1 //===-- JITEmitter.cpp - Write machine code to executable memory ----------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines a MachineCodeEmitter object that is used by the JIT to
11 // write machine code to memory and remember where relocatable values are.
13 //===----------------------------------------------------------------------===//
15 #define DEBUG_TYPE "jit"
17 #include "llvm/Constant.h"
18 #include "llvm/Module.h"
19 #include "llvm/CodeGen/MachineCodeEmitter.h"
20 #include "llvm/CodeGen/MachineFunction.h"
21 #include "llvm/CodeGen/MachineConstantPool.h"
22 #include "llvm/CodeGen/MachineRelocation.h"
23 #include "llvm/Target/TargetData.h"
24 #include "llvm/Target/TargetJITInfo.h"
25 #include "llvm/Support/Debug.h"
26 #include "llvm/ADT/Statistic.h"
27 #include "llvm/System/Memory.h"
31 Statistic<> NumBytes("jit", "Number of bytes of machine code compiled");
36 //===----------------------------------------------------------------------===//
37 // JITMemoryManager code.
40 /// JITMemoryManager - Manage memory for the JIT code generation in a logical,
41 /// sane way. This splits a large block of MAP_NORESERVE'd memory into two
42 /// sections, one for function stubs, one for the functions themselves. We
43 /// have to do this because we may need to emit a function stub while in the
44 /// middle of emitting a function, and we don't know how large the function we
45 /// are emitting is. This never bothers to release the memory, because when
46 /// we are ready to destroy the JIT, the program exits.
47 class JITMemoryManager {
48 sys::MemoryBlock MemBlock; // Virtual memory block allocated RWX
49 unsigned char *MemBase; // Base of block of memory, start of stub mem
50 unsigned char *FunctionBase; // Start of the function body area
51 unsigned char *CurStubPtr, *CurFunctionPtr;
56 inline unsigned char *allocateStub(unsigned StubSize);
57 inline unsigned char *startFunctionBody();
58 inline void endFunctionBody(unsigned char *FunctionEnd);
62 JITMemoryManager::JITMemoryManager() {
63 // Allocate a 16M block of memory...
64 MemBlock = sys::Memory::AllocateRWX((16 << 20));
65 MemBase = reinterpret_cast<unsigned char*>(MemBlock.base());
66 FunctionBase = MemBase + 512*1024; // Use 512k for stubs
68 // Allocate stubs backwards from the function base, allocate functions forward
69 // from the function base.
70 CurStubPtr = CurFunctionPtr = FunctionBase;
73 JITMemoryManager::~JITMemoryManager() {
74 sys::Memory::ReleaseRWX(MemBlock);
77 unsigned char *JITMemoryManager::allocateStub(unsigned StubSize) {
78 CurStubPtr -= StubSize;
79 if (CurStubPtr < MemBase) {
80 std::cerr << "JIT ran out of memory for function stubs!\n";
86 unsigned char *JITMemoryManager::startFunctionBody() {
87 // Round up to an even multiple of 8 bytes, this should eventually be target
89 return (unsigned char*)(((intptr_t)CurFunctionPtr + 7) & ~7);
92 void JITMemoryManager::endFunctionBody(unsigned char *FunctionEnd) {
93 assert(FunctionEnd > CurFunctionPtr);
94 CurFunctionPtr = FunctionEnd;
97 //===----------------------------------------------------------------------===//
98 // JIT lazy compilation code.
101 /// JITResolver - Keep track of, and resolve, call sites for functions that
102 /// have not yet been compiled.
104 /// MCE - The MachineCodeEmitter to use to emit stubs with.
105 MachineCodeEmitter &MCE;
107 /// LazyResolverFn - The target lazy resolver function that we actually
108 /// rewrite instructions to use.
109 TargetJITInfo::LazyResolverFn LazyResolverFn;
111 // FunctionToStubMap - Keep track of the stub created for a particular
112 // function so that we can reuse them if necessary.
113 std::map<Function*, void*> FunctionToStubMap;
115 // StubToFunctionMap - Keep track of the function that each stub corresponds
117 std::map<void*, Function*> StubToFunctionMap;
120 JITResolver(MachineCodeEmitter &mce) : MCE(mce) {
122 TheJIT->getJITInfo().getLazyResolverFunction(JITCompilerFn);
125 /// getFunctionStub - This returns a pointer to a function stub, creating
126 /// one on demand as needed.
