path: root/js/src/jit/arm/disasm/Disasm-arm.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 */
// Copyright 2011 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// 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.
//
//   disasm::NameConverter converter;
//   disasm::Disassembler d(converter);
//   for (uint8_t* pc = begin; pc < end;) {
//     disasm::EmbeddedVector<char, disasm::ReasonableBufferSize> buffer;
//     uint8_t* prev_pc = pc;
//     pc += d.InstructionDecode(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 "jit/arm/disasm/Disasm-arm.h"

#ifdef JS_DISASM_ARM

#include <stdarg.h>
#include <stdio.h>
#include <string.h>

#include "jit/arm/disasm/Constants-arm.h"

namespace js {
namespace jit {
namespace disasm {


// Helper function for printing to a Vector.
static int
MOZ_FORMAT_PRINTF(2, 3)
SNPrintF(V8Vector<char> str, const char* format, ...)
{
    va_list args;
    va_start(args, format);
    int result = vsnprintf(str.start(), str.length(), format, args);
    va_end(args);
    return result;
}


//------------------------------------------------------------------------------

// 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,
            V8Vector<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(uint8_t* instruction);

    static bool IsConstantPoolAt(uint8_t* instr_ptr);
    static int ConstantPoolSizeAt(uint8_t* instr_ptr);

  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(Instruction* instr, const char* format);
    void PrintMovwMovt(Instruction* instr);
    int FormatVFPinstruction(Instruction* instr, const char* format);
    void PrintCondition(Instruction* instr);
    void PrintShiftRm(Instruction* instr);
    void PrintShiftImm(Instruction* instr);
    void PrintShiftSat(Instruction* instr);
    void PrintPU(Instruction* instr);
    void PrintSoftwareInterrupt(SoftwareInterruptCodes svc);

    // Handle formatting of instructions and their options.
    int FormatRegister(Instruction* instr, const char* option);
    void FormatNeonList(int Vd, int type);
    void FormatNeonMemory(int Rn, int align, int Rm);
    int FormatOption(Instruction* instr, const char* option);
    void Format(Instruction* instr, const char* format);
    void Unknown(Instruction* 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(Instruction* instr);
    void DecodeType2(Instruction* instr);
    void DecodeType3(Instruction* instr);
    void DecodeType4(Instruction* instr);
    void DecodeType5(Instruction* instr);
    void DecodeType6(Instruction* instr);
    // Type 7 includes special Debugger instructions.
    int DecodeType7(Instruction* instr);
    // For VFP support.
    void DecodeTypeVFP(Instruction* instr);
    void DecodeType6CoprocessorIns(Instruction* instr);

    void DecodeSpecialCondition(Instruction* instr);

    void DecodeVMOVBetweenCoreAndSinglePrecisionRegisters(Instruction* instr);
    void DecodeVCMP(Instruction* instr);
    void DecodeVCVTBetweenDoubleAndSingle(Instruction* instr);
    void DecodeVCVTBetweenFloatingPointAndInteger(Instruction* instr);

    const disasm::NameConverter& converter_;
    V8Vector<char> out_buffer_;
    int out_buffer_pos_;

    // Disallow copy and assign.
    Decoder(const Decoder&) = delete;
    void operator=(const Decoder&) = delete;
};


// 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_ < int(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* const cond_names[kNumberOfConditions] = {
    "eq", "ne", "cs" , "cc" , "mi" , "pl" , "vs" , "vc" ,
    "hi", "ls", "ge", "lt", "gt", "le", "", "invalid",
};


// Print the condition guarding the instruction.
void
Decoder::PrintCondition(Instruction* instr)
{
    Print(cond_names[instr->ConditionValue()]);
}


// 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(VFPRegisters::Name(reg, false));
}


// Print the VFP D register name according to the active name converter.
void
Decoder::PrintDRegister(int reg)
{
    Print(VFPRegisters::Name(reg, true));
}


// 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* const shift_names[kNumberOfShifts] = {
    "lsl", "lsr", "asr", "ror"
};


// Print the register shift operands for the instruction. Generally used for
// data processing instructions.
void
Decoder::PrintShiftRm(Instruction* instr)
{
    ShiftOp shift = instr->ShiftField();
    int shift_index = instr->ShiftValue();
    int shift_amount = instr->ShiftAmountValue();
    int rm = instr->RmValue();

    PrintRegister(rm);

    if ((instr->RegShiftValue() == 0) && (shift == LSL) && (shift_amount == 0)) {
        // Special case for using rm only.
        return;
    }
    if (instr->RegShiftValue() == 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_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                    ", %s #%d",
                                    shift_names[shift_index],
                                    shift_amount);
    } else {
        // by register
        int rs = instr->RsValue();
        out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                    ", %s ", shift_names[shift_index]);
        PrintRegister(rs);
    }
}


static inline uint32_t
RotateRight32(uint32_t value, uint32_t shift)
{
    if (shift == 0) return value;
    return (value >> shift) | (value << (32 - shift));
}


// Print the immediate operand for the instruction. Generally used for data
// processing instructions.
void
Decoder::PrintShiftImm(Instruction* instr)
{
    int rotate = instr->RotateValue() * 2;
    int immed8 = instr->Immed8Value();
    int imm = RotateRight32(immed8, rotate);
    out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_, "#%d", imm);
}


// Print the optional shift and immediate used by saturating instructions.
void
Decoder::PrintShiftSat(Instruction* instr)
{
    int shift = instr->Bits(11, 7);
    if (shift > 0) {
        out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                    ", %s #%d",
                                    shift_names[instr->Bit(6) * 2],
                                    instr->Bits(11, 7));
    }
}


// Print PU formatting to reduce complexity of FormatOption.
void
Decoder::PrintPU(Instruction* instr)
{
    switch (instr->PUField()) {
      case da_x: {
        Print("da");
        break;
      }
      case ia_x: {
        Print("ia");
        break;
      }
      case db_x: {
        Print("db");
        break;
      }
      case ib_x: {
        Print("ib");
        break;
      }
      default: {
        MOZ_CRASH();
        break;
      }
    }
}


// Print SoftwareInterrupt codes. Factoring this out reduces the complexity of
// the FormatOption method.
void
Decoder::PrintSoftwareInterrupt(SoftwareInterruptCodes svc)
{
    switch (svc) {
      case kCallRtRedirected:
        Print("call rt redirected");
        return;
      case kBreakpoint:
        Print("breakpoint");
        return;
      default:
        if (svc >= kStopCode) {
            out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                        "%d - 0x%x",
                                        svc & kStopCodeMask,
                                        svc & kStopCodeMask);
        } else {
            out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                        "%d",
                                        svc);
        }
        return;
    }
}


// Handle all register based formatting in this function to reduce the
// complexity of FormatOption.
int
Decoder::FormatRegister(Instruction* instr, const char* format)
{
    MOZ_ASSERT(format[0] == 'r');
    if (format[1] == 'n') {  // 'rn: Rn register
        int reg = instr->RnValue();
        PrintRegister(reg);
        return 2;
    } else if (format[1] == 'd') {  // 'rd: Rd register
        int reg = instr->RdValue();
        PrintRegister(reg);
        return 2;
    } else if (format[1] == 's') {  // 'rs: Rs register
        int reg = instr->RsValue();
        PrintRegister(reg);
        return 2;
    } else if (format[1] == 'm') {  // 'rm: Rm register
        int reg = instr->RmValue();
        PrintRegister(reg);
        return 2;
    } else if (format[1] == 't') {  // 'rt: Rt register
        int reg = instr->RtValue();
        PrintRegister(reg);
        return 2;
    } else if (format[1] == 'l') {
        // 'rlist: register list for load and store multiple instructions
        MOZ_ASSERT(STRING_STARTS_WITH(format, "rlist"));
        int rlist = instr->RlistValue();
        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;
    }
    MOZ_CRASH();
    return -1;
}


