1 //===-- llvm/CodeGen/MachineCodeEmitter.h - Code emission -------*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file defines an abstract interface that is used by the machine code 11 // emission framework to output the code. This allows machine code emission to 12 // be separated from concerns such as resolution of call targets, and where the 13 // machine code will be written (memory or disk, f.e.). 14 // 15 //===----------------------------------------------------------------------===// 16 17 #ifndef LLVM_CODEGEN_MACHINECODEEMITTER_H 18 #define LLVM_CODEGEN_MACHINECODEEMITTER_H 19 20 #include "llvm/IR/DebugLoc.h" 21 #include "llvm/Support/DataTypes.h" 22 #include <string> 23 24 namespace llvm { 25 26 class MachineBasicBlock; 27 class MachineConstantPool; 28 class MachineJumpTableInfo; 29 class MachineFunction; 30 class MachineModuleInfo; 31 class MachineRelocation; 32 class Value; 33 class GlobalValue; 34 class Function; 35 class MCSymbol; 36 37 /// MachineCodeEmitter - This class defines two sorts of methods: those for 38 /// emitting the actual bytes of machine code, and those for emitting auxiliary 39 /// structures, such as jump tables, relocations, etc. 40 /// 41 /// Emission of machine code is complicated by the fact that we don't (in 42 /// general) know the size of the machine code that we're about to emit before 43 /// we emit it. As such, we preallocate a certain amount of memory, and set the 44 /// BufferBegin/BufferEnd pointers to the start and end of the buffer. As we 45 /// emit machine instructions, we advance the CurBufferPtr to indicate the 46 /// location of the next byte to emit. In the case of a buffer overflow (we 47 /// need to emit more machine code than we have allocated space for), the 48 /// CurBufferPtr will saturate to BufferEnd and ignore stores. Once the entire 49 /// function has been emitted, the overflow condition is checked, and if it has 50 /// occurred, more memory is allocated, and we reemit the code into it. 51 /// 52 class MachineCodeEmitter { 53 virtual void anchor(); 54 protected: 55 /// BufferBegin/BufferEnd - Pointers to the start and end of the memory 56 /// allocated for this code buffer. 57 uint8_t *BufferBegin, *BufferEnd; 58 /// CurBufferPtr - Pointer to the next byte of memory to fill when emitting 59 /// code. This is guaranteed to be in the range [BufferBegin,BufferEnd]. If 60 /// this pointer is at BufferEnd, it will never move due to code emission, and 61 /// all code emission requests will be ignored (this is the buffer overflow 62 /// condition). 63 uint8_t *CurBufferPtr; 64 65 public: 66 virtual ~MachineCodeEmitter() {} 67 68 /// startFunction - This callback is invoked when the specified function is 69 /// about to be code generated. This initializes the BufferBegin/End/Ptr 70 /// fields. 71 /// 72 virtual void startFunction(MachineFunction &F) = 0; 73 74 /// finishFunction - This callback is invoked when the specified function has 75 /// finished code generation. If a buffer overflow has occurred, this method 76 /// returns true (the callee is required to try again), otherwise it returns 77 /// false. 78 /// 79 virtual bool finishFunction(MachineFunction &F) = 0; 80 81 /// emitByte - This callback is invoked when a byte needs to be written to the 82 /// output stream. 83 /// 84 void emitByte(uint8_t B) { 85 if (CurBufferPtr != BufferEnd) 86 *CurBufferPtr++ = B; 87 } 88 89 /// emitWordLE - This callback is invoked when a 32-bit word needs to be 90 /// written to the output stream in little-endian format. 91 /// 92 void emitWordLE(uint32_t W) { 93 if (4 <= BufferEnd-CurBufferPtr) { 94 emitWordLEInto(CurBufferPtr, W); 95 } else { 96 CurBufferPtr = BufferEnd; 97 } 98 } 99 100 /// emitWordLEInto - This callback is invoked when a 32-bit word needs to be 101 /// written to an arbitrary buffer in little-endian format. Buf must have at 102 /// least 4 bytes of available space. 