xref: /gem5/src/arch/x86/isa/microops/regop.isa

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// All rights reserved.
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// Authors: Gabe Black

//////////////////////////////////////////////////////////////////////////
//
// RegOp Microop templates
//
//////////////////////////////////////////////////////////////////////////

def template MicroRegOpExecute {{
        Fault %(class_name)s::execute(%(CPU_exec_context)s *xc,
                Trace::InstRecord *traceData) const
        {
            Fault fault = NoFault;

            DPRINTF(X86, "The data size is %d\n", dataSize);
            %(op_decl)s;
            %(op_rd)s;

            if(%(cond_check)s)
            {
                %(code)s;
                %(flag_code)s;
            }
            else
            {
                %(else_code)s;
            }

            //Write the resulting state to the execution context
            if(fault == NoFault)
            {
                %(op_wb)s;
            }
            return fault;
        }
}};

def template MicroRegOpImmExecute {{
        Fault %(class_name)s::execute(%(CPU_exec_context)s *xc,
                Trace::InstRecord *traceData) const
        {
            Fault fault = NoFault;

            %(op_decl)s;
            %(op_rd)s;

            if(%(cond_check)s)
            {
                %(code)s;
                %(flag_code)s;
            }
            else
            {
                %(else_code)s;
            }

            //Write the resulting state to the execution context
            if(fault == NoFault)
            {
                %(op_wb)s;
            }
            return fault;
        }
}};

def template MicroRegOpDeclare {{
    class %(class_name)s : public %(base_class)s
    {
      protected:
        void buildMe();

      public:
        %(class_name)s(ExtMachInst _machInst,
                const char * instMnem,
                bool isMicro, bool isDelayed, bool isFirst, bool isLast,
                InstRegIndex _src1, InstRegIndex _src2, InstRegIndex _dest,
                uint8_t _dataSize, uint16_t _ext);

        %(class_name)s(ExtMachInst _machInst,
                const char * instMnem,
                InstRegIndex _src1, InstRegIndex _src2, InstRegIndex _dest,
                uint8_t _dataSize, uint16_t _ext);

        %(BasicExecDeclare)s
    };
}};

def template MicroRegOpImmDeclare {{

    class %(class_name)s : public %(base_class)s
    {
      protected:
        void buildMe();

      public:
        %(class_name)s(ExtMachInst _machInst,
                const char * instMnem,
                bool isMicro, bool isDelayed, bool isFirst, bool isLast,
                InstRegIndex _src1, uint16_t _imm8, InstRegIndex _dest,
                uint8_t _dataSize, uint16_t _ext);

        %(class_name)s(ExtMachInst _machInst,
                const char * instMnem,
                InstRegIndex _src1, uint16_t _imm8, InstRegIndex _dest,
                uint8_t _dataSize, uint16_t _ext);

        %(BasicExecDeclare)s
    };
}};

def template MicroRegOpConstructor {{

    inline void %(class_name)s::buildMe()
    {
        %(constructor)s;
    }

    inline %(class_name)s::%(class_name)s(
            ExtMachInst machInst, const char * instMnem,
            InstRegIndex _src1, InstRegIndex _src2, InstRegIndex _dest,
            uint8_t _dataSize, uint16_t _ext) :
        %(base_class)s(machInst, "%(mnemonic)s", instMnem,
                false, false, false, false,
                _src1, _src2, _dest, _dataSize, _ext,
                %(op_class)s)
    {
        buildMe();
    }

    inline %(class_name)s::%(class_name)s(
            ExtMachInst machInst, const char * instMnem,
            bool isMicro, bool isDelayed, bool isFirst, bool isLast,
            InstRegIndex _src1, InstRegIndex _src2, InstRegIndex _dest,
            uint8_t _dataSize, uint16_t _ext) :
        %(base_class)s(machInst, "%(mnemonic)s", instMnem,
                isMicro, isDelayed, isFirst, isLast,
                _src1, _src2, _dest, _dataSize, _ext,
                %(op_class)s)
    {
        buildMe();
    }
}};

def template MicroRegOpImmConstructor {{

    inline void %(class_name)s::buildMe()
    {
        %(constructor)s;
    }

    inline %(class_name)s::%(class_name)s(
            ExtMachInst machInst, const char * instMnem,
            InstRegIndex _src1, uint16_t _imm8, InstRegIndex _dest,
            uint8_t _dataSize, uint16_t _ext) :
        %(base_class)s(machInst, "%(mnemonic)s", instMnem,
                false, false, false, false,
                _src1, _imm8, _dest, _dataSize, _ext,
                %(op_class)s)
    {
        buildMe();
    }

    inline %(class_name)s::%(class_name)s(
            ExtMachInst machInst, const char * instMnem,
            bool isMicro, bool isDelayed, bool isFirst, bool isLast,
            InstRegIndex _src1, uint16_t _imm8, InstRegIndex _dest,
            uint8_t _dataSize, uint16_t _ext) :
        %(base_class)s(machInst, "%(mnemonic)s", instMnem,
                isMicro, isDelayed, isFirst, isLast,
                _src1, _imm8, _dest, _dataSize, _ext,
                %(op_class)s)
    {
        buildMe();
    }
}};

output header {{
    void
    divide(uint64_t dividend, uint64_t divisor,
            uint64_t &quotient, uint64_t &remainder);

    enum SegmentSelectorCheck {
      SegNoCheck, SegCSCheck, SegCallGateCheck, SegIntGateCheck,
      SegSoftIntGateCheck, SegSSCheck, SegIretCheck, SegIntCSCheck,
      SegTRCheck, SegTSSCheck, SegInGDTCheck, SegLDTCheck
    };

    enum LongModeDescriptorType {
        LDT64 = 2,
        AvailableTSS64 = 9,
        BusyTSS64 = 0xb,
        CallGate64 = 0xc,
        IntGate64 = 0xe,
        TrapGate64 = 0xf
    };
}};

output decoder {{
    void
    divide(uint64_t dividend, uint64_t divisor,
            uint64_t &quotient, uint64_t &remainder)
    {
        //Check for divide by zero.
        if (divisor == 0)
            panic("Divide by zero!\\n");
        //If the divisor is bigger than the dividend, don't do anything.
        if (divisor <= dividend) {
            //Shift the divisor so it's msb lines up with the dividend.
            int dividendMsb = findMsbSet(dividend);
            int divisorMsb = findMsbSet(divisor);
            int shift = dividendMsb - divisorMsb;
            divisor <<= shift;
            //Compute what we'll add to the quotient if the divisor isn't
            //now larger than the dividend.
            uint64_t quotientBit = 1;
            quotientBit <<= shift;
            //If we need to step back a bit (no pun intended) because the
            //divisor got too to large, do that here. This is the "or two"
            //part of one or two bit division.
            if (divisor > dividend) {
                quotientBit >>= 1;
                divisor >>= 1;
            }
            //Decrement the remainder and increment the quotient.
            quotient += quotientBit;
            remainder -= divisor;
        }
    }
}};

