vendor/llvm/llvm-trunk-r240225

1 files changed, 608 insertions, 0 deletions

diff --git a/lib/Transforms/Instrumentation/SafeStack.cpp b/lib/Transforms/Instrumentation/SafeStack.cpp
new file mode 100644
index 0000000000000..13c5412183133
--- /dev/null
+++ b/lib/Transforms/Instrumentation/SafeStack.cpp
@@ -0,0 +1,608 @@
+//===-- 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/Transforms/Instrumentation.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/Triple.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/DIBuilder.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/IRBuilder.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/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/ModuleUtils.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "safestack"
+
+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(NumUnsafeStackRestorePoints, "Number of setjmps and landingpads");
+
+} // namespace llvm
+
+namespace {
+
+/// Check whether a given alloca instruction (AI) should 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 IsSafeStackAlloca(const AllocaInst *AI) {
+  // 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 Instruction *, 8> WorkList;
+  WorkList.push_back(AI);
+
+  // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc.
+  while (!WorkList.empty()) {
+    const Instruction *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:
+        // Loading from a pointer is safe.
+        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.
+          return false;
+        // Storing to the pointee is safe.
+        break;
+
+      case Instruction::GetElementPtr:
+        if (!cast<const GetElementPtrInst>(I)->hasAllConstantIndices())
+          // GEP with non-constant indices can lead to memory errors.
+          // This also applies to inbounds GEPs, as the inbounds attribute
+          // represents an assumption that the address is in bounds, rather than
+          // an assertion that it is.
+          return false;
+
+        // We assume that GEP on static alloca with constant indices is safe,
+        // otherwise a compiler would detect it and warn during compilation.
+
+        if (!isa<const ConstantInt>(AI->getArraySize()))
+          // However, if the array size itself is not constant, the access
+          // might still be unsafe at runtime.
+          return false;
+
+      /* fallthrough */
+
+      case Instruction::BitCast:
+      case Instruction::IntToPtr:
+      case Instruction::PHI:
+      case Instruction::PtrToInt:
+      case Instruction::Select:
+        // The object can be safe or not, depending on how the result of the
+        // instruction is used.
+        if (Visited.insert(I).second)
+          WorkList.push_back(cast<const Instruction>(I));
+        break;
+
+      case Instruction::Call:
+      case Instruction::Invoke: {
+        // FIXME: add support for memset and memcpy intrinsics.
+        ImmutableCallSite CS(I);
+
+        // 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'
+        // 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 && !CS.doesNotCapture(A - B))
+            // The parameter is not marked 'nocapture' - unsafe.
+            return false;
+        continue;
+      }
+
+      default:
+        // The object is unsafe if it is used in any other way.
+        return false;
+      }
+    }
+  }
+
+  // All uses of the alloca are safe, we can place it on the safe stack.
+  return true;
+}
+
+/// 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 unsafe ways.
+class SafeStack : public FunctionPass {
+  const DataLayout *DL;
+
+  Type *StackPtrTy;
+  Type *IntPtrTy;
+  Type *Int32Ty;
+  Type *Int8Ty;
+
+  Constant *UnsafeStackPtr;
+
+  /// 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 constant representing a pointer to the unsafe stack
+  /// pointer.
+  Constant *getOrCreateUnsafeStackPtr(Module &M);
+
+  /// \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<ReturnInst *> &Returns,
+                 SmallVectorImpl<Instruction *> &StackRestorePoints);
+
+  /// \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(Function &F,
+                                        ArrayRef<AllocaInst *> StaticAllocas,
+                                        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(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);
+
+public:
+  static char ID; // Pass identification, replacement for typeid.
+  SafeStack() : FunctionPass(ID), DL(nullptr) {
+    initializeSafeStackPass(*PassRegistry::getPassRegistry());
+  }
+
+  virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+    AU.addRequired<AliasAnalysis>();
+  }
+
+  virtual bool doInitialization(Module &M) {
+    DL = &M.getDataLayout();
+
+    StackPtrTy = Type::getInt8PtrTy(M.getContext());
+    IntPtrTy = DL->getIntPtrType(M.getContext());
+    Int32Ty = Type::getInt32Ty(M.getContext());
+    Int8Ty = Type::getInt8Ty(M.getContext());
+
+    UnsafeStackPtr = getOrCreateUnsafeStackPtr(M);
+
+    return false;
+  }
+
+  bool runOnFunction(Function &F);
+
+}; // class SafeStack
+
+Constant *SafeStack::getOrCreateUnsafeStackPtr(Module &M) {
+  // The unsafe stack pointer is stored in a global variable with a magic name.
+  const char *kUnsafeStackPtrVar = "__safestack_unsafe_stack_ptr";
+
+  auto UnsafeStackPtr =
+      dyn_cast_or_null<GlobalVariable>(M.getNamedValue(kUnsafeStackPtrVar));
+
+  if (!UnsafeStackPtr) {
+    // 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(
+        /*Module=*/M, /*Type=*/StackPtrTy,
+        /*isConstant=*/false, /*Linkage=*/GlobalValue::ExternalLinkage,
+        /*Initializer=*/0, /*Name=*/kUnsafeStackPtrVar,
+        /*InsertBefore=*/nullptr,
+        /*ThreadLocalMode=*/GlobalValue::InitialExecTLSModel);
+  } else {
+    // The variable exists, check its type and attributes.
