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/Analysis/LibCallSemantics.h"
  35 #include "llvm/IR/CallSite.h"
  36 #include "llvm/IR/DataLayout.h"
  37 #include "llvm/IR/DebugInfo.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 kSanCovWithCheckName = "__sanitizer_cov_with_check";
  59 static const char *const kSanCovIndirCallName = "__sanitizer_cov_indir_call16";
  60 static const char *const kSanCovTraceEnter = "__sanitizer_cov_trace_func_enter";
  61 static const char *const kSanCovTraceBB = "__sanitizer_cov_trace_basic_block";
  62 static const char *const kSanCovTraceCmp = "__sanitizer_cov_trace_cmp";
  63 static const char *const kSanCovTraceSwitch = "__sanitizer_cov_trace_switch";
  64 static const char *const kSanCovModuleCtorName = "sancov.module_ctor";
  65 static const uint64_t    kSanCtorAndDtorPriority = 2;
  66
  67 static cl::opt<int> ClCoverageLevel("sanitizer-coverage-level",
  68        cl::desc("Sanitizer Coverage. 0: none, 1: entry block, 2: all blocks, "
  69                 "3: all blocks and critical edges, "
  70                 "4: above plus indirect calls"),
  71        cl::Hidden, cl::init(0));
  72
  73 static cl::opt<unsigned> ClCoverageBlockThreshold(
  74     "sanitizer-coverage-block-threshold",
  75     cl::desc("Use a callback with a guard check inside it if there are"
  76              " more than this number of blocks."),
  77     cl::Hidden, cl::init(500));
  78
  79 static cl::opt<bool>
  80     ClExperimentalTracing("sanitizer-coverage-experimental-tracing",
  81                           cl::desc("Experimental basic-block tracing: insert "
  82                                    "callbacks at every basic block"),
  83                           cl::Hidden, cl::init(false));
  84
  85 static cl::opt<bool>
  86     ClExperimentalCMPTracing("sanitizer-coverage-experimental-trace-compares",
  87                              cl::desc("Experimental tracing of CMP and similar "
  88                                       "instructions"),
  89                              cl::Hidden, cl::init(false));
  90
  91 // Experimental 8-bit counters used as an additional search heuristic during
  92 // coverage-guided fuzzing.
  93 // The counters are not thread-friendly:
  94 //   - contention on these counters may cause significant slowdown;
  95 //   - the counter updates are racy and the results may be inaccurate.
  96 // They are also inaccurate due to 8-bit integer overflow.
  97 static cl::opt<bool> ClUse8bitCounters("sanitizer-coverage-8bit-counters",
  98                                        cl::desc("Experimental 8-bit counters"),
  99                                        cl::Hidden, cl::init(false));
 100
 101 namespace {
 102
 103 SanitizerCoverageOptions getOptions(int LegacyCoverageLevel) {
 104   SanitizerCoverageOptions Res;
 105   switch (LegacyCoverageLevel) {
 106   case 0:
 107     Res.CoverageType = SanitizerCoverageOptions::SCK_None;
 108     break;
 109   case 1:
 110     Res.CoverageType = SanitizerCoverageOptions::SCK_Function;
 111     break;
 112   case 2:
 113     Res.CoverageType = SanitizerCoverageOptions::SCK_BB;
 114     break;
 115   case 3:
 116     Res.CoverageType = SanitizerCoverageOptions::SCK_Edge;
 117     break;
 118   case 4:
 119     Res.CoverageType = SanitizerCoverageOptions::SCK_Edge;
 120     Res.IndirectCalls = true;
 121     break;
 122   }
 123   return Res;
 124 }
 125
 126 SanitizerCoverageOptions OverrideFromCL(SanitizerCoverageOptions Options) {
 127   // Sets CoverageType and IndirectCalls.
