My program works in QEMU, not on real machine
Posted: Thu Jul 25, 2019 9:31 am
I have made a simple program in asm:
I compiled it with NASM (nasm test1.txt), then I used program HexWorkshop to copy it to my flash drive at sector 0 (boot sector). Then I plugged the flash drive to my computer and booted from it. It printed
just as I expected.
Then I tried to make some more complicated programs. For those I needed to store some data in memory. These programs did not work at all, only in QEMU. (I will not post them here becouse they are quite long). Later I found that problems were caused when I was using data from RAM (like storing and reading variables). I have made a simple modification of the program at the top of this post:
I compiled it with NASM (nasm test2.txt), then I tested it with QEMU-it worked. It printed same as test1. But when I tried to run it on real computer it did not work-it just moved cursor (looked like it printed space). I have no idea why it works like that. Can you explain me why it does this?
Code: Select all
bits 16
org 0x7C00
start:
mov ah, 0xE
mov al, "a"
int 0x10
stop:
jmp stop
times 510-($-$$) db 0
dw 0xAA55Code: Select all
aThen I tried to make some more complicated programs. For those I needed to store some data in memory. These programs did not work at all, only in QEMU. (I will not post them here becouse they are quite long). Later I found that problems were caused when I was using data from RAM (like storing and reading variables). I have made a simple modification of the program at the top of this post:
Code: Select all
bits 16
org 0x7C00
start:
mov [letter], byte "a"
mov ah, 0xE
mov al, [letter]
int 0x10
stop:
jmp stop
letter: db 0
times 510-($-$$) db 0
dw 0xAA55