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/sched.h>
27
28static char func_name[KSYM_NAME_LEN] = "kernel_clone";
29module_param_string(func, func_name, KSYM_NAME_LEN, 0644);
30MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the"
31			" function's execution time");
32
33/* per-instance private data */
34struct my_data {
35	ktime_t entry_stamp;
36};
37
38/* Here we use the entry_handler to timestamp function entry */
39static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
40{
41	struct my_data *data;
42
43	if (!current->mm)
44		return 1;	/* Skip kernel threads */
45
46	data = (struct my_data *)ri->data;
47	data->entry_stamp = ktime_get();
48	return 0;
49}
50NOKPROBE_SYMBOL(entry_handler);
51
52/*
53 * Return-probe handler: Log the return value and duration. Duration may turn
54 * out to be zero consistently, depending upon the granularity of time
55 * accounting on the platform.
56 */
57static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
58{
59	unsigned long retval = regs_return_value(regs);
60	struct my_data *data = (struct my_data *)ri->data;
61	s64 delta;
62	ktime_t now;
63
64	now = ktime_get();
65	delta = ktime_to_ns(ktime_sub(now, data->entry_stamp));
66	pr_info("%s returned %lu and took %lld ns to execute\n",
67			func_name, retval, (long long)delta);
68	return 0;
69}
70NOKPROBE_SYMBOL(ret_handler);
71
72static struct kretprobe my_kretprobe = {
73	.handler		= ret_handler,
74	.entry_handler		= entry_handler,
75	.data_size		= sizeof(struct my_data),
76	/* Probe up to 20 instances concurrently. */
77	.maxactive		= 20,
78};
79
80static int __init kretprobe_init(void)
81{
82	int ret;
83
84	my_kretprobe.kp.symbol_name = func_name;
85	ret = register_kretprobe(&my_kretprobe);
86	if (ret < 0) {
87		pr_err("register_kretprobe failed, returned %d\n", ret);
88		return ret;
89	}
90	pr_info("Planted return probe at %s: %p\n",
91			my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr);
92	return 0;
93}
94
95static void __exit kretprobe_exit(void)
96{
97	unregister_kretprobe(&my_kretprobe);
98	pr_info("kretprobe at %p unregistered\n", my_kretprobe.kp.addr);
99
100	/* nmissed > 0 suggests that maxactive was set too low. */
101	pr_info("Missed probing %d instances of %s\n",
102		my_kretprobe.nmissed, my_kretprobe.kp.symbol_name);
103}
104
105module_init(kretprobe_init)
106module_exit(kretprobe_exit)
107MODULE_LICENSE("GPL");
108