disassembler/disassembler_x86.cc

/*
 * Copyright (C) 2012 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "disassembler_x86.h"

#include <inttypes.h>

#include <ostream>
#include <sstream>

#include "base/logging.h"
#include "base/stringprintf.h"
#include "thread.h"

namespace art {
namespace x86 {

size_t DisassemblerX86::Dump(std::ostream& os, const uint8_t* begin) {
  return DumpInstruction(os, begin);
}

void DisassemblerX86::Dump(std::ostream& os, const uint8_t* begin, const uint8_t* end) {
  size_t length = 0;
  for (const uint8_t* cur = begin; cur < end; cur += length) {
    length = DumpInstruction(os, cur);
  }
}

static const char* gReg8Names[]  = {
  "al", "cl", "dl", "bl", "ah", "ch", "dh", "bh"
};
static const char* gExtReg8Names[] = {
  "al", "cl", "dl", "bl", "spl", "bpl", "sil", "dil",
  "r8l", "r9l", "r10l", "r11l", "r12l", "r13l", "r14l", "r15l"
};
static const char* gReg16Names[] = {
  "ax", "cx", "dx", "bx", "sp", "bp", "si", "di",
  "r8w", "r9w", "r10w", "r11w", "r12w", "r13w", "r14w", "r15w"
};
static const char* gReg32Names[] = {
  "eax", "ecx", "edx", "ebx", "esp", "ebp", "esi", "edi",
  "r8d", "r9d", "r10d", "r11d", "r12d", "r13d", "r14d", "r15d"
};
static const char* gReg64Names[] = {
  "rax", "rcx", "rdx", "rbx", "rsp", "rbp", "rsi", "rdi",
  "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15"
};

// 64-bit opcode REX modifier.
constexpr uint8_t REX_W = 8U /* 0b1000 */;
constexpr uint8_t REX_R = 4U /* 0b0100 */;
constexpr uint8_t REX_X = 2U /* 0b0010 */;
constexpr uint8_t REX_B = 1U /* 0b0001 */;

static void DumpReg0(std::ostream& os, uint8_t rex, size_t reg,
                     bool byte_operand, uint8_t size_override) {
  DCHECK_LT(reg, (rex == 0) ? 8u : 16u);
  bool rex_w = (rex & REX_W) != 0;
  if (byte_operand) {
    os << ((rex == 0) ? gReg8Names[reg] : gExtReg8Names[reg]);
  } else if (rex_w) {
    os << gReg64Names[reg];
  } else if (size_override == 0x66) {
    os << gReg16Names[reg];
  } else {
    os << gReg32Names[reg];
  }
}

static void DumpAnyReg(std::ostream& os, uint8_t rex, size_t reg,
                       bool byte_operand, uint8_t size_override, RegFile reg_file) {
  if (reg_file == GPR) {
    DumpReg0(os, rex, reg, byte_operand, size_override);
  } else if (reg_file == SSE) {
    os << "xmm" << reg;
  } else {
    os << "mm" << reg;
  }
}

static void DumpReg(std::ostream& os, uint8_t rex, uint8_t reg,
                    bool byte_operand, uint8_t size_override, RegFile reg_file) {
  bool rex_r = (rex & REX_R) != 0;
  size_t reg_num = rex_r ? (reg + 8) : reg;
  DumpAnyReg(os, rex, reg_num, byte_operand, size_override, reg_file);
}

static void DumpRmReg(std::ostream& os, uint8_t rex, uint8_t reg,
                      bool byte_operand, uint8_t size_override, RegFile reg_file) {
  bool rex_b = (rex & REX_B) != 0;
  size_t reg_num = rex_b ? (reg + 8) : reg;
  DumpAnyReg(os, rex, reg_num, byte_operand, size_override, reg_file);
}

static void DumpAddrReg(std::ostream& os, uint8_t rex, uint8_t reg) {
  if (rex != 0) {
    os << gReg64Names[reg];
  } else {
    os << gReg32Names[reg];
  }
}

static void DumpBaseReg(std::ostream& os, uint8_t rex, uint8_t reg) {
  bool rex_b = (rex & REX_B) != 0;
  size_t reg_num = rex_b ? (reg + 8) : reg;
  DumpAddrReg(os, rex, reg_num);
}

static void DumpOpcodeReg(std::ostream& os, uint8_t rex, uint8_t reg,
                          bool byte_operand, uint8_t size_override) {
  bool rex_b = (rex & REX_B) != 0;
  size_t reg_num = rex_b ? (reg + 8) : reg;
  DumpReg0(os, rex, reg_num, byte_operand, size_override);
}

enum SegmentPrefix {
  kCs = 0x2e,
  kSs = 0x36,
  kDs = 0x3e,
  kEs = 0x26,
  kFs = 0x64,
  kGs = 0x65,
};

static void DumpSegmentOverride(std::ostream& os, uint8_t segment_prefix) {
  switch (segment_prefix) {
    case kCs: os << "cs:"; break;
    case kSs: os << "ss:"; break;
    case kDs: os << "ds:"; break;
    case kEs: os << "es:"; break;
    case kFs: os << "fs:"; break;
    case kGs: os << "gs:"; break;
    default: break;
  }
}

// Do not inline to avoid Clang stack frame problems. b/18733806
NO_INLINE
static std::string DumpCodeHex(const uint8_t* begin, const uint8_t* end) {
  std::stringstream hex;
  for (size_t i = 0; begin + i < end; ++i) {
    hex << StringPrintf("%02X", begin[i]);
  }
  return hex.str();
}

std::string DisassemblerX86::DumpAddress(uint8_t mod, uint8_t rm, uint8_t rex64, uint8_t rex_w,
                                         bool no_ops, bool byte_operand, bool byte_second_operand,
                                         uint8_t* prefix, bool load, RegFile src_reg_file,
                                         RegFile dst_reg_file, const uint8_t** instr,
                                         uint32_t* address_bits) {
  std::ostringstream address;
  if (mod == 0 && rm == 5) {
    if (!supports_rex_) {  // Absolute address.
      *address_bits = *reinterpret_cast<const uint32_t*>(*instr);
      address << StringPrintf("[0x%x]", *address_bits);
    } else {  // 64-bit RIP relative addressing.
      address << StringPrintf("[RIP + 0x%x]",  *reinterpret_cast<const uint32_t*>(*instr));
    }
    (*instr) += 4;
  } else if (rm == 4 && mod != 3) {  // SIB
    uint8_t sib = **instr;
    (*instr)++;
    uint8_t scale = (sib >> 6) & 3;
    uint8_t index = (sib >> 3) & 7;
    uint8_t base = sib & 7;
    address << "[";