 128   SanitizerCoverageOptions CLOpts = getOptions(ClCoverageLevel);
 129   Options.CoverageType = std::max(Options.CoverageType, CLOpts.CoverageType);
 130   Options.IndirectCalls |= CLOpts.IndirectCalls;
 131   Options.TraceBB |= ClExperimentalTracing;
 132   Options.TraceCmp |= ClExperimentalCMPTracing;
 133   Options.Use8bitCounters |= ClUse8bitCounters;
 134   return Options;
 135 }
 136
 137 class SanitizerCoverageModule : public ModulePass {
 138  public:
 139   SanitizerCoverageModule(
 140       const SanitizerCoverageOptions &Options = SanitizerCoverageOptions())
 141       : ModulePass(ID), Options(OverrideFromCL(Options)) {}
 142   bool runOnModule(Module &M) override;
 143   bool runOnFunction(Function &F);
 144   static char ID;  // Pass identification, replacement for typeid
 145   const char *getPassName() const override {
 146     return "SanitizerCoverageModule";
 147   }
 148
 149  private:
 150   void InjectCoverageForIndirectCalls(Function &F,
 151                                       ArrayRef<Instruction *> IndirCalls);
 152   void InjectTraceForCmp(Function &F, ArrayRef<Instruction *> CmpTraceTargets);
 153   void InjectTraceForSwitch(Function &F,
 154                             ArrayRef<Instruction *> SwitchTraceTargets);
 155   bool InjectCoverage(Function &F, ArrayRef<BasicBlock *> AllBlocks);
 156   void SetNoSanitizeMetadata(Instruction *I);
 157   void InjectCoverageAtBlock(Function &F, BasicBlock &BB, bool UseCalls);
 158   unsigned NumberOfInstrumentedBlocks() {
 159     return SanCovFunction->getNumUses() +
 160            SanCovWithCheckFunction->getNumUses() + SanCovTraceBB->getNumUses() +
 161            SanCovTraceEnter->getNumUses();
 162   }
 163   Function *SanCovFunction;
 164   Function *SanCovWithCheckFunction;
 165   Function *SanCovIndirCallFunction;
 166   Function *SanCovTraceEnter, *SanCovTraceBB;
 167   Function *SanCovTraceCmpFunction;
 168   Function *SanCovTraceSwitchFunction;
 169   InlineAsm *EmptyAsm;
 170   Type *IntptrTy, *Int64Ty, *Int64PtrTy;
 171   Module *CurModule;
 172   LLVMContext *C;
 173   const DataLayout *DL;
 174
 175   GlobalVariable *GuardArray;
 176   GlobalVariable *EightBitCounterArray;
 177
 178   SanitizerCoverageOptions Options;
 179 };
 180
 181 }  // namespace
 182
 183 bool SanitizerCoverageModule::runOnModule(Module &M) {
 184   if (Options.CoverageType == SanitizerCoverageOptions::SCK_None)
 185     return false;
 186   C = &(M.getContext());
 187   DL = &M.getDataLayout();
 188   CurModule = &M;
 189   IntptrTy = Type::getIntNTy(*C, DL->getPointerSizeInBits());
 190   Type *VoidTy = Type::getVoidTy(*C);
 191   IRBuilder<> IRB(*C);
 192   Type *Int8PtrTy = PointerType::getUnqual(IRB.getInt8Ty());
 193   Type *Int32PtrTy = PointerType::getUnqual(IRB.getInt32Ty());
 194   Int64PtrTy = PointerType::getUnqual(IRB.getInt64Ty());
 195   Int64Ty = IRB.getInt64Ty();
 196
 197   SanCovFunction = checkSanitizerInterfaceFunction(
 198       M.getOrInsertFunction(kSanCovName, VoidTy, Int32PtrTy, nullptr));
 199   SanCovWithCheckFunction = checkSanitizerInterfaceFunction(
 200       M.getOrInsertFunction(kSanCovWithCheckName, VoidTy, Int32PtrTy, nullptr));
 201   SanCovIndirCallFunction =
 202       checkSanitizerInterfaceFunction(M.getOrInsertFunction(
 203           kSanCovIndirCallName, VoidTy, IntptrTy, IntptrTy, nullptr));
 204   SanCovTraceCmpFunction =
 205       checkSanitizerInterfaceFunction(M.getOrInsertFunction(
 206           kSanCovTraceCmp, VoidTy, Int64Ty, Int64Ty, Int64Ty, nullptr));
 207   SanCovTraceSwitchFunction =
 208       checkSanitizerInterfaceFunction(M.getOrInsertFunction(
 209           kSanCovTraceSwitch, VoidTy, Int64Ty, Int64PtrTy, nullptr));
 210
 211   // We insert an empty inline asm after cov callbacks to avoid callback merge.
