LLVM API Documentation
00001 //===-- JITEmitter.cpp - Write machine code to executable memory ----------===// 00002 // 00003 // The LLVM Compiler Infrastructure 00004 // 00005 // This file was developed by the LLVM research group and is distributed under 00006 // the University of Illinois Open Source License. See LICENSE.TXT for details. 00007 // 00008 //===----------------------------------------------------------------------===// 00009 // 00010 // This file defines a MachineCodeEmitter object that is used by the JIT to 00011 // write machine code to memory and remember where relocatable values are. 00012 // 00013 //===----------------------------------------------------------------------===// 00014 00015 #define DEBUG_TYPE "jit" 00016 #include "JIT.h" 00017 #include "llvm/Constant.h" 00018 #include "llvm/Module.h" 00019 #include "llvm/CodeGen/MachineCodeEmitter.h" 00020 #include "llvm/CodeGen/MachineFunction.h" 00021 #include "llvm/CodeGen/MachineConstantPool.h" 00022 #include "llvm/CodeGen/MachineRelocation.h" 00023 #include "llvm/Target/TargetData.h" 00024 #include "llvm/Target/TargetJITInfo.h" 00025 #include "llvm/Support/Debug.h" 00026 #include "llvm/ADT/Statistic.h" 00027 #include "llvm/System/Memory.h" 00028 using namespace llvm; 00029 00030 namespace { 00031 Statistic<> NumBytes("jit", "Number of bytes of machine code compiled"); 00032 JIT *TheJIT = 0; 00033 } 00034 00035 00036 //===----------------------------------------------------------------------===// 00037 // JITMemoryManager code. 00038 // 00039 namespace { 00040 /// JITMemoryManager - Manage memory for the JIT code generation in a logical, 00041 /// sane way. This splits a large block of MAP_NORESERVE'd memory into two 00042 /// sections, one for function stubs, one for the functions themselves. We 00043 /// have to do this because we may need to emit a function stub while in the 00044 /// middle of emitting a function, and we don't know how large the function we 00045 /// are emitting is. This never bothers to release the memory, because when 00046 /// we are ready to destroy the JIT, the program exits. 00047 class JITMemoryManager { 00048 sys::MemoryBlock MemBlock; // Virtual memory block allocated RWX 00049 unsigned char *MemBase; // Base of block of memory, start of stub mem 00050 unsigned char *FunctionBase; // Start of the function body area 00051 unsigned char *CurStubPtr, *CurFunctionPtr; 00052 public: 00053 JITMemoryManager(); 00054 00055 inline unsigned char *allocateStub(unsigned StubSize); 00056 inline unsigned char *startFunctionBody(); 00057 inline void endFunctionBody(unsigned char *FunctionEnd); 00058 }; 00059 } 00060 00061 JITMemoryManager::JITMemoryManager() { 00062 // Allocate a 16M block of memory... 00063 MemBlock = sys::Memory::AllocateRWX((16 << 20)); 00064 MemBase = reinterpret_cast<unsigned char*>(MemBlock.base()); 00065 FunctionBase = MemBase + 512*1024; // Use 512k for stubs 00066 00067 // Allocate stubs backwards from the function base, allocate functions forward 00068 // from the function base. 00069 CurStubPtr = CurFunctionPtr = FunctionBase; 00070 } 00071 00072 unsigned char *JITMemoryManager::allocateStub(unsigned StubSize) { 00073 CurStubPtr -= StubSize; 00074 if (CurStubPtr < MemBase) { 00075 std::cerr << "JIT ran out of memory for function stubs!\n"; 00076 abort(); 00077 } 00078 return CurStubPtr; 00079 } 00080 00081 unsigned char *JITMemoryManager::startFunctionBody() { 00082 // Round up to an even multiple of 8 bytes, this should eventually be target 00083 // specific. 