xref: /gem5/src/arch/mips/isa/formats/branch.isa

// -*- mode:c++ -*-

////////////////////////////////////////////////////////////////////
//
// Control transfer instructions
//

output header {{

#include <iostream>
    using namespace std;

    /**
     * Base class for instructions whose disassembly is not purely a
     * function of the machine instruction (i.e., it depends on the
     * PC).  This class overrides the disassemble() method to check
     * the PC and symbol table values before re-using a cached
     * disassembly string.  This is necessary for branches and jumps,
     * where the disassembly string includes the target address (which
     * may depend on the PC and/or symbol table).
     */
    class PCDependentDisassembly : public MipsStaticInst
    {
      protected:
        /// Cached program counter from last disassembly
        mutable Addr cachedPC;

        /// Cached symbol table pointer from last disassembly
        mutable const SymbolTable *cachedSymtab;

        /// Constructor
        PCDependentDisassembly(const char *mnem, MachInst _machInst,
                               OpClass __opClass)
            : MipsStaticInst(mnem, _machInst, __opClass),
              cachedPC(0), cachedSymtab(0)
        {
        }

        const std::string &
        disassemble(Addr pc, const SymbolTable *symtab) const;
    };

    /**
     * Base class for branches (PC-relative control transfers),
     * conditional or unconditional.
     */
    class Branch : public PCDependentDisassembly
    {
      protected:
        /// target address (signed) Displacement .
        int32_t disp;

        /// Constructor.
        Branch(const char *mnem, MachInst _machInst, OpClass __opClass)
            : PCDependentDisassembly(mnem, _machInst, __opClass),
              disp(OFFSET << 2)
        {
            //If Bit 17 is 1 then Sign Extend
            if ( (disp & 0x00020000) > 0  ) {
                disp |= 0xFFFE0000;
            }
        }

        Addr branchTarget(Addr branchPC) const;

        std::string
        generateDisassembly(Addr pc, const SymbolTable *symtab) const;
    };

    /**
     * Base class for jumps (register-indirect control transfers).  In
     * the Mips ISA, these are always unconditional.
     */
    class Jump : public PCDependentDisassembly
    {
      protected:

        /// Displacement to target address (signed).
        int32_t disp;

        uint32_t target;

      public:
        /// Constructor
        Jump(const char *mnem, MachInst _machInst, OpClass __opClass)
            : PCDependentDisassembly(mnem, _machInst, __opClass),
              disp(JMPTARG << 2)
        {
        }

        Addr branchTarget(ThreadContext *tc) const;

        std::string
        generateDisassembly(Addr pc, const SymbolTable *symtab) const;
    };
}};

output decoder {{
    Addr
    Branch::branchTarget(Addr branchPC) const
    {
        return branchPC + 4 + disp;
    }

    Addr
    Jump::branchTarget(ThreadContext *tc) const
    {
        Addr NPC = tc->readPC() + 4;
        uint64_t Rb = tc->readIntReg(_srcRegIdx[0]);
        return (Rb & ~3) | (NPC & 1);
    }

    const std::string &
    PCDependentDisassembly::disassemble(Addr pc,
                                        const SymbolTable *symtab) const
    {
        if (!cachedDisassembly ||
            pc != cachedPC || symtab != cachedSymtab)
        {
            if (cachedDisassembly)
                delete cachedDisassembly;

            cachedDisassembly =
                new std::string(generateDisassembly(pc, symtab));
            cachedPC = pc;
            cachedSymtab = symtab;
        }

        return *cachedDisassembly;
    }

    std::string
    Branch::generateDisassembly(Addr pc, const SymbolTable *symtab) const
    {
        std::stringstream ss;

        ccprintf(ss, "%-10s ", mnemonic);

        // There's only one register arg (RA), but it could be
        // either a source (the condition for conditional
        // branches) or a destination (the link reg for
        // unconditional branches)
        if (_numSrcRegs == 1) {
            printReg(ss, _srcRegIdx[0]);
            ss << ", ";
        } else if(_numSrcRegs == 2) {
            printReg(ss, _srcRegIdx[0]);
            ss << ", ";
            printReg(ss, _srcRegIdx[1]);
            ss << ", ";
        }

        Addr target = pc + 4 + disp;

        std::string str;
        if (symtab && symtab->findSymbol(target, str))
            ss << str;
        else
            ccprintf(ss, "0x%x", target);

        return ss.str();
    }

    std::string
    Jump::generateDisassembly(Addr pc, const SymbolTable *symtab) const
    {
        std::stringstream ss;

        ccprintf(ss, "%-10s ", mnemonic);

        if ( mnemonic == "jal" ) {
            Addr npc = pc + 4;
            ccprintf(ss,"0x%x",(npc & 0xF0000000) | disp);
        } else if (_numSrcRegs == 0) {
            std::string str;
            if (symtab && symtab->findSymbol(disp, str))
                ss << str;
            else
                ccprintf(ss, "0x%x", disp);
        } else if (_numSrcRegs == 1) {
             printReg(ss, _srcRegIdx[0]);
        } else if(_numSrcRegs == 2) {
            printReg(ss, _srcRegIdx[0]);
            ss << ", ";
            printReg(ss, _srcRegIdx[1]);
        }

        return ss.str();
    }
}};

def format Branch(code,*opt_flags) {{
    not_taken_code = '  NNPC = NNPC;\n'
    not_taken_code += '} \n'

    #Build Instruction Flags
    #Use Link & Likely Flags to Add Link/Condition Code
    inst_flags = ('IsDirectControl', )
    for x in opt_flags:
        if x == 'Link':
            code += 'R31 = NNPC;\n'
        elif x == 'Likely':
            not_taken_code = '  NPC = NNPC;\n'
            not_taken_code += '  NNPC = NNPC + 4;\n'
            not_taken_code += '} \n'
            inst_flags = ('IsCondDelaySlot', )
        else:
            inst_flags += (x, )

    if 'cond == 1' in code:
         inst_flags += ('IsCondControl', )
    else:
         inst_flags += ('IsUncondControl', )

    #Condition code
    code = 'bool cond;\n' + code
    code += 'if (cond) {\n'
    code += '  NNPC = NPC + disp;\n'
    code += '} else {\n'
    code += not_taken_code

    iop = InstObjParams(name, Name, 'Branch', CodeBlock(code), inst_flags)
    header_output = BasicDeclare.subst(iop)
    decoder_output = BasicConstructor.subst(iop)
    decode_block = BasicDecode.subst(iop)
    exec_output = BasicExecute.subst(iop)
}};

def format Jump(code, *opt_flags) {{
    #Build Instruction Flags
    #Use Link Flag to Add Link Code
    inst_flags = ('IsIndirectControl', 'IsUncondControl')
    for x in opt_flags:
        if x == 'Link':
            code = 'R31 = NNPC;\n' + code
        elif x == 'ClearHazards':
            code += '/* Code Needed to Clear Execute & Inst Hazards */\n'
        else:
            inst_flags += (x, )

    iop = InstObjParams(name, Name, 'Jump', CodeBlock(code), inst_flags)
    header_output = BasicDeclare.subst(iop)
    decoder_output = BasicConstructor.subst(iop)
    decode_block = BasicDecode.subst(iop)
    exec_output = BasicExecute.subst(iop)
}};