Move SafeStack to CodeGen.

It depends on the target machinery, that's not available for instrumentation passes. llvm-svn: 258942
2016-01-27 16:53:42 +00:00
parent a73a0cfaf4
commit 390c33cd18
8 changed files with 26 additions and 25 deletions
--- a/llvm/lib/CodeGen/SafeStack.cpp
+++ b/llvm/lib/CodeGen/SafeStack.cpp
@@ -0,0 +1,760 @@
+//===-- SafeStack.cpp - Safe Stack Insertion ------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass splits the stack into the safe stack (kept as-is for LLVM backend)
+// and the unsafe stack (explicitly allocated and managed through the runtime
+// support library).
+//
+// http://clang.llvm.org/docs/SafeStack.html
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/Triple.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DIBuilder.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/Format.h"
+#include "llvm/Support/MathExtras.h"
+#include "llvm/Support/raw_os_ostream.h"
+#include "llvm/Target/TargetLowering.h"
+#include "llvm/Target/TargetSubtargetInfo.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/ModuleUtils.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "safestack"
+
+enum UnsafeStackPtrStorageVal { ThreadLocalUSP, SingleThreadUSP };
+
+static cl::opt<UnsafeStackPtrStorageVal> USPStorage("safe-stack-usp-storage",
+    cl::Hidden, cl::init(ThreadLocalUSP),
+    cl::desc("Type of storage for the unsafe stack pointer"),
+    cl::values(clEnumValN(ThreadLocalUSP, "thread-local",
+                          "Thread-local storage"),
+               clEnumValN(SingleThreadUSP, "single-thread",
+                          "Non-thread-local storage"),
+               clEnumValEnd));
+
+namespace llvm {
+
+STATISTIC(NumFunctions, "Total number of functions");
+STATISTIC(NumUnsafeStackFunctions, "Number of functions with unsafe stack");
+STATISTIC(NumUnsafeStackRestorePointsFunctions,
+          "Number of functions that use setjmp or exceptions");
+
+STATISTIC(NumAllocas, "Total number of allocas");
+STATISTIC(NumUnsafeStaticAllocas, "Number of unsafe static allocas");
+STATISTIC(NumUnsafeDynamicAllocas, "Number of unsafe dynamic allocas");
+STATISTIC(NumUnsafeByValArguments, "Number of unsafe byval arguments");
+STATISTIC(NumUnsafeStackRestorePoints, "Number of setjmps and landingpads");
+
+} // namespace llvm
+
+namespace {
+
+/// Rewrite an SCEV expression for a memory access address to an expression that
+/// represents offset from the given alloca.
+///
+/// The implementation simply replaces all mentions of the alloca with zero.
+class AllocaOffsetRewriter : public SCEVRewriteVisitor<AllocaOffsetRewriter> {
+  const Value *AllocaPtr;
+
+public:
+  AllocaOffsetRewriter(ScalarEvolution &SE, const Value *AllocaPtr)
+      : SCEVRewriteVisitor(SE), AllocaPtr(AllocaPtr) {}
+
+  const SCEV *visitUnknown(const SCEVUnknown *Expr) {
+    if (Expr->getValue() == AllocaPtr)
+      return SE.getZero(Expr->getType());
+    return Expr;
+  }
+};
+
+/// The SafeStack pass splits the stack of each function into the safe
+/// stack, which is only accessed through memory safe dereferences (as
+/// determined statically), and the unsafe stack, which contains all
+/// local variables that are accessed in ways that we can't prove to
+/// be safe.
+class SafeStack : public FunctionPass {
+  const TargetMachine *TM;
+  const TargetLoweringBase *TL;
+  const DataLayout *DL;
+  ScalarEvolution *SE;
+
+  Type *StackPtrTy;
+  Type *IntPtrTy;
+  Type *Int32Ty;
+  Type *Int8Ty;
+
+  Value *UnsafeStackPtr = nullptr;
+
+  /// Unsafe stack alignment. Each stack frame must ensure that the stack is
+  /// aligned to this value. We need to re-align the unsafe stack if the
+  /// alignment of any object on the stack exceeds this value.
