[PATCH] elf: Properly set sh_offset for .tbss sections

[H.J. Lu]

On Tue, Apr 29, 2025 at 8:05 AM Alan Modra <amodra@gmail.com> wrote:
>
> On Mon, Apr 28, 2025 at 08:08:56AM +0200, Jan Beulich wrote:
> > On 28.04.2025 04:47, H.J. Lu wrote:
> > > Set sh_offset for .tbss sections to their nominal offset after aligning.
> > > They are not loaded from disk so the value doesn't really matter, except
> > > when the .tbss section is the first one in a PT_TLS segment.  In that
> > > case, it sets the p_offset for the PT_TLS segment, which according to
> > > the ELF gABI ought to satisfy p_offset % p_align == p_vaddr % p_align.
> > >
> > > bfd/
> > >
> > > PR ld/32896
> > > * elf.c (assign_file_positions_for_load_sections): Properly set
> > > sh_offset for .tbss sections.
> >
> > Why does the order of checks (PT_LOAD then SHT_NOBITS) need changing here?
> > While pre-existing, I'm also having a hard time seeing why among SHT_NOBITS
> > sections SHF_TLS ones would need special casing here. While I agree that
> > the usual requirements have to be met by PT_TLS, the entire change feels
> > like it's papering over an issue elsewhere (presumably in the laying out of
> > load segments).
>
> The patch is OK.  Please apply.
>
> Jan, there is a lot of history to this code.  sh_offset for SHT_NOBITS
> is somewhat arbitrary since those sections are not loaded from the
> image.  p_offset for a program header with p_filesz zero is likewise
> arbitrary, except that the gABI makes no exception regarding alignment
> modulo p_align for such headers.
>
> The problem is that various other tools break (or have been broken in
> the past) when we make what seems like logical changes to our code,
> such as the one you point out, that all SHT_NOBITS sections ought to
> be treated the same here.  See pr12921 and pr25662.
>
> --
> Alan Modra

I'd like to avoid putting sh_offset of .tbss sections beyond EOF.
I will see what I can do.

-- 
H.J.