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0 pointsvkoskiv15d ago0 comments

My hobby x86 kernel. I'm targeting my 80486DX2-66 PC with 32MB of RAM. This project has had a few false starts over the years, where I lacked the prerequisite knowledge to be able to properly debug things. So while the initial commit is from 2020, most of the progress is from the ~180 or so commits I've done in the last month since I picked it up again in early February. A month ago it booted from a floppy and printed some debug info to the screen showing it set up GDT, IDT and some static page tables. Now I have basic virtual memory with kmalloc()/kfree(), task switching, user mode and a few syscalls, and just this past weekend I got my floppy driver to a state where it can now (semi-)reliably detect and read data off floppy disks. I already have a userspace prototype of an ext2 parser I wrote for this in 2024, so all I need to do now is to bring that code in to the kernel and I should have filesystem support!

It's been a ton of fun to work on. Every subsystem is still flaky so I run into the wackiest bugs imaginable. I'm really grateful for the resources[1] and incredible tooling[2] that enable me to work out my frequent mistakes. I can hardly fathom how Torvalds did this with just his PC running Minix!

No idea how long I'll keep working on it. I think I'd be pretty happy if I got a real-world, non-trivial program running on top of it, but in the meantime it is serving as a good distraction from life worries at least :]

[1]: Intel 80386 Reference Manual, Linux man pages, wiki.osdev.org, various datasheets and the occasional query to ChatGPT free tier.

[2]: QEMU+gdb, Bochs, GCC 9 & binutils

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medbar15d ago

Very cool! I just added a ps/2 keyboard driver to my kernel and I’m looking into scheduler / user mode and FAT filesystem support at the moment

vkoskivOP14d ago

Nice! My keyboard code is still very bare bones, so I interact with my system using debug commands assigned to individual keys.

Since we're both working on a similar project, I think it could be fun to talk about OS development and share our findings (and weird bugs!) I have this same username just about everywhere, so do reach out if you're interested! Best of luck with your project either way :]

medbar9d ago

Gladly! Since my last comment I added sound support through an ac97 driver. It was fairly straightforward in hindsight, only had an issue with the interrupt not being handled - turns out my ISR stubs weren't fleshed out to handle IRQs, just the cpu exceptions. Also had a minor bug where addresses outside of the kernel weren't getting translated properly, which I hadn't tested before and assumed to be correct.

I probably could have saved myself 2+ hours of debugging if I had simply stopped working off of assumptions that my driver code was wrong (it was, but that just took reading the spec and checking out some drivers for reference) and doing a root cause analysis with `objdump` or through QEMU. Still surprised how far you can go with vanilla debugging prints - when I started this project, I was sure that I'd become fluent in gdb as a byproduct, but I stopped using it once it would break when the stack became corrupted and haven't tried it since.

Discussion is the reason I made the jump from lurking to having an account on HN. Happy to talk - reached out to you on twitter. And good luck to you as well :^)

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