let {{
    # Make these empty strings so that concatenating onto
    # them will always work.
    header_output = ""
    decoder_output = ""
    exec_output = ""

    immTemplates = (
            MicroRegOpImmDeclare,
            MicroRegOpImmConstructor,
            MicroRegOpImmExecute)

    regTemplates = (
            MicroRegOpDeclare,
            MicroRegOpConstructor,
            MicroRegOpExecute)

    class RegOpMeta(type):
        def buildCppClasses(self, name, Name, suffix, \
                code, flag_code, cond_check, else_code):

            # Globals to stick the output in
            global header_output
            global decoder_output
            global exec_output

            # Stick all the code together so it can be searched at once
            allCode = "|".join((code, flag_code, cond_check, else_code))

            # If op2 is used anywhere, make register and immediate versions
            # of this code.
            matcher = re.compile("(?<!\\w)(?P<prefix>s?)op2(?P<typeQual>\\.\\w+)?")
            match = matcher.search(allCode)
            if match:
                typeQual = ""
                if match.group("typeQual"):
                    typeQual = match.group("typeQual")
                src2_name = "%spsrc2%s" % (match.group("prefix"), typeQual)
                self.buildCppClasses(name, Name, suffix,
                        matcher.sub(src2_name, code),
                        matcher.sub(src2_name, flag_code),
                        matcher.sub(src2_name, cond_check),
                        matcher.sub(src2_name, else_code))
                self.buildCppClasses(name + "i", Name, suffix + "Imm",
                        matcher.sub("imm8", code),
                        matcher.sub("imm8", flag_code),
                        matcher.sub("imm8", cond_check),
                        matcher.sub("imm8", else_code))
                return

            # If there's something optional to do with flags, generate
            # a version without it and fix up this version to use it.
            if flag_code != "" or cond_check != "true":
                self.buildCppClasses(name, Name, suffix,
                        code, "", "true", else_code)
                suffix = "Flags" + suffix

            # If psrc1 or psrc2 is used, we need to actually insert code to
            # compute it.
            matcher = re.compile("(?<!\w)psrc1(?!\w)")
            if matcher.search(allCode):
                code = "uint64_t psrc1 = pick(SrcReg1, 0, dataSize);" + code
            matcher = re.compile("(?<!\w)psrc2(?!\w)")
            if matcher.search(allCode):
                code = "uint64_t psrc2 = pick(SrcReg2, 1, dataSize);" + code
            # Also make available versions which do sign extension
            matcher = re.compile("(?<!\w)spsrc1(?!\w)")
            if matcher.search(allCode):
                code = "int64_t spsrc1 = signedPick(SrcReg1, 0, dataSize);" + code
            matcher = re.compile("(?<!\w)spsrc2(?!\w)")
            if matcher.search(allCode):
                code = "int64_t spsrc2 = signedPick(SrcReg2, 1, dataSize);" + code

            base = "X86ISA::RegOp"

            # If imm8 shows up in the code, use the immediate templates, if
            # not, hopefully the register ones will be correct.
            templates = regTemplates
            matcher = re.compile("(?<!\w)imm8(?!\w)")
            if matcher.search(allCode):
                base += "Imm"
                templates = immTemplates

            # Get everything ready for the substitution
            iop = InstObjParams(name, Name + suffix, base,
                    {"code" : code,
                     "flag_code" : flag_code,
                     "cond_check" : cond_check,
                     "else_code" : else_code})

            # Generate the actual code (finally!)
            header_output += templates[0].subst(iop)
            decoder_output += templates[1].subst(iop)
            exec_output += templates[2].subst(iop)


        def __new__(mcls, Name, bases, dict):
            abstract = False
            name = Name.lower()
            if "abstract" in dict:
                abstract = dict['abstract']
                del dict['abstract']

            cls = super(RegOpMeta, mcls).__new__(mcls, Name, bases, dict)
            if not abstract:
                cls.className = Name
                cls.base_mnemonic = name
                code = cls.code
                flag_code = cls.flag_code
                cond_check = cls.cond_check
                else_code = cls.else_code

                # Set up the C++ classes
                mcls.buildCppClasses(cls, name, Name, "",
                        code, flag_code, cond_check, else_code)

                # Hook into the microassembler dict
                global microopClasses
                microopClasses[name] = cls

                allCode = "|".join((code, flag_code, cond_check, else_code))

                # If op2 is used anywhere, make register and immediate versions
                # of this code.
                matcher = re.compile("op2(?P<typeQual>\\.\\w+)?")
                if matcher.search(allCode):
                    microopClasses[name + 'i'] = cls
            return cls


    class RegOp(X86Microop):
        __metaclass__ = RegOpMeta
        # This class itself doesn't act as a microop
        abstract = True

        # Default template parameter values
        flag_code = ""
        cond_check = "true"
        else_code = ";"

        def __init__(self, dest, src1, op2, flags = None, dataSize = "env.dataSize"):
            self.dest = dest
            self.src1 = src1
            self.op2 = op2
            self.flags = flags
            self.dataSize = dataSize
            if flags is None:
                self.ext = 0
            else:
                if not isinstance(flags, (list, tuple)):
                    raise Exception, "flags must be a list or tuple of flags"
                self.ext = " | ".join(flags)
                self.className += "Flags"

        def getAllocator(self, *microFlags):
            className = self.className
            if self.mnemonic == self.base_mnemonic + 'i':
                className += "Imm"
            allocator = '''new %(class_name)s(machInst, macrocodeBlock
                    %(flags)s, %(src1)s, %(op2)s, %(dest)s,
                    %(dataSize)s, %(ext)s)''' % {
                "class_name" : className,
                "flags" : self.microFlagsText(microFlags),
                "src1" : self.src1, "op2" : self.op2,
                "dest" : self.dest,
                "dataSize" : self.dataSize,
                "ext" : self.ext}
            return allocator

