c - An Error occured while compiling Linux Kernel 2.6 with a new System Call -

i added new system call in linux kernel 2.6.33 including essential user-side , kernel-side parts, while compiling got follwing error:

arch/x86/built-in.o: in function `sys_call_table': (.rodata+0x724): undefined reference `sys_my_sys_call' make: *** [.tmp_vmlinux1] error 1 

i tried change kernal version (2.6.32.21) error occurs. let's show simple code of "hello! world." syscall:

#include <linux/kernel.h>  asmlinkage long sys_hello(void) {     printk("hello world\n");     return 0; }