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Re: Adding static-PIE support to binutils


Ping.

On Wed, Jun 24, 2015 at 12:18:47AM -0400, Rich Felker 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.
> 
> An alternative seems to be using a separate set of linker scripts to
> throw away the .interp section when the output is static PIE. I tested
> this a long time ago with some success (see
> http://stackoverflow.com/a/10545163/379897 which shows a method) but
> it seems like a hack.
> 
> Can anyone offer feedback on my approach and whether it would be
> acceptable for upstream?
> 
> Rich


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