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
  27 static char func_name[NAME_MAX] = "do_fork";
  28 module_param_string(func, func_name, NAME_MAX, S_IRUGO);
  29 MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the"
  30                         " function's execution time");
  31
  32 /* per-instance private data */
  33 struct my_data {
  34         ktime_t entry_stamp;
  35 };
  36
  37 /* Here we use the entry_hanlder to timestamp function entry */
  38 static 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  */
  55 static 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
  69 static 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
  77 static 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
  93 static 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
 104 module_init(kretprobe_init)
 105 module_exit(kretprobe_exit)
 106 MODULE_LICENSE("GPL");