    class LogicRegOp(RegOp):
        abstract = True
        flag_code = '''
            //Don't have genFlags handle the OF or CF bits
            uint64_t mask = CFBit | ECFBit | OFBit;
            ccFlagBits = genFlags(ccFlagBits, ext & ~mask, DestReg, psrc1, op2);
            //If a logic microop wants to set these, it wants to set them to 0.
            ccFlagBits &= ~(CFBit & ext);
            ccFlagBits &= ~(ECFBit & ext);
            ccFlagBits &= ~(OFBit & ext);
        '''

    class FlagRegOp(RegOp):
        abstract = True
        flag_code = \
            "ccFlagBits = genFlags(ccFlagBits, ext, DestReg, psrc1, op2);"

    class SubRegOp(RegOp):
        abstract = True
        flag_code = \
            "ccFlagBits = genFlags(ccFlagBits, ext, DestReg, psrc1, ~op2, true);"

    class CondRegOp(RegOp):
        abstract = True
        cond_check = "checkCondition(ccFlagBits, ext)"

    class RdRegOp(RegOp):
        abstract = True
        def __init__(self, dest, src1=None, dataSize="env.dataSize"):
            if not src1:
                src1 = dest
            super(RdRegOp, self).__init__(dest, src1, \
                    "InstRegIndex(NUM_INTREGS)", None, dataSize)

    class WrRegOp(RegOp):
        abstract = True
        def __init__(self, src1, src2, flags=None, dataSize="env.dataSize"):
            super(WrRegOp, self).__init__("InstRegIndex(NUM_INTREGS)", \
                    src1, src2, flags, dataSize)

    class Add(FlagRegOp):
        code = 'DestReg = merge(DestReg, psrc1 + op2, dataSize);'

    class Or(LogicRegOp):
        code = 'DestReg = merge(DestReg, psrc1 | op2, dataSize);'

    class Adc(FlagRegOp):
        code = '''
            CCFlagBits flags = ccFlagBits;
            DestReg = merge(DestReg, psrc1 + op2 + flags.cf, dataSize);
            '''

    class Sbb(SubRegOp):
        code = '''
            CCFlagBits flags = ccFlagBits;
            DestReg = merge(DestReg, psrc1 - op2 - flags.cf, dataSize);
            '''

    class And(LogicRegOp):
        code = 'DestReg = merge(DestReg, psrc1 & op2, dataSize)'

    class Sub(SubRegOp):
        code = 'DestReg = merge(DestReg, psrc1 - op2, dataSize)'

    class Xor(LogicRegOp):
        code = 'DestReg = merge(DestReg, psrc1 ^ op2, dataSize)'

    class Mul1s(WrRegOp):
        code = '''
            ProdLow = psrc1 * op2;
            int halfSize = (dataSize * 8) / 2;
            uint64_t shifter = (1ULL << halfSize);
            uint64_t hiResult;
            uint64_t psrc1_h = psrc1 / shifter;
            uint64_t psrc1_l = psrc1 & mask(halfSize);
            uint64_t psrc2_h = (op2 / shifter) & mask(halfSize);
            uint64_t psrc2_l = op2 & mask(halfSize);
            hiResult = ((psrc1_l * psrc2_h + psrc1_h * psrc2_l +
                        ((psrc1_l * psrc2_l) / shifter)) /shifter) +
                       psrc1_h * psrc2_h;
            if (bits(psrc1, dataSize * 8 - 1))
                hiResult -= op2;
            if (bits(op2, dataSize * 8 - 1))
                hiResult -= psrc1;
            ProdHi = hiResult;
            '''
        flag_code = '''
            if ((-ProdHi & mask(dataSize * 8)) !=
                    bits(ProdLow, dataSize * 8 - 1)) {
                ccFlagBits = ccFlagBits | (ext & (CFBit | OFBit | ECFBit));
            } else {
                ccFlagBits = ccFlagBits & ~(ext & (CFBit | OFBit | ECFBit));
            }
        '''

    class Mul1u(WrRegOp):
        code = '''
            ProdLow = psrc1 * op2;
            int halfSize = (dataSize * 8) / 2;
            uint64_t shifter = (1ULL << halfSize);
            uint64_t psrc1_h = psrc1 / shifter;
            uint64_t psrc1_l = psrc1 & mask(halfSize);
            uint64_t psrc2_h = (op2 / shifter) & mask(halfSize);
            uint64_t psrc2_l = op2 & mask(halfSize);
            ProdHi = ((psrc1_l * psrc2_h + psrc1_h * psrc2_l +
                      ((psrc1_l * psrc2_l) / shifter)) / shifter) +
                     psrc1_h * psrc2_h;
            '''
        flag_code = '''
            if (ProdHi) {
                ccFlagBits = ccFlagBits | (ext & (CFBit | OFBit | ECFBit));
            } else {
                ccFlagBits = ccFlagBits & ~(ext & (CFBit | OFBit | ECFBit));
            }
        '''

    class Mulel(RdRegOp):
        code = 'DestReg = merge(SrcReg1, ProdLow, dataSize);'

    class Muleh(RdRegOp):
        def __init__(self, dest, src1=None, flags=None, dataSize="env.dataSize"):
            if not src1:
                src1 = dest
            super(RdRegOp, self).__init__(dest, src1, \
                    "InstRegIndex(NUM_INTREGS)", flags, dataSize)
        code = 'DestReg = merge(SrcReg1, ProdHi, dataSize);'

    # One or two bit divide
    class Div1(WrRegOp):
        code = '''
            //These are temporaries so that modifying them later won't make
            //the ISA parser think they're also sources.
            uint64_t quotient = 0;
            uint64_t remainder = psrc1;
            //Similarly, this is a temporary so changing it doesn't make it
            //a source.
            uint64_t divisor = op2;
            //This is a temporary just for consistency and clarity.
            uint64_t dividend = remainder;
            //Do the division.
            divide(dividend, divisor, quotient, remainder);
            //Record the final results.
            Remainder = remainder;
            Quotient = quotient;
            Divisor = divisor;
            '''

