FeatMaker: Automated Feature Engineering for Search Strategy of Symbolic Execution

We present FeatMaker, a novel technique that automatically generates state features to enhance the search strategy of symbolic execution. Search strategies, designed to address the well-known state-explosion problem, prioritize which program states to explore. These strategies typically depend on a ”state feature” that describes a specific property of program states, using this feature to score and rank them. Recently, search strategies employing multiple state features have shown superior performance over traditional strategies that use a single, generic feature. However, the process of designing these features remains largely manual. Moreover, manually crafting state features is both time-consuming and prone to yielding unsatisfactory results. The goal of this paper is to fully automate the process of generating state features for search strategies from scratch. The key idea is to leverage path-conditions, which are basic but vital information maintained by symbolic execution, as state features. A challenge arises when employing all path-conditions as state features, as it results in an excessive number of state features. To address this, we present a specialized algorithm that iteratively generates and refines state features based on data accumulated during symbolic execution. Experimental results on 15 open-source C programs show that FeatMaker significantly outperforms existing search strategies that rely on manually-designed features, both in terms of branch coverage and bug detection. Notably, FeatMaker achieved an average of 35.3% higher branch coverage than state-of-the-art strategies and discovered 15 unique bugs. Of these, six were detected exclusively by FeatMaker.