 212   EmptyAsm = InlineAsm::get(FunctionType::get(IRB.getVoidTy(), false),
 213                             StringRef(""), StringRef(""),
 214                             /*hasSideEffects=*/true);
 215
 216   SanCovTraceEnter = checkSanitizerInterfaceFunction(
 217       M.getOrInsertFunction(kSanCovTraceEnter, VoidTy, Int32PtrTy, nullptr));
 218   SanCovTraceBB = checkSanitizerInterfaceFunction(
 219       M.getOrInsertFunction(kSanCovTraceBB, VoidTy, Int32PtrTy, nullptr));
 220
 221   // At this point we create a dummy array of guards because we don't
 222   // know how many elements we will need.
 223   Type *Int32Ty = IRB.getInt32Ty();
 224   Type *Int8Ty = IRB.getInt8Ty();
 225
 226   GuardArray =
 227       new GlobalVariable(M, Int32Ty, false, GlobalValue::ExternalLinkage,
 228                          nullptr, "__sancov_gen_cov_tmp");
 229   if (Options.Use8bitCounters)
 230     EightBitCounterArray =
 231         new GlobalVariable(M, Int8Ty, false, GlobalVariable::ExternalLinkage,
 232                            nullptr, "__sancov_gen_cov_tmp");
 233
 234   for (auto &F : M)
 235     runOnFunction(F);
 236
 237   auto N = NumberOfInstrumentedBlocks();
 238
 239   // Now we know how many elements we need. Create an array of guards
 240   // with one extra element at the beginning for the size.
 241   Type *Int32ArrayNTy = ArrayType::get(Int32Ty, N + 1);
 242   GlobalVariable *RealGuardArray = new GlobalVariable(
 243       M, Int32ArrayNTy, false, GlobalValue::PrivateLinkage,
 244       Constant::getNullValue(Int32ArrayNTy), "__sancov_gen_cov");
 245
 246
 247   // Replace the dummy array with the real one.
 248   GuardArray->replaceAllUsesWith(
 249       IRB.CreatePointerCast(RealGuardArray, Int32PtrTy));
 250   GuardArray->eraseFromParent();
 251
 252   GlobalVariable *RealEightBitCounterArray;
 253   if (Options.Use8bitCounters) {
 254     // Make sure the array is 16-aligned.
 255     static const int kCounterAlignment = 16;
 256     Type *Int8ArrayNTy =
 257         ArrayType::get(Int8Ty, RoundUpToAlignment(N, kCounterAlignment));
 258     RealEightBitCounterArray = new GlobalVariable(
 259         M, Int8ArrayNTy, false, GlobalValue::PrivateLinkage,
 260         Constant::getNullValue(Int8ArrayNTy), "__sancov_gen_cov_counter");
 261     RealEightBitCounterArray->setAlignment(kCounterAlignment);
 262     EightBitCounterArray->replaceAllUsesWith(
 263         IRB.CreatePointerCast(RealEightBitCounterArray, Int8PtrTy));
 264     EightBitCounterArray->eraseFromParent();
 265   }
 266
 267   // Create variable for module (compilation unit) name
 268   Constant *ModNameStrConst =
 269       ConstantDataArray::getString(M.getContext(), M.getName(), true);
 270   GlobalVariable *ModuleName =
 271       new GlobalVariable(M, ModNameStrConst->getType(), true,
 272                          GlobalValue::PrivateLinkage, ModNameStrConst);
 273
 274   Function *CtorFunc;
 275   std::tie(CtorFunc, std::ignore) = createSanitizerCtorAndInitFunctions(
 276       M, kSanCovModuleCtorName, kSanCovModuleInitName,
 277       {Int32PtrTy, IntptrTy, Int8PtrTy, Int8PtrTy},
 278       {IRB.CreatePointerCast(RealGuardArray, Int32PtrTy),
 279        ConstantInt::get(IntptrTy, N),
 280        Options.Use8bitCounters
 281            ? IRB.CreatePointerCast(RealEightBitCounterArray, Int8PtrTy)
 282            : Constant::getNullValue(Int8PtrTy),
 283        IRB.CreatePointerCast(ModuleName, Int8PtrTy)});
 284
 285   appendToGlobalCtors(M, CtorFunc, kSanCtorAndDtorPriority);
 286
 287   return true;
 288 }
 289
 290 bool SanitizerCoverageModule::runOnFunction(Function &F) {
 291   if (F.empty()) return false;
 292   if (F.getName().find(".module_ctor") != std::string::npos)
 293     return false;  // Should not instrument sanitizer init functions.
