[PATCH] D28272: ELF: Reserve space for copy relocations of read-only symbols in relro.

Peter Collingbourne via llvm-commits llvm-commits at lists.llvm.org
Thu Jan 5 13:38:48 PST 2017


On Thu, Jan 5, 2017 at 1:17 PM, Rafael Avila de Espindola <
rafael.espindola at gmail.com> wrote:

> Peter Collingbourne via Phabricator <reviews at reviews.llvm.org> writes:
>
> > Relatedly, I discovered a bug in this patch. We can't use SHT_NOBITS for
> the new section because we need to lay out all NOBITS sections contiguously
> at the end of the LOAD. RELRO also needs to be contiguous (there can only
> be one RELRO header), so we can't have another RELRO covering part of the
> bss.
>
> You could move the RELRO to the end of the regular RW PT_LOAD, no? That
> way it
> will be just before the nobits sections and the nobits sections could
> start with RELRO ones. That way the RELRO segment would span the end of
> the regular (non-nobits) sections and the start of the nobits ones.
>

Yes, I think that would work, thanks. So the layout would be:

non-RELRO non-NOBITS
[page alignment]
RELRO non-NOBITS
RELRO NOBITS
[page alignment]
non-RELRO NOBITS

The downside is that there would be an extra page alignment, but that
doesn't seem too important.

Thanks,
-- 
-- 
Peter
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