Re: [Nasm-users] can't write argv[0] on stdout

[Frank K. <fbk...@zy...>]

Holger Hanrath wrote:
> Hi all,
> 
> i want to write 3 bytes of argv[0] on stdout but it doesn't work. 
> Return code -14 (EFAULT Bad address). Am i missing something here? 
> 
> System is archlinux 2009.08 x86_64 kernel 2.6.31-rc6 
> nasm 2.05.01 Binutils 2.19.1.20090418
> 
> 
> 
> stdout	equ	1
> write	equ	4
> exit	equ	1
> 
> section .text
> 	global	_start
> _start:	
> 	pop	rax		; rax = argc
> 	pop	rax		; rax = argv[0]
> 
> 	mov	rdx,	3	; write 3 bytes
> 	mov	rcx,	rax	; rcx = rax = argv[0]
> 	mov	rbx,	stdout	
> 	mov	rax,	write	
> 	int	0x80
> 	
> 	mov	rbx,	0
> 	mov	rax,	exit
> 	int	0x80

64-bit does it a "bit" differently (from the late and sorely missed 
Chuck Crayne:

section .data
     string1 db  "Hello World!",10,0

section .text
     global _start

     _start:
         ; calculate the length of string
         mov     rdi, string1
         mov     rcx, -1
         xor     al,al
         cld
         repnz scasb

         ; place the length of the string in RDX
         mov     rdx, -2
         sub     rdx, rcx

         ; print the string using write() system call
         mov     rsi, string1
         push    0x1
         pop     rax
         mov     rdi,rax
         syscall

         ; exit from the application here
         xor     rdi,rdi
         push    0x3c
         pop     rax
         syscall

That won't do what you want, of course, but will give you an idea which 
registers are used. (the push/pop is just shorter - probably want to use 
"-Ox" to use it) I assume the stack is set up the same for 64-bit as for 
32-bit(?). Let us know how it works - 64-bit examples are in short 
supply, still...

Best,
Frank