The commands supporting cross-compilation are proposing the --list-targets and --target options.
The --list-targets option lists all the supported targets that can be passed as an argument to --target.
$ guix build --list-targets The available targets are: - aarch64-linux-gnu - arm-linux-gnueabihf - i586-pc-gnu - i686-linux-gnu - i686-w64-mingw32 - mips64el-linux-gnu - powerpc-linux-gnu - powerpc64le-linux-gnu - riscv64-linux-gnu - x86_64-linux-gnu - x86_64-w64-mingw32
Targets are specified as GNU triplets (see GNU configuration triplets in Autoconf).
Those triplets are passed to GCC and the other underlying compilers possibly involved when building a package, a system image or any other GNU Guix output.
$ guix build --target=aarch64-linux-gnu hello /gnu/store/9926by9qrxa91ijkhw9ndgwp4bn24g9h-hello-2.12 $ file /gnu/store/9926by9qrxa91ijkhw9ndgwp4bn24g9h-hello-2.12/bin/hello /gnu/store/9926by9qrxa91ijkhw9ndgwp4bn24g9h-hello-2.12/bin/hello: ELF 64-bit LSB executable, ARM aarch64 …
The major benefit of cross-compilation is that there are no performance penaly compared to emulation using QEMU. There are however higher risks that some packages fail to cross-compile because few users are using this mechanism extensively.