    # Step divide
    class Div2(RegOp):
        code = '''
            uint64_t dividend = Remainder;
            uint64_t divisor = Divisor;
            uint64_t quotient = Quotient;
            uint64_t remainder = dividend;
            int remaining = op2;
            //If we overshot, do nothing. This lets us unrool division loops a
            //little.
            if (remaining) {
                //Shift in bits from the low order portion of the dividend
                while(dividend < divisor && remaining) {
                    dividend = (dividend << 1) | bits(SrcReg1, remaining - 1);
                    quotient <<= 1;
                    remaining--;
                }
                remainder = dividend;
                //Do the division.
                divide(dividend, divisor, quotient, remainder);
            }
            //Keep track of how many bits there are still to pull in.
            DestReg = merge(DestReg, remaining, dataSize);
            //Record the final results
            Remainder = remainder;
            Quotient = quotient;
        '''
        flag_code = '''
            if (DestReg == 0)
                ccFlagBits = ccFlagBits | (ext & EZFBit);
            else
                ccFlagBits = ccFlagBits & ~(ext & EZFBit);
        '''

    class Divq(RdRegOp):
        code = 'DestReg = merge(SrcReg1, Quotient, dataSize);'

    class Divr(RdRegOp):
        code = 'DestReg = merge(SrcReg1, Remainder, dataSize);'

    class Mov(CondRegOp):
        code = 'DestReg = merge(SrcReg1, op2, dataSize)'
        else_code = 'DestReg = merge(DestReg, DestReg, dataSize);'

    # Shift instructions

    class Sll(RegOp):
        code = '''
            uint8_t shiftAmt = (op2 & ((dataSize == 8) ? mask(6) : mask(5)));
            DestReg = merge(DestReg, psrc1 << shiftAmt, dataSize);
            '''
        flag_code = '''
            // If the shift amount is zero, no flags should be modified.
            if (shiftAmt) {
                //Zero out any flags we might modify. This way we only have to
                //worry about setting them.
                ccFlagBits = ccFlagBits & ~(ext & (CFBit | ECFBit | OFBit));
                int CFBits = 0;
                //Figure out if we -would- set the CF bits if requested.
                if (shiftAmt <= dataSize * 8 &&
                        bits(SrcReg1, dataSize * 8 - shiftAmt)) {
                    CFBits = 1;
                }
                //If some combination of the CF bits need to be set, set them.
                if ((ext & (CFBit | ECFBit)) && CFBits)
                    ccFlagBits = ccFlagBits | (ext & (CFBit | ECFBit));
                //Figure out what the OF bit should be.
                if ((ext & OFBit) && (CFBits ^ bits(DestReg, dataSize * 8 - 1)))
                    ccFlagBits = ccFlagBits | OFBit;
                //Use the regular mechanisms to calculate the other flags.
                ccFlagBits = genFlags(ccFlagBits, ext & ~(CFBit | ECFBit | OFBit),
                        DestReg, psrc1, op2);
            }
        '''

    class Srl(RegOp):
        code = '''
            uint8_t shiftAmt = (op2 & ((dataSize == 8) ? mask(6) : mask(5)));
            // Because what happens to the bits shift -in- on a right shift
            // is not defined in the C/C++ standard, we have to mask them out
            // to be sure they're zero.
            uint64_t logicalMask = mask(dataSize * 8 - shiftAmt);
            DestReg = merge(DestReg, (psrc1 >> shiftAmt) & logicalMask, dataSize);
            '''
        flag_code = '''
            // If the shift amount is zero, no flags should be modified.
            if (shiftAmt) {
                //Zero out any flags we might modify. This way we only have to
                //worry about setting them.
                ccFlagBits = ccFlagBits & ~(ext & (CFBit | ECFBit | OFBit));
                //If some combination of the CF bits need to be set, set them.
                if ((ext & (CFBit | ECFBit)) && 
                        shiftAmt <= dataSize * 8 &&
                        bits(SrcReg1, shiftAmt - 1)) {
                    ccFlagBits = ccFlagBits | (ext & (CFBit | ECFBit));
                }
                //Figure out what the OF bit should be.
                if ((ext & OFBit) && bits(SrcReg1, dataSize * 8 - 1))
                    ccFlagBits = ccFlagBits | OFBit;
                //Use the regular mechanisms to calculate the other flags.
                ccFlagBits = genFlags(ccFlagBits, ext & ~(CFBit | ECFBit | OFBit),
                        DestReg, psrc1, op2);
            }
        '''

    class Sra(RegOp):
        code = '''
            uint8_t shiftAmt = (op2 & ((dataSize == 8) ? mask(6) : mask(5)));
            // Because what happens to the bits shift -in- on a right shift
            // is not defined in the C/C++ standard, we have to sign extend
            // them manually to be sure.
            uint64_t arithMask = (shiftAmt == 0) ? 0 :
                -bits(psrc1, dataSize * 8 - 1) << (dataSize * 8 - shiftAmt);
            DestReg = merge(DestReg, (psrc1 >> shiftAmt) | arithMask, dataSize);
            '''
        flag_code = '''
            // If the shift amount is zero, no flags should be modified.
            if (shiftAmt) {
                //Zero out any flags we might modify. This way we only have to
                //worry about setting them.
                ccFlagBits = ccFlagBits & ~(ext & (CFBit | ECFBit | OFBit));
                //If some combination of the CF bits need to be set, set them.
                uint8_t effectiveShift =
                    (shiftAmt <= dataSize * 8) ? shiftAmt : (dataSize * 8);
                if ((ext & (CFBit | ECFBit)) &&
                        bits(SrcReg1, effectiveShift - 1)) {
                    ccFlagBits = ccFlagBits | (ext & (CFBit | ECFBit));
                }
                //Use the regular mechanisms to calculate the other flags.
                ccFlagBits = genFlags(ccFlagBits, ext & ~(CFBit | ECFBit | OFBit),
                        DestReg, psrc1, op2);
            }
        '''

    class Ror(RegOp):
        code = '''
            uint8_t shiftAmt =
                (op2 & ((dataSize == 8) ? mask(6) : mask(5)));
            uint8_t realShiftAmt = shiftAmt % (dataSize * 8);
            if(realShiftAmt)
            {
                uint64_t top = psrc1 << (dataSize * 8 - realShiftAmt);
                uint64_t bottom = bits(psrc1, dataSize * 8, realShiftAmt);
                DestReg = merge(DestReg, top | bottom, dataSize);
            }
            else
                DestReg = merge(DestReg, DestReg, dataSize);
            '''
        flag_code = '''
            // If the shift amount is zero, no flags should be modified.
            if (shiftAmt) {
                //Zero out any flags we might modify. This way we only have to
                //worry about setting them.
                ccFlagBits = ccFlagBits & ~(ext & (CFBit | ECFBit | OFBit));
                //Find the most and second most significant bits of the result.
                int msb = bits(DestReg, dataSize * 8 - 1);
                int smsb = bits(DestReg, dataSize * 8 - 2);
                //If some combination of the CF bits need to be set, set them.
                if ((ext & (CFBit | ECFBit)) && msb)
                    ccFlagBits = ccFlagBits | (ext & (CFBit | ECFBit));
                //Figure out what the OF bit should be.
                if ((ext & OFBit) && (msb ^ smsb))
                    ccFlagBits = ccFlagBits | OFBit;
                //Use the regular mechanisms to calculate the other flags.
                ccFlagBits = genFlags(ccFlagBits, ext & ~(CFBit | ECFBit | OFBit),
                        DestReg, psrc1, op2);
            }
        '''

