Static and Dynamic Analysis of Timed Distributed Traces

This paper presents an algorithm for checking global predicates from distributed traces of cyber-physical systems. For an individual agent, such as a mobile phone or a robot, a trace is a finite sequence of state observations and message histories. Each observation has a possibly inaccurate timestamp from the agent's local clock. The challenge is to symbolically over approximate the reachable states of the entire system from the unsynchronized traces of the individual agents. The presented algorithm first approximates the time of occurrence of each event, based on the synchronization errors of the local clocks, and then over approximates the reach sets of the continuous variables between consecutive observations. The algorithm is shown to be sound, it is also complete for a class of agents with restricted continuous dynamics and when the traces have precise information about timing synchronization inaccuracies. The algorithm is implemented in an SMT solver-based tool for analyzing distributed Android apps. Experimental results illustrate that interesting properties like safe separation, correct geocast delivery, and distributed deadlocks can be checked for up-to twenty agents in minutes.