127 void *getFunctionStub(Function *F);
129 /// AddCallbackAtLocation - If the target is capable of rewriting an
130 /// instruction without the use of a stub, record the location of the use so
131 /// we know which function is being used at the location.
132 void *AddCallbackAtLocation(Function *F, void *Location) {
133 /// Get the target-specific JIT resolver function.
134 StubToFunctionMap[Location] = F;
135 return (void*)LazyResolverFn;
138 /// JITCompilerFn - This function is called to resolve a stub to a compiled
139 /// address. If the LLVM Function corresponding to the stub has not yet
140 /// been compiled, this function compiles it first.
141 static void *JITCompilerFn(void *Stub);
145 /// getJITResolver - This function returns the one instance of the JIT resolver.
147 static JITResolver &getJITResolver(MachineCodeEmitter *MCE = 0) {
148 static JITResolver TheJITResolver(*MCE);
149 return TheJITResolver;
152 /// getFunctionStub - This returns a pointer to a function stub, creating
153 /// one on demand as needed.
154 void *JITResolver::getFunctionStub(Function *F) {
155 // If we already have a stub for this function, recycle it.
156 void *&Stub = FunctionToStubMap[F];
157 if (Stub) return Stub;
159 // Call the lazy resolver function unless we already KNOW it is an external
160 // function, in which case we just skip the lazy resolution step.
161 void *Actual = (void*)LazyResolverFn;
162 if (F->hasExternalLinkage())
163 Actual = TheJIT->getPointerToFunction(F);
165 // Otherwise, codegen a new stub. For now, the stub will call the lazy
166 // resolver function.
167 Stub = TheJIT->getJITInfo().emitFunctionStub(Actual, MCE);
169 if (F->hasExternalLinkage()) {
170 // If we are getting the stub for an external function, we really want the
171 // address of the stub in the GlobalAddressMap for the JIT, not the address
172 // of the external function.
173 TheJIT->updateGlobalMapping(F, Stub);
176 DEBUG(std::cerr << "JIT: Stub emitted at [" << Stub << "] for function '"
177 << F->getName() << "'\n");
179 // Finally, keep track of the stub-to-Function mapping so that the
180 // JITCompilerFn knows which function to compile!
181 StubToFunctionMap[Stub] = F;
185 /// JITCompilerFn - This function is called when a lazy compilation stub has
186 /// been entered. It looks up which function this stub corresponds to, compiles
187 /// it if necessary, then returns the resultant function pointer.
188 void *JITResolver::JITCompilerFn(void *Stub) {
189 JITResolver &JR = getJITResolver();
191 // The address given to us for the stub may not be exactly right, it might be
192 // a little bit after the stub. As such, use upper_bound to find it.
193 std::map<void*, Function*>::iterator I =
194 JR.StubToFunctionMap.upper_bound(Stub);
195 assert(I != JR.StubToFunctionMap.begin() && "This is not a known stub!");
196 Function *F = (--I)->second;
198 // The target function will rewrite the stub so that the compilation callback
199 // function is no longer called from this stub.
200 JR.StubToFunctionMap.erase(I);
202 DEBUG(std::cerr << "JIT: Lazily resolving function '" << F->getName()
203 << "' In stub ptr = " << Stub << " actual ptr = "
204 << I->first << "\n");
206 void *Result = TheJIT->getPointerToFunction(F);
208 // We don't need to reuse this stub in the future, as F is now compiled.
209 JR.FunctionToStubMap.erase(F);
211 // FIXME: We could rewrite all references to this stub if we knew them.
216 // getPointerToFunctionOrStub - If the specified function has been
217 // code-gen'd, return a pointer to the function. If not, compile it, or use
218 // a stub to implement lazy compilation if available.
220 void *JIT::getPointerToFunctionOrStub(Function *F) {
221 // If we have already code generated the function, just return the address.
