Re: livepatch: reuse module loader code to write relocations

From: Jessica Yu
Date: Fri Nov 13 2015 - 02:16:33 EST

+++ Josh Poimboeuf [12/11/15 14:32 -0600]:
On Thu, Nov 12, 2015 at 03:22:44PM -0500, Jessica Yu wrote:
Looking into this more, I think we do need one __klp_rela section per
function being patched. Each rela section is linked to the section to
which the relocations apply via the rela section's sh_info field. In
SHT_RELA sections, the sh_info field contains the section index to
which the relocs apply. We cannot have one single combined rela
section per object as the call to apply_relocate_add() simply won't
work, because we would have relocs that apply to different functions
(and hence different sections).

So I guess instead of a single field in klp_object specifying the
__klp_rela section index, we could probably just have an array of
section indices.

Ok, makes sense, sounds like we need multiple klp relas per object.

I still don't quite understand the benefit of caching the klp_rela
section indices. What problem does it solve? It seems simpler to just
iterate over all the sections in klp_write_object_relocations().

I was trying to accomodate Miroslav's dislike of klp_reloc_sec :-)
But now that we are sure that we need multiple __klp_rela sections
per object, I think an array of indices might still be somewhat
complicated (we need to figure out its size and everything, a list
here would be easier). I think it might be fine to leave things the
way they are here.

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