1 /* 2 * kretprobe_example.c 3 * 4 * Here's a sample kernel module showing the use of return probes to 5 * report the return value and total time taken for probed function 6 * to run. 7 * 8 * usage: insmod kretprobe_example.ko func=<func_name> 9 * 10 * If no func_name is specified, _do_fork is instrumented 11 * 12 * For more information on theory of operation of kretprobes, see 13 * Documentation/kprobes.txt 14 * 15 * Build and insert the kernel module as done in the kprobe example. 16 * You will see the trace data in /var/log/messages and on the console 17 * whenever the probed function returns. (Some messages may be suppressed 18 * if syslogd is configured to eliminate duplicate messages.) 19 */ 20 21 #include <linux/kernel.h> 22 #include <linux/module.h> 23 #include <linux/kprobes.h> 24 #include <linux/ktime.h> 25 #include <linux/limits.h> 26 #include <linux/sched.h> 27 28 static char func_name[NAME_MAX] = "_do_fork"; 29 module_param_string(func, func_name, NAME_MAX, S_IRUGO); 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 51 /* 52 * Return-probe handler: Log the return value and duration. Duration may turn 53 * out to be zero consistently, depending upon the granularity of time 54 * accounting on the platform. 55 */ 56 static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs) 57 { 58 unsigned long retval = regs_return_value(regs); 59 struct my_data *data = (struct my_data *)ri->data; 60 s64 delta; 61 ktime_t now; 62 63 now = ktime_get(); 64 delta = ktime_to_ns(ktime_sub(now, data->entry_stamp)); 65 pr_info("%s returned %lu and took %lld ns to execute\n", 66 func_name, retval, (long long)delta); 67 return 0; 68 } 69 70 static struct kretprobe my_kretprobe = { 71 .handler = ret_handler, 72 .entry_handler = entry_handler, 73 .data_size = sizeof(struct my_data), 74 /* Probe up to 20 instances concurrently. */ 75 .maxactive = 20, 76 }; 77 78 static int __init kretprobe_init(void) 79 { 80 int ret; 81 82 my_kretprobe.kp.symbol_name = func_name; 83 ret = register_kretprobe(&my_kretprobe); 84 if (ret < 0) { 85 pr_err("register_kretprobe failed, returned %d\n", ret); 86 return -1; 87 } 88 pr_info("Planted return probe at %s: %p\n", 89 my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr); 90 return 0; 91 } 92 93 static void __exit kretprobe_exit(void) 94 { 95 unregister_kretprobe(&my_kretprobe); 96 pr_info("kretprobe at %p unregistered\n", my_kretprobe.kp.addr); 97 98 /* nmissed > 0 suggests that maxactive was set too low. */ 99 pr_info("Missed probing %d instances of %s\n", 100 my_kretprobe.nmissed, my_kretprobe.kp.symbol_name); 101 } 102 103 module_init(kretprobe_init) 104 module_exit(kretprobe_exit) 105 MODULE_LICENSE("GPL"); 106