OCaml plans on POWER7/POWER8 (ppc64, ppc64le) in Rawhide

[Richard W.M. Jones]

OCaml is a statically-safe programming language derived from ML which
compiles to very fast native code.  It contains native code backends
for most architectures (all Fedora primary & secondary arches except
s/390x in fact).

Currently Fedora downstream carries two non-upstream backends:
For ppc64 (big endian), a backend was written many years ago by David
Woodhouse and was upstream for a time, but was dropped when the
PlayStation 3 stopped supporting Linux.  For ppc64le (little endian /
POWER8) IBM's Michel Normand contributed a native code backend last
year.  The upstream project always carried a ppc (32 bit) backend, but
we didn't use it and it's not very interesting for us.

  https://git.fedorahosted.org/cgit/fedora-ocaml.git/log/?h=fedora-24-4.02

Red Hat and IBM have provided help and loaned equipment to the
upstream project, and as a result upstream have now added ppc64 and
ppc64le backends.  This work was merged at the end of August.  These
backends were inspired by the Red Hat & IBM work but are not
derivatives.  For details see:

  https://github.com/ocaml/ocaml/pull/225

So what I want to do is add the new backends [actually it's a single,
combined and extended ppc/ppc64/ppc64le backend] to Fedora Rawhide,
and drop our non-upstream backends.

I have so far cherry-picked the merge commit on top of our Fedora
OCaml tree, and I have dropped the downstream ppc64/ppc64le commits
from our tree.  (This is not pushed yet so doesn't appear in the
git.fedorahosted.org link above.)

I have tested it on ppc64le to check that the compiler compiles
itself.  A scratch build of the compiler with the new backend is here
(I reserve the right to make further changes, this is just a
preliminary test build):

  http://ppc.koji.fedoraproject.org/koji/taskinfo?taskID=2741551

I used this to compile some ocaml-* packages on ppc64le, with -- it
has to be said -- mixed results.  There are two compiler bugs
revealed.  This compiler won't be able to compile all the ocaml-*
packages on POWER.  However because of the depth of dependencies, I
cannot easily do scratch builds to find out which packages will be
broken.

Hence I'd like to do a full rebuild, again, to see what breaks.  This
*shouldn't affect primary architectures at all*, but will probably
leave some broken ocaml-* packages on the ppc64/ppc64le secondary
arches.

We've actually done two complete rebuilds during the F24 development
cycle already, which in a way is good because it means I know how long
it should take, and I'm confident that the scripts I use will work
again:

  http://git.annexia.org/?p=goals.git;a=blob;f=fedora_ocaml_rebuild.ml;h=13a8c016b34a3d92cbb118d44b87c9b32d6d09af;hb=HEAD

So I'm pretty confident the primary arch rebuild will go fine, since
it's not affected by any of the above changes - it's basically just a
release bump.  We don't even need to use a side tag for this because
the "old" and "new" packages can be mixed on x86 - they are the same.

The plan for ppc64/ppc64le would then be to fix the bugs revealed in
the rebuild with upstream help.

Any comments?

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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