// Handle all VFP register based formatting in this function to reduce the
// complexity of FormatOption.
int
Decoder::FormatVFPRegister(Instruction* instr, const char* format)
{
    MOZ_ASSERT((format[0] == 'S') || (format[0] == 'D'));

    VFPRegPrecision precision =
        format[0] == 'D' ? kDoublePrecision : kSinglePrecision;

    int retval = 2;
    int reg = -1;
    if (format[1] == 'n') {
        reg = instr->VFPNRegValue(precision);
    } else if (format[1] == 'm') {
        reg = instr->VFPMRegValue(precision);
    } else if (format[1] == 'd') {
        if ((instr->TypeValue() == 7) &&
            (instr->Bit(24) == 0x0) &&
            (instr->Bits(11, 9) == 0x5) &&
            (instr->Bit(4) == 0x1)) {
            // vmov.32 has Vd in a different place.
            reg = instr->Bits(19, 16) | (instr->Bit(7) << 4);
        } else {
            reg = instr->VFPDRegValue(precision);
        }

        if (format[2] == '+') {
            int immed8 = instr->Immed8Value();
            if (format[0] == 'S') reg += immed8 - 1;
            if (format[0] == 'D') reg += (immed8 / 2 - 1);
        }
        if (format[2] == '+') retval = 3;
    } else {
        MOZ_CRASH();
    }

    if (precision == kSinglePrecision) {
        PrintSRegister(reg);
    } else {
        PrintDRegister(reg);
    }

    return retval;
}


int
Decoder::FormatVFPinstruction(Instruction* instr, const char* format)
{
    Print(format);
    return 0;
}


void
Decoder::FormatNeonList(int Vd, int type)
{
    if (type == nlt_1) {
        out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                    "{d%d}", Vd);
    } else if (type == nlt_2) {
        out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                    "{d%d, d%d}", Vd, Vd + 1);
    } else if (type == nlt_3) {
        out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                    "{d%d, d%d, d%d}", Vd, Vd + 1, Vd + 2);
    } else if (type == nlt_4) {
        out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                    "{d%d, d%d, d%d, d%d}", Vd, Vd + 1, Vd + 2, Vd + 3);
    }
}


void
Decoder::FormatNeonMemory(int Rn, int align, int Rm)
{
    out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                "[r%d", Rn);
    if (align != 0) {
        out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                    ":%d", (1 << align) << 6);
    }
    if (Rm == 15) {
        Print("]");
    } else if (Rm == 13) {
        Print("]!");
    } else {
        out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                    "], r%d", Rm);
    }
}


// Print the movw or movt instruction.
void
Decoder::PrintMovwMovt(Instruction* instr)
{
    int imm = instr->ImmedMovwMovtValue();
    int rd = instr->RdValue();
    PrintRegister(rd);
    out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_, ", #%d", imm);
}


// 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(Instruction* 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
        MOZ_ASSERT(STRING_STARTS_WITH(format, "cond"));
        PrintCondition(instr);
        return 4;
      }
      case 'd': {  // 'd: vmov double immediate.
        double d = instr->DoubleImmedVmov();
        out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_, "#%g", d);
        return 1;
      }
      case 'f': {  // 'f: bitfield instructions - v7 and above.
        uint32_t lsbit = instr->Bits(11, 7);
        uint32_t width = instr->Bits(20, 16) + 1;
        if (instr->Bit(21) == 0) {
            // BFC/BFI:
            // Bits 20-16 represent most-significant bit. Covert to width.
            width -= lsbit;
            MOZ_ASSERT(width > 0);
        }
        MOZ_ASSERT((width + lsbit) <= 32);
        out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                    "#%d, #%d", lsbit, width);
        return 1;
      }
      case 'h': {  // 'h: halfword operation for extra loads and stores
        if (instr->HasH()) {
            Print("h");
        } else {
            Print("b");
        }
        return 1;
      }
      case 'i': {  // 'i: immediate value from adjacent bits.
        // Expects tokens in the form imm%02d@%02d, i.e. imm05@07, imm10@16
        int width = (format[3] - '0') * 10 + (format[4] - '0');
        int lsb   = (format[6] - '0') * 10 + (format[7] - '0');

        MOZ_ASSERT((width >= 1) && (width <= 32));
        MOZ_ASSERT((lsb >= 0) && (lsb <= 31));
        MOZ_ASSERT((width + lsb) <= 32);

        out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                    "%d",
                                    instr->Bits(width + lsb - 1, lsb));
        return 8;
      }
      case 'l': {  // 'l: branch and link
        if (instr->HasLink()) {
            Print("l");
        }
        return 1;
      }
      case 'm': {
        if (format[1] == 'w') {
            // 'mw: movt/movw instructions.
            PrintMovwMovt(instr);
            return 2;
        }
        if (format[1] == 'e') {  // 'memop: load/store instructions.
            MOZ_ASSERT(STRING_STARTS_WITH(format, "memop"));
            if (instr->HasL()) {
                Print("ldr");
            } else {
                if ((instr->Bits(27, 25) == 0) && (instr->Bit(20) == 0) &&
                    (instr->Bits(7, 6) == 3) && (instr->Bit(4) == 1)) {
                    if (instr->Bit(5) == 1) {
                        Print("strd");
                    } else {
                        Print("ldrd");
                    }
                    return 5;
                }
                Print("str");
            }
            return 5;
        }
        // 'msg: for simulator break instructions
        MOZ_ASSERT(STRING_STARTS_WITH(format, "msg"));
        uint8_t* str =
            reinterpret_cast<uint8_t*>(instr->InstructionBits() & 0x0fffffff);
        out_buffer_pos_ += 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
            MOZ_ASSERT(STRING_STARTS_WITH(format, "off12"));
            out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                        "%d", instr->Offset12Value());
            return 5;
        } else if (format[3] == '0') {
            // 'off0to3and8to19 16-bit immediate encoded in bits 19-8 and 3-0.
            MOZ_ASSERT(STRING_STARTS_WITH(format, "off0to3and8to19"));
            out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                        "%d",
                                        (instr->Bits(19, 8) << 4) +
                                        instr->Bits(3, 0));
            return 15;
        }
        // 'off8: 8-bit offset for extra load and store instructions
        MOZ_ASSERT(STRING_STARTS_WITH(format, "off8"));
        int offs8 = (instr->ImmedHValue() << 4) | instr->ImmedLValue();
        out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_, "%d", offs8);
        return 4;
      }
      case 'p': {  // 'pu: P and U bits for load and store instructions
        MOZ_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 or 'shift_sat.
            if (format[6] == 'o') {  // 'shift_op
                MOZ_ASSERT(STRING_STARTS_WITH(format, "shift_op"));
                if (instr->TypeValue() == 0) {
                    PrintShiftRm(instr);
                } else {
                    MOZ_ASSERT(instr->TypeValue() == 1);
                    PrintShiftImm(instr);
                }
                return 8;
            } else if (format[6] == 's') {  // 'shift_sat.
                MOZ_ASSERT(STRING_STARTS_WITH(format, "shift_sat"));
                PrintShiftSat(instr);
                return 9;
            } else {  // 'shift_rm
                MOZ_ASSERT(STRING_STARTS_WITH(format, "shift_rm"));
                PrintShiftRm(instr);
                return 8;
            }
        } else if (format[1] == 'v') {  // 'svc
            MOZ_ASSERT(STRING_STARTS_WITH(format, "svc"));
            PrintSoftwareInterrupt(instr->SvcValue());
            return 3;
        } else if (format[1] == 'i') {  // 'sign: signed extra loads and stores
            MOZ_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
        MOZ_ASSERT(STRING_STARTS_WITH(format, "target"));
        int off = (instr->SImmed24Value() << 2) + 8;
        out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                    "%+d -> %s",
                                    off,
                                    converter_.NameOfAddress(
                                        reinterpret_cast<uint8_t*>(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: {
        MOZ_CRASH();
        break;
      }
    }
    MOZ_CRASH();
    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(Instruction* 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';
}


