aurora-os/bootloader-kernel.asm at master · QuirkyCodex/aurora-os · GitHub

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; Aurora OS Bootloader with Kernel Loading
; Loads Aurora kernel and switches to protected mode

org 0x7C00
bits 16

start:
    jmp main
    times 3-($-$$) db 0

main:
    ; Set up segments and stack
    cli
    xor ax, ax
    mov ds, ax
    mov es, ax
    mov ss, ax
    mov sp, 0x7C00
    sti

    ; Save boot drive
    mov [boot_drive], dl

    ; Clear screen
    mov ax, 0x0003
    int 0x10
    mov ax, 0x0600
    mov bh, 0x1F
    xor cx, cx
    mov dx, 0x184F
    int 0x10

    ; Display loading message
    mov ah, 0x02
    mov bh, 0
    mov dh, 5
    mov dl, 5
    int 0x10
    mov si, loading_msg
    call print_str

    ; Load kernel from disk sectors 2-5
    mov bx, 0x1000      ; Load address
    mov ah, 0x02        ; Read function
    mov al, 4           ; Number of sectors
    mov ch, 0           ; Cylinder 0
    mov cl, 2           ; Sector 2
    mov dh, 0           ; Head 0
    mov dl, [boot_drive]
    int 0x13
    jc disk_error

    ; Skip signature check for now
    ; Just assume kernel loaded successfully

    ; Success - switch to protected mode
    mov si, success_msg
    call print_str
    call switch_to_pm

    ; Shouldn't reach here
    jmp $

disk_error:
    mov si, disk_err_msg
    call print_str
    jmp reboot

invalid_kernel:
    mov si, kernel_err_msg
    call print_str
    jmp reboot

reboot:
    mov si, reboot_msg
    call print_str
    call wait_key
    int 0x19

; Switch to protected mode
switch_to_pm:
    cli
    lgdt [gdt_descriptor]

    mov eax, cr0
    or eax, 1
    mov cr0, eax

    jmp CODE_SEG:protected_mode

bits 32
protected_mode:
    ; Set up segments
    mov ax, DATA_SEG
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
    mov ss, ax
    mov esp, 0x90000

    ; Enable A20 line
    in al, 0x92
    or al, 2
    out 0x92, al

    ; Jump to kernel
    jmp 0x1000

    ; Halt if kernel returns
    cli
    hlt

print_str:
    lodsb
    test al, al
    jz .done
    mov ah, 0x0E
    int 0x10
    jmp print_str
.done:
    ret

wait_key:
    mov ah, 0
    int 0x16
    ret

; Messages
loading_msg: db "🌠 Loading Aurora kernel...", 0x0D, 0x0A, 0
success_msg: db "✅ Kernel loaded! Switching...", 0x0D, 0x0A, 0
disk_err_msg: db "❌ Disk error!", 0x0D, 0x0A, 0
kernel_err_msg: db "❌ Invalid kernel!", 0x0D, 0x0A, 0
reboot_msg: db "Press any key to reboot...", 0x0D, 0x0A, 0

; GDT
gdt_start:
    gdt_null:
        dd 0
        dd 0

    gdt_code:
        dw 0xFFFF      ; Limit
        dw 0            ; Base
        db 0
        db 10011010b   ; Present, Ring 0, Code, Readable
        db 11001111b   ; Granularity, 32-bit
        db 0

    gdt_data:
        dw 0xFFFF      ; Limit
        dw 0            ; Base
        db 0
        db 10010010b   ; Present, Ring 0, Data, Writable
        db 11001111b   ; Granularity, 32-bit
        db 0

gdt_end:

gdt_descriptor:
    dw gdt_end - gdt_start - 1
    dd gdt_start

CODE_SEG equ gdt_code - gdt_start
DATA_SEG equ gdt_data - gdt_start

boot_drive: db 0

times 510 - ($ - $$) db 0
dw 0xAA55