Helmut Seidl

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Robert Cowan

The University of Sydney

Alexey Belousov

Russian State University for the Humanities

Antonis K . Petrides

Open University of Cyprus

Silvia Barbantani

Università Cattolica del Sacro Cuore (Catholic University of the Sacred Heart)

ivana petrovic

University of Virginia

Gennaro Tedeschi

Università degli Studi di Trieste

Rita Pierini

Università degli Studi di Firenze (University of Florence)

Francesca Romana Berno

Università degli Studi "La Sapienza" di Roma

Thomas Nelson

University of Oxford

mario lentano

University of Siena / Università di Siena

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Papers by Helmut Seidl

Goblint: Thread-Modular Abstract Interpretation Using Side-Effecting Constraints

Tools and Algorithms for the Construction and Analysis of Systems, 2021

Goblintis a static analysis framework for C programs specializing in data race analysis. It relie... more

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Deciding Equivalence of Separated Non-nested Attribute Systems in Polynomial Time

Lecture Notes in Computer Science, 2019

In 1982, Courcelle and Franchi-Zannettacci showed that the equivalence problem of separated non-n... more In 1982, Courcelle and Franchi-Zannettacci showed that the equivalence problem of separated non-nested attribute systems can be reduced to the equivalence problem of total deterministic separated basic macro tree transducers. They also gave a procedure for deciding equivalence of transducer in the latter class. Here, we reconsider this equivalence problem. We present a new alternative decision procedure and prove that it runs in polynomial time. We also consider extensions of this result to partial transducers and to the case where parameters of transducers accumulate strings instead of trees.

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18 13192 – Tree Transducers and Formal Methods Participants

The aim of this Dagstuhl Seminar was to bring together researchers from various research areas re... more The aim of this Dagstuhl Seminar was to bring together researchers from various research areas related to the theory and application of tree transducers. Recently, interest in tree transducers has been revived due to surprising new applications in areas such as XML databases, security verification, programming language theory, and linguistics. This seminar therefore aimed to inspire the exchange of theoretical results and information regarding the practical requirements related to tree transducers. Seminar 5.–8. May, 2013 – www.dagstuhl.de/13192 1998 ACM Subject Classification F.1.1 Models of Computation

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Equivalence of Linear Tree Transducers with Output in the Free Group

Developments in Language Theory, 2020

We show that equivalence of deterministic linear tree transducers can be decided in polynomial ti... more We show that equivalence of deterministic linear tree transducers can be decided in polynomial time when their outputs are interpreted over the free group. Due to the cancellation properties offered by the free group, the required constructions are not only more general, but also simpler than the corresponding constructions for proving equivalence of deterministic linear tree-to-word transducers.

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Definability Results for Top-Down Tree Transducers

Developments in Language Theory, 2021

We prove that for a given deterministic top-down transducer with look-ahead it is decidable wheth... more

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Improving Thread-Modular Abstract Interpretation

Static Analysis, 2021

We give thread-modular non-relational value analyses as abstractions of a local trace semantics. ... more We give thread-modular non-relational value analyses as abstractions of a local trace semantics. The semantics as well as the analyses are formulated by means of global invariants and side-effecting constraint systems. We show that a generalization of the analysis provided by the static analyzer Goblint as well as a natural improvement of Antoine Miné's approach can be obtained as instances of this general scheme. We show that these two analyses are incomparable w.r.t. precision and provide a refinement which improves on both precision-wise. We also report on a preliminary experimental comparison of the given analyses on a meaningful suite of benchmarks.

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Reachability for Dynamic Parametric Processes

Lecture Notes in Computer Science, 2017

In a dynamic parametric process every subprocess may spawn arbitrarily many, identical child proc... more In a dynamic parametric process every subprocess may spawn arbitrarily many, identical child processes, that may communicate either over global variables, or over local variables that are shared with their parent. We show that reachability for dynamic parametric processes is decidable under mild assumptions. These assumptions are e.g. met if individual processes are realized by pushdown systems, or even higherorder pushdown systems. We also provide algorithms for subclasses of pushdown dynamic parametric processes, with complexity ranging between NP and DEXPTIME.

