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From: Balbir Singh <bsingharora@gmail.com>
Date: Mon, 13 Nov 2017 19:38:36 +1100
Message-ID: <CAKTCnzm63vVGctVarw24v1JY2N7Kc3WdmoW88q2fniEAqXkP_w@mail.gmail.com>
Subject: Re: [PATCH v3] kernel/module_64.c: Add REL24 relocation support of
 livepatch symbols
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
 Torsten Duwe <duwe@lst.de>,
 Aravinda Prasad <aravinda@linux.vnet.ibm.com>, Jessica Yu <jeyu@kernel.org>,
 Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>,
 "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)"
 <linuxppc-dev@lists.ozlabs.org>, live-patching@vger.kernel.org
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On Fri, Nov 10, 2017 at 2:28 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> On Fri, Nov 10, 2017 at 01:06:25PM +1100, Balbir Singh wrote:
>> On Fri, Nov 10, 2017 at 2:19 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>> > FWIW, I think it won't matter anyway.  I'm currently pursuing the option
>> > of inserting nops after local calls, because it has less runtime
>> > complexity than using a stub.
>> >
>> > I think I've figured out a way to do it with a GCC plugin, but if that
>> > doesn't work I'll try the asm listing sed approach suggested by Michael.
>> >
>>
>> A plugin that runs for the new kernel with the patch? Just for
>> specific files involved in the patch?
>
> The plugin will affect the code generation of all functions in the patch
> module.  So all calls in all replacement functions will have the nops.
>
> Here's a prototype (not yet fully tested):
>
>   https://github.com/jpoimboe/kpatch/blob/TODO-ppc-fix/kpatch-build/gcc-plugins/ppc64le-plugin.c
>


Thanks! I looked at it briefly, I need to catch up with gcc plugins,
code < 1000 was interesting.
I guess now we don't need to pass via the new kpatch helper stub, we
would just replace the no-ops
and be done! I'd have to look closer, but I wonder what happens if a
function has no global entry
point

(See http://mpe.github.io/posts/2016/05/23/kernel-live-patching-for-ppc64le/)
section
Understanding the TOC & entry points and the example of int_to_scsilun()

Balbir Singh.