The LK kernel is an SMP-aware kernel designed for small systems ported to a variety of platforms and cpu architectures.
See https://github.com/littlekernel/lk for the latest version.
This will get you a interactive prompt into LK which is running in qemu arm machine 'virt' emulation. type 'help' for commands.
Note: for ubuntu x86-64: sudo apt-get install gcc-arm-none-eabi or fetch a prebuilt toolchain from https://newos.org/toolchains/x86_64-elf-10.2.0-Linux-x86_64.tar.xz