RFC/PATCH: ld falsely issues .gnu.warning message for unreferenced dynamic symbols

[Grigory Zagorodnev <grigory_zagorodnev at linux dot intel dot com>]

Hi!
In the conditions described below, ld 2.17.50.0.13 falsely issues 
warning message associated with a symbol via .gnu.warning extension. 
Test-case illustrating the problem and a fix proposal are attached to 
this mail.

I'd appreciate any help in reviewing the problem and proposed patch.

Conditions:
Main executable is linked against two dynamic libraries libcall.so and 
libstub.so. First library (libcall.so) is linked against third dynamic 
library liberal.so. Two of these libraries, libstub and libreal, define 
symbol "func2". Neither executable nor any shared library reference this 
symbol.

The problem:
While building executable, ld emits warning message, defined in 
.gnu.warning.func2 section of libstub.so, regardless of missing 
references to this symbol. That seems to be wrong.

The test-case:
Run make to see the message "libreal.so: warning: warning: func2 is not 
implemented and will always fail". This message is unexpected.

Proposed solution:
In order to ignore multiple definitions of a dynamic symbol, for any 
extra copy if the symbol, linker replaces its definition section with 
"*UND*" stub. Thus this symbol is treated as undefined later on.

Proposed fix uses BSF_GLOBAL flag to distinguish between naturally 
undefined symbols and synthetically undefined.

Patch applied to ld version 2.17.50.0.13 20070212, bootstrapped and 
regtested at x86_64-redhat-linux.


Once again, both the problem and proposed patch needs to be reviewed. 
I'd appreciate any help on this.

- Grigory

Attachment: def_warn_test.tgz
Description: Binary data

2007-02-15  Grigory Zagorodnev <grigory.zagorodnev@linux.intel.com>

     * linker.c: avoid falsely .gnu.warning message for 
         unreferenced dynamic symbols
         
diff -r -up org/bfd/linker.c src/bfd/linker.c
--- org/bfd/linker.c	2006-10-31 17:18:29.000000000 +0300
+++ src/bfd/linker.c	2007-02-15 15:42:41.000000000 +0300
@@ -1908,7 +1908,7 @@ _bfd_generic_link_add_one_symbol (struct
 
 	case WARNC:
 	  /* Issue a warning and cycle.  */
-	  if (h->u.i.warning != NULL)
+	  if (h->u.i.warning != NULL && !(flags & BSF_GLOBAL))
 	    {
 	      if (! (*info->callbacks->warning) (info, h->u.i.warning,
 						 h->root.string, abfd,