Automatic Generation and Validation of Instruction Encoders and Decoders

Abstract

AbstractVerification of instruction encoders and decoders is essential for formalizing manipulation of machine code. The existing approaches cannot guarantee the critical consistency property, i.e., that an encoder and its corresponding decoder are mutual inverses of each other. We observe that consistent encoder-decoder pairs can be automatically derived from bijections inherently embedded in instruction formats. Based on this observation, we develop a framework for writing specifications that capture these bijections, for automatically generating encoders and decoders from these specifications, and for formally validating the consistency and soundness of the generated encoders and decoders by synthesizing proofs in Coq and discharging verification conditions using SMT solvers. We apply this framework to a subset of X86-32 instructions to illustrate its effectiveness in these regards. We also demonstrate that the generated encoders and decoders have reasonable performance.