    // REX.x is bit 3 of index.
    if ((rex64 & REX_X) != 0) {
      index += 8;
    }

    // Mod = 0 && base = 5 (ebp): no base (ignores REX.b).
    bool has_base = false;
    if (base != 5 || mod != 0) {
      has_base = true;
      DumpBaseReg(address, rex64, base);
    }

    // Index = 4 (esp/rsp) is disallowed.
    if (index != 4) {
      if (has_base) {
        address << " + ";
      }
      DumpAddrReg(address, rex64, index);
      if (scale != 0) {
        address << StringPrintf(" * %d", 1 << scale);
      }
    }

    if (mod == 0) {
      if (base == 5) {
        if (index != 4) {
          address << StringPrintf(" + %d", *reinterpret_cast<const int32_t*>(*instr));
        } else {
          // 64-bit low 32-bit absolute address, redundant absolute address encoding on 32-bit.
          *address_bits = *reinterpret_cast<const uint32_t*>(*instr);
          address << StringPrintf("%d", *address_bits);
        }
        (*instr) += 4;
      }
    } else if (mod == 1) {
      address << StringPrintf(" + %d", *reinterpret_cast<const int8_t*>(*instr));
      (*instr)++;
    } else if (mod == 2) {
      address << StringPrintf(" + %d", *reinterpret_cast<const int32_t*>(*instr));
      (*instr) += 4;
    }
    address << "]";
  } else {
    if (mod == 3) {
      if (!no_ops) {
        DumpRmReg(address, rex_w, rm, byte_operand || byte_second_operand,
                  prefix[2], load ? src_reg_file : dst_reg_file);
      }
    } else {
      address << "[";
      DumpBaseReg(address, rex64, rm);
      if (mod == 1) {
        address << StringPrintf(" + %d", *reinterpret_cast<const int8_t*>(*instr));
        (*instr)++;
      } else if (mod == 2) {
        address << StringPrintf(" + %d", *reinterpret_cast<const int32_t*>(*instr));
        (*instr) += 4;
      }
      address << "]";
    }
  }
  return address.str();
}

size_t DisassemblerX86::DumpInstruction(std::ostream& os, const uint8_t* instr) {
  const uint8_t* begin_instr = instr;
  bool have_prefixes = true;
  uint8_t prefix[4] = {0, 0, 0, 0};
  do {
    switch (*instr) {
        // Group 1 - lock and repeat prefixes:
      case 0xF0:
      case 0xF2:
      case 0xF3:
        prefix[0] = *instr;
        break;
        // Group 2 - segment override prefixes:
      case kCs:
      case kSs:
      case kDs:
      case kEs:
      case kFs:
      case kGs:
        prefix[1] = *instr;
        break;
        // Group 3 - operand size override:
      case 0x66:
        prefix[2] = *instr;
        break;
        // Group 4 - address size override:
      case 0x67:
        prefix[3] = *instr;
        break;
      default:
        have_prefixes = false;
        break;
    }
    if (have_prefixes) {
      instr++;
    }
  } while (have_prefixes);
  uint8_t rex = (supports_rex_ && (*instr >= 0x40) && (*instr <= 0x4F)) ? *instr : 0;
  if (rex != 0) {
    instr++;
  }
  const char** modrm_opcodes = nullptr;
  bool has_modrm = false;
  bool reg_is_opcode = false;
  size_t immediate_bytes = 0;
  size_t branch_bytes = 0;
  std::string opcode_tmp;    // Storage to keep StringPrintf result alive.
  const char* opcode0 = "";  // Prefix part.
  const char* opcode1 = "";  // Main opcode.
  const char* opcode2 = "";  // Sub-opcode. E.g., jump type.
  const char* opcode3 = "";  // Mod-rm part.
  const char* opcode4 = "";  // Suffix part.
  bool store = false;  // stores to memory (ie rm is on the left)
  bool load = false;  // loads from memory (ie rm is on the right)
  bool byte_operand = false;  // true when the opcode is dealing with byte operands
  // true when the source operand is a byte register but the target register isn't
  // (ie movsxb/movzxb).
  bool byte_second_operand = false;
  bool target_specific = false;  // register name depends on target (64 vs 32 bits).
  bool ax = false;  // implicit use of ax
  bool cx = false;  // implicit use of cx
  bool reg_in_opcode = false;  // low 3-bits of opcode encode register parameter
  bool no_ops = false;
  RegFile src_reg_file = GPR;
  RegFile dst_reg_file = GPR;
  switch (*instr) {
#define DISASSEMBLER_ENTRY(opname, \
                     rm8_r8, rm32_r32, \
                     r8_rm8, r32_rm32, \
                     ax8_i8, ax32_i32) \
  case rm8_r8:   opcode1 = #opname; store = true; has_modrm = true; byte_operand = true; break; \
  case rm32_r32: opcode1 = #opname; store = true; has_modrm = true; break; \
  case r8_rm8:   opcode1 = #opname; load = true; has_modrm = true; byte_operand = true; break; \
  case r32_rm32: opcode1 = #opname; load = true; has_modrm = true; break; \
  case ax8_i8:   opcode1 = #opname; ax = true; immediate_bytes = 1; byte_operand = true; break; \
  case ax32_i32: opcode1 = #opname; ax = true; immediate_bytes = 4; break;

