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