1 //===-- SanitizerCoverage.cpp - coverage instrumentation for sanitizers ---===// 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 // Coverage instrumentation that works with AddressSanitizer 11 // and potentially with other Sanitizers. 12 // 13 // We create a Guard variable with the same linkage 14 // as the function and inject this code into the entry block (CoverageLevel=1) 15 // or all blocks (CoverageLevel>=2): 16 // if (Guard < 0) { 17 // __sanitizer_cov(&Guard); 18 // } 19 // The accesses to Guard are atomic. The rest of the logic is 20 // in __sanitizer_cov (it's fine to call it more than once). 21 // 22 // With CoverageLevel>=3 we also split critical edges this effectively 23 // instrumenting all edges. 24 // 25 // CoverageLevel>=4 add indirect call profiling implented as a function call. 26 // 27 // This coverage implementation provides very limited data: 28 // it only tells if a given function (block) was ever executed. No counters. 29 // But for many use cases this is what we need and the added slowdown small. 30 // 31 //===----------------------------------------------------------------------===// 32 33 #include "llvm/Transforms/Instrumentation.h" 34 #include "llvm/ADT/ArrayRef.h" 35 #include "llvm/ADT/SmallVector.h" 36 #include "llvm/IR/CallSite.h" 37 #include "llvm/IR/DataLayout.h" 38 #include "llvm/IR/Function.h" 39 #include "llvm/IR/IRBuilder.h" 40 #include "llvm/IR/InlineAsm.h" 41 #include "llvm/IR/LLVMContext.h" 42 #include "llvm/IR/MDBuilder.h" 43 #include "llvm/IR/Module.h" 44 #include "llvm/IR/Type.h" 45 #include "llvm/Support/CommandLine.h" 46 #include "llvm/Support/Debug.h" 47 #include "llvm/Support/raw_ostream.h" 48 #include "llvm/Transforms/Scalar.h" 49 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 50 #include "llvm/Transforms/Utils/ModuleUtils.h" 51 52 using namespace llvm; 53 54 #define DEBUG_TYPE "sancov" 55 56 static const char *const kSanCovModuleInitName = "__sanitizer_cov_module_init"; 57 static const char *const kSanCovName = "__sanitizer_cov"; 58 static const char *const kSanCovIndirCallName = "__sanitizer_cov_indir_call16"; 59 static const char *const kSanCovTraceEnter = "__sanitizer_cov_trace_func_enter"; 60 static const char *const kSanCovTraceBB = "__sanitizer_cov_trace_basic_block"; 61 static const char *const kSanCovModuleCtorName = "sancov.module_ctor"; 62 static const uint64_t kSanCtorAndDtorPriority = 2; 63 64 static cl::opt<int> ClCoverageLevel("sanitizer-coverage-level", 65 cl::desc("Sanitizer Coverage. 0: none, 1: entry block, 2: all blocks, " 66 "3: all blocks and critical edges, " 67 "4: above plus indirect calls"), 68 cl::Hidden, cl::init(0)); 69 70 static cl::opt<int> ClCoverageBlockThreshold( 71 "sanitizer-coverage-block-threshold", 72 cl::desc("Add coverage instrumentation only to the entry block if there " 73 "are more than this number of blocks."), 74 cl::Hidden, cl::init(1500)); 75 76 static cl::opt<bool> 77 ClExperimentalTracing("sanitizer-coverage-experimental-tracing", 78 cl::desc("Experimental basic-block tracing: insert " 79 "callbacks at every basic block"), 80 cl::Hidden, cl::init(false)); 81 82 namespace { 83 84 class SanitizerCoverageModule : public ModulePass { 85 public: 86 SanitizerCoverageModule(int CoverageLevel = 0) 87 : ModulePass(ID), 88 CoverageLevel(std::max(CoverageLevel, (int)ClCoverageLevel)) {} 89 bool runOnModule(Module &M) override; 90 bool runOnFunction(Function &F); 91 static char ID; // Pass identification, replacement for typeid 92 const char *getPassName() const override { 93 return "SanitizerCoverageModule"; 94 } 95 96 void getAnalysisUsage(AnalysisUsage &AU) const override { 97 AU.addRequired<DataLayoutPass>(); 98 } 99 100 private: 101 void InjectCoverageForIndirectCalls(Function &F, 102 ArrayRef<Instruction *> IndirCalls); 103 bool InjectCoverage(Function &F, ArrayRef<BasicBlock *> AllBlocks, 104 ArrayRef<Instruction *> IndirCalls); 105 void InjectCoverageAtBlock(Function &F, BasicBlock &BB); 106 Function *SanCovFunction; 107 Function *SanCovIndirCallFunction; 108 Function *SanCovModuleInit; 109 Function *SanCovTraceEnter, *SanCovTraceBB; 110 InlineAsm *EmptyAsm; 111 Type *IntptrTy; 112 LLVMContext *C; 113 114 GlobalVariable *GuardArray; 115 116 int CoverageLevel; 117 }; 118 119 } // namespace 120 121 static Function *checkInterfaceFunction(Constant *FuncOrBitcast) { 122 if (Function *F = dyn_cast<Function>(FuncOrBitcast)) 123 return F; 124 std::string Err; 125 raw_string_ostream Stream(Err); 126 Stream << "SanitizerCoverage interface function redefined: " 127 << *FuncOrBitcast; 128 report_fatal_error(Err); 129 } 130 131 bool SanitizerCoverageModule::runOnModule(Module &M) { 132 if (!CoverageLevel) return false; 133 C = &(M.getContext()); 134 DataLayoutPass *DLP = &getAnalysis<DataLayoutPass>(); 135 IntptrTy = Type::getIntNTy(*C, DLP->getDataLayout().getPointerSizeInBits()); 136 Type *VoidTy = Type::getVoidTy(*C); 137 IRBuilder<> IRB(*C); 138 Type *Int32PtrTy = PointerType::getUnqual(IRB.getInt32Ty()); 139 140 Function *CtorFunc = 141 Function::Create(FunctionType::get(VoidTy, false), 142 GlobalValue::InternalLinkage, kSanCovModuleCtorName, &M); 143 ReturnInst::Create(*C, BasicBlock::Create(*C, "", CtorFunc)); 144 appendToGlobalCtors(M, CtorFunc, kSanCtorAndDtorPriority); 145 146 SanCovFunction = checkInterfaceFunction( 147 M.getOrInsertFunction(kSanCovName, VoidTy, Int32PtrTy, nullptr)); 148 SanCovIndirCallFunction = checkInterfaceFunction(M.getOrInsertFunction( 149 kSanCovIndirCallName, VoidTy, IntptrTy, IntptrTy, nullptr)); 150 SanCovModuleInit = checkInterfaceFunction( 151 M.getOrInsertFunction(kSanCovModuleInitName, Type::getVoidTy(*C), 152 Int32PtrTy, IntptrTy, nullptr)); 153 SanCovModuleInit->setLinkage(Function::ExternalLinkage); 154 // We insert an empty inline asm after cov callbacks to avoid callback merge. 155 EmptyAsm = InlineAsm::get(FunctionType::get(IRB.getVoidTy(), false), 156 StringRef(""), StringRef(""), 157 /*hasSideEffects=*/true); 158 159 if (ClExperimentalTracing) { 160 SanCovTraceEnter = checkInterfaceFunction( 161 M.getOrInsertFunction(kSanCovTraceEnter, VoidTy, Int32PtrTy, nullptr)); 162 SanCovTraceBB = checkInterfaceFunction( 163 M.getOrInsertFunction(kSanCovTraceBB, VoidTy, Int32PtrTy, nullptr)); 164 } 165 166 // At this point we create a dummy array of guards because we don't 167 // know how many elements we will need. 168 Type *Int32Ty = IRB.getInt32Ty(); 169 GuardArray = 170 new GlobalVariable(M, Int32Ty, false, GlobalValue::ExternalLinkage, 171 nullptr, "__sancov_gen_cov_tmp"); 172 173 for (auto &F : M) 174 runOnFunction(F); 175 176 // Now we know how many elements we need. Create an array of guards 177 // with one extra element at the beginning for the size. 178 Type *Int32ArrayNTy = 179 ArrayType::get(Int32Ty, SanCovFunction->getNumUses() + 1); 180 GlobalVariable *RealGuardArray = new GlobalVariable( 181 M, Int32ArrayNTy, false, GlobalValue::PrivateLinkage, 182 Constant::getNullValue(Int32ArrayNTy), "__sancov_gen_cov"); 183 184 // Replace the dummy array with the real one. 185 GuardArray->replaceAllUsesWith( 186 IRB.CreatePointerCast(RealGuardArray, Int32PtrTy)); 187 GuardArray->eraseFromParent(); 188 189 // Call __sanitizer_cov_module_init 190 IRB.SetInsertPoint(CtorFunc->getEntryBlock().getTerminator()); 191 IRB.CreateCall2(SanCovModuleInit, 192 IRB.CreatePointerCast(RealGuardArray, Int32PtrTy), 193 ConstantInt::get(IntptrTy, SanCovFunction->getNumUses())); 194 return true; 195 } 196 197 bool SanitizerCoverageModule::runOnFunction(Function &F) { 198 if (F.empty()) return false; 199 if (F.getName().find(".module_ctor") != std::string::npos) 200 return false; // Should not instrument sanitizer init functions. 