text: //===-- DataFlowSanitizer.cpp - dynamic data flow analysis ----------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  /// \file
  /// This file is a part of DataFlowSanitizer, a generalised dynamic data flow
  /// analysis.
  ///
  /// Unlike other Sanitizer tools, this tool is not designed to detect a specific
  /// class of bugs on its own.  Instead, it provides a generic dynamic data flow
  /// analysis framework to be used by clients to help detect application-specific
  /// issues within their own code.
  ///
  /// The analysis is based on automatic propagation of data flow labels (also
  /// known as taint labels) through a program as it performs computation.  Each
  /// byte of application memory is backed by two bytes of shadow memory which
  /// hold the label.  On Linux/x86_64, memory is laid out as follows:
  ///
  /// +--------------------+ 0x800000000000 (top of memory)
  /// | application memory |
  /// +--------------------+ 0x700000008000 (kAppAddr)
  /// |                    |
  /// |       unused       |
  /// |                    |
  /// +--------------------+ 0x200200000000 (kUnusedAddr)
  /// |    union table     |
  /// +--------------------+ 0x200000000000 (kUnionTableAddr)
  /// |   shadow memory    |
  /// +--------------------+ 0x000000010000 (kShadowAddr)
  /// | reserved by kernel |
  /// +--------------------+ 0x000000000000
  ///
  /// To derive a shadow memory address from an application memory address,
  /// bits 44-46 are cleared to bring the address into the range
  /// [0x000000008000,0x100000000000).  Then the address is shifted left by 1 to
  /// account for the double byte representation of shadow labels and move the
  /// address into the shadow memory range.  See the function
  /// DataFlowSanitizer::getShadowAddress below.
  ///
  /// For more information, please refer to the design document:
  /// http://clang.llvm.org/docs/DataFlowSanitizerDesign.html
  
  #include "llvm/Transforms/Instrumentation.h"
  #include "llvm/ADT/DenseMap.h"
  #include "llvm/ADT/DenseSet.h"
  #include "llvm/ADT/DepthFirstIterator.h"
  #include "llvm/ADT/StringExtras.h"
  #include "llvm/ADT/Triple.h"
  #include "llvm/Analysis/ValueTracking.h"
  #include "llvm/IR/Dominators.h"
  #include "llvm/IR/DebugInfo.h"
  #include "llvm/IR/IRBuilder.h"
  #include "llvm/IR/InlineAsm.h"
  #include "llvm/IR/InstVisitor.h"
  #include "llvm/IR/LLVMContext.h"
  #include "llvm/IR/MDBuilder.h"
  #include "llvm/IR/Type.h"
  #include "llvm/IR/Value.h"
  #include "llvm/Pass.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Support/SpecialCaseList.h"
  #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  #include "llvm/Transforms/Utils/Local.h"
  #include <algorithm>
  #include <iterator>
  #include <set>
  #include <utility>
  
  using namespace llvm;
  
  // External symbol to be used when generating the shadow address for
  // architectures with multiple VMAs. Instead of using a constant integer
  // the runtime will set the external mask based on the VMA range.
  static const char *const kDFSanExternShadowPtrMask = "__dfsan_shadow_ptr_mask";
  
  // The -dfsan-preserve-alignment flag controls whether this pass assumes that
  // alignment requirements provided by the input IR are correct.  For example,
  // if the input IR contains a load with alignment 8, this flag will cause
  // the shadow load to have alignment 16.  This flag is disabled by default as
  // we have unfortunately encountered too much code (including Clang itself;
  // see PR14291) which performs misaligned access.
  static cl::opt<bool> ClPreserveAlignment(
      "dfsan-preserve-alignment",
      cl::desc("respect alignment requirements provided by input IR"), cl::Hidden,
      cl::init(false));
  
  // The ABI list files control how shadow parameters are passed. The pass treats
  // every function labelled "uninstrumented" in the ABI list file as conforming
  // to the "native" (i.e. unsanitized) ABI.  Unless the ABI list contains
  // additional annotations for those functions, a call to one of those functions
  // will produce a warning message, as the labelling behaviour of the function is
  // unknown.  The other supported annotations are "functional" and "discard",
  // which are described below under DataFlowSanitizer::WrapperKind.
  static cl::list<std::string> ClABIListFiles(
      "dfsan-abilist",
      cl::desc("File listing native ABI functions and how the pass treats them"),
      cl::Hidden);
  
  // Controls whether the pass uses IA_Args or IA_TLS as the ABI for instrumented
  // functions (see DataFlowSanitizer::InstrumentedABI below).
  static cl::opt<bool> ClArgsABI(
      "dfsan-args-abi",
      cl::desc("Use the argument ABI rather than the TLS ABI"),
      cl::Hidden);
  
  // Controls whether the pass includes or ignores the labels of pointers in load
  // instructions.
  static cl::opt<bool> ClCombinePointerLabelsOnLoad(
      "dfsan-combine-pointer-labels-on-load",
      cl::desc("Combine the label of the pointer with the label of the data when "
               "loading from memory."),
      cl::Hidden, cl::init(true));
  
  // Controls whether the pass includes or ignores the labels of pointers in
  // stores instructions.
  static cl::opt<bool> ClCombinePointerLabelsOnStore(
      "dfsan-combine-pointer-labels-on-store",
      cl::desc("Combine the label of the pointer with the label of the data when "
               "storing in memory."),
      cl::Hidden, cl::init(false));
  
  static cl::opt<bool> ClDebugNonzeroLabels(
      "dfsan-debug-nonzero-labels",
      cl::desc("Insert calls to __dfsan_nonzero_label on observing a parameter, "
               "load or return with a nonzero label"),
      cl::Hidden);
  
  
  namespace {
  
  StringRef GetGlobalTypeString(const GlobalValue &G) {
    // Types of GlobalVariables are always pointer types.
    Type *GType = G.getType()->getElementType();
    // For now we support blacklisting struct types only.
    if (StructType *SGType = dyn_cast<StructType>(GType)) {
      if (!SGType->isLiteral())
        return SGType->getName();
    }
    return "<unknown type>";
  }
  
  class DFSanABIList {
    std::unique_ptr<SpecialCaseList> SCL;
  
   public:
    DFSanABIList() {}
  
    void set(std::unique_ptr<SpecialCaseList> List) { SCL = std::move(List); }
  
    /// Returns whether either this function or its source file are listed in the
    /// given category.
    bool isIn(const Function &F, StringRef Category) const {
      return isIn(*F.getParent(), Category) ||
             SCL->inSection("fun", F.getName(), Category);
    }
  
    /// Returns whether this global alias is listed in the given category.
    ///
    /// If GA aliases a function, the alias's name is matched as a function name
    /// would be.  Similarly, aliases of globals are matched like globals.
    bool isIn(const GlobalAlias &GA, StringRef Category) const {
      if (isIn(*GA.getParent(), Category))
        return true;
  
      if (isa<FunctionType>(GA.getType()->getElementType()))
        return SCL->inSection("fun", GA.getName(), Category);
  
      return SCL->inSection("global", GA.getName(), Category) ||
             SCL->inSection("type", GetGlobalTypeString(GA), Category);
    }
  
    /// Returns whether this module is listed in the given category.
    bool isIn(const Module &M, StringRef Category) const {
      return SCL->inSection("src", M.getModuleIdentifier(), Category);
    }
  };
  
  class DataFlowSanitizer : public ModulePass {
    friend struct DFSanFunction;
    friend class DFSanVisitor;
  
    enum {
      ShadowWidth = 16
    };
  
    /// Which ABI should be used for instrumented functions?
    enum InstrumentedABI {
      /// Argument and return value labels are passed through additional
      /// arguments and by modifying the return type.
      IA_Args,
  
      /// Argument and return value labels are passed through TLS variables
      /// __dfsan_arg_tls and __dfsan_retval_tls.
      IA_TLS
    };
  
    /// How should calls to uninstrumented functions be handled?
    enum WrapperKind {
      /// This function is present in an uninstrumented form but we don't know
      /// how it should be handled.  Print a warning and call the function anyway.
      /// Don't label the return value.
      WK_Warning,
  
      /// This function does not write to (user-accessible) memory, and its return
      /// value is unlabelled.
      WK_Discard,
  
      /// This function does not write to (user-accessible) memory, and the label
      /// of its return value is the union of the label of its arguments.
      WK_Functional,
  
      /// Instead of calling the function, a custom wrapper __dfsw_F is called,
      /// where F is the name of the function.  This function may wrap the
      /// original function or provide its own implementation.  This is similar to
      /// the IA_Args ABI, except that IA_Args uses a struct return type to
      /// pass the return value shadow in a register, while WK_Custom uses an
      /// extra pointer argument to return the shadow.  This allows the wrapped
      /// form of the function type to be expressed in C.
      WK_Custom
    };
  