// The disassembler may end up decoding data inlined in the code. We do not want
// it to crash if the data does not ressemble any known instruction.
#define VERIFY(condition) \
    if(!(condition)) {    \
        Unknown(instr);   \
        return;           \
    }


// For currently unimplemented decodings the disassembler calls Unknown(instr)
// which will just print "unknown" of the instruction bits.
void
Decoder::Unknown(Instruction* instr)
{
    Format(instr, "unknown");
}


void
Decoder::DecodeType01(Instruction* instr)
{
    int type = instr->TypeValue();
    if ((type == 0) && instr->IsSpecialType0()) {
        // multiply instruction or extra loads and stores
        if (instr->Bits(7, 4) == 9) {
            if (instr->Bit(24) == 0) {
                // 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 {
                        if (instr->Bit(22) == 0) {
                            // The MLA instruction description (A 4.1.28) refers to the order
                            // of registers as "Rd, Rm, Rs, Rn". But confusingly it uses the
                            // Rn field to encode the Rd register and the Rd field to encode
                            // the Rn register.
                            Format(instr, "mla'cond's 'rn, 'rm, 'rs, 'rd");
                        } else {
                            // The MLS instruction description (A 4.1.29) 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, "mls'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 {
                if (instr->Bits(ExclusiveOpHi, ExclusiveOpLo) == ExclusiveOpcode) {
                    if (instr->Bit(ExclusiveLoad) == 1) {
                        switch (instr->Bits(ExclusiveSizeHi, ExclusiveSizeLo)) {
                          case ExclusiveWord:
                            Format(instr, "ldrex'cond 'rt, ['rn]");
                            break;
                          case ExclusiveDouble:
                            Format(instr, "ldrexd'cond 'rt, ['rn]");
                            break;
                          case ExclusiveByte:
                            Format(instr, "ldrexb'cond 'rt, ['rn]");
                            break;
                          case ExclusiveHalf:
                            Format(instr, "ldrexh'cond 'rt, ['rn]");
                            break;
                        }
                    } else {
                        // The documentation names the low four bits of the
                        // store-exclusive instructions "Rt" but canonically
                        // for disassembly they are really "Rm".
                        switch (instr->Bits(ExclusiveSizeHi, ExclusiveSizeLo)) {
                          case ExclusiveWord:
                            Format(instr, "strex'cond 'rd, 'rm, ['rn]");
                            break;
                          case ExclusiveDouble:
                            Format(instr, "strexd'cond 'rd, 'rm, ['rn]");
                            break;
                          case ExclusiveByte:
                            Format(instr, "strexb'cond 'rd, 'rm, ['rn]");
                            break;
                          case ExclusiveHalf:
                            Format(instr, "strexh'cond 'rd, 'rm, ['rn]");
                            break;
                        }
                    }
                } else {
                    Unknown(instr);
                }
            }
        } else if ((instr->Bit(20) == 0) && ((instr->Bits(7, 4) & 0xd) == 0xd)) {
            // ldrd, strd
            switch (instr->PUField()) {
              case da_x: {
                if (instr->Bit(22) == 0) {
                    Format(instr, "'memop'cond's 'rd, ['rn], -'rm");
                } else {
                    Format(instr, "'memop'cond's 'rd, ['rn], #-'off8");
                }
                break;
              }
              case ia_x: {
                if (instr->Bit(22) == 0) {
                    Format(instr, "'memop'cond's 'rd, ['rn], +'rm");
                } else {
                    Format(instr, "'memop'cond's 'rd, ['rn], #+'off8");
                }
                break;
              }
              case db_x: {
                if (instr->Bit(22) == 0) {
                    Format(instr, "'memop'cond's 'rd, ['rn, -'rm]'w");
                } else {
                    Format(instr, "'memop'cond's 'rd, ['rn, #-'off8]'w");
                }
                break;
              }
              case ib_x: {
                if (instr->Bit(22) == 0) {
                    Format(instr, "'memop'cond's 'rd, ['rn, +'rm]'w");
                } else {
                    Format(instr, "'memop'cond's 'rd, ['rn, #+'off8]'w");
                }
                break;
              }
              default: {
                // The PU field is a 2-bit field.
                MOZ_CRASH();
                break;
              }
            }
        } else {
            // extra load/store instructions
            switch (instr->PUField()) {
              case da_x: {
                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 ia_x: {
                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 db_x: {
                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 ib_x: {
                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.
                MOZ_CRASH();
                break;
              }
            }
            return;
        }
    } else if ((type == 0) && instr->IsMiscType0()) {
        if (instr->Bits(22, 21) == 1) {
            switch (instr->BitField(7, 4)) {
              case BX:
                Format(instr, "bx'cond 'rm");
                break;
              case BLX:
                Format(instr, "blx'cond 'rm");
                break;
              case BKPT:
                Format(instr, "bkpt 'off0to3and8to19");
                break;
              default:
                Unknown(instr);  // not used by V8
                break;
            }
        } else if (instr->Bits(22, 21) == 3) {
            switch (instr->BitField(7, 4)) {
              case CLZ:
                Format(instr, "clz'cond 'rd, 'rm");
                break;
              default:
                Unknown(instr);  // not used by V8
                break;
            }
        } else {
            Unknown(instr);  // not used by V8
        }
    } else if ((type == 1) && instr->IsNopType1()) {
        Format(instr, "nop'cond");
    } 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 {
                Format(instr, "movw'cond 'mw");
            }
            break;
          }
          case TEQ: {
            if (instr->HasS()) {
                Format(instr, "teq'cond 'rn, 'shift_op");
            } else {
                // Other instructions matching this pattern are handled in the
                // miscellaneous instructions part above.
                MOZ_CRASH();
            }
            break;
          }
          case CMP: {
            if (instr->HasS()) {
                Format(instr, "cmp'cond 'rn, 'shift_op");
            } else {
                Format(instr, "movt'cond 'mw");
            }
            break;
          }
          case CMN: {
            if (instr->HasS()) {
                Format(instr, "cmn'cond 'rn, 'shift_op");
            } else {
                // Other instructions matching this pattern are handled in the
                // miscellaneous instructions part above.
                MOZ_CRASH();
            }
            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.
            MOZ_CRASH();
            break;
          }
        }
    }
}