DISASSEMBLER_ENTRY(add,
  0x00 /* RegMem8/Reg8 */,     0x01 /* RegMem32/Reg32 */,
  0x02 /* Reg8/RegMem8 */,     0x03 /* Reg32/RegMem32 */,
  0x04 /* Rax8/imm8 opcode */, 0x05 /* Rax32/imm32 */)
DISASSEMBLER_ENTRY(or,
  0x08 /* RegMem8/Reg8 */,     0x09 /* RegMem32/Reg32 */,
  0x0A /* Reg8/RegMem8 */,     0x0B /* Reg32/RegMem32 */,
  0x0C /* Rax8/imm8 opcode */, 0x0D /* Rax32/imm32 */)
DISASSEMBLER_ENTRY(adc,
  0x10 /* RegMem8/Reg8 */,     0x11 /* RegMem32/Reg32 */,
  0x12 /* Reg8/RegMem8 */,     0x13 /* Reg32/RegMem32 */,
  0x14 /* Rax8/imm8 opcode */, 0x15 /* Rax32/imm32 */)
DISASSEMBLER_ENTRY(sbb,
  0x18 /* RegMem8/Reg8 */,     0x19 /* RegMem32/Reg32 */,
  0x1A /* Reg8/RegMem8 */,     0x1B /* Reg32/RegMem32 */,
  0x1C /* Rax8/imm8 opcode */, 0x1D /* Rax32/imm32 */)
DISASSEMBLER_ENTRY(and,
  0x20 /* RegMem8/Reg8 */,     0x21 /* RegMem32/Reg32 */,
  0x22 /* Reg8/RegMem8 */,     0x23 /* Reg32/RegMem32 */,
  0x24 /* Rax8/imm8 opcode */, 0x25 /* Rax32/imm32 */)
DISASSEMBLER_ENTRY(sub,
  0x28 /* RegMem8/Reg8 */,     0x29 /* RegMem32/Reg32 */,
  0x2A /* Reg8/RegMem8 */,     0x2B /* Reg32/RegMem32 */,
  0x2C /* Rax8/imm8 opcode */, 0x2D /* Rax32/imm32 */)
DISASSEMBLER_ENTRY(xor,
  0x30 /* RegMem8/Reg8 */,     0x31 /* RegMem32/Reg32 */,
  0x32 /* Reg8/RegMem8 */,     0x33 /* Reg32/RegMem32 */,
  0x34 /* Rax8/imm8 opcode */, 0x35 /* Rax32/imm32 */)
DISASSEMBLER_ENTRY(cmp,
  0x38 /* RegMem8/Reg8 */,     0x39 /* RegMem32/Reg32 */,
  0x3A /* Reg8/RegMem8 */,     0x3B /* Reg32/RegMem32 */,
  0x3C /* Rax8/imm8 opcode */, 0x3D /* Rax32/imm32 */)

#undef DISASSEMBLER_ENTRY
  case 0x50: case 0x51: case 0x52: case 0x53: case 0x54: case 0x55: case 0x56: case 0x57:
    opcode1 = "push";
    reg_in_opcode = true;
    target_specific = true;
    break;
  case 0x58: case 0x59: case 0x5A: case 0x5B: case 0x5C: case 0x5D: case 0x5E: case 0x5F:
    opcode1 = "pop";
    reg_in_opcode = true;
    target_specific = true;
    break;
  case 0x63:
    if ((rex & REX_W) != 0) {
      opcode1 = "movsxd";
      has_modrm = true;
      load = true;
    } else {
      // In 32-bit mode (!supports_rex_) this is ARPL, with no REX prefix the functionality is the
      // same as 'mov' but the use of the instruction is discouraged.
      opcode_tmp = StringPrintf("unknown opcode '%02X'", *instr);
      opcode1 = opcode_tmp.c_str();
    }
    break;
  case 0x68: opcode1 = "push"; immediate_bytes = 4; break;
  case 0x69: opcode1 = "imul"; load = true; has_modrm = true; immediate_bytes = 4; break;
  case 0x6A: opcode1 = "push"; immediate_bytes = 1; break;
  case 0x6B: opcode1 = "imul"; load = true; has_modrm = true; immediate_bytes = 1; break;
  case 0x70: case 0x71: case 0x72: case 0x73: case 0x74: case 0x75: case 0x76: case 0x77:
  case 0x78: case 0x79: case 0x7A: case 0x7B: case 0x7C: case 0x7D: case 0x7E: case 0x7F:
    static const char* condition_codes[] =
    {"o", "no", "b/nae/c", "nb/ae/nc", "z/eq",  "nz/ne", "be/na", "nbe/a",
     "s", "ns", "p/pe",    "np/po",    "l/nge", "nl/ge", "le/ng", "nle/g"
    };
    opcode1 = "j";
    opcode2 = condition_codes[*instr & 0xF];
    branch_bytes = 1;
    break;
  case 0x86: case 0x87:
    opcode1 = "xchg";
    store = true;
    has_modrm = true;
    byte_operand = (*instr == 0x86);
    break;
  case 0x88: opcode1 = "mov"; store = true; has_modrm = true; byte_operand = true; break;
  case 0x89: opcode1 = "mov"; store = true; has_modrm = true; break;
  case 0x8A: opcode1 = "mov"; load = true; has_modrm = true; byte_operand = true; break;
  case 0x8B: opcode1 = "mov"; load = true; has_modrm = true; break;