+  ///
+  /// 16 seems like a reasonable upper bound on the alignment of objects that we
+  /// might expect to appear on the stack on most common targets.
+  enum { StackAlignment = 16 };
+
+  /// \brief Build a value representing a pointer to the unsafe stack pointer.
+  Value *getOrCreateUnsafeStackPtr(IRBuilder<> &IRB, Function &F);
+
+  /// \brief Find all static allocas, dynamic allocas, return instructions and
+  /// stack restore points (exception unwind blocks and setjmp calls) in the
+  /// given function and append them to the respective vectors.
+  void findInsts(Function &F, SmallVectorImpl<AllocaInst *> &StaticAllocas,
+                 SmallVectorImpl<AllocaInst *> &DynamicAllocas,
+                 SmallVectorImpl<Argument *> &ByValArguments,
+                 SmallVectorImpl<ReturnInst *> &Returns,
+                 SmallVectorImpl<Instruction *> &StackRestorePoints);
+
+  /// \brief Calculate the allocation size of a given alloca. Returns 0 if the
+  /// size can not be statically determined.
+  uint64_t getStaticAllocaAllocationSize(const AllocaInst* AI);
+
+  /// \brief Allocate space for all static allocas in \p StaticAllocas,
+  /// replace allocas with pointers into the unsafe stack and generate code to
+  /// restore the stack pointer before all return instructions in \p Returns.
+  ///
+  /// \returns A pointer to the top of the unsafe stack after all unsafe static
+  /// allocas are allocated.
+  Value *moveStaticAllocasToUnsafeStack(IRBuilder<> &IRB, Function &F,
+                                        ArrayRef<AllocaInst *> StaticAllocas,
+                                        ArrayRef<Argument *> ByValArguments,
+                                        ArrayRef<ReturnInst *> Returns);
+
+  /// \brief Generate code to restore the stack after all stack restore points
+  /// in \p StackRestorePoints.
+  ///
+  /// \returns A local variable in which to maintain the dynamic top of the
+  /// unsafe stack if needed.
+  AllocaInst *
+  createStackRestorePoints(IRBuilder<> &IRB, Function &F,
+                           ArrayRef<Instruction *> StackRestorePoints,
+                           Value *StaticTop, bool NeedDynamicTop);
+
+  /// \brief Replace all allocas in \p DynamicAllocas with code to allocate
+  /// space dynamically on the unsafe stack and store the dynamic unsafe stack
+  /// top to \p DynamicTop if non-null.
+  void moveDynamicAllocasToUnsafeStack(Function &F, Value *UnsafeStackPtr,
+                                       AllocaInst *DynamicTop,
+                                       ArrayRef<AllocaInst *> DynamicAllocas);
+
+  bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize);
+
+  bool IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
+                          const Value *AllocaPtr, uint64_t AllocaSize);
+  bool IsAccessSafe(Value *Addr, uint64_t Size, const Value *AllocaPtr,
+                    uint64_t AllocaSize);
+
+public:
+  static char ID; // Pass identification, replacement for typeid.
