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Tutorial 01 - Wait Forever

tl;dr

Project skeleton is set up; Code just halts all CPU cores executing the kernel code.

Toolchain: cargo xbuild tools (xrustc, xclippy) and the aarch64-unknown-none-softfloat target are used for building AArch64 bare-metal code.
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 is organized into kernel, arch and BSP (Board Support Package) parts.
- Conditional compilation includes respective arch and BSP according to user-supplied arguments.
Custom link.ld linker script.
- Load address at 0x80_000
- Only .text section.
main.rs: Important inner attributes:
- #![no_std], #![no_main]
Assembly _start() function that executes wfe (Wait For Event), halting all cores that are executing _start().
We (have to) define a #[panic_handler] function.
- Just waits infinitely for a cpu event.

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

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