  case 0x0F:  // 2 byte extended opcode
    instr++;
    switch (*instr) {
      case 0x10: case 0x11:
        if (prefix[0] == 0xF2) {
          opcode1 = "movsd";
          prefix[0] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[0] == 0xF3) {
          opcode1 = "movss";
          prefix[0] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[2] == 0x66) {
          opcode1 = "movupd";
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          opcode1 = "movups";
        }
        has_modrm = true;
        src_reg_file = dst_reg_file = SSE;
        load = *instr == 0x10;
        store = !load;
        break;
      case 0x12: case 0x13:
        if (prefix[2] == 0x66) {
          opcode1 = "movlpd";
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[0] == 0) {
          opcode1 = "movlps";
        }
        has_modrm = true;
        src_reg_file = dst_reg_file = SSE;
        load = *instr == 0x12;
        store = !load;
        break;
      case 0x16: case 0x17:
        if (prefix[2] == 0x66) {
          opcode1 = "movhpd";
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[0] == 0) {
          opcode1 = "movhps";
        }
        has_modrm = true;
        src_reg_file = dst_reg_file = SSE;
        load = *instr == 0x16;
        store = !load;
        break;
      case 0x28: case 0x29:
        if (prefix[2] == 0x66) {
          opcode1 = "movapd";
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[0] == 0) {
          opcode1 = "movaps";
        }
        has_modrm = true;
        src_reg_file = dst_reg_file = SSE;
        load = *instr == 0x28;
        store = !load;
        break;
      case 0x2A:
        if (prefix[2] == 0x66) {
          opcode1 = "cvtpi2pd";
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[0] == 0xF2) {
          opcode1 = "cvtsi2sd";
          prefix[0] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[0] == 0xF3) {
          opcode1 = "cvtsi2ss";
          prefix[0] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          opcode1 = "cvtpi2ps";
        }
        load = true;
        has_modrm = true;
        dst_reg_file = SSE;
        break;
      case 0x2C:
        if (prefix[2] == 0x66) {
          opcode1 = "cvttpd2pi";
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[0] == 0xF2) {
          opcode1 = "cvttsd2si";
          prefix[0] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[0] == 0xF3) {
          opcode1 = "cvttss2si";
          prefix[0] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          opcode1 = "cvttps2pi";
        }
        load = true;
        has_modrm = true;
        src_reg_file = SSE;
        break;
      case 0x2D:
        if (prefix[2] == 0x66) {
          opcode1 = "cvtpd2pi";
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[0] == 0xF2) {
          opcode1 = "cvtsd2si";
          prefix[0] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[0] == 0xF3) {
          opcode1 = "cvtss2si";
          prefix[0] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          opcode1 = "cvtps2pi";
        }
        load = true;
        has_modrm = true;
        src_reg_file = SSE;
        break;
      case 0x2E:
        opcode0 = "u";
        FALLTHROUGH_INTENDED;
      case 0x2F:
        if (prefix[2] == 0x66) {
          opcode1 = "comisd";
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          opcode1 = "comiss";
        }
        has_modrm = true;
        load = true;
        src_reg_file = dst_reg_file = SSE;
        break;
      case 0x38:  // 3 byte extended opcode
        instr++;
        if (prefix[2] == 0x66) {
          switch (*instr) {
            case 0x01:
              opcode1 = "phaddw";
              prefix[2] = 0;
              has_modrm = true;
              load = true;
              src_reg_file = dst_reg_file = SSE;
              break;
            case 0x02:
              opcode1 = "phaddd";
              prefix[2] = 0;
              has_modrm = true;
              load = true;
              src_reg_file = dst_reg_file = SSE;
              break;
            case 0x40:
              opcode1 = "pmulld";
              prefix[2] = 0;
              has_modrm = true;
              load = true;
              src_reg_file = dst_reg_file = SSE;
              break;
            default:
              opcode_tmp = StringPrintf("unknown opcode '0F 38 %02X'", *instr);
              opcode1 = opcode_tmp.c_str();
          }
        } else {
          opcode_tmp = StringPrintf("unknown opcode '0F 38 %02X'", *instr);
          opcode1 = opcode_tmp.c_str();
        }
        break;
      case 0x3A:  // 3 byte extended opcode
        instr++;
        if (prefix[2] == 0x66) {
          switch (*instr) {
            case 0x0A:
              opcode1 = "roundss";
              prefix[2] = 0;
              has_modrm = true;
              store = true;
              src_reg_file = SSE;
              dst_reg_file = SSE;
              immediate_bytes = 1;
              break;
            case 0x0B:
              opcode1 = "roundsd";
              prefix[2] = 0;
              has_modrm = true;
              store = true;
              src_reg_file = SSE;
              dst_reg_file = SSE;
              immediate_bytes = 1;
              break;
            case 0x14:
              opcode1 = "pextrb";
              prefix[2] = 0;
              has_modrm = true;
              store = true;
              src_reg_file = SSE;
              immediate_bytes = 1;
              break;
          case 0x15:
              opcode1 = "pextrw";
              prefix[2] = 0;
              has_modrm = true;
              store = true;
              src_reg_file = SSE;
              immediate_bytes = 1;
              break;
            case 0x16:
              opcode1 = "pextrd";
              prefix[2] = 0;
              has_modrm = true;
              store = true;
              src_reg_file = SSE;
              immediate_bytes = 1;
              break;
            default:
              opcode_tmp = StringPrintf("unknown opcode '0F 3A %02X'", *instr);
              opcode1 = opcode_tmp.c_str();
          }
        } else {
          opcode_tmp = StringPrintf("unknown opcode '0F 3A %02X'", *instr);
          opcode1 = opcode_tmp.c_str();
        }
        break;
      case 0x40: case 0x41: case 0x42: case 0x43: case 0x44: case 0x45: case 0x46: case 0x47:
      case 0x48: case 0x49: case 0x4A: case 0x4B: case 0x4C: case 0x4D: case 0x4E: case 0x4F:
        opcode1 = "cmov";
        opcode2 = condition_codes[*instr & 0xF];
        has_modrm = true;
        load = true;
        break;
      case 0x50: case 0x51: case 0x52: case 0x53: case 0x54: case 0x55: case 0x56: case 0x57:
      case 0x58: case 0x59: case 0x5C: case 0x5D: case 0x5E: case 0x5F: {
        switch (*instr) {
          case 0x50: opcode1 = "movmsk"; break;
