Ananth N Mavinakayanahalli | 804defe | 2008-03-04 14:28:38 -0800 | [diff] [blame] | 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 | * |
Petr Mladek | 54aea45 | 2015-10-01 15:37:11 -0700 | [diff] [blame^] | 10 | * If no func_name is specified, _do_fork is instrumented |
Ananth N Mavinakayanahalli | 804defe | 2008-03-04 14:28:38 -0800 | [diff] [blame] | 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> |
Alexey Dobriyan | 8abf919 | 2009-08-13 10:05:43 +0000 | [diff] [blame] | 26 | #include <linux/sched.h> |
Ananth N Mavinakayanahalli | 804defe | 2008-03-04 14:28:38 -0800 | [diff] [blame] | 27 | |
Petr Mladek | 54aea45 | 2015-10-01 15:37:11 -0700 | [diff] [blame^] | 28 | static char func_name[NAME_MAX] = "_do_fork"; |
Ananth N Mavinakayanahalli | 804defe | 2008-03-04 14:28:38 -0800 | [diff] [blame] | 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 | int 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 | printk(KERN_INFO "%s returned %d 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 | printk(KERN_INFO "register_kretprobe failed, returned %d\n", |
| 86 | ret); |
| 87 | return -1; |
| 88 | } |
| 89 | printk(KERN_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 | printk(KERN_INFO "kretprobe at %p unregistered\n", |
| 98 | my_kretprobe.kp.addr); |
| 99 | |
| 100 | /* nmissed > 0 suggests that maxactive was set too low. */ |
| 101 | printk(KERN_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"); |