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.
http://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/x86.html
You've seen this part of the handbook, yes?
In particular:
http://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/x86-system-calls.html
Calling your attention to the example code shown just before section 11.3.2, which shows
how to open a file:
open:
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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