+    if (UnsafeStackPtr->getValueType() != StackPtrTy) {
+      report_fatal_error(Twine(kUnsafeStackPtrVar) + " must have void* type");
+    }
+
+    if (!UnsafeStackPtr->isThreadLocal()) {
+      report_fatal_error(Twine(kUnsafeStackPtrVar) + " must be thread-local");
+    }
+  }
+
+  return UnsafeStackPtr;
+}
+
+void SafeStack::findInsts(Function &F,
+                          SmallVectorImpl<AllocaInst *> &StaticAllocas,
+                          SmallVectorImpl<AllocaInst *> &DynamicAllocas,
+                          SmallVectorImpl<ReturnInst *> &Returns,
+                          SmallVectorImpl<Instruction *> &StackRestorePoints) {
+  for (Instruction &I : inst_range(&F)) {
+    if (auto AI = dyn_cast<AllocaInst>(&I)) {
+      ++NumAllocas;
+
+      if (IsSafeStackAlloca(AI))
+        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");
+    }
+  }
+}
+
+AllocaInst *
+SafeStack::createStackRestorePoints(Function &F,
+                                    ArrayRef<Instruction *> StackRestorePoints,
+                                    Value *StaticTop, bool NeedDynamicTop) {
+  if (StackRestorePoints.empty())
+    return nullptr;
+
+  IRBuilder<> IRB(StaticTop
+                      ? cast<Instruction>(StaticTop)->getNextNode()
+                      : (Instruction *)F.getEntryBlock().getFirstInsertionPt());
+
+  // 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(cast<Instruction>(I->getNextNode()));
+    Value *CurrentTop = DynamicTop ? IRB.CreateLoad(DynamicTop) : StaticTop;
+    IRB.CreateStore(CurrentTop, UnsafeStackPtr);
+  }
+
+  return DynamicTop;
+}
+
+Value *
+SafeStack::moveStaticAllocasToUnsafeStack(Function &F,
+                                          ArrayRef<AllocaInst *> StaticAllocas,
+                                          ArrayRef<ReturnInst *> Returns) {
+  if (StaticAllocas.empty())
+    return nullptr;
+
+  IRBuilder<> IRB(F.getEntryBlock().getFirstInsertionPt());
+  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 (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(cast<Instruction>(BasePointer->getNextNode()));
+    BasePointer = cast<Instruction>(IRB.CreateIntToPtr(
+        IRB.CreateAnd(IRB.CreatePtrToInt(BasePointer, IntPtrTy),
+                      ConstantInt::get(IntPtrTy, ~uint64_t(MaxAlignment - 1))),
+        StackPtrTy));
+  }
+
+  // Allocate space for every unsafe static AllocaInst on the unsafe stack.
+  int64_t StaticOffset = 0; // Current stack top.
+  for (AllocaInst *AI : StaticAllocas) {
+    IRB.SetInsertPoint(AI);
+
+    auto CArraySize = cast<ConstantInt>(AI->getArraySize());
+    Type *Ty = AI->getAllocatedType();
+
+    uint64_t Size = DL->getTypeAllocSize(Ty) * CArraySize->getZExtValue();
+    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 = RoundUpToAlignment(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, NewAI, DIB, /*Deref=*/true);
+    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 = RoundUpToAlignment(StaticOffset, StackAlignment);
+
+  // Update shadow stack pointer in the function epilogue.
+  IRB.SetInsertPoint(cast<Instruction>(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.CreateIntToPtr(SP, 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) {
+  auto AA = &getAnalysis<AliasAnalysis>();
+
+  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;
+  }
+
+  {
+    // 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));
+  }
+
+  if (AA->onlyReadsMemory(&F)) {
+    // XXX: we don't protect against information leak attacks for now.
+    DEBUG(dbgs() << "[SafeStack]     function only reads memory\n");
+    return false;
+  }
+
+  ++NumFunctions;
+
+  SmallVector<AllocaInst *, 16> StaticAllocas;
+  SmallVector<AllocaInst *, 4> DynamicAllocas;
+  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, Returns, StackRestorePoints);
+
+  if (StaticAllocas.empty() && DynamicAllocas.empty() &&
+      StackRestorePoints.empty())
+    return false; // Nothing to do in this function.
+
+  if (!StaticAllocas.empty() || !DynamicAllocas.empty())
+    ++NumUnsafeStackFunctions; // This function has the unsafe stack.
+
+  if (!StackRestorePoints.empty())
+    ++NumUnsafeStackRestorePointsFunctions;
+
+  // The top of the unsafe stack after all unsafe static allocas are allocated.
+  Value *StaticTop = moveStaticAllocasToUnsafeStack(F, StaticAllocas, 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(
+      F, StackRestorePoints, StaticTop, !DynamicAllocas.empty());
+
+  // Handle dynamic allocas.
+  moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop,
+                                  DynamicAllocas);
+
+  DEBUG(dbgs() << "[SafeStack]     safestack applied\n");
+  return true;
+}
+
+} // end anonymous namespace
+
+char SafeStack::ID = 0;
+INITIALIZE_PASS_BEGIN(SafeStack, "safe-stack",
+                      "Safe Stack instrumentation pass", false, false)
+INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
+INITIALIZE_PASS_END(SafeStack, "safe-stack", "Safe Stack instrumentation pass",
+                    false, false)
+
+FunctionPass *llvm::createSafeStackPass() { return new SafeStack(); }