1 files changed, 41 insertions, 1 deletions
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);