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1// SPDX-License-Identifier: GPL-2.0-only2/*3 * kretprobe_example.c4 *5 * Here's a sample kernel module showing the use of return probes to6 * report the return value and total time taken for probed function7 * to run.8 *9 * usage: insmod kretprobe_example.ko func=<func_name>10 *11 * If no func_name is specified, kernel_clone is instrumented12 *13 * For more information on theory of operation of kretprobes, see14 * Documentation/trace/kprobes.rst15 *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 console18 * whenever the probed function returns. (Some messages may be suppressed19 * 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/sched.h>27 28static char func_name[KSYM_NAME_LEN] = "kernel_clone";29module_param_string(func, func_name, KSYM_NAME_LEN, 0644);30MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the"31 " function's execution time");32 33/* per-instance private data */34struct my_data {35 ktime_t entry_stamp;36};37 38/* Here we use the entry_handler to timestamp function entry */39static 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}50NOKPROBE_SYMBOL(entry_handler);51 52/*53 * Return-probe handler: Log the return value and duration. Duration may turn54 * out to be zero consistently, depending upon the granularity of time55 * accounting on the platform.56 */57static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)58{59 unsigned long retval = regs_return_value(regs);60 struct my_data *data = (struct my_data *)ri->data;61 s64 delta;62 ktime_t now;63 64 now = ktime_get();65 delta = ktime_to_ns(ktime_sub(now, data->entry_stamp));66 pr_info("%s returned %lu and took %lld ns to execute\n",67 func_name, retval, (long long)delta);68 return 0;69}70NOKPROBE_SYMBOL(ret_handler);71 72static struct kretprobe my_kretprobe = {73 .handler = ret_handler,74 .entry_handler = entry_handler,75 .data_size = sizeof(struct my_data),76 /* Probe up to 20 instances concurrently. */77 .maxactive = 20,78};79 80static int __init kretprobe_init(void)81{82 int ret;83 84 my_kretprobe.kp.symbol_name = func_name;85 ret = register_kretprobe(&my_kretprobe);86 if (ret < 0) {87 pr_err("register_kretprobe failed, returned %d\n", ret);88 return ret;89 }90 pr_info("Planted return probe at %s: %p\n",91 my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr);92 return 0;93}94 95static void __exit kretprobe_exit(void)96{97 unregister_kretprobe(&my_kretprobe);98 pr_info("kretprobe at %p unregistered\n", my_kretprobe.kp.addr);99 100 /* nmissed > 0 suggests that maxactive was set too low. */101 pr_info("Missed probing %d instances of %s\n",102 my_kretprobe.nmissed, my_kretprobe.kp.symbol_name);103}104 105module_init(kretprobe_init)106module_exit(kretprobe_exit)107MODULE_DESCRIPTION("sample kernel module showing the use of return probes");108MODULE_LICENSE("GPL");109