    class Rcr(RegOp):
        code = '''
            uint8_t shiftAmt =
                (op2 & ((dataSize == 8) ? mask(6) : mask(5)));
            uint8_t realShiftAmt = shiftAmt % (dataSize * 8 + 1);
            if(realShiftAmt)
            {
                CCFlagBits flags = ccFlagBits;
                uint64_t top = flags.cf << (dataSize * 8 - realShiftAmt);
                if (realShiftAmt > 1)
                    top |= psrc1 << (dataSize * 8 - realShiftAmt + 1);
                uint64_t bottom = bits(psrc1, dataSize * 8 - 1, realShiftAmt);
                DestReg = merge(DestReg, top | bottom, dataSize);
            }
            else
                DestReg = merge(DestReg, DestReg, dataSize);
            '''
        flag_code = '''
            // If the shift amount is zero, no flags should be modified.
            if (shiftAmt) {
                int origCFBit = (ccFlagBits & CFBit) ? 1 : 0;
                //Zero out any flags we might modify. This way we only have to
                //worry about setting them.
                ccFlagBits = ccFlagBits & ~(ext & (CFBit | ECFBit | OFBit));
                //Figure out what the OF bit should be.
                if ((ext & OFBit) && (origCFBit ^
                                      bits(SrcReg1, dataSize * 8 - 1))) {
                    ccFlagBits = ccFlagBits | OFBit;
                }
                //If some combination of the CF bits need to be set, set them.
                if ((ext & (CFBit | ECFBit)) &&
                        (realShiftAmt == 0) ? origCFBit :
                        bits(SrcReg1, realShiftAmt - 1)) {
                    ccFlagBits = ccFlagBits | (ext & (CFBit | ECFBit));
                }
                //Use the regular mechanisms to calculate the other flags.
                ccFlagBits = genFlags(ccFlagBits, ext & ~(CFBit | ECFBit | OFBit),
                        DestReg, psrc1, op2);
            }
        '''

    class Rol(RegOp):
        code = '''
            uint8_t shiftAmt =
                (op2 & ((dataSize == 8) ? mask(6) : mask(5)));
            uint8_t realShiftAmt = shiftAmt % (dataSize * 8);
            if(realShiftAmt)
            {
                uint64_t top = psrc1 << realShiftAmt;
                uint64_t bottom =
                    bits(psrc1, dataSize * 8 - 1, dataSize * 8 - realShiftAmt);
                DestReg = merge(DestReg, top | bottom, dataSize);
            }
            else
                DestReg = merge(DestReg, DestReg, dataSize);
            '''
        flag_code = '''
            // If the shift amount is zero, no flags should be modified.
            if (shiftAmt) {
                //Zero out any flags we might modify. This way we only have to
                //worry about setting them.
                ccFlagBits = ccFlagBits & ~(ext & (CFBit | ECFBit | OFBit));
                //The CF bits, if set, would be set to the lsb of the result.
                int lsb = DestReg & 0x1;
                int msb = bits(DestReg, dataSize * 8 - 1);
                //If some combination of the CF bits need to be set, set them.
                if ((ext & (CFBit | ECFBit)) && lsb)
                    ccFlagBits = ccFlagBits | (ext & (CFBit | ECFBit));
                //Figure out what the OF bit should be.
                if ((ext & OFBit) && (msb ^ lsb))
                    ccFlagBits = ccFlagBits | OFBit;
                //Use the regular mechanisms to calculate the other flags.
                ccFlagBits = genFlags(ccFlagBits, ext & ~(CFBit | ECFBit | OFBit),
                        DestReg, psrc1, op2);
            }
        '''

    class Rcl(RegOp):
        code = '''
            uint8_t shiftAmt =
                (op2 & ((dataSize == 8) ? mask(6) : mask(5)));
            uint8_t realShiftAmt = shiftAmt % (dataSize * 8 + 1);
            if(realShiftAmt)
            {
                CCFlagBits flags = ccFlagBits;
                uint64_t top = psrc1 << realShiftAmt;
                uint64_t bottom = flags.cf << (realShiftAmt - 1);
                if(shiftAmt > 1)
                    bottom |=
                        bits(psrc1, dataSize * 8 - 1,
                                   dataSize * 8 - realShiftAmt + 1);
                DestReg = merge(DestReg, top | bottom, dataSize);
            }
            else
                DestReg = merge(DestReg, DestReg, dataSize);
            '''
        flag_code = '''
            // If the shift amount is zero, no flags should be modified.
            if (shiftAmt) {
                int origCFBit = (ccFlagBits & CFBit) ? 1 : 0;
                //Zero out any flags we might modify. This way we only have to
                //worry about setting them.
                ccFlagBits = ccFlagBits & ~(ext & (CFBit | ECFBit | OFBit));
                int msb = bits(DestReg, dataSize * 8 - 1);
                int CFBits = bits(SrcReg1, dataSize * 8 - realShiftAmt);
                //If some combination of the CF bits need to be set, set them.
                if ((ext & (CFBit | ECFBit)) && 
                        (realShiftAmt == 0) ? origCFBit : CFBits)
                    ccFlagBits = ccFlagBits | (ext & (CFBit | ECFBit));
                //Figure out what the OF bit should be.
                if ((ext & OFBit) && (msb ^ CFBits))
                    ccFlagBits = ccFlagBits | OFBit;
                //Use the regular mechanisms to calculate the other flags.
                ccFlagBits = genFlags(ccFlagBits, ext & ~(CFBit | ECFBit | OFBit),
                        DestReg, psrc1, op2);
            }
        '''