          case 0x51: opcode1 = "sqrt"; break;
          case 0x52: opcode1 = "rsqrt"; break;
          case 0x53: opcode1 = "rcp"; break;
          case 0x54: opcode1 = "and"; break;
          case 0x55: opcode1 = "andn"; break;
          case 0x56: opcode1 = "or"; break;
          case 0x57: opcode1 = "xor"; break;
          case 0x58: opcode1 = "add"; break;
          case 0x59: opcode1 = "mul"; break;
          case 0x5C: opcode1 = "sub"; break;
          case 0x5D: opcode1 = "min"; break;
          case 0x5E: opcode1 = "div"; break;
          case 0x5F: opcode1 = "max"; break;
          default: LOG(FATAL) << "Unreachable"; UNREACHABLE();
        }
        if (prefix[2] == 0x66) {
          opcode2 = "pd";
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[0] == 0xF2) {
          opcode2 = "sd";
          prefix[0] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[0] == 0xF3) {
          opcode2 = "ss";
          prefix[0] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          opcode2 = "ps";
        }
        load = true;
        has_modrm = true;
        src_reg_file = dst_reg_file = SSE;
        break;
      }
      case 0x5A:
        if (prefix[2] == 0x66) {
          opcode1 = "cvtpd2ps";
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[0] == 0xF2) {
          opcode1 = "cvtsd2ss";
          prefix[0] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[0] == 0xF3) {
          opcode1 = "cvtss2sd";
          prefix[0] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          opcode1 = "cvtps2pd";
        }
        load = true;
        has_modrm = true;
        src_reg_file = dst_reg_file = SSE;
        break;
      case 0x5B:
        if (prefix[2] == 0x66) {
          opcode1 = "cvtps2dq";
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[0] == 0xF2) {
          opcode1 = "bad opcode F2 0F 5B";
        } else if (prefix[0] == 0xF3) {
          opcode1 = "cvttps2dq";
          prefix[0] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          opcode1 = "cvtdq2ps";
        }
        load = true;
        has_modrm = true;
        src_reg_file = dst_reg_file = SSE;
        break;
      case 0x60: case 0x61: case 0x62: case 0x6C:
        if (prefix[2] == 0x66) {
          src_reg_file = dst_reg_file = SSE;
          prefix[2] = 0;  // Clear prefix now. It has served its purpose as part of the opcode.
        } else {
          src_reg_file = dst_reg_file = MMX;
        }
        switch (*instr) {
          case 0x60: opcode1 = "punpcklbw"; break;
          case 0x61: opcode1 = "punpcklwd"; break;
          case 0x62: opcode1 = "punpckldq"; break;
          case 0x6c: opcode1 = "punpcklqdq"; break;
        }
        load = true;
        has_modrm = true;
        break;
      case 0x6E:
        if (prefix[2] == 0x66) {
          dst_reg_file = SSE;
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          dst_reg_file = MMX;
        }
        opcode1 = "movd";
        load = true;
        has_modrm = true;
        break;
      case 0x6F:
        if (prefix[2] == 0x66) {
          src_reg_file = dst_reg_file = SSE;
          opcode1 = "movdqa";
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[0] == 0xF3) {
          src_reg_file = dst_reg_file = SSE;
          opcode1 = "movdqu";
          prefix[0] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          dst_reg_file = MMX;
          opcode1 = "movq";
        }
        load = true;
        has_modrm = true;
        break;
      case 0x70:
        if (prefix[2] == 0x66) {
          opcode1 = "pshufd";
          prefix[2] = 0;
          has_modrm = true;
          store = true;
          src_reg_file = dst_reg_file = SSE;
          immediate_bytes = 1;
        } else if (prefix[0] == 0xF2) {
          opcode1 = "pshuflw";
          prefix[0] = 0;
          has_modrm = true;
          store = true;
          src_reg_file = dst_reg_file = SSE;
          immediate_bytes = 1;
        } else {
          opcode_tmp = StringPrintf("unknown opcode '0F %02X'", *instr);
          opcode1 = opcode_tmp.c_str();
        }
        break;
      case 0x71:
        if (prefix[2] == 0x66) {
          dst_reg_file = SSE;
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          dst_reg_file = MMX;
        }
        static const char* x71_opcodes[] = {
            "unknown-71", "unknown-71", "psrlw", "unknown-71",
            "psraw",      "unknown-71", "psllw", "unknown-71"};
        modrm_opcodes = x71_opcodes;
        reg_is_opcode = true;
        has_modrm = true;
        store = true;
        immediate_bytes = 1;
        break;
      case 0x72:
        if (prefix[2] == 0x66) {
          dst_reg_file = SSE;
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          dst_reg_file = MMX;
        }
        static const char* x72_opcodes[] = {
            "unknown-72", "unknown-72", "psrld", "unknown-72",
            "psrad",      "unknown-72", "pslld", "unknown-72"};
        modrm_opcodes = x72_opcodes;
        reg_is_opcode = true;
        has_modrm = true;
        store = true;
        immediate_bytes = 1;
        break;
      case 0x73:
        if (prefix[2] == 0x66) {
          dst_reg_file = SSE;
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          dst_reg_file = MMX;
        }
        static const char* x73_opcodes[] = {
            "unknown-73", "unknown-73", "psrlq", "psrldq",
            "unknown-73", "unknown-73", "psllq", "unknown-73"};
        modrm_opcodes = x73_opcodes;
        reg_is_opcode = true;
        has_modrm = true;
        store = true;
        immediate_bytes = 1;
        break;
      case 0x7C:
        if (prefix[0] == 0xF2) {
          opcode1 = "haddps";
          prefix[0] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else if (prefix[2] == 0x66) {
          opcode1 = "haddpd";
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          opcode_tmp = StringPrintf("unknown opcode '0F %02X'", *instr);
          opcode1 = opcode_tmp.c_str();
          break;
        }
        src_reg_file = dst_reg_file = SSE;
        has_modrm = true;
        load = true;
        break;
      case 0x7E:
        if (prefix[2] == 0x66) {
          src_reg_file = SSE;
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          src_reg_file = MMX;
        }
        opcode1 = "movd";
        has_modrm = true;
        store = true;
        break;
      case 0x80: case 0x81: case 0x82: case 0x83: case 0x84: case 0x85: case 0x86: case 0x87:
      case 0x88: case 0x89: case 0x8A: case 0x8B: case 0x8C: case 0x8D: case 0x8E: case 0x8F:
        opcode1 = "j";
        opcode2 = condition_codes[*instr & 0xF];
        branch_bytes = 4;
        break;
      case 0x90: case 0x91: case 0x92: case 0x93: case 0x94: case 0x95: case 0x96: case 0x97:
      case 0x98: case 0x99: case 0x9A: case 0x9B: case 0x9C: case 0x9D: case 0x9E: case 0x9F:
