+/// \param [out] IsLarge is set to true if a protectable array is found and
+/// it is "large" ( >= ssp-buffer-size). In the case of a structure with
+/// multiple arrays, this gets set if any of them is large.
+bool StackProtector::ContainsProtectableArray(Type *Ty, bool &IsLarge,
+ bool Strong,
+ bool InStruct) const {
+ if (!Ty)
+ return false;
+ if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
+ if (!AT->getElementType()->isIntegerTy(8)) {
+ // If we're on a non-Darwin platform or we're inside of a structure, don't
+ // add stack protectors unless the array is a character array.
+ // However, in strong mode any array, regardless of type and size,
+ // triggers a protector.
+ if (!Strong && (InStruct || !Trip.isOSDarwin()))
+ return false;
+ }
+
+ // If an array has more than SSPBufferSize bytes of allocated space, then we
+ // emit stack protectors.
+ if (SSPBufferSize <= M->getDataLayout().getTypeAllocSize(AT)) {
+ IsLarge = true;
+ return true;
+ }
+
+ if (Strong)
+ // Require a protector for all arrays in strong mode
+ return true;
+ }
+
+ const StructType *ST = dyn_cast<StructType>(Ty);
+ if (!ST)
+ return false;
+
+ bool NeedsProtector = false;
+ for (StructType::element_iterator I = ST->element_begin(),
+ E = ST->element_end();
+ I != E; ++I)
+ if (ContainsProtectableArray(*I, IsLarge, Strong, true)) {
+ // If the element is a protectable array and is large (>= SSPBufferSize)
+ // then we are done. If the protectable array is not large, then
+ // keep looking in case a subsequent element is a large array.
+ if (IsLarge)
+ return true;
+ NeedsProtector = true;
+ }
+
+ return NeedsProtector;
+}
+
+bool StackProtector::HasAddressTaken(const Instruction *AI) {
+ for (const User *U : AI->users()) {
+ if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
+ if (AI == SI->getValueOperand())
+ return true;
+ } else if (const PtrToIntInst *SI = dyn_cast<PtrToIntInst>(U)) {
+ if (AI == SI->getOperand(0))
+ return true;
+ } else if (isa<CallInst>(U)) {
+ return true;
+ } else if (isa<InvokeInst>(U)) {
+ return true;
+ } else if (const SelectInst *SI = dyn_cast<SelectInst>(U)) {
+ if (HasAddressTaken(SI))
+ return true;
+ } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
+ // Keep track of what PHI nodes we have already visited to ensure
+ // they are only visited once.
+ if (VisitedPHIs.insert(PN).second)
+ if (HasAddressTaken(PN))
+ return true;
+ } else if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
+ if (HasAddressTaken(GEP))
+ return true;
+ } else if (const BitCastInst *BI = dyn_cast<BitCastInst>(U)) {
+ if (HasAddressTaken(BI))
+ return true;
+ }
+ }
+ return false;
+}
+
+/// \brief Check whether or not this function needs a stack protector based
+/// upon the stack protector level.
+///
+/// We use two heuristics: a standard (ssp) and strong (sspstrong).
+/// The standard heuristic which will add a guard variable to functions that
+/// call alloca with a either a variable size or a size >= SSPBufferSize,
+/// functions with character buffers larger than SSPBufferSize, and functions
+/// with aggregates containing character buffers larger than SSPBufferSize. The
+/// strong heuristic will add a guard variables to functions that call alloca
+/// regardless of size, functions with any buffer regardless of type and size,
+/// functions with aggregates that contain any buffer regardless of type and
+/// size, and functions that contain stack-based variables that have had their
+/// address taken.
+bool StackProtector::RequiresStackProtector() {
+ bool Strong = false;
+ bool NeedsProtector = false;
+ if (F->hasFnAttribute(Attribute::StackProtectReq)) {
+ NeedsProtector = true;
+ Strong = true; // Use the same heuristic as strong to determine SSPLayout
+ } else if (F->hasFnAttribute(Attribute::StackProtectStrong))
+ Strong = true;
+ else if (!F->hasFnAttribute(Attribute::StackProtect))
+ return false;
+
+ for (const BasicBlock &BB : *F) {
+ for (const Instruction &I : BB) {
+ if (const AllocaInst *AI = dyn_cast<AllocaInst>(&I)) {
+ if (AI->isArrayAllocation()) {
+ // SSP-Strong: Enable protectors for any call to alloca, regardless
+ // of size.
+ if (Strong)
+ return true;
+
+ if (const auto *CI = dyn_cast<ConstantInt>(AI->getArraySize())) {
+ if (CI->getLimitedValue(SSPBufferSize) >= SSPBufferSize) {
+ // A call to alloca with size >= SSPBufferSize requires
+ // stack protectors.
+ Layout.insert(std::make_pair(AI, SSPLK_LargeArray));
+ NeedsProtector = true;
+ } else if (Strong) {
+ // Require protectors for all alloca calls in strong mode.
+ Layout.insert(std::make_pair(AI, SSPLK_SmallArray));
+ NeedsProtector = true;
+ }
+ } else {
+ // A call to alloca with a variable size requires protectors.
