[asan] ASan Linux MIPS32 support (llvm part), patch by Jyun-Yan Y
[oota-llvm.git] / lib / Transforms / Instrumentation / AddressSanitizer.cpp
index b97e3425bccaae4d7dc3582851630939eaf1f463..22851b46e8ac699122b0c1caca8f0b0bf6d323cb 100644 (file)
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Type.h"
 #include "llvm/InstVisitor.h"
+#include "llvm/Support/CallSite.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/DataTypes.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/Endian.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Support/system_error.h"
-#include "llvm/Target/TargetMachine.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/BlackList.h"
 #include "llvm/Transforms/Utils/Local.h"
@@ -55,6 +56,7 @@ static const uint64_t kDefaultShadowOffset32 = 1ULL << 29;
 static const uint64_t kDefaultShadowOffset64 = 1ULL << 44;
 static const uint64_t kDefaultShort64bitShadowOffset = 0x7FFF8000;  // < 2G.
 static const uint64_t kPPC64_ShadowOffset64 = 1ULL << 41;
+static const uint64_t kMIPS32_ShadowOffset32 = 0x0aaa8000;
 
 static const size_t kMaxStackMallocSize = 1 << 16;  // 64K
 static const uintptr_t kCurrentStackFrameMagic = 0x41B58AB3;
@@ -64,11 +66,13 @@ static const char *kAsanModuleCtorName = "asan.module_ctor";
 static const char *kAsanModuleDtorName = "asan.module_dtor";
 static const int   kAsanCtorAndCtorPriority = 1;
 static const char *kAsanReportErrorTemplate = "__asan_report_";
+static const char *kAsanReportLoadN = "__asan_report_load_n";
+static const char *kAsanReportStoreN = "__asan_report_store_n";
 static const char *kAsanRegisterGlobalsName = "__asan_register_globals";
 static const char *kAsanUnregisterGlobalsName = "__asan_unregister_globals";
 static const char *kAsanPoisonGlobalsName = "__asan_before_dynamic_init";
 static const char *kAsanUnpoisonGlobalsName = "__asan_after_dynamic_init";
-static const char *kAsanInitName = "__asan_init_v1";
+static const char *kAsanInitName = "__asan_init_v3";
 static const char *kAsanHandleNoReturnName = "__asan_handle_no_return";
 static const char *kAsanMappingOffsetName = "__asan_mapping_offset";
 static const char *kAsanMappingScaleName = "__asan_mapping_scale";
@@ -205,6 +209,8 @@ static ShadowMapping getShadowMapping(const Module &M, int LongSize,
   bool IsMacOSX = TargetTriple.getOS() == llvm::Triple::MacOSX;
   bool IsPPC64 = TargetTriple.getArch() == llvm::Triple::ppc64;
   bool IsX86_64 = TargetTriple.getArch() == llvm::Triple::x86_64;
+  bool IsMIPS32 = TargetTriple.getArch() == llvm::Triple::mips ||
+                  TargetTriple.getArch() == llvm::Triple::mipsel;
 
   ShadowMapping Mapping;
 
@@ -214,7 +220,8 @@ static ShadowMapping getShadowMapping(const Module &M, int LongSize,
   Mapping.OrShadowOffset = !IsPPC64 && !ClShort64BitOffset;
 
   Mapping.Offset = (IsAndroid || ZeroBaseShadow) ? 0 :
-      (LongSize == 32 ? kDefaultShadowOffset32 :
+      (LongSize == 32 ?
+       (IsMIPS32 ? kMIPS32_ShadowOffset32 : kDefaultShadowOffset32) :
        IsPPC64 ? kPPC64_ShadowOffset64 : kDefaultShadowOffset64);
   if (!ZeroBaseShadow && ClShort64BitOffset && IsX86_64 && !IsMacOSX) {
     assert(LongSize == 64);
@@ -241,7 +248,7 @@ static size_t RedzoneSizeForScale(int MappingScale) {
 
