Sound reasoning about integral data types with a reusable SMT solver interface

Abstract

We extend the Leon verification system for Scala with support for bit-vector reasoning, thus addressing one of its fundamental soundness limitation with respect to the treatment of integers primitives. We leverage significant progresses recently achieved in SMT solving by developing a solver-independent interface to easily configure the back-end of Leon. Our interface is based on the emerging SMT-LIB standard for SMT solvers, and we release a Scala library offering full support for the latest version of the standard.We use the standard BigInt Scala library to represent mathematical integers, whereas we correctly model Int as 32-bit integers. We ensure safety of arithmetic by checking for division by zero and correctly modeling division and modulo. We conclude with a performance comparison between the sound representation of Ints and the cleaner abstract representation using mathematical integers, and discuss the trade-off involved.

System FR: formalized foundations for the stainless verifier

“…A motivation for our work are implementations that verify polymorphic functional programs using SMT solvers [Suter et al 2011;Vazou et al 2014]. To focus on foundations, we look at simpler verifiers that do not perform invariant inference and are mostly based on unfolding recursive definitions and encoding of higher-order functions into SMT theories [Blanc and Kuncak 2015;Suter et al 2011;Voirol et al 2015]. A recent implementation of such a verifier is the Stainless system [LARA 2019], which handles a subset of Scala [Odersky et al 2008].…”