Building on non-FreeBSD hosts

Currently, FreeBSD can only be built on a FreeBSD host. However, most CI systems do not include FreeBSD build slaves by default. If we allow FreeBSD to be compiled on a non-FreeBSD host (current target is Linux and macOS) it would be much easier to use these CI systems. Furthermore, it would allow developers who do not have a FreeBSD system at work to use that to work on FreeBSD.

• Some build tools depend on host headers being compatible with target headers (e.g. localedef). This would require some refactoring of the xlocale headers to fix properly.
• The version of clang contained in the FreeBSD source tree cannot be bootstrapped with the makefiles from base since the config headers depend on FreeBSD
  • Could build the bootstrap clang using CMake+ninja (which should also be much faster than the current Makefile solution), but that will be a lot of effort
  • Current solution is to use upstream clang
    • However, some features such as ifunc-noplt are not in upstream clang
• The build system often falls back to invoking binaries in $PATH
  • This can cause strange build errors if that binary was not bootstrapped and an incompatible versions is executed
  • can also happen when building on FreeBSD (e.g. running dtc from an old FreeBSD version)
  • Building with a clean $PATH D16815 fixes this problem since it requires all bootstrap tools to be listed explicitly

A mostly working prototype can be found at github.com/arichardson/freebsd in the branch crossbuild-aug2018. This branch is regularly merged with HEAD.

Since Linux and macOS don't include a version of bmake by default, building should be done using the script tools/build/make.py which will bootstrap bmake (and libbsd on Linux) before attempting to build. Additionally it will set the required XCC,XLD etc variables that are needed to build with an ExternalToolchain. If you have a recent version of bmake installed using homebrew or another package manager you can also set the required variables manually (the easiest way to obtain them is by running tools/build/make.py --debug)

Usage:

MAKEOBJDIRPREFIX=... ./tools/build/make.py buildworld TARGET=foo TARGET_ARCH=bar ...

tools/build/make.py should work out-of-the box on macOS with clang and libarchive installed via homebrew:

brew install clang libarchive

You will need a recent version of clang (ideally 10.0) and the libarchive + libbz2 headers.

Since make.py will bootstrap libbsd you will also need autoconf+automake installed.

See tools/build/cross-build/docker/<distribution>/Dockerfile for the required packages for some distributions.

The GitHub repo also contains a script tools/build/cross-build/docker-make.py that will attempt to build inside a docker container. It also contains dockerfiles with clang+other build tools preinstalled for openSUSE, Ubuntu, Arch Linux.

MAKEOBJDIRPREFIX=... ./tools/build/cross-build/docker-make.py --local-docker-image <opensuse|ubuntu|arch> buildworld TARGET=foo TARGET_ARCH=bar ...