 /// AddressSanitizer: instrument the code in module to find memory bugs.
 struct AddressSanitizer : public FunctionPass {
-  AddressSanitizer(bool CheckInitOrder = false,
+  AddressSanitizer(bool CheckInitOrder = true,
                    bool CheckUseAfterReturn = false,
                    bool CheckLifetime = false,
                    StringRef BlacklistFile = StringRef(),
@@ -257,20 +264,20 @@ struct AddressSanitizer : public FunctionPass {
     return "AddressSanitizerFunctionPass";
   }
   void instrumentMop(Instruction *I);
-  void instrumentAddress(Instruction *OrigIns, IRBuilder<> &IRB,
-                         Value *Addr, uint32_t TypeSize, bool IsWrite);
+  void instrumentAddress(Instruction *OrigIns, Instruction *InsertBefore,
+                         Value *Addr, uint32_t TypeSize, bool IsWrite,
+                         Value *SizeArgument);
   Value *createSlowPathCmp(IRBuilder<> &IRB, Value *AddrLong,
                            Value *ShadowValue, uint32_t TypeSize);
   Instruction *generateCrashCode(Instruction *InsertBefore, Value *Addr,
-                                 bool IsWrite, size_t AccessSizeIndex);
+                                 bool IsWrite, size_t AccessSizeIndex,
+                                 Value *SizeArgument);
   bool instrumentMemIntrinsic(MemIntrinsic *MI);
   void instrumentMemIntrinsicParam(Instruction *OrigIns, Value *Addr,
                                    Value *Size,
                                    Instruction *InsertBefore, bool IsWrite);
   Value *memToShadow(Value *Shadow, IRBuilder<> &IRB);
   bool runOnFunction(Function &F);
-  void createInitializerPoisonCalls(Module &M,
-                                    Value *FirstAddr, Value *LastAddr);
   bool maybeInsertAsanInitAtFunctionEntry(Function &F);
   void emitShadowMapping(Module &M, IRBuilder<> &IRB) const;
   virtual bool doInitialization(Module &M);
@@ -300,6 +307,8 @@ struct AddressSanitizer : public FunctionPass {
   OwningPtr<BlackList> BL;
   // This array is indexed by AccessIsWrite and log2(AccessSize).
   Function *AsanErrorCallback[2][kNumberOfAccessSizes];
+  // This array is indexed by AccessIsWrite.
+  Function *AsanErrorCallbackSized[2];
   InlineAsm *EmptyAsm;
   SetOfDynamicallyInitializedGlobals DynamicallyInitializedGlobals;
 
@@ -308,7 +317,7 @@ struct AddressSanitizer : public FunctionPass {
 
 class AddressSanitizerModule : public ModulePass {
  public:
-  AddressSanitizerModule(bool CheckInitOrder = false,
+  AddressSanitizerModule(bool CheckInitOrder = true,
                          StringRef BlacklistFile = StringRef(),
                          bool ZeroBaseShadow = false)
       : ModulePass(ID),
@@ -326,8 +335,7 @@ class AddressSanitizerModule : public ModulePass {
   void initializeCallbacks(Module &M);
 
   bool ShouldInstrumentGlobal(GlobalVariable *G);
-  void createInitializerPoisonCalls(Module &M, Value *FirstAddr,
-                                    Value *LastAddr);
+  void createInitializerPoisonCalls(Module &M, GlobalValue *ModuleName);
   size_t RedzoneSize() const {
     return RedzoneSizeForScale(Mapping.Scale);
   }
@@ -516,7 +524,7 @@ ModulePass *llvm::createAddressSanitizerModulePass(
 }
 
 static size_t TypeSizeToSizeIndex(uint32_t TypeSize) {
-  size_t Res = CountTrailingZeros_32(TypeSize / 8);
+  size_t Res = countTrailingZeros(TypeSize / 8);
   assert(Res < kNumberOfAccessSizes);
   return Res;
 }
@@ -524,9 +532,12 @@ static size_t TypeSizeToSizeIndex(uint32_t TypeSize) {
 // Create a constant for Str so that we can pass it to the run-time lib.
 static GlobalVariable *createPrivateGlobalForString(Module &M, StringRef Str) {
   Constant *StrConst = ConstantDataArray::getString(M.getContext(), Str);
-  return new GlobalVariable(M, StrConst->getType(), true,
+  GlobalVariable *GV = new GlobalVariable(M, StrConst->getType(), true,
                             GlobalValue::PrivateLinkage, StrConst,
                             kAsanGenPrefix);
+  GV->setUnnamedAddr(true);  // Ok to merge these.
+  GV->setAlignment(1);  // Strings may not be merged w/o setting align 1.
+  return GV;
 }
 
