Forking disassembler and simulator for Thumb2 support;...

src/arm/disasm-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.
+
+// A Disassembler object is used to disassemble a block of code instruction by
+// instruction. The default implementation of the NameConverter object can be
+// overriden to modify register names or to do symbol lookup on addresses.
+//
+// The example below will disassemble a block of code and print it to stdout.
+//
+//   NameConverter converter;
+//   Disassembler d(converter);
+//   for (byte* pc = begin; pc < end;) {
+//     char buffer[128];
+//     buffer[0] = '\0';
+//     byte* prev_pc = pc;
+//     pc += d.InstructionDecode(buffer, sizeof buffer, pc);
+//     printf("%p    %08x      %s\n",
+//            prev_pc, *reinterpret_cast<int32_t*>(prev_pc), buffer);
+//   }
+//
+// The Disassembler class also has a convenience method to disassemble a block
+// of code into a FILE*, meaning that the above functionality could also be
+// achieved by just calling Disassembler::Disassemble(stdout, begin, end);
+
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdarg.h>
+#include <string.h>
+#ifndef WIN32
+#include <stdint.h>
+#endif
+
+#include "v8.h"
+
+#include "constants-arm.h"
+#include "disasm.h"
+#include "macro-assembler.h"
+#include "instr-thumb2.h"
+#include "platform.h"
+
+
+namespace assembler {
+namespace arm {
+
+namespace v8i = v8::internal;
+
+
+//------------------------------------------------------------------------------
+
+// Decoder decodes and disassembles instructions into an output buffer.
+// It uses the converter to convert register names and call destinations into
+// more informative description.
+class Decoder {
+ public:
+  Decoder(const disasm::NameConverter& converter,
+          v8::internal::Vector<char> out_buffer)
+    : converter_(converter),
+      out_buffer_(out_buffer),
+      out_buffer_pos_(0) {
+    out_buffer_[out_buffer_pos_] = '\0';
+  }
+
+  ~Decoder() {}
+
+  // Writes one disassembled instruction into 'buffer' (0-terminated).
+  // Returns the length of the disassembled machine instruction in bytes.
+  int InstructionDecode(byte* instruction);
+  int InstructionDecodeArm(byte* instruction);
+  int InstructionDecodeThumb2(const InstrThumb2& instr);
+
+ private:
+  // Bottleneck functions to print into the out_buffer.
+  void PrintChar(const char ch);
+  void Print(const char* str);
+
+  // Printing of common values.
+  void PrintRegister(int reg);
+  void PrintSRegister(int reg);
+  void PrintDRegister(int reg);
+  int FormatVFPRegister(Instr* instr, const char* format);
+  int FormatVFPinstruction(Instr* instr, const char* format);
+  void PrintCondition(Instr* instr);
+  void PrintShiftRm(Instr* instr);
+  void PrintShiftRm(const InstrThumb2& instr);
+  void PrintShiftImm(Instr* instr);
+  void PrintShiftImm(const InstrThumb2& instr);
+  void PrintPU(Instr* instr);
+  void PrintSoftwareInterrupt(SoftwareInterruptCodes swi);
+
+  // Handle formatting of instructions and their options.
+  int FormatRegister(Instr* instr, const char* option);
+  int FormatRegister(const InstrThumb2& instr, const char* option);
+  int FormatOption(Instr* instr, const char* option);
+  int FormatOption(const InstrThumb2& instr, const char* option);
+  void Format(Instr* instr, const char* format);
+  void Format(const InstrThumb2& instr, const char* format);
+  void Unknown(Instr* instr);
+  void Unknown(const InstrThumb2& instr);
+
+  // Each of these functions decodes one particular instruction type, a 3-bit
+  // field in the instruction encoding.
+  // Types 0 and 1 are combined as they are largely the same except for the way
+  // they interpret the shifter operand.
+  void DecodeType01(Instr* instr);
+  void DecodeType2(Instr* instr);
+  void DecodeType3(Instr* instr);
+  void DecodeType4(Instr* instr);
+  void DecodeType5(Instr* instr);
+  void DecodeType6(Instr* instr);
+  void DecodeType7(Instr* instr);
+  void DecodeUnconditional(Instr* instr);
+  // For VFP support.
+  void DecodeTypeVFP(Instr* instr);
+  void DecodeType6CoprocessorIns(Instr* instr);
+
+
+  const disasm::NameConverter& converter_;
+  v8::internal::Vector<char> out_buffer_;
+  int out_buffer_pos_;
+
+  DISALLOW_COPY_AND_ASSIGN(Decoder);
+};
+
+
+// Support for assertions in the Decoder formatting functions.
+#define STRING_STARTS_WITH(string, compare_string) \
+  (strncmp(string, compare_string, strlen(compare_string)) == 0)
+
+
+// Append the ch to the output buffer.
+void Decoder::PrintChar(const char ch) {
+  out_buffer_[out_buffer_pos_++] = ch;
+}
+
+
+// Append the str to the output buffer.
+void Decoder::Print(const char* str) {
+  char cur = *str++;
+  while (cur != '\0' && (out_buffer_pos_ < (out_buffer_.length() - 1))) {
+    PrintChar(cur);
+    cur = *str++;
+  }
+  out_buffer_[out_buffer_pos_] = 0;
+}
+
+
+// These condition names are defined in a way to match the native disassembler
+// formatting. See for example the command "objdump -d <binary file>".
+static const char* cond_names[max_condition] = {
+  "eq", "ne", "cs" , "cc" , "mi" , "pl" , "vs" , "vc" ,
+  "hi", "ls", "ge", "lt", "gt", "le", "", "invalid",
+};
+
+
+// Print the condition guarding the instruction.