    Module *Mod;
    LLVMContext *Ctx;
    IntegerType *ShadowTy;
    PointerType *ShadowPtrTy;
    IntegerType *IntptrTy;
    ConstantInt *ZeroShadow;
    ConstantInt *ShadowPtrMask;
    ConstantInt *ShadowPtrMul;
    Constant *ArgTLS;
    Constant *RetvalTLS;
    void *(*GetArgTLSPtr)();
    void *(*GetRetvalTLSPtr)();
    Constant *GetArgTLS;
    Constant *GetRetvalTLS;
    Constant *ExternalShadowMask;
    FunctionType *DFSanUnionFnTy;
    FunctionType *DFSanUnionLoadFnTy;
    FunctionType *DFSanUnimplementedFnTy;
    FunctionType *DFSanSetLabelFnTy;
    FunctionType *DFSanNonzeroLabelFnTy;
    FunctionType *DFSanVarargWrapperFnTy;
    Constant *DFSanUnionFn;
    Constant *DFSanCheckedUnionFn;
    Constant *DFSanUnionLoadFn;
    Constant *DFSanUnimplementedFn;
    Constant *DFSanSetLabelFn;
    Constant *DFSanNonzeroLabelFn;
    Constant *DFSanVarargWrapperFn;
    MDNode *ColdCallWeights;
    DFSanABIList ABIList;
    DenseMap<Value *, Function *> UnwrappedFnMap;
    AttributeSet ReadOnlyNoneAttrs;
    bool DFSanRuntimeShadowMask;
  
    Value *getShadowAddress(Value *Addr, Instruction *Pos);
    bool isInstrumented(const Function *F);
    bool isInstrumented(const GlobalAlias *GA);
    FunctionType *getArgsFunctionType(FunctionType *T);
    FunctionType *getTrampolineFunctionType(FunctionType *T);
    FunctionType *getCustomFunctionType(FunctionType *T);
    InstrumentedABI getInstrumentedABI();
    WrapperKind getWrapperKind(Function *F);
    void addGlobalNamePrefix(GlobalValue *GV);
    Function *buildWrapperFunction(Function *F, StringRef NewFName,
                                   GlobalValue::LinkageTypes NewFLink,
                                   FunctionType *NewFT);
    Constant *getOrBuildTrampolineFunction(FunctionType *FT, StringRef FName);
  
   public:
    DataFlowSanitizer(
        const std::vector<std::string> &ABIListFiles = std::vector<std::string>(),
        void *(*getArgTLS)() = nullptr, void *(*getRetValTLS)() = nullptr);
    static char ID;
    bool doInitialization(Module &M) override;
    bool runOnModule(Module &M) override;
  };
  
  struct DFSanFunction {
    DataFlowSanitizer &DFS;
    Function *F;
    DominatorTree DT;
    DataFlowSanitizer::InstrumentedABI IA;
    bool IsNativeABI;
    Value *ArgTLSPtr;
    Value *RetvalTLSPtr;
    AllocaInst *LabelReturnAlloca;
    DenseMap<Value *, Value *> ValShadowMap;
    DenseMap<AllocaInst *, AllocaInst *> AllocaShadowMap;
    std::vector<std::pair<PHINode *, PHINode *> > PHIFixups;
    DenseSet<Instruction *> SkipInsts;
    std::vector<Value *> NonZeroChecks;
    bool AvoidNewBlocks;
  
    struct CachedCombinedShadow {
      BasicBlock *Block;
      Value *Shadow;
    };
    DenseMap<std::pair<Value *, Value *>, CachedCombinedShadow>
        CachedCombinedShadows;
    DenseMap<Value *, std::set<Value *>> ShadowElements;
  
    DFSanFunction(DataFlowSanitizer &DFS, Function *F, bool IsNativeABI)
        : DFS(DFS), F(F), IA(DFS.getInstrumentedABI()),
          IsNativeABI(IsNativeABI), ArgTLSPtr(nullptr), RetvalTLSPtr(nullptr),
          LabelReturnAlloca(nullptr) {
      DT.recalculate(*F);
      // FIXME: Need to track down the register allocator issue which causes poor
      // performance in pathological cases with large numbers of basic blocks.
      AvoidNewBlocks = F->size() > 1000;
    }
    Value *getArgTLSPtr();
    Value *getArgTLS(unsigned Index, Instruction *Pos);
    Value *getRetvalTLS();
    Value *getShadow(Value *V);
    void setShadow(Instruction *I, Value *Shadow);
    Value *combineShadows(Value *V1, Value *V2, Instruction *Pos);
    Value *combineOperandShadows(Instruction *Inst);
    Value *loadShadow(Value *ShadowAddr, uint64_t Size, uint64_t Align,
                      Instruction *Pos);
    void storeShadow(Value *Addr, uint64_t Size, uint64_t Align, Value *Shadow,
                     Instruction *Pos);
  };
  
  class DFSanVisitor : public InstVisitor<DFSanVisitor> {
   public:
    DFSanFunction &DFSF;
    DFSanVisitor(DFSanFunction &DFSF) : DFSF(DFSF) {}
  
    void visitOperandShadowInst(Instruction &I);
  
    void visitBinaryOperator(BinaryOperator &BO);
    void visitCastInst(CastInst &CI);
    void visitCmpInst(CmpInst &CI);
    void visitGetElementPtrInst(GetElementPtrInst &GEPI);
    void visitLoadInst(LoadInst &LI);
    void visitStoreInst(StoreInst &SI);
    void visitReturnInst(ReturnInst &RI);
    void visitCallSite(CallSite CS);
    void visitPHINode(PHINode &PN);
    void visitExtractElementInst(ExtractElementInst &I);
    void visitInsertElementInst(InsertElementInst &I);
    void visitShuffleVectorInst(ShuffleVectorInst &I);
    void visitExtractValueInst(ExtractValueInst &I);
    void visitInsertValueInst(InsertValueInst &I);
    void visitAllocaInst(AllocaInst &I);
    void visitSelectInst(SelectInst &I);
    void visitMemSetInst(MemSetInst &I);
    void visitMemTransferInst(MemTransferInst &I);
  };
  
  }
  
  char DataFlowSanitizer::ID;
  INITIALIZE_PASS(DataFlowSanitizer, "dfsan",
                  "DataFlowSanitizer: dynamic data flow analysis.", false, false)
  
  ModulePass *
  llvm::createDataFlowSanitizerPass(const std::vector<std::string> &ABIListFiles,
                                    void *(*getArgTLS)(),
                                    void *(*getRetValTLS)()) {
    return new DataFlowSanitizer(ABIListFiles, getArgTLS, getRetValTLS);
  }
  
  DataFlowSanitizer::DataFlowSanitizer(
      const std::vector<std::string> &ABIListFiles, void *(*getArgTLS)(),
      void *(*getRetValTLS)())
      : ModulePass(ID), GetArgTLSPtr(getArgTLS), GetRetvalTLSPtr(getRetValTLS),
        DFSanRuntimeShadowMask(false) {
    std::vector<std::string> AllABIListFiles(std::move(ABIListFiles));
    AllABIListFiles.insert(AllABIListFiles.end(), ClABIListFiles.begin(),
                           ClABIListFiles.end());
    ABIList.set(SpecialCaseList::createOrDie(AllABIListFiles));
  }
  
  FunctionType *DataFlowSanitizer::getArgsFunctionType(FunctionType *T) {
    llvm::SmallVector<Type *, 4> ArgTypes(T->param_begin(), T->param_end());
    ArgTypes.append(T->getNumParams(), ShadowTy);
    if (T->isVarArg())
      ArgTypes.push_back(ShadowPtrTy);
    Type *RetType = T->getReturnType();
    if (!RetType->isVoidTy())
      RetType = StructType::get(RetType, ShadowTy, (Type *)nullptr);
    return FunctionType::get(RetType, ArgTypes, T->isVarArg());
  }
  
  FunctionType *DataFlowSanitizer::getTrampolineFunctionType(FunctionType *T) {
    assert(!T->isVarArg());
    llvm::SmallVector<Type *, 4> ArgTypes;
    ArgTypes.push_back(T->getPointerTo());
    ArgTypes.append(T->param_begin(), T->param_end());
    ArgTypes.append(T->getNumParams(), ShadowTy);
    Type *RetType = T->getReturnType();
    if (!RetType->isVoidTy())
      ArgTypes.push_back(ShadowPtrTy);
    return FunctionType::get(T->getReturnType(), ArgTypes, false);
  }
  
  FunctionType *DataFlowSanitizer::getCustomFunctionType(FunctionType *T) {
    llvm::SmallVector<Type *, 4> ArgTypes;
    for (FunctionType::param_iterator i = T->param_begin(), e = T->param_end();
         i != e; ++i) {
      FunctionType *FT;
      if (isa<PointerType>(*i) && (FT = dyn_cast<FunctionType>(cast<PointerType>(
                                       *i)->getElementType()))) {
        ArgTypes.push_back(getTrampolineFunctionType(FT)->getPointerTo());
        ArgTypes.push_back(Type::getInt8PtrTy(*Ctx));
      } else {
        ArgTypes.push_back(*i);
      }
    }
    for (unsigned i = 0, e = T->getNumParams(); i != e; ++i)
      ArgTypes.push_back(ShadowTy);
    if (T->isVarArg())
      ArgTypes.push_back(ShadowPtrTy);
    Type *RetType = T->getReturnType();
    if (!RetType->isVoidTy())
      ArgTypes.push_back(ShadowPtrTy);
    return FunctionType::get(T->getReturnType(), ArgTypes, T->isVarArg());
  }
  
  bool DataFlowSanitizer::doInitialization(Module &M) {
    llvm::Triple TargetTriple(M.getTargetTriple());
    bool IsX86_64 = TargetTriple.getArch() == llvm::Triple::x86_64;
    bool IsMIPS64 = TargetTriple.getArch() == llvm::Triple::mips64 ||
                    TargetTriple.getArch() == llvm::Triple::mips64el;
    bool IsAArch64 = TargetTriple.getArch() == llvm::Triple::aarch64 ||
                     TargetTriple.getArch() == llvm::Triple::aarch64_be;
  
    const DataLayout &DL = M.getDataLayout();
  
