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Repulverized



Joined: 18 Jul 2011
Posts: 9
Location: Detroit
Repulverized
I am having trouble with some os code. i am writing a text program for it and am using this code for it

_typer:
xor ah, ah
int 0x16

mov si, charmsg
call print_string

mov ah, 0x0e
mov bl, 0x16
int 0x10

jmp _typer

it is part of the kernel. I made a cursor that is controlled by the keyboard to make programs run. I used this to define charmsg

charmsg db '', '$'

i put the dollar sign to stop from getting a unhanded exception. but all it does is print the dollar sign.
Post 11 Sep 2011, 04:33
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17624
Location: In your JS exploiting you and your system
revolution
We have no ides what you have done. Are you checking for $ as a string terminator in the print_string code? Perhaps you need to show your print_string source code?
Post 11 Sep 2011, 05:00
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Repulverized



Joined: 18 Jul 2011
Posts: 9
Location: Detroit
Repulverized
my print_string code is this

print_string:
lodsb
cmp al, 24h
je print_string_eof
mov ah, 0eh
int 10h
jmp print_string

print_string_eof:
ret
Post 11 Sep 2011, 05:05
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
Location: Argentina
LocoDelAssembly
The code is completely expected to print "$", notice that when you return form your print_string, AL is loaded with "$" (because you destroyed caller's AL value with lodsb), and since you are calling int 0x10 from you main loop you get the $ printed. Your code as is should be printing one "$" per keystroke.

I would like to suggest a fix, but it is unclear to me what are you trying to do. Perhaps you could do some sort of narration about what keyboard events the user is doing and how the program should react to them? (including a pseudo-screenshot also)
Post 11 Sep 2011, 05:50
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Dex4u



Joined: 08 Feb 2005
Posts: 1601
Location: web
Dex4u
You need to tell us, what your trying to do.
Post 11 Sep 2011, 22:22
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