 294   // Don't instrument functions using SEH for now. Splitting basic blocks like
 295   // we do for coverage breaks WinEHPrepare.
 296   // FIXME: Remove this when SEH no longer uses landingpad pattern matching.
 297   if (F.hasPersonalityFn() &&
 298       isAsynchronousEHPersonality(classifyEHPersonality(F.getPersonalityFn())))
 299     return false;
 300   if (Options.CoverageType >= SanitizerCoverageOptions::SCK_Edge)
 301     SplitAllCriticalEdges(F);
 302   SmallVector<Instruction*, 8> IndirCalls;
 303   SmallVector<BasicBlock*, 16> AllBlocks;
 304   SmallVector<Instruction*, 8> CmpTraceTargets;
 305   SmallVector<Instruction*, 8> SwitchTraceTargets;
 306   for (auto &BB : F) {
 307     AllBlocks.push_back(&BB);
 308     for (auto &Inst : BB) {
 309       if (Options.IndirectCalls) {
 310         CallSite CS(&Inst);
 311         if (CS && !CS.getCalledFunction())
 312           IndirCalls.push_back(&Inst);
 313       }
 314       if (Options.TraceCmp) {
 315         if (isa<ICmpInst>(&Inst))
 316           CmpTraceTargets.push_back(&Inst);
 317         if (isa<SwitchInst>(&Inst))
 318           SwitchTraceTargets.push_back(&Inst);
 319       }
 320     }
 321   }
 322   InjectCoverage(F, AllBlocks);
 323   InjectCoverageForIndirectCalls(F, IndirCalls);
 324   InjectTraceForCmp(F, CmpTraceTargets);
 325   InjectTraceForSwitch(F, SwitchTraceTargets);
 326   return true;
 327 }
 328
 329 bool SanitizerCoverageModule::InjectCoverage(Function &F,
 330                                              ArrayRef<BasicBlock *> AllBlocks) {
 331   switch (Options.CoverageType) {
 332   case SanitizerCoverageOptions::SCK_None:
 333     return false;
 334   case SanitizerCoverageOptions::SCK_Function:
 335     InjectCoverageAtBlock(F, F.getEntryBlock(), false);
 336     return true;
 337   default: {
 338     bool UseCalls = ClCoverageBlockThreshold < AllBlocks.size();
 339     for (auto BB : AllBlocks)
 340       InjectCoverageAtBlock(F, *BB, UseCalls);
 341     return true;
 342   }
 343   }
 344 }
 345
 346 // On every indirect call we call a run-time function
 347 // __sanitizer_cov_indir_call* with two parameters:
 348 //   - callee address,
 349 //   - global cache array that contains kCacheSize pointers (zero-initialized).
 350 //     The cache is used to speed up recording the caller-callee pairs.
 351 // The address of the caller is passed implicitly via caller PC.
 352 // kCacheSize is encoded in the name of the run-time function.
 353 void SanitizerCoverageModule::InjectCoverageForIndirectCalls(
 354     Function &F, ArrayRef<Instruction *> IndirCalls) {
 355   if (IndirCalls.empty()) return;
 356   const int kCacheSize = 16;
 357   const int kCacheAlignment = 64;  // Align for better performance.
