Voyage to Linux Kernel Day 12 program errors

I am trying the program from Linux For You magazine Day 12 of Voyage to Linux Kernel
June 2009 edition.
From Aasis Vinayaks column following is the program on my Ubuntu laptop


#include
#include
#include
extern void *sys_table[];
asmlinkage int(*main_sys_exit)(int);
asmlinkage int alt_exit_function(int err_code)
{
printk("Sys_exit called with err_code=%d\n",err_code);
return main_sys_exit(err_code);
}

int init_module()
{
main_sys_exit=sys_table[__NR_exit];
sys_table[__NR_exit]=alt_exit_function;
}
void cleanup_module()
{
sys_table[__NR_exit]=main_sys_exit;
}

Has given a lot of errors discussed on Kernel Newbies mailing list.
Here
http://www.spinics.net/lists/newbies/msg39896.html
Seems to have been the longest discussion in the history of Linux Kernel Newbies mailing list.
Please do suggest if you feel any correction is needed in the program.