Category Archives: Papers and Slides

Safe and Secure Software – An Invitation to Ada 2012

The aim of this booklet is to show how the study of Ada in general, and the features introduced by Ada 2005 and Ada 2012 in particular, can help anyone designing safe and secure software regardless of the programming language in which the software is eventually written. After all, successful implementers of safe and secure software write in the spirit of Ada in any language!

To download the booklet, please visit this page.

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Using Formal Verification in the Landing Field

An article which I co-authored was just published in the May-June special issue of IEEE Software on Safety-Critical Software. It’s called Testing or Formal Verification: DO-178C Alternatives and Industrial Experience, and it talks about how to use formal verification instead of testing for software in civilian airplanes (for which DO-178C applies). It is based on the experience of Airbus and Dassault-Aviation in the application of formal verification with the Frama-C platform.

We describe:

  • What the avionics certification standard DO-178C asks in replacement for test coverage, which does not apply when one uses formal verification instead of testing.
  • How formal verification tools can help with these alternate objectives.
  • The solutions that Airbus and Dassault-Aviation have implemented to cover these objectives.

We’ll be happy to get some feedback from others! Please comment. This paper is copyrighted by IEEE, and reproduced here with their permission. You can also access it on IEEE Software website.

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DO-178C/ED-12C vs DO-178B/ED-12B: Changes and Improvements

This document identifies all the changes in the new release DO-178C/ED-12C, explains their rationale, and highlights the impact of these changes on the various software processes. The PDF can be downloaded here.

© Frédéric Pothon, 2012
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

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Safe and reliable embedded linux programming

Dr José Ruiz gave this talk at yesterday’s Embed with Linux conference in Lorient, France. The talk provides an overview of techniques to design and implement reliable embedded applications. The goal is to achieve safe and analyzable behavior by construction, including handling parallel multiprocessor systems in an efficient and predictable way. The means to attain this objective is to statically configure the application to run on embedded linux platforms, and then to use run-time support to enforce constraints imposed to the system.

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Formalization and Comparison of MCDC and Object Branch Coverage Criteria

This paper was presented by Jerome Guitton at the recent ERTS 2012 conference:
This paper presents formal results derived from the COUVERTURE project, whose goal was to develop tools to support structural coverage analysis of unin- strumented safety-critical software. After briefly introducing the project context and explaining the need for formal foundations, we focus on the relationships between machine branch coverage and the DO-178B Modified Condition/Decision Coverage (MCDC) criterion. A thorough understanding of those relationships is important, since it provides the foundation for knowing where efficient execution trace techniques can be used to demonstrate compliance with the MCDC criterion. We first present several conjectures that were tested using Alloy models, then provide a formally verified characterization of the situations when coverage of object control-flow edges implies MCDC compliance.The full paper can de downloaded here.

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Integrating Formal Program Verification with Testing

This is the paper that Yannick Moy presented at the recent ERTS 2012 conference:
Verification activities mandated for critical software are essential to achieve the required level of confidence expected in life-critical or business-critical software. They are becoming increasingly costly as, over time, they require the development and maintenance of a large body of functional and robustness tests on larger and more complex applications. Formal program verification offers a way to reduce these costs while providing stronger guarantees than testing. Addressing verification activities with formal verification is supported by upcoming standards such as do-178c for software development in avionics. In the Hi-Lite project, we pursue the integration of formal verification with testing for projects developed in C or Ada. In this paper, we discuss the conditions under which this integration is at least as strong as testing alone. We describe associated costs and benefits, using a simple banking database application as a case study. The full paper can de downloaded here.

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Compilation of Heterogeneous Models: Motivations and Challenges

This is the paper that Matteo Bordin presented at the recent ERTS 2012 conference:
The widespread use of model driven engineering in the development of software-intensive systems, including high- integrity embedded systems, gave rise to a “Tower of Babel” of modeling languages. System architects may use languages such as OMG SysML and MARTE, SAE AADL or EAST-ADL; control and command engineers tend to use graphical tools such as MathWorks Simulink/Stateflow or Esterel Technologies SCADE, or textual languages such as MathWorks Embedded Matlab; software engineers usually rely on OMG UML; and, of course, many in- house domain specific languages are equally used at any step of the development process. This heterogeneity of modeling formalisms raises several questions on the verification and code generation for systems described using heterogeneous models: How can we ensure consistency across multiple modeling views? How can we generate code, which is optimized with respect to multiple modeling views? How can we ensure model-level verification is consistent with the run-time behavior of the generated executable application?

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Prove Your Plane Now!

The DO-333 is now available! (ok, that’s not free: 215$ for an electronic version, or 300$ for a hard copy, pfew!)

Under this amazingly explicit name is hiding the formal methods supplement for DO-178C. Or, said otherwise, the document that allows you, as a developer of avionics software, to replace tests/reviews/analyses by formal methods. Or you, as a provider of techniques and tools for formal methods, to find customers in the avionics market. Ah yes, because the new version of the certification standard for avionics software, DO-178C, has been also issued at the same time. So that starts today!

Here is what the abstract of this doc says:

This supplement identifies the additions, modifications and substitutions to DO-178C and DO-278A objectives when formal methods are used as part of a software life cycle, and the additional guidance required. It discusses those aspects of airworthiness certification that pertain to the production of software, using formal methods for systems approved using DO-178C.

Formal methods are mathematically-based techniques for the specification, development and verification of software aspects of digital systems. The mathematical basis of formal methods consists of formal logic, discrete mathematics and computer-readable languages. The use of formal methods is motivated by the expectation that, as in other engineering disciplines, performing appropriate mathematical analyses can contribute to establishing the correctness and robustness of a design.

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Best Paper Award for Results of Verification Competition

Last year, the conference VSTTE 2010 organized a competition of software verification systems (language + tools), to improve understanding of each system’s pros and cons. Rod Chapman from Altran Praxis participated with the SPARK language and toolset, and solved the first problem even beyond what the subject asked. We have since provided solutions in SPARK to all five problems, like other teams, which formed the basis for a report that you can find on this page.

This report was deemed important enough by the organizers of the Formal Methods conference 2011 that they have granted it the best paper award.

Furthermore, the page of the competition contains an archive with all solutions in many different languages and systems… you can even DIY!

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Language Vulnerabilities for Dummies

In case you do not know the series of books “for Dummies”, its principle is to explore a subject from the ground up, with rich explanations and examples for non-experts. That’s in my view a valid alternative title for the recently published “Guidance to Avoiding Vulnerabilities in Programming Languages through Language Selection and Use”. Rich (around 70 vulnerabilities explored) + detailed (130 pages!) + accessible (it contains the best discussion I’ve read of unspecified/implementation-defined/undefined behavior).

The ISO/IEC committee has produced here a language-neutral evaluation of the ways in which a language may “come in the way”, and how to avoid traps and pitfalls either upfront (in language design) or in the field (through coding standards and use of static analysis tools). This is a must-read for anyone whose task is to establish coding guidelines, recommend the usage of a static analysis tool, or choose a programming language for some project.

While Ada and SPARK naturally stand as the languages with fewer vulnerabilities, it also shows the many uses of static analysis tools, from coding standard checking (like GNATcheck) to static analysis (like CodePeer) and formal proof (like SPARK toolset). The recommendations also match well the restrictions for the Alfa subset of Ada that we are defining in project Hi-Lite. (See for example the discussion of aliasing in section 6.39 “Passing Parameters and Return Values”.)

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