 358   Type *Ty = ArrayType::get(IntptrTy, kCacheSize);
 359   for (auto I : IndirCalls) {
 360     IRBuilder<> IRB(I);
 361     CallSite CS(I);
 362     Value *Callee = CS.getCalledValue();
 363     if (isa<InlineAsm>(Callee)) continue;
 364     GlobalVariable *CalleeCache = new GlobalVariable(
 365         *F.getParent(), Ty, false, GlobalValue::PrivateLinkage,
 366         Constant::getNullValue(Ty), "__sancov_gen_callee_cache");
 367     CalleeCache->setAlignment(kCacheAlignment);
 368     IRB.CreateCall(SanCovIndirCallFunction,
 369                    {IRB.CreatePointerCast(Callee, IntptrTy),
 370                     IRB.CreatePointerCast(CalleeCache, IntptrTy)});
 371   }
 372 }
 373
 374 // For every switch statement we insert a call:
 375 // __sanitizer_cov_trace_switch(CondValue,
 376 //      {NumCases, ValueSizeInBits, Case0Value, Case1Value, Case2Value, ... })
 377
 378 void SanitizerCoverageModule::InjectTraceForSwitch(
 379     Function &F, ArrayRef<Instruction *> SwitchTraceTargets) {
 380   for (auto I : SwitchTraceTargets) {
 381     if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) {
 382       IRBuilder<> IRB(I);
 383       SmallVector<Constant *, 16> Initializers;
 384       Value *Cond = SI->getCondition();
 385       if (Cond->getType()->getScalarSizeInBits() >
 386           Int64Ty->getScalarSizeInBits())
 387         continue;
 388       Initializers.push_back(ConstantInt::get(Int64Ty, SI->getNumCases()));
 389       Initializers.push_back(
 390           ConstantInt::get(Int64Ty, Cond->getType()->getScalarSizeInBits()));
 391       if (Cond->getType()->getScalarSizeInBits() <
 392           Int64Ty->getScalarSizeInBits())
 393         Cond = IRB.CreateIntCast(Cond, Int64Ty, false);
 394       for (auto It: SI->cases()) {
 395         Constant *C = It.getCaseValue();
 396         if (C->getType()->getScalarSizeInBits() <
 397             Int64Ty->getScalarSizeInBits())
 398           C = ConstantExpr::getCast(CastInst::ZExt, It.getCaseValue(), Int64Ty);
 399         Initializers.push_back(C);
 400       }
 401       ArrayType *ArrayOfInt64Ty = ArrayType::get(Int64Ty, Initializers.size());
 402       GlobalVariable *GV = new GlobalVariable(
 403           *CurModule, ArrayOfInt64Ty, false, GlobalVariable::InternalLinkage,
 404           ConstantArray::get(ArrayOfInt64Ty, Initializers),
 405           "__sancov_gen_cov_switch_values");
 406       IRB.CreateCall(SanCovTraceSwitchFunction,
 407                      {Cond, IRB.CreatePointerCast(GV, Int64PtrTy)});
 408     }
 409   }
 410 }
 411
 412
 413 void SanitizerCoverageModule::InjectTraceForCmp(
 414     Function &F, ArrayRef<Instruction *> CmpTraceTargets) {
 415   for (auto I : CmpTraceTargets) {
 416     if (ICmpInst *ICMP = dyn_cast<ICmpInst>(I)) {
 417       IRBuilder<> IRB(ICMP);
 418       Value *A0 = ICMP->getOperand(0);
 419       Value *A1 = ICMP->getOperand(1);
 420       if (!A0->getType()->isIntegerTy()) continue;
 421       uint64_t TypeSize = DL->getTypeStoreSizeInBits(A0->getType());
 422       // __sanitizer_cov_trace_cmp((type_size << 32) | predicate, A0, A1);
 423       IRB.CreateCall(
 424           SanCovTraceCmpFunction,
 425           {ConstantInt::get(Int64Ty, (TypeSize << 32) | ICMP->getPredicate()),
 426            IRB.CreateIntCast(A0, Int64Ty, true),
 427            IRB.CreateIntCast(A1, Int64Ty, true)});
 428     }
 429   }
 430 }
 431
 432 void SanitizerCoverageModule::SetNoSanitizeMetadata(Instruction *I) {
 433   I->setMetadata(
 434       I->getParent()->getParent()->getParent()->getMDKindID("nosanitize"),
 435       MDNode::get(*C, None));
 436 }
 437
 438 void SanitizerCoverageModule::InjectCoverageAtBlock(Function &F, BasicBlock &BB,
 439                                                     bool UseCalls) {
 440   // Don't insert coverage for unreachable blocks: we will never call
 441   // __sanitizer_cov() for them, so counting them in
 442   // NumberOfInstrumentedBlocks() might complicate calculation of code coverage
 443   // percentage. Also, unreachable instructions frequently have no debug
 444   // locations.
