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, kernel_clone is instrumented 12 * 13 * For more information on theory of operation of kretprobes, see 14 * Documentation/trace/kprobes.rst 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] = "kernel_clone"; 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 NOKPROBE_SYMBOL(entry_handler); 52 53 /* 54 * Return-probe handler: Log the return value and duration. Duration may turn 55 * out to be zero consistently, depending upon the granularity of time 56 * accounting on the platform. 57 */ 58 static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs) 59 { 60 unsigned long retval = regs_return_value(regs); 61 struct my_data *data = (struct my_data *)ri->data; 62 s64 delta; 63 ktime_t now; 64 65 now = ktime_get(); 66 delta = ktime_to_ns(ktime_sub(now, data->entry_stamp)); 67 pr_info("%s returned %lu and took %lld ns to execute\n", 68 func_name, retval, (long long)delta); 69 return 0; 70 } 71 NOKPROBE_SYMBOL(ret_handler); 72 73 static struct kretprobe my_kretprobe = { 74 .handler = ret_handler, 75 .entry_handler = entry_handler, 76 .data_size = sizeof(struct my_data), 77 /* Probe up to 20 instances concurrently. */ 78 .maxactive = 20, 79 }; 80 81 static int __init kretprobe_init(void) 82 { 83 int ret; 84 85 my_kretprobe.kp.symbol_name = func_name; 86 ret = register_kretprobe(&my_kretprobe); 87 if (ret < 0) { 88 pr_err("register_kretprobe failed, returned %d\n", ret); 89 return -1; 90 } 91 pr_info("Planted return probe at %s: %p\n", 92 my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr); 93 return 0; 94 } 95 96 static void __exit kretprobe_exit(void) 97 { 98 unregister_kretprobe(&my_kretprobe); 99 pr_info("kretprobe at %p unregistered\n", my_kretprobe.kp.addr); 100 101 /* nmissed > 0 suggests that maxactive was set too low. */ 102 pr_info("Missed probing %d instances of %s\n", 103 my_kretprobe.nmissed, my_kretprobe.kp.symbol_name); 104 } 105 106 module_init(kretprobe_init) 107 module_exit(kretprobe_exit) 108 MODULE_LICENSE("GPL"); 109