src/disassembler_arm.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_arm.h"

#include "stringprintf.h"

#include <iostream>

namespace art {
namespace arm {

DisassemblerArm::DisassemblerArm() {
}

void DisassemblerArm::Dump(std::ostream& os, const uint8_t* begin, const uint8_t* end) {
  if ((reinterpret_cast<intptr_t>(begin) & 1) == 0) {
    for (const uint8_t* cur = begin; cur < end; cur += 4) {
      DumpArm(os, cur);
    }
  } else {
    // remove thumb specifier bits
    begin = reinterpret_cast<const uint8_t*>(reinterpret_cast<uintptr_t>(begin) & ~1);
    end = reinterpret_cast<const uint8_t*>(reinterpret_cast<uintptr_t>(end) & ~1);
    for (const uint8_t* cur = begin; cur < end;) {
      cur += DumpThumb16(os, cur);
    }
  }
}

static const char* kConditionCodeNames[] = {
  "eq",  // 0000 - equal
  "ne",  // 0001 - not-equal
  "cs",  // 0010 - carry-set, greater than, equal or unordered
  "cc",  // 0011 - carry-clear, less than
  "mi",  // 0100 - minus, negative
  "pl",  // 0101 - plus, positive or zero
  "vs",  // 0110 - overflow
  "vc",  // 0111 - no overflow
  "hi",  // 1000 - unsigned higher
  "ls",  // 1001 - unsigned lower or same
  "ge",  // 1010 - signed greater than or equal
  "lt",  // 1011 - signed less than
  "gt",  // 1100 - signed greater than
  "le",  // 1101 - signed less than or equal
  "",    // 1110 - always
  "nv",  // 1111 - never (mostly obsolete, but might be a clue that we're mistranslating)
};

void DisassemblerArm::DumpCond(std::ostream& os, uint32_t cond) {
  if (cond < 15) {
    os << kConditionCodeNames[cond];
  } else {
    os << "Unexpected condition: " << cond;
  }
}

void DisassemblerArm::DumpReg(std::ostream& os, uint32_t reg) {
  switch (reg) {
    case 13: os << "sp"; break;
    case 14: os << "lr"; break;
    case 15: os << "pc"; break;
    default: os << "r" << reg; break;
  }
}

void DisassemblerArm::DumpBranchTarget(std::ostream& os, const uint8_t* instr_ptr, int32_t imm32) {
  os << imm32 << " (" << reinterpret_cast<const void*>(instr_ptr + imm32) << ")";
}

static uint32_t ReadU16(const uint8_t* ptr) {
  return ptr[0] | (ptr[1] << 8);
}

static uint32_t ReadU32(const uint8_t* ptr) {
  return ptr[0] | (ptr[1] << 8) | (ptr[2] << 16) | (ptr[3] << 24);
}

static const char* kDataProcessingOperations[] = {
  "and", "eor", "sub", "rsb", "add", "adc", "sbc", "rsc",
  "tst", "teq", "cmp", "cmn", "orr", "mov", "bic", "mvn",
};

struct ArmRegister {
  ArmRegister(uint32_t r) : r(r) { CHECK_LE(r, 15U); }
  uint32_t r;
};
std::ostream& operator<<(std::ostream& os, const ArmRegister& r) {
  if (r.r == 13) {
    os << "sp";
  } else if (r.r == 14) {
    os << "lr";
  } else if (r.r == 15) {
    os << "pc";
  } else {
    os << "r" << r.r;
  }
  return os;
}

struct Rd : ArmRegister {
  Rd(uint32_t instruction) : ArmRegister((instruction >> 12) & 0xf) {}
};
typedef Rd Rt;
struct Rn : ArmRegister {
  Rn(uint32_t instruction) : ArmRegister((instruction >> 16) & 0xf) {}
};

struct Rm {
  Rm(uint32_t instruction) : shift((instruction >> 4) & 0xff), rm(instruction & 0xf) {}
  uint32_t shift;
  ArmRegister rm;
};
std::ostream& operator<<(std::ostream& os, const Rm& r) {
  os << r.rm;
  if (r.shift != 0) {
    os << "-shift-" << r.shift; // TODO
  }
  return os;
}

