Runtime Verification Based on Register Automata

Abstract

We propose TOPL automata as a new method for runtime verification of systems with unbounded resource generation. Paradigmatic such systems are object-oriented programs which can dynamically generate an unbounded number of fresh object identities during their execution. Our formalism is based on register automata, a particularly successful approach in automata over infinite alphabets which administers a finite-state machine with boundedly many inputstoring registers. We show that TOPL automata are equally expressive to register automata and yet suitable to express properties of programs. Compared to other runtime verification methods, our technique can handle a class of properties beyond the reach of current tools. We show in particular that properties which require value updates are not expressible with current techniques yet are naturally captured by TOPL machines. On the practical side, we present a tool for runtime verification of Java programs via TOPL properties, where the trade-off between the coverage and the overhead of the monitoring system is tunable by means of a number of parameters. We validate our technique by checking properties involving multiple objects and chaining of values on large open source projects.

Reachability in Pushdown Register Automata

“…12 12 Here we view the bijection π as an r-manipulation with component π 0 empty and π 1 = π . Moreover, we write R || (π ; R α • ) for the condition…”

“…Here, documents contain data values whose range is potentially unbounded and queries are allowed to perform comparison tests on such data. A similar scenario occurs in reference-based programming languages, such as object-oriented [6,2,12,17] or ML-like languages [18,19]. In such languages, memory is managed with the help of reference names that can be created afresh and compared for equality but are otherwise abstract.…”

History-Register Automata

“…Hence, any machine designed for analysing such programs is expected to operate on an infinite alphabet of names. The latter need has brought about the introduction of automata over infinite alphabets in program analysis, starting from prototypical machines for mobile calculi [23] and variable programs [18], and recently developing towards automata for verification tasks such as equivalence checks of ML programs [24,25], context-bounded analysis of concurrent programs [7,3] and runtime program monitoring [14].…”

Bisimilarity in Fresh-Register Automata

“…They consist of finite-state control and finitely many registers for storing elements from the infinite alphabet. Since their introduction by Kaminski and Francez [14] as a candidate formalism for capturing regularity in the infinite-alphabet setting, they have been actively researched especially in the database and verification communities: selected applications include the study of markup languages [19] and run-time verification [11]. While register automata can detect symbols that are currently not stored in registers (local freshness), the bounded number of registers means that they are not in general capable of recognising inputs that are genuinely fresh in the sense that they occur in the computation for the first time (global freshness).…”