Re: Unable to access memory address.

On Fri, 25 Mar 2005 [email protected] wrote:
> Also might want an exit call on the end..  otherwise it'll keep on executing 
> whatever is after the code you load in to memory..  keep reading down a bit in 
> that article, it mentions this and shows you how to do an exit syscall in asm..
> 
> 	; for the program to properly exit instead of segfaulting right here
> 	; ( it doesn't seem to like to fall off the end of a program ), call 
> 	; a sys_exit
> 
> 	mov	eax,1
> 	mov	ebx,0
> 	int	80h
> 
> Joshua Roys

I changed `_start' to `main' because during the linking fase it keeps
complaining about define's.

~: cat prog.asm
section	.text		; declaring our .text segment
        global	_start	; telling where program execution should start

_start: 		; this is where code starts getting exec'ed
        pop	ebx	; get first thing off of stack and put into ebx
        dec	ebx	; decrement the value of ebx by one
        pop	ebp	; get next 2 things off stack and put into ebx
        pop	ebp

        mov     eax,1    ; exit
        mov     ebx,0
        int     80h

~: nasm -f elf prog.asm
~: gcc prog.o -o prog
prog.o: In function `_start':
prog.o(.text+0x0): multiple definition of `_start'
/usr/lib/crt1.o(.text+0x0): first defined here 
/usr/lib/crt1.o: In function `_start': 
/usr/lib/crt1.o(.text+0x18): undefined reference to `main' 
collect2: ld returned 1 exit status

I'm a bit lost here I guess.. ;-)

J.