Efficient Emptiness Check for Timed B\"uchi Automata (Extended version)

The B\"uchi non-emptiness problem for timed automata refers to deciding if a given automaton has an infinite non-Zeno run satisfying the B\"uchi accepting condition. The standard solution to this problem involves adding an auxiliary clock to take care of the non-Zenoness. In this paper, it is shown that this simple transformation may sometimes result in an exponential blowup. A construction avoiding this blowup is proposed. It is also shown that in many cases, non-Zenoness can be ascertained without extra construction. An on-the-fly algorithm for the non-emptiness problem, using non-Zenoness construction only when required, is proposed. Experiments carried out with a prototype implementation of the algorithm are reported.Comment: Published in the Special Issue on Computer Aided Verification - CAV 2010; Formal Methods in System Design, 201

An empirical investigation into branch coverage for C programs using CUTE and AUSTIN

Automated test data generation has remained a topic of considerable interest for several decades because it lies at the heart of attempts to automate the process of Software Testing. This paper reports the results of an empirical study using the dynamic symbolic-execution tool. CUTE, and a search based tool, AUSTIN on five non-trivial open source applications. The aim is to provide practitioners with an assessment of what can be achieved by existing techniques with little or no specialist knowledge and to provide researchers with baseline data against which to measure subsequent work. To achieve this, each tool is applied 'as is', with neither additional tuning nor supporting harnesses and with no adjustments applied to the subject programs under test. The mere fact that these tools can be applied 'out of the box' in this manner reflects the growing maturity of Automated test data generation. However, as might be expected, the study reveals opportunities for improvement and suggests ways to hybridize these two approaches that have hitherto been developed entirely independently. (C) 2010 Elsevier Inc. All rights reserved

Automatic Inference of Code Transforms and Search Spaces for Automatic Patch Generation Systems

We present a new system, Genesis, that processes sets of human patches to automatically infer code transforms and search spaces for automatic patch generation. We present results that characterize the effectiveness of the Genesis inference algorithms and the resulting complete Genesis patch generation system working with real-world patches and errors collected from top 1000 github Java software development projects. To the best of our knowledge, Genesis is the first system to automatically infer patch generation transforms or candidate patch search spaces from successful patches

Fuzzing Embedded Systems Using Debug Interfaces

Fuzzing embedded systems is hard. Their key components - microcontrollers - are highly diverse and cannot be easily virtualized; their software may not be changed or instrumented. However, we observe that many, if not most, microcontrollers feature a debug interface through which a debug probe (typically controllable via GDB, the GNU debugger) can set a limited number of hardware breakpoints. Using these, we extract partial coverage feedback even for uninstrumented binary code; and thus enable effective fuzzing for embedded systems through a generic, widespread mechanism. In its evaluation on four different microcontroller boards, our prototypical implementation GDBFuzz quickly reaches high code coverage and detects known and new vulnerabilities. As it can be applied to any program and system that GDB can debug, GDBFuzz is one of the least demanding and most versatile coverage-guided fuzzers