  The end of Moore's Law has ushered in a diversity of hardware not seen in
decades. Operating system (and system software) portability is accordingly
becoming increasingly critical. Simultaneously, there has been tremendous
progress in program synthesis. We set out to explore the feasibility of using
modern program synthesis to generate the machine-dependent parts of an
operating system. Our ultimate goal is to generate new ports automatically from
descriptions of new machines. One of the issues involved is writing
specifications, both for machine-dependent operating system functionality and
for instruction set architectures. We designed two domain-specific languages:
Alewife for machine-independent specifications of machine-dependent operating
system functionality and Cassiopea for describing instruction set architecture
semantics. Automated porting also requires an implementation. We developed a
toolchain that, given an Alewife specification and a Cassiopea machine
description, specializes the machine-independent specification to the target
instruction set architecture and synthesizes an implementation in assembly
language with a customized symbolic execution engine. Using this approach, we
demonstrate successful synthesis of a total of 140 OS components from two
pre-existing OSes for four real hardware platforms. We also developed several
optimization methods for OS-related assembly synthesis to improve scalability.
The effectiveness of our languages and ability to synthesize code for all 140
specifications is evidence of the feasibility of program synthesis for
machine-dependent OS code. However, many research challenges remain; we also
discuss the benefits and limitations of our synthesis-based approach to
automated OS porting.
