As discussed above, the GNU distribution is self-contained, and
self-containment is achieved by relying on pre-built “bootstrap binaries”
(see 引导). These binaries are specific to an operating system
kernel, CPU architecture, and application binary interface (ABI). Thus, to
port the distribution to a platform that is not yet supported, one must
build those bootstrap binaries, and update the (gnu packages
bootstrap) module to use them on that platform.
Fortunately, Guix can cross compile those bootstrap binaries. When everything goes well, and assuming the GNU tool chain supports the target platform, this can be as simple as running a command like this one:
guix build --target=armv5tel-linux-gnueabi bootstrap-tarballs
For this to work, it is first required to register a new platform as defined
in the (guix platform) module. A platform is making the connection
between a GNU triplet (see GNU configuration
triplets in Autoconf), the equivalent system in Nix
notation, the name of the glibc-dynamic-linker, and the corresponding
Linux architecture name if applicable (see Platforms).
Once the bootstrap tarball are built, the (gnu packages bootstrap)
module needs to be updated to refer to these binaries on the target
platform. That is, the hashes and URLs of the bootstrap tarballs for the
new platform must be added alongside those of the currently supported
platforms. The bootstrap Guile tarball is treated specially: it is expected
to be available locally, and gnu/local.mk has rules to download it
for the supported architectures; a rule for the new platform must be added
as well.
In practice, there may be some complications. First, it may be that the
extended GNU triplet that specifies an ABI (like the eabi suffix
above) is not recognized by all the GNU tools. Typically, glibc recognizes
some of these, whereas GCC uses an extra --with-abi configure flag
(see gcc.scm for examples of how to handle this). Second, some of
the required packages could fail to build for that platform. Lastly, the
generated binaries could be broken for some reason.