struct Imm12 {
  Imm12(uint32_t instruction) : rotate((instruction >> 8) & 0xf), imm(instruction & 0xff) {}
  uint32_t rotate;
  uint32_t imm;
};
std::ostream& operator<<(std::ostream& os, const Imm12& rhs) {
  uint32_t imm = (rhs.imm >> (2 * rhs.rotate)) | (rhs.imm << (32 - (2 * rhs.rotate)));
  os << "#" << imm;
  return os;
}

struct RegisterList {
  RegisterList(uint32_t instruction) : register_list(instruction & 0xffff) {}
  uint32_t register_list;
};
std::ostream& operator<<(std::ostream& os, const RegisterList& rhs) {
  if (rhs.register_list == 0) {
    os << "<no register list?>";
    return os;
  }
  bool first = true;
  for (size_t i = 0; i < 16; i++) {
    if ((rhs.register_list & (1 << i)) != 0) {
      if (first) {
        os << "{";
        first = false;
      } else {
        os << ", ";
      }
      os << ArmRegister(i);
    }
  }
  os << "}";
  return os;
}

void DisassemblerArm::DumpArm(std::ostream& os, const uint8_t* instr_ptr) {
  uint32_t instruction = ReadU32(instr_ptr);
  uint32_t cond = (instruction >> 28) & 0xf;
  uint32_t op1 = (instruction >> 25) & 0x7;
  std::ostringstream opcode;
  std::ostringstream args;
  switch (op1) {
    case 0:
    case 1: // Data processing instructions.
      {
        if ((instruction & 0x0fffffd0) == 0x012fff10) { // BX and BLX (register)
          opcode << (((instruction >> 5) & 1) ? "blx" : "bx");
          args << ArmRegister(instruction & 0xf);
          break;
        }
        bool i = (instruction & (1 << 25)) != 0;
        bool s = (instruction & (1 << 20)) != 0;
        opcode << kDataProcessingOperations[(instruction >> 21) & 0xf]
               << kConditionCodeNames[cond]
               << (s ? "s" : "");
        args << Rd(instruction) << ", ";
        if (i) {
          args << Rn(instruction) << ", " << Imm12(instruction);
        } else {
          args << Rm(instruction);
        }
      }
      break;
    case 2: // Load/store word and unsigned byte.
      {
        bool p = (instruction & (1 << 24)) != 0;
        bool b = (instruction & (1 << 22)) != 0;
        bool w = (instruction & (1 << 21)) != 0;
        bool l = (instruction & (1 << 20)) != 0;
        opcode << (l ? "ldr" : "str") << (b ? "b" : "") << kConditionCodeNames[cond];
        args << Rt(instruction) << ", ";
        if (Rn(instruction).r == 0xf) {
          UNIMPLEMENTED(FATAL) << "literals";
        } else {
          bool wback = !p || w;
          if (p && !wback) {
            args << "[" << Rn(instruction) << ", " << Imm12(instruction) << "]";
          } else if (p && wback) {
            args << "[" << Rn(instruction) << ", " << Imm12(instruction) << "]!";
          } else if (!p && wback) {
            args << "[" << Rn(instruction) << "], " << Imm12(instruction);
          } else {
            LOG(FATAL) << p << " " << w;
          }
        }
      }
      break;
    case 4: // Load/store multiple.
      {
        bool p = (instruction & (1 << 24)) != 0;
        bool u = (instruction & (1 << 23)) != 0;
        bool w = (instruction & (1 << 21)) != 0;
        bool l = (instruction & (1 << 20)) != 0;
        opcode << (l ? "ldm" : "stm")
               << (u ? 'i' : 'd')
               << (p ? 'b' : 'a')
               << kConditionCodeNames[cond];
        args << Rn(instruction) << (w ? "!" : "") << ", " << RegisterList(instruction);
      }
      break;
    default:
      opcode << "???";
      break;
    }
    // TODO: a more complete ARM disassembler could generate wider opcodes.
    os << StringPrintf("\t\t\t%p: %08x\t%-7s ", instr_ptr, instruction, opcode.str().c_str()) << args.str() << '\n';
}

