Problems with FreeBSD assembly

Charlie Kester corky1951 at
Thu Nov 12 01:32:45 UTC 2009

On Wed 11 Nov 2009 at 11:43:21 PST David Jackson wrote:
>I am having great difficulty running a very simple assembler program 
>on FreeBSD on x86 in my efforts to learn some assembly programming on 
>FreeBSD.  I have tried to compile the following with nasm, however i 
>get nothing in response when I attempt to run this program:
>       section .data
>       hello   db      'Hello, World!', 0xa
>       hbytes  equ     $ - hello
>       section .text
>       global  _start
>       _start:
>       push    dword hbytes
>       push    dword hello
>       push    dword 1
>       mov eax,0x4
>       int 0x80
>       add esp,12
>       push    dword 0
>       mov eax,0x1
>       int 0x80
>nasm -f elf -o hello1s.o hello1.s
>ld -s -o hello1s hello1s.o
>./hello1s prints nothing.
>What is wrong here? It should print "hello world".  Thanks in advance
>for   your help, it is greatly appreciated.

You've seen this part of the handbook, yes?

In particular:

Calling your attention to the example code shown just before section 11.3.2, which shows 
how to open a file:

     push    dword mode
     push    dword flags
     push    dword path
     mov eax, 5
     push    eax     ; Or any other dword
     int 80h
     add esp, byte 16

Notice that the system call number (or any other dword) should also be
pushed onto the stack before the int 80h.

So try this:

	push    dword hbytes
	push    dword hello
	push    dword 1			; stdout
	mov 	eax,0x4
	push	eax				; or any other dword
	int 	0x80
	add 	esp,16			; don't forget to account for the extra dword!

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