+  SafeStack(const TargetMachine *TM)
+      : FunctionPass(ID), TM(TM), TL(nullptr), DL(nullptr) {
+    initializeSafeStackPass(*PassRegistry::getPassRegistry());
+  }
+  SafeStack() : SafeStack(nullptr) {}
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.addRequired<ScalarEvolutionWrapperPass>();
+  }
+
+  bool doInitialization(Module &M) override {
+    DL = &M.getDataLayout();
+
+    StackPtrTy = Type::getInt8PtrTy(M.getContext());
+    IntPtrTy = DL->getIntPtrType(M.getContext());
+    Int32Ty = Type::getInt32Ty(M.getContext());
+    Int8Ty = Type::getInt8Ty(M.getContext());
+
+    return false;
+  }
+
+  bool runOnFunction(Function &F) override;
+}; // class SafeStack
+
+uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) {
+  uint64_t Size = DL->getTypeAllocSize(AI->getAllocatedType());
+  if (AI->isArrayAllocation()) {
+    auto C = dyn_cast<ConstantInt>(AI->getArraySize());
+    if (!C)
+      return 0;
+    Size *= C->getZExtValue();
+  }
+  return Size;
+}
+
+bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize,
+                             const Value *AllocaPtr, uint64_t AllocaSize) {
+  AllocaOffsetRewriter Rewriter(*SE, AllocaPtr);
+  const SCEV *Expr = Rewriter.visit(SE->getSCEV(Addr));
+
+  uint64_t BitWidth = SE->getTypeSizeInBits(Expr->getType());
+  ConstantRange AccessStartRange = SE->getUnsignedRange(Expr);
+  ConstantRange SizeRange =
+      ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize));
+  ConstantRange AccessRange = AccessStartRange.add(SizeRange);
+  ConstantRange AllocaRange =
+      ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize));
+  bool Safe = AllocaRange.contains(AccessRange);
+
+  DEBUG(dbgs() << "[SafeStack] "
+               << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
+               << *AllocaPtr << "\n"
+               << "            Access " << *Addr << "\n"
+               << "            SCEV " << *Expr
+               << " U: " << SE->getUnsignedRange(Expr)
+               << ", S: " << SE->getSignedRange(Expr) << "\n"
+               << "            Range " << AccessRange << "\n"
+               << "            AllocaRange " << AllocaRange << "\n"
+               << "            " << (Safe ? "safe" : "unsafe") << "\n");
+
+  return Safe;
+}
+
+bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
+                                   const Value *AllocaPtr,
+                                   uint64_t AllocaSize) {
+  // All MemIntrinsics have destination address in Arg0 and size in Arg2.
+  if (MI->getRawDest() != U) return true;
+  const auto *Len = dyn_cast<ConstantInt>(MI->getLength());
+  // Non-constant size => unsafe. FIXME: try SCEV getRange.
+  if (!Len) return false;
+  return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize);
+}
+
+/// Check whether a given allocation must be put on the safe
+/// stack or not. The function analyzes all uses of AI and checks whether it is
+/// only accessed in a memory safe way (as decided statically).
+bool SafeStack::IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize) {
+  // Go through all uses of this alloca and check whether all accesses to the
+  // allocated object are statically known to be memory safe and, hence, the
+  // object can be placed on the safe stack.
+  SmallPtrSet<const Value *, 16> Visited;
+  SmallVector<const Value *, 8> WorkList;
+  WorkList.push_back(AllocaPtr);
+
+  // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc.
+  while (!WorkList.empty()) {
+    const Value *V = WorkList.pop_back_val();
+    for (const Use &UI : V->uses()) {
+      auto I = cast<const Instruction>(UI.getUser());
+      assert(V == UI.get());
+
+      switch (I->getOpcode()) {
+      case Instruction::Load: {
+        if (!IsAccessSafe(UI, DL->getTypeStoreSize(I->getType()), AllocaPtr,
+                          AllocaSize))
+          return false;
+        break;
+      }
+      case Instruction::VAArg:
+        // "va-arg" from a pointer is safe.
+        break;
+      case Instruction::Store: {
+        if (V == I->getOperand(0)) {
+          // Stored the pointer - conservatively assume it may be unsafe.
+          DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
+                       << "\n            store of address: " << *I << "\n");
+          return false;
+        }
+
+        if (!IsAccessSafe(UI, DL->getTypeStoreSize(I->getOperand(0)->getType()),
+                          AllocaPtr, AllocaSize))
+          return false;
+        break;
+      }
+      case Instruction::Ret: {
+        // Information leak.