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Abstract Interpretation over Zones without Widening

We present a practical algorithm for computing least solutions of systems of (fixpoint-)equations... more We present a practical algorithm for computing least solutions of systems of (fixpoint-)equations over the integers with, besides other monotone operators, addition, multiplication by positive constants, maximum, and minimum. The algorithm is based on maxstrategy iteration. Its worst-case running-time (w.r.t. a uniform cost measure) is independent of the sizes of occurring numbers. We apply this algorithm to compute the abstract semantics of programs over integer intervals as well as over integer zones.

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Static race detection for device drivers: the Goblint approach

Proceedings of the 31st IEEE/ACM International Conference on Automated Software Engineering, 2016

Device drivers rely on fine-grained locking to ensure safe access to shared data structures. For ... more Device drivers rely on fine-grained locking to ensure safe access to shared data structures. For human testers, concurrency makes such code notoriously hard to debug; for automated reasoning, dynamically allocated memory and low-level pointer manipulation poses significant challenges. We present a flexible approach to data race analysis, implemented in the open source Goblint static analysis framework that combines different pointer and value analyses in order to handle a wide range of locking idioms, including locks allocated dynamically as well as locks stored in arrays. To the best of our knowledge, this is the most ambitious effort, having lasted well over ten years, to create a fully automated static race detection tool that can deal with most of the intricate locking schemes found in Linux device drivers. Our evaluation shows that these analyses are sufficiently precise, but practical use of these techniques requires inferring environmental and domain-specific assumptions. CCS Concepts •Theory of computation → Program analysis; •Software and its engineering → Software safety;

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Enforcing Termination of Interprocedural Analysis

Static Analysis, 2016

Interprocedural analysis by means of partial tabulation of summary functions may not terminate wh... more Interprocedural analysis by means of partial tabulation of summary functions may not terminate when the same procedure is analyzed for infinitely many abstract calling contexts or when the abstract domain has infinite strictly ascending chains. As a remedy, we present a novel local solver for general abstract equation systems, be they monotonic or not, and prove that this solver fails to terminate only when infinitely many variables are encountered. We clarify in which sense the computed results are sound. Moreover, we show that interprocedural analysis performed by this novel local solver, is guaranteed to terminate for all non-recursive programs-irrespective of whether the complete lattice is infinite or has infinite strictly ascending or descending chains.

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An Analysis of Universal Information Flow Based on Self-Composition

2015 IEEE 28th Computer Security Foundations Symposium, 2015

We introduce a novel way of proving information flow properties of a program based on its self-co... more We introduce a novel way of proving information flow properties of a program based on its self-composition. Similarly to the universal information flow type system of Hunt and Sands, our analysis explicitly computes the dependencies of variables in the final state on variables in the initial state. Accordingly, the analysis result is independent of specific information flow lattices, and allows to derive information flow w.r.t. any of these. While our analysis runs in polynomial time, we prove that it never loses precision against the type system of Hunt and Sands, and may gain extra precision by taking similarities between different branches of conditionals into account. Also, we indicate how it can be smoothly generalized to an interprocedural analysis.

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Tree Transducers and Formal Methods (Dagstuhl Seminar 13192) Information Visualization-Towards Multivariate Network Visualization (Dagstuhl Seminar 13201) Automated Reasoning on Conceptual Schemas (Dagstuhl Seminar 13211) Computational Methods Aiding Early-Stage Drug Design (Dagstuhl Seminar 13212)

Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibli... more Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available in the Internet at http://dnb.d-nb.de. License This work is licensed under a Creative Commons Attribution 3.0 Unported license: CC-BY. In brief, this license authorizes each and everybody to share (to copy, distribute and transmit) the work under the following conditions, without impairing or restricting the authors' moral rights: Attribution: The work must be attributed to its authors. The copyright is retained by the corresponding authors. Digital Object Identifier: 10.4230/DagRep.3.5.i Aims and Scope The periodical Dagstuhl Reports documents the program and the results of Dagstuhl Seminars and Dagstuhl Perspectives Workshops. In principal, for each Dagstuhl Seminar or Dagstuhl Perspectives Workshop a report is published that contains the following: an executive summary of the seminar program and the fundamental results, an overview of the talks given during the seminar (summarized as talk abstracts), and summaries from working groups (if applicable). This basic framework can be extended by suitable contributions that are related to the program of the seminar, e.g. summaries from panel discussions or open problem sessions.

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Stratified guarded first-order transition systems

Formal Methods in System Design

First-order transition systems are a convenient formalism to specify parametric systems such as m... more First-order transition systems are a convenient formalism to specify parametric systems such as multi-agent workflows or distributed algorithms. In general, any nontrivial question about such systems is undecidable. Here, we present three subclasses of first-order transition systems where every universal invariant can effectively be decided via fixpoint iteration. These subclasses are defined in terms of syntactical restrictions: negation, stratification and guardedness. While guardedness represents a particular pattern how input predicates control existential quantifiers, stratification limits the information flow between predicates. Guardedness implies that the weakest precondition for every universal invariant is again universal, while the remaining sufficient criteria enforce that either the number of occurring negated literals decreases in every iteration, or the number of required instances of input predicates or the number of first-order variables remains bounded. We argue fo...

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Three improvements to the top-down solver

Mathematical Structures in Computer Science, 2022

The local solver TD is a generic fixpoint engine which explores a given system of equations on de... more The local solver TD is a generic fixpoint engine which explores a given system of equations on demand. It has been successfully applied to the interprocedural analysis of procedural languages. The solver TD gains efficiency by detecting dependencies between unknowns on the fly. This algorithm has been recently extended to deal with widening and narrowing as well. In particular, it has been equipped with an automatic detection of widening and narrowing points. That version, however, is only guaranteed to terminate under two conditions: only finitely many unknowns are encountered, and all right-hand sides are monotonic. While the first condition is unavoidable, the second limits the applicability of the solver. Another limitation is that the solver maintains the current abstract values of all encountered unknowns instead of a minimal set sufficient for performing the iteration. By consuming unnecessarily much space, interprocedural analyses may not succeed on seemingly small programs....

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Counterexample- and Simulation-Guided Floating-Point Loop Invariant Synthesis

Static Analysis, 2020

We present an automated procedure for synthesizing sound inductive invariants for floating-point ... more We present an automated procedure for synthesizing sound inductive invariants for floating-point numerical loops. Our procedure generates invariants of the form of a convex polynomial inequality that tightly bounds the values of loop variables. Such invariants are a prerequisite for reasoning about the safety and roundoff errors of floating-point programs. Unlike previous approaches that rely on policy iteration, linear algebra or semi-definite programming, we propose a heuristic procedure based on simulation and counterexample-guided refinement. We observe that this combination is remarkably effective and general and can handle both linear and nonlinear loop bodies, nondeterministic values as well as conditional statements. Our evaluation shows that our approach can efficiently synthesize loop invariants for existing benchmarks from literature, but that it is also able to find invariants for nonlinear loops that today’s tools cannot handle.

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Proving Absence of Starvation by Means of Abstract Interpretation and Model Checking

Automated Technology for Verification and Analysis, 2017

The Avionics Application Software Standard Interface ARINC 653 is meant to increase predictabilit... more The Avionics Application Software Standard Interface ARINC 653 is meant to increase predictability of safety-critical software systems. It allows to coordinate multiple tasks by means of priorities, semaphores, setting and waiting for events as well as by sending suspend and resume signals. Thus, it is a major challenge to verify that no such tightly coupled task gets ultimately stuck, e.g., by infinitely waiting for an event or a resume signal by another task. We explain how abstract interpretation together with model checking may nicely cooperate to guarantee absence of such concurrency flaws and report on practical experiments. R. Vogler-This work is supported by the ITEA3 project 14014 ASSUME.

