LXR linux/samples/kprobes/kretprobe

   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
  27static char func_name[NAME_MAX] = "do_fork";
  28module_param_string(func, func_name, NAME_MAX, S_IRUGO);
  29MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the"
  30                        " function's execution time");
  31
  32/* per-instance private data */
  33struct my_data {
  34        ktime_t entry_stamp;
  35};
  36
  37/* Here we use the entry_hanlder to timestamp function entry */
  38static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
  39{
  40        struct my_data *data;
  41
  42        if (!current->mm)
  43                return 1;       /* Skip kernel threads */
  44
  45        data = (struct my_data *)ri->data;
  46        data->entry_stamp = ktime_get();
  47        return 0;
  48}
  49
  50/*
  51 * Return-probe handler: Log the return value and duration. Duration may turn
  52 * out to be zero consistently, depending upon the granularity of time
  53 * accounting on the platform.
  54 */
  55static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
  56{
  57        int retval = regs_return_value(regs);
  58        struct my_data *data = (struct my_data *)ri->data;
  59        s64 delta;
  60        ktime_t now;
  61
  62        now = ktime_get();
  63        delta = ktime_to_ns(ktime_sub(now, data->entry_stamp));
  64        printk(KERN_INFO "%s returned %d and took %lld ns to execute\n",
  65                        func_name, retval, (long long)delta);
  66        return 0;
  67}
  68
  69static struct kretprobe my_kretprobe = {
  70        .handler                = ret_handler,
  71        .entry_handler          = entry_handler,
  72        .data_size              = sizeof(struct my_data),
  73        /* Probe up to 20 instances concurrently. */
  74        .maxactive              = 20,
  75};
  76
  77static int __init kretprobe_init(void)
  78{
  79        int ret;
  80
  81        my_kretprobe.kp.symbol_name = func_name;
  82        ret = register_kretprobe(&my_kretprobe);
  83        if (ret < 0) {
  84                printk(KERN_INFO "register_kretprobe failed, returned %d\n",
  85                                ret);
  86                return -1;
  87        }
  88        printk(KERN_INFO "Planted return probe at %s: %p\n",
  89                        my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr);
  90        return 0;
  91}
  92
  93static void __exit kretprobe_exit(void)
  94{
  95        unregister_kretprobe(&my_kretprobe);
  96        printk(KERN_INFO "kretprobe at %p unregistered\n",
  97                        my_kretprobe.kp.addr);
  98
  99        /* nmissed > 0 suggests that maxactive was set too low. */
 100        printk(KERN_INFO "Missed probing %d instances of %s\n",
 101                my_kretprobe.nmissed, my_kretprobe.kp.symbol_name);
 102}
 103
 104module_init(kretprobe_init)
 105module_exit(kretprobe_exit)
 106MODULE_LICENSE("GPL");
 107