The Case for Flexible ISAs: Unleashing Hardware and Software

For a long time the Instruction Set Architecture (ISA) has been the firm contract between software and hardware. This firm contract plays an important role by decoupling the development of software from hardware micro-architectural features, enabling both to evolve independently. Nonetheless, it also condemns the ISA to become larger, more cluttered and inefficient as new instructions are incorporated over the years and deprecated instructions are left untouched to keep legacy compatibility. In this work we propose OpenISA, a flexible ISA that enables both the software and the hardware to evolve independently and discuss how OpenISA 1.0 was designed to enable efficient OpenISA software emulation on alien ISAs, which is key to free the user from hardware lock-ins. Our results show that software compiled to OpenISA can be latter emulated on x86 and ARM processors with very little overhead achieving near native performance, under 10% for the majority of programs.