lib/Transforms/Instrumentation/SanitizerCoverage.cpp

   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 (SCK_Function)
  15 // or all blocks (SCK_BB):
  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 SCK_Edge we also split critical edges this effectively
  23 // instrumenting all edges.
  24 //
  25 // This coverage implementation provides very limited data:
  26 // it only tells if a given function (block) was ever executed. No counters.
  27 // But for many use cases this is what we need and the added slowdown small.
  28 //
  29 //===----------------------------------------------------------------------===//
  30
  31 #include "llvm/Transforms/Instrumentation.h"
  32 #include "llvm/ADT/ArrayRef.h"
  33 #include "llvm/ADT/SmallVector.h"
  34 #include "llvm/IR/CallSite.h"
  35 #include "llvm/IR/DataLayout.h"
  36 #include "llvm/IR/DebugInfo.h"
  37 #include "llvm/IR/Function.h"
  38 #include "llvm/IR/IRBuilder.h"
  39 #include "llvm/IR/InlineAsm.h"
  40 #include "llvm/IR/LLVMContext.h"
  41 #include "llvm/IR/MDBuilder.h"
  42 #include "llvm/IR/Module.h"
  43 #include "llvm/IR/Type.h"
  44 #include "llvm/Support/CommandLine.h"
  45 #include "llvm/Support/Debug.h"
  46 #include "llvm/Support/raw_ostream.h"
  47 #include "llvm/Transforms/Scalar.h"
  48 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  49 #include "llvm/Transforms/Utils/ModuleUtils.h"
  50
  51 using namespace llvm;
  52
  53 #define DEBUG_TYPE "sancov"
  54
  55 static const char *const kSanCovModuleInitName = "__sanitizer_cov_module_init";
  56 static const char *const kSanCovName = "__sanitizer_cov";
  57 static const char *const kSanCovWithCheckName = "__sanitizer_cov_with_check";
  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 kSanCovTraceCmp = "__sanitizer_cov_trace_cmp";
  62 static const char *const kSanCovTraceSwitch = "__sanitizer_cov_trace_switch";
  63 static const char *const kSanCovModuleCtorName = "sancov.module_ctor";
  64 static const uint64_t    kSanCtorAndDtorPriority = 2;
  65
  66 static cl::opt<int> ClCoverageLevel("sanitizer-coverage-level",
  67        cl::desc("Sanitizer Coverage. 0: none, 1: entry block, 2: all blocks, "
  68                 "3: all blocks and critical edges, "
  69                 "4: above plus indirect calls"),
  70        cl::Hidden, cl::init(0));
  71
  72 static cl::opt<unsigned> ClCoverageBlockThreshold(
  73     "sanitizer-coverage-block-threshold",
  74     cl::desc("Use a callback with a guard check inside it if there are"
  75              " more than this number of blocks."),
  76     cl::Hidden, cl::init(500));
  77
  78 static cl::opt<bool>
  79     ClExperimentalTracing("sanitizer-coverage-experimental-tracing",
  80                           cl::desc("Experimental basic-block tracing: insert "
  81                                    "callbacks at every basic block"),
  82                           cl::Hidden, cl::init(false));
  83
  84 static cl::opt<bool>
  85     ClExperimentalCMPTracing("sanitizer-coverage-experimental-trace-compares",
  86                              cl::desc("Experimental tracing of CMP and similar "
  87                                       "instructions"),
  88                              cl::Hidden, cl::init(false));
  89
  90 // Experimental 8-bit counters used as an additional search heuristic during
  91 // coverage-guided fuzzing.
  92 // The counters are not thread-friendly:
  93 //   - contention on these counters may cause significant slowdown;
  94 //   - the counter updates are racy and the results may be inaccurate.
  95 // They are also inaccurate due to 8-bit integer overflow.