+void Decoder::PrintCondition(Instr* instr) {
+  Print(cond_names[instr->ConditionField()]);
+}
+
+
+// Print the register name according to the active name converter.
+void Decoder::PrintRegister(int reg) {
+  Print(converter_.NameOfCPURegister(reg));
+}
+
+// Print the VFP S register name according to the active name converter.
+void Decoder::PrintSRegister(int reg) {
+  Print(assembler::arm::VFPRegisters::Name(reg));
+}
+
+// Print the  VFP D register name according to the active name converter.
+void Decoder::PrintDRegister(int reg) {
+  Print(assembler::arm::VFPRegisters::Name(reg + 32));
+}
+
+
+// These shift names are defined in a way to match the native disassembler
+// formatting. See for example the command "objdump -d <binary file>".
+static const char* shift_names[max_shift] = {
+  "lsl", "lsr", "asr", "ror"
+};
+
+
+// Print the register shift operands for the instruction. Generally used for
+// data processing instructions.
+void Decoder::PrintShiftRm(Instr* instr) {
+  Shift shift = instr->ShiftField();
+  int shift_amount = instr->ShiftAmountField();
+  int rm = instr->RmField();
+
+  PrintRegister(rm);
+
+  if ((instr->RegShiftField() == 0) && (shift == LSL) && (shift_amount == 0)) {
+    // Special case for using rm only.
+    return;
+  }
+  if (instr->RegShiftField() == 0) {
+    // by immediate
+    if ((shift == ROR) && (shift_amount == 0)) {
+      Print(", RRX");
+      return;
+    } else if (((shift == LSR) || (shift == ASR)) && (shift_amount == 0)) {
+      shift_amount = 32;
+    }
+    out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+                                         ", %s #%d",
+                                         shift_names[shift], shift_amount);
+  } else {
+    // by register
+    int rs = instr->RsField();
+    out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+                                         ", %s ", shift_names[shift]);
+    PrintRegister(rs);
+  }
+}
+
+void Decoder::PrintShiftRm(const InstrThumb2& instr) {
+  int shift = instr.Type();
+  int shift_amount = instr.Imm();
+  int rm = instr.Rm();
+
+  PrintRegister(rm);
+
+  if (instr.Variant() != VARIANT_REGISTER_SHIFTED_REGISTER) {
+    if (shift == no_shift) {
+      // Special case for using rm only.
+      return;
+    }
+    if (shift == RRX) {
+      Print(", RRX");
+      return;
+    }
+    out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+                                         ", %s #%d",
+                                         shift_names[shift], shift_amount);
+  } else {
+    UNIMPLEMENTED();
+//    // by register
+//   int rs = instr->Rs();
+//    out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+//                                         ", %s ", shift_names[shift]);
+//    PrintRegister(rs);
+  }
+}
+
+
+
+// Print the immediate operand for the instruction. Generally used for data
+// processing instructions.
+void Decoder::PrintShiftImm(Instr* instr) {
+  int rotate = instr->RotateField() * 2;
+  int immed8 = instr->Immed8Field();
+  int imm = (immed8 >> rotate) | (immed8 << (32 - rotate));
+  out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+                                       "#%d", imm);
+}
+
+void Decoder::PrintShiftImm(const InstrThumb2& instr) {
+  out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+                                       "#%d", instr.Imm());
+}
+
+
+// Print PU formatting to reduce complexity of FormatOption.
+void Decoder::PrintPU(Instr* instr) {
+  switch (instr->PUField()) {
+    case 0: {
+      Print("da");
+      break;
+    }
+    case 1: {
+      Print("ia");
+      break;
+    }
+    case 2: {
+      Print("db");
+      break;
+    }
+    case 3: {
+      Print("ib");
+      break;
+    }
+    default: {
+      UNREACHABLE();
+      break;
+    }
+  }
+}
+
+
+// Print SoftwareInterrupt codes. Factoring this out reduces the complexity of
+// the FormatOption method.
+void Decoder::PrintSoftwareInterrupt(SoftwareInterruptCodes swi) {
+  switch (swi) {
+    case call_rt_redirected:
+      Print("call_rt_redirected");
+      return;
+    case break_point:
+      Print("break_point");
+      return;
+    default:
+      out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+                                           "%d",
+                                           swi);
+      return;
+  }
+}
+
+
+// Handle all register based formatting in this function to reduce the
+// complexity of FormatOption.
+int Decoder::FormatRegister(Instr* instr, const char* format) {
+  ASSERT(format[0] == 'r');
+  if (format[1] == 'n') {  // 'rn: Rn register
+    int reg = instr->RnField();
+    PrintRegister(reg);
+    return 2;
+  } else if (format[1] == 'd') {  // 'rd: Rd register
+    int reg = instr->RdField();
+    PrintRegister(reg);
+    return 2;
+  } else if (format[1] == 's') {  // 'rs: Rs register
+    int reg = instr->RsField();
+    PrintRegister(reg);
+    return 2;
+  } else if (format[1] == 'm') {  // 'rm: Rm register
+    int reg = instr->RmField();
+    PrintRegister(reg);
+    return 2;
+  } else if (format[1] == 't') {  // 'rt: Rt register
+    int reg = instr->RtField();
+    PrintRegister(reg);
+    return 2;
+  } else if (format[1] == 'l') {
+    // 'rlist: register list for load and store multiple instructions
+    ASSERT(STRING_STARTS_WITH(format, "rlist"));
+    int rlist = instr->RlistField();
+    int reg = 0;
+    Print("{");
+    // Print register list in ascending order, by scanning the bit mask.
