1 //===-- Emitter.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"
32 Statistic<> NumBytes("jit", "Number of bytes of machine code compiled");
35 /// JITMemoryManager - Manage memory for the JIT code generation in a logical,
36 /// sane way. This splits a large block of MAP_NORESERVE'd memory into two
37 /// sections, one for function stubs, one for the functions themselves. We
38 /// have to do this because we may need to emit a function stub while in the
39 /// middle of emitting a function, and we don't know how large the function we
40 /// are emitting is. This never bothers to release the memory, because when
41 /// we are ready to destroy the JIT, the program exits.
42 class JITMemoryManager {
43 sys::MemoryBlock MemBlock; // Virtual memory block allocated RWX
44 unsigned char *MemBase; // Base of block of memory, start of stub mem
45 unsigned char *FunctionBase; // Start of the function body area
46 unsigned char *CurStubPtr, *CurFunctionPtr;
50 inline unsigned char *allocateStub(unsigned StubSize);
51 inline unsigned char *startFunctionBody();
52 inline void endFunctionBody(unsigned char *FunctionEnd);
56 JITMemoryManager::JITMemoryManager() {
57 // Allocate a 16M block of memory...
58 MemBlock = sys::Memory::AllocateRWX((16 << 20));
59 MemBase = reinterpret_cast<unsigned char*>(MemBlock.base());
60 FunctionBase = MemBase + 512*1024; // Use 512k for stubs
62 // Allocate stubs backwards from the function base, allocate functions forward
63 // from the function base.
64 CurStubPtr = CurFunctionPtr = FunctionBase;
67 unsigned char *JITMemoryManager::allocateStub(unsigned StubSize) {
68 CurStubPtr -= StubSize;
69 if (CurStubPtr < MemBase) {
70 std::cerr << "JIT ran out of memory for function stubs!\n";
76 unsigned char *JITMemoryManager::startFunctionBody() {
77 // Round up to an even multiple of 8 bytes, this should eventually be target
79 return (unsigned char*)(((intptr_t)CurFunctionPtr + 7) & ~7);
82 void JITMemoryManager::endFunctionBody(unsigned char *FunctionEnd) {
83 assert(FunctionEnd > CurFunctionPtr);
84 CurFunctionPtr = FunctionEnd;
90 /// Emitter - The JIT implementation of the MachineCodeEmitter, which is used
91 /// to output functions to memory for execution.
92 class Emitter : public MachineCodeEmitter {
93 JITMemoryManager MemMgr;
95 // CurBlock - The start of the current block of memory. CurByte - The
96 // current byte being emitted to.
97 unsigned char *CurBlock, *CurByte;
99 // When outputting a function stub in the context of some other function, we
100 // save CurBlock and CurByte here.
101 unsigned char *SavedCurBlock, *SavedCurByte;
103 // ConstantPoolAddresses - Contains the location for each entry in the
105 std::vector<void*> ConstantPoolAddresses;
107 /// Relocations - These are the relocations that the function needs, as
109 std::vector<MachineRelocation> Relocations;
111 Emitter(JIT &jit) { TheJIT = &jit; }
113 virtual void startFunction(MachineFunction &F);
114 virtual void finishFunction(MachineFunction &F);
115 virtual void emitConstantPool(MachineConstantPool *MCP);
116 virtual void startFunctionStub(const Function &F, unsigned StubSize);
117 virtual void* finishFunctionStub(const Function &F);
118 virtual void emitByte(unsigned char B);
119 virtual void emitWord(unsigned W);
120 virtual void emitWordAt(unsigned W, unsigned *Ptr);
122 virtual void addRelocation(const MachineRelocation &MR) {
123 Relocations.push_back(MR);
126 virtual uint64_t getCurrentPCValue();
127 virtual uint64_t getCurrentPCOffset();
128 virtual uint64_t getGlobalValueAddress(GlobalValue *V);
129 virtual uint64_t getGlobalValueAddress(const char *Name);
130 virtual uint64_t getConstantPoolEntryAddress(unsigned Entry);
132 // forceCompilationOf - Force the compilation of the specified function, and
133 // return its address, because we REALLY need the address now.
135 // FIXME: This is JIT specific!
137 virtual uint64_t forceCompilationOf(Function *F);
141 MachineCodeEmitter *JIT::createEmitter(JIT &jit) {
142 return new Emitter(jit);
145 void Emitter::startFunction(MachineFunction &F) {
146 CurByte = CurBlock = MemMgr.startFunctionBody();
147 TheJIT->addGlobalMapping(F.getFunction(), CurBlock);
150 void Emitter::finishFunction(MachineFunction &F) {
151 MemMgr.endFunctionBody(CurByte);
152 ConstantPoolAddresses.clear();
153 NumBytes += CurByte-CurBlock;
155 if (!Relocations.empty()) {
156 // Resolve the relocations to concrete pointers.