void
Decoder::DecodeType2(Instruction* instr)
{
    switch (instr->PUField()) {
      case da_x: {
        if (instr->HasW()) {
            Unknown(instr);  // not used in V8
            return;
        }
        Format(instr, "'memop'cond'b 'rd, ['rn], #-'off12");
        break;
      }
      case ia_x: {
          if (instr->HasW()) {
            Unknown(instr);  // not used in V8
            return;
        }
        Format(instr, "'memop'cond'b 'rd, ['rn], #+'off12");
        break;
      }
      case db_x: {
        Format(instr, "'memop'cond'b 'rd, ['rn, #-'off12]'w");
        break;
      }
      case ib_x: {
        Format(instr, "'memop'cond'b 'rd, ['rn, #+'off12]'w");
        break;
      }
      default: {
        // The PU field is a 2-bit field.
        MOZ_CRASH();
        break;
      }
    }
}


void
Decoder::DecodeType3(Instruction* instr)
{
    switch (instr->PUField()) {
      case da_x: {
        VERIFY(!instr->HasW());
        Format(instr, "'memop'cond'b 'rd, ['rn], -'shift_rm");
        break;
      }
      case ia_x: {
        if (instr->Bit(4) == 0) {
            Format(instr, "'memop'cond'b 'rd, ['rn], +'shift_rm");
        } else {
            if (instr->Bit(5) == 0) {
                switch (instr->Bits(22, 21)) {
                  case 0:
                    if (instr->Bit(20) == 0) {
                        if (instr->Bit(6) == 0) {
                            Format(instr, "pkhbt'cond 'rd, 'rn, 'rm, lsl #'imm05@07");
                        } else {
                            if (instr->Bits(11, 7) == 0) {
                                Format(instr, "pkhtb'cond 'rd, 'rn, 'rm, asr #32");
                            } else {
                                Format(instr, "pkhtb'cond 'rd, 'rn, 'rm, asr #'imm05@07");
                            }
                        }
                    } else {
                        MOZ_CRASH();
                    }
                    break;
                  case 1:
                    MOZ_CRASH();
                    break;
                  case 2:
                    MOZ_CRASH();
                    break;
                  case 3:
                    Format(instr, "usat 'rd, #'imm05@16, 'rm'shift_sat");
                    break;
                }
            } else {
                switch (instr->Bits(22, 21)) {
                  case 0:
                    MOZ_CRASH();
                    break;
                  case 1:
                    if (instr->Bits(9, 6) == 1) {
                        if (instr->Bit(20) == 0) {
                            if (instr->Bits(19, 16) == 0xF) {
                                switch (instr->Bits(11, 10)) {
                                  case 0:
                                    Format(instr, "sxtb'cond 'rd, 'rm");
                                    break;
                                  case 1:
                                    Format(instr, "sxtb'cond 'rd, 'rm, ror #8");
                                    break;
                                  case 2:
                                    Format(instr, "sxtb'cond 'rd, 'rm, ror #16");
                                    break;
                                  case 3:
                                    Format(instr, "sxtb'cond 'rd, 'rm, ror #24");
                                    break;
                                }
                            } else {
                                switch (instr->Bits(11, 10)) {
                                  case 0:
                                    Format(instr, "sxtab'cond 'rd, 'rn, 'rm");
                                    break;
                                  case 1:
                                    Format(instr, "sxtab'cond 'rd, 'rn, 'rm, ror #8");
                                    break;
                                  case 2:
                                    Format(instr, "sxtab'cond 'rd, 'rn, 'rm, ror #16");
                                    break;
                                  case 3:
                                    Format(instr, "sxtab'cond 'rd, 'rn, 'rm, ror #24");
                                    break;
                                }
                            }
                        } else {
                            if (instr->Bits(19, 16) == 0xF) {
                                switch (instr->Bits(11, 10)) {
                                  case 0:
                                    Format(instr, "sxth'cond 'rd, 'rm");
                                    break;
                                  case 1:
                                    Format(instr, "sxth'cond 'rd, 'rm, ror #8");
                                    break;
                                  case 2:
                                    Format(instr, "sxth'cond 'rd, 'rm, ror #16");
                                    break;
                                  case 3:
                                    Format(instr, "sxth'cond 'rd, 'rm, ror #24");
                                    break;
                                }
                            } else {
                                switch (instr->Bits(11, 10)) {
                                  case 0:
                                    Format(instr, "sxtah'cond 'rd, 'rn, 'rm");
                                    break;
                                  case 1:
                                    Format(instr, "sxtah'cond 'rd, 'rn, 'rm, ror #8");
                                    break;
                                  case 2:
                                    Format(instr, "sxtah'cond 'rd, 'rn, 'rm, ror #16");
                                    break;
                                  case 3:
                                    Format(instr, "sxtah'cond 'rd, 'rn, 'rm, ror #24");
                                    break;
                                }
                            }
                        }
                    } else {
                        MOZ_CRASH();
                    }
                    break;
                  case 2:
                    if ((instr->Bit(20) == 0) && (instr->Bits(9, 6) == 1)) {
                        if (instr->Bits(19, 16) == 0xF) {
                            switch (instr->Bits(11, 10)) {
                              case 0:
                                Format(instr, "uxtb16'cond 'rd, 'rm");
                                break;
                              case 1:
                                Format(instr, "uxtb16'cond 'rd, 'rm, ror #8");
                                break;
                              case 2:
                                Format(instr, "uxtb16'cond 'rd, 'rm, ror #16");
                                break;
                              case 3:
                                Format(instr, "uxtb16'cond 'rd, 'rm, ror #24");
                                break;
                            }
                        } else {
                            MOZ_CRASH();
                        }
                    } else {
                        MOZ_CRASH();
                    }
                    break;
                  case 3:
                    if ((instr->Bits(9, 6) == 1)) {
                        if ((instr->Bit(20) == 0)) {
                            if (instr->Bits(19, 16) == 0xF) {
                                switch (instr->Bits(11, 10)) {
                                  case 0:
                                    Format(instr, "uxtb'cond 'rd, 'rm");
                                    break;
                                  case 1:
                                    Format(instr, "uxtb'cond 'rd, 'rm, ror #8");
                                    break;
                                  case 2:
                                    Format(instr, "uxtb'cond 'rd, 'rm, ror #16");
                                    break;
                                  case 3:
                                    Format(instr, "uxtb'cond 'rd, 'rm, ror #24");
                                    break;
                                }
                            } else {
                                switch (instr->Bits(11, 10)) {
                                  case 0:
                                    Format(instr, "uxtab'cond 'rd, 'rn, 'rm");
                                    break;
                                  case 1:
                                    Format(instr, "uxtab'cond 'rd, 'rn, 'rm, ror #8");
                                    break;
                                  case 2:
                                    Format(instr, "uxtab'cond 'rd, 'rn, 'rm, ror #16");
                                    break;
                                  case 3:
                                    Format(instr, "uxtab'cond 'rd, 'rn, 'rm, ror #24");
                                    break;
                                }
                            }
                        } else {
                            if (instr->Bits(19, 16) == 0xF) {
                                switch (instr->Bits(11, 10)) {
                                  case 0:
                                    Format(instr, "uxth'cond 'rd, 'rm");
                                    break;
                                  case 1:
                                    Format(instr, "uxth'cond 'rd, 'rm, ror #8");
                                    break;
                                  case 2:
                                    Format(instr, "uxth'cond 'rd, 'rm, ror #16");
                                    break;
                                  case 3:
                                    Format(instr, "uxth'cond 'rd, 'rm, ror #24");
                                    break;
                                }
                            } else {
                                switch (instr->Bits(11, 10)) {
                                  case 0:
                                    Format(instr, "uxtah'cond 'rd, 'rn, 'rm");
                                    break;
                                  case 1:
                                    Format(instr, "uxtah'cond 'rd, 'rn, 'rm, ror #8");
                                    break;
                                  case 2:
                                    Format(instr, "uxtah'cond 'rd, 'rn, 'rm, ror #16");
                                    break;
                                  case 3:
                                    Format(instr, "uxtah'cond 'rd, 'rn, 'rm, ror #24");
                                    break;
                                }
                            }
                        }
                    } else {
                        MOZ_CRASH();
                    }
                    break;
                }
            }
        }
        break;
      }
      case db_x: {
        if (instr->Bits(22, 20) == 0x5) {
            if (instr->Bits(7, 4) == 0x1) {
                if (instr->Bits(15, 12) == 0xF) {
                    Format(instr, "smmul'cond 'rn, 'rm, 'rs");
                } else {
                    // SMMLA (in V8 notation matching ARM ISA format)
                    Format(instr, "smmla'cond 'rn, 'rm, 'rs, 'rd");
                }
                break;
            }
        }
        bool FLAG_enable_sudiv = true; // Flag doesn't exist in our engine.
        if (FLAG_enable_sudiv) {
            if (instr->Bits(5, 4) == 0x1) {
                if ((instr->Bit(22) == 0x0) && (instr->Bit(20) == 0x1)) {
                    if (instr->Bit(21) == 0x1) {
                        // UDIV (in V8 notation matching ARM ISA format) rn = rm/rs
                        Format(instr, "udiv'cond'b 'rn, 'rm, 'rs");
                    } else {
                        // SDIV (in V8 notation matching ARM ISA format) rn = rm/rs
                        Format(instr, "sdiv'cond'b 'rn, 'rm, 'rs");
                    }
                    break;
                }
            }
        }
        Format(instr, "'memop'cond'b 'rd, ['rn, -'shift_rm]'w");
        break;
      }
      case ib_x: {
        if (instr->HasW() && (instr->Bits(6, 4) == 0x5)) {
            uint32_t widthminus1 = static_cast<uint32_t>(instr->Bits(20, 16));
            uint32_t lsbit = static_cast<uint32_t>(instr->Bits(11, 7));
            uint32_t msbit = widthminus1 + lsbit;
            if (msbit <= 31) {
                if (instr->Bit(22)) {
                    Format(instr, "ubfx'cond 'rd, 'rm, 'f");
                } else {
                    Format(instr, "sbfx'cond 'rd, 'rm, 'f");
                }
            } else {
                MOZ_CRASH();
            }
        } else if (!instr->HasW() && (instr->Bits(6, 4) == 0x1)) {
            uint32_t lsbit = static_cast<uint32_t>(instr->Bits(11, 7));
            uint32_t msbit = static_cast<uint32_t>(instr->Bits(20, 16));
            if (msbit >= lsbit) {
                if (instr->RmValue() == 15) {
                    Format(instr, "bfc'cond 'rd, 'f");
                } else {
                    Format(instr, "bfi'cond 'rd, 'rm, 'f");
                }
            } else {
                MOZ_CRASH();
            }
        } else {
            Format(instr, "'memop'cond'b 'rd, ['rn, +'shift_rm]'w");
        }
        break;
      }
      default: {
        // The PU field is a 2-bit field.
        MOZ_CRASH();
        break;
      }
    }
}


