Steps for compiling the kernel with Clang

Dependencies

We still defer to binutils for assembling and linking (though we happily accept bug reports from trying LLVM's equivalents).

For cross-compiling, you need to have the cross-target versions of binutils in your $PATH:

$ sudo apt install binutils-aarch64-linux-gnu

Note: The minimal version of Clang required to build the kernel is hard to exactly pin down, due to the large combinations of kernel [LTS] branch, target ISA, kernel configurations. Test your combination, and report issues in our bug tracker. Clang 4 was used to ship a Clang built arm64 kernel on the Google Pixel phone.

Compiling for host

$ make CC=clang HOSTCC=clang

Cross compiling

$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang

Note that unlike gcc/binutils, clang ships with support for all backends by default (you can configure them off, but this is considered an antipattern). ARCH= specifies the kernel's notion of target ISA. These can be found in the kernel sources under the arch/ directory. CROSS_COMPILE is a prefix for binutils tools. KBUILD will literally run $ $CROSS_COMPILE-as and $ $CROSS_COMPILE-ld, so verify that you've installed the correct cross version of binutils and they're accessible from your $PATH.