    class Sld(RegOp):
        code = '''
            uint8_t shiftAmt = (op2 & ((dataSize == 8) ? mask(6) : mask(5)));
            uint8_t dataBits = dataSize * 8;
            uint8_t realShiftAmt = shiftAmt % (2 * dataBits);
            uint64_t result;
            if (realShiftAmt == 0) {
                result = psrc1;
            } else if (realShiftAmt < dataBits) {
                result = (psrc1 << realShiftAmt) |
                         (DoubleBits >> (dataBits - realShiftAmt));
            } else {
                result = (DoubleBits << (realShiftAmt - dataBits)) |
                         (psrc1 >> (2 * dataBits - realShiftAmt));
            }
            DestReg = merge(DestReg, result, dataSize);
            '''
        flag_code = '''
            // If the shift amount is zero, no flags should be modified.
            if (shiftAmt) {
                //Zero out any flags we might modify. This way we only have to
                //worry about setting them.
                ccFlagBits = ccFlagBits & ~(ext & (CFBit | ECFBit | OFBit));
                int CFBits = 0;
                //Figure out if we -would- set the CF bits if requested.
                if ((realShiftAmt == 0 &&
                        bits(DoubleBits, 0)) ||
                    (realShiftAmt <= dataBits &&
                     bits(SrcReg1, dataBits - realShiftAmt)) ||
                    (realShiftAmt > dataBits &&
                     bits(DoubleBits, 2 * dataBits - realShiftAmt))) {
                    CFBits = 1;
                }
                //If some combination of the CF bits need to be set, set them.
                if ((ext & (CFBit | ECFBit)) && CFBits)
                    ccFlagBits = ccFlagBits | (ext & (CFBit | ECFBit));
                //Figure out what the OF bit should be.
                if ((ext & OFBit) && (bits(SrcReg1, dataBits - 1) ^
                                      bits(result, dataBits - 1)))
                    ccFlagBits = ccFlagBits | OFBit;
                //Use the regular mechanisms to calculate the other flags.
                ccFlagBits = genFlags(ccFlagBits, ext & ~(CFBit | ECFBit | OFBit),
                        DestReg, psrc1, op2);
            }
        '''

    class Srd(RegOp):
        code = '''
            uint8_t shiftAmt = (op2 & ((dataSize == 8) ? mask(6) : mask(5)));
            uint8_t dataBits = dataSize * 8;
            uint8_t realShiftAmt = shiftAmt % (2 * dataBits);
            uint64_t result;
            if (realShiftAmt == 0) {
                result = psrc1;
            } else if (realShiftAmt < dataBits) {
                // Because what happens to the bits shift -in- on a right
                // shift is not defined in the C/C++ standard, we have to
                // mask them out to be sure they're zero.
                uint64_t logicalMask = mask(dataBits - realShiftAmt);
                result = ((psrc1 >> realShiftAmt) & logicalMask) |
                         (DoubleBits << (dataBits - realShiftAmt));
            } else {
                uint64_t logicalMask = mask(2 * dataBits - realShiftAmt);
                result = ((DoubleBits >> (realShiftAmt - dataBits)) &
                          logicalMask) |
                         (psrc1 << (2 * dataBits - realShiftAmt));
            }
            DestReg = merge(DestReg, result, dataSize);
            '''
        flag_code = '''
            // If the shift amount is zero, no flags should be modified.
            if (shiftAmt) {
                //Zero out any flags we might modify. This way we only have to
                //worry about setting them.
                ccFlagBits = ccFlagBits & ~(ext & (CFBit | ECFBit | OFBit));
                int CFBits = 0;
                //If some combination of the CF bits need to be set, set them.
                if ((realShiftAmt == 0 &&
                            bits(DoubleBits, dataBits - 1)) ||
                        (realShiftAmt <= dataBits &&
                         bits(SrcReg1, realShiftAmt - 1)) ||
                        (realShiftAmt > dataBits &&
                         bits(DoubleBits, realShiftAmt - dataBits - 1))) {
                    CFBits = 1;
                }
                //If some combination of the CF bits need to be set, set them.
                if ((ext & (CFBit | ECFBit)) && CFBits)
                    ccFlagBits = ccFlagBits | (ext & (CFBit | ECFBit));
                //Figure out what the OF bit should be.
                if ((ext & OFBit) && (bits(SrcReg1, dataBits - 1) ^
                                      bits(result, dataBits - 1)))
                    ccFlagBits = ccFlagBits | OFBit;
                //Use the regular mechanisms to calculate the other flags.
                ccFlagBits = genFlags(ccFlagBits, ext & ~(CFBit | ECFBit | OFBit),
                        DestReg, psrc1, op2);
            }
        '''

    class Mdb(WrRegOp):
        code = 'DoubleBits = psrc1 ^ op2;'

    class Wrip(WrRegOp, CondRegOp):
        code = 'RIP = psrc1 + sop2 + CSBase'
        else_code="RIP = RIP;"

    class Wruflags(WrRegOp):
        code = 'ccFlagBits = psrc1 ^ op2'

    class Wrflags(WrRegOp):
        code = '''
            MiscReg newFlags = psrc1 ^ op2;
            MiscReg userFlagMask = 0xDD5;
            // Get only the user flags
            ccFlagBits = newFlags & userFlagMask;
            // Get everything else
            nccFlagBits = newFlags & ~userFlagMask;
        '''

    class Rdip(RdRegOp):
        code = 'DestReg = RIP - CSBase'

    class Ruflags(RdRegOp):
        code = 'DestReg = ccFlagBits'

    class Rflags(RdRegOp):
        code = 'DestReg = ccFlagBits | nccFlagBits'

    class Ruflag(RegOp):
        code = '''
            int flag = bits(ccFlagBits, imm8);
            DestReg = merge(DestReg, flag, dataSize);
            ccFlagBits = (flag == 0) ? (ccFlagBits | EZFBit) :
                                       (ccFlagBits & ~EZFBit);
            '''
        def __init__(self, dest, imm, flags=None, \
                dataSize="env.dataSize"):
            super(Ruflag, self).__init__(dest, \
                    "InstRegIndex(NUM_INTREGS)", imm, flags, dataSize)

    class Rflag(RegOp):
        code = '''
            MiscReg flagMask = 0x3F7FDD5;
            MiscReg flags = (nccFlagBits | ccFlagBits) & flagMask;
            int flag = bits(flags, imm8);
            DestReg = merge(DestReg, flag, dataSize);
            ccFlagBits = (flag == 0) ? (ccFlagBits | EZFBit) :
                                       (ccFlagBits & ~EZFBit);
            '''
        def __init__(self, dest, imm, flags=None, \
                dataSize="env.dataSize"):
            super(Rflag, self).__init__(dest, \
                    "InstRegIndex(NUM_INTREGS)", imm, flags, dataSize)