157 for (unsigned i = 0, e = Relocations.size(); i != e; ++i) {
158 MachineRelocation &MR = Relocations[i];
160 if (MR.isGlobalValue()) {
161 assert(0 && "Unimplemented!\n");
163 ResultPtr = TheJIT->getPointerToNamedFunction(MR.getString());
165 MR.setResultPointer(ResultPtr);
168 TheJIT->getJITInfo().relocate(CurBlock, &Relocations[0],
172 DEBUG(std::cerr << "Finished CodeGen of [" << (void*)CurBlock
173 << "] Function: " << F.getFunction()->getName()
174 << ": " << CurByte-CurBlock << " bytes of text, "
175 << Relocations.size() << " relocations\n");
179 void Emitter::emitConstantPool(MachineConstantPool *MCP) {
180 const std::vector<Constant*> &Constants = MCP->getConstants();
181 if (Constants.empty()) return;
183 std::vector<unsigned> ConstantOffset;
184 ConstantOffset.reserve(Constants.size());
186 // Calculate how much space we will need for all the constants, and the offset
187 // each one will live in.
188 unsigned TotalSize = 0;
189 for (unsigned i = 0, e = Constants.size(); i != e; ++i) {
190 const Type *Ty = Constants[i]->getType();
191 unsigned Size = TheJIT->getTargetData().getTypeSize(Ty);
192 unsigned Alignment = TheJIT->getTargetData().getTypeAlignment(Ty);
193 // Make sure to take into account the alignment requirements of the type.
194 TotalSize = (TotalSize + Alignment-1) & ~(Alignment-1);
196 // Remember the offset this element lives at.
197 ConstantOffset.push_back(TotalSize);
198 TotalSize += Size; // Reserve space for the constant.
201 // Now that we know how much memory to allocate, do so.
202 char *Pool = new char[TotalSize];
204 // Actually output all of the constants, and remember their addresses.
205 for (unsigned i = 0, e = Constants.size(); i != e; ++i) {
206 void *Addr = Pool + ConstantOffset[i];
207 TheJIT->InitializeMemory(Constants[i], Addr);
208 ConstantPoolAddresses.push_back(Addr);
212 void Emitter::startFunctionStub(const Function &F, unsigned StubSize) {
213 SavedCurBlock = CurBlock; SavedCurByte = CurByte;
214 CurByte = CurBlock = MemMgr.allocateStub(StubSize);
217 void *Emitter::finishFunctionStub(const Function &F) {
218 NumBytes += CurByte-CurBlock;
219 DEBUG(std::cerr << "Finished CodeGen of [0x" << std::hex
220 << (uintptr_t)CurBlock
221 << std::dec << "] Function stub for: " << F.getName()
222 << ": " << CurByte-CurBlock << " bytes of text\n");
223 std::swap(CurBlock, SavedCurBlock);
224 CurByte = SavedCurByte;
225 return SavedCurBlock;
228 void Emitter::emitByte(unsigned char B) {
229 *CurByte++ = B; // Write the byte to memory
232 void Emitter::emitWord(unsigned W) {
233 // This won't work if the endianness of the host and target don't agree! (For
234 // a JIT this can't happen though. :)
235 *(unsigned*)CurByte = W;
236 CurByte += sizeof(unsigned);
239 void Emitter::emitWordAt(unsigned W, unsigned *Ptr) {
243 uint64_t Emitter::getGlobalValueAddress(GlobalValue *V) {
244 // Try looking up the function to see if it is already compiled, if not return
246 if (Function *F = dyn_cast<Function>(V)) {
247 void *Addr = TheJIT->getPointerToGlobalIfAvailable(F);
248 if (Addr == 0 && F->hasExternalLinkage()) {
249 // Do not output stubs for external functions.
250 Addr = TheJIT->getPointerToFunction(F);
252 return (intptr_t)Addr;
254 return (intptr_t)TheJIT->getOrEmitGlobalVariable(cast<GlobalVariable>(V));
257 uint64_t Emitter::getGlobalValueAddress(const char *Name) {
258 return (intptr_t)TheJIT->getPointerToNamedFunction(Name);
261 // getConstantPoolEntryAddress - Return the address of the 'ConstantNum' entry
262 // in the constant pool that was last emitted with the 'emitConstantPool'
265 uint64_t Emitter::getConstantPoolEntryAddress(unsigned ConstantNum) {
266 assert(ConstantNum < ConstantPoolAddresses.size() &&
267 "Invalid ConstantPoolIndex!");
268 return (intptr_t)ConstantPoolAddresses[ConstantNum];
271 // getCurrentPCValue - This returns the address that the next emitted byte
272 // will be output to.
274 uint64_t Emitter::getCurrentPCValue() {
275 return (intptr_t)CurByte;
278 uint64_t Emitter::getCurrentPCOffset() {
279 return (intptr_t)CurByte-(intptr_t)CurBlock;
282 uint64_t Emitter::forceCompilationOf(Function *F) {
283 return (intptr_t)TheJIT->getPointerToFunction(F);
286 // getPointerToNamedFunction - This function is used as a global wrapper to
287 // JIT::getPointerToNamedFunction for the purpose of resolving symbols when
288 // bugpoint is debugging the JIT. In that scenario, we are loading an .so and
289 // need to resolve function(s) that are being mis-codegenerated, so we need to
290 // resolve their addresses at runtime, and this is the way to do it.
292 void *getPointerToNamedFunction(const char *Name) {
293 Module &M = TheJIT->getModule();
294 if (Function *F = M.getNamedFunction(Name))
295 return TheJIT->getPointerToFunction(F);
296 return TheJIT->getPointerToNamedFunction(Name);