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Finding inductive invariants using satisfiability modulo theories and convex optimization

Abstract : Static analysis concerns itself with deriving program properties which holduniversally for all program executions.Such properties are used for proving program properties (e.g. there neveroccurs an overflow or other runtime error regardless of a particular execution) and are almostinvariably established using inductive invariants: properties which holdfor the initial state and imply themselves under the program transition, and thushold universally due to induction.A traditional approach for finding numerical invariants is using abstractinterpretation, which can be seen as interpreting the program in the abstractdomain of choice, only tracking properties of interest.Yet even in the intervals abstract domain (upper and lower boundsfor each variable) such computation does not necessarily converge, and theanalysis has to resort to the use of widenings to enforceconvergence at the cost of precision.An alternative game-theoretic approach called policy iteration,guarantees to findthe least inductive invariant in the chosen abstract domain under the finitenumber of iterations.Yet the original description of the algorithm includes a number of drawbacks:it requires converting the entire program to an equation system,does not integrate with other approaches,and is unable to benefit from other analyses.Our new algorithm for running local policy iteration (LPI)instead formulates policy iteration as traditional Kleene iteration,with a widening operator that guarantees to return the least inductiveinvariant in the domain after finitely many applications.Local policy iteration runs in template linear constraint domains whichrequires setting in advance the ``shape'' of the derived invariant (e.g.x + 2y for deriving x + 2y leq 10).Our second theoretical contribution involves development and comparison ofa number of different template synthesis strategies, when used in conjunctionwith LPI.Additionally, we present an approach for generating abstract reachabilitytrees using abstract interpretation,enabling the construction of counterexample traces,which in turns lets us generate new templates using Craig interpolants.In our third contribution we bring our attention to interprocedural andpotentially recursive programs.We develop an algorithm parameterizable with any abstract interpretation forsummary generation, and we study it's parameterization with LPI.The resulting approach is able to generate least inductive invariants in the domain for a fixed number of summaries for recursive programs.Our final theoretical contribution is a novel "formula slicing''method for finding potentially disjunctive inductive invariantsfrom program fragments obtained by symbolic execution.We implement all of these techniques in the open-source state-of-the-artCPAchecker program analysis framework, enabling communication and collaborationbetween different analyses.The techniques mentioned above rely onsatisfiability modulo theories solvers,which are capable ofgiving solutions tofirst-order formulas over certain theories or showingthat none exists.In order to simplify communication with such toolswe present the JavaSMT library, which provides a generic interface for suchcommunication.The library has shown itself to be a valuable tool, and is already used by manyresearchers.
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Submitted on : Friday, January 12, 2018 - 3:08:46 PM
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Egor George Karpenkov. Finding inductive invariants using satisfiability modulo theories and convex optimization. Performance [cs.PF]. Université Grenoble Alpes, 2017. English. ⟨NNT : 2017GREAM015⟩. ⟨tel-01681555v2⟩



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