Arm 32 Kernel Example

build.sh

#!/bin/bash

set -e

clear
zig build-exe -target arm-freestanding-eabi -mcpu baseline -T linker.ld -fsingle-threaded -fno-omit-frame-pointer -O ReleaseFast --name kernel kernel.zig
llvm-objdump -dt kernel
llvm-objcopy -O binary kernel kernel.bin

# cp kernel.bin disk.img
# fallocate -l 64M disk.img
dd if=/dev/zero of=disk.img bs=1M count=64
dd if=kernel.bin of=disk.img conv=notrunc

qemu-system-arm -drive if=pflash,file=disk.img,format=raw -M virt -serial stdio

kernel.zig

export fn _start() linksection(".text._start") callconv(.Naked) void {
    const data = @intToPtr(*volatile u8, 0x9000000);
    for ("Hello\r\n") |c| {
        data.* = c;
    }

    while (true) {}
}

linker.ld

MEMORY
{
     flash  (RX) : ORIGIN = 0x00000000, LENGTH = 32M
      dram (RWX) : ORIGIN = 0x40000000, LENGTH = 16M
}

ENTRY(_start)
SECTIONS {
    . = ORIGIN(flash);

    __kernel_flash_start = .;

    .text : {
        *(.text._start)
        *(.text)
        *(.text.*)
    } > flash

    .rodata : {
        . = ALIGN(4);
        *(.rodata)
        *(.rodata.*)
    } > flash

    . = ALIGN(4);

   __kernel_flash_end = . ;

    .stack (NOLOAD) : {
        . = ALIGN(4096);
        kernel_stack_start = .;
        . += 0x8000; 
        kernel_stack = .;
    } > dram

    .data : AT (__kernel_flash_end){
        __kernel_data_start = .;

        *(.data)
        *(.data.*)

        *(.sdata)
        *(.sdata.*)

        . = ALIGN(4);
        __kernel_data_end = .;
    } > dram

    .bss (NOLOAD) : {
        __kernel_bss_start = .;

        *(.bss)
        *(.bss.*)
        *(.sbss)
        *(.sbss.*)

        . = ALIGN(4);
        __kernel_bss_end = .;
    } > dram

}