os-tutorial/13-kernel-barebones/

[org 0x7c00]
KERNEL_OFFSET equ 0x1000 ; The same one we used when linking the kernel

mov [BOOT_DRIVE], dl ; Remember that the BIOS sets us the boot drive in 'dl' on boot
mov bp, 0x9000
mov sp, bp

mov bx, MSG_REAL_MODE 
call print
call print_nl

call load_kernel ; read the kernel from disk
call switch_to_pm ; disable interrupts, load GDT,  etc. Finally jumps to 'BEGIN_PM'
jmp $ ; Never executed

%include "../05-bootsector-functions-strings/boot_sect_print.asm"
%include "../05-bootsector-functions-strings/boot_sect_print_hex.asm"
%include "../07-bootsector-disk/boot_sect_disk.asm"
%include "../09-32bit-gdt/32bit-gdt.asm"
%include "../08-32bit-print/32bit-print.asm"
%include "../10-32bit-enter/32bit-switch.asm"

[bits 16]
load_kernel:
mov bx, MSG_LOAD_KERNEL
call print
call print_nl

mov bx, KERNEL_OFFSET ; Read from disk and store in 0x1000
mov dh, 2
mov dl, [BOOT_DRIVE]
call disk_load
ret

[bits 32]
BEGIN_PM:
mov ebx, MSG_PROT_MODE
call print_string_pm
call KERNEL_OFFSET ; Give control to the kernel
jmp $ ; Stay here when the kernel returns control to us (if ever)

BOOT_DRIVE db 0 ; It is a good idea to store it in memory because 'dl' may get overwritten
MSG_REAL_MODE db "Started in 16-bit Real Mode", 0
MSG_PROT_MODE db "Landed in 32-bit Protected Mode", 0
MSG_LOAD_KERNEL db "Loading kernel into memory", 0

; padding
times 510 - ($-$$) db 0
dw 0xaa55