    class Sext(RegOp):
        code = '''
            IntReg val = psrc1;
            // Mask the bit position so that it wraps.
            int bitPos = op2 & (dataSize * 8 - 1);
            int sign_bit = bits(val, bitPos, bitPos);
            uint64_t maskVal = mask(bitPos+1);
            val = sign_bit ? (val | ~maskVal) : (val & maskVal);
            DestReg = merge(DestReg, val, dataSize);
            '''
        flag_code = '''
            if (!sign_bit)
                ccFlagBits = ccFlagBits &
                    ~(ext & (CFBit | ECFBit | ZFBit | EZFBit));
            else
                ccFlagBits = ccFlagBits |
                    (ext & (CFBit | ECFBit | ZFBit | EZFBit));
            '''

    class Zext(RegOp):
        code = 'DestReg = merge(DestReg, bits(psrc1, op2, 0), dataSize);'

    class Rddr(RegOp):
        def __init__(self, dest, src1, flags=None, dataSize="env.dataSize"):
            super(Rddr, self).__init__(dest, \
                    src1, "InstRegIndex(NUM_INTREGS)", flags, dataSize)
        code = '''
            CR4 cr4 = CR4Op;
            DR7 dr7 = DR7Op;
            if ((cr4.de == 1 && (src1 == 4 || src1 == 5)) || src1 >= 8) {
                fault = new InvalidOpcode();
            } else if (dr7.gd) {
                fault = new DebugException();
            } else {
                DestReg = merge(DestReg, DebugSrc1, dataSize);
            }
        '''

    class Wrdr(RegOp):
        def __init__(self, dest, src1, flags=None, dataSize="env.dataSize"):
            super(Wrdr, self).__init__(dest, \
                    src1, "InstRegIndex(NUM_INTREGS)", flags, dataSize)
        code = '''
            CR4 cr4 = CR4Op;
            DR7 dr7 = DR7Op;
            if ((cr4.de == 1 && (dest == 4 || dest == 5)) || dest >= 8) {
                fault = new InvalidOpcode();
            } else if ((dest == 6 || dest == 7) && bits(psrc1, 63, 32) &&
                    machInst.mode.mode == LongMode) {
                fault = new GeneralProtection(0);
            } else if (dr7.gd) {
                fault = new DebugException();
            } else {
                DebugDest = psrc1;
            }
        '''

    class Rdcr(RegOp):
        def __init__(self, dest, src1, flags=None, dataSize="env.dataSize"):
            super(Rdcr, self).__init__(dest, \
                    src1, "InstRegIndex(NUM_INTREGS)", flags, dataSize)
        code = '''
            if (src1 == 1 || (src1 > 4 && src1 < 8) || (src1 > 8)) {
                fault = new InvalidOpcode();
            } else {
                DestReg = merge(DestReg, ControlSrc1, dataSize);
            }
        '''

    class Wrcr(RegOp):
        def __init__(self, dest, src1, flags=None, dataSize="env.dataSize"):
            super(Wrcr, self).__init__(dest, \
                    src1, "InstRegIndex(NUM_INTREGS)", flags, dataSize)
        code = '''
            if (dest == 1 || (dest > 4 && dest < 8) || (dest > 8)) {
                fault = new InvalidOpcode();
            } else {
                // There are *s in the line below so it doesn't confuse the
                // parser. They may be unnecessary.
                //Mis*cReg old*Val = pick(Cont*rolDest, 0, dat*aSize);
                MiscReg newVal = psrc1;

                // Check for any modifications that would cause a fault.
                switch(dest) {
                  case 0:
                    {
                        Efer efer = EferOp;
                        CR0 cr0 = newVal;
                        CR4 oldCr4 = CR4Op;
                        if (bits(newVal, 63, 32) ||
                                (!cr0.pe && cr0.pg) ||
                                (!cr0.cd && cr0.nw) ||
                                (cr0.pg && efer.lme && !oldCr4.pae))
                            fault = new GeneralProtection(0);
                    }
                    break;
                  case 2:
                    break;
                  case 3:
                    break;
                  case 4:
                    {
                        CR4 cr4 = newVal;
                        // PAE can't be disabled in long mode.
                        if (bits(newVal, 63, 11) ||
                                (machInst.mode.mode == LongMode && !cr4.pae))
                            fault = new GeneralProtection(0);
                    }
                    break;
                  case 8:
                    {
                        if (bits(newVal, 63, 4))
                            fault = new GeneralProtection(0);
                    }
                  default:
                    panic("Unrecognized control register %d.\\n", dest);
                }
                ControlDest = newVal;
            }
            '''

    # Microops for manipulating segmentation registers
    class SegOp(CondRegOp):
        abstract = True
        def __init__(self, dest, src1, flags=None, dataSize="env.dataSize"):
            super(SegOp, self).__init__(dest, \
                    src1, "InstRegIndex(NUM_INTREGS)", flags, dataSize)

    class Wrbase(SegOp):
        code = '''
            SegBaseDest = psrc1;
        '''

    class Wrlimit(SegOp):
        code = '''
            SegLimitDest = psrc1;
        '''

    class Wrsel(SegOp):
        code = '''
            SegSelDest = psrc1;
        '''

    class WrAttr(SegOp):
        code = '''
            SegAttrDest = psrc1;
        '''

    class Rdbase(SegOp):
        code = '''
            DestReg = merge(DestReg, SegBaseSrc1, dataSize);
        '''

    class Rdlimit(SegOp):
        code = '''
            DestReg = merge(DestReg, SegLimitSrc1, dataSize);
        '''

    class RdAttr(SegOp):
        code = '''
            DestReg = merge(DestReg, SegAttrSrc1, dataSize);
        '''

    class Rdsel(SegOp):
        code = '''
            DestReg = merge(DestReg, SegSelSrc1, dataSize);
        '''

    class Rdval(RegOp):
        def __init__(self, dest, src1, flags=None, dataSize="env.dataSize"):
            super(Rdval, self).__init__(dest, src1, \
                    "InstRegIndex(NUM_INTREGS)", flags, dataSize)
        code = '''
            DestReg = MiscRegSrc1;
        '''

    class Wrval(RegOp):
        def __init__(self, dest, src1, flags=None, dataSize="env.dataSize"):
            super(Wrval, self).__init__(dest, src1, \
                    "InstRegIndex(NUM_INTREGS)", flags, dataSize)
        code = '''
            MiscRegDest = SrcReg1;
        '''

