Listing 1. example 2.c
#include <linux/kernel.h>
#include <linux/module.h>
#include <sys/syscall.h>
extern void *sys_call_table[];
asmlinkage int (*original_sys_exit)(int);
asmlinkage int our_fake_exit_function(int error_code)
{
/*print message on console every time we
*are called*/
printk("HEY! sys_exit called with error_code=%d\n",error_code);
/*call the original sys_exit*/
return original_sys_exit(error_code);
}
/*this function is called when the module is
*loaded (initialization)*/
int init_module()
{
/*store reference to the original sys_exit*/
original_sys_exit=sys_call_table[__NR_exit];
/*manipulate sys_call_table to call our
*fake exit function instead
*of sys_exit*/
sys_call_table[__NR_exit]=our_fake_exit_function;
}
/*this function is called when the module is
*unloaded*/
void cleanup_module()
{
/*make __NR_exit point to the original
*sys_exit when our module
*is unloaded*/
sys_call_table[__NR_exit]=original_sys_exit;
}
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