This is a set of Makefile helper targets, a Linux kernel config, and a small init program which produce a Linux bzImage file which can run directly as an EFI application without interaction with persistent storage (probably via PXE boot). The kernel config is very specific and doesn't target a broad range of hardware. It doesn't include all the proper drivers or other robust system support. This could serve as a base for a node in a server cluster started using a custom orchestration system, somewhat similar to running Fedora CoreOS as a simplified Kubernetes node. At least that's the idea.
The /init directory contains the source code for a simple static init program that only depends on the sanitized kernel headers. It uses code snippets from the Linux source tree at tools/include/nolibc/nolibc.h, for using system calls and some other libc-like functions. The init program also uses io_uring, currently for a simple echo program, based on liburing code.
This was sloppily thrown together so documentation is poor and the Makefile is brittle, and so on.
The Makefile target build-all builds the whole thing (except for installing prerequisites). Prerequisites can be installed with the apt-* targets. The kernel is first compiled without an initramfs to produce modules.builtin and other files required to properly install generated kernel modules. The enabled kernel modules are then built, followed by a build of bzImage, which will partially build the kernel again, this time with a built-in initramfs (generated from the spec in initramfs.conf and target 'build'). The initramfs contains /init, which is executed by the kernel on startup (it has to be that exact file path for some reason, see: https://www.kernel.org/doc/Documentation/filesystems/ramfs-rootfs-initramfs.txt). Modules are signed using the key generated from kernel_keygen.conf. The file boot.conf is not currently used because bootconfig doesn't seem to compile, but this would otherwise be used to specify extra kernel arguments and bake them into bzImage in an efficient way.
Makefile targets 'run' and 'run-efi' use qemu-system-x86_64 to provided a way to run the kernel from a terminal.