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Ocaml-Android

Notes on trying/using/fixing Vouillon's ocaml-android cross-compiler with OPAM based on Vouillon's android opam repo.

Status: Fixed a few bugs. All seems to work (except for the issues Vouillon noted with running bytecode executables). Slightly clunky having to build target-specific OPAM packages.

Contents:

  • Ocaml on Android
  • ocaml-android's approach to cross-compiling
  • making a cross-compiler

Ocaml on Android

Keigo seems to be the root of much OCaml on Android work. His patch is Ocaml 3.12.1 (and NDK n7). He also wrote an initial top-level. This includes vouillon which was active approx. Feb 2013, and Vernoux's Ocaml top-level for Android.

Vouillon's version appears to be Ocaml 4.00.1 and include LWT according to this post. He also has an Opam respository for this.

OK, here is my fork of vouillon's android opam repo.

Problems with Vouillon's opam/cross compiler:

  • 4.00.1 ocamlbuild does NOT Use ocamlfind for ocamlmklib and does NOT include -ocamlmklib override option. Hopefully fixed in this ocamlbuild patch and applied by my opam compiler spec 4.00.1+mirage-android in my opam repo.
  • One package in Vouillon's opam repository have hard-coded paths, i.e. https://github.com/vouillon/opam-android-repository/blob/master/packages/android-lwt.2.4.3/opam has /home/jerome/.opam/4.00.1/bin/arm-linux-androideabi-ocamlfind. Edit in ~/.opam/repo/android/packages/android-lwt.2.4.3/opam to "%{prefix}%/bin/arm-linux-androideabi-ocamlfind"; fixed in my opam repo.
  • android-ocamlfind doesn't specific an ocamlfind version and should (1.3.3): edit ~/.opam/repo/android/packages/android-ocamlfind.1.3.3/opam. Fixed in my opam repo.
  • Ocaml-android doesn't seem to use toolchain ld in config/Makefile PARTIALLD (blows up in mirage-platform). Fixed in my fork of ocaml-android [0.1.10-ld](https://github.com/cgreenhalgh/ocaml-android/archive/0.1.10-ldocaml-android's approach to cross-compiling.tar.gz) and referenced in my opam repo.
  • android-ocamlfind (opam files/Android.conf.in) is missing ldconf(android) from findlib.conf.d/android.conf (should be .../arm-linux-androideabi/lib/ocaml/ld.conf), so that it mixes up host and target libraries. Fixed in my opam repo.

Build with my fork of opam repo:

  • add repo as per github readme: opam repo add android https://github.com/cgreenhalgh/opam-android-repository.git
  • opam switch 4.00.1+mirage-android - includes ocamlbuild patch from my ocaml fork which should make ocamlbuild use ocamlfind for ocamlmklib for correct toolchain support
  • opam install ocaml-android - includes my fix for using toolchain ld
  • opam install android-ocamlfind

To test it out try the instructions under Test on Keigo's page... but (having used opam)

echo 'print_endline "Hello, OCaml-Android!";;' > hello.ml
ocamlfind -toolchain android ocamlopt hello.ml -o hello
file hello
adb push hello /data/local/tmp
adb shell /data/local/tmp/hello
> Hello, OCaml-Android!
  • "opam install android-lwt" - includes fix for path in opam repo.

Note ocaml-android adds a symlink to camlp4 libraries on the system in $(ANDROID_PREFIX)/lib/ocaml/camlp4 (since these will be running on the host, not the target).

Note that (as reported in the readme) there is a problem building/running bytecode executables made with ocaml-android.

ocaml-android's approach to cross-compiling

Vouillon has created target-specific opam packages which includes custom build configuration, which typically overrides the choice of ocamlfind.

The ocaml cross-compiler is installed within but essentially independently of the current opam switch compiler. The cross-compiler is made available as a custom toolchain in ocamlfind (or by using a target-specific ocamlfind). In practice this is a separate installation (could be a separate findlib.conf) rather a typical toolchain fix, as it specifies its own destdir, stdlib and ldconf, not just the various build tools.