size_t DisassemblerArm::DumpThumb32(std::ostream& os, const uint8_t* instr_ptr) {
  uint32_t instr = (ReadU16(instr_ptr) << 16) | ReadU16(instr_ptr + 2);
  // |111|1 1|1000000|0000|1111110000000000|
  // |5 3|2 1|0987654|3  0|5    0    5    0|
  // |---|---|-------|----|----------------|
  // |332|2 2|2222222|1111|1111110000000000|
  // |1 9|8 7|6543210|9  6|5    0    5    0|
  // |---|---|-------|----|----------------|
  // |111|op1| op2   |    |                |
  uint32_t op1 = (instr >> 27) & 3;
  if (op1 == 0) {
    return DumpThumb16(os, instr_ptr);
  }

  uint32_t op2 = (instr >> 20) & 0x7F;
  std::ostringstream opcode;
  std::ostringstream args;
  switch (op1) {
    case 0:
      break;
    case 1:
      switch (op2) {
        case 0x00: case 0x01: case 0x02: case 0x03: case 0x08: case 0x09: case 0x0A: case 0x0B:
        case 0x10: case 0x11: case 0x12: case 0x13: case 0x18: case 0x19: case 0x1A: case 0x1B: {
          // |111|11|10|00|0|00|0000|1111110000000000|
          // |5 3|21|09|87|6|54|3  0|5    0    5    0|
          // |---|--|--|--|-|--|----|----------------|
          // |332|22|22|22|2|22|1111|1111110000000000|
          // |1 9|87|65|43|2|10|9  6|5    0    5    0|
          // |---|--|--|--|-|--|----|----------------|
          // |111|01|00|op|0|WL| Rn |                |
          // |111|01| op2      |    |                |
          // STM - 111 01 00-01-0-W0 nnnn rrrrrrrrrrrrrrrr
          // LDM - 111 01 00-01-0-W1 nnnn rrrrrrrrrrrrrrrr
          // PUSH- 111 01 00-01-0-10 1101 0M0rrrrrrrrrrrrr
          // POP - 111 01 00-01-0-11 1101 PM0rrrrrrrrrrrrr
          uint32_t op = (instr >> 23) & 3;
          uint32_t W = (instr >> 21) & 1;
          uint32_t L = (instr >> 20) & 1;
          uint32_t Rn = (instr >> 16) & 0xF;
          if (op == 1 || op == 2) {
            if (op == 1) {
              if (L == 0) {
                opcode << "stm";
                DumpReg(args, Rn);
                if (W == 0) {
                  args << ", ";
                } else {
                  args << "!, ";
                }
              } else {
                if (Rn != 13) {
                  opcode << "ldm";
                  DumpReg(args, Rn);
                  if (W == 0) {
                    args << ", ";
                  } else {
                    args << "!, ";
                  }
                } else {
                  opcode << "pop";
                }
              }
            } else {
              if (L == 0) {
                if (Rn != 13) {
                  opcode << "stmdb";
                  DumpReg(args, Rn);
                  if (W == 0) {
                    args << ", ";
                  } else {
                    args << "!, ";
                  }
                } else {
                  opcode << "push";
                }
              } else {
                opcode << "ldmdb";
                DumpReg(args, Rn);
                if (W == 0) {
                  args << ", ";
                } else {
                  args << "!, ";
                }
              }
            }
            args << RegisterList(instr);
          }
          break;
        }
        default:
          break;
      }
      break;
    case 2:
      if ((instr & 0x8000) == 0 && (op2 & 0x20) == 0) {
        // Data-processing (modified immediate)
        // |111|11|10|0000|0|0000|1|111|1100|00000000|
        // |5 3|21|09|8765|4|3  0|5|4 2|10 8|7 5    0|
        // |---|--|--|----|-|----|-|---|----|--------|
        // |332|22|22|2222|2|1111|1|111|1100|00000000|
        // |1 9|87|65|4321|0|9  6|5|4 2|10 8|7 5    0|
        // |---|--|--|----|-|----|-|---|----|--------|
        // |111|10|i0| op3|S| Rn |0|iii| Rd |iiiiiiii|
        //  111 10 x0 xxxx x xxxx opxxx xxxx xxxxxxxx
        //  111 10 00 0110 0 0000 1 000 0000 10101101 - f0c080ad
        uint32_t i = (instr >> 26) & 1;
        uint32_t op3 = (instr >> 21) & 0xF;
        uint32_t S = (instr >> 20) & 1;
        uint32_t Rn = (instr >> 16) & 0xF;
        uint32_t imm3 = (instr >> 12) & 7;
        uint32_t Rd = (instr >> 8) & 0xF;
        uint32_t imm8 = instr & 0xFF;
        int32_t imm32 = (i << 12) | (imm3 << 8) | imm8;
        switch (op3) {
          case 0x0: opcode << "and"; break;
          case 0x1: opcode << "bic"; break;
          case 0x2: opcode << "orr"; break;
          case 0x3: opcode << "orn"; break;
          case 0x4: opcode << "eor"; break;
          case 0x8: opcode << "add"; break;
          case 0xA: opcode << "adc"; break;
          case 0xB: opcode << "sbc"; break;
          case 0xD: opcode << "sub"; break;
          case 0xE: opcode << "rsb"; break;
          default: opcode << "UNKNOWN DPMI-" << op3; break;
        }
        if (S == 1) {
          opcode << "s";
        }
        DumpReg(args, Rd);
        args << ", ";
        DumpReg(args, Rn);
        args << ", ThumbExpand(" << imm32 << ")";
      } else if ((instr & 0x8000) == 0 && (op2 & 0x20) != 0) {
        // Data-processing (plain binary immediate)
        // |111|11|10|00000|0000|1|111110000000000|
        // |5 3|21|09|87654|3  0|5|4   0    5    0|
        // |---|--|--|-----|----|-|---------------|
        // |332|22|22|22222|1111|1|111110000000000|
        // |1 9|87|65|43210|9  6|5|4   0    5    0|
        // |---|--|--|-----|----|-|---------------|
        // |111|10|x1| op3 | Rn |0|xxxxxxxxxxxxxxx|
        uint32_t op3 = (instr >> 20) & 0x1F;
        uint32_t Rn = (instr >> 16) & 0xF;
        switch (op3) {
          case 0x04: {
            // MOVW Rd, #imm16     - 111 10 i0 0010 0 iiii 0 iii dddd iiiiiiii
            uint32_t Rd = (instr >> 8) & 0xF;
            uint32_t i = (instr >> 26) & 1;
            uint32_t imm3 = (instr >> 12) & 0x7;
            uint32_t imm8 = instr & 0xFF;
            uint32_t imm16 = (Rn << 12) | (i << 11) | (imm3 << 8) | imm8;
            opcode << "movw";
            DumpReg(args, Rd);
            args << ", #" << imm16;
            break;
          }
          case 0x0A: {
            // SUB.W Rd, Rn #imm12 - 111 10 i1 0101 0 nnnn 0 iii dddd iiiiiiii
            uint32_t Rd = (instr >> 8) & 0xF;
            uint32_t i = (instr >> 26) & 1;
            uint32_t imm3 = (instr >> 12) & 0x7;
            uint32_t imm8 = instr & 0xFF;
            uint32_t imm12 = (i << 11) | (imm3 << 8) | imm8;
            opcode << "sub.w";
            DumpReg(args, Rd);
            args << ", ";
            DumpReg(args, Rn);
            args << ", #" << imm12;
            break;
          }
          default:
            break;
        }
      } else {
        // Branches and miscellaneous control
        // |111|11|1000000|0000|1|111|1100|00000000|
        // |5 3|21|0987654|3  0|5|4 2|10 8|7 5    0|
        // |---|--|-------|----|-|---|----|--------|
        // |332|22|2222222|1111|1|111|1100|00000000|
        // |1 9|87|6543210|9  6|5|4 2|10 8|7 5    0|
        // |---|--|-------|----|-|---|----|--------|
        // |111|10| op2   |    |1|op3|op4 |        |

