[clang] [PAC] Fix a crash when signing a pointer to a function with an incomplete enum parameter (PR #99595)

[Akira Hatanaka via cfe-commits]

https://github.com/ahatanak created https://github.com/llvm/llvm-project/pull/99595

Use type int as the underlying type when the enum type is incomplete.

>From 14612f84704edbcc3b3bcb20d6e114890e1c3998 Mon Sep 17 00:00:00 2001
From: Akira Hatanaka <ahatanak at gmail.com>
Date: Thu, 18 Jul 2024 17:59:46 -0700
Subject: [PATCH] [PAC] Fix a crash when signing a pointer to a function with
 an incomplete enum parameter

Use type int as the underlying type when the enum type is incomplete.
---
 clang/lib/AST/ASTContext.cpp                             | 6 ++++--
 clang/test/CodeGen/ptrauth-function-type-discriminator.c | 7 +++++++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index a8e599f7ebe04..9eb529c29bebb 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -3222,14 +3222,16 @@ static void encodeTypeForFunctionPointerAuth(const ASTContext &Ctx,
     OS << "<objc_object>";
     return;
 
-  case Type::Enum:
+  case Type::Enum: {
     // C11 6.7.2.2p4:
     //   Each enumerated type shall be compatible with char, a signed integer
     //   type, or an unsigned integer type.
     //
     // So we have to treat enum types as integers.
+    QualType UnderlyingType = cast<EnumType>(T)->getDecl()->getIntegerType();
     return encodeTypeForFunctionPointerAuth(
-        Ctx, OS, cast<EnumType>(T)->getDecl()->getIntegerType());
+        Ctx, OS, UnderlyingType.isNull() ? Ctx.IntTy : UnderlyingType);
+  }
 
   case Type::FunctionNoProto:
   case Type::FunctionProto: {
diff --git a/clang/test/CodeGen/ptrauth-function-type-discriminator.c b/clang/test/CodeGen/ptrauth-function-type-discriminator.c
index 5dea48fe5915b..54634ed528fb3 100644
--- a/clang/test/CodeGen/ptrauth-function-type-discriminator.c
+++ b/clang/test/CodeGen/ptrauth-function-type-discriminator.c
@@ -19,6 +19,13 @@ void (*test_constant_null)(int) = 0;
 // CHECK: @test_constant_cast = global ptr ptrauth (ptr @f, i32 0, i64 2712)
 void (*test_constant_cast)(int) = (void (*)(int))f;
 
+#ifndef __cplusplus
+// CHECKC: @enum_func_ptr = global ptr ptrauth (ptr @enum_func, i32 0, i64 2712)
+enum Enum0;
+void enum_func(enum Enum0);
+void (*enum_func_ptr)(enum Enum0) = enum_func;
+#endif
+
 // CHECK: @test_opaque = global ptr ptrauth (ptr @f, i32 0)
 void *test_opaque =
 #ifdef __cplusplus