Expression-Based Aliasing for OO–languages

Abstract

Abstract. Alias analysis has been an interesting research topic in verification and optimization of programs. The undecidability of determining whether two expressions in a program may reference to the same object is the main source of the challenges raised in alias analysis. In this paper we propose an extension of a previously introduced alias calculus based on program expressions, to the setting of unbounded program executions such as infinite loops and recursive calls. Moreover, we devise a corresponding executable specification in the K-framework. An important property of our extension is that, in a non-concurrent setting, the corresponding alias expressions can be over-approximated in terms of a notion of regular expressions. This further enables us to show that the associated K-machinery implements an algorithm that always stops and provides a sound over-approximation of the "may aliasing" information, where soundness stands for the lack of false negatives. As a case study, we analyze the integration and further applications of the alias calculus in SCOOP. The latter is an object-oriented programming model for concurrency, recently formalized in Maude; K definitions can be compiled into Maude for execution.

On the verification of SCOOP programs

“…where, intuitively, "eval(a, s)" evaluates s and puts the result on channel a, "wait(a)" enables processor p to use the evaluation result, "write(t, a.data)" sets the value of t to a.data, St is a call stack, and Γ is a typing environment [30] containing the class hierarchy of a program and all the type definitions. At this point it is easy to understand that the K-rule for assignments with r and r 1 as in (25). The integration of all the K-rules of the alias calculus on top of the Maude formalization of SCOOP is achieved by following a similar approach.…”

Coffman deadlocks in SCOOP

“…Then, one of the processors that managed to lock the necessary resources is ("randomly") enabled to proceed to the asynchronous execution of its instruction stack, according to the strategy parallelism{lock} . The last step of the strategy calls the rule [deadlock-on] implementing the Coffman deadlock detection as in (1). (For a detailed description of SCOOP and its Maude formalization we refer the interested reader to the work in [8].…”

“…We present the integration of a deadlock detection mechanism on top of the formalization in [8]. We also briefly analyze how a simplified, abstract semantics of SCOOP based on a notion of "may alias" expressions [4,1] can be exploited in order to improve the deadlock detection procedure.…”

“…We refer, for instance, to the recent work in [3] that introduces a framework for detecting deadlocks by identifying circular dependencies in the (finite state) model of so-called contracts that abstract methods in an OO-language. The integration of a deadlock analyzer in SCOOP on top of Maude is an orthogonal approach that belongs to a more ambitious goal, namely the construction of a RL-based toolbox for SCOOP programs including a may alias analyzer, as thoroughly presented in [1] and a type checker.…”