4 files changed, 60 insertions, 19 deletions
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 2b0086d22a7..193e4f122af 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -4409,10 +4409,7 @@ RValue CodeGenFunction::EmitCall(QualType CalleeType, const CGCallee &OrigCallee
       SanitizerScope SanScope(this);
       llvm::Constant *FTRTTIConst =
           CGM.GetAddrOfRTTIDescriptor(QualType(FnType, 0), /*ForEH=*/true);
-      llvm::Type *PrefixStructTyElems[] = {
-        PrefixSig->getType(),
-        FTRTTIConst->getType()
-      };
+      llvm::Type *PrefixStructTyElems[] = {PrefixSig->getType(), Int32Ty};
       llvm::StructType *PrefixStructTy = llvm::StructType::get(
           CGM.getLLVMContext(), PrefixStructTyElems, /*isPacked=*/true);
 
@@ -4433,8 +4430,10 @@ RValue CodeGenFunction::EmitCall(QualType CalleeType, const CGCallee &OrigCallee
       EmitBlock(TypeCheck);
       llvm::Value *CalleeRTTIPtr =
           Builder.CreateConstGEP2_32(PrefixStructTy, CalleePrefixStruct, 0, 1);
-      llvm::Value *CalleeRTTI =
+      llvm::Value *CalleeRTTIEncoded =
           Builder.CreateAlignedLoad(CalleeRTTIPtr, getPointerAlign());
+      llvm::Value *CalleeRTTI =
+          DecodeAddrUsedInPrologue(CalleePtr, CalleeRTTIEncoded);
       llvm::Value *CalleeRTTIMatch =
           Builder.CreateICmpEQ(CalleeRTTI, FTRTTIConst);
       llvm::Constant *StaticData[] = {
diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index a9a1a53be20..1c9fc367940 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -429,6 +429,43 @@ bool CodeGenFunction::ShouldXRayInstrumentFunction() const {
   return CGM.getCodeGenOpts().XRayInstrumentFunctions;
 }
 
+llvm::Constant *
+CodeGenFunction::EncodeAddrForUseInPrologue(llvm::Function *F,
+                                            llvm::Constant *Addr) {
+  // Addresses stored in prologue data can't require run-time fixups and must
+  // be PC-relative. Run-time fixups are undesirable because they necessitate
+  // writable text segments, which are unsafe. And absolute addresses are
+  // undesirable because they break PIE mode.
+
+  // Add a layer of indirection through a private global. Taking its address
+  // won't result in a run-time fixup, even if Addr has linkonce_odr linkage.
+  auto *GV = new llvm::GlobalVariable(CGM.getModule(), Addr->getType(),
+                                      /*isConstant=*/true,
+                                      llvm::GlobalValue::PrivateLinkage, Addr);
+
+  // Create a PC-relative address.
+  auto *GOTAsInt = llvm::ConstantExpr::getPtrToInt(GV, IntPtrTy);
+  auto *FuncAsInt = llvm::ConstantExpr::getPtrToInt(F, IntPtrTy);
+  auto *PCRelAsInt = llvm::ConstantExpr::getSub(GOTAsInt, FuncAsInt);
+  return (IntPtrTy == Int32Ty)
+             ? PCRelAsInt
+             : llvm::ConstantExpr::getTrunc(PCRelAsInt, Int32Ty);
+}
+
+llvm::Value *
+CodeGenFunction::DecodeAddrUsedInPrologue(llvm::Value *F,
+                                          llvm::Value *EncodedAddr) {
+  // Reconstruct the address of the global.
+  auto *PCRelAsInt = Builder.CreateSExt(EncodedAddr, IntPtrTy);
+  auto *FuncAsInt = Builder.CreatePtrToInt(F, IntPtrTy, "func_addr.int");
+  auto *GOTAsInt = Builder.CreateAdd(PCRelAsInt, FuncAsInt, "global_addr.int");
+  auto *GOTAddr = Builder.CreateIntToPtr(GOTAsInt, Int8PtrPtrTy, "global_addr");
+
+  // Load the original pointer through the global.
+  return Builder.CreateLoad(Address(GOTAddr, getPointerAlign()),
+                            "decoded_addr");
+}
+
 /// EmitFunctionInstrumentation - Emit LLVM code to call the specified
 /// instrumentation function with the current function and the call site, if
 /// function instrumentation is enabled.
@@ -856,7 +893,10 @@ void CodeGenFunction::StartFunction(GlobalDecl GD,
               CGM.getTargetCodeGenInfo().getUBSanFunctionSignature(CGM)) {
         llvm::Constant *FTRTTIConst =
             CGM.GetAddrOfRTTIDescriptor(FD->getType(), /*ForEH=*/true);
-        llvm::Constant *PrologueStructElems[] = { PrologueSig, FTRTTIConst };
+        llvm::Constant *FTRTTIConstEncoded =
+            EncodeAddrForUseInPrologue(Fn, FTRTTIConst);
+        llvm::Constant *PrologueStructElems[] = {PrologueSig,
+                                                 FTRTTIConstEncoded};
         llvm::Constant *PrologueStructConst =
             llvm::ConstantStruct::getAnon(PrologueStructElems, /*Packed=*/true);
         Fn->setPrologueData(PrologueStructConst);
diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index a3b9beb2988..33bf74b5d39 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -1776,6 +1776,15 @@ public:
   /// EmitMCountInstrumentation - Emit call to .mcount.
   void EmitMCountInstrumentation();
 
+  /// Encode an address into a form suitable for use in a function prologue.
+  llvm::Constant *EncodeAddrForUseInPrologue(llvm::Function *F,
+                                             llvm::Constant *Addr);
+
+  /// Decode an address used in a function prologue, encoded by \c
+  /// EncodeAddrForUseInPrologue.
+  llvm::Value *DecodeAddrUsedInPrologue(llvm::Value *F,
+                                        llvm::Value *EncodedAddr);
+
   /// EmitFunctionProlog - Emit the target specific LLVM code to load the
   /// arguments for the given function. This is also responsible for naming the
   /// LLVM function arguments.
diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index 10fa2ea322c..934e155ccdf 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -1086,8 +1086,8 @@ public:
   getUBSanFunctionSignature(CodeGen::CodeGenModule &CGM) const override {
     unsigned Sig = (0xeb << 0) |  // jmp rel8
                    (0x06 << 8) |  //           .+0x08
-                   ('F' << 16) |
-                   ('T' << 24);
+                   ('v' << 16) |
+                   ('2' << 24);
     return llvm::ConstantInt::get(CGM.Int32Ty, Sig);
   }
 
@@ -2277,17 +2277,10 @@ public:
 
   llvm::Constant *
   getUBSanFunctionSignature(CodeGen::CodeGenModule &CGM) const override {
-    unsigned Sig;
-    if (getABIInfo().has64BitPointers())
-      Sig = (0xeb << 0) |  // jmp rel8
-            (0x0a << 8) |  //           .+0x0c
-            ('F' << 16) |
-            ('T' << 24);
-    else
-      Sig = (0xeb << 0) |  // jmp rel8
-            (0x06 << 8) |  //           .+0x08
-            ('F' << 16) |
-            ('T' << 24);
+    unsigned Sig = (0xeb << 0) | // jmp rel8
+                   (0x06 << 8) | //           .+0x08
+                   ('v' << 16) |
+                   ('2' << 24);
     return llvm::ConstantInt::get(CGM.Int32Ty, Sig);
   }