Re: Adding static-PIE support to binutils

[Rich Felker <dalias at libc dot org>]

On Mon, Aug 17, 2015 at 02:19:34PM -0700, H.J. Lu wrote:
> On Tue, Jun 23, 2015 at 9:18 PM, Rich Felker <dalias@libc.org> wrote:
> > For background on the static PIE model I'm working with, see the
> > following post to the GCC list:
> >
> > https://gcc.gnu.org/ml/gcc/2015-06/msg00008.html
> >
> > So far, I've been prototyping static PIE support by having GCC pass
> > the following options to ld instead of -static -pie:
> >
> >         -static -shared -Bsymbolic
> >
> > This partly works, but since ld does not know it's producing a main
> > executable, it misses important details, including the ability to link
> > initial-exec and local-exec model TLS code correctly, as well as
> > various linking optimizations. So I think the right way forward is
> > making ld accept -static and -pie together to do the right thing.
> >
> > In elflink.c, _bfd_elf_link_create_dynamic_sections assumes that
> > executables should always have a .interp section.
> > bfd_elf_size_dynamic_sections asserts this assumption again, and the
> > individual elf??-*.c files also do so in *_elf_size_dynamic_sections
> > where they set a default interpreter. (Is this even useful? Most of
> > the names are out of touch with reality, and GCC always passes an
> > explicit -dynamic-linker anyway, so I think this code should just be
> > removed.)
> >
> > Now I have a working prototype by changing the info->executable
> > condition to info->executable && info->dynamic, and having lexsup.c
> > store the value of input_flags.dynamic in link_info.dynamic after
> > processing the command line, but I'm not sure if this is the right
> > approach.
> 
> It is OK to use -static/-Bstatic/-non_shared with -shared and -pie.
> I think you want --no-dynamic-linker.

Yes, I was concerned someone might say that. I could certainly add a
--no-dynamic-linker option, but then how should it work on the gcc
side? Having to use -Wl,--no-dynamic-linker to get static-pie would be
a significant obstacle to actual usage, I think. The gcc specs could
automatically pass --no-dynamic-linker when -static is passed to gcc,
assuming users who want to do weird mixes of static and dynamic
linking would use -Wl,-Bstatic rather than -static. After all, gcc
needs to know it's asking for static-pie anyway in order to use the
right startfile. Does that seem reasonable?

Rich