GNATprove Tips and Tricks: a Lemma for Sorted Arrays

We report on the creation of the first lemma of a new lemma library on arrays: a lemma on transitivity of the order in arrays.

Automatic Generation of Frame Conditions for Array Components

One of the most important challenges for SPARK users is to come up with adequate contracts and annotations, allowing GNATprove to verify the expected properties in a modular way. Among the annotations mandated by the SPARK toolset, the hardest to come up with are probably loop invariants. A previous post explains how GNATprove can automatically infer loop invariants for preservation of unmodified record components, and so, even if the record is itself nested inside a record or an array. Recently, this generation was improved to also support the simplest cases of partial array updates. We describe in this post in which cases GNATprove can, or cannot, infer loop invariants for preservation of unmodified array components.

Verifying Tasking in Extended, Relaxed Style

Tasking was one of the big features introduced in the previous release of SPARK 2014. However, GNATprove only supported tasking-related constructs allowed by the Ravenscar profile. Now it also supports the more relaxed GNAT Extended Ravenscar profile.

Simplifying our product versioning

Looking at the list of product versions that were expected for 2017 it became clear that we had to review the way we were handling product versioning.

SPARK 2014 Rationale: Support for Type Invariants

Type invariants are used to model properties that should always hold for users of a data type but can be broken inside the data type implementation. Type invariant are part of Ada 2012 but were not supported in SPARK until SPARK Pro 17.

Automatic Generation of Frame Conditions for Record Components

Formal verification tools like GNATprove rely on the user to provide loop invariants to describe the actions performed inside loops. Though the preservation of variables which are not modified in the loop need not be mentioned in the invariant, it is in general necessary to state explicitly the preservation of unmodified object parts, such as record fields or array elements. These preservation properties form the loop’s frame condition. As it may seem obvious to the user, the frame condition is unfortunately often forgotten when writing a loop invariant, leading to unprovable checks. To alleviate this problem, the GNATprove tool now generates automatically frame conditions for preserved record components. In this post, we describe this new feature on an example.

GNATprove Tips and Tricks: Using the Lemma Library

A well-know result of computing theory is that the theory of arithmetic is undecidable. This has practical consequences in automatic proof of programs which manipulate numbers. The provers that we use in SPARK have a good support for addition and subtraction, but much weaker support for multiplication and division. This means that as soon as the program has multiplications and divisions, it is likely that some checks won't be proved automatically. Until recently, the only way forward was either to complete the proof using an interactive prover (like Coq or Isabelle/HOL) or to justify manually the message about an unproved check. There is now a better way to prove automatically such checks, using the recent SPARK lemma library.

Quantifying over Elements of a Container

Containers holding several items of the same type such as arrays, lists, or sets are a common occurrence in computer programs. Stating a property over such containers often involves quantifying over the elements they contain. The way quantified formulas over containers are translated for proof can be tuned in GNATprove using a specific annotation.

Provably safe programming at Embedded World

AdaCore continues to build reliable and secure software for embedded software development tools. Last month, we attended Embedded World 2016, one of the largest conferences of its kind in Europe, to present our embedded solutions and our expertise for safety, and mission critical applications in a variety of domains.

Embedded Product Line Updates

Embedded products are not stand alone, this allows them to have safety, mission critical and real-time requirements that they wouldn’t necessarily have otherwise. The embedded product line provides analyzable, verifiable, and certifiable software for both static and dynamic analysis tools.

QGen 2.1 Release!

Embedded World will see the latest release of QGen, the qualifiable and customisable code generator for Simulink® and Stateflow® models!

Formal Verification Made Easy!

We are pleased to announce our latest release of SPARK Pro! A product that has been jointly developed alongside our partner Altran and following the global AdaCore Tech Days, you can now see the SPARK 2014 talk, Formal Verification Made Easy by AdaCore’s Hristian Kirtchev, on YouTube.

SPARK 2014 Rationale: Support for Ravenscar

As presented in a recent post by Pavlos, the upcoming release of SPARK Pro will support concurrency features of Ada, with the restrictions defined in the Ravenscar profile of Ada. This profile restricts concurrency so that concurrent programs are deterministic and schedulable. SPARK analysis makes it possible to prove that shared data is protected against data races, that deadlocks cannot occur and that no other run-time errors related to concurrency can be encountered when running the program. In this post, I revisit the example given by Pavlos to show SPARK features and GNATprove analysis in action.

SPARK 2016 Supports Ravenscar!

The new big feature of the SPARK 2016 release is the support of the Ravenscar profile. Users can now use protected objects and tasks to write concurrent code. On uniprocessor computers the toolset can ensure that no deadlocks or data races will occur and that no tasks will terminate. Read this blog post to learn more and see the new feature in practice.

SPARK 16: Generating Counterexamples for Failed Proofs

While the analysis of failed proofs is one of the most challenging aspects of formal verification, it would be much easier if a tool would automatically find values of variables showing why a proof fails. SPARK Pro 16, to be released in 2016, is going to introduce such a feature. If a proof fails, it attempts to generate a counterexample exhibiting the problem. This post introduces this new feature, developed in the scope of the ProofInUse laboratory.

GNATprove Tips and Tricks: User Profiles

One of the most difficult tasks when using proof techniques is to interact with provers, in particular to progressively increase proof power until everything that should be proved is proved. Until the last release, increasing the proof power meant operating on three separate switches. There is now a simpler solution based on a new switch --level, together with a simpler proof panel in GPS for new users.

HIS Conference 2015, Bristol

We are excited to be sponsoring and exhibiting at the 2nd annual High Integrity Software conference, taking place on 5th November 2015 at The Royal Marriott Hotel in Bristol.

AdaCore Tech Days 2015

SPARK 2014 Rationale: Variables That Are Constant

The SPARK tools now support yet another feature that allows users to better specify the intended behavior of their programs. This new feature enables users to declare that specific variables can only be updated during the elaboration of their enclosing package. Read on if you want to know more...

New Book About SPARK 2014

I am very pleased to announce that a book is now available for those who want to learn formal verification with SPARK 2014. This book was written by Prof. John McCormick from University of Northern Iowa and Prof. Peter Chapin from Vermont Technical College. We've been interacting a lot with them since they started in 2013, and the result of these interactions is quite satisfying!