[opam-devel] [MirageOS-devel] Cross-compiling OCaml, Mirage OS for rumprun, OPAM integration

[Thomas Gazagnaire]

> And, as I just found out now, it's not just the native packages, it's *all*
> packages that need to be rebuilt. So, for Mirage I'd have to produce
> -rumprun variants of all its dependent packages, right? This would include
> teaching the "mirage configure" script about them.

We already partly do that to cross-compile the C stubs for Xen (such as gmp for the TLS stack to work on Xen). The upcoming 2.5.0 release of mirage will have improved support for this. See gmp-xen[1] and some ugly ocamlfind hackery to pass the right options at link time, used by mirage configure[2] when generating the Makefile.

Clearly the situation will not scale well as we will have to patch every package using C stubs. I'm looking forward to have full support cross-compilation in the whole toolchain (to start with the build tools).

--
Thomas

[1]: https://github.com/ocaml/opam-repository/tree/master/packages/gmp-xen/gmp-xen.6.0.0
[2]: https://github.com/ocaml/opam-repository/blob/master/packages/zarith/zarith.1.3/files/xen_linkopts.patch
[3]: https://github.com/mirage/mirage/blob/master/lib/mirage.ml#L2248

> 
> This begs the question, why did you use the approach of building the
> cross-compiler as a normal OPAM package, rather than as a compiler package?
> 
> If I understand correctly how "OPAM switch" works, then the latter option
> would at least get rid of the need to deal with the -android (or -rumprun)
> renaming of packages since each compiler has its own set of packages.
> 
> Obviously, there'd still have to be some way of getting
> the OCAMLFIND_TOOLCHAIN and/or other cross-compilation patches into the
> system but at first glance it seems like it would be more flexible than
> adding suffixes to package names.
> 
> Thoughts?
> 
> Martin
> 
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