00084 return (unsigned char*)(((intptr_t)CurFunctionPtr + 7) & ~7); 00085 } 00086 00087 void JITMemoryManager::endFunctionBody(unsigned char *FunctionEnd) { 00088 assert(FunctionEnd > CurFunctionPtr); 00089 CurFunctionPtr = FunctionEnd; 00090 } 00091 00092 //===----------------------------------------------------------------------===// 00093 // JIT lazy compilation code. 00094 // 00095 namespace { 00096 /// JITResolver - Keep track of, and resolve, call sites for functions that 00097 /// have not yet been compiled. 00098 class JITResolver { 00099 /// MCE - The MachineCodeEmitter to use to emit stubs with. 00100 MachineCodeEmitter &MCE; 00101 00102 /// LazyResolverFn - The target lazy resolver function that we actually 00103 /// rewrite instructions to use. 00104 TargetJITInfo::LazyResolverFn LazyResolverFn; 00105 00106 // FunctionToStubMap - Keep track of the stub created for a particular 00107 // function so that we can reuse them if necessary. 00108 std::map<Function*, void*> FunctionToStubMap; 00109 00110 // StubToFunctionMap - Keep track of the function that each stub corresponds 00111 // to. 00112 std::map<void*, Function*> StubToFunctionMap; 00113 00114 public: 00115 JITResolver(MachineCodeEmitter &mce) : MCE(mce) { 00116 LazyResolverFn = 00117 TheJIT->getJITInfo().getLazyResolverFunction(JITCompilerFn); 00118 } 00119 00120 /// getFunctionStub - This returns a pointer to a function stub, creating 00121 /// one on demand as needed. 00122 void *getFunctionStub(Function *F); 00123 00124 /// AddCallbackAtLocation - If the target is capable of rewriting an 00125 /// instruction without the use of a stub, record the location of the use so 00126 /// we know which function is being used at the location. 00127 void *AddCallbackAtLocation(Function *F, void *Location) { 00128 /// Get the target-specific JIT resolver function. 00129 StubToFunctionMap[Location] = F; 00130 return (void*)LazyResolverFn; 00131 } 00132 00133 /// JITCompilerFn - This function is called to resolve a stub to a compiled 00134 /// address. If the LLVM Function corresponding to the stub has not yet 00135 /// been compiled, this function compiles it first. 00136 static void *JITCompilerFn(void *Stub); 00137 }; 00138 } 00139 00140 /// getJITResolver - This function returns the one instance of the JIT resolver. 00141 /// 00142 static JITResolver &getJITResolver(MachineCodeEmitter *MCE = 0) { 00143 static JITResolver TheJITResolver(*MCE); 00144 return TheJITResolver; 00145 } 00146 00147 /// getFunctionStub - This returns a pointer to a function stub, creating 00148 /// one on demand as needed. 00149 void *JITResolver::getFunctionStub(Function *F) { 00150 // If we already have a stub for this function, recycle it. 00151 void *&Stub = FunctionToStubMap[F]; 00152 if (Stub) return Stub; 00153 00154 // Call the lazy resolver function unless we already KNOW it is an external 00155 // function, in which case we just skip the lazy resolution step. 00156 void *Actual = (void*)LazyResolverFn; 00157 if (F->hasExternalLinkage()) 00158 Actual = TheJIT->getPointerToFunction(F); 00159 00160 // Otherwise, codegen a new stub. For now, the stub will call the lazy 00161 // resolver function. 00162 Stub = TheJIT->getJITInfo().emitFunctionStub(Actual, MCE); 00163 00164 if (F->hasExternalLinkage()) { 00165 // If we are getting the stub for an external function, we really want the 00166 // address of the stub in the GlobalAddressMap for the JIT, not the address 00167 // of the external function. 