  96 static cl::opt<bool> ClUse8bitCounters("sanitizer-coverage-8bit-counters",
  97                                        cl::desc("Experimental 8-bit counters"),
  98                                        cl::Hidden, cl::init(false));
  99
 100 namespace {
 101
 102 SanitizerCoverageOptions getOptions(int LegacyCoverageLevel) {
 103   SanitizerCoverageOptions Res;
 104   switch (LegacyCoverageLevel) {
 105   case 0:
 106     Res.CoverageType = SanitizerCoverageOptions::SCK_None;
 107     break;
 108   case 1:
 109     Res.CoverageType = SanitizerCoverageOptions::SCK_Function;
 110     break;
 111   case 2:
 112     Res.CoverageType = SanitizerCoverageOptions::SCK_BB;
 113     break;
 114   case 3:
 115     Res.CoverageType = SanitizerCoverageOptions::SCK_Edge;
 116     break;
 117   case 4:
 118     Res.CoverageType = SanitizerCoverageOptions::SCK_Edge;
 119     Res.IndirectCalls = true;
 120     break;
 121   }
 122   return Res;
 123 }
 124
 125 SanitizerCoverageOptions OverrideFromCL(SanitizerCoverageOptions Options) {
 126   // Sets CoverageType and IndirectCalls.
 127   SanitizerCoverageOptions CLOpts = getOptions(ClCoverageLevel);
 128   Options.CoverageType = std::max(Options.CoverageType, CLOpts.CoverageType);
 129   Options.IndirectCalls |= CLOpts.IndirectCalls;
 130   Options.TraceBB |= ClExperimentalTracing;
 131   Options.TraceCmp |= ClExperimentalCMPTracing;
 132   Options.Use8bitCounters |= ClUse8bitCounters;
 133   return Options;
 134 }
 135
 136 class SanitizerCoverageModule : public ModulePass {
 137  public:
 138   SanitizerCoverageModule(
 139       const SanitizerCoverageOptions &Options = SanitizerCoverageOptions())
 140       : ModulePass(ID), Options(OverrideFromCL(Options)) {}
 141   bool runOnModule(Module &M) override;
 142   bool runOnFunction(Function &F);
 143   static char ID;  // Pass identification, replacement for typeid
 144   const char *getPassName() const override {
 145     return "SanitizerCoverageModule";
 146   }
 147
 148  private:
 149   void InjectCoverageForIndirectCalls(Function &F,
 150                                       ArrayRef<Instruction *> IndirCalls);
 151   void InjectTraceForCmp(Function &F, ArrayRef<Instruction *> CmpTraceTargets);
 152   void InjectTraceForSwitch(Function &F,
 153                             ArrayRef<Instruction *> SwitchTraceTargets);
 154   bool InjectCoverage(Function &F, ArrayRef<BasicBlock *> AllBlocks);
 155   void SetNoSanitizeMetadata(Instruction *I);
 156   void InjectCoverageAtBlock(Function &F, BasicBlock &BB, bool UseCalls);
 157   unsigned NumberOfInstrumentedBlocks() {
 158     return SanCovFunction->getNumUses() + SanCovWithCheckFunction->getNumUses();
 159   }
 160   Function *SanCovFunction;
 161   Function *SanCovWithCheckFunction;
 162   Function *SanCovIndirCallFunction;
 163   Function *SanCovTraceEnter, *SanCovTraceBB;
 164   Function *SanCovTraceCmpFunction;
 165   Function *SanCovTraceSwitchFunction;
 166   InlineAsm *EmptyAsm;
 167   Type *IntptrTy, *Int64Ty, *Int64PtrTy;
 168   Module *CurModule;
 169   LLVMContext *C;
 170   const DataLayout *DL;
 171
 172   GlobalVariable *GuardArray;
 173   GlobalVariable *EightBitCounterArray;
 174
 175   SanitizerCoverageOptions Options;
 176 };
 177
 178 }  // namespace
 179
 180 bool SanitizerCoverageModule::runOnModule(Module &M) {
 181   if (Options.CoverageType == SanitizerCoverageOptions::SCK_None)
 182     return false;
 183   C = &(M.getContext());
 184   DL = &M.getDataLayout();
 185   CurModule = &M;
 186   IntptrTy = Type::getIntNTy(*C, DL->getPointerSizeInBits());
 187   Type *VoidTy = Type::getVoidTy(*C);
 188   IRBuilder<> IRB(*C);
 189   Type *Int8PtrTy = PointerType::getUnqual(IRB.getInt8Ty());
 190   Type *Int32PtrTy = PointerType::getUnqual(IRB.getInt32Ty());
 191   Int64PtrTy = PointerType::getUnqual(IRB.getInt64Ty());
 192   Int64Ty = IRB.getInt64Ty();
 193
 194   SanCovFunction = checkSanitizerInterfaceFunction(
 195       M.getOrInsertFunction(kSanCovName, VoidTy, Int32PtrTy, nullptr));
 196   SanCovWithCheckFunction = checkSanitizerInterfaceFunction(
 197       M.getOrInsertFunction(kSanCovWithCheckName, VoidTy, Int32PtrTy, nullptr));
 198   SanCovIndirCallFunction =
 199       checkSanitizerInterfaceFunction(M.getOrInsertFunction(
 200           kSanCovIndirCallName, VoidTy, IntptrTy, IntptrTy, nullptr));
 201   SanCovTraceCmpFunction =
 202       checkSanitizerInterfaceFunction(M.getOrInsertFunction(
 203           kSanCovTraceCmp, VoidTy, Int64Ty, Int64Ty, Int64Ty, nullptr));
 204   SanCovTraceSwitchFunction =
 205       checkSanitizerInterfaceFunction(M.getOrInsertFunction(
 206           kSanCovTraceSwitch, VoidTy, Int64Ty, Int64PtrTy, nullptr));
 207
 208   // We insert an empty inline asm after cov callbacks to avoid callback merge.
