Simple OSDEV Project

Dependencies

• zig: 0.14.0
• qemu-system-riscv64 with the virt machine

Zig version 0.14.0 is needed.

I recommend using zvm

# make sure the version is correct
$ zig version
0.14.0

# make sure the virt machine exists
$ qemu-system-riscv64 -machine ?
Supported machines are:
microchip-icicle-kit Microchip PolarFire SoC Icicle Kit
none                 empty machine
shakti_c             RISC-V Board compatible with Shakti SDK
sifive_e             RISC-V Board compatible with SiFive E SDK
sifive_u             RISC-V Board compatible with SiFive U SDK
spike                RISC-V Spike board (default)
virt                 RISC-V VirtIO board

Code structure

• Commonly shared code shall be placed in libs/
• All assembly files must be placed in kernel/asm/

Running

$ zig build run

Debugging

1. Dependencies

• gdb (you can use lldb if you prefer)
• llvm-addr2line (optional)
• llvm-objdump (optional)

2. Setting up GDB (optional)

We need to allow gdb to autoload commands from our .gdbinit. This is just a nice qol feature. I recommend setting this up, as it saves a lot of time. If you are using lldb, this step would be different.

$ echo "add-auto-load-safe-path $(pwd)/.gdbinit" >> ~/.config/gdb/gdbinit

3. Debug!

$ zig build run-dbg

In another terminal window (in the same directory), open gdb. I recommend using tmux for this, as it makes switching between panes and creating splits easy.

$ gdb

That should be it! Here are some commond gdb aliases that you might use:

• b <function name/address>: set a breakpoint
• p $<register name>: view the contents of a register (p/x for hex)
• p <variable name>: view contents of the variable (p/x for hex)
• n: next line,
• s: step
• si: step instruction
• c: continue execution until breakpoint
• i r: list all registers and their values
• i thr: list all risc-v harts and their states

4. Extras

When you encounter a panic, you can run llvm-addr2line <sepc> with the value of the sepc csr to retrieve the exact line in your code where the panic occured!

You can also run zig build objdump to view the objdump. I recommend piping the output into less, as it dumps a lot of lines to your stdout.