  Programmable switches have emerged as powerful and flexible alternatives to
fixed-function forwarding devices. But because of the unique hardware
constraints of network switches, the design and implementation of compilers
targeting these devices is tedious and error prone. Despite the important role
that compilers play in software development, there is a dearth of tools for
testing compilers for programmable network devices. We present Druzhba, a
programmable switch simulator used for testing compilers targeting programmable
packet-processing substrates. We show that we can model the low-level behavior
of a switch's programmable hardware. We further show how our machine model can
be used by compiler developers to target Druzhba as a compiler backend.
Generated machine code programs are fed into Druzhba and tested using a
fuzzing-based approach that allows compiler developers to test the correctness
of their compilers. Using a program-synthesis-based compiler as a case study,
we demonstrate how Druzhba has been successful in testing compiler-generated
machine code for our simulated switch pipeline instruction set.