 209   EmptyAsm = InlineAsm::get(FunctionType::get(IRB.getVoidTy(), false),
 210                             StringRef(""), StringRef(""),
 211                             /*hasSideEffects=*/true);
 212
 213   if (Options.TraceBB) {
 214     SanCovTraceEnter = checkSanitizerInterfaceFunction(
 215         M.getOrInsertFunction(kSanCovTraceEnter, VoidTy, Int32PtrTy, nullptr));
 216     SanCovTraceBB = checkSanitizerInterfaceFunction(
 217         M.getOrInsertFunction(kSanCovTraceBB, VoidTy, Int32PtrTy, nullptr));
 218   }
 219
 220   // At this point we create a dummy array of guards because we don't
 221   // know how many elements we will need.
 222   Type *Int32Ty = IRB.getInt32Ty();
 223   Type *Int8Ty = IRB.getInt8Ty();
 224
 225   GuardArray =
 226       new GlobalVariable(M, Int32Ty, false, GlobalValue::ExternalLinkage,
 227                          nullptr, "__sancov_gen_cov_tmp");
 228   if (Options.Use8bitCounters)
 229     EightBitCounterArray =
 230         new GlobalVariable(M, Int8Ty, false, GlobalVariable::ExternalLinkage,
 231                            nullptr, "__sancov_gen_cov_tmp");
 232
 233   for (auto &F : M)
 234     runOnFunction(F);
 235
 236   auto N = NumberOfInstrumentedBlocks();
 237
 238   // Now we know how many elements we need. Create an array of guards
 239   // with one extra element at the beginning for the size.
 240   Type *Int32ArrayNTy = ArrayType::get(Int32Ty, N + 1);
 241   GlobalVariable *RealGuardArray = new GlobalVariable(
 242       M, Int32ArrayNTy, false, GlobalValue::PrivateLinkage,
 243       Constant::getNullValue(Int32ArrayNTy), "__sancov_gen_cov");
 244
 245
 246   // Replace the dummy array with the real one.
 247   GuardArray->replaceAllUsesWith(
 248       IRB.CreatePointerCast(RealGuardArray, Int32PtrTy));
 249   GuardArray->eraseFromParent();
 250
 251   GlobalVariable *RealEightBitCounterArray;
 252   if (Options.Use8bitCounters) {
 253     // Make sure the array is 16-aligned.
