Directing a Search Towards Execution Properties with a Learned Fitness Function

Abstract

Search based software testing is a popular and successful approach both in academia and industry. SBST methods typically aim to increase coverage whereas searching for executions with specific properties is largely unresearched. Fitness functions for execution properties often possess search landscapes that are difficult or intractable. We demonstrate how machine learning techniques can convert a property that is not searchable, in this case crashes, into one that is. Through experimentation on 6000 C programs drawn from the Codeflaws repository, we demonstrate a strong, program independent correlation between crashing executions and library function call patterns within those executions as discovered by a neural net. We then exploit the correlation to produce a searchable fitness landscape to modify American Fuzzy Lop, a widely used fuzz testing tool. On a test set of previously unseen programs drawn from Codeflaws, a search strategy based on a crash targeting fitness function outperformed a baseline in 80.1% of cases. The experiments were then repeated on three real world programs: the VLC media player, and the libjpeg and mpg321 libraries. The correlation between library call traces and crashes generalises as indicated by ROC AUC scores of 0.91, 0.88 and 0.61. The produced search landscape however is not convenient due to plateaus. This is likely because these programs do not use standard C libraries as often as do those in Codeflaws. This limitation can be overcome by considering a more powerful observation domain and a broader training corpus in future work. Despite limited generalisability of the experimental setup, this research opens new possibilities in the intersection of machine learning, fitness functions, and search based testing in general.