    Mod = &M;
    Ctx = &M.getContext();
    ShadowTy = IntegerType::get(*Ctx, ShadowWidth);
    ShadowPtrTy = PointerType::getUnqual(ShadowTy);
    IntptrTy = DL.getIntPtrType(*Ctx);
    ZeroShadow = ConstantInt::getSigned(ShadowTy, 0);
    ShadowPtrMul = ConstantInt::getSigned(IntptrTy, ShadowWidth / 8);
    if (IsX86_64)
      ShadowPtrMask = ConstantInt::getSigned(IntptrTy, ~0x700000000000LL);
    else if (IsMIPS64)
      ShadowPtrMask = ConstantInt::getSigned(IntptrTy, ~0xF000000000LL);
    // AArch64 supports multiple VMAs and the shadow mask is set at runtime.
    else if (IsAArch64)
      DFSanRuntimeShadowMask = true;
    else
      report_fatal_error("unsupported triple");
  
    Type *DFSanUnionArgs[2] = { ShadowTy, ShadowTy };
    DFSanUnionFnTy =
        FunctionType::get(ShadowTy, DFSanUnionArgs, /*isVarArg=*/ false);
    Type *DFSanUnionLoadArgs[2] = { ShadowPtrTy, IntptrTy };
    DFSanUnionLoadFnTy =
        FunctionType::get(ShadowTy, DFSanUnionLoadArgs, /*isVarArg=*/ false);
    DFSanUnimplementedFnTy = FunctionType::get(
        Type::getVoidTy(*Ctx), Type::getInt8PtrTy(*Ctx), /*isVarArg=*/false);
    Type *DFSanSetLabelArgs[3] = { ShadowTy, Type::getInt8PtrTy(*Ctx), IntptrTy };
    DFSanSetLabelFnTy = FunctionType::get(Type::getVoidTy(*Ctx),
                                          DFSanSetLabelArgs, /*isVarArg=*/false);
    DFSanNonzeroLabelFnTy = FunctionType::get(
        Type::getVoidTy(*Ctx), None, /*isVarArg=*/false);
    DFSanVarargWrapperFnTy = FunctionType::get(
        Type::getVoidTy(*Ctx), Type::getInt8PtrTy(*Ctx), /*isVarArg=*/false);
  
    if (GetArgTLSPtr) {
      Type *ArgTLSTy = ArrayType::get(ShadowTy, 64);
      ArgTLS = nullptr;
      GetArgTLS = ConstantExpr::getIntToPtr(
          ConstantInt::get(IntptrTy, uintptr_t(GetArgTLSPtr)),
          PointerType::getUnqual(
              FunctionType::get(PointerType::getUnqual(ArgTLSTy),
                                (Type *)nullptr)));
    }
    if (GetRetvalTLSPtr) {
      RetvalTLS = nullptr;
      GetRetvalTLS = ConstantExpr::getIntToPtr(
          ConstantInt::get(IntptrTy, uintptr_t(GetRetvalTLSPtr)),
          PointerType::getUnqual(
              FunctionType::get(PointerType::getUnqual(ShadowTy),
                                (Type *)nullptr)));
    }
  
    ColdCallWeights = MDBuilder(*Ctx).createBranchWeights(1, 1000);
    return true;
  }
  
  bool DataFlowSanitizer::isInstrumented(const Function *F) {
    return !ABIList.isIn(*F, "uninstrumented");
  }
  
  bool DataFlowSanitizer::isInstrumented(const GlobalAlias *GA) {
    return !ABIList.isIn(*GA, "uninstrumented");
  }
  
  DataFlowSanitizer::InstrumentedABI DataFlowSanitizer::getInstrumentedABI() {
    return ClArgsABI ? IA_Args : IA_TLS;
  }
  
  DataFlowSanitizer::WrapperKind DataFlowSanitizer::getWrapperKind(Function *F) {
    if (ABIList.isIn(*F, "functional"))
      return WK_Functional;
    if (ABIList.isIn(*F, "discard"))
      return WK_Discard;
    if (ABIList.isIn(*F, "custom"))
      return WK_Custom;
  
    return WK_Warning;
  }
  
  void DataFlowSanitizer::addGlobalNamePrefix(GlobalValue *GV) {
    std::string GVName = GV->getName(), Prefix = "dfs$";
    GV->setName(Prefix + GVName);
  
    // Try to change the name of the function in module inline asm.  We only do
    // this for specific asm directives, currently only ".symver", to try to avoid
    // corrupting asm which happens to contain the symbol name as a substring.
    // Note that the substitution for .symver assumes that the versioned symbol
    // also has an instrumented name.
    std::string Asm = GV->getParent()->getModuleInlineAsm();
    std::string SearchStr = ".symver " + GVName + ",";
    size_t Pos = Asm.find(SearchStr);
    if (Pos != std::string::npos) {
      Asm.replace(Pos, SearchStr.size(),
                  ".symver " + Prefix + GVName + "," + Prefix);
      GV->getParent()->setModuleInlineAsm(Asm);
    }
  }
  
  Function *
  DataFlowSanitizer::buildWrapperFunction(Function *F, StringRef NewFName,
                                          GlobalValue::LinkageTypes NewFLink,
                                          FunctionType *NewFT) {
    FunctionType *FT = F->getFunctionType();
    Function *NewF = Function::Create(NewFT, NewFLink, NewFName,
                                      F->getParent());
    NewF->copyAttributesFrom(F);
    NewF->removeAttributes(
      AttributeSet::ReturnIndex,
      AttributeSet::get(F->getContext(), AttributeSet::ReturnIndex,
                      AttributeFuncs::typeIncompatible(NewFT->getReturnType())));
  
    BasicBlock *BB = BasicBlock::Create(*Ctx, "entry", NewF);
    if (F->isVarArg()) {
      NewF->removeAttributes(
          AttributeSet::FunctionIndex,
          AttributeSet().addAttribute(*Ctx, AttributeSet::FunctionIndex,
                                      "split-stack"));
      CallInst::Create(DFSanVarargWrapperFn,
                       IRBuilder<>(BB).CreateGlobalStringPtr(F->getName()), "",
                       BB);
      new UnreachableInst(*Ctx, BB);
    } else {
      std::vector<Value *> Args;
      unsigned n = FT->getNumParams();
      for (Function::arg_iterator ai = NewF->arg_begin(); n != 0; ++ai, --n)
        Args.push_back(&*ai);
      CallInst *CI = CallInst::Create(F, Args, "", BB);
      if (FT->getReturnType()->isVoidTy())
        ReturnInst::Create(*Ctx, BB);
      else
        ReturnInst::Create(*Ctx, CI, BB);
    }
  
    return NewF;
  }
  
  Constant *DataFlowSanitizer::getOrBuildTrampolineFunction(FunctionType *FT,
                                                            StringRef FName) {
    FunctionType *FTT = getTrampolineFunctionType(FT);
    Constant *C = Mod->getOrInsertFunction(FName, FTT);
    Function *F = dyn_cast<Function>(C);
    if (F && F->isDeclaration()) {
      F->setLinkage(GlobalValue::LinkOnceODRLinkage);
      BasicBlock *BB = BasicBlock::Create(*Ctx, "entry", F);
      std::vector<Value *> Args;
      Function::arg_iterator AI = F->arg_begin(); ++AI;
      for (unsigned N = FT->getNumParams(); N != 0; ++AI, --N)
        Args.push_back(&*AI);
      CallInst *CI =
          CallInst::Create(&F->getArgumentList().front(), Args, "", BB);
      ReturnInst *RI;
      if (FT->getReturnType()->isVoidTy())
        RI = ReturnInst::Create(*Ctx, BB);
      else
        RI = ReturnInst::Create(*Ctx, CI, BB);
  
      DFSanFunction DFSF(*this, F, /*IsNativeABI=*/true);
      Function::arg_iterator ValAI = F->arg_begin(), ShadowAI = AI; ++ValAI;
      for (unsigned N = FT->getNumParams(); N != 0; ++ValAI, ++ShadowAI, --N)
        DFSF.ValShadowMap[&*ValAI] = &*ShadowAI;
      DFSanVisitor(DFSF).visitCallInst(*CI);
      if (!FT->getReturnType()->isVoidTy())
        new StoreInst(DFSF.getShadow(RI->getReturnValue()),
                      &F->getArgumentList().back(), RI);
    }
  
    return C;
  }
  
  bool DataFlowSanitizer::runOnModule(Module &M) {
    if (ABIList.isIn(M, "skip"))
      return false;
  
    if (!GetArgTLSPtr) {
      Type *ArgTLSTy = ArrayType::get(ShadowTy, 64);
      ArgTLS = Mod->getOrInsertGlobal("__dfsan_arg_tls", ArgTLSTy);
      if (GlobalVariable *G = dyn_cast<GlobalVariable>(ArgTLS))
        G->setThreadLocalMode(GlobalVariable::InitialExecTLSModel);
    }
    if (!GetRetvalTLSPtr) {
      RetvalTLS = Mod->getOrInsertGlobal("__dfsan_retval_tls", ShadowTy);
      if (GlobalVariable *G = dyn_cast<GlobalVariable>(RetvalTLS))
        G->setThreadLocalMode(GlobalVariable::InitialExecTLSModel);
    }
  
