blob: 5dc1bf3baa98b3a1598c8b957af0fef27b74017f [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0-only
* kretprobe_example.c
* Here's a sample kernel module showing the use of return probes to
* report the return value and total time taken for probed function
* to run.
* usage: insmod kretprobe_example.ko func=<func_name>
* If no func_name is specified, kernel_clone is instrumented
* For more information on theory of operation of kretprobes, see
* Documentation/trace/kprobes.rst
* Build and insert the kernel module as done in the kprobe example.
* You will see the trace data in /var/log/messages and on the console
* whenever the probed function returns. (Some messages may be suppressed
* if syslogd is configured to eliminate duplicate messages.)
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/kprobes.h>
#include <linux/ktime.h>
#include <linux/limits.h>
#include <linux/sched.h>
static char func_name[NAME_MAX] = "kernel_clone";
module_param_string(func, func_name, NAME_MAX, S_IRUGO);
MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the"
" function's execution time");
/* per-instance private data */
struct my_data {
ktime_t entry_stamp;
/* Here we use the entry_hanlder to timestamp function entry */
static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
struct my_data *data;
if (!current->mm)
return 1; /* Skip kernel threads */
data = (struct my_data *)ri->data;
data->entry_stamp = ktime_get();
return 0;
* Return-probe handler: Log the return value and duration. Duration may turn
* out to be zero consistently, depending upon the granularity of time
* accounting on the platform.
static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
unsigned long retval = regs_return_value(regs);
struct my_data *data = (struct my_data *)ri->data;
s64 delta;
ktime_t now;
now = ktime_get();
delta = ktime_to_ns(ktime_sub(now, data->entry_stamp));
pr_info("%s returned %lu and took %lld ns to execute\n",
func_name, retval, (long long)delta);
return 0;
static struct kretprobe my_kretprobe = {
.handler = ret_handler,
.entry_handler = entry_handler,
.data_size = sizeof(struct my_data),
/* Probe up to 20 instances concurrently. */
.maxactive = 20,
static int __init kretprobe_init(void)
int ret; = func_name;
ret = register_kretprobe(&my_kretprobe);
if (ret < 0) {
pr_err("register_kretprobe failed, returned %d\n", ret);
return -1;
pr_info("Planted return probe at %s: %p\n",,;
return 0;
static void __exit kretprobe_exit(void)
pr_info("kretprobe at %p unregistered\n",;
/* nmissed > 0 suggests that maxactive was set too low. */
pr_info("Missed probing %d instances of %s\n",