Use real addr instead of placeholder for signed type info vt ptrs

Author: kovdan01

clang/lib/CodeGen/ItaniumCXXABI.cpp

@@ -3975,18 +3975,9 @@ void ItaniumRTTIBuilder::BuildVTablePointer(const Type *Ty) {
 
   if (const auto &Schema =
           CGM.getCodeGenOpts().PointerAuth.CXXTypeInfoVTablePointer) {
-    llvm::PointerType *PtrTy = llvm::PointerType::get(
-        CGM.getLLVMContext(),
-        CGM.getModule().getDataLayout().getProgramAddressSpace());
-    llvm::Constant *StorageAddress =
-        (Schema.isAddressDiscriminated()
-             ? llvm::ConstantExpr::getIntToPtr(
-                   llvm::ConstantInt::get(
-                       CGM.IntPtrTy,
-                       llvm::ConstantPtrAuth::
-                           AddrDiscriminator_CXXTypeInfoVTablePointer),
-                   PtrTy)
-             : nullptr);
+    // If address discrimination is enabled, we'll re-write that to actual
+    // storage address later in ItaniumRTTIBuilder::BuildTypeInfo.
+    llvm::Constant *StorageAddress = nullptr;
     VTable = CGM.getConstantSignedPointer(VTable, Schema, StorageAddress,
                                           GlobalDecl(), QualType(Ty, 0));
   }
@@ -4107,6 +4098,7 @@ llvm::Constant *ItaniumRTTIBuilder::BuildTypeInfo(
       llvm::GlobalValue::DLLStorageClassTypes DLLStorageClass) {
   // Add the vtable pointer.
   BuildVTablePointer(cast<Type>(Ty));
+  size_t VTablePointerIdx = Fields.size() - 1;
 
   // And the name.
   llvm::GlobalVariable *TypeName = GetAddrOfTypeName(Ty, Linkage);
@@ -4222,7 +4214,6 @@ llvm::Constant *ItaniumRTTIBuilder::BuildTypeInfo(
   }
 
   llvm::Constant *Init = llvm::ConstantStruct::getAnon(Fields);
-
   SmallString<256> Name;
   llvm::raw_svector_ostream Out(Name);
   CGM.getCXXABI().getMangleContext().mangleCXXRTTI(Ty, Out);
@@ -4231,6 +4222,32 @@ llvm::Constant *ItaniumRTTIBuilder::BuildTypeInfo(
   llvm::GlobalVariable *GV =
       new llvm::GlobalVariable(M, Init->getType(),
                                /*isConstant=*/true, Linkage, Init, Name);
+  if (const auto &Schema =
+          CGM.getCodeGenOpts().PointerAuth.CXXTypeInfoVTablePointer) {
+    if (Schema.isAddressDiscriminated()) {
+      // If type info vtable pointer is signed with address discrimination
+      // enabled, we need to place actual storage address (which was unknown
+      // during construction in ItaniumRTTIBuilder::BuildVTablePointer) in the
+      // corresponding field.
+      ConstantInitBuilder Builder(CGM);
+      auto InitBuilder = Builder.beginStruct();
+      for (size_t I = 0; I < Fields.size(); ++I) {
+        if (I != VTablePointerIdx) {
+          InitBuilder.add(Fields[I]);
+          continue;
+        }
+        auto *SignedVTablePointer = cast<llvm::ConstantPtrAuth>(Fields[I]);
+        llvm::Constant *UnsignedVtablePointer =
+            SignedVTablePointer->getPointer();
+        llvm::Constant *StorageAddress =
+            InitBuilder.getAddrOfCurrentPosition(CGM.UnqualPtrTy);
+        InitBuilder.add(CGM.getConstantSignedPointer(
+            UnsignedVtablePointer, Schema, StorageAddress, GlobalDecl(),
+            QualType(cast<Type>(Ty), 0)));
+      }
+      InitBuilder.finishAndSetAsInitializer(GV);
+    }
+  }
 