        uint32_t op3 = (instr >> 12) & 7;
        //uint32_t op4 = (instr >> 8) & 0xF;
        switch (op3) {
          case 0:
            if ((op2 & 0x38) != 0x38) {
              // Conditional branch
              // |111|11|1|0000|000000|1|1|1 |1|1 |10000000000|
              // |5 3|21|0|9876|543  0|5|4|3 |2|1 |0    5    0|
              // |---|--|-|----|------|-|-|--|-|--|-----------|
              // |332|22|2|2222|221111|1|1|1 |1|1 |10000000000|
              // |1 9|87|6|5432|109  6|5|4|3 |2|1 |0    5    0|
              // |---|--|-|----|------|-|-|--|-|--|-----------|
              // |111|10|S|cond| imm6 |1|0|J1|0|J2| imm11     |
              uint32_t S = (instr >> 26) & 1;
              uint32_t J2 = (instr >> 11) & 1;
              uint32_t J1 = (instr >> 13) & 1;
              uint32_t imm6 = (instr >> 16) & 0x3F;
              uint32_t imm11 = instr & 0x7FF;
              uint32_t cond = (instr >> 22) & 0xF;
              int32_t imm32 = (S << 20) |  (J2 << 19) | (J1 << 18) | (imm6 << 12) | (imm11 << 1);
              imm32 = (imm32 << 11) >> 11;  // sign extend 21bit immediate
              opcode << "b";
              DumpCond(opcode, cond);
              opcode << ".w";
              DumpBranchTarget(args, instr_ptr + 4, imm32);
            }
            break;
          case 2:
          case 1: case 3:
            break;
          case 4: case 6: case 5: case 7: {
            // BL, BLX (immediate)
            // |111|11|1|0000000000|11|1 |1|1 |10000000000|
            // |5 3|21|0|9876543  0|54|3 |2|1 |0    5    0|
            // |---|--|-|----------|--|--|-|--|-----------|
            // |332|22|2|2222221111|11|1 |1|1 |10000000000|
            // |1 9|87|6|5    0   6|54|3 |2|1 |0    5    0|
            // |---|--|-|----------|--|--|-|--|-----------|
            // |111|10|S| imm10    |11|J1|L|J2| imm11     |
            uint32_t S = (instr >> 26) & 1;
            uint32_t J2 = (instr >> 11) & 1;
            uint32_t L = (instr >> 12) & 1;
            uint32_t J1 = (instr >> 13) & 1;
            uint32_t imm10 = (instr >> 16) & 0x3FF;
            uint32_t imm11 = instr & 0x7FF;
            if (L == 0) {
              opcode << "bx";
            } else {
              opcode << "blx";
            }
            uint32_t I1 = ~(J1 ^ S);
            uint32_t I2 = ~(J2 ^ S);
            int32_t imm32 = (S << 24) | (I1 << 23) | (I2 << 22) | (imm10 << 12) | (imm11 << 1);
            imm32 = (imm32 << 8) >> 8;  // sign extend 24 bit immediate.
            DumpBranchTarget(args, instr_ptr + 4, imm32);
            break;
          }
        }
      }
      break;
    case 3:
      switch (op2) {
        case 0x00: case 0x02: case 0x04: case 0x06:  // 000xxx0
        case 0x08: case 0x0A: case 0x0C: case 0x0E: {
          // Store single data item
          // |111|11|100|000|0|0000|1111|110000|000000|
          // |5 3|21|098|765|4|3  0|5  2|10   6|5    0|
          // |---|--|---|---|-|----|----|------|------|
          // |332|22|222|222|2|1111|1111|110000|000000|
          // |1 9|87|654|321|0|9  6|5  2|10   6|5    0|
          // |---|--|---|---|-|----|----|------|------|
          // |111|11|000|op3|0|    |    |  op4 |      |

