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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 */ |
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 | { |
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 | |
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 | |
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 |
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