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

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

On Wed, Sep 2, 2020 at 6:05 AM Alan Modra <amodra@gmail.com> wrote:
>
> On Wed, Sep 02, 2020 at 04:56:48AM -0700, H.J. Lu wrote:
> > On Wed, Sep 2, 2020 at 1:12 AM Alan Modra <amodra@gmail.com> wrote:
> > >
> > > On Wed, Sep 02, 2020 at 08:52:06AM +0200, Martin Liška wrote:
> > > > On 8/28/20 4:50 PM, H.J. Lu via Binutils wrote:
> > > > > PR ld/26530 test still failed.
> > > >
> > > > Hello.
> > > >
> > > > Is there any progress on this please?
> > >
> > > I think what we want is the following, and some tweaking of the
> > > testsuite to remove FAIL: PR ld/15146 (1).  That test relied on not
> > > loading a shared lib due to an IR symbol reference, but the logic
> > > added by git commit 3d5bef4c0871 has already been reverted.
> > >
> > > diff --git a/bfd/elflink.c b/bfd/elflink.c
> > > index 5c085b14b7..346f534911 100644
> > > --- a/bfd/elflink.c
> > > +++ b/bfd/elflink.c
> > > @@ -4977,11 +4977,7 @@ elf_link_add_object_symbols (bfd *abfd, struct bfd_link_info *info)
> > >              object and a shared object.  */
> > >           bfd_boolean dynsym = FALSE;
> > >
> > > -         /* Plugin symbols aren't normal.  Don't set def_regular or
> > > -            ref_regular for them, or make them dynamic.  */
> > > -         if ((abfd->flags & BFD_PLUGIN) != 0)
> > > -           ;
> > > -         else if (! dynamic)
> > > +         if (! dynamic)
> > >             {
> > >               if (! definition)
> > >                 {
> > > @@ -5162,10 +5158,6 @@ 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 +5184,7 @@ 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;
> >
> > Will it add a shared library to DT_NEEDED even if the IR symbol reference is
> > removed by LTO?
>
> Yes.  That can't be helped.  I know we worried about unnecessary
> --as-needed shared libraries in the past when IR symbols disappear
> after LTO, but I can't see a simple and reliable way for the linker to
> be correct.

My patch isn't very complicated.

> It's reasonably obvious that we need to load archive elements when
> they define IR referenced symbols, because the archive element might
> be an LTO object.  What's not so obvious is whether loading of shared
> libraries should follow the same rule.  I think they should, in order
> for LTO to get symbol resolution correct in corner cases.  Basically
> LTO needs to know what shared libraries are loaded before
> recompilation.  See commit a896df97b952 log comments.

There is dynamic_def for this purpose.

-- 
H.J.