Re: [PATCH] Re: Don't relax undefined symbols on ppc.

[Douglas B Rupp <rupp at adacore dot com>]

On 07/23/2018 07:01 PM, Alan Modra wrote:
> On Mon, Jul 23, 2018 at 07:38:44AM -0700, Douglas B Rupp wrote:
> > On 07/09/2018 06:27 PM, Alan Modra wrote:
> > > On Mon, Jul 09, 2018 at 01:58:33PM -0700, Douglas B Rupp wrote:
> > > > There is a problem with --relax in the partial link trying to relax the
> > > > undefined symbols, leading to the RTP failing at startup with signal 11.
> > >
> > > Please describe the problem in detail.  ld -r --relax non-pic is
> > > supposed to work for ppc32, with a branch to an undefined symbol being
> > > resolved to a trampoline which has relocations to the symbol.  Are the
> > > emitted relocations wrong?
> > >
> > > > I solicit comments on the attached patch, which causes undefined symbols to
> > > > be ignored during the relax process.  Leaving them to be relaxed and
> > > > resolved during the final link.
> > >
> > > If ld -r mashes together sections such that the resulting output
> > > section size exceeds the reach of a branch, then it may not be
> > > possible to for branches to reach trampolines placed at the end of the
> > > section.  That's the problem ld -r --relax is trying to solve, by
> > > placing trampolines at the end of each input section.
> >
> > The problem is that "tsec" is the undefined section and basically a no-op in
> > the following line, so existing trampolines are found when they shouldn't be
> > found.
> >
> > elf32-ppc.c: if (f->tsec == tsec && f->toff == toff)
>
> But for undefined syms and relocatable linking, toff is the symbol
> index.  Or at least it is supposed to be.  I do see a bug where the
> reloc addend could be added to toff, but that is unlikely to trigger.
>
> > The attached patch fixes it.
>
> I don't see how adding "abfd" to the branch fixup struct can possibly
> help.  "abfd" is a constant for any one invocation of
> ppc_elf_relax_section!

I don't know what to tell you, it does fix the problem.
I can take another look at it at some future date and try to provide 
more detail.
--Doug