On Thu 2016-08-18 14:03:13, Jessica Yu wrote:
> +++ Petr Mladek [18/08/16 11:51 +0200]:
> >On Wed 2016-08-17 20:58:29, Jessica Yu wrote:
> >>Implement arch_klp_init_object_loaded() for x86, which applies
> >>alternatives/paravirt patches. This fixes the order in which relocations
> >>and alternatives/paravirt patches are applied.
> >>
> >>--- /dev/null
> >>+++ b/arch/x86/kernel/livepatch.c
> >>+ for (s = info->sechdrs; s < info->sechdrs + info->hdr.e_shnum; s++) {
> >>+ /* Apply per-object .klp.arch sections */
> >>+ cnt = sscanf(info->secstrings + s->sh_name,
> >>+ ".klp.arch.%55[^.].%127s",
> >>+ sec_objname, secname);
> >>+ if (cnt != 2)
> >>+ continue;
> >>+ if (strcmp(sec_objname, objname))
> >>+ continue;
> >>+ if (!strcmp(".altinstructions", secname))
> >
> >The previous version of the patch compared against "altinstructions"
> >(without the dot). I admit that I haven't tested it but the dot
> >looks suspicious here.
>
> Good eye, I should have explained why the dot is needed in the strcmp..
> So, the new documentation states that any arch-specific sections to
> be applied by livepatch are to be prefixed with the string
> ".klp.arch.$objname.", note the required dot at the end of this prefix.
>
> So for example, if we have a .parainstructions section with a patch
> for the kvm module, the prefixed section name would look like:
>
> .klp.arch.kvm..parainstructions
> ^ prefix ^^ original name ^
>
> That extra dot looks weird, but it is needed when we have section names
> like "__ftr_fixup" on powerpc. Without the extra dot at the end of
> ".klp.arch.$objname." We'd get names like ".klp.arch.$objname__ftr_fixup",
> and we wouldn't be able to tell where the objname ends and where the
> section name begins. But with ".klp.arch.$objname.__ftr_fixup", we
> have a hard delimeter and know that after the dot after $objname comes
> the original section name.
That is a bit unfortunate but it makes perfect sense.
Thanks a lot for explanation.
Best Regards,
Petr
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