Re: A weak symbol patch

[hjl@varesearch.com (H.J. Lu)]

> 
>    Date: Tue, 6 Jul 1999 13:34:12 -0700 (PDT)
>    From: hjl@varesearch.com (H.J. Lu)
> 
>    I believe there is a linker bug regarding the weak symbol handling. I
>    have sent 2 testcases for the bug. Here is a patch. Could you please
>    take a look?
> 
> I am about to check in the appended patch, which is based on yours.  I
> think this will fix your test case.
> 

You missed a piece in mine. If you don't set ELF_LINK_HASH_REF_REGULAR
when clearing ELF_LINK_HASH_DEF_REGULAR, no relocation will be
generated at all and you will get a linker error:

# cc -o wfoo2 -O -g -B./ -DWEAK main.c wbar2.o libfoo.so -Wl,-rpath,.
./ld: /tmp/ccKTop3y.o: warning: unresolvable relocation against symbol `deallocate' from .text section

if deallocate is referenced and defined as weak in main.c.

It should be better to set both ELF_LINK_HASH_REF_REGULAR and
ELF_LINK_HASH_DEF_REGULAR when a symbol is both defined and referenced
in the same object. But I don't think we do it currently.

> Ian
> 
> Index: elflink.h
> ===================================================================
> RCS file: /cvs/binutils/binutils/bfd/elflink.h,v
> retrieving revision 1.9
> diff -u -r1.9 elflink.h
> --- elflink.h	1999/07/01 23:20:07	1.9
> +++ elflink.h	1999/07/07 18:18:39
> @@ -492,14 +492,19 @@
>       represent variables; this can cause confusion in principle, but
>       any such confusion would seem to indicate an erroneous program or
>       shared library.  We also permit a common symbol in a regular
> -     object to override a weak symbol in a shared object.  */
> +     object to override a weak symbol in a shared object.
>  
> +     We prefer a non-weak definition in a shared library to a weak
> +     definition in the executable.  */
> +
>    if (newdyn
>        && newdef
>        && (olddef
>  	  || (h->root.type == bfd_link_hash_common
>  	      && (bind == STB_WEAK
> -		  || ELF_ST_TYPE (sym->st_info) == STT_FUNC))))
> +		  || ELF_ST_TYPE (sym->st_info) == STT_FUNC)))
> +      && (h->root.type != bfd_link_hash_defweak
> +	  || bind == STB_WEAK))
>      {
>        *override = true;
>        newdef = false;
> @@ -543,7 +548,10 @@
>  
>       As above, we again permit a common symbol in a regular object to
>       override a definition in a shared object if the shared object
> -     symbol is a function or is weak.  */
> +     symbol is a function or is weak.
> +
> +     As above, we permit a non-weak definition in a shared object to
> +     override a weak definition in a regular object.  */
>  
>    if (! newdyn
>        && (newdef
> @@ -552,7 +560,9 @@
>  		  || h->type == STT_FUNC)))
>        && olddyn
>        && olddef
> -      && (h->elf_link_hash_flags & ELF_LINK_HASH_DEF_DYNAMIC) != 0)
> +      && (h->elf_link_hash_flags & ELF_LINK_HASH_DEF_DYNAMIC) != 0
> +      && (bind != STB_WEAK
> +	  || h->root.type == bfd_link_hash_defweak))
>      {
>        /* Change the hash table entry to undefined, and let
>  	 _bfd_generic_link_add_one_symbol do the right thing with the
> @@ -626,6 +636,31 @@
>        h->verinfo.vertree = NULL;
>      }
>  
> +  /* Handle the special case of a weak definition in a regular object
> +     followed by a non-weak definition in a shared object.  In this
> +     case, we prefer the definition in the shared object.  To make
> +     this work we have to frob the flags.  */
> +  if (olddef
> +      && ! olddyn
> +      && h->root.type == bfd_link_hash_defweak
> +      && newdef
> +      && newdyn
> +      && bind != STB_WEAK)
> +    h->elf_link_hash_flags &= ~ ELF_LINK_HASH_DEF_REGULAR;
> +
> +  /* Handle the special case of a non-weak definition in a shared
> +     object followed by a weak definition in a regular object.  In
> +     this case we prefer to definition in the shared object.  To make
> +     this work we have to tell the caller to not treat the new symbol
> +     as a definition.  */
> +  if (olddef
> +      && olddyn
> +      && h->root.type != bfd_link_hash_defweak
> +      && newdef
> +      && ! newdyn
> +      && bind == STB_WEAK)
> +    *override = true;
> +
>    return true;
>  }
>  
> 

Here is the patch against yours.

-- 
H.J. Lu (hjl@gnu.org)
---
--- elflink.h.ian	Wed Jul  7 13:46:13 1999
+++ elflink.h	Wed Jul  7 13:46:59 1999
@@ -642,7 +642,10 @@ elf_merge_symbol (abfd, info, name, sym,
       && newdef
       && newdyn
       && bind != STB_WEAK)
-    h->elf_link_hash_flags &= ~ ELF_LINK_HASH_DEF_REGULAR;
+    {
+      h->elf_link_hash_flags &= ~ ELF_LINK_HASH_DEF_REGULAR;
+      h->elf_link_hash_flags |= ELF_LINK_HASH_REF_REGULAR;
+    }
 
   /* Handle the special case of a non-weak definition in a shared
      object followed by a weak definition in a regular object.  In