 static bool GlobalWasGeneratedByAsan(GlobalVariable *G) {
@@ -548,21 +559,17 @@ Value *AddressSanitizer::memToShadow(Value *Shadow, IRBuilder<> &IRB) {
 void AddressSanitizer::instrumentMemIntrinsicParam(
     Instruction *OrigIns,
     Value *Addr, Value *Size, Instruction *InsertBefore, bool IsWrite) {
+  IRBuilder<> IRB(InsertBefore);
+  if (Size->getType() != IntptrTy)
+    Size = IRB.CreateIntCast(Size, IntptrTy, false);
   // Check the first byte.
-  {
-    IRBuilder<> IRB(InsertBefore);
-    instrumentAddress(OrigIns, IRB, Addr, 8, IsWrite);
-  }
+  instrumentAddress(OrigIns, InsertBefore, Addr, 8, IsWrite, Size);
   // Check the last byte.
-  {
-    IRBuilder<> IRB(InsertBefore);
-    Value *SizeMinusOne = IRB.CreateSub(
-        Size, ConstantInt::get(Size->getType(), 1));
-    SizeMinusOne = IRB.CreateIntCast(SizeMinusOne, IntptrTy, false);
-    Value *AddrLong = IRB.CreatePointerCast(Addr, IntptrTy);
-    Value *AddrPlusSizeMinisOne = IRB.CreateAdd(AddrLong, SizeMinusOne);
-    instrumentAddress(OrigIns, IRB, AddrPlusSizeMinisOne, 8, IsWrite);
-  }
+  IRB.SetInsertPoint(InsertBefore);
+  Value *SizeMinusOne = IRB.CreateSub(Size, ConstantInt::get(IntptrTy, 1));
+  Value *AddrLong = IRB.CreatePointerCast(Addr, IntptrTy);
+  Value *AddrLast = IRB.CreateAdd(AddrLong, SizeMinusOne);
+  instrumentAddress(OrigIns, InsertBefore, AddrLast, 8, IsWrite, Size);
 }
 
 // Instrument memset/memmove/memcpy
@@ -641,14 +648,24 @@ void AddressSanitizer::instrumentMop(Instruction *I) {
   assert(OrigTy->isSized());
   uint32_t TypeSize = TD->getTypeStoreSizeInBits(OrigTy);
 
-  if (TypeSize != 8  && TypeSize != 16 &&
-      TypeSize != 32 && TypeSize != 64 && TypeSize != 128) {
-    // Ignore all unusual sizes.
-    return;
-  }
+  assert((TypeSize % 8) == 0);
 
+  // Instrument a 1-, 2-, 4-, 8-, or 16- byte access with one check.
+  if (TypeSize == 8  || TypeSize == 16 ||
+      TypeSize == 32 || TypeSize == 64 || TypeSize == 128)
+    return instrumentAddress(I, I, Addr, TypeSize, IsWrite, 0);
+  // Instrument unusual size (but still multiple of 8).
+  // We can not do it with a single check, so we do 1-byte check for the first
+  // and the last bytes. We call __asan_report_*_n(addr, real_size) to be able
+  // to report the actual access size.
   IRBuilder<> IRB(I);
-  instrumentAddress(I, IRB, Addr, TypeSize, IsWrite);
+  Value *LastByte =  IRB.CreateIntToPtr(
+      IRB.CreateAdd(IRB.CreatePointerCast(Addr, IntptrTy),
+                    ConstantInt::get(IntptrTy, TypeSize / 8 - 1)),
+      OrigPtrTy);
+  Value *Size = ConstantInt::get(IntptrTy, TypeSize / 8);
+  instrumentAddress(I, I, Addr, 8, IsWrite, Size);
+  instrumentAddress(I, I, LastByte, 8, IsWrite, Size);
 }
 
 // Validate the result of Module::getOrInsertFunction called for an interface
@@ -664,10 +681,12 @@ static Function *checkInterfaceFunction(Constant *FuncOrBitcast) {
 
 Instruction *AddressSanitizer::generateCrashCode(
     Instruction *InsertBefore, Value *Addr,
-    bool IsWrite, size_t AccessSizeIndex) {
+    bool IsWrite, size_t AccessSizeIndex, Value *SizeArgument) {
   IRBuilder<> IRB(InsertBefore);
-  CallInst *Call = IRB.CreateCall(AsanErrorCallback[IsWrite][AccessSizeIndex],
-                                  Addr);
+  CallInst *Call = SizeArgument
+    ? IRB.CreateCall2(AsanErrorCallbackSized[IsWrite], Addr, SizeArgument)
+    : IRB.CreateCall(AsanErrorCallback[IsWrite][AccessSizeIndex], Addr);
+
   // We don't do Call->setDoesNotReturn() because the BB already has
   // UnreachableInst at the end.
   // This EmptyAsm is required to avoid callback merge.
@@ -694,8 +713,10 @@ Value *AddressSanitizer::createSlowPathCmp(IRBuilder<> &IRB, Value *AddrLong,
 }
 
