Re: [PATCH v2] Support for SHF_GNU_RETAIN ELF Section Flag

[Alan Modra <amodra@gmail.com>]

On Fri, Oct 02, 2020 at 01:30:23PM +0100, Jozef Lawrynowicz wrote:
> On Thu, Oct 01, 2020 at 09:09:07PM +0930, Alan Modra via Binutils wrote:
> > On Thu, Oct 01, 2020 at 11:50:33AM +0100, Jozef Lawrynowicz wrote:
> > > --- a/bfd/elflink.c
> > > +++ b/bfd/elflink.c
> > > @@ -14102,7 +14102,8 @@ bfd_elf_gc_sections (bfd *abfd, struct bfd_link_info *info)
> > >  			|| (elf_section_data (o)->this_hdr.sh_type
> > >  			    == SHT_FINI_ARRAY)))
> > >  		|| (elf_section_data (o)->this_hdr.sh_type == SHT_NOTE
> > > -		    && elf_next_in_group (o) == NULL )))
> > > +		    && elf_next_in_group (o) == NULL)
> > > +		|| (elf_section_flags (o) & SHF_GNU_RETAIN)))
> > 
> > Flag bits in SHF_MASKOS depend on OS, so this needs a test of OSABI.
> > That can be done by checking elf_tdata (sub)->has_gnu_osabi for the
> > appropriate bit.
> > 
> 
> Fixed the two OSABI issues in the attached patch.

I didn't mention it, but readelf has two occurrences of decoding
SHF_GNU_UNIQUE.  They both need fixing, not just the first one.

> > > +* Add support for the SHF_GNU_RETAIN ELF section flag.
> > > +  This flag specifies that the section should not be garbage collected by the
> > > +  linker if it is unused.
> > 
> > I would drop "if it is unused".  The phrase doesn't really add
> > anything to a user's understanding.
> > 
> 
> I don't really have a strong opinion either way, but I thought "if it is
> unused" might be helpful to add to the description since "garbage
> collection" is not precisely defined in ELF.

The reason I don't particularly like "if it is unused" is that it
sounds like something said by someone who doesn't really understand
linker garbage collection.  "used" and "referenced by a relocation
from a kept section" are only loosely related.  And indeed the whole
purpose of SHF_GNU_RETAIN is surely to keep needed sections, ones that
are used for some purpose.

-- 
Alan Modra
Australia Development Lab, IBM