Instrument and Unit Test an Asm-only OS Kernel by Turning it into an Anykernel

OS kernel development is often connected with time consuming testing process and non-trivial debug technics. Although emulators like QEMU and Bochs ease this work significantly, nothing can compare with convenience of userspace developer environment. Moving parts of the kernel to the userspace binary is not straightforward, especially if the kernel has almost no compatibility with POSIX and is written entirely in assembly. Still, sometimes it is doable. The talk shares experience, architecture and design decisions of compiling VFS, block, and some other subsystems of KolibriOS as Linux® interactive shell program and a FUSE filesystem. Implemented unit testing framework and coverage collection tool for assembly (flat assembler) programs are also discussed.