+        return false;
+      }
+
+      case Instruction::Call:
+      case Instruction::Invoke: {
+        ImmutableCallSite CS(I);
+
+        if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
+          if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
+              II->getIntrinsicID() == Intrinsic::lifetime_end)
+            continue;
+        }
+
+        if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
+          if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
+            DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
+                         << "\n            unsafe memintrinsic: " << *I
+                         << "\n");
+            return false;
+          }
+          continue;
+        }
+
+        // LLVM 'nocapture' attribute is only set for arguments whose address
+        // is not stored, passed around, or used in any other non-trivial way.
+        // We assume that passing a pointer to an object as a 'nocapture
+        // readnone' argument is safe.
+        // FIXME: a more precise solution would require an interprocedural
+        // analysis here, which would look at all uses of an argument inside
+        // the function being called.
+        ImmutableCallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end();
+        for (ImmutableCallSite::arg_iterator A = B; A != E; ++A)
+          if (A->get() == V)
+            if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) ||
+                                               CS.doesNotAccessMemory()))) {
+              DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
+                           << "\n            unsafe call: " << *I << "\n");
+              return false;
+            }
+        continue;
+      }
+
+      default:
+        if (Visited.insert(I).second)
+          WorkList.push_back(cast<const Instruction>(I));
+      }
+    }
+  }
+
+  // All uses of the alloca are safe, we can place it on the safe stack.
+  return true;
+}
+
+Value *SafeStack::getOrCreateUnsafeStackPtr(IRBuilder<> &IRB, Function &F) {
+  // Check if there is a target-specific location for the unsafe stack pointer.
+  if (TL)
+    if (Value *V = TL->getSafeStackPointerLocation(IRB))
+      return V;
+
+  // Otherwise, assume the target links with compiler-rt, which provides a
+  // thread-local variable with a magic name.
+  Module &M = *F.getParent();
+  const char *UnsafeStackPtrVar = "__safestack_unsafe_stack_ptr";
+  auto UnsafeStackPtr =
+      dyn_cast_or_null<GlobalVariable>(M.getNamedValue(UnsafeStackPtrVar));
+
+  bool UseTLS = USPStorage == ThreadLocalUSP;
+
+  if (!UnsafeStackPtr) {
+    auto TLSModel = UseTLS ?
+        GlobalValue::InitialExecTLSModel :
+        GlobalValue::NotThreadLocal;
+    // The global variable is not defined yet, define it ourselves.
+    // We use the initial-exec TLS model because we do not support the
+    // variable living anywhere other than in the main executable.
+    UnsafeStackPtr = new GlobalVariable(
+        M, StackPtrTy, false, GlobalValue::ExternalLinkage, nullptr,
+        UnsafeStackPtrVar, nullptr, TLSModel);
+  } else {
+    // The variable exists, check its type and attributes.
+    if (UnsafeStackPtr->getValueType() != StackPtrTy)
+      report_fatal_error(Twine(UnsafeStackPtrVar) + " must have void* type");
+    if (UseTLS != UnsafeStackPtr->isThreadLocal())
+      report_fatal_error(Twine(UnsafeStackPtrVar) + " must " +
+                         (UseTLS ? "" : "not ") + "be thread-local");
+  }
+  return UnsafeStackPtr;
+}
+
+void SafeStack::findInsts(Function &F,
+                          SmallVectorImpl<AllocaInst *> &StaticAllocas,
+                          SmallVectorImpl<AllocaInst *> &DynamicAllocas,
+                          SmallVectorImpl<Argument *> &ByValArguments,
+                          SmallVectorImpl<ReturnInst *> &Returns,
+                          SmallVectorImpl<Instruction *> &StackRestorePoints) {
+  for (Instruction &I : instructions(&F)) {
+    if (auto AI = dyn_cast<AllocaInst>(&I)) {
+      ++NumAllocas;
+
+      uint64_t Size = getStaticAllocaAllocationSize(AI);
+      if (IsSafeStackAlloca(AI, Size))
+        continue;
+
+      if (AI->isStaticAlloca()) {
+        ++NumUnsafeStaticAllocas;
+        StaticAllocas.push_back(AI);
+      } else {
+        ++NumUnsafeDynamicAllocas;
+        DynamicAllocas.push_back(AI);
+      }
+    } else if (auto RI = dyn_cast<ReturnInst>(&I)) {
+      Returns.push_back(RI);
+    } else if (auto CI = dyn_cast<CallInst>(&I)) {
+      // setjmps require stack restore.