 void AddressSanitizer::instrumentAddress(Instruction *OrigIns,
-                                         IRBuilder<> &IRB, Value *Addr,
-                                         uint32_t TypeSize, bool IsWrite) {
+                                         Instruction *InsertBefore,
+                                         Value *Addr, uint32_t TypeSize,
+                                         bool IsWrite, Value *SizeArgument) {
+  IRBuilder<> IRB(InsertBefore);
   Value *AddrLong = IRB.CreatePointerCast(Addr, IntptrTy);
 
   Type *ShadowTy  = IntegerType::get(
@@ -727,13 +748,13 @@ void AddressSanitizer::instrumentAddress(Instruction *OrigIns,
     CrashTerm = SplitBlockAndInsertIfThen(cast<Instruction>(Cmp), true);
   }
 
-  Instruction *Crash =
-      generateCrashCode(CrashTerm, AddrLong, IsWrite, AccessSizeIndex);
+  Instruction *Crash = generateCrashCode(
+      CrashTerm, AddrLong, IsWrite, AccessSizeIndex, SizeArgument);
   Crash->setDebugLoc(OrigIns->getDebugLoc());
 }
 
 void AddressSanitizerModule::createInitializerPoisonCalls(
-    Module &M, Value *FirstAddr, Value *LastAddr) {
+    Module &M, GlobalValue *ModuleName) {
   // We do all of our poisoning and unpoisoning within _GLOBAL__I_a.
   Function *GlobalInit = M.getFunction("_GLOBAL__I_a");
   // If that function is not present, this TU contains no globals, or they have
@@ -745,7 +766,8 @@ void AddressSanitizerModule::createInitializerPoisonCalls(
   IRBuilder<> IRB(GlobalInit->begin()->getFirstInsertionPt());
 
   // Add a call to poison all external globals before the given function starts.
-  IRB.CreateCall2(AsanPoisonGlobals, FirstAddr, LastAddr);
+  Value *ModuleNameAddr = ConstantExpr::getPointerCast(ModuleName, IntptrTy);
+  IRB.CreateCall(AsanPoisonGlobals, ModuleNameAddr);
 
   // Add calls to unpoison all globals before each return instruction.
   for (Function::iterator I = GlobalInit->begin(), E = GlobalInit->end();
@@ -819,7 +841,7 @@ void AddressSanitizerModule::initializeCallbacks(Module &M) {
   IRBuilder<> IRB(*C);
   // Declare our poisoning and unpoisoning functions.
   AsanPoisonGlobals = checkInterfaceFunction(M.getOrInsertFunction(
-      kAsanPoisonGlobalsName, IRB.getVoidTy(), IntptrTy, IntptrTy, NULL));
+      kAsanPoisonGlobalsName, IRB.getVoidTy(), IntptrTy, NULL));
   AsanPoisonGlobals->setLinkage(Function::ExternalLinkage);
   AsanUnpoisonGlobals = checkInterfaceFunction(M.getOrInsertFunction(
       kAsanUnpoisonGlobalsName, IRB.getVoidTy(), NULL));
@@ -868,11 +890,12 @@ bool AddressSanitizerModule::runOnModule(Module &M) {
   //   size_t size;
   //   size_t size_with_redzone;
   //   const char *name;
+  //   const char *module_name;
   //   size_t has_dynamic_init;
   // We initialize an array of such structures and pass it to a run-time call.
   StructType *GlobalStructTy = StructType::get(IntptrTy, IntptrTy,
                                                IntptrTy, IntptrTy,
-                                               IntptrTy, NULL);
+                                               IntptrTy, IntptrTy, NULL);
   SmallVector<Constant *, 16> Initializers(n), DynamicInit;
 
 
@@ -880,9 +903,13 @@ bool AddressSanitizerModule::runOnModule(Module &M) {
   assert(CtorFunc);
   IRBuilder<> IRB(CtorFunc->getEntryBlock().getTerminator());
 
