Want to build your own kernel in Rust? See the Bare Metal Rust page for more resources and more posts in this series. There's just a few more posts to go until we have keyboard I/O!
Hacking on kernels in Rust is a lot of fun, but it can also result in massive frustration when QEMU starts rebooting continuously because of a triple fault. One good way to minimize frustration is to wander on over to the ever-helpful OSDev wiki. It's sort of like having an experienced kernel developer on hand to give grouchy but sanity-saving advice.
The OSDev Beginner Mistakes page, in particular, has saved me a couple times already. But there's one bit of advice that I want to focus on today, which I've marked in boldface below:
Beginners often ask "What is the easiest way to do X?" rather than "What is the best, proper, correct way to do X?". This is dangerous as the newcomer doesn't invest time into understanding the superior way to implement something, but instead picks a conceptually simpler method copied from a tutorial. Indeed, the simpler route is often too simple and ends up causing more problems in the long run, because the beginner is ignorant of the superior alternative and doesn't know when it is better to switch. What's so bad about taking the hard route instead?
Common examples include being too lazy to use a Cross-Compiler, developing in Real Mode instead of Protected Mode or Long Mode, relying on BIOS calls rather than writing real hardware drivers, using flat binaries instead of ELF, and so on. Experienced developers use the superior alternatives for a reason…
So what does that mean, "being too lazy to use a cross-compiler"? It means
cheating, and using our regular rustc setup to build ordinary user-space
code, and then trying to run it in kernel space. This will actually work,
at least for a while. But eventually, we may find ourselves engaged in
multiweek debugging nightmares.
So today, I'm going to talk about the sanity-saving difference between
--target x86_64-unknown-linux-gnu and --target x86_64-unknown-none-gnu,
and how to get your Rust compiler ready for the kernel world.