+    while (rlist != 0) {
+      if ((rlist & 1) != 0) {
+        PrintRegister(reg);
+        if ((rlist >> 1) != 0) {
+          Print(", ");
+        }
+      }
+      reg++;
+      rlist >>= 1;
+    }
+    Print("}");
+    return 5;
+  }
+  UNREACHABLE();
+  return -1;
+}
+
+int Decoder::FormatRegister(const InstrThumb2& instr, const char* format) {
+  ASSERT(format[0] == 'r');
+  if (format[1] == 'n') {  // 'rn: Rn register
+    int reg = instr.Rn();
+    PrintRegister(reg);
+    return 2;
+  } else if (format[1] == 'd') {  // 'rd: Rd register
+    int reg = instr.Rd();
+    PrintRegister(reg);
+    return 2;
+  } else if (format[1] == 's') {  // 'rs: Rs register
+    int reg = instr.Rs();
+    PrintRegister(reg);
+    return 2;
+  } else if (format[1] == 'm') {  // 'rm: Rm register
+    int reg = instr.Rm();
+    PrintRegister(reg);
+    return 2;
+  } else if (format[1] == 't') {  // 'rt: Rt register
+    int reg = instr.Rt();
+    PrintRegister(reg);
+    return 2;
+  } else if (format[1] == 'l') {
+    // 'rlist: register list for load and store multiple instructions
+    ASSERT(STRING_STARTS_WITH(format, "rlist"));
+    UNIMPLEMENTED();
+//    int rlist = instr->RlistField();
+//    int reg = 0;
+//    Print("{");
+//    // Print register list in ascending order, by scanning the bit mask.
+//    while (rlist != 0) {
+//      if ((rlist & 1) != 0) {
+//        PrintRegister(reg);
+//        if ((rlist >> 1) != 0) {
+//          Print(", ");
+//        }
+//      }
+//      reg++;
+//      rlist >>= 1;
+//    }
+//    Print("}");
+    return 5;
+  }
+  UNREACHABLE();
+  return -1;
+}
+
+
+// Handle all VFP register based formatting in this function to reduce the
+// complexity of FormatOption.
+int Decoder::FormatVFPRegister(Instr* instr, const char* format) {
+  ASSERT((format[0] == 'S') || (format[0] == 'D'));
+
+  if (format[1] == 'n') {
+    int reg = instr->VnField();
+    if (format[0] == 'S') PrintSRegister(((reg << 1) | instr->NField()));
+    if (format[0] == 'D') PrintDRegister(reg);
+    return 2;
+  } else if (format[1] == 'm') {
+    int reg = instr->VmField();
+    if (format[0] == 'S') PrintSRegister(((reg << 1) | instr->MField()));
+    if (format[0] == 'D') PrintDRegister(reg);
+    return 2;
+  } else if (format[1] == 'd') {
+    int reg = instr->VdField();
+    if (format[0] == 'S') PrintSRegister(((reg << 1) | instr->DField()));
+    if (format[0] == 'D') PrintDRegister(reg);
+    return 2;
+  }
+
+  UNREACHABLE();
+  return -1;
+}
+
+
+int Decoder::FormatVFPinstruction(Instr* instr, const char* format) {
+    Print(format);
+    return 0;
+}
+
+
+// FormatOption takes a formatting string and interprets it based on
+// the current instructions. The format string points to the first
+// character of the option string (the option escape has already been
+// consumed by the caller.)  FormatOption returns the number of
+// characters that were consumed from the formatting string.
+int Decoder::FormatOption(Instr* instr, const char* format) {
+  switch (format[0]) {
+    case 'a': {  // 'a: accumulate multiplies
+      if (instr->Bit(21) == 0) {
+        Print("ul");
+      } else {
+        Print("la");
+      }
+      return 1;
+    }
+    case 'b': {  // 'b: byte loads or stores
+      if (instr->HasB()) {
+        Print("b");
+      }
+      return 1;
+    }
+    case 'c': {  // 'cond: conditional execution
+      ASSERT(STRING_STARTS_WITH(format, "cond"));
+      PrintCondition(instr);
+      return 4;
+    }
+    case 'h': {  // 'h: halfword operation for extra loads and stores
+      if (instr->HasH()) {
+        Print("h");
+      } else {
+        Print("b");
+      }
+      return 1;
+    }
+    case 'l': {  // 'l: branch and link
+      if (instr->HasLink()) {
+        Print("l");
+      }
+      return 1;
+    }
+    case 'm': {
+      if (format[1] == 'e') {  // 'memop: load/store instructions
+        ASSERT(STRING_STARTS_WITH(format, "memop"));
+        if (instr->HasL()) {
+          Print("ldr");
+        } else {
+          Print("str");
+        }
+        return 5;
+      }
+      // 'msg: for simulator break instructions
+      ASSERT(STRING_STARTS_WITH(format, "msg"));
+      byte* str =
+          reinterpret_cast<byte*>(instr->InstructionBits() & 0x0fffffff);
+      out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+                                           "%s", converter_.NameInCode(str));
+      return 3;
+    }
+    case 'o': {
+      if ((format[3] == '1') && (format[4] == '2')) {
+        // 'off12: 12-bit offset for load and store instructions
+        ASSERT(STRING_STARTS_WITH(format, "off12"));
+        out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+                                             "%d", instr->Offset12Field());
+        return 5;
+      } else if ((format[3] == '1') && (format[4] == '6')) {
+        ASSERT(STRING_STARTS_WITH(format, "off16to20"));
+        out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+                                           "%d", instr->Bits(20, 16) +1);
+        return 9;
+      } else if (format[3] == '7') {
+        ASSERT(STRING_STARTS_WITH(format, "off7to11"));
