Tutorial 01 - Wait Forever

tl;dr

  • The project skeleton is set up.
  • A small piece of assembly code runs that just halts all CPU cores executing the kernel code.

Building

  • Makefile targets:
    • doc: Generate documentation.
    • qemu: Run the kernel in QEMU
    • clippy
    • clean
    • readelf: Inspect the ELF output.
    • objdump: Inspect the assembly.
    • nm: Inspect the symbols.

Code to look at

  • BSP-specific kernel.ld linker script.
    • Load address at 0x8_0000
    • Only .text section.
  • main.rs: Important inner attributes:
    • #![no_std], #![no_main]
  • boot.s: Assembly _start() function that executes wfe (Wait For Event), halting all cores that are executing _start().
  • We (have to) define a #[panic_handler] function to make the compiler happy.
    • Make it unimplemented!() because it will be stripped out since it is not used.

Test it

In the project folder, invoke QEMU and observe the CPU core spinning on wfe:

$ make qemu
[...]
IN:
0x00080000:  d503205f  wfe
0x00080004:  17ffffff  b        #0x80000