          uint32_t op3 = (instr >> 21) & 7;
          //uint32_t op4 = (instr >> 6) & 0x3F;
          switch (op3) {
            case 0x2: case 0x6: {
              // STR.W Rt, [Rn, #imm12] - 111 11 000 110 0 nnnn tttt iiiiiiiiiiii
              // STR Rt, [Rn, #imm8]    - 111 11 000 010 0 nnnn tttt 1PUWiiiiiiii
              uint32_t Rn = (instr >> 16) & 0xF;
              uint32_t Rt = (instr >> 12) & 0xF;
              if (op3 == 2) {
                uint32_t P = (instr >> 10) & 1;
                uint32_t U = (instr >> 9) & 1;
                uint32_t W = (instr >> 8) & 1;
                uint32_t imm8 = instr & 0xFF;
                int32_t imm32 = (imm8 << 24) >> 24;  // sign-extend imm8
                if (Rn == 13 && P == 1 && U == 0 && W == 1) {
                  opcode << "push";
                  DumpReg(args, Rt);
                } else if (Rn == 15 || (P == 0 && W == 0)) {
                  opcode << "UNDEFINED";
                } else {
                  if (P == 1 && U == 1 && W == 0) {
                    opcode << "strt";
                  } else {
                    opcode << "str";
                  }
                  DumpReg(args, Rt);
                  args << ", [";
                  DumpReg(args, Rn);
                  if (P == 0 && W == 1) {
                    args << "], #" << imm32;
                  } else {
                    args << ", #" << imm32 << "]";
                    if (W == 1) {
                      args << "!";
                    }
                  }
                }
              } else if (op3 == 6) {
                uint32_t imm12 = instr & 0xFFF;
                opcode << "str.w";
                DumpReg(args, Rt);
                args << ", [";
                DumpReg(args, Rn);
                args << ", #" << imm12 << "]";
              }
              break;
            }
          }

