Integrating the Formal Methods part of Qualification

Mon Jul 11 11:21:12 UTC 2022

On 6 Jul 2022, at 20:07, Gedare Bloom <gedare at rtems.org> wrote:

On Sun, Jul 3, 2022 at 7:49 PM Chris Johns <chrisj at rtems.org> wrote:

On 2/7/2022 12:59 am, Andrew Butterfield wrote:

On 1 Jul 2022, at 00:59, Chris Johns <chrisj at rtems.org
<mailto:chrisj at rtems.org>> wrote:

On 28/6/2022 11:09 pm, Andrew.Butterfield at scss.tcd.ie
<mailto:Andrew.Butterfield at scss.tcd.ie> wrote:

Dear RTEMS Developers,

While the validation tests from the RTEMS pre-qualification activity are
now merged into the RTEMS master, the work done in investigating and
deploying formal methods techniques is not yet merged.

The activity had two main phases: a planning phase (Nov 2018-Oct 2019)
that explored various formal techniques, followed by an execution phase
(Oct 2019-Nov 2021) that then applied selected techniques to selected
parts of RTEMS. Some discussions occurred with the RTEMS community
via the mailings lists over this time. A short third phase (Nov 2021 - Dec 2021)
then reported on the outcomes. Each phase resulted in a technical report.

The key decision made was to use Promela/SPIN for test generation, and
to apply it to the Chains API, the Event Manager, and the SMP scheduler
thread queues. This involved developing models in the Promela language
and using the SPIN model-checker tool to both check their correctness
and to generate execution scenarios that could be used to generate tests.
Tools were developed using Python 3.8 to support this. Initial documentation
about tools and how to use them was put into the 2nd phase report.

Congratulations for the work and results you and others have managed to achieve.
It is exciting to see this happening with RTEMS and being made public.

We now come to the part where we explore the best way to integrate this
into RTEMS. I am proposing to do this under the guidance of Sebastian Huber.

The first suggested step is adding in new documentation to the RTEMS
Software Engineering manual, as a new Formal Methods chapter. This would
provide some motivation, as well as a "howto".

I assume that I would initially describe the proposed changes using the patch
review process described in the section on Preparing and Sending Patches in
the User Manual.

How do you feel I should best proceed?

It is hard for me to answer until I understand what is being submitted and who
maintains it? I am sure you understand this due to the specialised nature of the
work.

Indeed, I quite agree.  I have some short answers below, with suggestions.

Thanks.
+1

What will be submitted, ie SPIN files, scripts, etc?

Promela/SPIN model files (ASCII text, C-like syntax)
C template files (.h,.c) to assist test code generation
YAML files to provide a mapping from model concepts to RTEMS C test code
python scripts to automate the test generation
Documentation - largely RTEMS compliant sphinx sources (.rst)

Where are you looking to add these pieces?

Everything except the documentation could live in a top-level folder ('formal')
in rtems-central.
In fact there is no particular constraint from my perspective for where they can go.

Using rtems-central is fine.
Do they require anything currently located in rtems-central? Are the
models or YAML files related to the current specification files? I
know I'm guilty of not spending the time yet to deeply learn
rtems-central, but I would like to know that these files will fit
within that repo as it currently is intended to operate.

At the moment there is nothing in rtems-central directly related to this. All the python
scripts there support the tools/specs that Sebastian and colleagues developed.
I can see a new top-level script being added here to support the formal stuff.

It is possible that we might introduce a new specification item that integrates
in with the spec system that is used to trigger the Spin test generations. I'll discuss the
best wat to do this with Sebastian.

RSB should be taught how to build the necessary host tools to run Promela/SPIN.

Spin is open source under a BSD 3-clause license, available from spinroot.com,
and also via https://github.com/nimble-code/Spin. It is written in C and has very few
dependencies. I'm not sure what is involved in adding it to the RSB, but I guess
Sebastian will know.

The plan would be to add the pertinent parts of our project documentation into
new chapters
in the RTEMS software engineering manual. So that would be eng/ in the
rtems-docs repo.

Great.
+1

A new section in the eng should be suitable. I would actually
recommend using
https://docs.rtems.org/branches/master/eng/test-framework.html# as a
good example.

Thanks - that very helpful. I think our section should immediately follow that one.
All we need now is a suitable title.  "Formal Test Framework"?

How is the verification run against the code? Do we manage regression testing
and is that even possible?

The python scripts basically run SPIN in such a way as to generate scenarios
that model
correct behaviour which then get turned into standard RTEMS test programs. These all
get added into a new testsuite in the rtems repo (testsuites/models, say).
They are properly integrated into the RTEMS test system, so get built and run by
waf.
This is similar to how the tests generated by Sebastian in testsuites/validation
are handled.

From the perspective of a user that works out of git.rtems.org/rtems
<http://git.rtems.org/rtems>,
there will be no obvious impact - just some extra tests in among the ones that
already exist.

Thanks and this make sense.

I hope my simple questions highlight a lack of understand on how this works and
how we maintain it and use it once integrated.

I intend to continue to work and maintain this for the foreseeable future. I
would hope as this beds in that other Promela/SPIN users out there will also get
more involved over time.

Thank, it is appreciated.
I'm also interested in tracking this, and I might be able to go after
some resources on the US side. I'll be in touch on that later, but if
any US users are tracking this too, or you know any with interest, I'd
love to talk about it.

Indeed  - that would be good.

Andrew

It is expected that Promela models will be as static as the corresponding APIs.
They capture the specified behaviour of API calls, not their detailed
implementation.

The python scripts should also be fairly stable, although I can see some
tweaking for a while to improve workflow issues that might arise.

There are some extra python libraries that are required over and above what is
currently specified in rtems-central/requirements.txt

This all makes sense to me. Thank you for taking the time to respond.

Chris
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