Date:   Wed, 30 Aug 2017 13:00:25 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Joao Moreira <jmoreira@...e.de>
Cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        mbenes@...e.cz, mmarek@...e.cz, pmladek@...e.com, jikos@...e.cz,
        nstange@...e.de, jroedel@...e.de, matz@...e.de,
        khlebnikov@...dex-team.ru, jeyu@...nel.org
Subject: Re: [PATCH 0/8] livepatch: klp-convert tool

On Tue, Aug 29, 2017 at 04:01:32PM -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
> 
> Joao Moreira (2):
>   kbuild: Support for Symbols.list creation
>   documentation: Update on livepatch elf format
> 
> Josh Poimboeuf (5):
>   livepatch: Create and include UAPI headers
>   livepatch: Add klp-convert tool
>   livepatch: Add klp-convert annotation helpers
>   modpost: Integrate klp-convert
>   livepatch: Add sample livepatch module
> 
> Miroslav Benes (1):
>   modpost: Add modinfo flag to livepatch modules

Thanks a lot for picking these patches up and improving them.  I've only
glanced at the code, but so far it's looking good.  It may be a few
weeks before a I get a chance to do a proper review.

One quick question, possibly for Miroslav.  Do we have a plan yet for
dealing with GCC optimizations?

  https://lkml.kernel.org/r/20161110161053.heua3abuaekz4yy7@treble

I still like the '-fpreserve-function-abi' idea, but maybe it's not
realistic.

-- 
Josh

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