README

RJK (Robert's JOS Kernel)
=========================

RJK was my attempt to write a kernel for The JOS Project
<URL:https://jos.sourceforge.net/>, which had the goal of writing an Open
Source Java based Operating System (JOS).  I was actively involved with JOS
from around 1997 to 2002.

The goal with RJK was to provide a minimal set of low-level features to get a
Java Virtual Machine (JVM) running; the reset of the kernel, drivers, and OS
would be written in the Java language.

Multiboot (GRUB) is used to load the RJK kernel and initial OS module images.
The kernel is written in C and Assembly (using gcc) and only runs on i386
compatible processors.  A Linux system running on a i386/x86-64 processor (or
cross compiler) is needed to compile the kernel.

Late in 2024 I imported the old tar.gz releases into GIT.  Then made the
required changes to get RJK to compile with a modern version of gcc and to run
with the QEMU emulator.


Building and Running
--------------------

On a i386/x86-64 Linux system install a recent version of the gcc compiler,
make, gdb, and the QEMU emulator with i386 support.

To build:

  make clean all

To run:

  qemu-system-i386 -display none -debugcon stdio -m 4M -kernel kernel.elf -initrd module.elf

To debug the kernel with gdb:

  qemu-system-i386 -display none -debugcon stdio -m 4M -kernel kernel.elf -initrd module.elf -s -S

In a separate window run gdb:

  gdb kernel.elf --eval-command="target remote localhost:1234" --eval-command="break _start"