branch.isa revision 2686:f0d591379ac3
1// -*- mode:c++ -*- 2 3//////////////////////////////////////////////////////////////////// 4// 5// Control transfer instructions 6// 7 8output header {{ 9 10#include <iostream> 11 using namespace std; 12 13 /** 14 * Base class for instructions whose disassembly is not purely a 15 * function of the machine instruction (i.e., it depends on the 16 * PC). This class overrides the disassemble() method to check 17 * the PC and symbol table values before re-using a cached 18 * disassembly string. This is necessary for branches and jumps, 19 * where the disassembly string includes the target address (which 20 * may depend on the PC and/or symbol table). 21 */ 22 class PCDependentDisassembly : public MipsStaticInst 23 { 24 protected: 25 /// Cached program counter from last disassembly 26 mutable Addr cachedPC; 27 28 /// Cached symbol table pointer from last disassembly 29 mutable const SymbolTable *cachedSymtab; 30 31 /// Constructor 32 PCDependentDisassembly(const char *mnem, MachInst _machInst, 33 OpClass __opClass) 34 : MipsStaticInst(mnem, _machInst, __opClass), 35 cachedPC(0), cachedSymtab(0) 36 { 37 } 38 39 const std::string & 40 disassemble(Addr pc, const SymbolTable *symtab) const; 41 }; 42 43 /** 44 * Base class for branches (PC-relative control transfers), 45 * conditional or unconditional. 46 */ 47 class Branch : public PCDependentDisassembly 48 { 49 protected: 50 /// target address (signed) Displacement . 51 int32_t disp; 52 53 /// Constructor. 54 Branch(const char *mnem, MachInst _machInst, OpClass __opClass) 55 : PCDependentDisassembly(mnem, _machInst, __opClass), 56 disp(OFFSET << 2) 57 { 58 //If Bit 17 is 1 then Sign Extend 59 if ( (disp & 0x00020000) > 0 ) { 60 disp |= 0xFFFE0000; 61 } 62 } 63 64 Addr branchTarget(Addr branchPC) const; 65 66 std::string 67 generateDisassembly(Addr pc, const SymbolTable *symtab) const; 68 }; 69 70 /** 71 * Base class for jumps (register-indirect control transfers). In 72 * the Mips ISA, these are always unconditional. 73 */ 74 class Jump : public PCDependentDisassembly 75 { 76 protected: 77 78 /// Displacement to target address (signed). 79 int32_t disp; 80 81 uint32_t target; 82 83 public: 84 /// Constructor 85 Jump(const char *mnem, MachInst _machInst, OpClass __opClass) 86 : PCDependentDisassembly(mnem, _machInst, __opClass), 87 disp(JMPTARG << 2) 88 { 89 } 90 91 Addr branchTarget(ExecContext *xc) const; 92 93 std::string 94 generateDisassembly(Addr pc, const SymbolTable *symtab) const; 95 }; 96}}; 97 98output decoder {{ 99 Addr 100 Branch::branchTarget(Addr branchPC) const 101 { 102 return branchPC + 4 + disp; 103 } 104 105 Addr 106 Jump::branchTarget(ExecContext *xc) const 107 { 108 Addr NPC = xc->readPC() + 4; 109 uint64_t Rb = xc->readIntReg(_srcRegIdx[0]); 110 return (Rb & ~3) | (NPC & 1); 111 } 112 113 const std::string & 114 PCDependentDisassembly::disassemble(Addr pc, 115 const SymbolTable *symtab) const 116 { 117 if (!cachedDisassembly || 118 pc != cachedPC || symtab != cachedSymtab) 119 { 120 if (cachedDisassembly) 121 delete cachedDisassembly; 122 123 cachedDisassembly = 124 new std::string(generateDisassembly(pc, symtab)); 125 cachedPC = pc; 126 cachedSymtab = symtab; 127 } 128 129 return *cachedDisassembly; 130 } 131 132 std::string 133 Branch::generateDisassembly(Addr pc, const SymbolTable *symtab) const 134 { 135 std::stringstream ss; 136 137 ccprintf(ss, "%-10s ", mnemonic); 138 139 // There's only one register arg (RA), but it could be 140 // either a source (the condition for conditional 141 // branches) or a destination (the link reg for 142 // unconditional branches) 143 if (_numSrcRegs == 1) { 144 printReg(ss, _srcRegIdx[0]); 145 ss << ", "; 146 } else if(_numSrcRegs == 2) { 147 printReg(ss, _srcRegIdx[0]); 148 ss << ", "; 149 printReg(ss, _srcRegIdx[1]); 150 ss << ", "; 151 } 152 153 Addr target = pc + 4 + disp; 154 155 std::string str; 156 if (symtab && symtab->findSymbol(target, str)) 157 ss << str; 158 else 159 ccprintf(ss, "0x%x", target); 160 161 return ss.str(); 162 } 163 164 std::string 165 Jump::generateDisassembly(Addr pc, const SymbolTable *symtab) const 166 { 167 std::stringstream ss; 168 169 ccprintf(ss, "%-10s ", mnemonic); 170 171 if ( mnemonic == "jal" ) { 172 Addr npc = pc + 4; 173 ccprintf(ss,"0x%x",(npc & 0xF0000000) | disp); 174 } else if (_numSrcRegs == 0) { 175 std::string str; 176 if (symtab && symtab->findSymbol(disp, str)) 177 ss << str; 178 else 179 ccprintf(ss, "0x%x", disp); 180 } else if (_numSrcRegs == 1) { 181 printReg(ss, _srcRegIdx[0]); 182 } else if(_numSrcRegs == 2) { 183 printReg(ss, _srcRegIdx[0]); 184 ss << ", "; 185 printReg(ss, _srcRegIdx[1]); 186 } 187 188 return ss.str(); 189 } 190}}; 191 192def format Branch(code,*opt_flags) {{ 193 not_taken_code = ' NNPC = NNPC;\n' 194 not_taken_code += '} \n' 195 196 #Build Instruction Flags 197 #Use Link & Likely Flags to Add Link/Condition Code 198 inst_flags = ('IsDirectControl', ) 199 for x in opt_flags: 200 if x == 'Link': 201 code += 'R31 = NNPC;\n' 202 elif x == 'Likely': 203 not_taken_code = ' NPC = NNPC;\n' 204 not_taken_code += ' NNPC = NNPC + 4;\n' 205 not_taken_code += '} \n' 206 inst_flags = ('IsCondDelaySlot', ) 207 else: 208 inst_flags += (x, ) 209 210 if 'cond == 1' in code: 211 inst_flags += ('IsCondControl', ) 212 else: 213 inst_flags += ('IsUncondControl', ) 214 215 #Condition code 216 code = 'bool cond;\n' + code 217 code += 'if (cond) {\n' 218 code += ' NNPC = NPC + disp;\n' 219 code += '} else {\n' 220 code += not_taken_code 221 222 iop = InstObjParams(name, Name, 'Branch', CodeBlock(code), inst_flags) 223 header_output = BasicDeclare.subst(iop) 224 decoder_output = BasicConstructor.subst(iop) 225 decode_block = BasicDecode.subst(iop) 226 exec_output = BasicExecute.subst(iop) 227}}; 228 229def format Jump(code, *opt_flags) {{ 230 #Build Instruction Flags 231 #Use Link Flag to Add Link Code 232 inst_flags = ('IsIndirectControl', 'IsUncondControl') 233 for x in opt_flags: 234 if x == 'Link': 235 code = 'R31 = NNPC;\n' + code 236 elif x == 'ClearHazards': 237 code += '/* Code Needed to Clear Execute & Inst Hazards */\n' 238 else: 239 inst_flags += (x, ) 240 241 iop = InstObjParams(name, Name, 'Jump', CodeBlock(code), inst_flags) 242 header_output = BasicDeclare.subst(iop) 243 decoder_output = BasicConstructor.subst(iop) 244 decode_block = BasicDecode.subst(iop) 245 exec_output = BasicExecute.subst(iop) 246}}; 247 248 249 250 251