    ExternalShadowMask =
        Mod->getOrInsertGlobal(kDFSanExternShadowPtrMask, IntptrTy);
  
    DFSanUnionFn = Mod->getOrInsertFunction("__dfsan_union", DFSanUnionFnTy);
    if (Function *F = dyn_cast<Function>(DFSanUnionFn)) {
      F->addAttribute(AttributeSet::FunctionIndex, Attribute::NoUnwind);
      F->addAttribute(AttributeSet::FunctionIndex, Attribute::ReadNone);
      F->addAttribute(AttributeSet::ReturnIndex, Attribute::ZExt);
      F->addAttribute(1, Attribute::ZExt);
      F->addAttribute(2, Attribute::ZExt);
    }
    DFSanCheckedUnionFn = Mod->getOrInsertFunction("dfsan_union", DFSanUnionFnTy);
    if (Function *F = dyn_cast<Function>(DFSanCheckedUnionFn)) {
      F->addAttribute(AttributeSet::FunctionIndex, Attribute::NoUnwind);
      F->addAttribute(AttributeSet::FunctionIndex, Attribute::ReadNone);
      F->addAttribute(AttributeSet::ReturnIndex, Attribute::ZExt);
      F->addAttribute(1, Attribute::ZExt);
      F->addAttribute(2, Attribute::ZExt);
    }
    DFSanUnionLoadFn =
        Mod->getOrInsertFunction("__dfsan_union_load", DFSanUnionLoadFnTy);
    if (Function *F = dyn_cast<Function>(DFSanUnionLoadFn)) {
      F->addAttribute(AttributeSet::FunctionIndex, Attribute::NoUnwind);
      F->addAttribute(AttributeSet::FunctionIndex, Attribute::ReadOnly);
      F->addAttribute(AttributeSet::ReturnIndex, Attribute::ZExt);
    }
    DFSanUnimplementedFn =
        Mod->getOrInsertFunction("__dfsan_unimplemented", DFSanUnimplementedFnTy);
    DFSanSetLabelFn =
        Mod->getOrInsertFunction("__dfsan_set_label", DFSanSetLabelFnTy);
    if (Function *F = dyn_cast<Function>(DFSanSetLabelFn)) {
      F->addAttribute(1, Attribute::ZExt);
    }
    DFSanNonzeroLabelFn =
        Mod->getOrInsertFunction("__dfsan_nonzero_label", DFSanNonzeroLabelFnTy);
    DFSanVarargWrapperFn = Mod->getOrInsertFunction("__dfsan_vararg_wrapper",
                                                    DFSanVarargWrapperFnTy);
  
    std::vector<Function *> FnsToInstrument;
    llvm::SmallPtrSet<Function *, 2> FnsWithNativeABI;
    for (Function &i : M) {
      if (!i.isIntrinsic() &&
          &i != DFSanUnionFn &&
          &i != DFSanCheckedUnionFn &&
          &i != DFSanUnionLoadFn &&
          &i != DFSanUnimplementedFn &&
          &i != DFSanSetLabelFn &&
          &i != DFSanNonzeroLabelFn &&
          &i != DFSanVarargWrapperFn)
        FnsToInstrument.push_back(&i);
    }
  
    // Give function aliases prefixes when necessary, and build wrappers where the
    // instrumentedness is inconsistent.
    for (Module::alias_iterator i = M.alias_begin(), e = M.alias_end(); i != e;) {
      GlobalAlias *GA = &*i;
      ++i;
      // Don't stop on weak.  We assume people aren't playing games with the
      // instrumentedness of overridden weak aliases.
      if (auto F = dyn_cast<Function>(GA->getBaseObject())) {
        bool GAInst = isInstrumented(GA), FInst = isInstrumented(F);
        if (GAInst && FInst) {
          addGlobalNamePrefix(GA);
        } else if (GAInst != FInst) {
          // Non-instrumented alias of an instrumented function, or vice versa.
          // Replace the alias with a native-ABI wrapper of the aliasee.  The pass
          // below will take care of instrumenting it.
          Function *NewF =
              buildWrapperFunction(F, "", GA->getLinkage(), F->getFunctionType());
          GA->replaceAllUsesWith(ConstantExpr::getBitCast(NewF, GA->getType()));
          NewF->takeName(GA);
          GA->eraseFromParent();
          FnsToInstrument.push_back(NewF);
        }
      }
    }
  
    AttrBuilder B;
    B.addAttribute(Attribute::ReadOnly).addAttribute(Attribute::ReadNone);
    ReadOnlyNoneAttrs = AttributeSet::get(*Ctx, AttributeSet::FunctionIndex, B);
  
    // First, change the ABI of every function in the module.  ABI-listed
    // functions keep their original ABI and get a wrapper function.
    for (std::vector<Function *>::iterator i = FnsToInstrument.begin(),
                                           e = FnsToInstrument.end();
         i != e; ++i) {
      Function &F = **i;
      FunctionType *FT = F.getFunctionType();
  
      bool IsZeroArgsVoidRet = (FT->getNumParams() == 0 && !FT->isVarArg() &&
                                FT->getReturnType()->isVoidTy());
  
      if (isInstrumented(&F)) {
        // Instrumented functions get a 'dfs$' prefix.  This allows us to more
        // easily identify cases of mismatching ABIs.
        if (getInstrumentedABI() == IA_Args && !IsZeroArgsVoidRet) {
          FunctionType *NewFT = getArgsFunctionType(FT);
          Function *NewF = Function::Create(NewFT, F.getLinkage(), "", &M);
          NewF->copyAttributesFrom(&F);
          NewF->removeAttributes(
            AttributeSet::ReturnIndex,
            AttributeSet::get(NewF->getContext(), AttributeSet::ReturnIndex,
                      AttributeFuncs::typeIncompatible(NewFT->getReturnType())));
          for (Function::arg_iterator FArg = F.arg_begin(),
                                      NewFArg = NewF->arg_begin(),
                                      FArgEnd = F.arg_end();
               FArg != FArgEnd; ++FArg, ++NewFArg) {
            FArg->replaceAllUsesWith(&*NewFArg);
          }
          NewF->getBasicBlockList().splice(NewF->begin(), F.getBasicBlockList());
  
          for (Function::user_iterator UI = F.user_begin(), UE = F.user_end();
               UI != UE;) {
            BlockAddress *BA = dyn_cast<BlockAddress>(*UI);
            ++UI;
            if (BA) {
              BA->replaceAllUsesWith(
                  BlockAddress::get(NewF, BA->getBasicBlock()));
              delete BA;
            }
          }
          F.replaceAllUsesWith(
              ConstantExpr::getBitCast(NewF, PointerType::getUnqual(FT)));
          NewF->takeName(&F);
          F.eraseFromParent();
          *i = NewF;
          addGlobalNamePrefix(NewF);
        } else {
          addGlobalNamePrefix(&F);
        }
      } else if (!IsZeroArgsVoidRet || getWrapperKind(&F) == WK_Custom) {
        // Build a wrapper function for F.  The wrapper simply calls F, and is
        // added to FnsToInstrument so that any instrumentation according to its
        // WrapperKind is done in the second pass below.
        FunctionType *NewFT = getInstrumentedABI() == IA_Args
                                  ? getArgsFunctionType(FT)
                                  : FT;
        Function *NewF = buildWrapperFunction(
            &F, std::string("dfsw$") + std::string(F.getName()),
            GlobalValue::LinkOnceODRLinkage, NewFT);
        if (getInstrumentedABI() == IA_TLS)
          NewF->removeAttributes(AttributeSet::FunctionIndex, ReadOnlyNoneAttrs);
  
        Value *WrappedFnCst =
            ConstantExpr::getBitCast(NewF, PointerType::getUnqual(FT));
        F.replaceAllUsesWith(WrappedFnCst);
  
        UnwrappedFnMap[WrappedFnCst] = &F;
        *i = NewF;
  
        if (!F.isDeclaration()) {
          // This function is probably defining an interposition of an
          // uninstrumented function and hence needs to keep the original ABI.
          // But any functions it may call need to use the instrumented ABI, so
          // we instrument it in a mode which preserves the original ABI.
          FnsWithNativeABI.insert(&F);
  
          // This code needs to rebuild the iterators, as they may be invalidated
          // by the push_back, taking care that the new range does not include
          // any functions added by this code.
          size_t N = i - FnsToInstrument.begin(),
                 Count = e - FnsToInstrument.begin();
          FnsToInstrument.push_back(&F);
          i = FnsToInstrument.begin() + N;
          e = FnsToInstrument.begin() + Count;
        }
                 // Hopefully, nobody will try to indirectly call a vararg
                 // function... yet.
      } else if (FT->isVarArg()) {
        UnwrappedFnMap[&F] = &F;
        *i = nullptr;
      }
    }
  
    for (std::vector<Function *>::iterator i = FnsToInstrument.begin(),
                                           e = FnsToInstrument.end();
         i != e; ++i) {
      if (!*i || (*i)->isDeclaration())
        continue;
  
      removeUnreachableBlocks(**i);
  
      DFSanFunction DFSF(*this, *i, FnsWithNativeABI.count(*i));
  
