Cross compiling the FreeBSD Kernel

Wow, two post in one day already ;-)

There are two things I'd like to note. First, I noticed that cross-compiling seems a major issue for me. Don't know why that is.

Second, I need to remember Warner Losh's post on cross compiling FreeBSD. Essentialy, the procedure is:

$ export TARGET=powerpc
$ export TARGET_ARCH=powerpc
$ make kernel-toolchain
$ make buildkernel

Addendum: Unfortunately, this procedure works only on architectures already supported by FreeBSD and its build system. Therefore, it doesn't work for me. So here's the full story on how I got FreeBSD to at least compile.

Building the Toolchain

Building the toolchain is pretty straight forward. I've already written about how to build a cross compiler. On FreeBSD however, four things are different.

• The target is powerpc64-unknown-freebsd. I don't know if powerpc64-unknown-elf would have worked, too.
• The target is new, so a patch to the binutils sources is required.
• The GNU MP Bignum Library (GMP) is required. I used version GMP 4.2.1 and installed it in $PREFIX
• Finally, the MPFT Library needs to be built. I used version MPFT 2.3.0 and installed it in $PREFIX

Note that those steps have to be performed before the compiler is built. Since I didn't install the libraries in the standard locations, the LD_LIBRARY_PATH variable needs to be set before the compiler can be used:

$ export LD_LIBRARY_PATH=$PREFIX/lib

Building the Kernel

The basic procedure of building a kernel is outlined in the FreeBSD Developer's Handbook. Provided that the cross compiler has been installed in $PREFIX, these steps are required:

$ export MACHINE=powerpc64
$ export MACHINE_ARCH=powerpc64
$ export CC=${PREFIX}/${TARGET_PREFIX}-gcc
$ export NM=${PREFIX}/${TARGET_PREFIX}-nm
$ export LD=${PREFIX}/${TARGET_PREFIX}-ld
$ export SYSTEM_LD=${LD}
$ export OBJCOPY=${PREFIX}/${TARGET_PREFIX}-objcopy
$ cd /usr/src/sys/powerpc64/conf
$ config KERNCONF
$ cd ../compile/KERNCONF
$ make cleandepend && make depend
$ make kernel

Oh, of course this doesn't work with the stock FreeBSD sources. Instead, my FreeBSD 64-Bit PowerPC Mercurial repository needs to be used. Note that for convenience reasons, that tree includes a crossenv script which, when sourced, sets up the required environment variables.