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yackx/hello-boot.asm

Created December 10, 2014 10:56
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  1. yackx created this gist Dec 10, 2014.
    46 changes: 46 additions & 0 deletions hello-boot.asm
    View file
    Original file line number Diff line number Diff line change
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    ;----------------------------------------------;
    ;
    ; A minimal bootloader that prints a hello world
    ; then halts.
    ;
    ; nasm -f bin hello-boot.asm -o hello-boot.bin
    ;
    ; @YouriAckx
    ;
    ;----------------------------------------------;

    org 0x7c00 ; BIOS loads at this address

    bits 16 ; 16 bits real mode

    ; Print a welcome message.
    ; We have no DOS nor Linux kernel here.
    ; Therefore, we will use bios int 0x10.

    start:
    cli ; disable interrupts

    mov si, msg ; SI points to message
    mov ah, 0x0e ; print char service
    .loop lodsb ; AL <- [DS:SI] && SI++
    or al, al ; end of string?
    jz halt
    int 0x10 ; print char
    jmp .loop ; next char

    halt: hlt ; halt


    msg: db "Hello, World!", 0


    ;----------------------------------------------;
    ; Bootloader signature must be located
    ; at bytes #511 and #512.
    ; Fill with 0 in between.
    ; $ = address of the current line
    ; $$ = address of the 1st instruction
    ;----------------------------------------------;

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