Good points:

  • often no build-related changes to package source
  • typically small changes to opam build and remove specifications, which are fairly standard for packages using oasis

Bad points:

  • Cannot directly use existing opam packages, even for simple cases
  • doesn't work with standard ocamlbuild -use-ocamlfind because this doesn't have a standard way to override the choice of ocamlfind or specify a toolchain, and if it did uses the same ocamlfind to build both the plugin and other files. A partial work-around is to do ocamlbuild -just-plugin first, then set OCAMLFIND_CONF to just use the cross-compiler & libs and ocamlbuild again. In theory ocamlbuild -byte-plugin might also work, but when compiling it demands a unix stub DLL for the target but when running requires it for the build platform.

Making a cross-compiler

This but is just my notes to self, really working through the ocaml-android cross-compiler build process...

ocaml source - my fork.

For native compiler ./configure should work; just specify -prefix <install-path>. Standard build is then (something like):

./configure -prefix ~/android/ocaml-native
make world
make install

Or a more restrained build should do:

./configure -prefix ~/android/ocaml-native
make OTHERLIBRARIES="unix str num dynlink" BNG_ASM_LEVEL=0 world
make OTHERLIBRARIES="unix str num dynlink" BNG_ASM_LEVEL=0 install

Perhaps I should then make again but not install for the new prefix (otherwise ocamlbuild is kept and is configured for native prefix!) (this should include camlp4out, not opt/native):

./configure -prefix ~/android/ocaml-cross
make OTHERLIBRARIES="unix str num dynlink" BNG_ASM_LEVEL=0 world

The native C toolchain needs to be installed. ocaml-android uses the Android NDK which includes pre-built tools and is available for windows, Mac OS X and Linux (each 32 or 64 bit). E.g. Linux 64 bit NDK. Specific config used are SYSROOT .../platform/android-14/arch-arm and ANDROID_PATH .../toolchains/arm-linux-androideabi-4.7/prebuilt/$(ARCH)-x86/bin. Note that this eabi is not include by default with NDK r9 (try 4.6 or 4.8).

Following ocaml-android the next steps are:

  • configure for Android by copying in custom config/m.h, config/s.h and config/Makefile, including fixing up the installation and dependency paths in the Makefile
  • apply patches (which could have been done earlier) (patch -p 0 < ...), which are:
    • memory.patch - byterun/misc.h - header name clash
    • ocamlbuild.patch - ocamlbuild/ocaml_specific.ml - optional removal of shared library rule
    • system.patch - asmrun/signals_osdep.h, otherlibs/unix/getpw.c, otherlibs/unix/termios.c - workaround lack of sys/ucontext.h, lack of pw gecos and tcdrain
  • save byterun/ocamlrun
  • clean up native build (selective):
	make -C byterun clean
	make -C stdlib clean
	make -C otherlibs/unix clean
	make -C otherlibs/str clean
	make -C otherlibs/num clean
	make -C otherlibs/dynlink clean
  • build byterun and keep byterun/ocamlrun:
	make -C byterun all
	mkdir -p ~/android/ocaml-cross/bin
	cp byterun/ocamlrun ~/android/ocaml-cross/bin/ocamlrun.target
  • put back the native one:
	cp ~/android/ocaml-native/bin/ocamlrun byterun/
  • make the rest (be selective... don't world/coldstart!)
	make coreall opt-core otherlibraries otherlibrariesopt
	make ocamltoolsopt
	make install

Note: can't make camlp4out at this stage because of incompatible dllunix.so

  • possibly replace camlp4 stuff - not quite sure why at the moment:
	#rm -rf $(ANDROID_PREFIX)/lib/ocaml/camlp4
	#ln -sf $(STDLIB)/camlp4 $(ANDROID_PREFIX)/lib/ocaml/camlp4