Re: [MirageOS-devel] Structure of mirage-platform for Solo5

[Martin Lucina <martin@xxxxxxxxxx>]

On Friday, 20.05.2016 at 09:10, Hannes Mehnert wrote:
> >> The rationale behind this structure is threefold:
> >>
> >> 1) It has explicit contracts defining which interfaces each layer
> >> provides/depends on. Further, by not providing a separate "posix" package,
> >> we discourage adding more C code to support "random bits of POSIX native
> >> library X might need" which encourages the use of pure-OCaml libraries in
> >> Mirage.
> 
> I always appreciate this! :)
> 
> >> 2) I don't see a need for other OPAM packages to consume the posix and
> >> openlibm interfaces separately. These exist only to support the
> >> freestanding OCaml runtime. There's nothing Mirage-specific in this
> >> package, it is a freestanding build of asmrun on Solo5 interfaces, hence
> >> the name solo5-ocaml-runtime rather than mirage-solo5-ocaml.
> >>
> >> 3) I would eventually like to produce a "retargetable" freestanding OCaml
> >> runtime which would be shared by the Xen, Solo5 and other future non-UNIX
> >> targets. However, the first step is to get Solo5 upstreamed.
> 
> +1

Done, see the "ocaml-freestanding" repository here:

https://github.com/mato/ocaml-freestanding

Once Dan merges my PRs to his Solo5 forks of mirage and mirage-platform,
Mirage/Solo5 will shortly build against the restructured runtime (when Dan
merges my PRs to his Solo5 forks of mirage and mirage-platform).

At some point in the future (once Mirage/Solo5 has been upstreamed, still
a bunch of work needed for that) the mirage-xen-minios, xen-posix and
xen-ocaml packages can be replaced with ocaml-freestanding targetted
against Mini-OS.

> >> Thoughts? Are there any showstoppers with the proposed structure?  Is there
> >> a reason I've missed for the xen-ocaml / xen-posix split in
> >> mirage-platform?
> 
> The motivation was purely CPU cycle based.  GMP and zarith-xen (which
> takes esp. on ARM long to compile) depends on bits and pieces from
> xen-posix (some headers, and the CFLAGS/LDFLAGS).  It initially depended
> on mirage-xen, which depends on cstruct etc., and gets recompiled pretty
> often.  After having for a short period some cyclic dependencies (not a
> good idea), I ended up with the minimal package (mirage-xen-posix) to
> get GMP&zarith compiling.

Ah yes, zarith and GMP. My plan there is to have gmp-freestanding,
zarith-freestanding packages. These will depend only on ocaml-freestanding
(and indirectly on the solo5-kernel-XXX package) so should not get
recompiled often.

Out of curiosity (I have no idea what's actually involved), are there any
plans to replace zariith and GMP with pure-OCaml equivalents?

Martin

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