      // DFSanVisitor may create new basic blocks, which confuses df_iterator.
      // Build a copy of the list before iterating over it.
      llvm::SmallVector<BasicBlock *, 4> BBList(
          depth_first(&(*i)->getEntryBlock()));
  
      for (llvm::SmallVector<BasicBlock *, 4>::iterator i = BBList.begin(),
                                                        e = BBList.end();
           i != e; ++i) {
        Instruction *Inst = &(*i)->front();
        while (1) {
          // DFSanVisitor may split the current basic block, changing the current
          // instruction's next pointer and moving the next instruction to the
          // tail block from which we should continue.
          Instruction *Next = Inst->getNextNode();
          // DFSanVisitor may delete Inst, so keep track of whether it was a
          // terminator.
          bool IsTerminator = isa<TerminatorInst>(Inst);
          if (!DFSF.SkipInsts.count(Inst))
            DFSanVisitor(DFSF).visit(Inst);
          if (IsTerminator)
            break;
          Inst = Next;
        }
      }
  
      // We will not necessarily be able to compute the shadow for every phi node
      // until we have visited every block.  Therefore, the code that handles phi
      // nodes adds them to the PHIFixups list so that they can be properly
      // handled here.
      for (std::vector<std::pair<PHINode *, PHINode *> >::iterator
               i = DFSF.PHIFixups.begin(),
               e = DFSF.PHIFixups.end();
           i != e; ++i) {
        for (unsigned val = 0, n = i->first->getNumIncomingValues(); val != n;
             ++val) {
          i->second->setIncomingValue(
              val, DFSF.getShadow(i->first->getIncomingValue(val)));
        }
      }
  
      // -dfsan-debug-nonzero-labels will split the CFG in all kinds of crazy
      // places (i.e. instructions in basic blocks we haven't even begun visiting
      // yet).  To make our life easier, do this work in a pass after the main
      // instrumentation.
      if (ClDebugNonzeroLabels) {
        for (Value *V : DFSF.NonZeroChecks) {
          Instruction *Pos;
          if (Instruction *I = dyn_cast<Instruction>(V))
            Pos = I->getNextNode();
          else
            Pos = &DFSF.F->getEntryBlock().front();
          while (isa<PHINode>(Pos) || isa<AllocaInst>(Pos))
            Pos = Pos->getNextNode();
          IRBuilder<> IRB(Pos);
          Value *Ne = IRB.CreateICmpNE(V, DFSF.DFS.ZeroShadow);
          BranchInst *BI = cast<BranchInst>(SplitBlockAndInsertIfThen(
              Ne, Pos, /*Unreachable=*/false, ColdCallWeights));
          IRBuilder<> ThenIRB(BI);
          ThenIRB.CreateCall(DFSF.DFS.DFSanNonzeroLabelFn, {});
        }
      }
    }
  
    return false;
  }
  
  Value *DFSanFunction::getArgTLSPtr() {
    if (ArgTLSPtr)
      return ArgTLSPtr;
    if (DFS.ArgTLS)
      return ArgTLSPtr = DFS.ArgTLS;
  
    IRBuilder<> IRB(&F->getEntryBlock().front());
    return ArgTLSPtr = IRB.CreateCall(DFS.GetArgTLS, {});
  }
  
  Value *DFSanFunction::getRetvalTLS() {
    if (RetvalTLSPtr)
      return RetvalTLSPtr;
    if (DFS.RetvalTLS)
      return RetvalTLSPtr = DFS.RetvalTLS;
  
    IRBuilder<> IRB(&F->getEntryBlock().front());
    return RetvalTLSPtr = IRB.CreateCall(DFS.GetRetvalTLS, {});
  }
  
  Value *DFSanFunction::getArgTLS(unsigned Idx, Instruction *Pos) {
    IRBuilder<> IRB(Pos);
    return IRB.CreateConstGEP2_64(getArgTLSPtr(), 0, Idx);
  }
  
  Value *DFSanFunction::getShadow(Value *V) {
    if (!isa<Argument>(V) && !isa<Instruction>(V))
      return DFS.ZeroShadow;
    Value *&Shadow = ValShadowMap[V];
    if (!Shadow) {
      if (Argument *A = dyn_cast<Argument>(V)) {
        if (IsNativeABI)
          return DFS.ZeroShadow;
        switch (IA) {
        case DataFlowSanitizer::IA_TLS: {
          Value *ArgTLSPtr = getArgTLSPtr();
          Instruction *ArgTLSPos =
              DFS.ArgTLS ? &*F->getEntryBlock().begin()
                         : cast<Instruction>(ArgTLSPtr)->getNextNode();
          IRBuilder<> IRB(ArgTLSPos);
          Shadow = IRB.CreateLoad(getArgTLS(A->getArgNo(), ArgTLSPos));
          break;
        }
        case DataFlowSanitizer::IA_Args: {
          unsigned ArgIdx = A->getArgNo() + F->getArgumentList().size() / 2;
          Function::arg_iterator i = F->arg_begin();
          while (ArgIdx--)
            ++i;
          Shadow = &*i;
          assert(Shadow->getType() == DFS.ShadowTy);
          break;
        }
        }
        NonZeroChecks.push_back(Shadow);
      } else {
        Shadow = DFS.ZeroShadow;
      }
    }
    return Shadow;
  }
  
  void DFSanFunction::setShadow(Instruction *I, Value *Shadow) {
    assert(!ValShadowMap.count(I));
    assert(Shadow->getType() == DFS.ShadowTy);
    ValShadowMap[I] = Shadow;
  }
  
  Value *DataFlowSanitizer::getShadowAddress(Value *Addr, Instruction *Pos) {
    assert(Addr != RetvalTLS && "Reinstrumenting?");
    IRBuilder<> IRB(Pos);
    Value *ShadowPtrMaskValue;
    if (DFSanRuntimeShadowMask)
      ShadowPtrMaskValue = IRB.CreateLoad(IntptrTy, ExternalShadowMask);
    else
      ShadowPtrMaskValue = ShadowPtrMask;
    return IRB.CreateIntToPtr(
        IRB.CreateMul(
            IRB.CreateAnd(IRB.CreatePtrToInt(Addr, IntptrTy),
                          IRB.CreatePtrToInt(ShadowPtrMaskValue, IntptrTy)),
            ShadowPtrMul),
        ShadowPtrTy);
  }
  
  // Generates IR to compute the union of the two given shadows, inserting it
  // before Pos.  Returns the computed union Value.
  Value *DFSanFunction::combineShadows(Value *V1, Value *V2, Instruction *Pos) {
    if (V1 == DFS.ZeroShadow)
      return V2;
    if (V2 == DFS.ZeroShadow)
      return V1;
    if (V1 == V2)
      return V1;
  
    auto V1Elems = ShadowElements.find(V1);
    auto V2Elems = ShadowElements.find(V2);
    if (V1Elems != ShadowElements.end() && V2Elems != ShadowElements.end()) {
      if (std::includes(V1Elems->second.begin(), V1Elems->second.end(),
                        V2Elems->second.begin(), V2Elems->second.end())) {
        return V1;
      } else if (std::includes(V2Elems->second.begin(), V2Elems->second.end(),
                               V1Elems->second.begin(), V1Elems->second.end())) {
        return V2;
      }
    } else if (V1Elems != ShadowElements.end()) {
      if (V1Elems->second.count(V2))
        return V1;
    } else if (V2Elems != ShadowElements.end()) {
      if (V2Elems->second.count(V1))
        return V2;
    }
  
    auto Key = std::make_pair(V1, V2);
    if (V1 > V2)
      std::swap(Key.first, Key.second);
    CachedCombinedShadow &CCS = CachedCombinedShadows[Key];
    if (CCS.Block && DT.dominates(CCS.Block, Pos->getParent()))
      return CCS.Shadow;
  
    IRBuilder<> IRB(Pos);
    if (AvoidNewBlocks) {
      CallInst *Call = IRB.CreateCall(DFS.DFSanCheckedUnionFn, {V1, V2});
      Call->addAttribute(AttributeSet::ReturnIndex, Attribute::ZExt);
      Call->addAttribute(1, Attribute::ZExt);
      Call->addAttribute(2, Attribute::ZExt);
  
      CCS.Block = Pos->getParent();
      CCS.Shadow = Call;
    } else {
      BasicBlock *Head = Pos->getParent();
      Value *Ne = IRB.CreateICmpNE(V1, V2);
      BranchInst *BI = cast<BranchInst>(SplitBlockAndInsertIfThen(
          Ne, Pos, /*Unreachable=*/false, DFS.ColdCallWeights, &DT));
      IRBuilder<> ThenIRB(BI);
      CallInst *Call = ThenIRB.CreateCall(DFS.DFSanUnionFn, {V1, V2});
      Call->addAttribute(AttributeSet::ReturnIndex, Attribute::ZExt);
      Call->addAttribute(1, Attribute::ZExt);
      Call->addAttribute(2, Attribute::ZExt);
  
      BasicBlock *Tail = BI->getSuccessor(0);
      PHINode *Phi = PHINode::Create(DFS.ShadowTy, 2, "", &Tail->front());
      Phi->addIncoming(Call, Call->getParent());
      Phi->addIncoming(V1, Head);
  
      CCS.Block = Tail;
      CCS.Shadow = Phi;
    }
  
    std::set<Value *> UnionElems;
    if (V1Elems != ShadowElements.end()) {
      UnionElems = V1Elems->second;
    } else {
      UnionElems.insert(V1);
    }
    if (V2Elems != ShadowElements.end()) {
      UnionElems.insert(V2Elems->second.begin(), V2Elems->second.end());
    } else {
      UnionElems.insert(V2);
    }
    ShadowElements[CCS.Shadow] = std::move(UnionElems);
  
    return CCS.Shadow;
  }
  
  // A convenience function which folds the shadows of each of the operands
  // of the provided instruction Inst, inserting the IR before Inst.  Returns
  // the computed union Value.
  Value *DFSanFunction::combineOperandShadows(Instruction *Inst) {
    if (Inst->getNumOperands() == 0)
      return DFS.ZeroShadow;
  
