Invalid instructions?

[tsjk]

On my Mac OS X v10.15.7 (19H1824) I had to do

opam init \
  && eval $(opam env) \
  && opam pin add qcow.0.11.0 https://github.com/mirage/ocaml-qcow.git -n \
  && opam pin add qcow-tool.0.11.0 https://github.com/mirage/ocaml-qcow.git -n \
  && opam install uri qcow.0.11.0 conduit.2.1.0 lwt.5.3.0 qcow-tool.0.11.0 mirage.3.6.0 mirage-block-unix.2.12.0 \
            conf-libev logs fmt mirage-unix prometheus-app

to make this build. The notable difference is the addition of mirage.3.6.0. I'm not sure that exactly v3.6.0 is needed. I just took a version of the same age as other versioned packages. Without this addition compilation bails out due to the OS module missing.