
+        SetNZFlags(alu_out);
+        SetCFlag(CarryFrom(rn_val, operand2));
+        SetVFlag(OverflowFrom(alu_out, rn_val, operand2, true));
+      }
+      break;
+
+    case OP_SUB:
+      operand2 = GetOperand2(instr, &shifter_carry_out);
+      alu_out = rn_val - operand2;
+      set_register(instr.Rd(), alu_out);
+      if (instr.HasS()) {
+        SetNZFlags(alu_out);
+        SetCFlag(!BorrowFrom(rn_val, operand2));
+        SetVFlag(OverflowFrom(alu_out, rn_val, operand2, false));
+      }
+      break;
+
+    default:
+      PrintF("Unrecogized Thumb Instruction");
+      UNIMPLEMENTED();
+  }
+  if (!pc_modified_) {
+    set_register(pc, reinterpret_cast<int32_t>(adr) + instr.Size());
+  }
+}
+
+// Executes the current instruction.
+void Simulator::InstructionDecodeArm(Instr* instr) {
+  pc_modified_ = false;
+  if (instr->ConditionField() == special_condition) {
+    DecodeUnconditional(instr);
+  } else if (ConditionallyExecute(instr)) {
+    switch (instr->TypeField()) {
+      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: {
+        UNIMPLEMENTED();
+        break;
+      }
+    }
+  }
+  if (!pc_modified_) {
+    set_register(pc, reinterpret_cast<int32_t>(instr) + Instr::kInstrSize);
+  }
+}
+
+
+void Simulator::Execute() {
+  // 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();
+
+  if (::v8::internal::FLAG_stop_sim_at == 0) {
+    // Fast version of the dispatch loop without checking whether the simulator
+    // should be stopping at a particular executed instruction.
+    while (program_counter != end_sim_pc) {
+      icount_++;
+      InstructionDecode(program_counter);
+      program_counter = get_pc();
+    }
+  } else {
+    // FLAG_stop_sim_at is at the non-default value. Stop in the debugger when
+    // we reach the particular instuction count.
+    while (program_counter != end_sim_pc) {
+      icount_++;
+      if (icount_ == ::v8::internal::FLAG_stop_sim_at) {
+        Debugger dbg(this);
+        dbg.Debug();
+      } else if (program_counter & 1) {
+        InstructionDecode(program_counter);
+      }
+      program_counter = get_pc();
+    }
+  }
+}
+
+
+int32_t Simulator::Call(byte* entry, int argument_count, ...) {
+  va_list parameters;
+  va_start(parameters, argument_count);
+  // Setup arguments
+
+  // First four arguments passed in registers.
+  ASSERT(argument_count >= 4);
+  set_register(r0, va_arg(parameters, int32_t));
+  set_register(r1, va_arg(parameters, int32_t));
+  set_register(r2, va_arg(parameters, int32_t));
+  set_register(r3, va_arg(parameters, int32_t));
+
+  // Remaining arguments passed on stack.
+  int original_stack = get_register(sp);
+  // Compute position of stack on entry to generated code.
+  int entry_stack = (original_stack - (argument_count - 4) * sizeof(int32_t));
+  if (OS::ActivationFrameAlignment() != 0) {
+    entry_stack &= -OS::ActivationFrameAlignment();
+  }
+  // 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);
+
+  // 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);
+
+  // Setup 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 = icount_;
+  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);
+
+  // Start the simulation
+  Execute();
+
+  // Check that the callee-saved registers have been preserved.
+  CHECK_EQ(callee_saved_value, get_register(r4));
+  CHECK_EQ(callee_saved_value, get_register(r5));
+  CHECK_EQ(callee_saved_value, get_register(r6));
+  CHECK_EQ(callee_saved_value, get_register(r7));
+  CHECK_EQ(callee_saved_value, get_register(r8));
+  CHECK_EQ(callee_saved_value, get_register(r9));
+  CHECK_EQ(callee_saved_value, get_register(r10));
+  CHECK_EQ(callee_saved_value, get_register(r11));
+
+  // 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);
+
+  // Pop stack passed arguments.
+  CHECK_EQ(entry_stack, get_register(sp));
+  set_register(sp, original_stack);
+
+  int32_t result = get_register(r0);
+  return result;
+}
+
+
+uintptr_t Simulator::PushAddress(uintptr_t address) {
+  int new_sp = get_register(sp) - sizeof(uintptr_t);
+  uintptr_t* stack_slot = reinterpret_cast<uintptr_t*>(new_sp);
+  *stack_slot = address;
+  set_register(sp, new_sp);
+  return new_sp;
+}
+
+
+uintptr_t Simulator::PopAddress() {
+  int current_sp = get_register(sp);
+  uintptr_t* stack_slot = reinterpret_cast<uintptr_t*>(current_sp);
+  uintptr_t address = *stack_slot;
+  set_register(sp, current_sp + sizeof(uintptr_t));
+  return address;
+}
+
+
+} }  // namespace assembler::arm
+
+#endif  // !defined(__arm__)