1 files changed, 4 insertions, 0 deletions
diff --git a/gcc/c-pragma.c b/gcc/c-pragma.c
index 4bf7ce205ac..d5df3559597 100644
--- a/gcc/c-pragma.c
+++ b/gcc/c-pragma.c
@@ -287,6 +287,10 @@ apply_pragma_weak (decl, value)
     decl_attributes (&decl, build_tree_list (get_identifier ("alias"),
 				             build_tree_list (NULL, value)),
 		     0);
+  if (SUPPORTS_WEAK && DECL_EXTERNAL (decl) && TREE_USED (decl)
+      && TREE_SYMBOL_REFERENCED (DECL_ASSEMBLER_NAME (decl)))
+    warning_with_decl (decl, "applying #pragma weak `%s' after first use results in unspecified behavior");
+
   declare_weak (decl);
 }