Re: [Bug c++/41020] [4.5 Regression] Can't declare an extern "C" friend of a builtin function

[Dodji Seketeli <dodji at redhat dot com>]

Indeed. I am testing the patch below.

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 5eb389f..7c01ee2 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -104,6 +104,7 @@ static void store_parm_decls (tree);
 static void initialize_local_var (tree, tree);
 static void expand_static_init (tree, tree);
 static tree next_initializable_field (tree);
+static int decls_match_1 (tree, tree, bool);
 
 /* The following symbols are subsumed in the cp_global_trees array, and
    listed here individually for documentation purposes.
@@ -899,6 +900,14 @@ push_local_name (tree decl)
 int
 decls_match (tree newdecl, tree olddecl)
 {
+  return decls_match_1 (newdecl, olddecl, /* newdecl_is_friend  */ false);
+}
+
+/* Subroutine of decls_match.  */
+
+static int
+decls_match_1 (tree newdecl, tree olddecl, bool newdecl_is_friend)
+{
   int types_match;
 
   if (newdecl == olddecl)
@@ -934,9 +943,11 @@ decls_match (tree newdecl, tree olddecl)
 
 #ifdef NO_IMPLICIT_EXTERN_C
       /* A new declaration doesn't match a built-in one unless it
-	 is also extern "C".  */
+	 is also extern "C". Friend function re-declarations retain the
+	 the linkage of the original declaration though.  */
       if (DECL_BUILT_IN (olddecl)
-	  && DECL_EXTERN_C_P (olddecl) && !DECL_EXTERN_C_P (newdecl))
+	  && DECL_EXTERN_C_P (olddecl) && !DECL_EXTERN_C_P (newdecl)
+	  && !newdecl_is_friend)
 	return 0;
 #endif
 
@@ -1122,7 +1133,7 @@ duplicate_decls (tree newdecl, tree olddecl, bool newdecl_is_friend)
   if (newdecl == olddecl)
     return olddecl;
 
-  types_match = decls_match (newdecl, olddecl);
+  types_match = decls_match_1 (newdecl, olddecl, newdecl_is_friend);
 
   /* If either the type of the new decl or the type of the old decl is an
      error_mark_node, then that implies that we have already issued an