[PATCH] elf: Don't load archive element after dynamic definition

[Alan Modra]

On Fri, Aug 28, 2020 at 05:53:10AM -0700, H.J. Lu wrote:
> On Thu, Aug 27, 2020 at 6:59 PM Alan Modra <amodra@gmail.com> wrote:
> >
> > On Thu, Aug 27, 2020 at 07:05:15AM -0700, H.J. Lu wrote:
> > > On Thu, Aug 27, 2020 at 6:53 AM Alan Modra <amodra@gmail.com> wrote:
> > > >
> > > > On Tue, Aug 25, 2020 at 10:28:42AM -0700, H.J. Lu via Binutils wrote:
> > > > > Don't load the archive element after seeing a definition in a shared
> > > > > object.
> > > > >
> > > > > bfd/
> > > > >
> > > > >       PR ld/26530
> > > > >       * elflink.c (elf_link_add_object_symbols): Also preserve the
> > > > >       dynamic_def bit for --as-needed.
> > > > >       (elf_link_add_archive_symbols): Don't load the archive element
> > > > >       after seeing a definition in a shared object.
> > > >
> > > > This seems over complicated to me.  Why don't we just load the
> > > > as-needed shared library on the first pass?
> > > >
> > >
> > > In the first pass, when we are loading a shared object,  do we have
> > > the IR symbol resolution?
> >
> > No, but why should that matter?  Adding DT_NEEDED for an as-needed
> > library that turns out to not be needed after LTO is not a problem
> > IMO.  Also I think it may be necessary to load shared libraries on the
> > first pass for LTO to work properly in corner cases.  See the comment
> > in git commit a896df97b952.
> >
> > The condition we use to add --as-needed libraries is:
> >           if (!add_needed
> >               && matched
> >               && definition
> >               && ((dynsym
> >                    && h->ref_regular_nonweak)
> >                   || (h->ref_dynamic_nonweak
> >                       && (elf_dyn_lib_class (abfd) & DYN_AS_NEEDED) != 0
> >                       && !on_needed_list (elf_dt_name (abfd),
> >                                           htab->needed, NULL))))
> > Note the test of dynsym, but earlier
> >           /* Nor should we make plugin symbols dynamic.  */
> >           if ((abfd->flags & BFD_PLUGIN) != 0)
> >             dynsym = FALSE;
> >
> > So I'm thinking perhaps we should delete the above lines and instead
> > add the BFD_PLUGIN condition where we make symbols dynamic.
> >
> >           if (dynsym && (abfd->flags & BFD_PLUGIN) == 0 && h->dynindx == -1)
> >             {
> >               if (! bfd_elf_link_record_dynamic_symbol (info, h))
> >
> > I haven't tested the idea..
> >
> 
> I tested the patch enclosed here and it doesn't work.

Please explain "doesn't work".

> In the first pass, when we are loading a shared object, we can't assume
> that the shared object is needed simply because it satisfies a reference
> from an IR object without the IR symbol resolution.
> 
> -- 
> H.J.
> ----
> diff --git a/bfd/elflink.c b/bfd/elflink.c
> index 5c085b14b7..3c559bafc5 100644
> --- a/bfd/elflink.c
> +++ b/bfd/elflink.c
> @@ -5162,10 +5162,6 @@ elf_link_add_object_symbols (bfd *abfd, struct
> bfd_link_info *info)
>          && !bfd_link_relocatable (info))
>        dynsym = FALSE;
> 
> -    /* Nor should we make plugin symbols dynamic.  */
> -    if ((abfd->flags & BFD_PLUGIN) != 0)
> -      dynsym = FALSE;
> -
>      if (definition)
>        {
>          h->target_internal = isym->st_target_internal;
> @@ -5192,7 +5188,9 @@ elf_link_add_object_symbols (bfd *abfd, struct
> bfd_link_info *info)
>       }
>        }
> 
> -    if (dynsym && h->dynindx == -1)
> +    if (dynsym
> +        && (abfd->flags & BFD_PLUGIN) == 0
> +        && h->dynindx == -1)
>        {
>          if (! bfd_elf_link_record_dynamic_symbol (info, h))
>       goto error_free_vers;

-- 
Alan Modra
Australia Development Lab, IBM