Index: gcc/c-decl.c
===================================================================
RCS file: /cvsroot/gcc/gcc/gcc/c-decl.c,v
retrieving revision 1.300.2.6
diff -u -p -r1.300.2.6 c-decl.c
--- gcc/c-decl.c	26 Apr 2002 00:23:32 -0000	1.300.2.6
+++ gcc/c-decl.c	28 Apr 2002 09:20:07 -0000
@@ -1955,7 +1955,8 @@ duplicate_decls (newdecl, olddecl, diffe
     }
 
   /* Merge the storage class information.  */
-  DECL_WEAK (newdecl) |= DECL_WEAK (olddecl);
+  merge_weak (newdecl, olddecl);
+
   /* For functions, static overrides non-static.  */
   if (TREE_CODE (newdecl) == FUNCTION_DECL)
     {
Index: gcc/c-pragma.c
===================================================================
RCS file: /cvsroot/gcc/gcc/gcc/c-pragma.c,v
retrieving revision 1.46.6.3
diff -u -p -r1.46.6.3 c-pragma.c
--- gcc/c-pragma.c	22 Mar 2002 22:49:38 -0000	1.46.6.3
+++ gcc/c-pragma.c	28 Apr 2002 09:20:07 -0000
@@ -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 may result in unspecified behaviour");
+
   declare_weak (decl);
 }
 
Index: gcc/output.h
===================================================================
RCS file: /cvsroot/gcc/gcc/gcc/output.h,v
retrieving revision 1.94.2.1
diff -u -p -r1.94.2.1 output.h
--- gcc/output.h	23 Apr 2002 08:11:21 -0000	1.94.2.1
+++ gcc/output.h	28 Apr 2002 09:20:07 -0000
@@ -231,6 +231,8 @@ extern void mergeable_constant_section	P
 
 /* Declare DECL to be a weak symbol.  */
 extern void declare_weak		PARAMS ((tree));
+/* Merge weak status.  */
+extern void merge_weak			PARAMS ((tree, tree));
 #endif /* TREE_CODE */
 
 /* Emit any pending weak declarations.  */
Index: gcc/varasm.c
===================================================================
RCS file: /cvsroot/gcc/gcc/gcc/varasm.c,v
retrieving revision 1.250.2.7
diff -u -p -r1.250.2.7 varasm.c
--- gcc/varasm.c	25 Mar 2002 00:54:26 -0000	1.250.2.7
+++ gcc/varasm.c	28 Apr 2002 09:20:07 -0000
@@ -4990,6 +4990,32 @@ output_constructor (exp, size, align)
    to be emitted.  */
 static tree weak_decls;
 
+/* Merge weak status between NEWDECL and OLDDECL.  */
+
+void
+merge_weak (newdecl, olddecl)
+     tree newdecl;
+     tree olddecl;
+{
+  tree decl;
+
+  if ((! DECL_WEAK (newdecl) && ! DECL_WEAK (olddecl))
+      || (DECL_WEAK (newdecl) && DECL_WEAK (olddecl)))
+    return;
+
+  decl = DECL_WEAK (olddecl) ? newdecl : olddecl;
+
+  if (SUPPORTS_WEAK
+      && DECL_EXTERNAL (newdecl) && DECL_EXTERNAL (olddecl)
+      && (TREE_CODE (decl) != VAR_DECL
+	  || ! TREE_STATIC (decl))
+      && TREE_USED (decl)
+      && TREE_SYMBOL_REFERENCED (DECL_ASSEMBLER_NAME (decl)))
+    warning_with_decl (decl, "weak declaration of `%s' after first use may result in unspecified behaviour");
+
+  declare_weak (decl);
+}
+
 /* Declare DECL to be a weak symbol.  */
 
 void
@@ -4998,7 +5024,7 @@ declare_weak (decl)
 {
   if (! TREE_PUBLIC (decl))
     error_with_decl (decl, "weak declaration of `%s' must be public");
-  else if (TREE_ASM_WRITTEN (decl))
+  else if (TREE_CODE (decl) == FUNCTION_DECL && TREE_ASM_WRITTEN (decl))
     error_with_decl (decl, "weak declaration of `%s' must precede definition");
   else if (SUPPORTS_WEAK)
     {
@@ -5009,6 +5035,12 @@ declare_weak (decl)
     warning_with_decl (decl, "weak declaration of `%s' not supported");
 
   DECL_WEAK (decl) = 1;
+
+  if (DECL_RTL_SET_P (decl)
+      && GET_CODE (DECL_RTL (decl)) == MEM
+      && XEXP (DECL_RTL (decl), 0)
+      && GET_CODE (XEXP (DECL_RTL (decl), 0)) == SYMBOL_REF)
+    SYMBOL_REF_WEAK (XEXP (DECL_RTL (decl), 0)) = 1;
 }
 
 /* Emit any pending weak declarations.  */
Index: gcc/cp/decl.c
===================================================================
RCS file: /cvsroot/gcc/gcc/gcc/cp/decl.c,v
retrieving revision 1.866.2.25
diff -u -p -r1.866.2.25 decl.c
--- gcc/cp/decl.c	23 Apr 2002 23:52:07 -0000	1.866.2.25
+++ gcc/cp/decl.c	28 Apr 2002 09:20:08 -0000
@@ -3645,7 +3645,8 @@ duplicate_decls (newdecl, olddecl)
     }
 
   /* Merge the storage class information.  */
-  DECL_WEAK (newdecl) |= DECL_WEAK (olddecl);
+  merge_weak (newdecl, olddecl);
+
   DECL_ONE_ONLY (newdecl) |= DECL_ONE_ONLY (olddecl);
   DECL_DEFER_OUTPUT (newdecl) |= DECL_DEFER_OUTPUT (olddecl);
   TREE_PUBLIC (newdecl) = TREE_PUBLIC (olddecl);