        opcode1 = "set";
        opcode2 = condition_codes[*instr & 0xF];
        modrm_opcodes = nullptr;
        reg_is_opcode = true;
        has_modrm = true;
        store = true;
        break;
      case 0xA4:
        opcode1 = "shld";
        has_modrm = true;
        load = true;
        immediate_bytes = 1;
        break;
      case 0xA5:
        opcode1 = "shld";
        has_modrm = true;
        load = true;
        cx = true;
        break;
      case 0xAC:
        opcode1 = "shrd";
        has_modrm = true;
        load = true;
        immediate_bytes = 1;
        break;
      case 0xAD:
        opcode1 = "shrd";
        has_modrm = true;
        load = true;
        cx = true;
        break;
      case 0xAE:
        if (prefix[0] == 0xF3) {
          prefix[0] = 0;  // clear prefix now it's served its purpose as part of the opcode
          static const char* xAE_opcodes[] = {
              "rdfsbase",   "rdgsbase",   "wrfsbase",   "wrgsbase",
              "unknown-AE", "unknown-AE", "unknown-AE", "unknown-AE"};
          modrm_opcodes = xAE_opcodes;
          reg_is_opcode = true;
          has_modrm = true;
          uint8_t reg_or_opcode = (instr[1] >> 3) & 7;
          switch (reg_or_opcode) {
            case 0:
              prefix[1] = kFs;
              load = true;
              break;
            case 1:
              prefix[1] = kGs;
              load = true;
              break;
            case 2:
              prefix[1] = kFs;
              store = true;
              break;
            case 3:
              prefix[1] = kGs;
              store = true;
              break;
            default:
              load = true;
              break;
          }
        } else {
          static const char* xAE_opcodes[] = {
              "unknown-AE", "unknown-AE", "unknown-AE", "unknown-AE",
              "unknown-AE", "lfence",     "mfence",     "sfence"};
          modrm_opcodes = xAE_opcodes;
          reg_is_opcode = true;
          has_modrm = true;
          load = true;
          no_ops = true;
        }
        break;
      case 0xAF:
        opcode1 = "imul";
        has_modrm = true;
        load = true;
        break;
      case 0xB1:
        opcode1 = "cmpxchg";
        has_modrm = true;
        store = true;
        break;
      case 0xB6:
        opcode1 = "movzxb";
        has_modrm = true;
        load = true;
        byte_second_operand = true;
        break;
      case 0xB7:
        opcode1 = "movzxw";
        has_modrm = true;
        load = true;
        break;
      case 0xBE:
        opcode1 = "movsxb";
        has_modrm = true;
        load = true;
        byte_second_operand = true;
        rex |= (rex == 0 ? 0 : REX_W);
        break;
      case 0xBF:
        opcode1 = "movsxw";
        has_modrm = true;
        load = true;
        break;
      case 0xC3:
        opcode1 = "movnti";
        store = true;
        has_modrm = true;
        break;
      case 0xC5:
        if (prefix[2] == 0x66) {
          opcode1 = "pextrw";
          prefix[2] = 0;
          has_modrm = true;
          load = true;
          src_reg_file = SSE;
          immediate_bytes = 1;
        } else {
          opcode_tmp = StringPrintf("unknown opcode '0F %02X'", *instr);
          opcode1 = opcode_tmp.c_str();
        }
        break;
      case 0xC6:
        if (prefix[2] == 0x66) {
          opcode1 = "shufpd";
          prefix[2] = 0;
        } else {
          opcode1 = "shufps";
        }
        has_modrm = true;
        store = true;
        src_reg_file = dst_reg_file = SSE;
        immediate_bytes = 1;
        break;
      case 0xC7:
        static const char* x0FxC7_opcodes[] = {
            "unknown-0f-c7", "cmpxchg8b",     "unknown-0f-c7", "unknown-0f-c7",
            "unknown-0f-c7", "unknown-0f-c7", "unknown-0f-c7", "unknown-0f-c7"};
        modrm_opcodes = x0FxC7_opcodes;
        has_modrm = true;
        reg_is_opcode = true;
        store = true;
        break;
      case 0xC8: case 0xC9: case 0xCA: case 0xCB: case 0xCC: case 0xCD: case 0xCE: case 0xCF:
        opcode1 = "bswap";
        reg_in_opcode = true;
        break;
      case 0xD4:
        if (prefix[2] == 0x66) {
          src_reg_file = dst_reg_file = SSE;
          prefix[2] = 0;
        } else {
          src_reg_file = dst_reg_file = MMX;
        }
        opcode1 = "paddq";
        prefix[2] = 0;
        has_modrm = true;
        load = true;
        break;
      case 0xDB:
        if (prefix[2] == 0x66) {
          src_reg_file = dst_reg_file = SSE;
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          src_reg_file = dst_reg_file = MMX;
        }
        opcode1 = "pand";
        prefix[2] = 0;
        has_modrm = true;
        load = true;
        break;
      case 0xD5:
        if (prefix[2] == 0x66) {
          opcode1 = "pmullw";
          prefix[2] = 0;
          has_modrm = true;
          load = true;
          src_reg_file = dst_reg_file = SSE;
        } else {
          opcode_tmp = StringPrintf("unknown opcode '0F %02X'", *instr);
          opcode1 = opcode_tmp.c_str();
        }
        break;
      case 0xEB:
        if (prefix[2] == 0x66) {
          src_reg_file = dst_reg_file = SSE;
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          src_reg_file = dst_reg_file = MMX;
        }
        opcode1 = "por";
        prefix[2] = 0;
        has_modrm = true;
        load = true;
        break;
      case 0xEF:
        if (prefix[2] == 0x66) {
          src_reg_file = dst_reg_file = SSE;
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          src_reg_file = dst_reg_file = MMX;
        }
        opcode1 = "pxor";
        prefix[2] = 0;
        has_modrm = true;
        load = true;
        break;
      case 0xF4:
      case 0xF6:
      case 0xF8:
      case 0xF9:
      case 0xFA:
      case 0xFB:
      case 0xFC:
      case 0xFD:
      case 0xFE:
        if (prefix[2] == 0x66) {
          src_reg_file = dst_reg_file = SSE;
          prefix[2] = 0;  // clear prefix now it's served its purpose as part of the opcode
        } else {
          src_reg_file = dst_reg_file = MMX;
        }
        switch (*instr) {
          case 0xF4: opcode1 = "pmuludq"; break;
          case 0xF6: opcode1 = "psadbw"; break;
          case 0xF8: opcode1 = "psubb"; break;
          case 0xF9: opcode1 = "psubw"; break;
          case 0xFA: opcode1 = "psubd"; break;
          case 0xFB: opcode1 = "psubq"; break;
          case 0xFC: opcode1 = "paddb"; break;
          case 0xFD: opcode1 = "paddw"; break;
          case 0xFE: opcode1 = "paddd"; break;
        }
        prefix[2] = 0;
        has_modrm = true;
        load = true;
        break;
      default:
        opcode_tmp = StringPrintf("unknown opcode '0F %02X'", *instr);
