Very newbie question...

Very newbie question...

[Lorenzo]

Hi,

i have some problems with my first linux/nasm asm program.
This is a simple "hello world" program but i can't see the "hello world" 
on my screen and i don't find my error.
I work on 64bit amd system.
Someone can illuminate me? :)


Thx

-----------------------------------

section .text
    global   _start

msg   db   'hello, world!',0xa
len   equ   $ - msg

_start:
    push   ebp
    mov   ebp,esp

    push   len
    push   msg
    push   1
    mov   ebx,esp
    mov   eax,4
    int   0x80

    add   esp,12

    mov   ebx,0
    mov   eax,1
    int   0x80

RE: Very newbie question...

[John Rodriguez]

I am still newbie myself, but one thing that I noticed is that you pass some
parameters via registers and others via the stack pointer.

The write sys call takes 3 param (as you prob already know), the file
descriptor (1 = stdout), the pointer to the buffer, and its size.

The write sys call itself is syscall 4.

According to http://asm.sourceforge.net/articles/linasm.html
"For all syscalls, the syscall number goes in %eax. For syscalls that have
less than six args, the args go in %ebx,%ecx,%edx,%esi,%edi in order. The
return value of the syscall is stored in %eax."

Here is my own example that I wrote about a year ago.

section .data
hello   db  'Hello, World!', 0Ah
len     equ $-hello

section .text
global  _start
_start:
mov     edx, len
mov     ecx, hello
mov     ebx, 1
mov     eax, 4
int     80h
mov     ebx, 0
mov     eax, 1
int     80h

-----Original Message-----
From: linux-assembly-owner@vger.kernel.org
[mailto:linux-assembly-owner@vger.kernel.org] On Behalf Of Lorenzo
Sent: Friday, November 11, 2005 6:05 PM
To: linux-assembly@vger.kernel.org
Subject: Very newbie question...

Hi,

i have some problems with my first linux/nasm asm program.
This is a simple "hello world" program but i can't see the "hello world" 
on my screen and i don't find my error.
I work on 64bit amd system.
Someone can illuminate me? :)


Thx

-----------------------------------

section .text
    global   _start

msg   db   'hello, world!',0xa
len   equ   $ - msg

_start:
    push   ebp
    mov   ebp,esp

    push   len
    push   msg
    push   1
    mov   ebx,esp
    mov   eax,4
    int   0x80

    add   esp,12

    mov   ebx,0
    mov   eax,1
    int   0x80
-
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Re: Very newbie question...

[Frederic Marmond]

Hi,
in amd64, registers are different (64bits...) ;)
So, I think you'd better use the 64 bits name version
push rbp
mov rbp,rsp
...

What do you have as result in your case?
can you try it with gdb and step your prog?

Fred

Le Samedi 12 Novembre 2005 00:05, Lorenzo a écrit :
> Hi,
>
> i have some problems with my first linux/nasm asm program.
> This is a simple "hello world" program but i can't see the "hello world"
> on my screen and i don't find my error.
> I work on 64bit amd system.
> Someone can illuminate me? :)
>
>
> Thx
>
> -----------------------------------
>
> section .text
>     global   _start
>
> msg   db   'hello, world!',0xa
> len   equ   $ - msg
>
> _start:
>     push   ebp
>     mov   ebp,esp
>
>     push   len
>     push   msg
>     push   1
>     mov   ebx,esp
>     mov   eax,4
>     int   0x80
>
>     add   esp,12
>
>     mov   ebx,0
>     mov   eax,1
>     int   0x80
> -
> To unsubscribe from this list: send the line "unsubscribe linux-assembly"
> in the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
Frederic Marmond
-
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RE: Very newbie question...

[Brian Raiter]

> i have some problems with my first linux/nasm asm program.
> This is a simple "hello world" program but i can't see the "hello
> world" on my screen and i don't find my error.

As noted, you are confusing the function call method with the system
call method, and doing a little of both. You need to decide on one or
the other.

If you want to make direct kernel system calls, then follow the code
that was posted earlier. Alternately, if you wanted to use the POSIX
functions, your code would look something like this:

EXTERN write, _exit

; ...

	push	len
	push	hello
	push	1
	call	write
	add	esp, 12
	push	0
	call	_exit

b

Re: Very newbie question...

[Lorenzo]

I have tried to do a program like yours and all is ok.
The "Hello World" work well but i don't want to use this method.
In the same page,

http://asm.sourceforge.net/articles/linasm.html, there is another thing:

" Syscalls whos number of args is greater than five still expect the
syscall number to be in %eax, but the args are arranged in memory and the
pointer to the first arg is stored in %ebx."

I know that "Hello World" is composed of less then five args but i want to know both methods (put all in eax,ebx,ecx,edx,esi,edi registers or put the syscall in eax, push the others and put the pointer to the stack in ebx).
Thx :)



John Rodriguez wrote:

>I am still newbie myself, but one thing that I noticed is that you pass some
>parameters via registers and others via the stack pointer.
>
>The write sys call takes 3 param (as you prob already know), the file
>descriptor (1 = stdout), the pointer to the buffer, and its size.
>
>The write sys call itself is syscall 4.
>
>According to http://asm.sourceforge.net/articles/linasm.html
>"For all syscalls, the syscall number goes in %eax. For syscalls that have
>less than six args, the args go in %ebx,%ecx,%edx,%esi,%edi in order. The
>return value of the syscall is stored in %eax."
>
>Here is my own example that I wrote about a year ago.
>
>section .data
>hello   db  'Hello, World!', 0Ah
>len     equ $-hello
>
>section .text
>global  _start
>_start:
>mov     edx, len
>mov     ecx, hello
>mov     ebx, 1
>mov     eax, 4
>int     80h
>mov     ebx, 0
>mov     eax, 1
>int     80h
>

Re: Very newbie question...

[Lorenzo]

When i back in office i try to use 64bit registers.
At home i have a linux distribution (slackware, 32bit) installed over a 64bit hardware and i can't try (i think that i can't try but is possible that i don't know how :))
For the gdb is the same thing, when back in office i try.
Thx :)



Frederic Marmond wrote:

>Hi,
>in amd64, registers are different (64bits...) ;)
>So, I think you'd better use the 64 bits name version
>push rbp
>mov rbp,rsp
>...
>
>What do you have as result in your case?
>can you try it with gdb and step your prog?
>
>Fred
>  
>

Re: Very newbie question...

[Lorenzo]

Ah ok... now i understand some more things :)

Thx :)



Brian Raiter wrote:

>As noted, you are confusing the function call method with the system
>call method, and doing a little of both. You need to decide on one or
>the other.
>
>If you want to make direct kernel system calls, then follow the code
>that was posted earlier. Alternately, if you wanted to use the POSIX
>functions, your code would look something like this:
>
>EXTERN write, _exit
>
>; ...
>
>	push	len
>	push	hello
>	push	1
>	call	write
>	add	esp, 12
>	push	0
>	call	_exit
>
>b
>-
>To unsubscribe from this list: send the line "unsubscribe linux-assembly" in
>the body of a message to majordomo@vger.kernel.org
>More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>
>  
>