While correct, I always find the declaration of Mirage (and HaLVM for that matter) as an OS to be unhelpful. It is a cross compiler for OCaml (resp. Haskell) to the Xen ABI along with libraries for interacting with Xen primitives (inter-domain communication, etc).

Mirage is actually not just the Xen ABI. It includes a frontend that swaps in appropriate implementations of module signatures for other backends.

For instance, Andy Ray just got a kernel module target working: http://lists.xenproject.org/archives/html/mirageos-devel/201... (when this mode is complete, the network stack module will call directly into the FreeBSD kthread rather than invoking socket syscalls, for example). This is also how we plan to support the Raspberry Pi (use FreeBSD as a bootloader, with just one kernel thread running which runs the unikernel).

And there are also ongoing ports to JavaScript (to work as an IOCaml notebook, which is itself based on IPython).

All of these just need a recompilation with a different invocation of `mirage configure --<target>`.

I follow you work with great interest.

I had the fortune of using Oberon/Blue Bottle in the 90's and also some contact with Singularity.

So I am very passionate about OS done in memory safe languages and alternative OS designs outside the UNIX System V model.

Congratulations for the work achieved.

Today. Nothing prevents a future version to target hardware directly.

It has been mentioned multiple times that Xen ABI is just away of saving resources to focus on more important areas for the time being.