Abstract

Recent years have seen significant advances in dynamic software updating (DSU) systems, which allow programs to be patched on the fly. However, a significant challenge remains: How can we ensure the act of applying a patch does not itself introduce errors? In this paper, we address this problem by presenting a new systematic testing methodology for updatable programs. Our idea is to transform standard system tests into update tests that execute as before, but each transformed test applies a patch at a different update point during execution. To mitigate the increase in the number of tests, we developed an algorithm for test suite minimization that finds a subset of update points that, if fully tested, yields the equivalent to full update point coverage. We implemented our approach and evaluated it on OpenSSH and vsftpd, two widely used server applications. We found that minimization is highly effective; that when updates are allowed almost anywhere, many update tests fail; and that excluding type unsafe update points eliminates nearly, but not quite all, failing update tests.