+        out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+                                            "%d", instr->ShiftAmountField());
+        return 8;
+      }
+      // 'off8: 8-bit offset for extra load and store instructions
+      ASSERT(STRING_STARTS_WITH(format, "off8"));
+      int offs8 = (instr->ImmedHField() << 4) | instr->ImmedLField();
+      out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+                                           "%d", offs8);
+      return 4;
+    }
+    case 'p': {  // 'pu: P and U bits for load and store instructions
+      ASSERT(STRING_STARTS_WITH(format, "pu"));
+      PrintPU(instr);
+      return 2;
+    }
+    case 'r': {
+      return FormatRegister(instr, format);
+    }
+    case 's': {
+      if (format[1] == 'h') {  // 'shift_op or 'shift_rm
+        if (format[6] == 'o') {  // 'shift_op
+          ASSERT(STRING_STARTS_WITH(format, "shift_op"));
+          if (instr->TypeField() == 0) {
+            PrintShiftRm(instr);
+          } else {
+            ASSERT(instr->TypeField() == 1);
+            PrintShiftImm(instr);
+          }
+          return 8;
+        } else {  // 'shift_rm
+          ASSERT(STRING_STARTS_WITH(format, "shift_rm"));
+          PrintShiftRm(instr);
+          return 8;
+        }
+      } else if (format[1] == 'w') {  // 'swi
+        ASSERT(STRING_STARTS_WITH(format, "swi"));
+        PrintSoftwareInterrupt(instr->SwiField());
+        return 3;
+      } else if (format[1] == 'i') {  // 'sign: signed extra loads and stores
+        ASSERT(STRING_STARTS_WITH(format, "sign"));
+        if (instr->HasSign()) {
+          Print("s");
+        }
+        return 4;
+      }
+      // 's: S field of data processing instructions
+      if (instr->HasS()) {
+        Print("s");
+      }
+      return 1;
+    }
+    case 't': {  // 'target: target of branch instructions
+      ASSERT(STRING_STARTS_WITH(format, "target"));
+      int off = (instr->SImmed24Field() << 2) + 8;
+      out_buffer_pos_ += v8i::OS::SNPrintF(
+          out_buffer_ + out_buffer_pos_,
+          "%+d -> %s",
+          off,
+          converter_.NameOfAddress(reinterpret_cast<byte*>(instr) + off));
+      return 6;
+    }
+    case 'u': {  // 'u: signed or unsigned multiplies
+      // The manual gets the meaning of bit 22 backwards in the multiply
+      // instruction overview on page A3.16.2.  The instructions that
+      // exist in u and s variants are the following:
+      // smull A4.1.87
+      // umull A4.1.129
+      // umlal A4.1.128
+      // smlal A4.1.76
+      // For these 0 means u and 1 means s.  As can be seen on their individual
+      // pages.  The other 18 mul instructions have the bit set or unset in
+      // arbitrary ways that are unrelated to the signedness of the instruction.
+      // None of these 18 instructions exist in both a 'u' and an 's' variant.
+
+      if (instr->Bit(22) == 0) {
+        Print("u");
+      } else {
+        Print("s");
+      }
+      return 1;
+    }
+    case 'v': {
+      return FormatVFPinstruction(instr, format);
+    }
+    case 'S':
+    case 'D': {
+      return FormatVFPRegister(instr, format);
+    }
+    case 'w': {  // 'w: W field of load and store instructions
+      if (instr->HasW()) {
+        Print("!");
+      }
+      return 1;
+    }
+    default: {
+      UNREACHABLE();
+      break;
+    }
+  }
+  UNREACHABLE();
+  return -1;
+}
+
+int Decoder::FormatOption(const InstrThumb2& instr, const char* format) {
+  switch (format[0]) {
+// TODO(haustein) Re-enable code below
+//    case 'a': {  // 'a: accumulate multiplies
+//      if (instr->Bit(21) == 0) {
+//        Print("ul");
+//      } else {
+//        Print("la");
+//      }
+//      return 1;
+//    }
+//    case 'b': {  // 'b: byte loads or stores
+//      if (instr->HasB()) {
+//        Print("b");
+//      }
+//      return 1;
+//    }
+//    case 'c': {  // 'cond: conditional execution
+//      ASSERT(STRING_STARTS_WITH(format, "cond"));
+//      PrintCondition(instr);
+//      return 4;
+//    }
+//    case 'h': {  // 'h: halfword operation for extra loads and stores
+//      if (instr->HasH()) {
+//        Print("h");
+//      } else {
+//        Print("b");
+//      }
+//      return 1;
+//    }
+//    case 'l': {  // 'l: branch and link
+//      if (instr->HasLink()) {
+//       Print("l");
+//      }
+//      return 1;
+//    }
+//    case 'm': {
+//      if (format[1] == 'e') {  // 'memop: load/store instructions
+//        ASSERT(STRING_STARTS_WITH(format, "memop"));
+//       if (instr->HasL()) {
+//          Print("ldr");
+//        } else {
+//          Print("str");
+//        }
+//        return 5;
+//      }
+//      // 'msg: for simulator break instructions
+//      ASSERT(STRING_STARTS_WITH(format, "msg"));
+//      byte* str =
+//          reinterpret_cast<byte*>(instr->InstructionBits() & 0x0fffffff);
+//      out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+//                                           "%s", converter_.NameInCode(str));
+//      return 3;
+//    }
+//    case 'o': {
+//      if ((format[3] == '1') && (format[4] == '2')) {
+//        // 'off12: 12-bit offset for load and store instructions
+//        ASSERT(STRING_STARTS_WITH(format, "off12"));
