Writing Your Own OS on Ubuntu, Day 2

Recently I have been reading 30 Days OS from Scratch.

I use a laptop as my development environment and run Ubuntu inside VirtualBox.

The book mainly explains things in a Windows-centered way, but since I had the chance, I decided to do it on Ubuntu. These are my notes. I am using nasm. I know almost nothing about assembly, so I had quite a hard time starting from Chapter 2.

Notes:

DB "HELLO-OS "
DB "FAT12 "

The two lines above stop working if the number of spaces changes.

RESB 18 => TIMES 18 DB 0
RESB 0x7dfe-$ => 0x1fe-($-$$) DB 0
RESB 1469432 => TIMES 1469432 DB 0

After saving the following source code to a file:

$nasm helloos.asm -o helloos.img$ qemu-system-i386 -fda helloos.img

; helloos.asm

        ORG     0x7c00

        JMP     entry
        DB      0x90
        DB      "HELLOIPL"
        DW      512
        DB      1
        DW      1
        DB      2
        DW      224
        DW      2880
        DB      0xf0
        DW      9
        DW      18
        DW      2
        DD      0
        DD      2880
        DB      0, 0, 0x29
        DD      0xffffffff
        DB      "HELLO-OS   "
        DB      "FAT12   "
        TIMES   18 DB 0

entry:
        MOV     AX,0
        MOV     SS,AX
        MOV     SP,0x7c00
        MOV     DS,AX
        MOV     ES,AX

        MOV     SI,msg
putloop:
        MOV     AL,[SI]
        ADD     SI,1
        CMP     AL,0
        JE      fin
        MOV     AH,0x0e
        MOV     BX,15
        INT     0x10
        JMP     putloop
fin:
        HLT
        JMP     fin

msg:
        DB      0x0a, 0x0a
        DB      "hello, world"
        DB      0x0a
        DB      0

        TIMES   0x1fe-($-$$) DB 0

        DB      0x55, 0xaa

        DB      0xf0, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00
        TIMES   4600 DB 0
        DB      0xf0, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00
        TIMES   1469432 DB 0