samples/kprobes/kretprobe_example.c

   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");