1 /*
2 * kretprobe_example.c
3 *
4 * Here's a sample kernel module showing the use of return probes to
5 * report the return value and total time taken for probed function
6 * to run.
7 *
8 * usage: insmod kretprobe_example.ko func=<func_name>
9 *
10 * If no func_name is specified, do_fork is instrumented
11 *
12 * For more information on theory of operation of kretprobes, see
13 * Documentation/kprobes.txt
14 *
15 * Build and insert the kernel module as done in the kprobe example.
16 * You will see the trace data in /var/log/messages and on the console
17 * whenever the probed function returns. (Some messages may be suppressed
18 * if syslogd is configured to eliminate duplicate messages.)
19 */
20
21 #include <linux/kernel.h>
22 #include <linux/module.h>
23 #include <linux/kprobes.h>
24 #include <linux/ktime.h>
25 #include <linux/limits.h>
26 #include <linux/sched.h>
27
28 static char func_name[NAME_MAX] = "do_fork";
29 module_param_string(func, func_name, NAME_MAX, S_IRUGO);
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_hanlder to timestamp function entry */
entry_handler(struct kretprobe_instance * ri,struct pt_regs * regs)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
51 /*
52 * Return-probe handler: Log the return value and duration. Duration may turn
53 * out to be zero consistently, depending upon the granularity of time
54 * accounting on the platform.
55 */
ret_handler(struct kretprobe_instance * ri,struct pt_regs * regs)56 static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
57 {
58 int retval = regs_return_value(regs);
59 struct my_data *data = (struct my_data *)ri->data;
60 s64 delta;
61 ktime_t now;
62
63 now = ktime_get();
64 delta = ktime_to_ns(ktime_sub(now, data->entry_stamp));
65 printk(KERN_INFO "%s returned %d and took %lld ns to execute\n",
66 func_name, retval, (long long)delta);
67 return 0;
68 }
69
70 static struct kretprobe my_kretprobe = {
71 .handler = ret_handler,
72 .entry_handler = entry_handler,
73 .data_size = sizeof(struct my_data),
74 /* Probe up to 20 instances concurrently. */
75 .maxactive = 20,
76 };
77
kretprobe_init(void)78 static int __init kretprobe_init(void)
79 {
80 int ret;
81
82 my_kretprobe.kp.symbol_name = func_name;
83 ret = register_kretprobe(&my_kretprobe);
84 if (ret < 0) {
85 printk(KERN_INFO "register_kretprobe failed, returned %d\n",
86 ret);
87 return -1;
88 }
89 printk(KERN_INFO "Planted return probe at %s: %p\n",
90 my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr);
91 return 0;
92 }
93
kretprobe_exit(void)94 static void __exit kretprobe_exit(void)
95 {
96 unregister_kretprobe(&my_kretprobe);
97 printk(KERN_INFO "kretprobe at %p unregistered\n",
98 my_kretprobe.kp.addr);
99
100 /* nmissed > 0 suggests that maxactive was set too low. */
101 printk(KERN_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_LICENSE("GPL");
108