jannos: jannes' learning project for OS dev

Building a kernel for Qemu's riscv virtual machine from scratch in Rust.

• uses OpenSBI, a sort of BIOS that Qemu defaults to, to simplify some peripheral interactions
• I am trying to use as few dependencies and as little assembly as possible

Prerequisites

• Rust
• riscv64 target: rustup target add riscv64gc-unknown-none-elf
• qemu-system-riscv64 (e.g sudo dnf install qemu-system-riscv on Fedora)
• riscv64-unknown-elf toolchain (providing gdb and binutils)

To compile the latter from source see riscv-gnu-toolchain

build, run, debug

• make build to build the kernel ELF image
• make text dump dissassembled text section
• make qemu to run in qemu
• make qemu-gdb to run in debuggable qemu session
• make gdb to debug running debuggable qemu session

Notes

OpenSBI selects a hart as boot core and jumps to kernel. Kernel has to start up other harts by itself.

References

• https://github.com/mit-pdos/xv6-riscv
• https://osblog.stephenmarz.com/
• many more, TODO: add