    class Chks(RegOp):
        def __init__(self, dest, src1, src2=0,
                flags=None, dataSize="env.dataSize"):
            super(Chks, self).__init__(dest,
                    src1, src2, flags, dataSize)
        code = '''
            // The selector is in source 1 and can be at most 16 bits.
            SegSelector selector = DestReg;
            SegDescriptor desc = SrcReg1;
            HandyM5Reg m5reg = M5Reg;

            switch (imm8)
            {
              case SegNoCheck:
                break;
              case SegCSCheck:
                // Make sure it's the right type
                if (desc.s == 0 || desc.type.codeOrData != 1) {
                    fault = new GeneralProtection(0);
                } else if (m5reg.cpl != desc.dpl) {
                    fault = new GeneralProtection(0);
                }
                break;
              case SegCallGateCheck:
                panic("CS checks for far calls/jumps through call gates"
                        "not implemented.\\n");
                break;
              case SegSoftIntGateCheck:
                // Check permissions.
                if (desc.dpl < m5reg.cpl) {
                    fault = new GeneralProtection(selector);
                    break;
                }
                // Fall through on purpose
              case SegIntGateCheck:
                // Make sure the gate's the right type.
                if ((m5reg.mode == LongMode && (desc.type & 0xe) != 0xe) ||
                        ((desc.type & 0x6) != 0x6)) {
                    fault = new GeneralProtection(0);
                }
                break;
              case SegSSCheck:
                if (selector.si || selector.ti) {
                    if (!desc.p) {
                        fault = new StackFault(selector);
                    }
                } else {
                    if ((m5reg.submode != SixtyFourBitMode ||
                                m5reg.cpl == 3) ||
                            !(desc.s == 1 &&
                            desc.type.codeOrData == 0 && desc.type.w) ||
                            (desc.dpl != m5reg.cpl) ||
                            (selector.rpl != m5reg.cpl)) {
                        fault = new GeneralProtection(selector);
                    }
                }
                break;
              case SegIretCheck:
                {
                    if ((!selector.si && !selector.ti) ||
                            (selector.rpl < m5reg.cpl) ||
                            !(desc.s == 1 && desc.type.codeOrData == 1) ||
                            (!desc.type.c && desc.dpl != selector.rpl) ||
                            (desc.type.c && desc.dpl > selector.rpl)) {
                        fault = new GeneralProtection(selector);
                    } else if (!desc.p) {
                        fault = new SegmentNotPresent(selector);
                    }
                    break;
                }
              case SegIntCSCheck:
                if (m5reg.mode == LongMode) {
                    if (desc.l != 1 || desc.d != 0) {
                        fault = new GeneralProtection(selector);
                    }
                } else {
                    panic("Interrupt CS checks not implemented "
                            "in legacy mode.\\n");
                }
                break;
              case SegTRCheck:
                if (!selector.si || selector.ti) {
                    fault = new GeneralProtection(selector);
                }
                break;
              case SegTSSCheck:
                if (!desc.p) {
                    fault = new SegmentNotPresent(selector);
                } else if (!(desc.type == 0x9 ||
                        (desc.type == 1 &&
                         m5reg.mode != LongMode))) {
                    fault = new GeneralProtection(selector);
                }
                break;
              case SegInGDTCheck:
                if (selector.ti) {
                    fault = new GeneralProtection(selector);
                }
                break;
              case SegLDTCheck:
                if (!desc.p) {
                    fault = new SegmentNotPresent(selector);
                } else if (desc.type != 0x2) {
                    fault = new GeneralProtection(selector);
                }
                break;
              default:
                panic("Undefined segment check type.\\n");
            }
        '''
        flag_code = '''
            // Check for a NULL selector and set ZF,EZF appropriately.
            ccFlagBits = ccFlagBits & ~(ext & (ZFBit | EZFBit));
            if (!selector.si && !selector.ti)
                ccFlagBits = ccFlagBits | (ext & (ZFBit | EZFBit));
        '''

    class Wrdh(RegOp):
        code = '''
            SegDescriptor desc = SrcReg1;

            uint64_t target = bits(SrcReg2, 31, 0) << 32;
            switch(desc.type) {
              case LDT64:
              case AvailableTSS64:
              case BusyTSS64:
                replaceBits(target, 23, 0, desc.baseLow);
                replaceBits(target, 31, 24, desc.baseHigh);
                break;
              case CallGate64:
              case IntGate64:
              case TrapGate64:
                replaceBits(target, 15, 0, bits(desc, 15, 0));
                replaceBits(target, 31, 16, bits(desc, 63, 48));
                break;
              default:
                panic("Wrdh used with wrong descriptor type!\\n");
            }
            DestReg = target;
        '''

    class Wrtsc(WrRegOp):
        code = '''
            TscOp = psrc1;
        '''

    class Rdtsc(RdRegOp):
        code = '''
            DestReg = TscOp;
        '''

    class Rdm5reg(RdRegOp):
        code = '''
            DestReg = M5Reg;
        '''

    class Wrdl(RegOp):
        code = '''
            SegDescriptor desc = SrcReg1;
            SegSelector selector = SrcReg2;
            if (selector.si || selector.ti) {
                if (!desc.p)
                    panic("Segment not present.\\n");
                SegAttr attr = 0;
                attr.dpl = desc.dpl;
                attr.unusable = 0;
                attr.defaultSize = desc.d;
                attr.longMode = desc.l;
                attr.avl = desc.avl;
                attr.granularity = desc.g;
                attr.present = desc.p;
                attr.system = desc.s;
                attr.type = desc.type;
                if (!desc.s) {
                    // The expand down bit happens to be set for gates.
                    if (desc.type.e) {
                        panic("Gate descriptor encountered.\\n");
                    }
                    attr.readable = 1;
                    attr.writable = 1;
                    attr.expandDown = 0;
                } else {
                    if (desc.type.codeOrData) {
                        attr.expandDown = 0;
                        attr.readable = desc.type.r;
                        attr.writable = 0;
                    } else {
                        attr.expandDown = desc.type.e;
                        attr.readable = 1;
                        attr.writable = desc.type.w;
                    }
                }
                Addr base = desc.baseLow | (desc.baseHigh << 24);
                Addr limit = desc.limitLow | (desc.limitHigh << 16);
                if (desc.g)
                    limit = (limit << 12) | mask(12);
                SegBaseDest = base;
                SegLimitDest = limit;
                SegAttrDest = attr;
            } else {
                SegBaseDest = SegBaseDest;
                SegLimitDest = SegLimitDest;
                SegAttrDest = SegAttrDest;
            }
        '''
}};