+//        out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+//                                             "%d", instr->Offset12Field());
+//        return 5;
+//      } else if ((format[3] == '1') && (format[4] == '6')) {
+//        ASSERT(STRING_STARTS_WITH(format, "off16to20"));
+//        out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+//                                           "%d", instr->Bits(20, 16) +1);
+//        return 9;
+//      } else if (format[3] == '7') {
+//        ASSERT(STRING_STARTS_WITH(format, "off7to11"));
+//        out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+//                                            "%d", instr->ShiftAmountField());
+//        return 8;
+//      }
+//      // 'off8: 8-bit offset for extra load and store instructions
+//      ASSERT(STRING_STARTS_WITH(format, "off8"));
+//      int offs8 = (instr->ImmedHField() << 4) | instr->ImmedLField();
+//      out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+//                                           "%d", offs8);
+//      return 4;
+//    }
+//    case 'p': {  // 'pu: P and U bits for load and store instructions
+//      ASSERT(STRING_STARTS_WITH(format, "pu"));
+//      PrintPU(instr);
+//      return 2;
+//    }
+    case 'r': {
+      return FormatRegister(instr, format);
+    }
+    case 's': {
+      if (format[1] == 'h') {  // 'shift_op or 'shift_rm
+        if (format[6] == 'o') {  // 'shift_op
+          ASSERT(STRING_STARTS_WITH(format, "shift_op"));
+          if (instr.Type() == 0) {
+            PrintShiftRm(instr);
+          } else {
+            ASSERT(instr.Type() == 1);
+            PrintShiftImm(instr);
+          }
+          return 8;
+        } else {  // 'shift_rm
+          ASSERT(STRING_STARTS_WITH(format, "shift_rm"));
+          PrintShiftRm(instr);
+          return 8;
+        }
+// TODO(haustein) Re-enable code below
+//    } else if (format[1] == 'w') {  // 'swi
+//      ASSERT(STRING_STARTS_WITH(format, "swi"));
+//      PrintSoftwareInterrupt(instr->SwiField());
+//      return 3;
+//    } else if (format[1] == 'i') {  // 'sign: signed extra loads and stores
+//      ASSERT(STRING_STARTS_WITH(format, "sign"));
+//      if (instr->HasSign()) {
+//        Print("s");
+//      return 4;
+      }
+      // 's: S field of data processing instructions
+      if (instr.HasS()) {
+        Print("s");
+      }
+      return 1;
+    }
+// TODO(haustein) Re-enable code for 't', 'u', 'v', 'S', 'D', 'w' below.
+//  case 't': {  // 'target: target of branch instructions
+//    ASSERT(STRING_STARTS_WITH(format, "target"));
+//    int off = (instr->SImmed24Field() << 2) + 8;
+//    out_buffer_pos_ += v8i::OS::SNPrintF(
+//        out_buffer_ + out_buffer_pos_,
+//        "%+d -> %s",
+//        off,
+//        converter_.NameOfAddress(reinterpret_cast<byte*>(instr) + off));
+//    return 6;
+//  }
+//  case 'u': {  // 'u: signed or unsigned multiplies
+//    // The manual gets the meaning of bit 22 backwards in the multiply
+//    // instruction overview on page A3.16.2.  The instructions that
+//    // exist in u and s variants are the following:
+//    // smull A4.1.87
+//    // umull A4.1.129
+//    // umlal A4.1.128
+//    // smlal A4.1.76
+//    // For these 0 means u and 1 means s.  As can be seen on their individual
+//    // pages.  The other 18 mul instructions have the bit set or unset in
+//    // arbitrary ways that are unrelated to the signedness of the instruction.
+//    // None of these 18 instructions exist in both a 'u' and an 's' variant.
+//
+//    if (instr->Bit(22) == 0) {
+//      Print("u");
+//    } else {
+//      Print("s");
+//    }
+//    return 1;
+//  }
+//  case 'v': {
+//    return FormatVFPinstruction(instr, format);
+//  }
+//  case 'S':
+//  case 'D': {
+//    return FormatVFPRegister(instr, format);
+//  }
+//  case 'w': {  // 'w: W field of load and store instructions
+//    if (instr->HasW()) {
+//      Print("!");
+//    }
+//    return 1;
+//  }
+    default: {
+      UNIMPLEMENTED();
+      break;
+    }
+  }
+  UNREACHABLE();
+  return -1;
+}
+
+
+// Format takes a formatting string for a whole instruction and prints it into
+// the output buffer. All escaped options are handed to FormatOption to be
+// parsed further.
+void Decoder::Format(Instr* instr, const char* format) {
+  char cur = *format++;
+  while ((cur != 0) && (out_buffer_pos_ < (out_buffer_.length() - 1))) {
+    if (cur == '\'') {  // Single quote is used as the formatting escape.
+      format += FormatOption(instr, format);
+    } else {
+      out_buffer_[out_buffer_pos_++] = cur;
+    }
+    cur = *format++;
+  }
+  out_buffer_[out_buffer_pos_]  = '\0';
+}
+
+
+void Decoder::Format(const InstrThumb2& instr, const char* format) {
+  char cur = *format++;
+  while ((cur != 0) && (out_buffer_pos_ < (out_buffer_.length() - 1))) {
+    if (cur == '\'') {  // Single quote is used as the formatting escape.
+      format += FormatOption(instr, format);
+    } else {
+      out_buffer_[out_buffer_pos_++] = cur;
+    }
+    cur = *format++;
+  }
+  out_buffer_[out_buffer_pos_]  = '\0';
+}
+
+
+
+// For currently unimplemented decodings the disassembler calls Unknown(instr)
+// which will just print "unknown" of the instruction bits.