00168 TheJIT->updateGlobalMapping(F, Stub); 00169 } 00170 00171 DEBUG(std::cerr << "JIT: Stub emitted at [" << Stub << "] for function '" 00172 << F->getName() << "'\n"); 00173 00174 // Finally, keep track of the stub-to-Function mapping so that the 00175 // JITCompilerFn knows which function to compile! 00176 StubToFunctionMap[Stub] = F; 00177 return Stub; 00178 } 00179 00180 /// JITCompilerFn - This function is called when a lazy compilation stub has 00181 /// been entered. It looks up which function this stub corresponds to, compiles 00182 /// it if necessary, then returns the resultant function pointer. 00183 void *JITResolver::JITCompilerFn(void *Stub) { 00184 JITResolver &JR = getJITResolver(); 00185 00186 // The address given to us for the stub may not be exactly right, it might be 00187 // a little bit after the stub. As such, use upper_bound to find it. 00188 std::map<void*, Function*>::iterator I = 00189 JR.StubToFunctionMap.upper_bound(Stub); 00190 assert(I != JR.StubToFunctionMap.begin() && "This is not a known stub!"); 00191 Function *F = (--I)->second; 00192 00193 // The target function will rewrite the stub so that the compilation callback 00194 // function is no longer called from this stub. 00195 JR.StubToFunctionMap.erase(I); 00196 00197 DEBUG(std::cerr << "JIT: Lazily resolving function '" << F->getName() 00198 << "' In stub ptr = " << Stub << " actual ptr = " 00199 << I->first << "\n"); 00200 00201 void *Result = TheJIT->getPointerToFunction(F); 00202 00203 // We don't need to reuse this stub in the future, as F is now compiled. 00204 JR.FunctionToStubMap.erase(F); 00205 00206 // FIXME: We could rewrite all references to this stub if we knew them. 00207 return Result; 00208 } 00209 00210 00211 // getPointerToFunctionOrStub - If the specified function has been 00212 // code-gen'd, return a pointer to the function. If not, compile it, or use 00213 // a stub to implement lazy compilation if available. 00214 // 00215 void *JIT::getPointerToFunctionOrStub(Function *F) { 00216 // If we have already code generated the function, just return the address. 00217 if (void *Addr = getPointerToGlobalIfAvailable(F)) 00218 return Addr; 00219 00220 // Get a stub if the target supports it 00221 return getJITResolver(MCE).getFunctionStub(F); 00222 } 00223 00224 00225 00226 //===----------------------------------------------------------------------===// 00227 // JITEmitter code. 00228 // 00229 namespace { 00230 /// JITEmitter - The JIT implementation of the MachineCodeEmitter, which is 00231 /// used to output functions to memory for execution. 00232 class JITEmitter : public MachineCodeEmitter { 00233 JITMemoryManager MemMgr; 00234 00235 // CurBlock - The start of the current block of memory. CurByte - The 00236 // current byte being emitted to. 00237 unsigned char *CurBlock, *CurByte; 00238 00239 // When outputting a function stub in the context of some other function, we 00240 // save CurBlock and CurByte here. 00241 unsigned char *SavedCurBlock, *SavedCurByte; 00242 00243 // ConstantPoolAddresses - Contains the location for each entry in the 00244 // constant pool. 00245 std::vector<void*> ConstantPoolAddresses; 00246 00247 /// Relocations - These are the relocations that the function needs, as 00248 /// emitted. 