    Value *Shadow = getShadow(Inst->getOperand(0));
    for (unsigned i = 1, n = Inst->getNumOperands(); i != n; ++i) {
      Shadow = combineShadows(Shadow, getShadow(Inst->getOperand(i)), Inst);
    }
    return Shadow;
  }
  
  void DFSanVisitor::visitOperandShadowInst(Instruction &I) {
    Value *CombinedShadow = DFSF.combineOperandShadows(&I);
    DFSF.setShadow(&I, CombinedShadow);
  }
  
  // Generates IR to load shadow corresponding to bytes [Addr, Addr+Size), where
  // Addr has alignment Align, and take the union of each of those shadows.
  Value *DFSanFunction::loadShadow(Value *Addr, uint64_t Size, uint64_t Align,
                                   Instruction *Pos) {
    if (AllocaInst *AI = dyn_cast<AllocaInst>(Addr)) {
      llvm::DenseMap<AllocaInst *, AllocaInst *>::iterator i =
          AllocaShadowMap.find(AI);
      if (i != AllocaShadowMap.end()) {
        IRBuilder<> IRB(Pos);
        return IRB.CreateLoad(i->second);
      }
    }
  
    uint64_t ShadowAlign = Align * DFS.ShadowWidth / 8;
    SmallVector<Value *, 2> Objs;
    GetUnderlyingObjects(Addr, Objs, Pos->getModule()->getDataLayout());
    bool AllConstants = true;
    for (SmallVector<Value *, 2>::iterator i = Objs.begin(), e = Objs.end();
         i != e; ++i) {
      if (isa<Function>(*i) || isa<BlockAddress>(*i))
        continue;
      if (isa<GlobalVariable>(*i) && cast<GlobalVariable>(*i)->isConstant())
        continue;
  
      AllConstants = false;
      break;
    }
    if (AllConstants)
      return DFS.ZeroShadow;
  
    Value *ShadowAddr = DFS.getShadowAddress(Addr, Pos);
    switch (Size) {
    case 0:
      return DFS.ZeroShadow;
    case 1: {
      LoadInst *LI = new LoadInst(ShadowAddr, "", Pos);
      LI->setAlignment(ShadowAlign);
      return LI;
    }
    case 2: {
      IRBuilder<> IRB(Pos);
      Value *ShadowAddr1 = IRB.CreateGEP(DFS.ShadowTy, ShadowAddr,
                                         ConstantInt::get(DFS.IntptrTy, 1));
      return combineShadows(IRB.CreateAlignedLoad(ShadowAddr, ShadowAlign),
                            IRB.CreateAlignedLoad(ShadowAddr1, ShadowAlign), Pos);
    }
    }
    if (!AvoidNewBlocks && Size % (64 / DFS.ShadowWidth) == 0) {
      // Fast path for the common case where each byte has identical shadow: load
      // shadow 64 bits at a time, fall out to a __dfsan_union_load call if any
      // shadow is non-equal.
      BasicBlock *FallbackBB = BasicBlock::Create(*DFS.Ctx, "", F);
      IRBuilder<> FallbackIRB(FallbackBB);
      CallInst *FallbackCall = FallbackIRB.CreateCall(
          DFS.DFSanUnionLoadFn,
          {ShadowAddr, ConstantInt::get(DFS.IntptrTy, Size)});
      FallbackCall->addAttribute(AttributeSet::ReturnIndex, Attribute::ZExt);
  
      // Compare each of the shadows stored in the loaded 64 bits to each other,
      // by computing (WideShadow rotl ShadowWidth) == WideShadow.
      IRBuilder<> IRB(Pos);
      Value *WideAddr =
          IRB.CreateBitCast(ShadowAddr, Type::getInt64PtrTy(*DFS.Ctx));
      Value *WideShadow = IRB.CreateAlignedLoad(WideAddr, ShadowAlign);
      Value *TruncShadow = IRB.CreateTrunc(WideShadow, DFS.ShadowTy);
      Value *ShlShadow = IRB.CreateShl(WideShadow, DFS.ShadowWidth);
      Value *ShrShadow = IRB.CreateLShr(WideShadow, 64 - DFS.ShadowWidth);
      Value *RotShadow = IRB.CreateOr(ShlShadow, ShrShadow);
      Value *ShadowsEq = IRB.CreateICmpEQ(WideShadow, RotShadow);
  
      BasicBlock *Head = Pos->getParent();
      BasicBlock *Tail = Head->splitBasicBlock(Pos->getIterator());
  
      if (DomTreeNode *OldNode = DT.getNode(Head)) {
        std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
  
        DomTreeNode *NewNode = DT.addNewBlock(Tail, Head);
        for (auto Child : Children)
          DT.changeImmediateDominator(Child, NewNode);
      }
  
      // In the following code LastBr will refer to the previous basic block's
      // conditional branch instruction, whose true successor is fixed up to point
      // to the next block during the loop below or to the tail after the final
      // iteration.
      BranchInst *LastBr = BranchInst::Create(FallbackBB, FallbackBB, ShadowsEq);
      ReplaceInstWithInst(Head->getTerminator(), LastBr);
      DT.addNewBlock(FallbackBB, Head);
  
      for (uint64_t Ofs = 64 / DFS.ShadowWidth; Ofs != Size;
           Ofs += 64 / DFS.ShadowWidth) {
        BasicBlock *NextBB = BasicBlock::Create(*DFS.Ctx, "", F);
        DT.addNewBlock(NextBB, LastBr->getParent());
        IRBuilder<> NextIRB(NextBB);
        WideAddr = NextIRB.CreateGEP(Type::getInt64Ty(*DFS.Ctx), WideAddr,
                                     ConstantInt::get(DFS.IntptrTy, 1));
        Value *NextWideShadow = NextIRB.CreateAlignedLoad(WideAddr, ShadowAlign);
        ShadowsEq = NextIRB.CreateICmpEQ(WideShadow, NextWideShadow);
        LastBr->setSuccessor(0, NextBB);
        LastBr = NextIRB.CreateCondBr(ShadowsEq, FallbackBB, FallbackBB);
      }
  
      LastBr->setSuccessor(0, Tail);
      FallbackIRB.CreateBr(Tail);
      PHINode *Shadow = PHINode::Create(DFS.ShadowTy, 2, "", &Tail->front());
      Shadow->addIncoming(FallbackCall, FallbackBB);
      Shadow->addIncoming(TruncShadow, LastBr->getParent());
      return Shadow;
    }
  
    IRBuilder<> IRB(Pos);
    CallInst *FallbackCall = IRB.CreateCall(
        DFS.DFSanUnionLoadFn, {ShadowAddr, ConstantInt::get(DFS.IntptrTy, Size)});
    FallbackCall->addAttribute(AttributeSet::ReturnIndex, Attribute::ZExt);
    return FallbackCall;
  }
  
  void DFSanVisitor::visitLoadInst(LoadInst &LI) {
    auto &DL = LI.getModule()->getDataLayout();
    uint64_t Size = DL.getTypeStoreSize(LI.getType());
    if (Size == 0) {
      DFSF.setShadow(&LI, DFSF.DFS.ZeroShadow);
      return;
    }
  
    uint64_t Align;
    if (ClPreserveAlignment) {
      Align = LI.getAlignment();
      if (Align == 0)
        Align = DL.getABITypeAlignment(LI.getType());
    } else {
      Align = 1;
    }
    IRBuilder<> IRB(&LI);
    Value *Shadow = DFSF.loadShadow(LI.getPointerOperand(), Size, Align, &LI);
    if (ClCombinePointerLabelsOnLoad) {
      Value *PtrShadow = DFSF.getShadow(LI.getPointerOperand());
      Shadow = DFSF.combineShadows(Shadow, PtrShadow, &LI);
    }
    if (Shadow != DFSF.DFS.ZeroShadow)
      DFSF.NonZeroChecks.push_back(Shadow);
  
