[PAC] Fix codegen for polymorphic class variables with consteval constructors #154858

ahatanak · 2025-08-21T23:39:16Z

Fix a bug in CodeGen where such variables could cause a compilation error or be emitted with an undef initializer when the vtable was signed with address discrimination.

rdar://155696134

constructors Fix a bug in CodeGen where such variables could cause a compilation error or be emitted with an undef initializer. rdar://155696134

llvmbot · 2025-08-21T23:39:47Z

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-codegen

Author: Akira Hatanaka (ahatanak)

Changes

Fix a bug in CodeGen where such variables could cause a compilation error or be emitted with an undef initializer.

rdar://155696134

Full diff: https://github.com/llvm/llvm-project/pull/154858.diff

2 Files Affected:

(modified) clang/lib/CodeGen/CGExprConstant.cpp (+4-3)
(modified) clang/test/CodeGenCXX/ptrauth-explicit-vtable-pointer-control.cpp (+29-8)

diff --git a/clang/lib/CodeGen/CGExprConstant.cpp b/clang/lib/CodeGen/CGExprConstant.cpp
index a96c1518d2a1d..3c1bdf9120d21 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -876,8 +876,9 @@ bool ConstStructBuilder::Build(const APValue &Val, const RecordDecl *RD,
 
     for (const BaseInfo &Base : Bases) {
       bool IsPrimaryBase = Layout.getPrimaryBase() == Base.Decl;
-      Build(Val.getStructBase(Base.Index), Base.Decl, IsPrimaryBase,
-            VTableClass, Offset + Base.Offset);
+      if (!Build(Val.getStructBase(Base.Index), Base.Decl, IsPrimaryBase,
+                 VTableClass, Offset + Base.Offset))
+        return false;
     }
   }
 
@@ -1627,7 +1628,7 @@ llvm::Constant *ConstantEmitter::tryEmitConstantExpr(const ConstantExpr *CE) {
   if (CE->isGLValue())
     RetType = CGM.getContext().getLValueReferenceType(RetType);
 
-  return emitAbstract(CE->getBeginLoc(), CE->getAPValueResult(), RetType);
+  return tryEmitAbstract(CE->getAPValueResult(), RetType);
 }
 
 llvm::Constant *
diff --git a/clang/test/CodeGenCXX/ptrauth-explicit-vtable-pointer-control.cpp b/clang/test/CodeGenCXX/ptrauth-explicit-vtable-pointer-control.cpp
index 1b103719fbe46..e33525c1ec0f9 100644
--- a/clang/test/CodeGenCXX/ptrauth-explicit-vtable-pointer-control.cpp
+++ b/clang/test/CodeGenCXX/ptrauth-explicit-vtable-pointer-control.cpp
@@ -1,31 +1,31 @@
-// RUN: %clang_cc1 %s -x c++ -std=c++11 -triple arm64-apple-ios -fptrauth-calls -fptrauth-intrinsics \
+// RUN: %clang_cc1 %s -x c++ -std=c++20 -triple arm64-apple-ios -fptrauth-calls -fptrauth-intrinsics \
 // RUN:   -emit-llvm -o - | FileCheck --check-prefixes=CHECK,NODISC %s
 
-// RUN: %clang_cc1 %s -x c++ -std=c++11 -triple arm64-apple-ios   -fptrauth-calls -fptrauth-intrinsics \
+// RUN: %clang_cc1 %s -x c++ -std=c++20 -triple arm64-apple-ios   -fptrauth-calls -fptrauth-intrinsics \
 // RUN:   -fptrauth-vtable-pointer-type-discrimination \
 // RUN:   -emit-llvm -o - | FileCheck --check-prefixes=CHECK,TYPE %s
 
-// RUN: %clang_cc1 %s -x c++ -std=c++11 -triple arm64-apple-ios   -fptrauth-calls -fptrauth-intrinsics \
+// RUN: %clang_cc1 %s -x c++ -std=c++20 -triple arm64-apple-ios   -fptrauth-calls -fptrauth-intrinsics \
 // RUN:   -fptrauth-vtable-pointer-address-discrimination \
 // RUN:   -emit-llvm -o - | FileCheck --check-prefixes=CHECK,ADDR %s
 
