Docker image to enable C/C++ cross-compilation targeting FreeBSD from a Linux host. The default compiler toolchain is GCC 4.2.4, to match the toolchain which shipped with the default FreeBSD target, 9.3. The image is based on Alpine Linux 3.12, so outside of the compiler and associated tools, it contains only a BusyBox-based userspace. Compared with other public and published containers, it provides

• working unprivileged compilation (docker run --user ...),
• target support for both amd64 and i386 (targets x86_64-freebsd9 and i386-freebsd9, respectively),
• intact termios headers, and
• a much smaller image size.

It's based on Marcelo Gornstein's tutorial and the SpectraLogic container.

$ docker run --rm \
             --user $(id --user):$(id --group) \
             --volume /path/to/some/source:/workdir \
             empterdose/freebsd-cross-build:9.3 \
             settarget x86_64-freebsd9 make

The container's working directory is /workdir. If you mount your source directory onto this path, you can use relative paths in your build commands.

By default, the container overrides none of Make's implicit variables, nor are there any unprefixed compiler tools on the PATH (gcc, g++, etc.). To use the toolchains contained within the container, either specifically invoke the prefixed utilities:

$ docker run ... i386-freebsd9-gcc -c -o foo.o foo.c

or use the settarget utility to launch a subshell with environment variables (including the PATH) set up for a particular target:

$ docker run ... --name build
# Build for 64-bit.
$ docker exec build settarget x86_64-freebsd9 make
# Do something to archive the build output.
# `make(1)` is not target-specific.
$ docker exec build make clean
# Build for 32-bit.
$ docker exec build settarget i386-freebsd9 make

The image is based on Alpine Linux, so any additional packages you might need can be installed via apk. Note that the image includes GNU Make, not BSD Make.

The Docker build is parameterized to support variation of the output without actual modification to the Dockerfile. When building the container with docker build, any of these parameters may be passed via --build-arg; or, when building via make, they may be passed as environment variables. When using Make, due to limitations inherent to Make's string handling, spaces in environment variable values will likely cause your computer to catch fire.

• ALPINE_VERSION: The version of Alpine Linux on which to base the image. (default: 3.12)
• FBSD_VERSION: The version of FreeBSD to target. (default: 9.3)
• FBSD_MIRROR: The mirror site/URL prefix for FreeBSD downloads. (default: http://ftp-archive.freebsd.org/pub/FreeBSD-Archive/old-releases)
• FBSD_AMD64_BASE_URL: The URL for the FreeBSD base.txz archive for the amd64 architecture. (default: ${FBSD_MIRROR}/amd64/${FBSD_VERSION}-RELEASE/base.txz)
• FBSD_I386_BASE_URL: The URL for the FreeBSD base.txz archive for the i386 architecture. (default: ${FBSD_MIRROR}/i386/${FBSD_VERSION}-RELEASE/base.txz)
• GNU_MIRROR: The mirror site/URL prefix for GNU downloads. (default: https://ftp.gnu.org/gnu)
• GCC_URL: The URL for the GCC source archive. This also defines which version of GCC to use. (default: ${GNU_MIRROR}/gcc/gcc-4.2.4/gcc-4.2.4.tar.bz2)
• BINUTILS_URL: The URL for the binutils source archive. This also defines which version of binutils to use. (default: ${GNU_MIRROR}/binutils/binutils-2.19.1a.tar.bz2)
• MAKEFLAGS: Flags to control Make's behaviour when compiling binutils and GCC. (default: -j 4)