        opcode1 = opcode_tmp.c_str();
        break;
    }
    break;
  case 0x80: case 0x81: case 0x82: case 0x83:
    static const char* x80_opcodes[] = {"add", "or", "adc", "sbb", "and", "sub", "xor", "cmp"};
    modrm_opcodes = x80_opcodes;
    has_modrm = true;
    reg_is_opcode = true;
    store = true;
    byte_operand = (*instr & 1) == 0;
    immediate_bytes = *instr == 0x81 ? 4 : 1;
    break;
  case 0x84: case 0x85:
    opcode1 = "test";
    has_modrm = true;
    load = true;
    byte_operand = (*instr & 1) == 0;
    break;
  case 0x8D:
    opcode1 = "lea";
    has_modrm = true;
    load = true;
    break;
  case 0x8F:
    opcode1 = "pop";
    has_modrm = true;
    reg_is_opcode = true;
    store = true;
    break;
  case 0x99:
    opcode1 = "cdq";
    break;
  case 0x9B:
    if (instr[1] == 0xDF && instr[2] == 0xE0) {
      opcode1 = "fstsw\tax";
      instr += 2;
    } else {
      opcode_tmp = StringPrintf("unknown opcode '%02X'", *instr);
      opcode1 = opcode_tmp.c_str();
    }
    break;
  case 0xA7:
    opcode1 = (prefix[2] == 0x66 ? "cmpsw" : "cmpsl");
    break;
  case 0xAF:
    opcode1 = (prefix[2] == 0x66 ? "scasw" : "scasl");
    break;
  case 0xB0: case 0xB1: case 0xB2: case 0xB3: case 0xB4: case 0xB5: case 0xB6: case 0xB7:
    opcode1 = "mov";
    immediate_bytes = 1;
    byte_operand = true;
    reg_in_opcode = true;
    byte_operand = true;
    break;
  case 0xB8: case 0xB9: case 0xBA: case 0xBB: case 0xBC: case 0xBD: case 0xBE: case 0xBF:
    if ((rex & REX_W) != 0) {
      opcode1 = "movabsq";
      immediate_bytes = 8;
      reg_in_opcode = true;
      break;
    }
    opcode1 = "mov";
    immediate_bytes = 4;
    reg_in_opcode = true;
    break;
  case 0xC0: case 0xC1:
  case 0xD0: case 0xD1: case 0xD2: case 0xD3:
    static const char* shift_opcodes[] =
        {"rol", "ror", "rcl", "rcr", "shl", "shr", "unknown-shift", "sar"};
    modrm_opcodes = shift_opcodes;
    has_modrm = true;
    reg_is_opcode = true;
    store = true;
    immediate_bytes = ((*instr & 0xf0) == 0xc0) ? 1 : 0;
    cx = (*instr == 0xD2) || (*instr == 0xD3);
    byte_operand = (*instr == 0xC0);
    break;
  case 0xC3: opcode1 = "ret"; break;
  case 0xC6:
    static const char* c6_opcodes[] = {"mov",        "unknown-c6", "unknown-c6",
                                       "unknown-c6", "unknown-c6", "unknown-c6",
                                       "unknown-c6", "unknown-c6"};
    modrm_opcodes = c6_opcodes;
    store = true;
    immediate_bytes = 1;
    has_modrm = true;
    reg_is_opcode = true;
    byte_operand = true;
    break;
  case 0xC7:
    static const char* c7_opcodes[] = {"mov",        "unknown-c7", "unknown-c7",
                                       "unknown-c7", "unknown-c7", "unknown-c7",
                                       "unknown-c7", "unknown-c7"};
    modrm_opcodes = c7_opcodes;
    store = true;
    immediate_bytes = 4;
    has_modrm = true;
    reg_is_opcode = true;
    break;
  case 0xCC: opcode1 = "int 3"; break;
  case 0xD9:
    if (instr[1] == 0xF8) {
      opcode1 = "fprem";
      instr++;
    } else {
      static const char* d9_opcodes[] = {"flds", "unknown-d9", "fsts", "fstps", "fldenv", "fldcw",
                                         "fnstenv", "fnstcw"};
      modrm_opcodes = d9_opcodes;
      store = true;
      has_modrm = true;
      reg_is_opcode = true;
    }
    break;
  case 0xDA:
    if (instr[1] == 0xE9) {
      opcode1 = "fucompp";
      instr++;
    } else {
      opcode_tmp = StringPrintf("unknown opcode '%02X'", *instr);
      opcode1 = opcode_tmp.c_str();
    }
    break;
  case 0xDB:
    static const char* db_opcodes[] = {"fildl",      "unknown-db", "unknown-db",
                                       "unknown-db", "unknown-db", "unknown-db",
                                       "unknown-db", "unknown-db"};
    modrm_opcodes = db_opcodes;
    load = true;
    has_modrm = true;
    reg_is_opcode = true;
    break;
  case 0xDD:
    static const char* dd_opcodes[] = {"fldl",   "fisttp", "fstl",
                                       "fstpl",  "frstor", "unknown-dd",
                                       "fnsave", "fnstsw"};
    modrm_opcodes = dd_opcodes;
    store = true;
    has_modrm = true;
    reg_is_opcode = true;
    break;
  case 0xDF:
    static const char* df_opcodes[] = {"fild",       "unknown-df", "unknown-df",
                                       "unknown-df", "unknown-df", "fildll",
                                       "unknown-df", "unknown-df"};
    modrm_opcodes = df_opcodes;
    load = true;
    has_modrm = true;
    reg_is_opcode = true;
    break;
  case 0xE3: opcode1 = "jecxz"; branch_bytes = 1; break;
  case 0xE8: opcode1 = "call"; branch_bytes = 4; break;
  case 0xE9: opcode1 = "jmp"; branch_bytes = 4; break;
  case 0xEB: opcode1 = "jmp"; branch_bytes = 1; break;
  case 0xF5: opcode1 = "cmc"; break;
  case 0xF6: case 0xF7:
    static const char* f7_opcodes[] = {
        "test", "unknown-f7", "not", "neg", "mul edx:eax, eax *",
        "imul edx:eax, eax *", "div edx:eax, edx:eax /",
        "idiv edx:eax, edx:eax /"};
    modrm_opcodes = f7_opcodes;
    has_modrm = true;
    reg_is_opcode = true;
    store = true;
    immediate_bytes = ((instr[1] & 0x38) == 0) ? 1 : 0;
    break;
  case 0xFF:
    {
      static const char* ff_opcodes[] = {
          "inc", "dec", "call", "call",
          "jmp", "jmp", "push", "unknown-ff"};
      modrm_opcodes = ff_opcodes;
      has_modrm = true;
      reg_is_opcode = true;
      load = true;
      const uint8_t opcode_digit = (instr[1] >> 3) & 7;
      // 'call', 'jmp' and 'push' are target specific instructions
      if (opcode_digit == 2 || opcode_digit == 4 || opcode_digit == 6) {
        target_specific = true;
      }
    }
    break;
  default:
    opcode_tmp = StringPrintf("unknown opcode '%02X'", *instr);
    opcode1 = opcode_tmp.c_str();
    break;
  }
  std::ostringstream args;
  // We force the REX prefix to be available for 64-bit target
  // in order to dump addr (base/index) registers correctly.
  uint8_t rex64 = supports_rex_ ? (rex | 0x40) : rex;
  // REX.W should be forced for 64-target and target-specific instructions (i.e., push or pop).
  uint8_t rex_w = (supports_rex_ && target_specific) ? (rex | 0x48) : rex;
  if (reg_in_opcode) {
    DCHECK(!has_modrm);
    DumpOpcodeReg(args, rex_w, *instr & 0x7, byte_operand, prefix[2]);
  }
  instr++;
  uint32_t address_bits = 0;
  if (has_modrm) {
    uint8_t modrm = *instr;
    instr++;
    uint8_t mod = modrm >> 6;
    uint8_t reg_or_opcode = (modrm >> 3) & 7;
    uint8_t rm = modrm & 7;
    std::string address = DumpAddress(mod, rm, rex64, rex_w, no_ops, byte_operand,
                                      byte_second_operand, prefix, load, src_reg_file, dst_reg_file,
                                      &instr, &address_bits);

