linux/samples/kprobes/kretprobe_example.c

// 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/sched.h>

static char func_name[KSYM_NAME_LEN] = …;
module_param_string(…);
MODULE_PARM_DESC(…) …;

/* per-instance private data */
struct my_data { … };

/* Here we use the entry_handler to timestamp function entry */
static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
{ … }
NOKPROBE_SYMBOL(entry_handler);

/*
 * 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)
{ … }
NOKPROBE_SYMBOL(ret_handler);

static struct kretprobe my_kretprobe = …;

static int __init kretprobe_init(void)
{ … }

static void __exit kretprobe_exit(void)
{ … }

module_init(kretprobe_init)
module_exit(kretprobe_exit)
MODULE_DESCRIPTION(…) …;
MODULE_LICENSE(…) …;