iinobos/boot.asm at main · iinob/iinobos · GitHub

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[org 0x7c00]
KERNEL_LOCATION equ 0x1000


mov [BOOT_DISK], dl


xor ax, ax
mov es, ax
mov ds, ax
mov bp, 0x8000
mov sp, bp

mov bx, KERNEL_LOCATION
mov dh, 2

mov ah, 0x02
mov al, dh
mov ch, 0x00
mov dh, 0x00
mov cl, 0x02
mov dl, [BOOT_DISK]
int 0x13


mov ah, 0x0
mov al, 0x3
int 0x10                ; init text interrupt


CODE_SEG equ GDT_code - GDT_start
DATA_SEG equ GDT_data - GDT_start

cli
lgdt [GDT_descriptor]
mov eax, cr0
or eax, 1
mov cr0, eax
jmp CODE_SEG:start_protected_mode

jmp $

BOOT_DISK: db 0

GDT_start:
    GDT_null:
        dd 0x0
        dd 0x0

    GDT_code:
        dw 0xffff
        dw 0x0
        db 0x0
        db 0b10011010
        db 0b11001111
        db 0x0

    GDT_data:
        dw 0xffff
        dw 0x0
        db 0x0
        db 0b10010010
        db 0b11001111
        db 0x0

GDT_end:

GDT_descriptor:
    dw GDT_end - GDT_start - 1
    dd GDT_start


[bits 32]
start_protected_mode:
    mov ax, DATA_SEG
	mov ds, ax
	mov ss, ax
	mov es, ax
	mov fs, ax
	mov gs, ax

	mov ebp, 0x90000		; 32 bit stack base pointer
	mov esp, ebp

    jmp KERNEL_LOCATION


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