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

[Alan Modra <amodra@gmail.com>]

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..

-- 
Alan Modra
Australia Development Lab, IBM