Developing kernels and testing them in virtual machines

Question

I like programming challenges, and writing a kernel seems a programming challenge.

Unfortunately, kernels are particularly hard to test because they are basically the core of operating systems and so they can't be easily ran on top of an operating system.

However, I know about applications called Virtual Machines that can emulate computer hardware.

What is the easiest/best way to develop and test kernels(C+Assembly) using Virtual Machines?

Answer 1

While BOCHS seems to be better at letting you know when something goes horribly wrong with your pet OS... it is very slooooow! I use VirtualPC for general purpose testing and BOCHS when things get murky.

Also, you will more than likely be booting the OS every 2 minutes, so it helps to have some sort of automated way to build a boot image & fire off the Virtual PC.

I built a GRUB boot floppy image with all the necessary stuff to get it to boot the Kernel.Bin from the root. I use a batch file to copy this file to the virtual project directory, use FAT Image Generator to copy my kernel to the image. Then just launch the VirtualPC project. Vola!

Excerpt from my batch file:

COPY Images\Base.vfd Images\Boot.vfd /Y
fat_imgen.exe modify Images\Boot.vfd -f Source\Bin\KERNEL.BIN
COPY Images\Boot.vfd Emulators\VirtualPC\ /Y
START Emulators\VirtualPC\MyOS.vmc

One last suggestion: Set the VirtualPC process priority to low - trust me on this one! I'd be happy to exchange some code!

Tools: DGJPP, NASM, GRUB.
Code: osdev.org, osdever.net

Answer 2

You might be interested in looking at HelenOS. Its a from scratch microkernel that has been ported to many architectures (boots just fine on bare metal) developed using simulators such as Simics and QEMU.

We use a static grub that is copied to the final ISO during the build process. Some things just have to be that way until the OS becomes self hosting. I highly recommend NOT implementing your own userspace C library unless you really do want to do everything from scratch .. you'll become self hosting much sooner :)

Though Simics is non-free, I highly recommend it (and its built in debugging/profiling tools) while making your kernel. Once you have some kind of kernel console and logger in place, QEMU does a very nice job.