Marco: A Stochastic Asynchronous Concolic Explorer

Concolic execution is a powerful program analysis technique for code path exploration. Despite recent advances that greatly improved the efficiency of concolic execution engines, path constraint solving remains a major bottleneck of concolic testing. An intelligent scheduler for inputs/branches becomes even more crucial. Our studies show that the previously under-studied branch-flipping policy adopted by state-of-the-art concolic execution engines has several limitations. We propose to assess each branch by its potential for new code coverage from a global view, concerning the path divergence probability at each branch. To validate this idea, we implemented a prototype Marco and evaluated it against the state-of-the-art concolic executor on 30 real-world programs from Google's Fuzzbench, Binutils, and UniBench. The result shows that Marco can outperform the baseline approach and make continuous progress after the baseline approach terminates.