LXR linux/samples/kprobes/kretprobe

   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * kretprobe_example.c
   4 *
   5 * Here's a sample kernel module showing the use of return probes to
   6 * report the return value and total time taken for probed function
   7 * to run.
   8 *
   9 * usage: insmod kretprobe_example.ko func=<func_name>
  10 *
  11 * If no func_name is specified, kernel_clone is instrumented
  12 *
  13 * For more information on theory of operation of kretprobes, see
  14 * Documentation/trace/kprobes.rst
  15 *
  16 * Build and insert the kernel module as done in the kprobe example.
  17 * You will see the trace data in /var/log/messages and on the console
  18 * whenever the probed function returns. (Some messages may be suppressed
  19 * if syslogd is configured to eliminate duplicate messages.)
  20 */
  21
  22#include <linux/kernel.h>
  23#include <linux/module.h>
  24#include <linux/kprobes.h>
  25#include <linux/ktime.h>
  26#include <linux/limits.h>
  27#include <linux/sched.h>
  28
  29static char func_name[NAME_MAX] = "kernel_clone";
  30module_param_string(func, func_name, NAME_MAX, S_IRUGO);
  31MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the"
  32                        " function's execution time");
  33
  34/* per-instance private data */
  35struct my_data {
  36        ktime_t entry_stamp;
  37};
  38
  39/* Here we use the entry_hanlder to timestamp function entry */
  40static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
  41{
  42        struct my_data *data;
  43
  44        if (!current->mm)
  45                return 1;       /* Skip kernel threads */
  46
  47        data = (struct my_data *)ri->data;
  48        data->entry_stamp = ktime_get();
  49        return 0;
  50}
  51NOKPROBE_SYMBOL(entry_handler);
  52
  53/*
  54 * Return-probe handler: Log the return value and duration. Duration may turn
  55 * out to be zero consistently, depending upon the granularity of time
  56 * accounting on the platform.
  57 */
  58static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
  59{
  60        unsigned long retval = regs_return_value(regs);
  61        struct my_data *data = (struct my_data *)ri->data;
  62        s64 delta;
  63        ktime_t now;
  64
  65        now = ktime_get();
  66        delta = ktime_to_ns(ktime_sub(now, data->entry_stamp));
  67        pr_info("%s returned %lu and took %lld ns to execute\n",
  68                        func_name, retval, (long long)delta);
  69        return 0;
  70}
  71NOKPROBE_SYMBOL(ret_handler);
  72
  73static struct kretprobe my_kretprobe = {
  74        .handler                = ret_handler,
  75        .entry_handler          = entry_handler,
  76        .data_size              = sizeof(struct my_data),
  77        /* Probe up to 20 instances concurrently. */
  78        .maxactive              = 20,
  79};
  80
  81static int __init kretprobe_init(void)
  82{
  83        int ret;
  84
  85        my_kretprobe.kp.symbol_name = func_name;
  86        ret = register_kretprobe(&my_kretprobe);
  87        if (ret < 0) {
  88                pr_err("register_kretprobe failed, returned %d\n", ret);
  89                return -1;
  90        }
  91        pr_info("Planted return probe at %s: %p\n",
  92                        my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr);
  93        return 0;
  94}
  95
  96static void __exit kretprobe_exit(void)
  97{
  98        unregister_kretprobe(&my_kretprobe);
  99        pr_info("kretprobe at %p unregistered\n", my_kretprobe.kp.addr);
 100
 101        /* nmissed > 0 suggests that maxactive was set too low. */
 102        pr_info("Missed probing %d instances of %s\n",
 103                my_kretprobe.nmissed, my_kretprobe.kp.symbol_name);
 104}
 105
 106module_init(kretprobe_init)
 107module_exit(kretprobe_exit)
 108MODULE_LICENSE("GPL");
 109