void
Decoder::DecodeType4(Instruction* instr)
{
    if (instr->Bit(22) != 0) {
        // Privileged mode currently not supported.
        Unknown(instr);
    } else {
        if (instr->HasL()) {
            Format(instr, "ldm'cond'pu 'rn'w, 'rlist");
        } else {
            Format(instr, "stm'cond'pu 'rn'w, 'rlist");
        }
    }
}


void
Decoder::DecodeType5(Instruction* instr)
{
    Format(instr, "b'l'cond 'target");
}


void
Decoder::DecodeType6(Instruction* instr)
{
    DecodeType6CoprocessorIns(instr);
}


int
Decoder::DecodeType7(Instruction* instr)
{
    if (instr->Bit(24) == 1) {
        if (instr->SvcValue() >= kStopCode) {
            Format(instr, "stop'cond 'svc");
            // Also print the stop message. Its address is encoded
            // in the following 4 bytes.
            out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                        "\n  %p  %08x       stop message: %s",
                                        reinterpret_cast<void*>(instr
                                                                + Instruction::kInstrSize),
                                        *reinterpret_cast<uint32_t*>(instr
                                                                     + Instruction::kInstrSize),
                                        *reinterpret_cast<char**>(instr
                                                                  + Instruction::kInstrSize));
            // We have decoded 2 * Instruction::kInstrSize bytes.
            return 2 * Instruction::kInstrSize;
        } else {
            Format(instr, "svc'cond 'svc");
        }
    } else {
        DecodeTypeVFP(instr);
    }
    return Instruction::kInstrSize;
}


// void Decoder::DecodeTypeVFP(Instruction* instr)
// vmov: Sn = Rt
// vmov: Rt = Sn
// vcvt: Dd = Sm
// vcvt: Sd = Dm
// vcvt.f64.s32 Dd, Dd, #<fbits>
// Dd = vabs(Dm)
// Sd = vabs(Sm)
// Dd = vneg(Dm)
// Sd = vneg(Sm)
// Dd = vadd(Dn, Dm)
// Sd = vadd(Sn, Sm)
// Dd = vsub(Dn, Dm)
// Sd = vsub(Sn, Sm)
// Dd = vmul(Dn, Dm)
// Sd = vmul(Sn, Sm)
// Dd = vmla(Dn, Dm)
// Sd = vmla(Sn, Sm)
// Dd = vmls(Dn, Dm)
// Sd = vmls(Sn, Sm)
// Dd = vdiv(Dn, Dm)
// Sd = vdiv(Sn, Sm)
// vcmp(Dd, Dm)
// vcmp(Sd, Sm)
// Dd = vsqrt(Dm)
// Sd = vsqrt(Sm)
// vmrs
// vmsr
void
Decoder::DecodeTypeVFP(Instruction* instr)
{
    VERIFY((instr->TypeValue() == 7) && (instr->Bit(24) == 0x0) );
    VERIFY(instr->Bits(11, 9) == 0x5);