 254     static const int kCounterAlignment = 16;
 255     Type *Int8ArrayNTy =
 256         ArrayType::get(Int8Ty, RoundUpToAlignment(N, kCounterAlignment));
 257     RealEightBitCounterArray = new GlobalVariable(
 258         M, Int8ArrayNTy, false, GlobalValue::PrivateLinkage,
 259         Constant::getNullValue(Int8ArrayNTy), "__sancov_gen_cov_counter");
 260     RealEightBitCounterArray->setAlignment(kCounterAlignment);
 261     EightBitCounterArray->replaceAllUsesWith(
 262         IRB.CreatePointerCast(RealEightBitCounterArray, Int8PtrTy));
 263     EightBitCounterArray->eraseFromParent();
 264   }
 265
 266   // Create variable for module (compilation unit) name
 267   Constant *ModNameStrConst =
 268       ConstantDataArray::getString(M.getContext(), M.getName(), true);
 269   GlobalVariable *ModuleName =
 270       new GlobalVariable(M, ModNameStrConst->getType(), true,
 271                          GlobalValue::PrivateLinkage, ModNameStrConst);
 272
 273   Function *CtorFunc;
 274   std::tie(CtorFunc, std::ignore) = createSanitizerCtorAndInitFunctions(
 275       M, kSanCovModuleCtorName, kSanCovModuleInitName,
 276       {Int32PtrTy, IntptrTy, Int8PtrTy, Int8PtrTy},
 277       {IRB.CreatePointerCast(RealGuardArray, Int32PtrTy),
 278        ConstantInt::get(IntptrTy, N),
 279        Options.Use8bitCounters
 280            ? IRB.CreatePointerCast(RealEightBitCounterArray, Int8PtrTy)
 281            : Constant::getNullValue(Int8PtrTy),
 282        IRB.CreatePointerCast(ModuleName, Int8PtrTy)});
 283
 284   appendToGlobalCtors(M, CtorFunc, kSanCtorAndDtorPriority);
 285
 286   return true;
 287 }
 288
 289 bool SanitizerCoverageModule::runOnFunction(Function &F) {
 290   if (F.empty()) return false;
 291   if (F.getName().find(".module_ctor") != std::string::npos)
 292     return false;  // Should not instrument sanitizer init functions.
 293   if (Options.CoverageType >= SanitizerCoverageOptions::SCK_Edge)
 294     SplitAllCriticalEdges(F);
 295   SmallVector<Instruction*, 8> IndirCalls;
 296   SmallVector<BasicBlock*, 16> AllBlocks;
 297   SmallVector<Instruction*, 8> CmpTraceTargets;
 298   SmallVector<Instruction*, 8> SwitchTraceTargets;
 299   for (auto &BB : F) {
 300     AllBlocks.push_back(&BB);
 301     for (auto &Inst : BB) {
 302       if (Options.IndirectCalls) {
 303         CallSite CS(&Inst);
 304         if (CS && !CS.getCalledFunction())
 305           IndirCalls.push_back(&Inst);
 306       }
 307       if (Options.TraceCmp) {
 308         if (isa<ICmpInst>(&Inst))
 309           CmpTraceTargets.push_back(&Inst);
 310         if (isa<SwitchInst>(&Inst))
 311           SwitchTraceTargets.push_back(&Inst);
 312       }
 313     }
 314   }
 315   InjectCoverage(F, AllBlocks);
 316   InjectCoverageForIndirectCalls(F, IndirCalls);
 317   InjectTraceForCmp(F, CmpTraceTargets);
 318   InjectTraceForSwitch(F, SwitchTraceTargets);
 319   return true;
 320 }
 321
 322 bool SanitizerCoverageModule::InjectCoverage(Function &F,
 323                                              ArrayRef<BasicBlock *> AllBlocks) {
 324   switch (Options.CoverageType) {
 325   case SanitizerCoverageOptions::SCK_None:
 326     return false;
 327   case SanitizerCoverageOptions::SCK_Function:
 328     InjectCoverageAtBlock(F, F.getEntryBlock(), false);
 329     return true;
 330   default: {
 331     bool UseCalls = ClCoverageBlockThreshold < AllBlocks.size();
 332     for (auto BB : AllBlocks)
 333       InjectCoverageAtBlock(F, *BB, UseCalls);
 334     return true;
 335   }
 336   }
 337 }
 338
 339 // On every indirect call we call a run-time function
 340 // __sanitizer_cov_indir_call* with two parameters:
 341 //   - callee address,
 342 //   - global cache array that contains kCacheSize pointers (zero-initialized).
 343 //     The cache is used to speed up recording the caller-callee pairs.
 344 // The address of the caller is passed implicitly via caller PC.
 345 // kCacheSize is encoded in the name of the run-time function.
 346 void SanitizerCoverageModule::InjectCoverageForIndirectCalls(
 347     Function &F, ArrayRef<Instruction *> IndirCalls) {
 348   if (IndirCalls.empty()) return;
 349   const int kCacheSize = 16;
 350   const int kCacheAlignment = 64;  // Align for better performance.