+      if (CI->getCalledFunction() && CI->canReturnTwice())
+        StackRestorePoints.push_back(CI);
+    } else if (auto LP = dyn_cast<LandingPadInst>(&I)) {
+      // Exception landing pads require stack restore.
+      StackRestorePoints.push_back(LP);
+    } else if (auto II = dyn_cast<IntrinsicInst>(&I)) {
+      if (II->getIntrinsicID() == Intrinsic::gcroot)
+        llvm::report_fatal_error(
+            "gcroot intrinsic not compatible with safestack attribute");
+    }
+  }
+  for (Argument &Arg : F.args()) {
+    if (!Arg.hasByValAttr())
+      continue;
+    uint64_t Size =
+        DL->getTypeStoreSize(Arg.getType()->getPointerElementType());
+    if (IsSafeStackAlloca(&Arg, Size))
+      continue;
+
+    ++NumUnsafeByValArguments;
+    ByValArguments.push_back(&Arg);
+  }
+}
+
+AllocaInst *
+SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F,
+                                    ArrayRef<Instruction *> StackRestorePoints,
+                                    Value *StaticTop, bool NeedDynamicTop) {
+  if (StackRestorePoints.empty())
+    return nullptr;
+
+  // We need the current value of the shadow stack pointer to restore
+  // after longjmp or exception catching.
+
+  // FIXME: On some platforms this could be handled by the longjmp/exception
+  // runtime itself.
+
+  AllocaInst *DynamicTop = nullptr;
+  if (NeedDynamicTop)
+    // If we also have dynamic alloca's, the stack pointer value changes
+    // throughout the function. For now we store it in an alloca.
+    DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr,
+                                  "unsafe_stack_dynamic_ptr");
+
+  if (!StaticTop)
+    // We need the original unsafe stack pointer value, even if there are
+    // no unsafe static allocas.
+    StaticTop = IRB.CreateLoad(UnsafeStackPtr, false, "unsafe_stack_ptr");
+
+  if (NeedDynamicTop)
+    IRB.CreateStore(StaticTop, DynamicTop);
+
+  // Restore current stack pointer after longjmp/exception catch.
+  for (Instruction *I : StackRestorePoints) {
+    ++NumUnsafeStackRestorePoints;
+
+    IRB.SetInsertPoint(I->getNextNode());
+    Value *CurrentTop = DynamicTop ? IRB.CreateLoad(DynamicTop) : StaticTop;
+    IRB.CreateStore(CurrentTop, UnsafeStackPtr);
+  }
+
+  return DynamicTop;
+}
+
+Value *SafeStack::moveStaticAllocasToUnsafeStack(
+    IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas,
+    ArrayRef<Argument *> ByValArguments, ArrayRef<ReturnInst *> Returns) {
+  if (StaticAllocas.empty() && ByValArguments.empty())
+    return nullptr;
+
+  DIBuilder DIB(*F.getParent());
+
+  // We explicitly compute and set the unsafe stack layout for all unsafe
+  // static alloca instructions. We save the unsafe "base pointer" in the
+  // prologue into a local variable and restore it in the epilogue.
+
+  // Load the current stack pointer (we'll also use it as a base pointer).
+  // FIXME: use a dedicated register for it ?
+  Instruction *BasePointer =
+      IRB.CreateLoad(UnsafeStackPtr, false, "unsafe_stack_ptr");
+  assert(BasePointer->getType() == StackPtrTy);
+
+  for (ReturnInst *RI : Returns) {
+    IRB.SetInsertPoint(RI);
+    IRB.CreateStore(BasePointer, UnsafeStackPtr);
+  }
+
+  // Compute maximum alignment among static objects on the unsafe stack.
