1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * kretprobe_example.c
4 *
5 * Here's a sample kernel module showing the use of return probes to
6 * report the return value and total time taken for probed function
7 * to run.
8 *
9 * usage: insmod kretprobe_example.ko func=<func_name>
10 *
11 * If no func_name is specified, kernel_clone is instrumented
12 *
13 * For more information on theory of operation of kretprobes, see
14 * Documentation/trace/kprobes.rst
15 *
16 * Build and insert the kernel module as done in the kprobe example.
17 * You will see the trace data in /var/log/messages and on the console
18 * whenever the probed function returns. (Some messages may be suppressed
19 * if syslogd is configured to eliminate duplicate messages.)
20 */
21
22#include <linux/kernel.h>
23#include <linux/module.h>
24#include <linux/kprobes.h>
25#include <linux/ktime.h>
26#include <linux/limits.h>
27#include <linux/sched.h>
28
29static char func_name[NAME_MAX] = "kernel_clone";
30module_param_string(func, func_name, NAME_MAX, S_IRUGO);
31MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the"
32			" function's execution time");
33
34/* per-instance private data */
35struct my_data {
36	ktime_t entry_stamp;
37};
38
39/* Here we use the entry_hanlder to timestamp function entry */
40static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
41{
42	struct my_data *data;
43
44	if (!current->mm)
45		return 1;	/* Skip kernel threads */
46
47	data = (struct my_data *)ri->data;
48	data->entry_stamp = ktime_get();
49	return 0;
50}
51NOKPROBE_SYMBOL(entry_handler);
52
53/*
54 * Return-probe handler: Log the return value and duration. Duration may turn
55 * out to be zero consistently, depending upon the granularity of time
56 * accounting on the platform.
57 */
58static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
59{
60	unsigned long retval = regs_return_value(regs);
61	struct my_data *data = (struct my_data *)ri->data;
62	s64 delta;
63	ktime_t now;
64
65	now = ktime_get();
66	delta = ktime_to_ns(ktime_sub(now, data->entry_stamp));
67	pr_info("%s returned %lu and took %lld ns to execute\n",
68			func_name, retval, (long long)delta);
69	return 0;
70}
71NOKPROBE_SYMBOL(ret_handler);
72
73static struct kretprobe my_kretprobe = {
74	.handler		= ret_handler,
75	.entry_handler		= entry_handler,
76	.data_size		= sizeof(struct my_data),
77	/* Probe up to 20 instances concurrently. */
78	.maxactive		= 20,
79};
80
81static int __init kretprobe_init(void)
82{
83	int ret;
84
85	my_kretprobe.kp.symbol_name = func_name;
86	ret = register_kretprobe(&my_kretprobe);
87	if (ret < 0) {
88		pr_err("register_kretprobe failed, returned %d\n", ret);
89		return ret;
90	}
91	pr_info("Planted return probe at %s: %p\n",
92			my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr);
93	return 0;
94}
95
96static void __exit kretprobe_exit(void)
97{
98	unregister_kretprobe(&my_kretprobe);
99	pr_info("kretprobe at %p unregistered\n", my_kretprobe.kp.addr);
100
101	/* nmissed > 0 suggests that maxactive was set too low. */
102	pr_info("Missed probing %d instances of %s\n",
103		my_kretprobe.nmissed, my_kretprobe.kp.symbol_name);
104}
105
106module_init(kretprobe_init)
107module_exit(kretprobe_exit)
108MODULE_LICENSE("GPL");
109