Early Verification of ISA Extension Specifications using Deep Reinforcement Learning

For IoT devices the demand in faster execution and at the same time lower energy consumption is a pressing problem. A very promising solution are Application-Specific Instruction-set Processors (ASIPs). They make use of custom instructions, which are added to the processor, forming the Instruction-Set Extension (ISE) of a given Instruction Set Architecture (ISA). While the selection process for the ISE is already challenging, an incorrect ISE specification leads to severe problems: errors and security vulnerabilities go undetected in the first formalization and in the worst case show up ultimately in the final implementation. In this paper, we propose an early verification approach for ISE specifications. Our novel approach is based on two ingredients: (i) Virtual Prototypes (VPs) to enable a rapid creation of an executable specification for the ISE; and (ii) Deep Reinforcement Learning (DRL) to search for ISE programs which violate the ISE specification intent. As case study we consider extensions of the RISC-V base ISA. We demonstrate the effectiveness of our approach for finding functional bugs in the executable specification of the ISE as well as specification gaps in the ISE leading to information leakage.