[clang] Do not diagnose conflicting types for cfi_unchecked_callee

[PiJoules]

Clang would complain about conflicting types between a function declaration and definition if the declaraion was marked with the attribute but the definition wasn't. Do not treat this as an error. It should only be necessary to mark the declaration with the attribute.

[llvmbot]

@llvm/pr-subscribers-clang

Author: None (PiJoules)

Changes

Clang would complain about conflicting types between a function declaration and definition if the declaraion was marked with the attribute but the definition wasn't. Do not treat this as an error. It should only be necessary to mark the declaration with the attribute.

---

Full diff: https://github.com/llvm/llvm-project/pull/157762.diff

2 Files Affected:

• (modified) clang/lib/Sema/SemaDecl.cpp (+17)
• (modified) clang/test/Frontend/cfi-unchecked-callee-attribute.cpp (+4)

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 7c1459e320167..91c4589b7b971 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -3877,6 +3877,23 @@ bool Sema::MergeFunctionDecl(FunctionDecl *New, NamedDecl *&OldD, Scope *S,
     RequiresAdjustment = true;
   }
 
+  // If the declaration is marked with cfi_unchecked_callee but the definition
+  // isn't, the definition is also cfi_unchecked_callee.
+  if (auto *FPT1 = OldType->getAs<FunctionProtoType>()) {
+    if (auto *FPT2 = NewType->getAs<FunctionProtoType>()) {
+      FunctionProtoType::ExtProtoInfo EPI1 = FPT1->getExtProtoInfo();
+      FunctionProtoType::ExtProtoInfo EPI2 = FPT2->getExtProtoInfo();
+
+      if (EPI1.CFIUncheckedCallee && !EPI2.CFIUncheckedCallee) {
+        EPI2.CFIUncheckedCallee = true;
+        NewQType = Context.getFunctionType(FPT2->getReturnType(),
+                                           FPT2->getParamTypes(), EPI2);
+        NewType = cast<FunctionType>(NewQType);
+        New->setType(NewQType);
+      }
+    }
+  }
+
   // Merge regparm attribute.
   if (OldTypeInfo.getHasRegParm() != NewTypeInfo.getHasRegParm() ||
       OldTypeInfo.getRegParm() != NewTypeInfo.getRegParm()) {
diff --git a/clang/test/Frontend/cfi-unchecked-callee-attribute.cpp b/clang/test/Frontend/cfi-unchecked-callee-attribute.cpp
index f2c4e9e2f8890..072f217ff7b19 100644
--- a/clang/test/Frontend/cfi-unchecked-callee-attribute.cpp
+++ b/clang/test/Frontend/cfi-unchecked-callee-attribute.cpp
@@ -233,3 +233,7 @@ void lambdas() {
     checked_func = checked_lambda;
   };
 }
+
+CFI_UNCHECKED_CALLEE
+void func(void);
+void func(void) {}  // No warning expected.

[erichkeane]

Does this need a release note?

[PiJoules]

Does this need a release note?

Added one