[PATCH] PR ld/19636: pie changes program behavior and generate unnecessary dynamic symbols

[Alan Modra]

On Wed, Feb 17, 2016 at 03:33:51PM -0800, H.J. Lu wrote:
> On Tue, Feb 16, 2016 at 9:23 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> > On Mon, Feb 15, 2016 at 07:00:32AM -0800, H.J. Lu wrote:
> >> I fixed x86.  Other backends need similar fix.  Any comments?

If you aren't going to fix other backends too, have you at least run
the testsuite for all the other ELF targets that use SYMBOLIC_BIND?

> -/* Will a symbol be bound to the definition within the shared
> -   library, if any.  A unique symbol can never be bound locally.  */
> -#define SYMBOLIC_BIND(INFO, H) \
> -    (!(H)->unique_global \
> -     && ((INFO)->symbolic || ((INFO)->dynamic && !(H)->dynamic)))
> +/* Will a symbol be bound to the definition within the PIC object, if
> +   any.  A unique symbol can never be bound locally.  Symbols are always
> +   bound locally in PIE, similar to -shared -Bsymbolic.  */
> +#define SYMBOLIC_BIND(INFO, H)						\
> +    (!(H)->unique_global						\
> +     && ((INFO)->symbolic						\
> +	 || ((INFO)->dynamic && !(H)->dynamic)				\
> +	 || bfd_link_pie (INFO)))

This probably should be bfd_link_executable rather than bfd_link_pie.

> diff --git a/bfd/elflink.c b/bfd/elflink.c
> index ac03ce5..10dece3 100644
> --- a/bfd/elflink.c
> +++ b/bfd/elflink.c
> @@ -632,7 +632,7 @@ bfd_elf_record_link_assignment (bfd *output_bfd,
>  
>    if ((h->def_dynamic
>         || h->ref_dynamic
> -       || bfd_link_pic (info)
> +       || bfd_link_dll (info)
>         || (bfd_link_pde (info)
>  	   && elf_hash_table (info)->is_relocatable_executable))

Should the bfd_link_pde test be removed here?

> @@ -2679,6 +2679,16 @@ _bfd_elf_adjust_dynamic_symbol (struct elf_link_hash_entry *h, void *data)
>  	      && (h->u.weakdef == NULL || h->u.weakdef->dynindx == -1))))
>      {
>        h->plt = elf_hash_table (eif->info)->init_plt_offset;
> +      /* Remove undefined weak symbol from the dynamic symbol table
> +	 in executable.  */
> +      if (h->root.type == bfd_link_hash_undefweak
> +	  && bfd_link_executable (eif->info)
> +	  && h->dynindx != -1)
> +	{
> +	  h->dynindx = -1;
> +	  _bfd_elf_strtab_delref (elf_hash_table (eif->info)->dynstr,
> +				  h->dynstr_index);
> +	}
>        return TRUE;
>      }
>  

This change is incorrect.  Some targets (even x86_64 with -fPIC)
support
  if (fun)
    fun ();
for an undefined weak fun at link time, making fun dynamic and
emitting dynamic relocs against fun.  So when the executable is linked
against a new shared library that provides fun, fun will be called.

Other than the above comments, the patch looks good.

-- 
Alan Modra
Australia Development Lab, IBM