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Binary Queries

Querying XML documents is a basic task for many XML applications. Typically, matches of queries a... more Querying XML documents is a basic task for many XML applications. Typically, matches of queries are located individually, i.e. a match is a single node in a queried document. k-ary queries, in contrast, simultaneously identify k locations in the document, which are connected via some specified relation. For example, in rule-based transformations (like XSLT transformations), a node to which a rule is applied and another node which is selected by the rule in the context of the first node could be identified together by a binary query defining the relation between these two nodes. Such a binary query would replace the match and the select pattern used to identify the first and the second node respectively. By eliminating the need for select patterns, binary queries would not only reduce the number of patterns in a transformation, but would also allow that all the pattern matching is done statically, i.e. before the transformation actually begins. We use the formalism of regular forest ...

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When Is a Bottom-Up Deterministic Tree Translation Top-Down Deterministic?

We consider two natural subclasses of deterministic top-down tree-to-tree transducers, namely, li... more We consider two natural subclasses of deterministic top-down tree-to-tree transducers, namely, linear and uniform-copying transducers. For both classes we show that it is decidable whether the translation of a transducer with look-ahead can be realized by a transducer without lookahead. The transducers constructed in this way, may still make use of inspection, i.e., have an additional tree automaton restricting the domain. We provide a second procedure which decides whether inspection can be removed and if so, constructs an equivalent transducer without inspection. The construction relies on a fixpoint algorithm that determines inspection requirements and on dedicated earliest normal forms for linear as well as uniform-copying transducers which can be constructed in polynomial time. As a consequence, equivalence of these transducers can be decided in polynomial time. Applying these results to deterministic bottom-up transducers, we obtain that it is decidable whether or not their translations can be realized by deterministic uniform-copying top-down transducers without look-ahead (but with inspection) -or without both look-ahead and inspection.

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Succinct Solvers

Universität Trier, Mathematik/Informatik, Forschungsbericht, 2001

We develop a solver algorithm which allows to eciently compute the optimal model of a very expres... more We develop a solver algorithm which allows to eciently compute the optimal model of a very expressive fragment of predicate logic. The succinct formulation of the algorithm is due to the disciplined use of continuations and memoisation. This facilitates giving a precise characterisation of the behaviour of the solver and to develop a complexity calculation which allows to obtain its formal complexity. Practical evaluations on a control-flow analysis of the ambient calculus shows a good match between theory and practice.

Verifying Security Policies in Multi-agent Workflows with Loops

Proceedings of the 2017 ACM SIGSAC Conference on Computer and Communications Security, 2017

We consider the automatic verification of information flow security policies of web-based workflo... more We consider the automatic verification of information flow security policies of web-based workflows, such as conference submission systems like EasyChair. Our workflow description language allows for loops, non-deterministic choice, and an unbounded number of participating agents. e information flow policies are specified in a temporal logic for hyperproperties. We show that the verification problem can be reduced to the satisfiability of a formula of first-order linear-time temporal logic, and provide decidability results for relevant classes of workflows and specifications. We report on experimental results obtained with an implementation of our approach on a series of benchmarks.

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Goblint: Thread-Modular Abstract Interpretation Using Side-Effecting Constraints

Tools and Algorithms for the Construction and Analysis of Systems, 2021

Goblintis a static analysis framework for C programs specializing in data race analysis. It relie... more

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Deciding Equivalence of Separated Non-nested Attribute Systems in Polynomial Time

Lecture Notes in Computer Science, 2019

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18 13192 – Tree Transducers and Formal Methods Participants

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Equivalence of Linear Tree Transducers with Output in the Free Group

Developments in Language Theory, 2020