-// RUN: %clang_cc1 %s -x c++ -std=c++11 -triple arm64-apple-ios   -fptrauth-calls -fptrauth-intrinsics \
+// RUN: %clang_cc1 %s -x c++ -std=c++20 -triple arm64-apple-ios   -fptrauth-calls -fptrauth-intrinsics \
 // RUN:   -fptrauth-vtable-pointer-type-discrimination \
 // RUN:   -fptrauth-vtable-pointer-address-discrimination \
 // RUN:   -emit-llvm -o - | FileCheck --check-prefixes=CHECK,BOTH %s
 
-// RUN: %clang_cc1 %s -x c++ -std=c++11 -triple aarch64-linux-gnu -fptrauth-calls -fptrauth-intrinsics \
+// RUN: %clang_cc1 %s -x c++ -std=c++20 -triple aarch64-linux-gnu -fptrauth-calls -fptrauth-intrinsics \
 // RUN:   -emit-llvm -o - | FileCheck --check-prefixes=CHECK,NODISC %s
 
-// RUN: %clang_cc1 %s -x c++ -std=c++11 -triple aarch64-linux-gnu -fptrauth-calls -fptrauth-intrinsics \
+// RUN: %clang_cc1 %s -x c++ -std=c++20 -triple aarch64-linux-gnu -fptrauth-calls -fptrauth-intrinsics \
 // RUN:   -fptrauth-vtable-pointer-type-discrimination \
 // RUN:   -emit-llvm -o - | FileCheck --check-prefixes=CHECK,TYPE %s
 
-// RUN: %clang_cc1 %s -x c++ -std=c++11 -triple aarch64-linux-gnu -fptrauth-calls -fptrauth-intrinsics \
+// RUN: %clang_cc1 %s -x c++ -std=c++20 -triple aarch64-linux-gnu -fptrauth-calls -fptrauth-intrinsics \
 // RUN:   -fptrauth-vtable-pointer-address-discrimination \
 // RUN:   -emit-llvm -o - | FileCheck --check-prefixes=CHECK,ADDR %s
 
-// RUN: %clang_cc1 %s -x c++ -std=c++11 -triple aarch64-linux-gnu -fptrauth-calls -fptrauth-intrinsics \
+// RUN: %clang_cc1 %s -x c++ -std=c++20 -triple aarch64-linux-gnu -fptrauth-calls -fptrauth-intrinsics \
 // RUN:   -fptrauth-vtable-pointer-type-discrimination \
 // RUN:   -fptrauth-vtable-pointer-address-discrimination \
 // RUN:   -emit-llvm -o - | FileCheck --check-prefixes=CHECK,BOTH %s
@@ -78,6 +78,27 @@ struct authenticated(default_key, default_address_discrimination, custom_discrim
   virtual void g();
 };
 
+// CHECK: @_ZTVN5test19ConstEvalE = external unnamed_addr constant { [3 x ptr] }, align 8
+// CHECK: @_ZN5test12ceE = global %{{.*}} { ptr ptrauth (ptr getelementptr inbounds inrange(-16, 8) ({ [3 x ptr] }, ptr @_ZTVN5test19ConstEvalE, i32 0, i32 0, i32 2), i32 2, i64 0, ptr @_ZN5test12ceE) }, align 8
+// CHECK: @_ZTVN5test116ConstEvalDerivedE = linkonce_odr unnamed_addr constant { [3 x ptr] } { [3 x ptr] [ptr null, ptr @_ZTIN5test116ConstEvalDerivedE, ptr ptrauth (ptr @_ZN5test19ConstEval1fEv, i32 0, i64 26259, ptr getelementptr inbounds ({ [3 x ptr] }, ptr @_ZTVN5test116ConstEvalDerivedE, i32 0, i32 0, i32 2))] },{{.*}}align 8
+// CHECK: @_ZN5test13cedE = global { ptr } { ptr ptrauth (ptr getelementptr inbounds inrange(-16, 8) ({ [3 x ptr] }, ptr @_ZTVN5test116ConstEvalDerivedE, i32 0, i32 0, i32 2), i32 2, i64 0, ptr @_ZN5test13cedE) }, align 8
+
+struct authenticated(default_key, address_discrimination, no_extra_discrimination) ConstEval {
+  consteval ConstEval() {}
+  virtual void f();
+};
+
+// clang used to bail out with error message "could not emit constant value abstractly".
+ConstEval ce;
+
+struct ConstEvalDerived : public ConstEval {
+public:
+  consteval ConstEvalDerived() {}
+};
+
+// clang used to emit an undef initializer.
+ConstEvalDerived ced;
+
 template <typename T>
 struct SubClass : T {
   virtual void g();

