Toccata

In this paper we present an approach to specify programs performing iterations. The idea is to specify iteration in terms of the nite sequence of the elements enumerated so far, and only those. In particular, we are able to deal with non-deterministic and possibly innite iteration. We show how to cope with the issue of an iteration no longer being consistent with mutable data. We validate our proposal using the deductive verication tool Why3 and two iteration paradigms, namely cursors and higher-order iterators. For each paradigm, we verify several implementations of iterators and client code. This is done in a modular way, i.e., the client code only relies on the specication of the iteration.

Unstructured (low-level) programs tend to be challenging to prove correct, since the control flow is arbitrary complex and there are no obvious points in the code where to insert logical assertions. In this paper, we present a system to formally verify ARM programs, based on a flow sequentialization methodology and a formalized ARM semantics. This system, built upon the why3 verification platform, takes an annotated ARM program, turns it into a set of purely sequential flow programs, translates these programs' instructions into the corresponding formalized opcodes and finally calls the Why3 VCGen to generate the verification conditions that can then be discharged by provers. A prototype has been implemented and used to verify several programming examples.

Keywords: Why3