1/*
 2 * Here's a sample kernel module showing the use of jprobes to dump
 3 * the arguments of _do_fork().
 4 *
 5 * For more information on theory of operation of jprobes, see
 6 * Documentation/kprobes.txt
 7 *
 8 * Build and insert the kernel module as done in the kprobe example.
 9 * You will see the trace data in /var/log/messages and on the
10 * console whenever _do_fork() is invoked to create a new process.
11 * (Some messages may be suppressed if syslogd is configured to
12 * eliminate duplicate messages.)
13 */
14
15#include <linux/kernel.h>
16#include <linux/module.h>
17#include <linux/kprobes.h>
18
19/*
20 * Jumper probe for _do_fork.
21 * Mirror principle enables access to arguments of the probed routine
22 * from the probe handler.
23 */
24
25/* Proxy routine having the same arguments as actual _do_fork() routine */
26static long j_do_fork(unsigned long clone_flags, unsigned long stack_start,
27	      unsigned long stack_size, int __user *parent_tidptr,
28	      int __user *child_tidptr, unsigned long tls)
29{
30	pr_info("jprobe: clone_flags = 0x%lx, stack_start = 0x%lx "
31		"stack_size = 0x%lx\n", clone_flags, stack_start, stack_size);
32
33	/* Always end with a call to jprobe_return(). */
34	jprobe_return();
35	return 0;
36}
37
38static struct jprobe my_jprobe = {
39	.entry			= j_do_fork,
40	.kp = {
41		.symbol_name	= "_do_fork",
42	},
43};
44
45static int __init jprobe_init(void)
46{
47	int ret;
48
49	ret = register_jprobe(&my_jprobe);
50	if (ret < 0) {
51		pr_err("register_jprobe failed, returned %d\n", ret);
52		return -1;
53	}
54	pr_info("Planted jprobe at %p, handler addr %p\n",
55	       my_jprobe.kp.addr, my_jprobe.entry);
56	return 0;
57}
58
59static void __exit jprobe_exit(void)
60{
61	unregister_jprobe(&my_jprobe);
62	pr_info("jprobe at %p unregistered\n", my_jprobe.kp.addr);
63}
64
65module_init(jprobe_init)
66module_exit(jprobe_exit)
67MODULE_LICENSE("GPL");