So I'd like to dive into this myself, as a means to have fun, experiment, learn and demystify.
Where should I start if I want to write a toy OS or kernel? For example, I've stumbled on the following resources until now, are they any good? Do you have any others to recommend?
- https://os.phil-opp.com/ (I don't know Rust, but I wanted to learn so this might be a good idea)
- https://pdos.csail.mit.edu/6.828/2022/xv6.html
Also, do you have any general tips/advice/insights in mind to share? Do you think it's a good idea for a hobby project?
Thanks in advance!
https://osdev.org is the defacto reference. Start with AMD64, don't bother with x86 (32-bit). Segmentation is a nightmare and there are less quirks with AMD64.
If/when you start reading the CPU manuals, use AMD's documentation. It's better than Intel's.
Write a toy kernel. The kernel is the first thing anyway and you'll need to know how it works to understand the rest. It defines the interface between userspace and the hardware. You have to define this yourself.
Second resource is #osdev on Libera. Be patient, ask good questions. Some of the smartest developers I've ever met hang out there, but their time is precious and you should know they have extremely strong opinions and are not afraid to share them (for better or worse). Incredible group of people that deserve a lot of respect.
I've written kernels in C and now my main OS (non-toy) kernel is in Rust. Rust is nice for this, but if you're learning then heed my advice and use C for some toy kernels to start. Otherwise the Rust stuff sort of gets in the way if you're not familiar both with the language and the concepts.
Get familiar with QEMU. Remember that it lies a lot when debugging kernels (issues it reports as bugs are most likely bugs in your kernel, for example). Don't bother with vbox/vmware for OS dev. They don't help much.
You can play with bootloaders to understand them (I do recommend) but remember they're annoying and it's generally better to start with a boot standard (such as Multiboot) so that GRUB/QEMU can boot into your kernel easier.
OSDev's wiki has a barebones guide. Follow it. Understand everything. It's imperative. Use GCC's annoying cross compilers as prescribed. Then you'll understand more why LLVM is easier to work with later on and will understand how cross compilation works. This will be important if/when you finally switch to Rust, too.
Finally, there's Reddit's r/osdev. It's less active and sometimes you get nasty Redditors responding, but there are a few frequents that are extremely helpful.
You can alternatively start with ARM if that's your fancy. Just know debugging and testing is more convoluted and there are less resources for beginners. #osdev people tend to like ARM more but seem to know more about x86 in general.
Hope that helps.
[6.S081](https://pdos.csail.mit.edu/6.828/2019/index.html) (MIT, xv6 RISC-V, 2019), [6.828](http://pdos.csail.mit.edu/6.828/2018/xv6.html) (MIT, xv6 x86, 2018), [CS140e](http://web.stanford.edu/class/cs140e/) (Stanford, RPi C, 2019), [CS140e](https://downey.io/blog/cs140e-writing-an-operating-system-in...) (Stanford, RPi Rust, 2018, more on [HN](https://news.ycombinator.com/item?id=16134618), [Andre](https://github.com/rust-embedded/rust-raspi3-OS-tutorials) (RPi Rust, 2019), [CS140](http://www.scs.stanford.edu/12au-cs140/) (Stanford, 2012), [CS194-24](http://www.cs.berkeley.edu/~kubitron/courses/cs194-24-S13/in...) (Berkeley), [Baking Pi](http://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/os/) (Cambridge, RPi asm, 2012), [OS from Scratch](http://www.cs.bham.ac.uk/~exr/lectures/opsys/10_11/lectures/...) (Birmingham, more in [HN](https://news.ycombinator.com/item?id=8380822)), [OS Development](http://littleosbook.github.io/), (RIT Stockholm, more on [HN](https://news.ycombinator.com/item?id=13258063)), [these](http://news.ycombinator.com/item?id=4834008) (CMU, UMD, MIT, Stanford, Harvard), [BrokenThorn](http://www.brokenthorn.com/Resources/OSDevIndex.html), [bkerndev](http://www.osdever.net/bkerndev/index.php), [JamesM](http://www.jamesmolloy.co.uk/tutorial_html/) ... [OSDev.org](http://wiki.osdev.org/) is recommended in many sources. Here is a recent roundup on [HN](https://news.ycombinator.com/item?id=22087701), and [another](https://news.ycombinator.com/item?id=22149866) (both Jan 2020). This [textbook](http://csapp.cs.cmu.edu/) provides a recent overview of Unix + C OS.
It is free as in beer
by Andrew Tanenbaum (Author), Albert Woodhull (Author)
ISBN-10 : 0131429388
ISBN-13 : 978-0131429383