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804defea AM |
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 | * | |
54aea454 | 10 | * If no func_name is specified, _do_fork is instrumented |
804defea AM |
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> | |
8abf9196 | 26 | #include <linux/sched.h> |
804defea | 27 | |
54aea454 | 28 | static char func_name[NAME_MAX] = "_do_fork"; |
804defea AM |
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 */ | |
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 | */ | |
56 | static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs) | |
57 | { | |
57c24b21 | 58 | unsigned long retval = regs_return_value(regs); |
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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)); | |
57c24b21 | 65 | pr_info("%s returned %lu and took %lld ns to execute\n", |
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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 | ||
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) { | |
61341314 | 85 | pr_err("register_kretprobe failed, returned %d\n", ret); |
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86 | return -1; |
87 | } | |
61341314 | 88 | pr_info("Planted return probe at %s: %p\n", |
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89 | my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr); |
90 | return 0; | |
91 | } | |
92 | ||
93 | static void __exit kretprobe_exit(void) | |
94 | { | |
95 | unregister_kretprobe(&my_kretprobe); | |
61341314 | 96 | pr_info("kretprobe at %p unregistered\n", my_kretprobe.kp.addr); |
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97 | |
98 | /* nmissed > 0 suggests that maxactive was set too low. */ | |
61341314 | 99 | pr_info("Missed probing %d instances of %s\n", |
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100 | my_kretprobe.nmissed, my_kretprobe.kp.symbol_name); |
101 | } | |
102 | ||
103 | module_init(kretprobe_init) | |
104 | module_exit(kretprobe_exit) | |
105 | MODULE_LICENSE("GPL"); |