201 if (CoverageLevel >= 3) 202 SplitAllCriticalEdges(F); 203 SmallVector<Instruction*, 8> IndirCalls; 204 SmallVector<BasicBlock*, 16> AllBlocks; 205 for (auto &BB : F) { 206 AllBlocks.push_back(&BB); 207 if (CoverageLevel >= 4) 208 for (auto &Inst : BB) { 209 CallSite CS(&Inst); 210 if (CS && !CS.getCalledFunction()) 211 IndirCalls.push_back(&Inst); 212 } 213 } 214 InjectCoverage(F, AllBlocks, IndirCalls); 215 return true; 216 } 217 218 bool 219 SanitizerCoverageModule::InjectCoverage(Function &F, 220 ArrayRef<BasicBlock *> AllBlocks, 221 ArrayRef<Instruction *> IndirCalls) { 222 if (!CoverageLevel) return false; 223 224 if (CoverageLevel == 1 || 225 (unsigned)ClCoverageBlockThreshold < AllBlocks.size()) { 226 InjectCoverageAtBlock(F, F.getEntryBlock()); 227 } else { 228 for (auto BB : AllBlocks) 229 InjectCoverageAtBlock(F, *BB); 230 } 231 InjectCoverageForIndirectCalls(F, IndirCalls); 232 return true; 233 } 234 235 // On every indirect call we call a run-time function 236 // __sanitizer_cov_indir_call* with two parameters: 237 // - callee address, 238 // - global cache array that contains kCacheSize pointers (zero-initialized). 239 // The cache is used to speed up recording the caller-callee pairs. 240 // The address of the caller is passed implicitly via caller PC. 241 // kCacheSize is encoded in the name of the run-time function. 242 void SanitizerCoverageModule::InjectCoverageForIndirectCalls( 243 Function &F, ArrayRef<Instruction *> IndirCalls) { 244 if (IndirCalls.empty()) return; 245 const int kCacheSize = 16; 246 const int kCacheAlignment = 64; // Align for better performance. 247 Type *Ty = ArrayType::get(IntptrTy, kCacheSize); 248 for (auto I : IndirCalls) { 249 IRBuilder<> IRB(I); 250 CallSite CS(I); 251 Value *Callee = CS.getCalledValue(); 252 if (dyn_cast<InlineAsm>(Callee)) continue; 253 GlobalVariable *CalleeCache = new GlobalVariable( 254 *F.getParent(), Ty, false, GlobalValue::PrivateLinkage, 255 Constant::getNullValue(Ty), "__sancov_gen_callee_cache"); 256 CalleeCache->setAlignment(kCacheAlignment); 257 IRB.CreateCall2(SanCovIndirCallFunction, 258 IRB.CreatePointerCast(Callee, IntptrTy), 259 IRB.CreatePointerCast(CalleeCache, IntptrTy)); 260 } 261 } 262 263 void SanitizerCoverageModule::InjectCoverageAtBlock(Function &F, 264 BasicBlock &BB) { 265 BasicBlock::iterator IP = BB.getFirstInsertionPt(), BE = BB.end(); 266 // Skip static allocas at the top of the entry block so they don't become 267 // dynamic when we split the block. If we used our optimized stack layout, 268 // then there will only be one alloca and it will come first. 269 for (; IP != BE; ++IP) { 270 AllocaInst *AI = dyn_cast<AllocaInst>(IP); 271 if (!AI || !AI->isStaticAlloca()) 272 break; 273 } 274 275 bool IsEntryBB = &BB == &F.getEntryBlock(); 276 DebugLoc EntryLoc = 277 IsEntryBB ? IP->getDebugLoc().getFnDebugLoc(*C) : IP->getDebugLoc(); 278 IRBuilder<> IRB(IP); 279 IRB.SetCurrentDebugLocation(EntryLoc); 280 SmallVector<Value *, 1> Indices; 281 Value *GuardP = IRB.CreateAdd( 282 IRB.CreatePointerCast(GuardArray, IntptrTy), 283 ConstantInt::get(IntptrTy, (1 + SanCovFunction->getNumUses()) * 4)); 284 Type *Int32PtrTy = PointerType::getUnqual(IRB.getInt32Ty()); 285 GuardP = IRB.CreateIntToPtr(GuardP, Int32PtrTy); 286 LoadInst *Load = IRB.CreateLoad(GuardP); 287 Load->setAtomic(Monotonic); 288 Load->setAlignment(4); 289 Load->setMetadata(F.getParent()->getMDKindID("nosanitize"), 290 MDNode::get(*C, None)); 291 Value *Cmp = IRB.CreateICmpSGE(Constant::getNullValue(Load->getType()), Load); 292 Instruction *Ins = SplitBlockAndInsertIfThen( 293 Cmp, IP, false, MDBuilder(*C).createBranchWeights(1, 100000)); 294 IRB.SetInsertPoint(Ins); 295 IRB.SetCurrentDebugLocation(EntryLoc); 296 // __sanitizer_cov gets the PC of the instruction using GET_CALLER_PC. 297 IRB.CreateCall(SanCovFunction, GuardP); 298 IRB.CreateCall(EmptyAsm); // Avoids callback merge. 299 300 if (ClExperimentalTracing) { 301 // Experimental support for tracing. 302 // Insert a callback with the same guard variable as used for coverage. 303 IRB.SetInsertPoint(IP); 304 IRB.CreateCall(IsEntryBB ? SanCovTraceEnter : SanCovTraceBB, GuardP); 305 } 306 } 307 308 char SanitizerCoverageModule::ID = 0; 309 INITIALIZE_PASS(SanitizerCoverageModule, "sancov", 310 "SanitizerCoverage: TODO." 311 "ModulePass", false, false) 312 ModulePass *llvm::createSanitizerCoverageModulePass(int CoverageLevel) { 313 return new SanitizerCoverageModule(CoverageLevel); 314 } 315