This is some early work using zig as a cross-compiler for building OCaml cross-compilation systems: opam-cross-lambda Status: It is currently severely untested but the aim is to be able to cross-compile to Linux from Windows/Mac/Linux for aarch64 and x86_64 CPU architectures simply by adding an op…

I’m stuck in a frenzy of teaching at the moment due to it being the height of the academic term here, but I just wanted to stop by and say ‘wow!’. I hadn’t realised that Zig supports cross-compilation out of the box, but I’ve been very impressed by using Ghostty recently that is written in it, and …

zig supports cross compilation of not just itself, but C, out of the box, with binutils/gcc compatible wrappers for aspp, ar, ranlib, gcc, etc. targeting a number of platforms. It’s quite incredible the backwards compatibility with C they built targeting numerous architectures and OSs they did

[image] chris-armstrong: targeting windows isn’t possible with this setup at this time, because flexdll hardcodes mingw binary names (e.g. x86_64-w64-mingw32-gcc) in its Makefile and the flexlink binary (it assumes these exist because targeting mingw32 is always a cross-compilation, even on Wind…

This could be great help, I’ll have to try it out with a patched copy in my test repo when I next get round to it

Ok, this gets very close, but the zig rc wrapper takes command line switches to be compatible with msvc’s rc tool instead of binutils’ windres, which means that it’s not a simple drop-in replacement for windres. I actually need to be able to override the whole call as this doesn’t work: zig rc -D …

Actually I take this back - I noticed I can just set which call to make with your patch. Thanks, that does help! The problems I’m hitting are now after that, where it tries to build the OCaml parts of flexlink with the bootstrap ocamlrun and ocamlc. I may be able to avoid those by building the flex…

This is very cool! A couple of very quick notes on the Windows side - flexdll has always been updated “as needed”, so patches to facilitate other builds are very much welcomed (if occasionally only slowly reviewed :see_no_evil:). If you’re building via opam, note that flexdll can be pinned - you ca…

Thanks - I meant I need to run the OCaml build of flexdll separately, not necessarily patch the build system of flexdll before running it. OCaml 5.3.0’s Makefile passes OCAMLC as ../boot/ocamlrun ../boot/ocamlc which is not what I want when cross-compiling. The Makfile.cross in the current main bra…

[image] chris-armstrong: (again, I really wish opam had the concept of a “subswitch” where you could just run the build and install for each package and its dependencies again, but with the toolchain parameter specifed (or for those that don’t use dune, a {with-toolchain} filter). Once I’ve figu…

This is a really great idea. Cross compilation is a big deal for me, I am learning zig for exactly this reason, but ocaml is such a nice language. Most of my time is spent in the julia world and this is again their big problem. If you can just get a binary that works! Thanks David

Early work experimenting with zig as a cross-compiler for OCaml

Ecosystem

chris-armstrong May 2, 2025, 12:52pm 17

I’ve written up a summary in a blog post of much of my progress I’ve described above: OCaml cross-compilation: an experiment

Topic		Replies	Views
Benefit of using zig cc? Ecosystem build	13	4649	December 31, 2022
Cross-compiling implementations / how they work Learning cross-compilation	16	5061	August 11, 2023
[ANN] Building the OCaml Toolchain with Bazel - PoC Ecosystem announce , cross-compilation , bazel , toolchains	7	1206	November 10, 2022
Cross compilation from OSX/Windows to Linux Ecosystem build , cross-compilation	5	3245	September 14, 2017
OCaml RFC#17: library linking proposal Ecosystem cross-compilation	26	2931	June 16, 2021

Early work experimenting with zig as a cross-compiler for OCaml

Related topics