    if (instr->Bit(4) == 0) {
        if (instr->Opc1Value() == 0x7) {
            // Other data processing instructions
            if ((instr->Opc2Value() == 0x0) && (instr->Opc3Value() == 0x1)) {
                // vmov register to register.
                if (instr->SzValue() == 0x1) {
                    Format(instr, "vmov'cond.f64 'Dd, 'Dm");
                } else {
                    Format(instr, "vmov'cond.f32 'Sd, 'Sm");
                }
            } else if ((instr->Opc2Value() == 0x0) && (instr->Opc3Value() == 0x3)) {
                // vabs
                if (instr->SzValue() == 0x1) {
                    Format(instr, "vabs'cond.f64 'Dd, 'Dm");
                } else {
                    Format(instr, "vabs'cond.f32 'Sd, 'Sm");
                }
            } else if ((instr->Opc2Value() == 0x1) && (instr->Opc3Value() == 0x1)) {
                // vneg
                if (instr->SzValue() == 0x1) {
                    Format(instr, "vneg'cond.f64 'Dd, 'Dm");
                } else {
                    Format(instr, "vneg'cond.f32 'Sd, 'Sm");
                }
            } else if ((instr->Opc2Value() == 0x7) && (instr->Opc3Value() == 0x3)) {
                DecodeVCVTBetweenDoubleAndSingle(instr);
            } else if ((instr->Opc2Value() == 0x8) && (instr->Opc3Value() & 0x1)) {
                DecodeVCVTBetweenFloatingPointAndInteger(instr);
            } else if ((instr->Opc2Value() == 0xA) && (instr->Opc3Value() == 0x3) &&
                       (instr->Bit(8) == 1)) {
                // vcvt.f64.s32 Dd, Dd, #<fbits>
                int fraction_bits = 32 - ((instr->Bits(3, 0) << 1) | instr->Bit(5));
                Format(instr, "vcvt'cond.f64.s32 'Dd, 'Dd");
                out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                            ", #%d", fraction_bits);
            } else if (((instr->Opc2Value() >> 1) == 0x6) &&
                       (instr->Opc3Value() & 0x1)) {
                DecodeVCVTBetweenFloatingPointAndInteger(instr);
            } else if (((instr->Opc2Value() == 0x4) || (instr->Opc2Value() == 0x5)) &&
                       (instr->Opc3Value() & 0x1)) {
                DecodeVCMP(instr);
            } else if (((instr->Opc2Value() == 0x1)) && (instr->Opc3Value() == 0x3)) {
                if (instr->SzValue() == 0x1) {
                    Format(instr, "vsqrt'cond.f64 'Dd, 'Dm");
                } else {
                    Format(instr, "vsqrt'cond.f32 'Sd, 'Sm");
                }
            } else if (instr->Opc3Value() == 0x0) {
                if (instr->SzValue() == 0x1) {
                    Format(instr, "vmov'cond.f64 'Dd, 'd");
                } else {
                    Unknown(instr);  // Not used by V8.
                }
            } else if (((instr->Opc2Value() == 0x6)) && instr->Opc3Value() == 0x3) {
                // vrintz - round towards zero (truncate)
                if (instr->SzValue() == 0x1) {
                    Format(instr, "vrintz'cond.f64.f64 'Dd, 'Dm");
                } else {
                    Format(instr, "vrintz'cond.f32.f32 'Sd, 'Sm");
                }
            } else {
                Unknown(instr);  // Not used by V8.
            }
        } else if (instr->Opc1Value() == 0x3) {
            if (instr->SzValue() == 0x1) {
                if (instr->Opc3Value() & 0x1) {
                    Format(instr, "vsub'cond.f64 'Dd, 'Dn, 'Dm");
                } else {
                    Format(instr, "vadd'cond.f64 'Dd, 'Dn, 'Dm");
                }
            } else {
                if (instr->Opc3Value() & 0x1) {
                    Format(instr, "vsub'cond.f32 'Sd, 'Sn, 'Sm");
                } else {
                    Format(instr, "vadd'cond.f32 'Sd, 'Sn, 'Sm");
                }
            }
        } else if ((instr->Opc1Value() == 0x2) && !(instr->Opc3Value() & 0x1)) {
            if (instr->SzValue() == 0x1) {
                Format(instr, "vmul'cond.f64 'Dd, 'Dn, 'Dm");
            } else {
                Format(instr, "vmul'cond.f32 'Sd, 'Sn, 'Sm");
            }
        } else if ((instr->Opc1Value() == 0x0) && !(instr->Opc3Value() & 0x1)) {
            if (instr->SzValue() == 0x1) {
                Format(instr, "vmla'cond.f64 'Dd, 'Dn, 'Dm");
            } else {
                Format(instr, "vmla'cond.f32 'Sd, 'Sn, 'Sm");
            }
        } else if ((instr->Opc1Value() == 0x0) && (instr->Opc3Value() & 0x1)) {
            if (instr->SzValue() == 0x1) {
                Format(instr, "vmls'cond.f64 'Dd, 'Dn, 'Dm");
            } else {
                Format(instr, "vmls'cond.f32 'Sd, 'Sn, 'Sm");
            }
        } else if ((instr->Opc1Value() == 0x4) && !(instr->Opc3Value() & 0x1)) {
            if (instr->SzValue() == 0x1) {
                Format(instr, "vdiv'cond.f64 'Dd, 'Dn, 'Dm");
            } else {
                Format(instr, "vdiv'cond.f32 'Sd, 'Sn, 'Sm");
            }
        } else {
            Unknown(instr);  // Not used by V8.
        }
    } else {
        if ((instr->VCValue() == 0x0) &&
            (instr->VAValue() == 0x0)) {
            DecodeVMOVBetweenCoreAndSinglePrecisionRegisters(instr);
        } else if ((instr->VLValue() == 0x0) &&
                   (instr->VCValue() == 0x1) &&
                   (instr->Bit(23) == 0x0)) {
            if (instr->Bit(21) == 0x0) {
                Format(instr, "vmov'cond.32 'Dd[0], 'rt");
            } else {
                Format(instr, "vmov'cond.32 'Dd[1], 'rt");
            }
        } else if ((instr->VLValue() == 0x1) &&
                   (instr->VCValue() == 0x1) &&
                   (instr->Bit(23) == 0x0)) {
            if (instr->Bit(21) == 0x0) {
                Format(instr, "vmov'cond.32 'rt, 'Dd[0]");
            } else {
                Format(instr, "vmov'cond.32 'rt, 'Dd[1]");
            }
        } else if ((instr->VCValue() == 0x0) &&
                   (instr->VAValue() == 0x7) &&
                   (instr->Bits(19, 16) == 0x1)) {
            if (instr->VLValue() == 0) {
                if (instr->Bits(15, 12) == 0xF) {
                    Format(instr, "vmsr'cond FPSCR, APSR");
                } else {
                    Format(instr, "vmsr'cond FPSCR, 'rt");
                }
            } else {
                if (instr->Bits(15, 12) == 0xF) {
                    Format(instr, "vmrs'cond APSR, FPSCR");
                } else {
                    Format(instr, "vmrs'cond 'rt, FPSCR");
                }
            }
        }
    }
}


void
Decoder::DecodeVMOVBetweenCoreAndSinglePrecisionRegisters(Instruction* instr)
{
    VERIFY((instr->Bit(4) == 1) && (instr->VCValue() == 0x0) &&
           (instr->VAValue() == 0x0));

    bool to_arm_register = (instr->VLValue() == 0x1);

    if (to_arm_register) {
        Format(instr, "vmov'cond 'rt, 'Sn");
    } else {
        Format(instr, "vmov'cond 'Sn, 'rt");
    }
}


void
Decoder::DecodeVCMP(Instruction* instr)
{
    VERIFY((instr->Bit(4) == 0) && (instr->Opc1Value() == 0x7));
    VERIFY(((instr->Opc2Value() == 0x4) || (instr->Opc2Value() == 0x5)) &&
           (instr->Opc3Value() & 0x1));