          break;
        }
        case 0x05: case 0x0D: case 0x15: case 0x1D: { // 00xx101
          // Load word
          // |111|11|10|0 0|00|0|0000|1111|110000|000000|
          // |5 3|21|09|8 7|65|4|3  0|5  2|10   6|5    0|
          // |---|--|--|---|--|-|----|----|------|------|
          // |332|22|22|2 2|22|2|1111|1111|110000|000000|
          // |1 9|87|65|4 3|21|0|9  6|5  2|10   6|5    0|
          // |---|--|--|---|--|-|----|----|------|------|
          // |111|11|00|op3|10|1| Rn | Rt | op4  |      |
          // |111|11| op2       |    |    | imm12       |
          uint32_t op3 = (instr >> 23) & 3;
          uint32_t op4 = (instr >> 6) & 0x3F;
          uint32_t Rn = (instr >> 16) & 0xF;
          uint32_t Rt = (instr >> 12) & 0xF;
          if (op3 == 1 || Rn == 15) {
            // LDR.W Rt, [Rn, #imm12]          - 111 11 00 00 101 nnnn tttt iiiiiiiiiiii
            // LDR.W Rt, [PC, #imm12]          - 111 11 00 0x 101 1111 tttt iiiiiiiiiiii
            uint32_t imm12 = instr & 0xFFF;
            opcode << "ldr.w";
            DumpReg(args, Rt);
            args << ", [";
            DumpReg(args, Rn);
            args << ", #" << imm12 << "]";
          } else if (op4 == 0) {
            // LDR.W Rt, [Rn, Rm{, LSL #imm2}] - 111 11 00 00 101 nnnn tttt 000000iimmmm
            uint32_t imm2 = (instr >> 4) & 0xF;
            uint32_t rm = instr & 0xF;
            opcode << "ldr.w";
            DumpReg(args, Rt);
            args << ", [";
            DumpReg(args, Rn);
            args << ", ";
            DumpReg(args, rm);
            if (imm2 != 0) {
              args << ", lsl #" << imm2;
            }
            args << "]";
          } else {
            // LDRT Rt, [Rn, #imm8]            - 111 11 00 00 101 nnnn tttt 1110iiiiiiii
            uint32_t imm8 = instr & 0xFF;
            opcode << "ldrt";
            DumpReg(args, Rt);
            args << ", [";
            DumpReg(args, Rn);
            args << ", #" << imm8 << "]";
          }
          break;
        }
      }
    default:
      break;
  }
  os << StringPrintf("\t\t\t%p: %08x\t%-7s ", instr_ptr, instr, opcode.str().c_str()) << args.str() << '\n';
  return 4;
}