-  // The addresses of the first and last dynamically initialized globals in
-  // this TU.  Used in initialization order checking.
-  Value *FirstDynamic = 0, *LastDynamic = 0;
+  bool HasDynamicallyInitializedGlobals = false;
+
+  GlobalVariable *ModuleName = createPrivateGlobalForString(
+      M, M.getModuleIdentifier());
+  // We shouldn't merge same module names, as this string serves as unique
+  // module ID in runtime.
+  ModuleName->setUnnamedAddr(false);
 
   for (size_t i = 0; i < n; i++) {
     static const uint64_t kMaxGlobalRedzone = 1 << 18;
@@ -913,11 +940,7 @@ bool AddressSanitizerModule::runOnModule(Module &M) {
         NewTy, G->getInitializer(),
         Constant::getNullValue(RightRedZoneTy), NULL);
 
-    SmallString<2048> DescriptionOfGlobal = G->getName();
-    DescriptionOfGlobal += " (";
-    DescriptionOfGlobal += M.getModuleIdentifier();
-    DescriptionOfGlobal += ")";
-    GlobalVariable *Name = createPrivateGlobalForString(M, DescriptionOfGlobal);
+    GlobalVariable *Name = createPrivateGlobalForString(M, G->getName());
 
     // Create a new global variable with enough space for a redzone.
     GlobalVariable *NewGlobal = new GlobalVariable(
@@ -941,15 +964,13 @@ bool AddressSanitizerModule::runOnModule(Module &M) {
         ConstantInt::get(IntptrTy, SizeInBytes),
         ConstantInt::get(IntptrTy, SizeInBytes + RightRedzoneSize),
         ConstantExpr::getPointerCast(Name, IntptrTy),
+        ConstantExpr::getPointerCast(ModuleName, IntptrTy),
         ConstantInt::get(IntptrTy, GlobalHasDynamicInitializer),
         NULL);
 
     // Populate the first and last globals declared in this TU.
-    if (CheckInitOrder && GlobalHasDynamicInitializer) {
-      LastDynamic = ConstantExpr::getPointerCast(NewGlobal, IntptrTy);
-      if (FirstDynamic == 0)
-        FirstDynamic = LastDynamic;
-    }
+    if (CheckInitOrder && GlobalHasDynamicInitializer)
+      HasDynamicallyInitializedGlobals = true;
 
     DEBUG(dbgs() << "NEW GLOBAL: " << *NewGlobal << "\n");
   }
@@ -960,8 +981,8 @@ bool AddressSanitizerModule::runOnModule(Module &M) {
       ConstantArray::get(ArrayOfGlobalStructTy, Initializers), "");
 
   // Create calls for poisoning before initializers run and unpoisoning after.
-  if (CheckInitOrder && FirstDynamic && LastDynamic)
-    createInitializerPoisonCalls(M, FirstDynamic, LastDynamic);
+  if (CheckInitOrder && HasDynamicallyInitializedGlobals)
+    createInitializerPoisonCalls(M, ModuleName);
   IRB.CreateCall2(AsanRegisterGlobals,
                   IRB.CreatePointerCast(AllGlobals, IntptrTy),
                   ConstantInt::get(IntptrTy, n));
@@ -997,6 +1018,10 @@ void AddressSanitizer::initializeCallbacks(Module &M) {
               FunctionName, IRB.getVoidTy(), IntptrTy, NULL));
     }
   }
+  AsanErrorCallbackSized[0] = checkInterfaceFunction(M.getOrInsertFunction(
+              kAsanReportLoadN, IRB.getVoidTy(), IntptrTy, IntptrTy, NULL));
+  AsanErrorCallbackSized[1] = checkInterfaceFunction(M.getOrInsertFunction(
+              kAsanReportStoreN, IRB.getVoidTy(), IntptrTy, IntptrTy, NULL));
 
   AsanHandleNoReturnFunc = checkInterfaceFunction(M.getOrInsertFunction(
       kAsanHandleNoReturnName, IRB.getVoidTy(), NULL));
@@ -1074,14 +1099,15 @@ bool AddressSanitizer::maybeInsertAsanInitAtFunctionEntry(Function &F) {
 bool AddressSanitizer::runOnFunction(Function &F) {
   if (BL->isIn(F)) return false;
   if (&F == AsanCtorFunction) return false;
+  if (F.getLinkage() == GlobalValue::AvailableExternallyLinkage) return false;
   DEBUG(dbgs() << "ASAN instrumenting:\n" << F << "\n");
   initializeCallbacks(*F.getParent());
 