+ Layout.insert(std::make_pair(AI, SSPLK_LargeArray));
+ NeedsProtector = true;
+ }
+ continue;
+ }
+
+ bool IsLarge = false;
+ if (ContainsProtectableArray(AI->getAllocatedType(), IsLarge, Strong)) {
+ Layout.insert(std::make_pair(AI, IsLarge ? SSPLK_LargeArray
+ : SSPLK_SmallArray));
+ NeedsProtector = true;
+ continue;
+ }
+
+ if (Strong && HasAddressTaken(AI)) {
+ ++NumAddrTaken;
+ Layout.insert(std::make_pair(AI, SSPLK_AddrOf));
+ NeedsProtector = true;
+ }
+ }
+ }
+ }
+
+ return NeedsProtector;
+}
+
+static bool InstructionWillNotHaveChain(const Instruction *I) {
+ return !I->mayHaveSideEffects() && !I->mayReadFromMemory() &&
+ isSafeToSpeculativelyExecute(I);
+}
+
+/// Identify if RI has a previous instruction in the "Tail Position" and return
+/// it. Otherwise return 0.
+///
+/// This is based off of the code in llvm::isInTailCallPosition. The difference
+/// is that it inverts the first part of llvm::isInTailCallPosition since
+/// isInTailCallPosition is checking if a call is in a tail call position, and
+/// we are searching for an unknown tail call that might be in the tail call
+/// position. Once we find the call though, the code uses the same refactored
+/// code, returnTypeIsEligibleForTailCall.
+static CallInst *FindPotentialTailCall(BasicBlock *BB, ReturnInst *RI,
+ const TargetLoweringBase *TLI) {
+ // Establish a reasonable upper bound on the maximum amount of instructions we
+ // will look through to find a tail call.
+ unsigned SearchCounter = 0;
+ const unsigned MaxSearch = 4;
+ bool NoInterposingChain = true;
+
+ for (BasicBlock::reverse_iterator I = std::next(BB->rbegin()), E = BB->rend();
+ I != E && SearchCounter < MaxSearch; ++I) {
+ Instruction *Inst = &*I;
+
+ // Skip over debug intrinsics and do not allow them to affect our MaxSearch
+ // counter.
+ if (isa<DbgInfoIntrinsic>(Inst))
+ continue;
+
+ // If we find a call and the following conditions are satisifed, then we
+ // have found a tail call that satisfies at least the target independent
+ // requirements of a tail call:
+ //
+ // 1. The call site has the tail marker.
+ //
+ // 2. The call site either will not cause the creation of a chain or if a
+ // chain is necessary there are no instructions in between the callsite and
+ // the call which would create an interposing chain.
+ //
+ // 3. The return type of the function does not impede tail call
+ // optimization.
+ if (CallInst *CI = dyn_cast<CallInst>(Inst)) {
+ if (CI->isTailCall() &&
+ (InstructionWillNotHaveChain(CI) || NoInterposingChain) &&
+ returnTypeIsEligibleForTailCall(BB->getParent(), CI, RI, *TLI))
+ return CI;
+ }
+
+ // If we did not find a call see if we have an instruction that may create
+ // an interposing chain.
+ NoInterposingChain =
+ NoInterposingChain && InstructionWillNotHaveChain(Inst);
+
+ // Increment max search.
+ SearchCounter++;
+ }
+
+ return nullptr;
+}
+
+/// Insert code into the entry block that stores the __stack_chk_guard
+/// variable onto the stack:
+///
+/// entry:
+/// StackGuardSlot = alloca i8*
+/// StackGuard = load __stack_chk_guard
+/// call void @llvm.stackprotect.create(StackGuard, StackGuardSlot)
+///
+/// Returns true if the platform/triple supports the stackprotectorcreate pseudo
+/// node.
+static bool CreatePrologue(Function *F, Module *M, ReturnInst *RI,
+ const TargetLoweringBase *TLI, const Triple &TT,
+ AllocaInst *&AI, Value *&StackGuardVar) {
+ bool SupportsSelectionDAGSP = false;
+ PointerType *PtrTy = Type::getInt8PtrTy(RI->getContext());
+ unsigned AddressSpace, Offset;
+ if (TLI->getStackCookieLocation(AddressSpace, Offset)) {
+ Constant *OffsetVal =
+ ConstantInt::get(Type::getInt32Ty(RI->getContext()), Offset);
+
+ StackGuardVar =
+ ConstantExpr::getIntToPtr(OffsetVal, PointerType::get(PtrTy,
+ AddressSpace));
+ } else if (TT.isOSOpenBSD()) {
+ StackGuardVar = M->getOrInsertGlobal("__guard_local", PtrTy);
+ cast<GlobalValue>(StackGuardVar)
+ ->setVisibility(GlobalValue::HiddenVisibility);
+ } else {
+ SupportsSelectionDAGSP = true;
+ StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", PtrTy);
+ }
+
+ IRBuilder<> B(&F->getEntryBlock().front());
+ AI = B.CreateAlloca(PtrTy, nullptr, "StackGuardSlot");
+ LoadInst *LI = B.CreateLoad(StackGuardVar, "StackGuard");
+ B.CreateCall(Intrinsic::getDeclaration(M, Intrinsic::stackprotector),
+ {LI, AI});
+
+ return SupportsSelectionDAGSP;
+}
+