    if (reg_is_opcode && modrm_opcodes != nullptr) {
      opcode3 = modrm_opcodes[reg_or_opcode];
    }

    // Add opcode suffixes to indicate size.
    if (byte_operand) {
      opcode4 = "b";
    } else if ((rex & REX_W) != 0) {
      opcode4 = "q";
    } else if (prefix[2] == 0x66) {
      opcode4 = "w";
    }

    if (load) {
      if (!reg_is_opcode) {
        DumpReg(args, rex, reg_or_opcode, byte_operand, prefix[2], dst_reg_file);
        args << ", ";
      }
      DumpSegmentOverride(args, prefix[1]);
      args << address;
    } else {
      DCHECK(store);
      DumpSegmentOverride(args, prefix[1]);
      args << address;
      if (!reg_is_opcode) {
        args << ", ";
        DumpReg(args, rex, reg_or_opcode, byte_operand, prefix[2], src_reg_file);
      }
    }
  }
  if (ax) {
    // If this opcode implicitly uses ax, ax is always the first arg.
    DumpReg(args, rex, 0 /* EAX */, byte_operand, prefix[2], GPR);
  }
  if (cx) {
    args << ", ";
    DumpReg(args, rex, 1 /* ECX */, true, prefix[2], GPR);
  }
  if (immediate_bytes > 0) {
    if (has_modrm || reg_in_opcode || ax || cx) {
      args << ", ";
    }
    if (immediate_bytes == 1) {
      args << StringPrintf("%d", *reinterpret_cast<const int8_t*>(instr));
      instr++;
    } else if (immediate_bytes == 4) {
      if (prefix[2] == 0x66) {  // Operand size override from 32-bit to 16-bit.
        args << StringPrintf("%d", *reinterpret_cast<const int16_t*>(instr));
        instr += 2;
      } else {
        args << StringPrintf("%d", *reinterpret_cast<const int32_t*>(instr));
        instr += 4;
      }
    } else {
      CHECK_EQ(immediate_bytes, 8u);
      args << StringPrintf("%" PRId64, *reinterpret_cast<const int64_t*>(instr));
      instr += 8;
    }
  } else if (branch_bytes > 0) {
    DCHECK(!has_modrm);
    int32_t displacement;
    if (branch_bytes == 1) {
      displacement = *reinterpret_cast<const int8_t*>(instr);
      instr++;
    } else {
      CHECK_EQ(branch_bytes, 4u);
      displacement = *reinterpret_cast<const int32_t*>(instr);
      instr += 4;
    }
    args << StringPrintf("%+d (", displacement)
         << FormatInstructionPointer(instr + displacement)
         << ")";
  }
  if (prefix[1] == kFs && !supports_rex_) {
    args << "  ; ";
    Thread::DumpThreadOffset<4>(args, address_bits);
  }
  if (prefix[1] == kGs && supports_rex_) {
    args << "  ; ";
    Thread::DumpThreadOffset<8>(args, address_bits);
  }
  const char* prefix_str;
  switch (prefix[0]) {
    case 0xF0: prefix_str = "lock "; break;
    case 0xF2: prefix_str = "repne "; break;
    case 0xF3: prefix_str = "repe "; break;
    case 0: prefix_str = ""; break;
    default: LOG(FATAL) << "Unreachable"; UNREACHABLE();
  }
  os << FormatInstructionPointer(begin_instr)
     << StringPrintf(": %22s    \t%-7s%s%s%s%s%s ", DumpCodeHex(begin_instr, instr).c_str(),
                     prefix_str, opcode0, opcode1, opcode2, opcode3, opcode4)
     << args.str() << '\n';
  return instr - begin_instr;
}  // NOLINT(readability/fn_size)

}  // namespace x86
}  // namespace art