   // Export the typeinfo in the same circumstances as the vtable is exported.
   auto GVDLLStorageClass = DLLStorageClass;

clang/test/CodeGenCXX/ptrauth-type-info-vtable.cpp

@@ -65,7 +65,7 @@ extern "C" int disc_std_type_info = __builtin_ptrauth_string_discriminator("_ZTV
 
 // NODISC: @_ZTI10TestStruct = constant { ptr, ptr } { ptr ptrauth (ptr getelementptr inbounds (ptr, ptr @_ZTVN10__cxxabiv117__class_type_infoE, i64 2), i32 2), ptr @_ZTS10TestStruct }, align 8
 
-// DISC: @_ZTI10TestStruct = constant { ptr, ptr } { ptr ptrauth (ptr getelementptr inbounds (ptr, ptr @_ZTVN10__cxxabiv117__class_type_infoE, i64 2), i32 2, i64 [[STDTYPEINFO_DISC]], ptr inttoptr (i64 1 to ptr)), ptr @_ZTS10TestStruct }, align 8
+// DISC: @_ZTI10TestStruct = constant { ptr, ptr } { ptr ptrauth (ptr getelementptr inbounds (ptr, ptr @_ZTVN10__cxxabiv117__class_type_infoE, i64 2), i32 2, i64 [[STDTYPEINFO_DISC]], ptr @_ZTI10TestStruct), ptr @_ZTS10TestStruct }, align 8
 
 struct TestStruct {
   virtual ~TestStruct();

llvm/include/llvm/IR/Constants.h

@@ -1067,18 +1067,12 @@ class ConstantPtrAuth final : public Constant {
     return !getAddrDiscriminator()->isNullValue();
   }
 
-  /// Constant values for the address discriminator which have special
-  /// significance to lowering in some contexts.
-  /// - For ctors/dtors, regular address discrimination can't
-  ///   be applied for them since uses of llvm.global_{c|d}tors are disallowed
-  ///   (see Verifier::visitGlobalVariable) and we can't emit getelementptr
-  ///   expressions referencing these special arrays.
-  /// - For vtable pointers of std::type_info and classes derived from it,
-  ///   we do not know the storage address when emitting ptrauth constant.
-  enum {
-    AddrDiscriminator_CtorsDtors = 1,
-    AddrDiscriminator_CXXTypeInfoVTablePointer = 1
-  };
+  /// A constant value for the address discriminator which has special
+  /// significance to ctors/dtors lowering. Regular address discrimination can't
+  /// be applied for them since uses of llvm.global_{c|d}tors are disallowed
+  /// (see Verifier::visitGlobalVariable) and we can't emit getelementptr
+  /// expressions referencing these special arrays.
+  enum { AddrDiscriminator_CtorsDtors = 1 };
 
   /// Whether the address uses a special address discriminator.
   /// These discriminators can't be used in real pointer-auth values; they

llvm/test/CodeGen/AArch64/ptrauth-type-info-vptr-discr.ll

@@ -14,7 +14,7 @@
 @_ZTVN10__cxxabiv117__class_type_infoE = external global [0 x ptr]
 
 @_ZTS10Disc   = constant [4 x i8] c"Disc", align 1
-@_ZTI10Disc   = constant { ptr, ptr } { ptr ptrauth (ptr getelementptr inbounds (ptr, ptr @_ZTVN10__cxxabiv117__class_type_infoE, i64 2), i32 2, i64 45546, ptr inttoptr (i64 1 to ptr)), ptr @_ZTS10Disc }, align 8
+@_ZTI10Disc   = constant { ptr, ptr } { ptr ptrauth (ptr getelementptr inbounds (ptr, ptr @_ZTVN10__cxxabiv117__class_type_infoE, i64 2), i32 2, i64 45546, ptr @_ZTI10Disc), ptr @_ZTS10Disc }, align 8
 
 @_ZTS10NoDisc = constant [6 x i8] c"NoDisc", align 1
 @_ZTI10NoDisc = constant { ptr, ptr } { ptr ptrauth (ptr getelementptr inbounds (ptr, ptr @_ZTVN10__cxxabiv117__class_type_infoE, i64 2), i32 2, i64 45546), ptr @_ZTS10NoDisc }, align 8