00249 std::vector<MachineRelocation> Relocations; 00250 public: 00251 JITEmitter(JIT &jit) { TheJIT = &jit; } 00252 00253 virtual void startFunction(MachineFunction &F); 00254 virtual void finishFunction(MachineFunction &F); 00255 virtual void emitConstantPool(MachineConstantPool *MCP); 00256 virtual void startFunctionStub(unsigned StubSize); 00257 virtual void* finishFunctionStub(const Function *F); 00258 virtual void emitByte(unsigned char B); 00259 virtual void emitWord(unsigned W); 00260 virtual void emitWordAt(unsigned W, unsigned *Ptr); 00261 00262 virtual void addRelocation(const MachineRelocation &MR) { 00263 Relocations.push_back(MR); 00264 } 00265 00266 virtual uint64_t getCurrentPCValue(); 00267 virtual uint64_t getCurrentPCOffset(); 00268 virtual uint64_t getConstantPoolEntryAddress(unsigned Entry); 00269 00270 private: 00271 void *getPointerToGlobal(GlobalValue *GV, void *Reference, bool NoNeedStub); 00272 }; 00273 } 00274 00275 MachineCodeEmitter *JIT::createEmitter(JIT &jit) { 00276 return new JITEmitter(jit); 00277 } 00278 00279 void *JITEmitter::getPointerToGlobal(GlobalValue *V, void *Reference, 00280 bool DoesntNeedStub) { 00281 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) { 00282 /// FIXME: If we straightened things out, this could actually emit the 00283 /// global immediately instead of queuing it for codegen later! 00284 return TheJIT->getOrEmitGlobalVariable(GV); 00285 } 00286 00287 // If we have already compiled the function, return a pointer to its body. 00288 Function *F = cast<Function>(V); 00289 void *ResultPtr = TheJIT->getPointerToGlobalIfAvailable(F); 00290 if (ResultPtr) return ResultPtr; 00291 00292 if (F->hasExternalLinkage() && F->isExternal()) { 00293 // If this is an external function pointer, we can force the JIT to 00294 // 'compile' it, which really just adds it to the map. 00295 if (DoesntNeedStub) 00296 return TheJIT->getPointerToFunction(F); 00297 00298 return getJITResolver(this).getFunctionStub(F); 00299 } 00300 00301 // Okay, the function has not been compiled yet, if the target callback 00302 // mechanism is capable of rewriting the instruction directly, prefer to do 00303 // that instead of emitting a stub. 00304 if (DoesntNeedStub) 00305 return getJITResolver(this).AddCallbackAtLocation(F, Reference); 00306 00307 // Otherwise, we have to emit a lazy resolving stub. 00308 return getJITResolver(this).getFunctionStub(F); 00309 } 00310 00311 void JITEmitter::startFunction(MachineFunction &F) { 00312 CurByte = CurBlock = MemMgr.startFunctionBody(); 00313 TheJIT->addGlobalMapping(F.getFunction(), CurBlock); 00314 } 00315 00316 void JITEmitter::finishFunction(MachineFunction &F) { 00317 MemMgr.endFunctionBody(CurByte); 00318 ConstantPoolAddresses.clear(); 00319 NumBytes += CurByte-CurBlock; 00320 00321 if (!Relocations.empty()) { 00322 // Resolve the relocations to concrete pointers. 00323 for (unsigned i = 0, e = Relocations.size(); i != e; ++i) { 00324 MachineRelocation &MR = Relocations[i]; 00325 void *ResultPtr; 00326 if (MR.isString()) 00327 ResultPtr = TheJIT->getPointerToNamedFunction(MR.getString()); 00328 else 00329 ResultPtr = getPointerToGlobal(MR.getGlobalValue(), 00330 CurBlock+MR.getMachineCodeOffset(), 00331 MR.doesntNeedFunctionStub()); 00332 MR.setResultPointer(ResultPtr); 00333 } 00334 00335 TheJIT->getJITInfo().relocate(CurBlock, &Relocations[0], 00336 Relocations.size()); 00337 } 00338 00339 DEBUG(std::cerr << "JIT: Finished CodeGen of [" << (void*)CurBlock 00340 << "] Function: " << F.getFunction()->getName() 00341 << ": " << CurByte-CurBlock << " bytes of text, " 00342 << Relocations.size() << " relocations\n"); 00343 Relocations.clear(); 00344 } 00345 00346 void JITEmitter::emitConstantPool(MachineConstantPool *MCP) { 00347 const std::vector<Constant*> &Constants = MCP->getConstants(); 00348 if (Constants.empty()) return; 00349 