1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * kretprobe_example.c 4 * 5 * Here's a sample kernel module showing the use of return probes to 6 * report the return value and total time taken for probed function 7 * to run. 8 * 9 * usage: insmod kretprobe_example.ko func=<func_name> 10 * 11 * If no func_name is specified, _do_fork is instrumented 12 * 13 * For more information on theory of operation of kretprobes, see 14 * Documentation/kprobes.txt 15 * 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 console 18 * whenever the probed function returns. (Some messages may be suppressed 19 * 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/limits.h> 27 #include <linux/sched.h> 28 29 static char func_name[NAME_MAX] = "_do_fork"; 30 module_param_string(func, func_name, NAME_MAX, S_IRUGO); 31 MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the" 32 " function's execution time"); 33 34 /* per-instance private data */ 35 struct my_data { 36 ktime_t entry_stamp; 37 }; 38 39 /* Here we use the entry_hanlder to timestamp function entry */ 40 static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs) 41 { 42 struct my_data *data; 43 44 if (!current->mm) 45 return 1; /* Skip kernel threads */ 46 47 data = (struct my_data *)ri->data; 48 data->entry_stamp = ktime_get(); 49 return 0; 50 } 51 52 /* 53 * Return-probe handler: Log the return value and duration. Duration may turn 54 * out to be zero consistently, depending upon the granularity of time 55 * accounting on the platform. 56 */ 57 static 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 } 70 71 static struct kretprobe my_kretprobe = { 72 .handler = ret_handler, 73 .entry_handler = entry_handler, 74 .data_size = sizeof(struct my_data), 75 /* Probe up to 20 instances concurrently. */ 76 .maxactive = 20, 77 }; 78 79 static int __init kretprobe_init(void) 80 { 81 int ret; 82 83 my_kretprobe.kp.symbol_name = func_name; 84 ret = register_kretprobe(&my_kretprobe); 85 if (ret < 0) { 86 pr_err("register_kretprobe failed, returned %d\n", ret); 87 return -1; 88 } 89 pr_info("Planted return probe at %s: %p\n", 90 my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr); 91 return 0; 92 } 93 94 static void __exit kretprobe_exit(void) 95 { 96 unregister_kretprobe(&my_kretprobe); 97 pr_info("kretprobe at %p unregistered\n", my_kretprobe.kp.addr); 98 99 /* nmissed > 0 suggests that maxactive was set too low. */ 100 pr_info("Missed probing %d instances of %s\n", 101 my_kretprobe.nmissed, my_kretprobe.kp.symbol_name); 102 } 103 104 module_init(kretprobe_init) 105 module_exit(kretprobe_exit) 106 MODULE_LICENSE("GPL"); 107