+void Decoder::Unknown(Instr* instr) {
+  Format(instr, "unknown");
+}
+
+
+void Decoder::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) {
+        // multiply instructions
+        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");
+          } 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 field
+          // RdHi == Rn field
+          // The order of registers is: <RdLo>, <RdHi>, <Rm>, <Rs>
+          Format(instr, "'um'al'cond's 'rd, 'rn, 'rm, 'rs");
+        }
+      } else {
+        Unknown(instr);  // not used by V8
+      }
+    } else {
+      // extra load/store instructions
+      switch (instr->PUField()) {
+        case 0: {
+          if (instr->Bit(22) == 0) {
+            Format(instr, "'memop'cond'sign'h 'rd, ['rn], -'rm");
+          } else {
+            Format(instr, "'memop'cond'sign'h 'rd, ['rn], #-'off8");
+          }
+          break;
+        }
+        case 1: {
+          if (instr->Bit(22) == 0) {
+            Format(instr, "'memop'cond'sign'h 'rd, ['rn], +'rm");
+          } else {
+            Format(instr, "'memop'cond'sign'h 'rd, ['rn], #+'off8");
+          }
+          break;
+        }
+        case 2: {
+          if (instr->Bit(22) == 0) {
+            Format(instr, "'memop'cond'sign'h 'rd, ['rn, -'rm]'w");
+          } else {
+            Format(instr, "'memop'cond'sign'h 'rd, ['rn, #-'off8]'w");
+          }
+          break;
+        }
+        case 3: {
+          if (instr->Bit(22) == 0) {
+            Format(instr, "'memop'cond'sign'h 'rd, ['rn, +'rm]'w");
+          } else {
+            Format(instr, "'memop'cond'sign'h 'rd, ['rn, #+'off8]'w");
+          }
+          break;
+        }
+        default: {
+          // The PU field is a 2-bit field.
+          UNREACHABLE();
+          break;
+        }
+      }
+      return;
+    }
+  } else {
+    switch (instr->OpcodeField()) {
+      case AND: {
+        Format(instr, "and'cond's 'rd, 'rn, 'shift_op");
+        break;
+      }
+      case EOR: {
+        Format(instr, "eor'cond's 'rd, 'rn, 'shift_op");
+        break;
+      }
+      case SUB: {
+        Format(instr, "sub'cond's 'rd, 'rn, 'shift_op");
+        break;
+      }
+      case RSB: {
+        Format(instr, "rsb'cond's 'rd, 'rn, 'shift_op");
+        break;
+      }
+      case ADD: {
+        Format(instr, "add'cond's 'rd, 'rn, 'shift_op");
+        break;
+      }
+      case ADC: {
+        Format(instr, "adc'cond's 'rd, 'rn, 'shift_op");
+        break;
+      }
+      case SBC: {
+        Format(instr, "sbc'cond's 'rd, 'rn, 'shift_op");
+        break;
+      }
+      case RSC: {
+        Format(instr, "rsc'cond's 'rd, 'rn, 'shift_op");
+        break;
+      }
+      case TST: {
+        if (instr->HasS()) {
+          Format(instr, "tst'cond 'rn, 'shift_op");
+        } else {
+          Unknown(instr);  // not used by V8
+        }
+        break;
+      }
+      case TEQ: {
+        if (instr->HasS()) {
+          Format(instr, "teq'cond 'rn, 'shift_op");
+        } else {
+          switch (instr->Bits(7, 4)) {
+            case BX:
+              Format(instr, "bx'cond 'rm");
+              break;
+            case BLX:
+              Format(instr, "blx'cond 'rm");
+              break;
+            default:
+              Unknown(instr);  // not used by V8
+              break;
+          }
+        }
+        break;
+      }
+      case CMP: {
+        if (instr->HasS()) {
+          Format(instr, "cmp'cond 'rn, 'shift_op");
+        } else {
+          Unknown(instr);  // not used by V8
+        }
+        break;
+      }
+      case CMN: {
+        if (instr->HasS()) {
+          Format(instr, "cmn'cond 'rn, 'shift_op");
+        } else {
+          switch (instr->Bits(7, 4)) {
+            case CLZ:
+              Format(instr, "clz'cond 'rd, 'rm");
+              break;
+            default:
+              Unknown(instr);  // not used by V8
+              break;
+          }
+        }
+        break;
+      }
+      case ORR: {
+        Format(instr, "orr'cond's 'rd, 'rn, 'shift_op");
+        break;
+      }
+      case MOV: {
+        Format(instr, "mov'cond's 'rd, 'shift_op");
+        break;
+      }
+      case BIC: {
+        Format(instr, "bic'cond's 'rd, 'rn, 'shift_op");
+        break;
+      }
+      case MVN: {
+        Format(instr, "mvn'cond's 'rd, 'shift_op");
+        break;
+      }
+      default: {
+        // The Opcode field is a 4-bit field.
+        UNREACHABLE();
+        break;
+      }
+    }
+  }
+}
+
+
+void Decoder::DecodeType2(Instr* instr) {
+  switch (instr->PUField()) {
+    case 0: {
+      if (instr->HasW()) {
+        Unknown(instr);  // not used in V8
+      }
+      Format(instr, "'memop'cond'b 'rd, ['rn], #-'off12");
+      break;
+    }
+    case 1: {
+      if (instr->HasW()) {
+        Unknown(instr);  // not used in V8
+      }
+      Format(instr, "'memop'cond'b 'rd, ['rn], #+'off12");
+      break;
+    }
+    case 2: {
+      Format(instr, "'memop'cond'b 'rd, ['rn, #-'off12]'w");
+      break;
+    }
+    case 3: {
+      Format(instr, "'memop'cond'b 'rd, ['rn, #+'off12]'w");
+      break;
+    }
+    default: {
+      // The PU field is a 2-bit field.
