OS Loader dont works

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sadosex

Joined: 26 Jan 2020
Posts: 2

sadosex 26 Jan 2020, 11:35

I make a bootstrap program to be installed on boot sector of TAILS, Windows however the software that i make only work showing the boot message to the user when s/he power on the PC and startup my OS bootloader. I dont know what are wrong at my source because my source works on MS-DOS however dont works in Windows or TAILS Linux. Read carefully my source in FASM:

Code:

org 0x100
OS_LOADER:
    cli       
    xor ax,ax
    mov ds,ax
    mov es,ax
    mov ss,ax
    mov sp,07C00h
    sti
    Kernel:

    MOV AX,1300h
    MOV BX,30h
    MOV CX,10Ch
    MOV DX,0
    PUSH CS
    POP ES
    MOV BP,7C68h
    INT 10h
    L1:
    IN AL,60H
    CMP AL,1
    JNZ L1
    JMP L2
    Texto db "",0   ;198 bytes message
    L2:
    mov ah,8
    mov dl,80H
    mov di,0
    push es
    mov es,di
    INT 13H
    pop es 
    sub cl,6

    mov ax,0000h
    mov es,ax
    mov bx,500h
    mov dl,80h
    mov al,01h
    mov ah,02h
    int 13h
    jmp 0000:0500h

    codesize:

    SETOR db 512 dup (0)

Please someone tell me where is my error in my source.

26 Jan 2020, 11:35

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20343
Location: In your JS exploiting you and your system

revolution 26 Jan 2020, 17:21

The first thing I notice is that you don't have the AA55 signature at the end of the 512-byte boot sector.

26 Jan 2020, 17:21

N-LG

Joined: 14 Feb 2019
Posts: 40
Location: france

N-LG 26 Jan 2020, 22:31

this program seem to be write for an execution in Dos (the .com format) because of the org 0x100 directive

there are almost no comments, it does not make reading possible, I am lazy to find out what each call corresponds to so that I can say what is wrong

26 Jan 2020, 22:31

DimonSoft

Joined: 03 Mar 2010
Posts: 1228
Location: Belarus

DimonSoft 27 Jan 2020, 13:53

Apart from other things already mentioned, you have no notion of filling CX and DH registers before reading from disk. int 13h/08h doesn’t return meaningful values for int 13h/02h and, for floppies, may not return meaningful values at all.

27 Jan 2020, 13:53

sadosex

Joined: 26 Jan 2020
Posts: 2

sadosex 27 Jan 2020, 14:45

That is my full source:

Code:

org 0x100
mov ax,201h
mov bx,SETOR
mov cx,1
mov dx,80H
int 13h

mov ah,8
mov dx,80H
mov di,0
push es
mov es,di
INT 13H
pop es

mov ax,301h
sub cl,6
mov dl,80H
MOV WORD[SETOR+510],0AA55H
mov bx,SETOR
INT 13H

LEA DI,[SETOR]
MOV SI,OS_LOADER
MOV CX,336
REP MOVSB

mov bx,SETOR
MOV WORD[SETOR+510],0AA55H
mov ax,301h
mov cx,1
mov dx,80H
INT 13H

ret
OS_LOADER:
            cli       
            xor ax,ax
            mov ds,ax
            mov es,ax
            mov ss,ax
            mov sp,07C00h
            sti
                Kernel:

MOV AX,1300h
MOV BX,30h
MOV CX,10Ch
MOV DX,0
PUSH CS
POP ES
MOV BP,7C68h
INT 10h
L1:
IN AL,60H
CMP AL,1
JNZ L1
JMP L2
Texto db "",0   ;message of 198 bytes
L2:
mov ah,8
mov dl,80H
mov di,0
push es
mov es,di
INT 13H
pop es
sub cl,6

mov ax,0000h
mov es,ax
mov bx,500h
mov dl,80h
mov al,01h
mov ah,02h
int 13h
jmp 0000:0500h

codesize:

SETOR db 512 dup (0)

Now tell me why i couldn't install my boot loader in Linux and Windows?

27 Jan 2020, 14:45

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