[PATCH] c: Error on va_arg with function type [PR105149]

[Jakub Jelinek via Gcc-patches]

Hi!

In the PR Joseph said that the C standard for va_arg talks about
pointers to object type and as a function type is not object type,
it is invalid.

The following patch diagnoses it in the FE, instead of ICEing later on
when optimizations are turned on (and with -O0 doing something weird
at runtime).

Bootstrapped/regtested on powerpc64le-linux, ok for trunk?

2022-04-07  Jakub Jelinek  <ja...@redhat.com>

        PR c/105149
        * c-typeck.cc (c_build_va_arg): Reject function types.

        * gcc.dg/pr105149.c: New test.

--- gcc/c/c-typeck.cc.jj        2022-03-23 10:29:20.172967605 +0100
+++ gcc/c/c-typeck.cc   2022-04-07 12:26:17.236469809 +0200
@@ -15896,6 +15896,12 @@ c_build_va_arg (location_t loc1, tree ex
                "type %qT", type);
       return error_mark_node;
     }
+  else if (TREE_CODE (type) == FUNCTION_TYPE)
+    {
+      error_at (loc2, "second argument to %<va_arg%> is a function type %qT",
+               type);
+      return error_mark_node;
+    }
   else if (warn_cxx_compat && TREE_CODE (type) == ENUMERAL_TYPE)
     warning_at (loc2, OPT_Wc___compat,
                "C++ requires promoted type, not enum type, in %<va_arg%>");
--- gcc/testsuite/gcc.dg/pr105149.c.jj  2022-04-07 12:39:08.202711511 +0200
+++ gcc/testsuite/gcc.dg/pr105149.c     2022-04-07 12:38:21.418364583 +0200
@@ -0,0 +1,16 @@
+/* PR c/105149 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+#include <stdarg.h>
+
+void
+foo (int s, ...)
+{
+  int e;
+  va_list ap;
+
+  va_start (ap, s);
+  e = va_arg (ap, int (void)) ();      /* { dg-error "second argument to 
'va_arg' is a function type" } */
+  va_end (ap);
+}

        Jakub