103 /// 104 static void emitWordLEInto(uint8_t *&Buf, uint32_t W) { 105 *Buf++ = (uint8_t)(W >> 0); 106 *Buf++ = (uint8_t)(W >> 8); 107 *Buf++ = (uint8_t)(W >> 16); 108 *Buf++ = (uint8_t)(W >> 24); 109 } 110 111 /// emitWordBE - This callback is invoked when a 32-bit word needs to be 112 /// written to the output stream in big-endian format. 113 /// 114 void emitWordBE(uint32_t W) { 115 if (4 <= BufferEnd-CurBufferPtr) { 116 *CurBufferPtr++ = (uint8_t)(W >> 24); 117 *CurBufferPtr++ = (uint8_t)(W >> 16); 118 *CurBufferPtr++ = (uint8_t)(W >> 8); 119 *CurBufferPtr++ = (uint8_t)(W >> 0); 120 } else { 121 CurBufferPtr = BufferEnd; 122 } 123 } 124 125 /// emitDWordLE - This callback is invoked when a 64-bit word needs to be 126 /// written to the output stream in little-endian format. 127 /// 128 void emitDWordLE(uint64_t W) { 129 if (8 <= BufferEnd-CurBufferPtr) { 130 *CurBufferPtr++ = (uint8_t)(W >> 0); 131 *CurBufferPtr++ = (uint8_t)(W >> 8); 132 *CurBufferPtr++ = (uint8_t)(W >> 16); 133 *CurBufferPtr++ = (uint8_t)(W >> 24); 134 *CurBufferPtr++ = (uint8_t)(W >> 32); 135 *CurBufferPtr++ = (uint8_t)(W >> 40); 136 *CurBufferPtr++ = (uint8_t)(W >> 48); 137 *CurBufferPtr++ = (uint8_t)(W >> 56); 138 } else { 139 CurBufferPtr = BufferEnd; 140 } 141 } 142 143 /// emitDWordBE - This callback is invoked when a 64-bit word needs to be 144 /// written to the output stream in big-endian format. 145 /// 146 void emitDWordBE(uint64_t W) { 147 if (8 <= BufferEnd-CurBufferPtr) { 148 *CurBufferPtr++ = (uint8_t)(W >> 56); 149 *CurBufferPtr++ = (uint8_t)(W >> 48); 150 *CurBufferPtr++ = (uint8_t)(W >> 40); 151 *CurBufferPtr++ = (uint8_t)(W >> 32); 152 *CurBufferPtr++ = (uint8_t)(W >> 24); 153 *CurBufferPtr++ = (uint8_t)(W >> 16); 154 *CurBufferPtr++ = (uint8_t)(W >> 8); 155 *CurBufferPtr++ = (uint8_t)(W >> 0); 156 } else { 157 CurBufferPtr = BufferEnd; 158 } 159 } 160 161 /// emitAlignment - Move the CurBufferPtr pointer up to the specified 162 /// alignment (saturated to BufferEnd of course). 163 void emitAlignment(unsigned Alignment) { 164 if (Alignment == 0) Alignment = 1; 165 166 if(Alignment <= (uintptr_t)(BufferEnd-CurBufferPtr)) { 167 // Move the current buffer ptr up to the specified alignment. 168 CurBufferPtr = 169 (uint8_t*)(((uintptr_t)CurBufferPtr+Alignment-1) & 170 ~(uintptr_t)(Alignment-1)); 171 } else { 172 CurBufferPtr = BufferEnd; 173 } 174 } 175 176 177 /// emitULEB128Bytes - This callback is invoked when a ULEB128 needs to be 178 /// written to the output stream. 179 void emitULEB128Bytes(uint64_t Value) { 180 do { 181 uint8_t Byte = Value & 0x7f; 182 Value >>= 7; 183 if (Value) Byte |= 0x80; 184 emitByte(Byte); 185 } while (Value); 186 } 187 188 /// emitSLEB128Bytes - This callback is invoked when a SLEB128 needs to be 189 /// written to the output stream. 190 void emitSLEB128Bytes(uint64_t Value) { 191 uint64_t Sign = Value >> (8 * sizeof(Value) - 1); 192 bool IsMore; 193 194 do { 195 uint8_t Byte = Value & 0x7f; 196 Value >>= 7; 197 IsMore = Value != Sign || ((Byte ^ Sign) & 0x40) != 0; 198 if (IsMore) Byte |= 0x80; 199 emitByte(Byte); 200 } while (IsMore); 201 } 202 203 /// emitString - This callback is invoked when a String needs to be 204 /// written to the output stream. 205 void emitString(const std::string &String) { 206 for (unsigned i = 0, N = static_cast<unsigned>(String.size()); 207 i < N; ++i) { 208 uint8_t C = String[i]; 209 emitByte(C); 210 } 211 emitByte(0); 212 } 213 214 /// emitInt32 - Emit a int32 directive. 215 void emitInt32(int32_t Value) { 216 if (4 <= BufferEnd-CurBufferPtr) { 217 *((uint32_t*)CurBufferPtr) = Value; 218 CurBufferPtr += 4; 219 } else { 220 CurBufferPtr = BufferEnd; 221 } 222 } 223 224 /// emitInt64 - Emit a int64 directive. 