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/sched.h> 27 28 static char func_name[KSYM_NAME_LEN] = "kernel_clone"; 29 module_param_string(func, func_name, KSYM_NAME_LEN, 0644); 30 MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the" 31 " function's execution time"); 32 33 /* per-instance private data */ 34 struct my_data { 35 ktime_t entry_stamp; 36 }; 37 38 /* Here we use the entry_hanlder to timestamp function entry */ 39 static 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 } 50 NOKPROBE_SYMBOL(entry_handler); 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 NOKPROBE_SYMBOL(ret_handler); 71 72 static 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 80 static 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 95 static 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 } 104 105 module_init(kretprobe_init) 106 module_exit(kretprobe_exit) 107 MODULE_LICENSE("GPL"); 108