222 if (void *Addr = getPointerToGlobalIfAvailable(F))
225 // Get a stub if the target supports it
226 return getJITResolver(MCE).getFunctionStub(F);
231 //===----------------------------------------------------------------------===//
235 /// JITEmitter - The JIT implementation of the MachineCodeEmitter, which is
236 /// used to output functions to memory for execution.
237 class JITEmitter : public MachineCodeEmitter {
238 JITMemoryManager MemMgr;
240 // CurBlock - The start of the current block of memory. CurByte - The
241 // current byte being emitted to.
242 unsigned char *CurBlock, *CurByte;
244 // When outputting a function stub in the context of some other function, we
245 // save CurBlock and CurByte here.
246 unsigned char *SavedCurBlock, *SavedCurByte;
248 // ConstantPoolAddresses - Contains the location for each entry in the
250 std::vector<void*> ConstantPoolAddresses;
252 /// Relocations - These are the relocations that the function needs, as
254 std::vector<MachineRelocation> Relocations;
256 JITEmitter(JIT &jit) { TheJIT = &jit; }
258 virtual void startFunction(MachineFunction &F);
259 virtual void finishFunction(MachineFunction &F);
260 virtual void emitConstantPool(MachineConstantPool *MCP);
261 virtual void startFunctionStub(unsigned StubSize);
262 virtual void* finishFunctionStub(const Function *F);
263 virtual void emitByte(unsigned char B);
264 virtual void emitWord(unsigned W);
265 virtual void emitWordAt(unsigned W, unsigned *Ptr);
267 virtual void addRelocation(const MachineRelocation &MR) {
268 Relocations.push_back(MR);
271 virtual uint64_t getCurrentPCValue();
272 virtual uint64_t getCurrentPCOffset();
273 virtual uint64_t getConstantPoolEntryAddress(unsigned Entry);
276 void *getPointerToGlobal(GlobalValue *GV, void *Reference, bool NoNeedStub);
280 MachineCodeEmitter *JIT::createEmitter(JIT &jit) {
281 return new JITEmitter(jit);
284 void *JITEmitter::getPointerToGlobal(GlobalValue *V, void *Reference,
285 bool DoesntNeedStub) {
286 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
287 /// FIXME: If we straightened things out, this could actually emit the
288 /// global immediately instead of queuing it for codegen later!
289 return TheJIT->getOrEmitGlobalVariable(GV);
292 // If we have already compiled the function, return a pointer to its body.
293 Function *F = cast<Function>(V);
294 void *ResultPtr = TheJIT->getPointerToGlobalIfAvailable(F);
295 if (ResultPtr) return ResultPtr;
297 if (F->hasExternalLinkage() && F->isExternal()) {
298 // If this is an external function pointer, we can force the JIT to
299 // 'compile' it, which really just adds it to the map.
301 return TheJIT->getPointerToFunction(F);
303 return getJITResolver(this).getFunctionStub(F);
306 // Okay, the function has not been compiled yet, if the target callback
307 // mechanism is capable of rewriting the instruction directly, prefer to do
308 // that instead of emitting a stub.
310 return getJITResolver(this).AddCallbackAtLocation(F, Reference);
312 // Otherwise, we have to emit a lazy resolving stub.
313 return getJITResolver(this).getFunctionStub(F);
316 void JITEmitter::startFunction(MachineFunction &F) {
317 CurByte = CurBlock = MemMgr.startFunctionBody();
318 TheJIT->addGlobalMapping(F.getFunction(), CurBlock);
321 void JITEmitter::finishFunction(MachineFunction &F) {
322 MemMgr.endFunctionBody(CurByte);
323 ConstantPoolAddresses.clear();
324 NumBytes += CurByte-CurBlock;
326 if (!Relocations.empty()) {
327 // Resolve the relocations to concrete pointers.
