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[PATCH] Mark __start/__stop symbols as PROTECTED in shared object

Alan Modra amodra@gmail.com
Wed Aug 16 01:55:00 GMT 2017 
On Tue, Aug 15, 2017 at 06:05:16PM -0700, H.J. Lu wrote:
> On Tue, Aug 15, 2017 at 5:50 PM, Alan Modra <amodra@gmail.com> wrote:
> > On Mon, Aug 14, 2017 at 05:10:02PM -0700, H.J. Lu wrote:
> >> On Mon, Aug 14, 2017 at 4:53 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> >> > When building shared objects, mark __start and __stop symbols as
> >> > PROTECTED and bind them as symbolic to support dlsym.  Also override
> >> > __start, __stop, .startof.  and .sizeof. symbols defined in a shared
> >> > object.
> >> >
> >> > OK for master?
> >> >
> >> > bfd/
> >> >
> >> > PR ld/21964
> >> > * elf-bfd.h (SYMBOLIC_BIND): TRUE for __start/__stop symbols.
> >> > * elflink.c (bfd_elf_define_start_stop): Override symbol defined
> >> > in a shared object.  Mark __start/__stop symbols as PROTECTED in
> >> > shared objects.
> >> >
> >>
> >> No need to mark them as protected when bind them symbolic.
> >
> > I think you should be making these symbols protected visibility.
> >
> 
> The question is if they should be bound symbolically.  If no, is there
> a use case? If yes, why PROTECTED?

If these linker provided symbols are made protected visibility then
that itself advertises their binding.  They bind locally within that
binary.  If you change SYMBOLIC_BIND then that is a magic linker
behaviour, not wrong, but not something that is obvious from the
object file.

Incidentally, your patch is in response to a use case that was broken
when you made them hidden in shared libraries.  I wonder whether they
shouldn't be protected in the executable too?  I can imagine a shared
library needing access to a special section in the executable.

-- 
Alan Modra
Australia Development Lab, IBM
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