+  unsigned MaxAlignment = 0;
+  for (Argument *Arg : ByValArguments) {
+    Type *Ty = Arg->getType()->getPointerElementType();
+    unsigned Align = std::max((unsigned)DL->getPrefTypeAlignment(Ty),
+                              Arg->getParamAlignment());
+    if (Align > MaxAlignment)
+      MaxAlignment = Align;
+  }
+  for (AllocaInst *AI : StaticAllocas) {
+    Type *Ty = AI->getAllocatedType();
+    unsigned Align =
+        std::max((unsigned)DL->getPrefTypeAlignment(Ty), AI->getAlignment());
+    if (Align > MaxAlignment)
+      MaxAlignment = Align;
+  }
+
+  if (MaxAlignment > StackAlignment) {
+    // Re-align the base pointer according to the max requested alignment.
+    assert(isPowerOf2_32(MaxAlignment));
+    IRB.SetInsertPoint(BasePointer->getNextNode());
+    BasePointer = cast<Instruction>(IRB.CreateIntToPtr(
+        IRB.CreateAnd(IRB.CreatePtrToInt(BasePointer, IntPtrTy),
+                      ConstantInt::get(IntPtrTy, ~uint64_t(MaxAlignment - 1))),
+        StackPtrTy));
+  }
+
+  int64_t StaticOffset = 0; // Current stack top.
+  IRB.SetInsertPoint(BasePointer->getNextNode());
+
+  for (Argument *Arg : ByValArguments) {
+    Type *Ty = Arg->getType()->getPointerElementType();
+
+    uint64_t Size = DL->getTypeStoreSize(Ty);
+    if (Size == 0)
+      Size = 1; // Don't create zero-sized stack objects.
+
+    // Ensure the object is properly aligned.
+    unsigned Align = std::max((unsigned)DL->getPrefTypeAlignment(Ty),
+                              Arg->getParamAlignment());
+
+    // Add alignment.
+    // NOTE: we ensure that BasePointer itself is aligned to >= Align.
+    StaticOffset += Size;
+    StaticOffset = alignTo(StaticOffset, Align);
+
+    Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8*
+                               ConstantInt::get(Int32Ty, -StaticOffset));
+    Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(),
+                                     Arg->getName() + ".unsafe-byval");
+
+    // Replace alloc with the new location.
+    replaceDbgDeclare(Arg, BasePointer, BasePointer->getNextNode(), DIB,
+                      /*Deref=*/true, -StaticOffset);
+    Arg->replaceAllUsesWith(NewArg);
+    IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
+    IRB.CreateMemCpy(Off, Arg, Size, Arg->getParamAlignment());
+  }
+
+  // Allocate space for every unsafe static AllocaInst on the unsafe stack.
+  for (AllocaInst *AI : StaticAllocas) {
+    IRB.SetInsertPoint(AI);
+
+    Type *Ty = AI->getAllocatedType();
+    uint64_t Size = getStaticAllocaAllocationSize(AI);
+    if (Size == 0)
+      Size = 1; // Don't create zero-sized stack objects.
+
+    // Ensure the object is properly aligned.
+    unsigned Align =
+        std::max((unsigned)DL->getPrefTypeAlignment(Ty), AI->getAlignment());
+
+    // Add alignment.
+    // NOTE: we ensure that BasePointer itself is aligned to >= Align.
+    StaticOffset += Size;
+    StaticOffset = alignTo(StaticOffset, Align);
+
+    Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8*
+                               ConstantInt::get(Int32Ty, -StaticOffset));
+    Value *NewAI = IRB.CreateBitCast(Off, AI->getType(), AI->getName());
+    if (AI->hasName() && isa<Instruction>(NewAI))
+      cast<Instruction>(NewAI)->takeName(AI);
+
+    // Replace alloc with the new location.
