Support cross-building the OCaml toolchain on macOS - #14
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July 7, 2026 00:19
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On a macOS host, targeting aarch64-linux is a cross build the arch check misses: the host and target arch are both aarch64, only the OS differs, so CROSS_COMPILE must be set explicitly to the <arch>-linux-gnu- prefix that Linux auto-selects. The messense/macos-cross-toolchains Homebrew tap provides that toolchain, so conf-<arch>-linux-gnu-gcc resolves on macOS too. Patch Makefile.cross so crossopt does not pass -function-sections to the host .opt tools (the macOS host ocamlopt is Mach-O and rejects it), keeping it for the target library; mark the packages available on macOS. Rewrite the crossopt version check without `case` inside `$(...)`, which macOS's bash 3.2 mis-parses (it reads the `)` in `5.5.*)` as closing the substitution).
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I'd like to cross-build Unikraft OCaml unikernels on an Apple Silicon Mac.
On a macOS host, targeting
aarch64-linuxis a cross build the arch check misses: host and target arch are both aarch64, only the OS differs, so the build falls back to the host compiler unlessCROSS_COMPILEis set. This sets it for{os = "macos"}to the same<arch>-linux-gnu-prefix Linux auto-selects. Themessense/macos-cross-toolchainsHomebrew tap provides that full toolchain (gcc and binutils underaarch64-linux-gnu-*), so the existingconf-<arch>-linux-gnu-gccdependency resolves on macOS too, with no divergent triple or gating.It also passes
--disable-function-sectionsto the OCaml configure on macOS, since crossopt's ocamlopt is built without function-sections support, and marks the packages available on macOS.The same
--disable-function-sectionsfinding drives the macOS support in the sibling ocaml-solo5 backend (mirage/ocaml-solo5#171).