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Date:   Tue, 26 Mar 2019 17:03:02 -0400
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Joao Moreira <jmoreira@...e.de>
Cc:     live-patching@...r.kernel.org, mbenes@...e.cz, pmladek@...e.cz,
        jikos@...e.cz, nstange@...e.de, jpoimboe@...hat.com,
        khlebnikov@...dex-team.ru, jeyu@...nel.org, matz@...e.de,
        linux-kernel@...r.kernel.org, yamada.masahiro@...ionext.com,
        linux-kbuild@...r.kernel.org, michal.lkml@...kovi.net
Subject: Re: [PATCH v2 0/8] klp-convert

On 3/26/19 4:18 PM, Joao Moreira wrote:
> 
> 
> On 3/18/19 4:18 PM, Joe Lawrence wrote:
>> On Fri, Mar 01, 2019 at 11:13:05AM -0300, Joao Moreira wrote:
>>> Livepatches may use symbols which are not contained in its own scope,
>>> and, because of that, may end up compiled with relocations that will
>>> only be resolved during module load. Yet, when the referenced symbols are
>>> not exported, solving this relocation requires information on the object
>>> that holds the symbol (either vmlinux or modules) and its position inside
>>> the object, as an object may contain multiple symbols with the same name.
>>> Providing such information must be done accordingly to what is specified
>>> in Documentation/livepatch/module-elf-format.txt.
>>>
>>> Currently, there is no trivial way to embed the required information as
>>> requested in the final livepatch elf object. klp-convert solves this
>>> problem in two different forms: (i) by relying on a symbol map, which is
>>> built during kernel compilation, to automatically infers the relocation
>>> targeted symbol, and, when such inference is not possible (ii) by using
>>> annotations in the elf object to convert the relocation accordingly to
>>> the specification, enabling it to be handled by the livepatch loader.
>>>
>>> Given the above, add support for symbol mapping in the form of
>>> Symbols.list file; add klp-convert tool; integrate klp-convert tool into
>>> kbuild; make livepatch modules discernible during kernel compilation
>>> pipeline; add data-structure and macros to enable users to annotate
>>> livepatch source code; make modpost stage compatible with livepatches;
>>> update livepatch-sample and update documentation.
>>>
>>> The patch was tested under three use-cases:
>>>
>>> use-case 1: There is a relocation in the lp that can be automatically
>>> resolved by klp-convert (tested by removing the annotations from
>>> samples/livepatch/livepatch-annotated-sample.c)
>>>
>>> use-case 2: There is a relocation in the lp that cannot be automatically
>>> resolved, as the name of the respective symbol appears in multiple
>>> objects. The livepatch contains an annotation to enable a correct
>>> relocation - reproducible with this livepatch sample:
>>> www.livewire.com.br/suse/klp/livepatch-sample.1.c
>>>
>>> use-case 3: There is a relocation in the lp that cannot be automatically
>>> resolved similarly as 2, but no annotation was provided in the livepatch,
>>> triggering an error during compilation - reproducible with this livepatch
>>> sample: www.livewire.com.br/suse/klp/livepatch-sample.2.c
>>>
>>> In comparison with v1, this version of the patch-set:
>>> - was rebased to kernel 4.19
>>> - adds a Symbols.list versioning information
>>> - brings bug fixes and code improvements to klp-convert sources
>>>
>>> This is a patch-set repost, given that a typo in a mail address prevented
>>> the original submission from being posted to lkml.
>>>
>>> [ ... snip ... ]
>>
>> Hi Joao,
>>
>> Apologies for taking so long to get to this patchset, but I finally
>> spent last week reviewing and testing.  My goal was to write a klp
>> self-test based on the implementation and your sample module.  Along the
>> way I spotted a few minor bugs and other small suggestions.  Instead of
>> dumping a bunch of code or patch content in my replies, I posted my
>> rebase and modified branch here:
>>
>>     https://github.com/joe-lawrence/linux/tree/klp-convert-v2-rebase-review
>>
>> I added subject line [squash] tags to individual commits that should be
>> considered fixups for patches in this set.  Those commit logs also
>> contain [joe: description] tags and my sign-offs for that purpose as
>> well.
>>
>> Hopefully this form of feedback will be easy to digest.  I'll reply to
>> the individual patchs here with high-level comments and a pointer to the
>> corresponding github patch.  Let me know if there are any questions.  If
>> it is easier to simply repost as a v3 with those changes, I can do that
>> as well -- whichever method is easier for you.
>>
> 
> Hi Joe, again thanks a lot for the review. To the things which I had
> something to say, I already replied to the respective messages. If none
> has issues with the fix for the ppc64le .TOC. symbols issue (on patch
> 5/8) and with the fix for the multi-used-m Makefile (on patch 2/8), I
> guess we are good for moving forward to a v3.
 >> If you don't mind, this is fine by me that you squash the changes and
> post the newer version. In fact, I can't figure out why my patch
> submissions did not appear in lkml (if someone knows what could be the
> reason, please, let me know), so I guess it would be nice to have it
> reachable this time.

I can do that... what I will do is collate all the comments, squash 
revisions, and update logs accordingly.  I'll post it up on github to 
let the 0-day lkp bot run through it and you can take a look to double 
check the series, attributions, etc before I post it here.

BTW, something I *just* noticed when putting together that toy 
out-of-tree module to test out multi-object livepatch modules is that we 
aren't considering out-of-tree symbols in Symbols.list.

Perhaps we can save that for v4 or beyond, but maybe we want to 
re-arrange the klp-convert arguments to "klp-convert <input.ko> <out.ko> 
<Symbols.list> [Symbols.list ...]" where we treat everything after 
<out.ko> as a symbol list file?  (This would assume we would generate a 
separate out-of-tree module Symbols.list file.)    /thinking-out-loud

-- Joe

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