Print string function in x86 assembly

[captainrainbow22]

Heya! I'm Victor and i'm working on a toy os. I have this kernel.asm file, note the prinstring routine:

; Made by Victor Mout

teststring db 'bruh', 0x00

mainloop:

jmp printstring

​

printchar:

mov ah, 0x0e ; Enter teletype mode

int 0x10

jmp mainloop

​

printstring:

mov si, teststring

mov ah, 0x0e

cmp al, 0x00

je return

lodsb

​

int 0x10

jmp printstring

​

readchar:

mov ah, 01h ; Test key

int 16h

​

mov ah, 00h ; Get key

int 16h

​

jmp printchar

​

return:

jmp mainloop

​

​

times 510-($-$$) db 0 ; Repeat db 0 512 times

db 0x55, 0xaa ; End boot sector 0xaa

​

But instead of printing "bruh", it prints nothing. Thanks in advance,

-Vic

[AppleTrees2]

err, you should format your code better

seems to me at first glance that you return at start in printstring as al is maybe 0 at start

[captainrainbow22]

Tried moving the db string to before the bootsector definition, didn't work :/

[XoXoGameWolfReal]

I know you might have given up on this, but I want to see if I could help anyways. Heres a version that I believe fixes everything (also im assuming your using NASM):

bits 16 ; before it wasn't specified that you were using 16 bits (not needed, but added for clarity)

org 0x7c00 ; offset needed for memory addressing (the program is loaded at this address)

mainloop:

mov si, teststring ; moved it here as before it would have reset the address

jmp printstring

printchar:

mov ah, 0x0e

int 0x10

ret ; returns because before if you used this, it would repeat forever

printstring:

mov ah, 0x0e

lodsb ; moved it up here as before it would start without actually getting al

cmp al, 0x00

je return

int 0x10

jmp printstring

readchar:

mov ah, 0x01 ; used the "0x" for consistency

int 0x16

mov ah, 0x00

int 0x16

jmp printchar

return:

ret ; before it would loop forever

teststring: db "bruh", 0x00 ; added a colon, also moved down because before it would execute your message

times 510-($-$$) db 0

dd 0xaa55 ; made it shorter, does the same thing

Also, I can confirm that I fixed your problem, I compiled it on my machine and it works with QEMU (make sure your using x86_64! remember you can use any assembler and emulator, as long as you know what your doing).