+    replaceDbgDeclareForAlloca(AI, BasePointer, DIB, /*Deref=*/true, -StaticOffset);
+    AI->replaceAllUsesWith(NewAI);
+    AI->eraseFromParent();
+  }
+
+  // Re-align BasePointer so that our callees would see it aligned as
+  // expected.
+  // FIXME: no need to update BasePointer in leaf functions.
+  StaticOffset = alignTo(StaticOffset, StackAlignment);
+
+  // Update shadow stack pointer in the function epilogue.
+  IRB.SetInsertPoint(BasePointer->getNextNode());
+
+  Value *StaticTop =
+      IRB.CreateGEP(BasePointer, ConstantInt::get(Int32Ty, -StaticOffset),
+                    "unsafe_stack_static_top");
+  IRB.CreateStore(StaticTop, UnsafeStackPtr);
+  return StaticTop;
+}
+
+void SafeStack::moveDynamicAllocasToUnsafeStack(
+    Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop,
+    ArrayRef<AllocaInst *> DynamicAllocas) {
+  DIBuilder DIB(*F.getParent());
+
+  for (AllocaInst *AI : DynamicAllocas) {
+    IRBuilder<> IRB(AI);
+
+    // Compute the new SP value (after AI).
+    Value *ArraySize = AI->getArraySize();
+    if (ArraySize->getType() != IntPtrTy)
+      ArraySize = IRB.CreateIntCast(ArraySize, IntPtrTy, false);
+
+    Type *Ty = AI->getAllocatedType();
+    uint64_t TySize = DL->getTypeAllocSize(Ty);
+    Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize));
+
+    Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(UnsafeStackPtr), IntPtrTy);
+    SP = IRB.CreateSub(SP, Size);
+
+    // Align the SP value to satisfy the AllocaInst, type and stack alignments.
+    unsigned Align = std::max(
+        std::max((unsigned)DL->getPrefTypeAlignment(Ty), AI->getAlignment()),
+        (unsigned)StackAlignment);
+
+    assert(isPowerOf2_32(Align));
+    Value *NewTop = IRB.CreateIntToPtr(
+        IRB.CreateAnd(SP, ConstantInt::get(IntPtrTy, ~uint64_t(Align - 1))),
+        StackPtrTy);
+
+    // Save the stack pointer.
+    IRB.CreateStore(NewTop, UnsafeStackPtr);
+    if (DynamicTop)
+      IRB.CreateStore(NewTop, DynamicTop);
+
+    Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
+    if (AI->hasName() && isa<Instruction>(NewAI))
+      NewAI->takeName(AI);
+
+    replaceDbgDeclareForAlloca(AI, NewAI, DIB, /*Deref=*/true);
+    AI->replaceAllUsesWith(NewAI);
+    AI->eraseFromParent();
+  }
+
+  if (!DynamicAllocas.empty()) {
+    // Now go through the instructions again, replacing stacksave/stackrestore.
+    for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) {
+      Instruction *I = &*(It++);
+      auto II = dyn_cast<IntrinsicInst>(I);
+      if (!II)
+        continue;
+
+      if (II->getIntrinsicID() == Intrinsic::stacksave) {
+        IRBuilder<> IRB(II);
+        Instruction *LI = IRB.CreateLoad(UnsafeStackPtr);
+        LI->takeName(II);
+        II->replaceAllUsesWith(LI);
+        II->eraseFromParent();
+      } else if (II->getIntrinsicID() == Intrinsic::stackrestore) {
+        IRBuilder<> IRB(II);
+        Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr);
+        SI->takeName(II);
+        assert(II->use_empty());
+        II->eraseFromParent();
+      }
+    }
+  }
+}
+
+bool SafeStack::runOnFunction(Function &F) {
+  DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n");
+
+  if (!F.hasFnAttribute(Attribute::SafeStack)) {
+    DEBUG(dbgs() << "[SafeStack]     safestack is not requested"
+                    " for this function\n");
+    return false;
+  }
+
+  if (F.isDeclaration()) {
+    DEBUG(dbgs() << "[SafeStack]     function definition"
+                    " is not available\n");
+    return false;
+  }
+
+  TL = TM ? TM->getSubtargetImpl(F)->getTargetLowering() : nullptr;
+  SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
+
+  {
+    // Make sure the regular stack protector won't run on this function
+    // (safestack attribute takes precedence).