-  // If needed, insert __asan_init before checking for AddressSafety attr.
+  // If needed, insert __asan_init before checking for SanitizeAddress attr.
   maybeInsertAsanInitAtFunctionEntry(F);
 
   if (!F.getAttributes().hasAttribute(AttributeSet::FunctionIndex,
-                                      Attribute::AddressSafety))
+                                      Attribute::SanitizeAddress))
     return false;
 
   if (!ClDebugFunc.empty() && ClDebugFunc != F.getName())
@@ -1110,12 +1136,12 @@ bool AddressSanitizer::runOnFunction(Function &F) {
       } else if (isa<MemIntrinsic>(BI) && ClMemIntrin) {
         // ok, take it.
       } else {
-        if (CallInst *CI = dyn_cast<CallInst>(BI)) {
+        CallSite CS(BI);
+        if (CS) {
           // A call inside BB.
           TempsToInstrument.clear();
-          if (CI->doesNotReturn()) {
-            NoReturnCalls.push_back(CI);
-          }
+          if (CS.doesNotReturn())
+            NoReturnCalls.push_back(CS.getInstruction());
         }
         continue;
       }
@@ -1248,6 +1274,10 @@ void FunctionStackPoisoner::poisonRedZones(
                                         RedzoneSize(),
                                         1ULL << Mapping.Scale,
                                         kAsanStackPartialRedzoneMagic);
+        Poison =
+            ASan.TD->isLittleEndian()
+                ? support::endian::byte_swap<uint32_t, support::little>(Poison)
+                : support::endian::byte_swap<uint32_t, support::big>(Poison);
       }
       Value *PartialPoison = ConstantInt::get(RZTy, Poison);
       IRB.CreateStore(PartialPoison, IRB.CreateIntToPtr(Ptr, RZPtrTy));
@@ -1291,10 +1321,10 @@ void FunctionStackPoisoner::poisonStack() {
         ConstantInt::get(IntptrTy, LocalStackSize), OrigStackBase);
   }
 
-  // This string will be parsed by the run-time (DescribeStackAddress).
+  // This string will be parsed by the run-time (DescribeAddressIfStack).
   SmallString<2048> StackDescriptionStorage;
   raw_svector_ostream StackDescription(StackDescriptionStorage);
-  StackDescription << F.getName() << " " << AllocaVec.size() << " ";
+  StackDescription << AllocaVec.size() << " ";
 
   // Insert poison calls for lifetime intrinsics for alloca.
   bool HavePoisonedAllocas = false;
@@ -1327,19 +1357,26 @@ void FunctionStackPoisoner::poisonStack() {
   }
   assert(Pos == LocalStackSize);
 
-  // Write the Magic value and the frame description constant to the redzone.
+  // The left-most redzone has enough space for at least 4 pointers.
+  // Write the Magic value to redzone[0].
   Value *BasePlus0 = IRB.CreateIntToPtr(LocalStackBase, IntptrPtrTy);
   IRB.CreateStore(ConstantInt::get(IntptrTy, kCurrentStackFrameMagic),
                   BasePlus0);
-  Value *BasePlus1 = IRB.CreateAdd(LocalStackBase,
-                                   ConstantInt::get(IntptrTy,
-                                                    ASan.LongSize/8));
-  BasePlus1 = IRB.CreateIntToPtr(BasePlus1, IntptrPtrTy);
+  // Write the frame description constant to redzone[1].
+  Value *BasePlus1 = IRB.CreateIntToPtr(
+    IRB.CreateAdd(LocalStackBase, ConstantInt::get(IntptrTy, ASan.LongSize/8)),
+    IntptrPtrTy);
   GlobalVariable *StackDescriptionGlobal =
       createPrivateGlobalForString(*F.getParent(), StackDescription.str());
   Value *Description = IRB.CreatePointerCast(StackDescriptionGlobal,
                                              IntptrTy);
   IRB.CreateStore(Description, BasePlus1);
+  // Write the PC to redzone[2].
+  Value *BasePlus2 = IRB.CreateIntToPtr(
+    IRB.CreateAdd(LocalStackBase, ConstantInt::get(IntptrTy,
+                                                   2 * ASan.LongSize/8)),
+    IntptrPtrTy);
+  IRB.CreateStore(IRB.CreatePointerCast(&F, IntptrTy), BasePlus2);
 
   // Poison the stack redzones at the entry.
   Value *ShadowBase = ASan.memToShadow(LocalStackBase, IRB);