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
29 static char func_name[NAME_MAX] = "kernel_clone";
30 module_param_string(func, func_name, NAME_MAX, S_IRUGO);
31 MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the"
32 " function's execution time");
33
34 /* per-instance private data */
35 struct my_data {
36 ktime_t entry_stamp;
37 };
38
39 /* Here we use the entry_hanlder to timestamp function entry */
entry_handler(struct kretprobe_instance * ri,struct pt_regs * regs)40 static 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 }
51 NOKPROBE_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 */
ret_handler(struct kretprobe_instance * ri,struct pt_regs * regs)58 static 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 }
71 NOKPROBE_SYMBOL(ret_handler);
72
73 static 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
kretprobe_init(void)81 static 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
kretprobe_exit(void)96 static 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
106 module_init(kretprobe_init)
107 module_exit(kretprobe_exit)
108 MODULE_LICENSE("GPL");
109