    DFSF.setShadow(&LI, Shadow);
  }
  
  void DFSanFunction::storeShadow(Value *Addr, uint64_t Size, uint64_t Align,
                                  Value *Shadow, Instruction *Pos) {
    if (AllocaInst *AI = dyn_cast<AllocaInst>(Addr)) {
      llvm::DenseMap<AllocaInst *, AllocaInst *>::iterator i =
          AllocaShadowMap.find(AI);
      if (i != AllocaShadowMap.end()) {
        IRBuilder<> IRB(Pos);
        IRB.CreateStore(Shadow, i->second);
        return;
      }
    }
  
    uint64_t ShadowAlign = Align * DFS.ShadowWidth / 8;
    IRBuilder<> IRB(Pos);
    Value *ShadowAddr = DFS.getShadowAddress(Addr, Pos);
    if (Shadow == DFS.ZeroShadow) {
      IntegerType *ShadowTy = IntegerType::get(*DFS.Ctx, Size * DFS.ShadowWidth);
      Value *ExtZeroShadow = ConstantInt::get(ShadowTy, 0);
      Value *ExtShadowAddr =
          IRB.CreateBitCast(ShadowAddr, PointerType::getUnqual(ShadowTy));
      IRB.CreateAlignedStore(ExtZeroShadow, ExtShadowAddr, ShadowAlign);
      return;
    }
  
    const unsigned ShadowVecSize = 128 / DFS.ShadowWidth;
    uint64_t Offset = 0;
    if (Size >= ShadowVecSize) {
      VectorType *ShadowVecTy = VectorType::get(DFS.ShadowTy, ShadowVecSize);
      Value *ShadowVec = UndefValue::get(ShadowVecTy);
      for (unsigned i = 0; i != ShadowVecSize; ++i) {
        ShadowVec = IRB.CreateInsertElement(
            ShadowVec, Shadow, ConstantInt::get(Type::getInt32Ty(*DFS.Ctx), i));
      }
      Value *ShadowVecAddr =
          IRB.CreateBitCast(ShadowAddr, PointerType::getUnqual(ShadowVecTy));
      do {
        Value *CurShadowVecAddr =
            IRB.CreateConstGEP1_32(ShadowVecTy, ShadowVecAddr, Offset);
        IRB.CreateAlignedStore(ShadowVec, CurShadowVecAddr, ShadowAlign);
        Size -= ShadowVecSize;
        ++Offset;
      } while (Size >= ShadowVecSize);
      Offset *= ShadowVecSize;
    }
    while (Size > 0) {
      Value *CurShadowAddr =
          IRB.CreateConstGEP1_32(DFS.ShadowTy, ShadowAddr, Offset);
      IRB.CreateAlignedStore(Shadow, CurShadowAddr, ShadowAlign);
      --Size;
      ++Offset;
    }
  }
  
  void DFSanVisitor::visitStoreInst(StoreInst &SI) {
    auto &DL = SI.getModule()->getDataLayout();
    uint64_t Size = DL.getTypeStoreSize(SI.getValueOperand()->getType());
    if (Size == 0)
      return;
  
    uint64_t Align;
    if (ClPreserveAlignment) {
      Align = SI.getAlignment();
      if (Align == 0)
        Align = DL.getABITypeAlignment(SI.getValueOperand()->getType());
    } else {
      Align = 1;
    }
  
    Value* Shadow = DFSF.getShadow(SI.getValueOperand());
    if (ClCombinePointerLabelsOnStore) {
      Value *PtrShadow = DFSF.getShadow(SI.getPointerOperand());
      Shadow = DFSF.combineShadows(Shadow, PtrShadow, &SI);
    }
    DFSF.storeShadow(SI.getPointerOperand(), Size, Align, Shadow, &SI);
  }
  
  void DFSanVisitor::visitBinaryOperator(BinaryOperator &BO) {
    visitOperandShadowInst(BO);
  }
  
  void DFSanVisitor::visitCastInst(CastInst &CI) { visitOperandShadowInst(CI); }
  
  void DFSanVisitor::visitCmpInst(CmpInst &CI) { visitOperandShadowInst(CI); }
  
  void DFSanVisitor::visitGetElementPtrInst(GetElementPtrInst &GEPI) {
    visitOperandShadowInst(GEPI);
  }
  
  void DFSanVisitor::visitExtractElementInst(ExtractElementInst &I) {
    visitOperandShadowInst(I);
  }
  
  void DFSanVisitor::visitInsertElementInst(InsertElementInst &I) {
    visitOperandShadowInst(I);
  }
  
  void DFSanVisitor::visitShuffleVectorInst(ShuffleVectorInst &I) {
    visitOperandShadowInst(I);
  }
  
  void DFSanVisitor::visitExtractValueInst(ExtractValueInst &I) {
    visitOperandShadowInst(I);
  }
  
  void DFSanVisitor::visitInsertValueInst(InsertValueInst &I) {
    visitOperandShadowInst(I);
  }
  
  void DFSanVisitor::visitAllocaInst(AllocaInst &I) {
    bool AllLoadsStores = true;
    for (User *U : I.users()) {
      if (isa<LoadInst>(U))
        continue;
  
      if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
        if (SI->getPointerOperand() == &I)
          continue;
      }
  
      AllLoadsStores = false;
      break;
    }
    if (AllLoadsStores) {
      IRBuilder<> IRB(&I);
      DFSF.AllocaShadowMap[&I] = IRB.CreateAlloca(DFSF.DFS.ShadowTy);
    }
    DFSF.setShadow(&I, DFSF.DFS.ZeroShadow);
  }
  
  void DFSanVisitor::visitSelectInst(SelectInst &I) {
    Value *CondShadow = DFSF.getShadow(I.getCondition());
    Value *TrueShadow = DFSF.getShadow(I.getTrueValue());
    Value *FalseShadow = DFSF.getShadow(I.getFalseValue());
  
    if (isa<VectorType>(I.getCondition()->getType())) {
      DFSF.setShadow(
          &I,
          DFSF.combineShadows(
              CondShadow, DFSF.combineShadows(TrueShadow, FalseShadow, &I), &I));
    } else {
      Value *ShadowSel;
      if (TrueShadow == FalseShadow) {
        ShadowSel = TrueShadow;
      } else {
        ShadowSel =
            SelectInst::Create(I.getCondition(), TrueShadow, FalseShadow, "", &I);
      }
      DFSF.setShadow(&I, DFSF.combineShadows(CondShadow, ShadowSel, &I));
    }
  }
  
  void DFSanVisitor::visitMemSetInst(MemSetInst &I) {
    IRBuilder<> IRB(&I);
    Value *ValShadow = DFSF.getShadow(I.getValue());
    IRB.CreateCall(DFSF.DFS.DFSanSetLabelFn,
                   {ValShadow, IRB.CreateBitCast(I.getDest(), Type::getInt8PtrTy(
                                                                  *DFSF.DFS.Ctx)),
                    IRB.CreateZExtOrTrunc(I.getLength(), DFSF.DFS.IntptrTy)});
  }
  
  void DFSanVisitor::visitMemTransferInst(MemTransferInst &I) {
    IRBuilder<> IRB(&I);
    Value *DestShadow = DFSF.DFS.getShadowAddress(I.getDest(), &I);
    Value *SrcShadow = DFSF.DFS.getShadowAddress(I.getSource(), &I);
    Value *LenShadow = IRB.CreateMul(
        I.getLength(),
        ConstantInt::get(I.getLength()->getType(), DFSF.DFS.ShadowWidth / 8));
    Value *AlignShadow;
    if (ClPreserveAlignment) {
      AlignShadow = IRB.CreateMul(I.getAlignmentCst(),
                                  ConstantInt::get(I.getAlignmentCst()->getType(),
                                                   DFSF.DFS.ShadowWidth / 8));
    } else {
      AlignShadow = ConstantInt::get(I.getAlignmentCst()->getType(),
                                     DFSF.DFS.ShadowWidth / 8);
    }
    Type *Int8Ptr = Type::getInt8PtrTy(*DFSF.DFS.Ctx);
    DestShadow = IRB.CreateBitCast(DestShadow, Int8Ptr);
    SrcShadow = IRB.CreateBitCast(SrcShadow, Int8Ptr);
    IRB.CreateCall(I.getCalledValue(), {DestShadow, SrcShadow, LenShadow,
                                        AlignShadow, I.getVolatileCst()});
  }
  
  void DFSanVisitor::visitReturnInst(ReturnInst &RI) {
    if (!DFSF.IsNativeABI && RI.getReturnValue()) {
      switch (DFSF.IA) {
      case DataFlowSanitizer::IA_TLS: {
        Value *S = DFSF.getShadow(RI.getReturnValue());
        IRBuilder<> IRB(&RI);
        IRB.CreateStore(S, DFSF.getRetvalTLS());
        break;
      }
      case DataFlowSanitizer::IA_Args: {
        IRBuilder<> IRB(&RI);
        Type *RT = DFSF.F->getFunctionType()->getReturnType();
        Value *InsVal =
            IRB.CreateInsertValue(UndefValue::get(RT), RI.getReturnValue(), 0);
        Value *InsShadow =
            IRB.CreateInsertValue(InsVal, DFSF.getShadow(RI.getReturnValue()), 1);
        RI.setOperand(0, InsShadow);
        break;
      }
      }
    }
  }
  
  void DFSanVisitor::visitCallSite(CallSite CS) {
    Function *F = CS.getCalledFunction();
    if ((F && F->isIntrinsic()) || isa<InlineAsm>(CS.getCalledValue())) {
      visitOperandShadowInst(*CS.getInstruction());
      return;
    }
  
    // Calls to this function are synthesized in wrappers, and we shouldn't
    // instrument them.
    if (F == DFSF.DFS.DFSanVarargWrapperFn)
      return;
  
    assert(!(cast<FunctionType>(
        CS.getCalledValue()->getType()->getPointerElementType())->isVarArg() &&
             dyn_cast<InvokeInst>(CS.getInstruction())));
  
    IRBuilder<> IRB(CS.getInstruction());
  
