How to return to main after jump?

Question

Well, I have this code:

SECTION .data
    message: db "Value = %d", 10, 0
    message2: db "End", 10, 0
SECTION .bss

SECTION .text

extern printf
global main

main:
    push ebp
    mov ebp, esp

    mov ebx, 0
    jmp loop
    push message2
    call printf
    mov esp, ebp
    pop ebp
    ret

loop: 
    push ebx 
    push message 
    call printf 
    inc ebx 
    cmp ebx, 100000
    jne loop 
    mov esp, ebp
    pop ebp

I would like know how to return back to main and then print message2?

Thanks for helps and sorry for my english.

You should clean outgoing arguments from the stack after a call, by the way. — gsg, Mar 12 '14 at 05:46
I tried it, but it returns segfault, may you post code in pastebin? — Victor Martins, Mar 13 '14 at 01:04

score 1 · Accepted Answer · answered Mar 22 '14 at 19:59

Problem is that you are calling C-function that uses cdecl calling convention (caller must clean the stack). This means that after the call, you must add the size of the arguments (in bytes) to the stackpointer. Your first printf takes 2 dword arguments (8 bytes) so you must add 8 to stackpointer after the call. Your second call passes one dword so you add 4 to the stackpointer.

This should work:

SECTION .data
        message: db "Value = %d", 10, 0
        message2: db "End", 10, 0
SECTION .bss

SECTION .text

extern printf
global main

main:
        push ebp
        mov ebp, esp

        mov ebx, 0
        call loop
        push message2
        call printf
        add esp, 4
        mov esp, ebp
        pop ebp
        ret

loop:
        push ebx
        push message
        call printf
        add esp, 8
        inc ebx
        cmp ebx, 10000
        jne loop
        ret

sarah · Answer 2 · 2014-03-12T05:10:39.497

0

try it this way:

SECTION .data

message: db "Value = %d", 10, 0

message2: db "End", 10, 0

SECTION .bss

SECTION .text

extern printf global main

main:

push ebp
mov ebp, esp

mov ebx, 0
call loop

push message2
call printf

mov esp, ebp
pop ebp
ret

loop:

push ebx
push message
call printf 
inc ebx 
cmp ebx, 100000
jne loop 

ret

edited Mar 12 '14 at 05:10

answered Mar 12 '14 at 04:43

sarah

116
6

Thanks for answer, but this way returns segfault. – Victor Martins Mar 12 '14 at 05:01
sorry, in loop, it should be push ebx, then push message, then call. – sarah Mar 12 '14 at 05:08
well, your code in pastebin looks correct to me, so i don't know...sorry! – sarah Mar 12 '14 at 06:06

score 0 · Answer 3 · edited May 23 '17 at 12:23

0

Probably not enough ranking to add as a comment...

push return address before jmp

see this: Substitutes for x86 assembly 'call' instruction?

edited May 23 '17 at 12:23

Community

1
1

answered Mar 12 '14 at 04:50

arshad

21
4

1

Thanks for your answer, but can you give me a example? – Victor Martins Mar 12 '14 at 05:02

How to return to main after jump?

3 Answers3