225 void emitInt64(uint64_t Value) { 226 if (8 <= BufferEnd-CurBufferPtr) { 227 *((uint64_t*)CurBufferPtr) = Value; 228 CurBufferPtr += 8; 229 } else { 230 CurBufferPtr = BufferEnd; 231 } 232 } 233 234 /// emitInt32At - Emit the Int32 Value in Addr. 235 void emitInt32At(uintptr_t *Addr, uintptr_t Value) { 236 if (Addr >= (uintptr_t*)BufferBegin && Addr < (uintptr_t*)BufferEnd) 237 (*(uint32_t*)Addr) = (uint32_t)Value; 238 } 239 240 /// emitInt64At - Emit the Int64 Value in Addr. 241 void emitInt64At(uintptr_t *Addr, uintptr_t Value) { 242 if (Addr >= (uintptr_t*)BufferBegin && Addr < (uintptr_t*)BufferEnd) 243 (*(uint64_t*)Addr) = (uint64_t)Value; 244 } 245 246 /// processDebugLoc - Records debug location information about a 247 /// MachineInstruction. This is called before emitting any bytes associated 248 /// with the instruction. Even if successive instructions have the same debug 249 /// location, this method will be called for each one. 250 virtual void processDebugLoc(DebugLoc DL, bool BeforePrintintInsn) {} 251 252 /// emitLabel - Emits a label 253 virtual void emitLabel(MCSymbol *Label) = 0; 254 255 /// allocateSpace - Allocate a block of space in the current output buffer, 256 /// returning null (and setting conditions to indicate buffer overflow) on 257 /// failure. Alignment is the alignment in bytes of the buffer desired. 258 virtual void *allocateSpace(uintptr_t Size, unsigned Alignment) { 259 emitAlignment(Alignment); 260 void *Result; 261 262 // Check for buffer overflow. 263 if (Size >= (uintptr_t)(BufferEnd-CurBufferPtr)) { 264 CurBufferPtr = BufferEnd; 265 Result = nullptr; 266 } else { 267 // Allocate the space. 268 Result = CurBufferPtr; 269 CurBufferPtr += Size; 270 } 271 272 return Result; 273 } 274 275 /// StartMachineBasicBlock - This should be called by the target when a new 276 /// basic block is about to be emitted. This way the MCE knows where the 277 /// start of the block is, and can implement getMachineBasicBlockAddress. 278 virtual void StartMachineBasicBlock(MachineBasicBlock *MBB) = 0; 279 280 /// getCurrentPCValue - This returns the address that the next emitted byte 281 /// will be output to. 282 /// 283 virtual uintptr_t getCurrentPCValue() const { 284 return (uintptr_t)CurBufferPtr; 285 } 286 287 /// getCurrentPCOffset - Return the offset from the start of the emitted 288 /// buffer that we are currently writing to. 289 virtual uintptr_t getCurrentPCOffset() const { 290 return CurBufferPtr-BufferBegin; 291 } 292 293 /// earlyResolveAddresses - True if the code emitter can use symbol addresses 294 /// during code emission time. The JIT is capable of doing this because it 295 /// creates jump tables or constant pools in memory on the fly while the 296 /// object code emitters rely on a linker to have real addresses and should 297 /// use relocations instead. 298 virtual bool earlyResolveAddresses() const = 0; 299 300 /// addRelocation - Whenever a relocatable address is needed, it should be 301 /// noted with this interface. 302 virtual void addRelocation(const MachineRelocation &MR) = 0; 303 304 /// FIXME: These should all be handled with relocations! 305 306 /// getConstantPoolEntryAddress - Return the address of the 'Index' entry in 307 /// the constant pool that was last emitted with the emitConstantPool method. 308 /// 309 virtual uintptr_t getConstantPoolEntryAddress(unsigned Index) const = 0; 310 311 /// getJumpTableEntryAddress - Return the address of the jump table with index 312 /// 'Index' in the function that last called initJumpTableInfo. 313 /// 314 virtual uintptr_t getJumpTableEntryAddress(unsigned Index) const = 0; 315 316 /// getMachineBasicBlockAddress - Return the address of the specified 317 /// MachineBasicBlock, only usable after the label for the MBB has been 318 /// emitted. 319 /// 320 virtual uintptr_t getMachineBasicBlockAddress(MachineBasicBlock *MBB) const= 0; 321 322 /// getLabelAddress - Return the address of the specified Label, only usable 323 /// after the LabelID has been emitted. 324 /// 325 virtual uintptr_t getLabelAddress(MCSymbol *Label) const = 0; 326 327 /// Specifies the MachineModuleInfo object. This is used for exception handling 328 /// purposes. 329 virtual void setModuleInfo(MachineModuleInfo* Info) = 0; 330 }; 331 332 } // End llvm namespace 333 334 #endif 335