 351   Type *Ty = ArrayType::get(IntptrTy, kCacheSize);
 352   for (auto I : IndirCalls) {
 353     IRBuilder<> IRB(I);
 354     CallSite CS(I);
 355     Value *Callee = CS.getCalledValue();
 356     if (isa<InlineAsm>(Callee)) continue;
 357     GlobalVariable *CalleeCache = new GlobalVariable(
 358         *F.getParent(), Ty, false, GlobalValue::PrivateLinkage,
 359         Constant::getNullValue(Ty), "__sancov_gen_callee_cache");
 360     CalleeCache->setAlignment(kCacheAlignment);
 361     IRB.CreateCall(SanCovIndirCallFunction,
 362                    {IRB.CreatePointerCast(Callee, IntptrTy),
 363                     IRB.CreatePointerCast(CalleeCache, IntptrTy)});
 364   }
 365 }
 366
 367 // For every switch statement we insert a call:
 368 // __sanitizer_cov_trace_switch(CondValue,
 369 //      {NumCases, ValueSizeInBits, Case0Value, Case1Value, Case2Value, ... })
 370
 371 void SanitizerCoverageModule::InjectTraceForSwitch(
 372     Function &F, ArrayRef<Instruction *> SwitchTraceTargets) {
 373   for (auto I : SwitchTraceTargets) {
 374     if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
 375       IRBuilder<> IRB(I);
 376       SmallVector<Constant *, 16> Initializers;
 377       Value *Cond = SI->getCondition();
 378       if (Cond->getType()->getScalarSizeInBits() >
 379           Int64Ty->getScalarSizeInBits())
 380         continue;
 381       Initializers.push_back(ConstantInt::get(Int64Ty, SI->getNumCases()));
 382       Initializers.push_back(
 383           ConstantInt::get(Int64Ty, Cond->getType()->getScalarSizeInBits()));
 384       if (Cond->getType()->getScalarSizeInBits() <
 385           Int64Ty->getScalarSizeInBits())
 386         Cond = IRB.CreateIntCast(Cond, Int64Ty, false);
 387       for (auto It: SI->cases()) {
 388         Constant *C = It.getCaseValue();
 389         if (C->getType()->getScalarSizeInBits() <
 390             Int64Ty->getScalarSizeInBits())
 391           C = ConstantExpr::getCast(CastInst::ZExt, It.getCaseValue(), Int64Ty);
 392         Initializers.push_back(C);
 393       }
 394       ArrayType *ArrayOfInt64Ty = ArrayType::get(Int64Ty, Initializers.size());
 395       GlobalVariable *GV = new GlobalVariable(
 396           *CurModule, ArrayOfInt64Ty, false, GlobalVariable::InternalLinkage,
 397           ConstantArray::get(ArrayOfInt64Ty, Initializers),
 398           "__sancov_gen_cov_switch_values");
 399       IRB.CreateCall(SanCovTraceSwitchFunction,
 400                      {Cond, IRB.CreatePointerCast(GV, Int64PtrTy)});
 401     }
 402   }
 403 }
 404
 405
 406 void SanitizerCoverageModule::InjectTraceForCmp(
 407     Function &F, ArrayRef<Instruction *> CmpTraceTargets) {
 408   for (auto I : CmpTraceTargets) {
 409     if (ICmpInst *ICMP = dyn_cast<ICmpInst>(I)) {
 410       IRBuilder<> IRB(ICMP);
 411       Value *A0 = ICMP->getOperand(0);
 412       Value *A1 = ICMP->getOperand(1);
 413       if (!A0->getType()->isIntegerTy()) continue;
 414       uint64_t TypeSize = DL->getTypeStoreSizeInBits(A0->getType());
 415       // __sanitizer_cov_trace_cmp((type_size << 32) | predicate, A0, A1);
 416       IRB.CreateCall(
 417           SanCovTraceCmpFunction,
 418           {ConstantInt::get(Int64Ty, (TypeSize << 32) | ICMP->getPredicate()),
 419            IRB.CreateIntCast(A0, Int64Ty, true),
 420            IRB.CreateIntCast(A1, Int64Ty, true)});
 421     }
 422   }
 423 }
 424
 425 void SanitizerCoverageModule::SetNoSanitizeMetadata(Instruction *I) {
 426   I->setMetadata(
 427       I->getParent()->getParent()->getParent()->getMDKindID("nosanitize"),
 428       MDNode::get(*C, None));
 429 }
 430
 431 void SanitizerCoverageModule::InjectCoverageAtBlock(Function &F, BasicBlock &BB,
 432                                                     bool UseCalls) {
 433   // Don't insert coverage for unreachable blocks: we will never call
 434   // __sanitizer_cov() for them, so counting them in
 435   // NumberOfInstrumentedBlocks() might complicate calculation of code coverage
 436   // percentage. Also, unreachable instructions frequently have no debug
 437   // locations.
