[MirageOS-devel] Issues with CLOCK on xen

[Toby Moore <toby.moore.0@xxxxxxxxx>]

Hi everyone,

I've been following this mailing list for a while now. I've finally 
managed to get a simple blog running on Mirage and AWS. I've put up a 
couple of posts of my experience (http://is-awesome.net) but I doubt 
there'll be anything that's new or exciting to readers here.
One outstanding issue is that I can't seem to get the CLOCK working 
properly on AWS. It's fine for a unix build, but I don't have another 
xen host available right now and the deploy test cycle to AWS is pretty 
painful. Trying to get the current time on AWS gets me this:
    Unsupported function gmtime called in Mini-OS kernel
    Do_exit called!
    base is 0x0 Page fault at linear address 8, rip cb67, regs 
000000000034f908, sp 34f9b0, our_sp 000000000034f8c8, code 0
    Page fault in pagetable walk (access to invalid memory?).

This is built with OCaml 4.01.0 with these OPAM packages:
    io-page                    1.1.1  Allocate memory pages suitable 
for aligned I/O
    mirage                     2.0.1  The Mirage library operating system
    mirage-clock-unix          1.0.0  A Mirage-compatible Clock library 
for Unix
    mirage-clock-xen           1.0.0  A Mirage-compatible Clock library 
for Xen
    mirage-conduit             2.0.0  Virtual package for the Mirage 
Conduit transpo
    mirage-console             2.0.0  A Mirage-compatible Console 
library for Xen an
    mirage-dns                 2.0.0  Virtual package for the Mirage 
DNS transports
    mirage-http                2.0.0  Mirage HTTP client and server 
driver for Unix
    mirage-net-unix            1.1.1  Ethernet network driver for 
Mirage, using tunt
    mirage-net-xen             1.1.3  Ethernet network device driver 
for Mirage/Xen
    mirage-types               2.0.1  Module type definitions for 
Mirage-compatible
    mirage-types-lwt           2.0.1  Lwt module type definitions for 
Mirage-compati
    mirage-unix                2.0.0  Mirage OS library for Unix 
compilation
    mirage-xen                 2.0.0  Mirage OS library for Xen compilation
    mirage-xen-minios          0.4.2  Xen MiniOS guest operating system 
library
I'm not directly passing a clock device, my config.ml has these bits in it:

    let main =
      foreign "Unikernel.Main" (http @-> console @-> kv_ro @-> kv_ro 
@-> job)
    let unix_libs =
      match get_mode () with
      | `Unix -> ["mirage-clock-unix"]
      | _ -> []

    let () =
        add_to_ocamlfind_libraries unix_libs;
        ...

This is mostly copied out of the skeleton examples. I know the clock 
interface has been changing a bit recently but it works fine under unix. 
My guess is that the clock driver is skipped because it's not referenced 
(except in my code) but I'm not sure how to do that properly. How can I 
force it to be included?
Thanks,
Toby


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