size_t DisassemblerArm::DumpThumb16(std::ostream& os, const uint8_t* instr_ptr) {
  uint16_t instr = ReadU16(instr_ptr);
  bool is_32bit = ((instr & 0xF000) == 0xF000) || ((instr & 0xF800) == 0xE800);
  if (is_32bit) {
    return DumpThumb32(os, instr_ptr);
  } else {
    std::ostringstream opcode;
    std::ostringstream args;
    uint16_t opcode1 = instr >> 10;
    if (opcode1 < 0x10) {
      // shift (immediate), add, subtract, move, and compare
      uint16_t opcode2 = instr >> 9;
      switch (opcode2) {
        case 0x0: case 0x1: case 0x2: case 0x3: case 0x4: case 0x5: case 0x6: case 0x7:
        case 0x8: case 0x9: case 0xA: case 0xB: {
          // Logical shift left     - 00 000xx xxxxxxxxx
          // Logical shift right    - 00 001xx xxxxxxxxx
          // Arithmetic shift right - 00 010xx xxxxxxxxx
          uint16_t imm5 = (instr >> 6) & 0x1F;
          uint16_t rm = (instr >> 3) & 7;
          uint16_t Rd = instr & 7;
          if (opcode2 <= 3) {
            opcode << "lsls";
          } else if (opcode2 <= 7) {
            opcode << "lsrs";
          } else {
            opcode << "asrs";
          }
          DumpReg(args, Rd);
          args << ", ";
          DumpReg(args, rm);
          args << ", #" << imm5;
          break;
        }
        case 0xC: case 0xD: case 0xE: case 0xF: {
          // Add register        - 00 01100 mmm nnn ddd
          // Sub register        - 00 01101 mmm nnn ddd
          // Add 3-bit immediate - 00 01110 iii nnn ddd
          // Sub 3-bit immediate - 00 01111 iii nnn ddd
          uint16_t imm3_or_Rm = (instr >> 6) & 7;
          uint16_t Rn = (instr >> 3) & 7;
          uint16_t Rd = instr & 7;
          if ((opcode2 & 2) != 0 && imm3_or_Rm == 0) {
            opcode << "mov";
          } else {
            if ((opcode2 & 1) == 0) {
              opcode << "adds";
            } else {
              opcode << "subs";
            }
          }
          DumpReg(args, Rd);
          args << ", ";
          DumpReg(args, Rn);
          if ((opcode2 & 2) == 0) {
            args << ", ";
            DumpReg(args, imm3_or_Rm);
          } else if (imm3_or_Rm != 0) {
            args << ", #" << imm3_or_Rm;
          }
          break;
        }
        case 0x10: case 0x11: case 0x12: case 0x13:
        case 0x14: case 0x15: case 0x16: case 0x17:
        case 0x18: case 0x19: case 0x1A: case 0x1B:
        case 0x1C: case 0x1D: case 0x1E: case 0x1F: {
          // MOVS Rd, #imm8 - 00100 ddd iiiiiiii
          // CMP  Rn, #imm8 - 00101 nnn iiiiiiii
          // ADDS Rn, #imm8 - 00110 nnn iiiiiiii
          // SUBS Rn, #imm8 - 00111 nnn iiiiiiii
          uint16_t Rn = (instr >> 8) & 7;
          uint16_t imm8 = instr & 0xFF;
          switch (opcode2 >> 2) {
            case 4: opcode << "movs"; break;
            case 5: opcode << "cmp"; break;
            case 6: opcode << "adds"; break;
            case 7: opcode << "subs"; break;
          }
          DumpReg(args, Rn);
          args << ", #" << imm8;
          break;
        }
        default:
          break;
      }
    } else if (opcode1 == 0x11) {
      // Special data instructions and branch and exchange
      uint16_t opcode2 = (instr >> 6) & 0x0F;
      switch (opcode2) {
        case 0x0: case 0x1: case 0x2: case 0x3: {
          // Add low registers  - 010001 0000 xxxxxx
          // Add high registers - 010001 0001/001x xxxxxx
          uint16_t DN = (instr >> 7) & 1;
          uint16_t rm = (instr >> 3) & 0xF;
          uint16_t Rdn = instr & 7;
          uint16_t DN_Rdn = (DN << 3) | Rdn;
          opcode << "add";
          DumpReg(args, DN_Rdn);
          args << ", ";
          DumpReg(args, rm);
          break;
        }
        case 0x8: case 0x9: case 0xA: case 0xB: {
          // Move low registers  - 010001 1000 xxxxxx
          // Move high registers - 010001 1001/101x xxxxxx
          uint16_t DN = (instr >> 7) & 1;
          uint16_t rm = (instr >> 3) & 0xF;
          uint16_t Rdn = instr & 7;
          uint16_t DN_Rdn = (DN << 3) | Rdn;