+    AttrBuilder B;
+    B.addAttribute(Attribute::StackProtect)
+        .addAttribute(Attribute::StackProtectReq)
+        .addAttribute(Attribute::StackProtectStrong);
+    F.removeAttributes(
+        AttributeSet::FunctionIndex,
+        AttributeSet::get(F.getContext(), AttributeSet::FunctionIndex, B));
+  }
+
+  ++NumFunctions;
+
+  SmallVector<AllocaInst *, 16> StaticAllocas;
+  SmallVector<AllocaInst *, 4> DynamicAllocas;
+  SmallVector<Argument *, 4> ByValArguments;
+  SmallVector<ReturnInst *, 4> Returns;
+
+  // Collect all points where stack gets unwound and needs to be restored
+  // This is only necessary because the runtime (setjmp and unwind code) is
+  // not aware of the unsafe stack and won't unwind/restore it prorerly.
+  // To work around this problem without changing the runtime, we insert
+  // instrumentation to restore the unsafe stack pointer when necessary.
+  SmallVector<Instruction *, 4> StackRestorePoints;
+
+  // Find all static and dynamic alloca instructions that must be moved to the
+  // unsafe stack, all return instructions and stack restore points.
+  findInsts(F, StaticAllocas, DynamicAllocas, ByValArguments, Returns,
+            StackRestorePoints);
+
+  if (StaticAllocas.empty() && DynamicAllocas.empty() &&
+      ByValArguments.empty() && StackRestorePoints.empty())
+    return false; // Nothing to do in this function.
+
+  if (!StaticAllocas.empty() || !DynamicAllocas.empty() ||
+      !ByValArguments.empty())
+    ++NumUnsafeStackFunctions; // This function has the unsafe stack.
+
+  if (!StackRestorePoints.empty())
+    ++NumUnsafeStackRestorePointsFunctions;
+
+  IRBuilder<> IRB(&F.front(), F.begin()->getFirstInsertionPt());
+  UnsafeStackPtr = getOrCreateUnsafeStackPtr(IRB, F);
+
+  // The top of the unsafe stack after all unsafe static allocas are allocated.
+  Value *StaticTop = moveStaticAllocasToUnsafeStack(IRB, F, StaticAllocas,
+                                                    ByValArguments, Returns);
+
+  // Safe stack object that stores the current unsafe stack top. It is updated
+  // as unsafe dynamic (non-constant-sized) allocas are allocated and freed.
+  // This is only needed if we need to restore stack pointer after longjmp
+  // or exceptions, and we have dynamic allocations.
+  // FIXME: a better alternative might be to store the unsafe stack pointer
+  // before setjmp / invoke instructions.
+  AllocaInst *DynamicTop = createStackRestorePoints(
+      IRB, F, StackRestorePoints, StaticTop, !DynamicAllocas.empty());
+
+  // Handle dynamic allocas.
+  moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop,
+                                  DynamicAllocas);
+
+  DEBUG(dbgs() << "[SafeStack]     safestack applied\n");
+  return true;
+}
+
+} // anonymous namespace
+
+char SafeStack::ID = 0;
+INITIALIZE_TM_PASS_BEGIN(SafeStack, "safe-stack",
+                         "Safe Stack instrumentation pass", false, false)
+INITIALIZE_TM_PASS_END(SafeStack, "safe-stack",
+                       "Safe Stack instrumentation pass", false, false)
+
+FunctionPass *llvm::createSafeStackPass(const llvm::TargetMachine *TM) {
+  return new SafeStack(TM);
+}