 438   if (isa<UnreachableInst>(BB.getTerminator()))
 439     return;
 440   BasicBlock::iterator IP = BB.getFirstInsertionPt();
 441
 442   bool IsEntryBB = &BB == &F.getEntryBlock();
 443   DebugLoc EntryLoc;
 444   if (IsEntryBB) {
 445     if (auto SP = getDISubprogram(&F))
 446       EntryLoc = DebugLoc::get(SP->getScopeLine(), 0, SP);
 447     // Keep static allocas and llvm.localescape calls in the entry block.  Even
 448     // if we aren't splitting the block, it's nice for allocas to be before
 449     // calls.
 450     IP = PrepareToSplitEntryBlock(BB, IP);
 451   } else {
 452     EntryLoc = IP->getDebugLoc();
 453   }
 454
 455   IRBuilder<> IRB(IP);
 456   IRB.SetCurrentDebugLocation(EntryLoc);
 457   Value *GuardP = IRB.CreateAdd(
 458       IRB.CreatePointerCast(GuardArray, IntptrTy),
 459       ConstantInt::get(IntptrTy, (1 + NumberOfInstrumentedBlocks()) * 4));
 460   Type *Int32PtrTy = PointerType::getUnqual(IRB.getInt32Ty());
 461   GuardP = IRB.CreateIntToPtr(GuardP, Int32PtrTy);
 462   if (UseCalls) {
 463     IRB.CreateCall(SanCovWithCheckFunction, GuardP);
 464   } else {
 465     LoadInst *Load = IRB.CreateLoad(GuardP);
 466     Load->setAtomic(Monotonic);
 467     Load->setAlignment(4);
 468     SetNoSanitizeMetadata(Load);
 469     Value *Cmp = IRB.CreateICmpSGE(Constant::getNullValue(Load->getType()), Load);
 470     Instruction *Ins = SplitBlockAndInsertIfThen(
 471         Cmp, IP, false, MDBuilder(*C).createBranchWeights(1, 100000));
 472     IRB.SetInsertPoint(Ins);
 473     IRB.SetCurrentDebugLocation(EntryLoc);
 474     // __sanitizer_cov gets the PC of the instruction using GET_CALLER_PC.
 475     IRB.CreateCall(SanCovFunction, GuardP);
 476     IRB.CreateCall(EmptyAsm, {}); // Avoids callback merge.
 477   }
 478
 479   if (Options.Use8bitCounters) {
 480     IRB.SetInsertPoint(IP);
 481     Value *P = IRB.CreateAdd(
 482         IRB.CreatePointerCast(EightBitCounterArray, IntptrTy),
 483         ConstantInt::get(IntptrTy, NumberOfInstrumentedBlocks() - 1));
 484     P = IRB.CreateIntToPtr(P, IRB.getInt8PtrTy());
 485     LoadInst *LI = IRB.CreateLoad(P);
 486     Value *Inc = IRB.CreateAdd(LI, ConstantInt::get(IRB.getInt8Ty(), 1));
 487     StoreInst *SI = IRB.CreateStore(Inc, P);
 488     SetNoSanitizeMetadata(LI);
 489     SetNoSanitizeMetadata(SI);
 490   }
 491
 492   if (Options.TraceBB) {
 493     // Experimental support for tracing.
 494     // Insert a callback with the same guard variable as used for coverage.
 495     IRB.SetInsertPoint(IP);
 496     IRB.CreateCall(IsEntryBB ? SanCovTraceEnter : SanCovTraceBB, GuardP);
 497   }
 498 }
 499
 500 char SanitizerCoverageModule::ID = 0;
 501 INITIALIZE_PASS(SanitizerCoverageModule, "sancov",
 502     "SanitizerCoverage: TODO."
 503     "ModulePass", false, false)
 504 ModulePass *llvm::createSanitizerCoverageModulePass(
 505     const SanitizerCoverageOptions &Options) {
 506   return new SanitizerCoverageModule(Options);
 507 }