          opcode << "mov";
          DumpReg(args, DN_Rdn);
          args << ", ";
          DumpReg(args, rm);
          break;
        }
        case 0x5: case 0x6: case 0x7: {
          // Compare high registers - 010001 0101/011x xxxxxx
          uint16_t N = (instr >> 7) & 1;
          uint16_t rm = (instr >> 3) & 0xF;
          uint16_t Rn = instr & 7;
          uint16_t N_Rn = (N << 3) | Rn;
          opcode << "cmp";
          DumpReg(args, N_Rn);
          args << ", ";
          DumpReg(args, rm);
          break;
        }
        case 0xC: case 0xD: case 0xE: case 0xF: {
          // Branch and exchange           - 010001 110x xxxxxx
          // Branch with link and exchange - 010001 111x xxxxxx
          uint16_t rm = instr >> 3 & 0xF;
          if ((opcode2 & 0x2) == 0) {
            opcode << "bx";
          } else {
            opcode << "blx";
          }
          DumpReg(args, rm);
          break;
        }
        default:
          break;
      }
    } else if ((instr & 0xF000) == 0xB000) {
      // Miscellaneous 16-bit instructions
      uint16_t opcode2 = (instr >> 5) & 0x7F;
      switch (opcode2) {
        case 0x00: case 0x01: case 0x02: case 0x03: case 0x04: case 0x05: case 0x06: case 0x07: {
          // Add immediate to SP        - 1011 00000 ii iiiii
          // Subtract immediate from SP - 1011 00001 ii iiiii
          int imm7 = instr & 0x7F;
          if ((opcode2 & 4) == 0) {
            opcode << "add";
          } else {
            opcode << "sub";
          }
          args << "sp, sp, #" << (imm7 << 2);
          break;
        }
        case 0x78: case 0x79: case 0x7A: case 0x7B:  // 1111xxx
        case 0x7C: case 0x7D: case 0x7E: case 0x7F: {
          // If-Then, and hints
          uint16_t opA = (instr >> 4) & 0xF;
          uint16_t opB = instr & 0xF;
          if (opB == 0) {
            switch (opA) {
              case 0: opcode << "nop"; break;
              case 1: opcode << "yield"; break;
              case 2: opcode << "wfe";  break;
              case 3: opcode << "sev"; break;
              default: break;
            }
          } else {
            opcode << "it";
            args << reinterpret_cast<void*>(opB) << " ";
            DumpCond(args, opA);
          }
          break;
        }
        default:
          break;
      }
    } else if (((instr & 0xF000) == 0x5000) || ((instr & 0xE000) == 0x6000) ||
        ((instr & 0xE000) == 0x8000)) {
      // Load/store single data item
      uint16_t opA = instr >> 12;
      //uint16_t opB = (instr >> 9) & 7;
      switch (opA) {
        case 0x6: {
          // STR Rt, Rn, #imm - 01100 iiiii nnn ttt
          // LDR Rt, Rn, #imm - 01101 iiiii nnn ttt
          uint16_t imm5 = (instr >> 6) & 0x1F;
          uint16_t Rn = (instr >> 3) & 7;
          uint16_t Rt = instr & 7;
          if ((instr & 0x800) == 0) {
            opcode << "str";
          } else {
            opcode << "ldr";
          }
          DumpReg(args, Rt);
          args << ", [";
          DumpReg(args, Rn);
          args << ", #" << (imm5 << 2) << "]";
          break;
        }
        case 0x9: {
          // STR Rt, [SP, #imm] - 01100 ttt iiiiiiii
          // LDR Rt, [SP, #imm] - 01101 ttt iiiiiiii
          uint16_t imm8 = instr & 0xFF;
          uint16_t Rt = (instr >> 8) & 7;
          if ((instr & 0x800) == 0) {
            opcode << "str";
          } else {
            opcode << "ldr";
          }
          DumpReg(args, Rt);
          args << ", [sp, #" << (imm8 << 2) << "]";
          break;
        }
        default:
          break;
      }
    } else if (opcode1 == 0x38 || opcode1 == 0x39) {
      uint16_t imm11 = instr & 0x7FFF;
      int32_t imm32 = imm11 << 1;
      imm32 = (imm32 << 20) >> 20;  // sign extend 12 bit immediate
      opcode << "b";
      DumpBranchTarget(args, instr_ptr + 4, imm32);
    }
    os << StringPrintf("\t\t\t%p: %04x    \t%-7s ", instr_ptr, instr, opcode.str().c_str()) << args.str() << '\n';
  }
  return 2;
}

}  // namespace arm
}  // namespace art