+      UNREACHABLE();
+      break;
+    }
+  }
+}
+
+
+void Decoder::DecodeType3(Instr* instr) {
+  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");
+      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) {
+          Format(instr, "ubfx'cond 'rd, 'rm, #'off7to11, #'off16to20");
+        } else {
+          UNREACHABLE();
+        }
+      } else {
+        Format(instr, "'memop'cond'b 'rd, ['rn, +'shift_rm]'w");
+      }
+      break;
+    }
+    default: {
+      // The PU field is a 2-bit field.
+      UNREACHABLE();
+      break;
+    }
+  }
+}
+
+
+void Decoder::DecodeType4(Instr* instr) {
+  ASSERT(instr->Bit(22) == 0);  // Privileged mode currently not supported.
+  if (instr->HasL()) {
+    Format(instr, "ldm'cond'pu 'rn'w, 'rlist");
+  } else {
+    Format(instr, "stm'cond'pu 'rn'w, 'rlist");
+  }
+}
+
+
+void Decoder::DecodeType5(Instr* instr) {
+  Format(instr, "b'l'cond 'target");
+}
+
+
+void Decoder::DecodeType6(Instr* instr) {
+  DecodeType6CoprocessorIns(instr);
+}
+
+
+void Decoder::DecodeType7(Instr* instr) {
+  if (instr->Bit(24) == 1) {
+    Format(instr, "swi'cond 'swi");
+  } else {
+    DecodeTypeVFP(instr);
+  }
+}
+
+void Decoder::DecodeUnconditional(Instr* instr) {
+  if (instr->Bits(7, 4) == 0xB && instr->Bits(27, 25) == 0 && instr->HasL()) {
+    Format(instr, "'memop'h'pu 'rd, ");
+    bool immediate = instr->HasB();
+    switch (instr->PUField()) {
+      case 0: {
+        // Post index, negative.
+        if (instr->HasW()) {
+          Unknown(instr);
+          break;
+        }
+        if (immediate) {
+          Format(instr, "['rn], #-'imm12");
+        } else {
+          Format(instr, "['rn], -'rm");
+        }
+        break;
+      }
+      case 1: {
+        // Post index, positive.
+        if (instr->HasW()) {
+          Unknown(instr);
+          break;
+        }
+        if (immediate) {
+          Format(instr, "['rn], #+'imm12");
+        } else {
+          Format(instr, "['rn], +'rm");
+        }
+        break;
+      }
+      case 2: {
+        // Pre index or offset, negative.
+        if (immediate) {
+          Format(instr, "['rn, #-'imm12]'w");
+        } else {
+          Format(instr, "['rn, -'rm]'w");
+        }
+        break;
+      }
+      case 3: {
+        // Pre index or offset, positive.
+        if (immediate) {
+          Format(instr, "['rn, #+'imm12]'w");
+        } else {
+          Format(instr, "['rn, +'rm]'w");
+        }
+        break;
+      }
+      default: {
+        // The PU field is a 2-bit field.
+        UNREACHABLE();
+        break;
+      }
+    }
+    return;
+  }
+  Format(instr, "break 'msg");
+}
+
+
+// void Decoder::DecodeTypeVFP(Instr* instr)
+// 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 Decoder::DecodeTypeVFP(Instr* instr) {
+  ASSERT((instr->TypeField() == 7) && (instr->Bit(24) == 0x0) );
+
+  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)) {
+      Format(instr, "vcvt.s32.f64'cond 'Sd, 'Dm");
+    } 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)) {
+      Format(instr, "vcvt.f64.s32'cond 'Dd, 'Sm");
+    } 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)) {
+        Format(instr, "vdiv.f64'cond 'Dd, 'Dn, 'Dm");
+    } 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)) {
+      Format(instr, "vcmp.f64'cond 'Dd, 'Dm");
+    } 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)
+          Format(instr, "vmrs'cond APSR, FPSCR");
+        else
+          Unknown(instr);  // Not used by V8.
+    } else {
+      Unknown(instr);  // 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)) {
+      Format(instr, "vadd.f64'cond 'Dd, 'Dn, 'Dm");
+    } else if ((instr->Bit(20) == 0x1) &&
+               (instr->Bits(11, 9) == 0x5) &&
+               (instr->Bit(8) == 0x1) &&
+               (instr->Bit(6) == 1) &&
+               (instr->Bit(4) == 0)) {
+      Format(instr, "vsub.f64'cond 'Dd, 'Dn, 'Dm");
+    } else if ((instr->Bit(20) == 0x0) &&
+               (instr->Bits(11, 9) == 0x5) &&
+               (instr->Bit(8) == 0x1) &&
+               (instr->Bit(6) == 0) &&
+               (instr->Bit(4) == 0)) {
+      Format(instr, "vmul.f64'cond 'Dd, 'Dn, 'Dm");
+    } else {
+      Unknown(instr);  // 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)) {
+      Format(instr, "vmov'cond 'Sn, 'rt");
+    } 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)) {
+      Format(instr, "vmov'cond 'rt, 'Sn");
+    } else {
+      Unknown(instr);  // Not used by V8.
+    }
+  }
+}
+
+
+// Decode Type 6 coprocessor instructions.
+// Dm = vmov(Rt, Rt2)
+// <Rt, Rt2> = vmov(Dm)
+// Ddst = MEM(Rbase + 4*offset).
+// MEM(Rbase + 4*offset) = Dsrc.
