Ingeniería Informática

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Analysis of invariants for efficient bounded verification
(2010-07) Galeotti, Juan Pablo; Rosner, Nicolás; López Pombo, Carlos G.; Frías, Marcelo
"SAT-based bounded veri cation of annotated code consists of translating the code together with the annotations to a propositional formula, and analyzing the formula for speci cation violations using a SAT-solver. If a violation is found, an execution trace exposing the error is exhibited. Code involving linked data structures with intricate invariants is particularly hard to analyze using these techniques. In this article we present TACO, a prototype tool which implements a novel, general and fully automated technique for the SAT-based analysis of JML-annotated Java sequential programs dealing with complex linked data structures. We instrument code analysis with a symmetry-breaking predicate that allows for the parallel, automated computation of tight bounds for Java elds. Experiments show that the translations to propositional formulas require signi cantly less propositional variables, leading in the experiments we have carried out to an improvement on the e ciency of the analysis of orders of magnitude, compared to the non instrumented SAT-based analysis. We show that, in somecases, our tool can uncover bugs that cannot be detected by state-of-the-art tools based on SAT-solving, model checking or SMT-solving."
Automated workarounds from Java program specifications based on SAT solving
(2018-11) Uva, Marcelo; Ponzio, Pablo; Regis, Germán; Aguirre, Nazareno; Frías, Marcelo
"The failures that bugs in software lead to can sometimes be bypassed by the so-called workarounds: when a (faulty) routine fails, alternative routines that the system offers can be used in place of the failing one, to circumvent the failure. Existing approaches to workaround-based system recovery consider workarounds that are produced from equivalent method sequences, utomatically computed from user-provided abstract models, or directly produced from user-provided equivalent sequences of operations. In this paper, we present two techniques for computing workarounds from Java code equipped with formal specifications, that improve previous approaches in two respects. First, the particular state where the failure originated is actively involved in computing workarounds, thus leading to repairs that are more state specific. Second, our techniques automatically compute workarounds on concrete program state characterizations, avoiding abstract software models and user-provided equivalences. The first technique uses SAT solving to compute a sequence of methods that is equivalent to a failing method on a specific failing state, but which can also be generalized to schemas for workaround reuse. The second technique directly exploits SAT to circumvent a failing method, building a state that mimics the (correct) behaviour of a failing routine, from a specific program state too. We perform an experimental evaluation based on case studies involving implementations of collections and a library for date arithmetic, showing that the techniques can effectively compute workarounds from complex contracts in an important number of cases, in time that makes them feasible to be used for run-time repairs. Our results also show that our state-specific workarounds enable us to produce repairs in many cases where previous workaround-based approaches are inapplicable."
Automated workarounds from Java Program specifications based on SAT solving
(2017) Uva, Marcelo; Ponzio, Pablo; Regis, Germán; Aguirre, Nazareno; Frías, Marcelo
"The failures that bugs in software lead to can sometimes be bypassed by the so called workarounds: when a (faulty) routine fails, alternative routines that the system offers can be used in place of the failing one, to circumvent the failure. Previous works have exploited this workarounds notion to automatically recover from runtime failures in some application domains. However, existing approaches that compute workarounds automatically either require the user to manually build an abstract model of the software under consideration, or to provide equivalent sequences of operations from which workarounds are computed, diminishing the automation of workaround-based system recovery. In this paper, we present two techniques that automatically compute workarounds from Java code equipped with formal specifications, avoiding abstract software models and user provided equivalences. These techniques employ SAT solving to compute workarounds on concrete program state characterizations. The first employs SAT solving to compute traditional workarounds, while the second directly exploits SAT solving to circumvent a failing method, building a state that mimics the (correct) behaviour of this failing routine. Our experiments, based on case studies involving implementations of collections and a library for date arithmetic, enable us to show that the techniques can effectively compute workarounds from complex contracts in an important number of cases, in time that makes them feasible to be used for run time repairs."
FLACK: Counterexample-guided fault localization for alloy models
(2021) Zheng, Guolong; Nguyen, Thanh Vu; Gutiérrez Brida, Simón; Regis, Germán; Frías, Marcelo; Aguirre, Nazareno; Bagher, Hamid
"Fault localization is a practical research topic that helps developers identify code locations that might cause bugs in a program. Most existing fault localization techniques are designed for imperative programs (e.g., C and Java) and rely on analyzing correct and incorrect executions of the program to identify suspicious statements. In this work, we introduce a fault localization approach for models written in a declarative language, where the models are not “executed,” but rather converted into a logical formula and solved using backend constraint solvers. We present FLACK, a tool that takes as input an Alloy model consisting of some violated assertion and returns a ranked list of suspicious expressions contributing to the assertion violation. The key idea is to analyze the differences between counterexamples, i.e., instances of the model that do not satisfy the assertion, and instances that do satisfy the assertion to find suspicious expressions in the input model. The experimental results show that FLACK is efficient (can handle complex, real world Alloy models with thousand lines of code within 5 seconds), accurate (can consistently rank buggy expressions in the top 1.9% of the suspicious list), and useful (can often narrow down the error to the exact location within the suspicious expressions)."
Reparación de programas distribuida: Stryker distribuido
(2017) Gilly, Francis Iván; Bejarano González, Fernando; Frías, Marcelo; Zemin, Luciano
"La herramienta "Stryker" implementa una técnica para reparar programas equipados con contratos. Esta técnica combina análisis dinámico (en tiempo de ejecución) con análisis estático para verificar las reparaciones candidatas y emplea un mecanismo para detectar y podar candidatos no viables aprovechando las especificaciones del programa. En este artículo se presenta "Stryker distribuido", una herramienta prototipo que implementa una mejora a la técnica de Stryker para permitir su escalamiento a múltiples computadoras. En esta nueva técnica se desarrolló un mecanismo de poda distribuida. La técnica fue evaluada para comparar su funcionamiento en múltiples computadoras utilizando un benchmark que pertenece a Stryker y que consiste en un conjunto de clases de Java con fallas. Los experimentos muestran que en general el tiempo de ejecución disminuye a medida que se aumenta la cantidad de computadoras que se utilizan. También se demostró que a mayores cantidades de fallas en el programa, se obtienen mayores reducciones en cuanto al tiempo."

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