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

["H.J. Lu" <hjl.tools@gmail.com>]

On Fri, Aug 28, 2020 at 7:49 AM Alan Modra <amodra@gmail.com> wrote:
>
> 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".

PR ld/26530 test still failed.

> > 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



-- 
H.J.