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
28 static char func_name[KSYM_NAME_LEN] = "kernel_clone";
29 module_param_string(func, func_name, KSYM_NAME_LEN, 0644);
30 MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the"
31 " function's execution time");
32
33 /* per-instance private data */
34 struct my_data {
35 ktime_t entry_stamp;
36 };
37
38 /* Here we use the entry_handler to timestamp function entry */
39 static 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 }
50 NOKPROBE_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 */
57 static 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 }
70 NOKPROBE_SYMBOL(ret_handler);
71
72 static 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
80 static 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
95 static 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
105 module_init(kretprobe_init)
106 module_exit(kretprobe_exit)
107 MODULE_DESCRIPTION("sample kernel module showing the use of return probes");
108 MODULE_LICENSE("GPL");
109
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