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Re: [PATCH] elf: Try not pointing empty PT_LOAD segment's offset past EOF
On Tue, Dec 10, 2019 at 09:44:28PM +0100, Bálint Réczey wrote:
> Hi,
>
> Florian Weimer <fweimer@redhat.com> ezt írta (időpont: 2019. dec. 10.,
> K, 14:23):
> >
> > * Alan Modra:
> >
> > > On Sat, Dec 07, 2019 at 05:22:13PM +0100, Bálint Réczey wrote:
> > >> diff --git a/bfd/elf.c b/bfd/elf.c
> > >> index 1aa2603ee8..e1a9a02eec 100644
> > >> --- a/bfd/elf.c
> > >> +++ b/bfd/elf.c
> > >> @@ -5752,7 +5752,12 @@ assign_file_positions_for_load_sections (bfd *abfd,
> > >> || (p->p_type == PT_NOTE && bfd_get_format (abfd) == bfd_core))
> > >> {
> > >> if (!m->includes_filehdr && !m->includes_phdrs)
> > >> - p->p_offset = off;
> > >> + if (no_contents)
> > >> + /* Try avoiding pointing past the EOF with this empty segment's
> > >> + p_offset. */
> > >> + p->p_offset = p->p_offset % maxpagesize;
> > >> + else
> > >> + p->p_offset = off;
> > >> else
> > >> {
> > >> file_ptr adjust;
> > >
> > > How did you test this patch? I suspect you are just leaving p_offset
> > > at zero and therefore will cause failures on glibc systems.
> >
> > I think glibc requires ordering by increasing virtual address, per the
> > specification. That does not seem to change here.
> >
> > Testing on glibc is of course recommended, though. It also needs to be
> > tested with various kernel versions.
>
> For the record I've tested the rebuilt gzip binary on Ubuntu's
> 5.0.0-37-generic and on 5.3.0-24-generic.
"p->p_offset = p->p_offset % maxpagesize" is not the best way to write
"p->p_offset = 0". So I'd reject this patch for not doing as the
submitter intended.
Using zero will almost certainly fail for some binaries.
--
Alan Modra
Australia Development Lab, IBM