How to loop?

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Rock24

Joined: 13 Feb 2015
Posts: 5

Rock24 20 Feb 2015, 00:15

Hello.
I would like to display 10 times text on the screen

Code:

format ELF64 executable  
entry _start 
segment readable executable
_start:
        mov rcx,1
loo:
        cmp rcx, 10
        jae endd
        
        mov rax,1
        mov rdi,1
        mov rsi,abc
        mov rdx,[dlg]
        syscall
        add rcx,1
        jmp loo
endd:

mov rax,60
syscall


segment writeable executable
abc db "abc", 0ah
dlg dq $ - abc

This code displays txt only once. What am I doing wrong?

20 Feb 2015, 00:15

typedef

Joined: 25 Jul 2010
Posts: 2909
Location: 0x77760000

typedef 20 Feb 2015, 00:17

loopnz

20 Feb 2015, 00:17

HaHaAnonymous

Joined: 02 Dec 2012
Posts: 1178
Location: Unknown

HaHaAnonymous 20 Feb 2015, 00:22

[ Post removed by author. ]

Last edited by HaHaAnonymous on 28 Feb 2015, 17:54; edited 1 time in total

20 Feb 2015, 00:22

Rock24

Joined: 13 Feb 2015
Posts: 5

Rock24 20 Feb 2015, 00:29

Thank you HaHaAnonymous, typedef.
I was sure that 'syscall' destroy only rax Smile

20 Feb 2015, 00:29

HaHaAnonymous

Joined: 02 Dec 2012
Posts: 1178
Location: Unknown

HaHaAnonymous 20 Feb 2015, 00:34

[ Post removed by author. ]

Last edited by HaHaAnonymous on 28 Feb 2015, 17:54; edited 1 time in total

20 Feb 2015, 00:34

Rock24

Joined: 13 Feb 2015
Posts: 5

Rock24 20 Feb 2015, 00:52

I have one question yet.
What if i use cx register instead rcx? This will change something in the loop / code?

20 Feb 2015, 00:52

HaHaAnonymous

Joined: 02 Dec 2012
Posts: 1178
Location: Unknown

HaHaAnonymous 20 Feb 2015, 01:00

[ Post removed by author. ]

Last edited by HaHaAnonymous on 28 Feb 2015, 17:54; edited 1 time in total

20 Feb 2015, 01:00

badc0de02

Joined: 25 Nov 2013
Posts: 215
Location: %x

badc0de02 20 Feb 2015, 01:57

so CX are the first 16 bits of the ecx Register and ecx the first 32 of the rax register
if rcx gets destroyed the other will get too

20 Feb 2015, 01:57

gens

Joined: 18 Feb 2013
Posts: 161

gens 20 Feb 2015, 02:06

http://www.logix.cz/michal/devel/amd64-regs/
good table

@badc0de02
"first 32 bits of rcx register"* Smile

20 Feb 2015, 02:06

nkeck72

Joined: 28 May 2015
Posts: 83
Location: 0000:7C00

nkeck72 28 May 2015, 20:59

Was being an idiot. As such, this post has been removed.

_________________
It may look hard, but it won't take long if you take it one byte at a time.

NOS: www.github.com/nkeck720/nos

28 May 2015, 20:59

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