    // Comparison.
    bool dp_operation = (instr->SzValue() == 1);
    bool raise_exception_for_qnan = (instr->Bit(7) == 0x1);

    if (dp_operation && !raise_exception_for_qnan) {
        if (instr->Opc2Value() == 0x4) {
            Format(instr, "vcmp'cond.f64 'Dd, 'Dm");
        } else if (instr->Opc2Value() == 0x5) {
            Format(instr, "vcmp'cond.f64 'Dd, #0.0");
        } else {
            Unknown(instr);  // invalid
        }
    } else if (!raise_exception_for_qnan) {
        if (instr->Opc2Value() == 0x4) {
            Format(instr, "vcmp'cond.f32 'Sd, 'Sm");
        } else if (instr->Opc2Value() == 0x5) {
            Format(instr, "vcmp'cond.f32 'Sd, #0.0");
        } else {
            Unknown(instr);  // invalid
        }
    } else {
        Unknown(instr);  // Not used by V8.
    }
}


void
Decoder::DecodeVCVTBetweenDoubleAndSingle(Instruction* instr)
{
    VERIFY((instr->Bit(4) == 0) && (instr->Opc1Value() == 0x7));
    VERIFY((instr->Opc2Value() == 0x7) && (instr->Opc3Value() == 0x3));

    bool double_to_single = (instr->SzValue() == 1);

    if (double_to_single) {
        Format(instr, "vcvt'cond.f32.f64 'Sd, 'Dm");
    } else {
        Format(instr, "vcvt'cond.f64.f32 'Dd, 'Sm");
    }
}


void
Decoder::DecodeVCVTBetweenFloatingPointAndInteger(Instruction* instr)
{
    VERIFY((instr->Bit(4) == 0) && (instr->Opc1Value() == 0x7));
    VERIFY(((instr->Opc2Value() == 0x8) && (instr->Opc3Value() & 0x1)) ||
           (((instr->Opc2Value() >> 1) == 0x6) && (instr->Opc3Value() & 0x1)));

    bool to_integer = (instr->Bit(18) == 1);
    bool dp_operation = (instr->SzValue() == 1);
    if (to_integer) {
        bool unsigned_integer = (instr->Bit(16) == 0);

        if (dp_operation) {
            if (unsigned_integer) {
                Format(instr, "vcvt'cond.u32.f64 'Sd, 'Dm");
            } else {
                Format(instr, "vcvt'cond.s32.f64 'Sd, 'Dm");
            }
        } else {
            if (unsigned_integer) {
                Format(instr, "vcvt'cond.u32.f32 'Sd, 'Sm");
            } else {
                Format(instr, "vcvt'cond.s32.f32 'Sd, 'Sm");
            }
        }
    } else {
        bool unsigned_integer = (instr->Bit(7) == 0);

        if (dp_operation) {
            if (unsigned_integer) {
                Format(instr, "vcvt'cond.f64.u32 'Dd, 'Sm");
            } else {
                Format(instr, "vcvt'cond.f64.s32 'Dd, 'Sm");
            }
        } else {
            if (unsigned_integer) {
                Format(instr, "vcvt'cond.f32.u32 'Sd, 'Sm");
            } else {
                Format(instr, "vcvt'cond.f32.s32 'Sd, 'Sm");
            }
        }
    }
}


// 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(Instruction* instr)
{
    VERIFY(instr->TypeValue() == 6);

    if (instr->CoprocessorValue() == 0xA) {
        switch (instr->OpcodeValue()) {
          case 0x8:
          case 0xA:
            if (instr->HasL()) {
                Format(instr, "vldr'cond 'Sd, ['rn - 4*'imm08@00]");
            } else {
                Format(instr, "vstr'cond 'Sd, ['rn - 4*'imm08@00]");
            }
            break;
          case 0xC:
          case 0xE:
            if (instr->HasL()) {
                Format(instr, "vldr'cond 'Sd, ['rn + 4*'imm08@00]");
            } else {
                Format(instr, "vstr'cond 'Sd, ['rn + 4*'imm08@00]");
            }
            break;
          case 0x4:
          case 0x5:
          case 0x6:
          case 0x7:
          case 0x9:
          case 0xB: {
            bool to_vfp_register = (instr->VLValue() == 0x1);
            if (to_vfp_register) {
                Format(instr, "vldm'cond'pu 'rn'w, {'Sd-'Sd+}");
            } else {
                Format(instr, "vstm'cond'pu 'rn'w, {'Sd-'Sd+}");
            }
            break;
          }
          default:
            Unknown(instr);  // Not used by V8.
        }
    } else if (instr->CoprocessorValue() == 0xB) {
        switch (instr->OpcodeValue()) {
          case 0x2:
            // Load and store double to two GP registers
            if (instr->Bits(7, 6) != 0 || instr->Bit(4) != 1) {
                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:
          case 0xA:
            if (instr->HasL()) {
                Format(instr, "vldr'cond 'Dd, ['rn - 4*'imm08@00]");
            } else {
                Format(instr, "vstr'cond 'Dd, ['rn - 4*'imm08@00]");
            }
            break;
          case 0xC:
          case 0xE:
            if (instr->HasL()) {
                Format(instr, "vldr'cond 'Dd, ['rn + 4*'imm08@00]");
            } else {
                Format(instr, "vstr'cond 'Dd, ['rn + 4*'imm08@00]");
            }
            break;
          case 0x4:
          case 0x5:
          case 0x6:
          case 0x7:
          case 0x9:
          case 0xB: {
            bool to_vfp_register = (instr->VLValue() == 0x1);
            if (to_vfp_register) {
                Format(instr, "vldm'cond'pu 'rn'w, {'Dd-'Dd+}");
            } else {
                Format(instr, "vstm'cond'pu 'rn'w, {'Dd-'Dd+}");
            }
            break;
          }
          default:
            Unknown(instr);  // Not used by V8.
        }
    } else {
        Unknown(instr);  // Not used by V8.
    }
}