 445   if (isa<UnreachableInst>(BB.getTerminator()))
 446     return;
 447   BasicBlock::iterator IP = BB.getFirstInsertionPt();
 448
 449   bool IsEntryBB = &BB == &F.getEntryBlock();
 450   DebugLoc EntryLoc;
 451   if (IsEntryBB) {
 452     if (auto SP = getDISubprogram(&F))
 453       EntryLoc = DebugLoc::get(SP->getScopeLine(), 0, SP);
 454     // Keep static allocas and llvm.localescape calls in the entry block.  Even
 455     // if we aren't splitting the block, it's nice for allocas to be before
 456     // calls.
 457     IP = PrepareToSplitEntryBlock(BB, IP);
 458   } else {
 459     EntryLoc = IP->getDebugLoc();
 460   }
 461
 462   IRBuilder<> IRB(&*IP);
 463   IRB.SetCurrentDebugLocation(EntryLoc);
 464   Value *GuardP = IRB.CreateAdd(
 465       IRB.CreatePointerCast(GuardArray, IntptrTy),
 466       ConstantInt::get(IntptrTy, (1 + NumberOfInstrumentedBlocks()) * 4));
 467   Type *Int32PtrTy = PointerType::getUnqual(IRB.getInt32Ty());
 468   GuardP = IRB.CreateIntToPtr(GuardP, Int32PtrTy);
 469   if (Options.TraceBB) {
 470     IRB.CreateCall(IsEntryBB ? SanCovTraceEnter : SanCovTraceBB, GuardP);
 471   } else if (UseCalls) {
 472     IRB.CreateCall(SanCovWithCheckFunction, GuardP);
 473   } else {
 474     LoadInst *Load = IRB.CreateLoad(GuardP);
 475     Load->setAtomic(Monotonic);
 476     Load->setAlignment(4);
 477     SetNoSanitizeMetadata(Load);
 478     Value *Cmp = IRB.CreateICmpSGE(Constant::getNullValue(Load->getType()), Load);
 479     Instruction *Ins = SplitBlockAndInsertIfThen(
 480         Cmp, &*IP, false, MDBuilder(*C).createBranchWeights(1, 100000));
 481     IRB.SetInsertPoint(Ins);
 482     IRB.SetCurrentDebugLocation(EntryLoc);
 483     // __sanitizer_cov gets the PC of the instruction using GET_CALLER_PC.
 484     IRB.CreateCall(SanCovFunction, GuardP);
 485     IRB.CreateCall(EmptyAsm, {}); // Avoids callback merge.
 486   }
 487
 488   if (Options.Use8bitCounters) {
 489     IRB.SetInsertPoint(&*IP);
 490     Value *P = IRB.CreateAdd(
 491         IRB.CreatePointerCast(EightBitCounterArray, IntptrTy),
 492         ConstantInt::get(IntptrTy, NumberOfInstrumentedBlocks() - 1));
 493     P = IRB.CreateIntToPtr(P, IRB.getInt8PtrTy());
 494     LoadInst *LI = IRB.CreateLoad(P);
 495     Value *Inc = IRB.CreateAdd(LI, ConstantInt::get(IRB.getInt8Ty(), 1));
 496     StoreInst *SI = IRB.CreateStore(Inc, P);
 497     SetNoSanitizeMetadata(LI);
 498     SetNoSanitizeMetadata(SI);
 499   }
 500 }
 501
 502 char SanitizerCoverageModule::ID = 0;
 503 INITIALIZE_PASS(SanitizerCoverageModule, "sancov",
 504     "SanitizerCoverage: TODO."
 505     "ModulePass", false, false)
 506 ModulePass *llvm::createSanitizerCoverageModulePass(
 507     const SanitizerCoverageOptions &Options) {
 508   return new SanitizerCoverageModule(Options);
 509 }