    DenseMap<Value *, Function *>::iterator i =
        DFSF.DFS.UnwrappedFnMap.find(CS.getCalledValue());
    if (i != DFSF.DFS.UnwrappedFnMap.end()) {
      Function *F = i->second;
      switch (DFSF.DFS.getWrapperKind(F)) {
      case DataFlowSanitizer::WK_Warning: {
        CS.setCalledFunction(F);
        IRB.CreateCall(DFSF.DFS.DFSanUnimplementedFn,
                       IRB.CreateGlobalStringPtr(F->getName()));
        DFSF.setShadow(CS.getInstruction(), DFSF.DFS.ZeroShadow);
        return;
      }
      case DataFlowSanitizer::WK_Discard: {
        CS.setCalledFunction(F);
        DFSF.setShadow(CS.getInstruction(), DFSF.DFS.ZeroShadow);
        return;
      }
      case DataFlowSanitizer::WK_Functional: {
        CS.setCalledFunction(F);
        visitOperandShadowInst(*CS.getInstruction());
        return;
      }
      case DataFlowSanitizer::WK_Custom: {
        // Don't try to handle invokes of custom functions, it's too complicated.
        // Instead, invoke the dfsw$ wrapper, which will in turn call the __dfsw_
        // wrapper.
        if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction())) {
          FunctionType *FT = F->getFunctionType();
          FunctionType *CustomFT = DFSF.DFS.getCustomFunctionType(FT);
          std::string CustomFName = "__dfsw_";
          CustomFName += F->getName();
          Constant *CustomF =
              DFSF.DFS.Mod->getOrInsertFunction(CustomFName, CustomFT);
          if (Function *CustomFn = dyn_cast<Function>(CustomF)) {
            CustomFn->copyAttributesFrom(F);
  
            // Custom functions returning non-void will write to the return label.
            if (!FT->getReturnType()->isVoidTy()) {
              CustomFn->removeAttributes(AttributeSet::FunctionIndex,
                                         DFSF.DFS.ReadOnlyNoneAttrs);
            }
          }
  
          std::vector<Value *> Args;
  
          CallSite::arg_iterator i = CS.arg_begin();
          for (unsigned n = FT->getNumParams(); n != 0; ++i, --n) {
            Type *T = (*i)->getType();
            FunctionType *ParamFT;
            if (isa<PointerType>(T) &&
                (ParamFT = dyn_cast<FunctionType>(
                     cast<PointerType>(T)->getElementType()))) {
              std::string TName = "dfst";
              TName += utostr(FT->getNumParams() - n);
              TName += "$";
              TName += F->getName();
              Constant *T = DFSF.DFS.getOrBuildTrampolineFunction(ParamFT, TName);
              Args.push_back(T);
              Args.push_back(
                  IRB.CreateBitCast(*i, Type::getInt8PtrTy(*DFSF.DFS.Ctx)));
            } else {
              Args.push_back(*i);
            }
          }
  
          i = CS.arg_begin();
          for (unsigned n = FT->getNumParams(); n != 0; ++i, --n)
            Args.push_back(DFSF.getShadow(*i));
  
          if (FT->isVarArg()) {
            auto *LabelVATy = ArrayType::get(DFSF.DFS.ShadowTy,
                                             CS.arg_size() - FT->getNumParams());
            auto *LabelVAAlloca = new AllocaInst(
                LabelVATy, "labelva", &DFSF.F->getEntryBlock().front());
  
            for (unsigned n = 0; i != CS.arg_end(); ++i, ++n) {
              auto LabelVAPtr = IRB.CreateStructGEP(LabelVATy, LabelVAAlloca, n);
              IRB.CreateStore(DFSF.getShadow(*i), LabelVAPtr);
            }
  
            Args.push_back(IRB.CreateStructGEP(LabelVATy, LabelVAAlloca, 0));
          }
  
          if (!FT->getReturnType()->isVoidTy()) {
            if (!DFSF.LabelReturnAlloca) {
              DFSF.LabelReturnAlloca =
                  new AllocaInst(DFSF.DFS.ShadowTy, "labelreturn",
                                 &DFSF.F->getEntryBlock().front());
            }
            Args.push_back(DFSF.LabelReturnAlloca);
          }
  
          for (i = CS.arg_begin() + FT->getNumParams(); i != CS.arg_end(); ++i)
            Args.push_back(*i);
  
          CallInst *CustomCI = IRB.CreateCall(CustomF, Args);
          CustomCI->setCallingConv(CI->getCallingConv());
          CustomCI->setAttributes(CI->getAttributes());
  
          if (!FT->getReturnType()->isVoidTy()) {
            LoadInst *LabelLoad = IRB.CreateLoad(DFSF.LabelReturnAlloca);
            DFSF.setShadow(CustomCI, LabelLoad);
          }
  
          CI->replaceAllUsesWith(CustomCI);
          CI->eraseFromParent();
          return;
        }
        break;
      }
      }
    }
  
    FunctionType *FT = cast<FunctionType>(
        CS.getCalledValue()->getType()->getPointerElementType());
    if (DFSF.DFS.getInstrumentedABI() == DataFlowSanitizer::IA_TLS) {
      for (unsigned i = 0, n = FT->getNumParams(); i != n; ++i) {
        IRB.CreateStore(DFSF.getShadow(CS.getArgument(i)),
                        DFSF.getArgTLS(i, CS.getInstruction()));
      }
    }
  
    Instruction *Next = nullptr;
    if (!CS.getType()->isVoidTy()) {
      if (InvokeInst *II = dyn_cast<InvokeInst>(CS.getInstruction())) {
        if (II->getNormalDest()->getSinglePredecessor()) {
          Next = &II->getNormalDest()->front();
        } else {
          BasicBlock *NewBB =
              SplitEdge(II->getParent(), II->getNormalDest(), &DFSF.DT);
          Next = &NewBB->front();
        }
      } else {
        assert(CS->getIterator() != CS->getParent()->end());
        Next = CS->getNextNode();
      }
  
      if (DFSF.DFS.getInstrumentedABI() == DataFlowSanitizer::IA_TLS) {
        IRBuilder<> NextIRB(Next);
        LoadInst *LI = NextIRB.CreateLoad(DFSF.getRetvalTLS());
        DFSF.SkipInsts.insert(LI);
        DFSF.setShadow(CS.getInstruction(), LI);
        DFSF.NonZeroChecks.push_back(LI);
      }
    }
  
    // Do all instrumentation for IA_Args down here to defer tampering with the
    // CFG in a way that SplitEdge may be able to detect.
    if (DFSF.DFS.getInstrumentedABI() == DataFlowSanitizer::IA_Args) {
      FunctionType *NewFT = DFSF.DFS.getArgsFunctionType(FT);
      Value *Func =
          IRB.CreateBitCast(CS.getCalledValue(), PointerType::getUnqual(NewFT));
      std::vector<Value *> Args;
  
      CallSite::arg_iterator i = CS.arg_begin(), e = CS.arg_end();
      for (unsigned n = FT->getNumParams(); n != 0; ++i, --n)
        Args.push_back(*i);
  
      i = CS.arg_begin();
      for (unsigned n = FT->getNumParams(); n != 0; ++i, --n)
        Args.push_back(DFSF.getShadow(*i));
  
      if (FT->isVarArg()) {
        unsigned VarArgSize = CS.arg_size() - FT->getNumParams();
        ArrayType *VarArgArrayTy = ArrayType::get(DFSF.DFS.ShadowTy, VarArgSize);
        AllocaInst *VarArgShadow =
            new AllocaInst(VarArgArrayTy, "", &DFSF.F->getEntryBlock().front());
        Args.push_back(IRB.CreateConstGEP2_32(VarArgArrayTy, VarArgShadow, 0, 0));
        for (unsigned n = 0; i != e; ++i, ++n) {
          IRB.CreateStore(
              DFSF.getShadow(*i),
              IRB.CreateConstGEP2_32(VarArgArrayTy, VarArgShadow, 0, n));
          Args.push_back(*i);
        }
      }
  
      CallSite NewCS;
      if (InvokeInst *II = dyn_cast<InvokeInst>(CS.getInstruction())) {
        NewCS = IRB.CreateInvoke(Func, II->getNormalDest(), II->getUnwindDest(),
                                 Args);
      } else {
        NewCS = IRB.CreateCall(Func, Args);
      }
      NewCS.setCallingConv(CS.getCallingConv());
      NewCS.setAttributes(CS.getAttributes().removeAttributes(
          *DFSF.DFS.Ctx, AttributeSet::ReturnIndex,
          AttributeFuncs::typeIncompatible(NewCS.getInstruction()->getType())));
  
      if (Next) {
        ExtractValueInst *ExVal =
            ExtractValueInst::Create(NewCS.getInstruction(), 0, "", Next);
        DFSF.SkipInsts.insert(ExVal);
        ExtractValueInst *ExShadow =
            ExtractValueInst::Create(NewCS.getInstruction(), 1, "", Next);
        DFSF.SkipInsts.insert(ExShadow);
        DFSF.setShadow(ExVal, ExShadow);
        DFSF.NonZeroChecks.push_back(ExShadow);
  
        CS.getInstruction()->replaceAllUsesWith(ExVal);
      }
  
      CS.getInstruction()->eraseFromParent();
    }
  }
  
  void DFSanVisitor::visitPHINode(PHINode &PN) {
    PHINode *ShadowPN =
        PHINode::Create(DFSF.DFS.ShadowTy, PN.getNumIncomingValues(), "", &PN);
  
    // Give the shadow phi node valid predecessors to fool SplitEdge into working.
    Value *UndefShadow = UndefValue::get(DFSF.DFS.ShadowTy);
    for (PHINode::block_iterator i = PN.block_begin(), e = PN.block_end(); i != e;
         ++i) {
      ShadowPN->addIncoming(UndefShadow, *i);
    }
  
    DFSF.PHIFixups.push_back(std::make_pair(&PN, ShadowPN));
    DFSF.setShadow(&PN, ShadowPN);
  }
  