A bunch of code that messes with low level stuff. That is:

• arch/riscv/: a bunch of samples on RISC-V running on M, S, or U mode.
• fs/btrfs: miscellanous tests on BTRFS.
• kernel/: samples that explore the API exposed by the Linux kernel, both from kernel and user space.
• lang/c: miscellanous code on the C programming language.

A lot of this is not taken solely from my brain, and I will give credit whenever it's relevant to each piece of code. For the rest of the code, the GPLv3+ license applies.