Add a diagnostic for K&R-style functions without a prototype.

Author: bwendling

clang/lib/Sema/SemaType.cpp

@@ -7955,8 +7955,13 @@ static bool handleFunctionTypeAttr(TypeProcessingState &state, ParsedAttr &attr,
       return false;
 
     const auto *FnTy = unwrapped.get()->getAs<FunctionProtoType>();
-    if (!FnTy)
+    if (!FnTy) {
+      S.Diag(attr.getLoc(), diag::err_attribute_wrong_decl_type)
+          << attr << attr.isRegularKeywordAttribute()
+          << ExpectedFunctionWithProtoType;
+      attr.setInvalid();
       return true;
+    }
 
     FunctionProtoType::ExtProtoInfo EPI = FnTy->getExtProtoInfo();
     EPI.ExtraAttributeInfo.CFISalt = Argument;

clang/test/Sema/attr-cfi-salt.c

@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -fsyntax-only -fsanitize=kcfi -verify %s
+// RUN: %clang_cc1 -std=c89 -DKNR -fsyntax-only -fsanitize=kcfi -verify %s
 
 #define __cfi_salt(S) __attribute__((cfi_salt(S)))
 
@@ -10,8 +11,10 @@ int bad3() __attribute__((cfi_salt("a", "b", "c"))); // expected-error{{'cfi_sal
 int foo(int a, int b) __cfi_salt("pepper"); // ok
 int foo(int a, int b) __cfi_salt("pepper"); // ok
 
+#ifndef KNR
 typedef int (*bar_t)(void) __cfi_salt("pepper"); // ok
 typedef int (*bar_t)(void) __cfi_salt("pepper"); // ok
+#endif
 
 // FIXME: Should we allow this?
 // int b(void) __cfi_salt("salt 'n") __cfi_salt("pepper");
@@ -49,3 +52,9 @@ void func4(int) [[clang::cfi_salt("test")]]; // ok
 void func4(int a) [[clang::cfi_salt("test")]] { } // ok
 void (* [[clang::cfi_salt("test")]] fp4)(int) = func4; // ok
 void (*fp4_noattr)(int) = func4; // expected-error{{incompatible function pointer types initializing 'void (*)(int)' with an expression of type 'void (int)'}}
+
+#ifdef KNR
+// K&R C function without a prototype
+void func() __attribute__((cfi_salt("pepper"))); // expected-error {{attribute only applies to non-K&R-style functions}}
+void (*fp)() __attribute__((cfi_salt("pepper")));  // expected-error {{attribute only applies to non-K&R-style functions}}
+#endif