linux/samples/kprobes/kretprobe_example.c
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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
  28static char func_name[NAME_MAX] = "do_fork";
  29module_param_string(func, func_name, NAME_MAX, S_IRUGO);
  30MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the"
  31                        " function's execution time");
  32
  33/* per-instance private data */
  34struct my_data {
  35        ktime_t entry_stamp;
  36};
  37
  38/* Here we use the entry_hanlder to timestamp function entry */
  39static 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 */
  56static 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
  70static 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
  78static 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
  94static 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
 105module_init(kretprobe_init)
 106module_exit(kretprobe_exit)
 107MODULE_LICENSE("GPL");
 108
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