void
Decoder::DecodeSpecialCondition(Instruction* instr)
{
    switch (instr->SpecialValue()) {
      case 5:
        if ((instr->Bits(18, 16) == 0) && (instr->Bits(11, 6) == 0x28) &&
            (instr->Bit(4) == 1)) {
            // vmovl signed
            if ((instr->VdValue() & 1) != 0) Unknown(instr);
            int Vd = (instr->Bit(22) << 3) | (instr->VdValue() >> 1);
            int Vm = (instr->Bit(5) << 4) | instr->VmValue();
            int imm3 = instr->Bits(21, 19);
            out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                        "vmovl.s%d q%d, d%d", imm3*8, Vd, Vm);
        } else {
            Unknown(instr);
        }
        break;
      case 7:
        if ((instr->Bits(18, 16) == 0) && (instr->Bits(11, 6) == 0x28) &&
            (instr->Bit(4) == 1)) {
            // vmovl unsigned
            if ((instr->VdValue() & 1) != 0) Unknown(instr);
            int Vd = (instr->Bit(22) << 3) | (instr->VdValue() >> 1);
            int Vm = (instr->Bit(5) << 4) | instr->VmValue();
            int imm3 = instr->Bits(21, 19);
            out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                        "vmovl.u%d q%d, d%d", imm3*8, Vd, Vm);
        } else {
            Unknown(instr);
        }
        break;
      case 8:
        if (instr->Bits(21, 20) == 0) {
            // vst1
            int Vd = (instr->Bit(22) << 4) | instr->VdValue();
            int Rn = instr->VnValue();
            int type = instr->Bits(11, 8);
            int size = instr->Bits(7, 6);
            int align = instr->Bits(5, 4);
            int Rm = instr->VmValue();
            out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                        "vst1.%d ", (1 << size) << 3);
            FormatNeonList(Vd, type);
            Print(", ");
            FormatNeonMemory(Rn, align, Rm);
        } else if (instr->Bits(21, 20) == 2) {
            // vld1
            int Vd = (instr->Bit(22) << 4) | instr->VdValue();
            int Rn = instr->VnValue();
            int type = instr->Bits(11, 8);
            int size = instr->Bits(7, 6);
            int align = instr->Bits(5, 4);
            int Rm = instr->VmValue();
            out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                        "vld1.%d ", (1 << size) << 3);
            FormatNeonList(Vd, type);
            Print(", ");
            FormatNeonMemory(Rn, align, Rm);
        } else {
            Unknown(instr);
        }
        break;
      case 0xA:
        if (instr->Bits(22, 20) == 7) {
            const char* option = "?";
            switch (instr->Bits(3, 0)) {
              case  2: option = "oshst"; break;
              case  3: option = "osh";   break;
              case  6: option = "nshst"; break;
              case  7: option = "nsh";   break;
              case 10: option = "ishst"; break;
              case 11: option = "ish";   break;
              case 14: option = "st";    break;
              case 15: option = "sy";    break;
            }
            switch (instr->Bits(7, 4)) {
              case 4:
                out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                            "dsb %s", option);
                break;
              case 5:
                out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                            "dmb %s", option);
                break;
              default:
                Unknown(instr);
            }
            break;
        }
        [[fallthrough]];
      case 0xB:
        if ((instr->Bits(22, 20) == 5) && (instr->Bits(15, 12) == 0xf)) {
            int Rn = instr->Bits(19, 16);
            int offset = instr->Bits(11, 0);
            if (offset == 0) {
                out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                            "pld [r%d]", Rn);
            } else if (instr->Bit(23) == 0) {
                out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                            "pld [r%d, #-%d]", Rn, offset);
            } else {
                out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                            "pld [r%d, #+%d]", Rn, offset);
            }
        } else {
            Unknown(instr);
        }
        break;
      case 0x1D:
        if (instr->Opc1Value() == 0x7 && instr->Bits(19, 18) == 0x2 &&
            instr->Bits(11, 9) == 0x5 && instr->Bits(7, 6) == 0x1 &&
            instr->Bit(4) == 0x0) {
            // VRINTA, VRINTN, VRINTP, VRINTM (floating-point)
            bool dp_operation = (instr->SzValue() == 1);
            int rounding_mode = instr->Bits(17, 16);
            switch (rounding_mode) {
              case 0x0:
                if (dp_operation) {
                    Format(instr, "vrinta.f64.f64 'Dd, 'Dm");
                } else {
                    Unknown(instr);
                }
                break;
              case 0x1:
                if (dp_operation) {
                    Format(instr, "vrintn.f64.f64 'Dd, 'Dm");
                } else {
                    Unknown(instr);
                }
                break;
              case 0x2:
                if (dp_operation) {
                    Format(instr, "vrintp.f64.f64 'Dd, 'Dm");
                } else {
                    Unknown(instr);
                }
                break;
              case 0x3:
                if (dp_operation) {
                    Format(instr, "vrintm.f64.f64 'Dd, 'Dm");
                } else {
                    Unknown(instr);
                }
                break;
              default:
                MOZ_CRASH();  // Case analysis is exhaustive.
                break;
            }
        } else {
            Unknown(instr);
        }
        break;
      default:
        Unknown(instr);
        break;
    }
}

#undef VERIFIY

bool
Decoder::IsConstantPoolAt(uint8_t* instr_ptr)
{
    int instruction_bits = *(reinterpret_cast<int*>(instr_ptr));
    return (instruction_bits & kConstantPoolMarkerMask) == kConstantPoolMarker;
}


int
Decoder::ConstantPoolSizeAt(uint8_t* instr_ptr)
{
    if (IsConstantPoolAt(instr_ptr)) {
        int instruction_bits = *(reinterpret_cast<int*>(instr_ptr));
        return DecodeConstantPoolLength(instruction_bits);
    } else {
        return -1;
    }
}


// Disassemble the instruction at *instr_ptr into the output buffer.
int
Decoder::InstructionDecode(uint8_t* instr_ptr)
{
    Instruction* instr = Instruction::At(instr_ptr);
    // Print raw instruction bytes.
    out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                "%08x       ",
                                instr->InstructionBits());
    if (instr->ConditionField() == kSpecialCondition) {
        DecodeSpecialCondition(instr);
        return Instruction::kInstrSize;
    }
    int instruction_bits = *(reinterpret_cast<int*>(instr_ptr));
    if ((instruction_bits & kConstantPoolMarkerMask) == kConstantPoolMarker) {
        out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_,
                                    "constant pool begin (length %d)",
                                    DecodeConstantPoolLength(instruction_bits));
        return Instruction::kInstrSize;
    } else if (instruction_bits == kCodeAgeJumpInstruction) {
        // The code age prologue has a constant immediatly following the jump
        // instruction.
        Instruction* target = Instruction::At(instr_ptr + Instruction::kInstrSize);
        DecodeType2(instr);
        SNPrintF(out_buffer_ + out_buffer_pos_,
                 " (0x%08x)", target->InstructionBits());
        return 2 * Instruction::kInstrSize;
    }
    switch (instr->TypeValue()) {
      case 0:
      case 1: {
        DecodeType01(instr);
        break;
      }
      case 2: {
        DecodeType2(instr);
        break;
      }
      case 3: {
        DecodeType3(instr);
        break;
      }
      case 4: {
        DecodeType4(instr);
        break;
      }
      case 5: {
        DecodeType5(instr);
        break;
      }
      case 6: {
        DecodeType6(instr);
        break;
      }
      case 7: {
        return DecodeType7(instr);
      }
      default: {
        // The type field is 3-bits in the ARM encoding.
        MOZ_CRASH();
        break;
      }
    }
    return Instruction::kInstrSize;
}


}  // namespace disasm


#undef STRING_STARTS_WITH
#undef VERIFY


//------------------------------------------------------------------------------

namespace disasm {


const char*
NameConverter::NameOfAddress(uint8_t* addr) const
{
    SNPrintF(tmp_buffer_, "%p", addr);
    return tmp_buffer_.start();
}


const char*
NameConverter::NameOfConstant(uint8_t* addr) const
{
    return NameOfAddress(addr);
}


const char*
NameConverter::NameOfCPURegister(int reg) const
{
    return disasm::Registers::Name(reg);
}


const char*
NameConverter::NameOfByteCPURegister(int reg) const
{
    MOZ_CRASH();  // ARM does not have the concept of a byte register
    return "nobytereg";
}


const char*
NameConverter::NameOfXMMRegister(int reg) const
{
    MOZ_CRASH();  // ARM does not have any XMM registers
    return "noxmmreg";
}


const char*
NameConverter::NameInCode(uint8_t* 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(V8Vector<char> buffer, uint8_t* instruction)
{
    Decoder d(converter_, buffer);
    return d.InstructionDecode(instruction);
}


int
Disassembler::ConstantPoolSizeAt(uint8_t* instruction)
{
    return Decoder::ConstantPoolSizeAt(instruction);
}


void
Disassembler::Disassemble(FILE* f, uint8_t* begin, uint8_t* end)
{
    NameConverter converter;
    Disassembler d(converter);
    for (uint8_t* pc = begin; pc < end;) {
        EmbeddedVector<char, ReasonableBufferSize> buffer;
        buffer[0] = '\0';
        uint8_t* 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
}  // namespace jit
}  // namespace js

#endif // JS_DISASM_ARM