ojhunt

LGTM, will probably need to be cherry-picked to llvm21 or have a release note.

ojhunt · 2025-08-22T00:32:52Z

clang/lib/CodeGen/CGExprConstant.cpp

@@ -876,8 +876,9 @@ bool ConstStructBuilder::Build(const APValue &Val, const RecordDecl *RD,

    for (const BaseInfo &Base : Bases) {
      bool IsPrimaryBase = Layout.getPrimaryBase() == Base.Decl;
-      Build(Val.getStructBase(Base.Index), Base.Decl, IsPrimaryBase,
-            VTableClass, Offset + Base.Offset);
+      if (!Build(Val.getStructBase(Base.Index), Base.Decl, IsPrimaryBase,


I do wonder if it's possible to make this fail without ptrauth as well

@cor3ntin or @AaronBallman any ideas of whether that might be possible?

Failing, in this context, means you have an APValue that made it through constant evaluation, so we know it's a constant, but for some reason we can't actually emit it as a constant.

That generally shouldn't happen: the things that we allow through constant evaluation very closely match the things we can actually emit to LLVM IR, normally. The only way it can happen, as far as I know, is if we're trying to emit an authenticated pointer as an abstract constant. (We were looking at doing something for pointers to dllimport variables on Windows at one point, I think, but that never got merged.)

@efriedma-quic so nothing other than ptrauth seems plausibly able to cause this given current functionality? Always annoying :D

…tructors (llvm#154858) Fix a bug in CodeGen where such variables could cause a compilation error or be emitted with an undef initializer when the vtable was signed with address discrimination. rdar://155696134

ahatanak · 2025-08-25T21:51:36Z

/cherry-pick e612f37

llvmbot · 2025-08-25T22:06:20Z

/pull-request #155319

…tructors (llvm#154858) Fix a bug in CodeGen where such variables could cause a compilation error or be emitted with an undef initializer when the vtable was signed with address discrimination. rdar://155696134 (cherry picked from commit e612f37)

[PAC] Fix codegen for polymorphic class variables with consteval

1c20fc8

constructors Fix a bug in CodeGen where such variables could cause a compilation error or be emitted with an undef initializer. rdar://155696134

ahatanak requested review from rjmccall, ojhunt and efriedma-quic August 21, 2025 23:39

llvmbot added clang Clang issues not falling into any other category clang:codegen IR generation bugs: mangling, exceptions, etc. labels Aug 21, 2025

ojhunt approved these changes Aug 22, 2025

View reviewed changes

ojhunt reviewed Aug 22, 2025

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asl added this to Pointer Authentication Tasks Aug 22, 2025

ojhunt merged commit e612f37 into llvm:main Aug 25, 2025
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github-project-automation bot moved this to Done in Pointer Authentication Tasks Aug 25, 2025

ahatanak added this to the LLVM 21.x Release milestone Aug 25, 2025

github-project-automation bot added this to LLVM Release Status Aug 25, 2025

github-project-automation bot moved this to Needs Triage in LLVM Release Status Aug 25, 2025

llvmbot moved this from Needs Triage to Done in LLVM Release Status Aug 25, 2025

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