+void Decoder::DecodeType6CoprocessorIns(Instr* instr) {
+  ASSERT((instr->TypeField() == 6));
+
+  if (instr->CoprocessorField() != 0xB) {
+    Unknown(instr);  // Not used by V8.
+  } else {
+    switch (instr->OpcodeField()) {
+      case 0x2:
+        // Load and store double to two GP registers
+        if (instr->Bits(7, 4) != 0x1) {
+          Unknown(instr);  // Not used by V8.
+        } else if (instr->HasL()) {
+          Format(instr, "vmov'cond 'rt, 'rn, 'Dm");
+        } else {
+          Format(instr, "vmov'cond 'Dm, 'rt, 'rn");
+        }
+        break;
+      case 0x8:
+        if (instr->HasL()) {
+          Format(instr, "vldr'cond 'Dd, ['rn - 4*'off8]");
+        } else {
+          Format(instr, "vstr'cond 'Dd, ['rn - 4*'off8]");
+        }
+        break;
+      case 0xC:
+        if (instr->HasL()) {
+          Format(instr, "vldr'cond 'Dd, ['rn + 4*'off8]");
+        } else {
+          Format(instr, "vstr'cond 'Dd, ['rn + 4*'off8]");
+        }
+        break;
+      default:
+        Unknown(instr);  // Not used by V8.
+        break;
+    }
+  }
+}
+
+
+// Disassemble the instruction at *instr_ptr into the output buffer.
+int Decoder::InstructionDecode(byte* instr_ptr) {
+  if (reinterpret_cast<int32_t>(instr_ptr) & 1) {
+    InstrThumb2 instr(instr_ptr);
+    return InstructionDecodeThumb2(instr);
+  } else {
+    return InstructionDecodeArm(instr_ptr);
+  }
+}
+
+int Decoder::InstructionDecodeArm(byte* instr_ptr) {
+  Instr* instr = Instr::At(instr_ptr);
+  // Print raw instruction bytes.
+  out_buffer_pos_ += v8i::OS::SNPrintF(out_buffer_ + out_buffer_pos_,
+                                       "%08x       ",
+                                       instr->InstructionBits());
+  if (instr->ConditionField() == special_condition) {
+    DecodeUnconditional(instr);
+    return Instr::kInstrSize;
+  }
+  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: {
+      // The type field is 3-bits in the ARM encoding.
+      UNREACHABLE();
+      break;
+    }
+  }
+  return Instr::kInstrSize;
+}
+
+
+int Decoder::InstructionDecodeThumb2(const InstrThumb2& instr) {
+  switch (instr.Op()) {
+    case OP_ADD:
+      Format(instr, "and's 'rd, 'rn, 'shift_op");
+      break;
+    case OP_AND:
+      Format(instr, "and's 'rd, 'rn, 'shift_op");
+      break;
+    case OP_SUB:
+      Format(instr, "sub's 'rd, 'rn, 'shift_op");
+      break;
+    default:
+      UNIMPLEMENTED();
+      break;
+  }
+  return instr.Size();
+}
+
+
+} }  // namespace assembler::arm
+
+
+
+//------------------------------------------------------------------------------
+
+namespace disasm {
+
+namespace v8i = v8::internal;
+
+
+const char* NameConverter::NameOfAddress(byte* addr) const {
+  static v8::internal::EmbeddedVector<char, 32> tmp_buffer;
+  v8::internal::OS::SNPrintF(tmp_buffer, "%p", addr);
+  return tmp_buffer.start();
+}
+
+
+const char* NameConverter::NameOfConstant(byte* addr) const {
+  return NameOfAddress(addr);
+}
+
+
+const char* NameConverter::NameOfCPURegister(int reg) const {
+  return assembler::arm::Registers::Name(reg);
+}
+
+
+const char* NameConverter::NameOfByteCPURegister(int reg) const {
+  UNREACHABLE();  // ARM does not have the concept of a byte register
+  return "nobytereg";
+}
+
+
+const char* NameConverter::NameOfXMMRegister(int reg) const {
+  UNREACHABLE();  // ARM does not have any XMM registers
+  return "noxmmreg";
+}
+
+
+const char* NameConverter::NameInCode(byte* addr) const {
+  // The default name converter is called for unknown code. So we will not try
+  // to access any memory.
+  return "";
+}
+
+
+//------------------------------------------------------------------------------
+
+Disassembler::Disassembler(const NameConverter& converter)
+    : converter_(converter) {}
+
+
+Disassembler::~Disassembler() {}
+
+
+int Disassembler::InstructionDecode(v8::internal::Vector<char> buffer,
+                                    byte* instruction) {
+  assembler::arm::Decoder d(converter_, buffer);
+  return d.InstructionDecode(instruction);
+}
+
+
+int Disassembler::ConstantPoolSizeAt(byte* instruction) {
+  int instruction_bits = *(reinterpret_cast<int*>(instruction));
+  if ((instruction_bits & 0xfff00000) == 0x03000000) {
+    return instruction_bits & 0x0000ffff;
+  } else {
+    return -1;
+  }
+}
+
+
+void Disassembler::Disassemble(FILE* f, byte* begin, byte* end) {
+  NameConverter converter;
+  Disassembler d(converter);
+  for (byte* pc = begin; pc < end;) {
+    v8::internal::EmbeddedVector<char, 128> buffer;
+    buffer[0] = '\0';
+    byte* prev_pc = pc;
+    pc += d.InstructionDecode(buffer, pc);
+    fprintf(f, "%p    %08x      %s\n",
+            prev_pc, *reinterpret_cast<int32_t*>(prev_pc), buffer.start());
+  }
+}
+
+
+}  // namespace disasm