// 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] = "kernel_clone";module_param_string(func, func_name, KSYM_NAME_LEN, 0644);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_handler 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;}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){	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;}NOKPROBE_SYMBOL(ret_handler); 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; 	my_kretprobe.kp.symbol_name = func_name;	ret = register_kretprobe(&my_kretprobe);	if (ret < 0) {		pr_err("register_kretprobe failed, returned %d\n", ret);		return ret;	}	pr_info("Planted return probe at %s: %p\n",			my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr);	return 0;} static void __exit kretprobe_exit(void){	unregister_kretprobe(&my_kretprobe);	pr_info("kretprobe at %p unregistered\n", my_kretprobe.kp.addr); 	/* nmissed > 0 suggests that maxactive was set too low. */	pr_info("Missed probing %d instances of %s\n",		my_kretprobe.nmissed, my_kretprobe.kp.symbol_name);} module_init(kretprobe_init)module_exit(kretprobe_exit)MODULE_DESCRIPTION("sample kernel module showing the use of return probes");MODULE_LICENSE("GPL");