To learn more about operating systems I've set up Xv6, a simple Unix-like operating system designed for teaching. It's loosely based on the v6 version of Unix.
Setup
I found some basic setup instructions at the bottom of the README:
You will need a RISC-V "newlib" tool chain from https://github.com/riscv/riscv-gnu-toolchain, and qemu compiled for riscv64-softmmu. Once they are installed, and in your shell search path, you can run "make qemu".
Looking at the toolchain installation, I noticed the following warning about case-insensitive file systems:
If building a linux toolchain on a MacOS system, or on a Windows system using the Linux subsystem or cygwin, you must ensure that the filesystem is case-sensitive. A build on a case-insensitive filesystem will fail when building glibc because _.os and _.oS files will clobber each other during the build eventually resulting in confusing link errors.
I'm using macOS Sonoma for this, so I'm using a case-insensitive file system (APFS). To avoid a world of pain here I instead decided to go with the prebuilt packages at https://github.com/riscv-software-src/homebrew-riscv.
brew tap riscv-software-src/riscv
brew install riscv-tools
brew install riscv64-elf-gdb
These commands initially failed for me. I needed to update to the latest Xcode command line tools to be able to install the homebrew packages. I ran xcode-select --install and followed the prompts.
I already had a compatible version of QEMU, I imagine that'd just be brew install qemu.
Then I cloned the Xv6 repo and ran make qemu, and it worked first time! You get a shell prompt and can run some base commands like ls and echo. To exit, I found that I can use Ctrl-A X.
Debugger
I'm starting the debugger by running make CPUS=1 qemu-gdb in one terminal, and then in another terminal run riscv64-elf-gdb. By running riscv64-elf-gdb from the Xv6 directory it will automatically load the .gdbinit file which sets up the debugger to connect to the QEMU instance.
Book
There's accompanying book for which the source can be found at https://github.com/mit-pdos/xv6-riscv-book. I've built a recent PDF of the book using the following commands:
brew install --cask mactex
make
This outputs a book.pdf file in the repository directory.
Course
Xv6 is used in an MIT course on operating systems. The currently latest version of this course is available at https://pdos.csail.mit.edu/6.828/2023/index.html. I also found a playlist with lecture recordings from 2020.