00350 std::vector<unsigned> ConstantOffset; 00351 ConstantOffset.reserve(Constants.size()); 00352 00353 // Calculate how much space we will need for all the constants, and the offset 00354 // each one will live in. 00355 unsigned TotalSize = 0; 00356 for (unsigned i = 0, e = Constants.size(); i != e; ++i) { 00357 const Type *Ty = Constants[i]->getType(); 00358 unsigned Size = TheJIT->getTargetData().getTypeSize(Ty); 00359 unsigned Alignment = TheJIT->getTargetData().getTypeAlignment(Ty); 00360 // Make sure to take into account the alignment requirements of the type. 00361 TotalSize = (TotalSize + Alignment-1) & ~(Alignment-1); 00362 00363 // Remember the offset this element lives at. 00364 ConstantOffset.push_back(TotalSize); 00365 TotalSize += Size; // Reserve space for the constant. 00366 } 00367 00368 // Now that we know how much memory to allocate, do so. 00369 char *Pool = new char[TotalSize]; 00370 00371 // Actually output all of the constants, and remember their addresses. 00372 for (unsigned i = 0, e = Constants.size(); i != e; ++i) { 00373 void *Addr = Pool + ConstantOffset[i]; 00374 TheJIT->InitializeMemory(Constants[i], Addr); 00375 ConstantPoolAddresses.push_back(Addr); 00376 } 00377 } 00378 00379 void JITEmitter::startFunctionStub(unsigned StubSize) { 00380 SavedCurBlock = CurBlock; SavedCurByte = CurByte; 00381 CurByte = CurBlock = MemMgr.allocateStub(StubSize); 00382 } 00383 00384 void *JITEmitter::finishFunctionStub(const Function *F) { 00385 NumBytes += CurByte-CurBlock; 00386 std::swap(CurBlock, SavedCurBlock); 00387 CurByte = SavedCurByte; 00388 return SavedCurBlock; 00389 } 00390 00391 void JITEmitter::emitByte(unsigned char B) { 00392 *CurByte++ = B; // Write the byte to memory 00393 } 00394 00395 void JITEmitter::emitWord(unsigned W) { 00396 // This won't work if the endianness of the host and target don't agree! (For 00397 // a JIT this can't happen though. :) 00398 *(unsigned*)CurByte = W; 00399 CurByte += sizeof(unsigned); 00400 } 00401 00402 void JITEmitter::emitWordAt(unsigned W, unsigned *Ptr) { 00403 *Ptr = W; 00404 } 00405 00406 // getConstantPoolEntryAddress - Return the address of the 'ConstantNum' entry 00407 // in the constant pool that was last emitted with the 'emitConstantPool' 00408 // method. 00409 // 00410 uint64_t JITEmitter::getConstantPoolEntryAddress(unsigned ConstantNum) { 00411 assert(ConstantNum < ConstantPoolAddresses.size() && 00412 "Invalid ConstantPoolIndex!"); 00413 return (intptr_t)ConstantPoolAddresses[ConstantNum]; 00414 } 00415 00416 // getCurrentPCValue - This returns the address that the next emitted byte 00417 // will be output to. 00418 // 00419 uint64_t JITEmitter::getCurrentPCValue() { 00420 return (intptr_t)CurByte; 00421 } 00422 00423 uint64_t JITEmitter::getCurrentPCOffset() { 00424 return (intptr_t)CurByte-(intptr_t)CurBlock; 00425 } 00426 00427 // getPointerToNamedFunction - This function is used as a global wrapper to 00428 // JIT::getPointerToNamedFunction for the purpose of resolving symbols when 00429 // bugpoint is debugging the JIT. In that scenario, we are loading an .so and 00430 // need to resolve function(s) that are being mis-codegenerated, so we need to 00431 // resolve their addresses at runtime, and this is the way to do it. 00432 extern "C" { 00433 void *getPointerToNamedFunction(const char *Name) { 00434 Module &M = TheJIT->getModule(); 00435 if (Function *F = M.getNamedFunction(Name)) 00436 return TheJIT->getPointerToFunction(F); 00437 return TheJIT->getPointerToNamedFunction(Name); 00438 } 00439 }