Implementing a basic system call

[phosse1]

Hi everyone,

I've got a small problem when I try to implement a 'hello world' system call. I've read the tutorials online aswell as textbooks for references, but when I recompile my kernel, I get an error.
I've pasted all required info and I'd be greatly appreciative for any assistance.

My System call... outputs 'Hello World'. This file compiles perfectly:

#include </usr/src/linux-source-2.6.24/include/linux/kernel.h>
#include </usr/src/linux-source-2.6.24/include/asm-x86/linkage.h>
asmlinkage (long sys_helloworld())
{
printk("HELLO WORLD!!");
return 1;
} 

Defining a new Sys call number in unistd_32.h:

// Location of file: /usr/src/linux/include/asm-x86/unistd_32.h
// BTW I also incremented the __NR_syscalls also
#define __NR_helloworld        325 

Now I add an entry into the system call table:

// Location of file: /usr/src/linux/arch/x86/kernel/syscall_table_32. 
.long sys_helloworld        /* For the added system call*/ 

Lastly, In the makefile, I add:

obj-y := helloworld.o 

But when I compile my kernel, I get an error, it compiles for 10-12 minutes before I get this error:

arch/x86/kernel/built-in.o: In function `sys_call_table':
(.rodata+0x514): undefined reference to `sys_helloworld'
make[1]: *** [.tmp_vmlinux1] Error 1
make[1]: Leaving directory `/usr/src/linux-source-2.6.24'
make: *** [debian/stamp-build-kernel] Error 2 

I would be VERY appreciative if anyone knows where I'm going wrong.

Thanks in advance,
p.