RTL functional test generation using factored concolic execution

Abstract

This thesis presents a novel concolic testing methodology and CORT, a test generation framework that uses it for high-level functional test generation. The test generation effort is visualized as the systematic unraveling of the control-flow response of the design over multiple (factored) explorations. We begin by transforming the Register Transfer Level (RTL) source for the design into a high-performance C++ compiled functional simulator which is instrumented for branch coverage. An exploration begins by simulating the design with concrete stimuli. Then, we perform an interleaved cycle-by-cycle symbolic evaluation over the concrete execution trace extracted from the Control Flow Graph (CFG) of the design. The purpose of this task is to dynamically discover means to divert the control flow of the system, by mutating primary-input stimulated control statements in this trace. We record the control-flow response as a Test Decision Tree (TDT), a new representation for the test generation effort. Successive explorations begin at system states heuristically selected from a global TDT, onto which each new decision tree resultant from an exploration is stitched.CORT succeeds at constructing functional tests for ITC99 and IWLS-2005 benchmarks that achieve high branch coverage using the fewest number of input vectors, faster than existing methods. Furthermore, we achieve orders of magnitude speedup compared to previous hybrid concrete and symbolic simulation based techniques. This work was supported in part by the DARPA CRAFT Verification Task (DARPA-BAA-15-55) and the National Science Foundation Project 1422054. This work would be incomplete without acknowledging the guidance and support of those who made it possible. To begin with, I owe my greatest thanks to my research mentor, Dr. Michael S. Hsiao for granting me the opportunity to engage in invigorating research and to participate as his research assistant. His excellent course on "Electronic Design Automation" in Spring 2016 piqued my curiosity and inspired me to pursue my Master's thesis under his tutelage. Throughout the span of the work that went into this thesis, he tirelessly guided and polished my work with his extensive background and experience in the field. I am honored to have received a chance to work with him.