328 for (unsigned i = 0, e = Relocations.size(); i != e; ++i) {
329 MachineRelocation &MR = Relocations[i];
332 ResultPtr = TheJIT->getPointerToNamedFunction(MR.getString());
334 ResultPtr = getPointerToGlobal(MR.getGlobalValue(),
335 CurBlock+MR.getMachineCodeOffset(),
336 MR.doesntNeedFunctionStub());
337 MR.setResultPointer(ResultPtr);
340 TheJIT->getJITInfo().relocate(CurBlock, &Relocations[0],
344 DEBUG(std::cerr << "JIT: Finished CodeGen of [" << (void*)CurBlock
345 << "] Function: " << F.getFunction()->getName()
346 << ": " << CurByte-CurBlock << " bytes of text, "
347 << Relocations.size() << " relocations\n");
351 void JITEmitter::emitConstantPool(MachineConstantPool *MCP) {
352 const std::vector<Constant*> &Constants = MCP->getConstants();
353 if (Constants.empty()) return;
355 std::vector<unsigned> ConstantOffset;
356 ConstantOffset.reserve(Constants.size());
358 // Calculate how much space we will need for all the constants, and the offset
359 // each one will live in.
360 unsigned TotalSize = 0;
361 for (unsigned i = 0, e = Constants.size(); i != e; ++i) {
362 const Type *Ty = Constants[i]->getType();
363 unsigned Size = (unsigned)TheJIT->getTargetData().getTypeSize(Ty);
364 unsigned Alignment = TheJIT->getTargetData().getTypeAlignment(Ty);
365 // Make sure to take into account the alignment requirements of the type.
366 TotalSize = (TotalSize + Alignment-1) & ~(Alignment-1);
368 // Remember the offset this element lives at.
369 ConstantOffset.push_back(TotalSize);
370 TotalSize += Size; // Reserve space for the constant.
373 // Now that we know how much memory to allocate, do so.
374 char *Pool = new char[TotalSize];
376 // Actually output all of the constants, and remember their addresses.
377 for (unsigned i = 0, e = Constants.size(); i != e; ++i) {
378 void *Addr = Pool + ConstantOffset[i];
379 TheJIT->InitializeMemory(Constants[i], Addr);
380 ConstantPoolAddresses.push_back(Addr);
384 void JITEmitter::startFunctionStub(unsigned StubSize) {
385 SavedCurBlock = CurBlock; SavedCurByte = CurByte;
386 CurByte = CurBlock = MemMgr.allocateStub(StubSize);
389 void *JITEmitter::finishFunctionStub(const Function *F) {
390 NumBytes += CurByte-CurBlock;
391 std::swap(CurBlock, SavedCurBlock);
392 CurByte = SavedCurByte;
393 return SavedCurBlock;
396 void JITEmitter::emitByte(unsigned char B) {
397 *CurByte++ = B; // Write the byte to memory
400 void JITEmitter::emitWord(unsigned W) {
401 // This won't work if the endianness of the host and target don't agree! (For
402 // a JIT this can't happen though. :)
403 *(unsigned*)CurByte = W;
404 CurByte += sizeof(unsigned);
407 void JITEmitter::emitWordAt(unsigned W, unsigned *Ptr) {
411 // getConstantPoolEntryAddress - Return the address of the 'ConstantNum' entry
412 // in the constant pool that was last emitted with the 'emitConstantPool'
415 uint64_t JITEmitter::getConstantPoolEntryAddress(unsigned ConstantNum) {
416 assert(ConstantNum < ConstantPoolAddresses.size() &&
417 "Invalid ConstantPoolIndex!");
418 return (intptr_t)ConstantPoolAddresses[ConstantNum];
421 // getCurrentPCValue - This returns the address that the next emitted byte
422 // will be output to.
424 uint64_t JITEmitter::getCurrentPCValue() {
425 return (intptr_t)CurByte;
428 uint64_t JITEmitter::getCurrentPCOffset() {
429 return (intptr_t)CurByte-(intptr_t)CurBlock;
432 // getPointerToNamedFunction - This function is used as a global wrapper to
433 // JIT::getPointerToNamedFunction for the purpose of resolving symbols when
434 // bugpoint is debugging the JIT. In that scenario, we are loading an .so and
435 // need to resolve function(s) that are being mis-codegenerated, so we need to
436 // resolve their addresses at runtime, and this is the way to do it.
438 void *getPointerToNamedFunction(const char *Name) {
439 Module &M = TheJIT->getModule();
440 if (Function *F = M.getNamedFunction(Name))
441 return TheJIT->getPointerToFunction(F);
442 return TheJIT->getPointerToNamedFunction(Name);