projects / deliverable / linux.git / blame
| Commit | Line | Data |
|---|---|---|
| 804defea AM |
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 | ||
| 27 | static char func_name[NAME_MAX] = "do_fork"; | |
| 28 | module_param_string(func, func_name, NAME_MAX, S_IRUGO); | |
| 29 | MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the" | |
| 30 | " function's execution time"); | |
| 31 | ||
| 32 | /* per-instance private data */ | |
| 33 | struct my_data { | |
| 34 | ktime_t entry_stamp; | |
| 35 | }; | |
| 36 | ||
| 37 | /* Here we use the entry_hanlder to timestamp function entry */ | |
| 38 | static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs) | |
| 39 | { | |
| 40 | struct my_data *data; | |
| 41 | ||
| 42 | if (!current->mm) | |
| 43 | return 1; /* Skip kernel threads */ | |
| 44 | ||
| 45 | data = (struct my_data *)ri->data; | |
| 46 | data->entry_stamp = ktime_get(); | |
| 47 | return 0; | |
| 48 | } | |
| 49 | ||
| 50 | /* | |
| 51 | * Return-probe handler: Log the return value and duration. Duration may turn | |
| 52 | * out to be zero consistently, depending upon the granularity of time | |
| 53 | * accounting on the platform. | |
| 54 | */ | |
| 55 | static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs) | |
| 56 | { | |
| 57 | int retval = regs_return_value(regs); | |
| 58 | struct my_data *data = (struct my_data *)ri->data; | |
| 59 | s64 delta; | |
| 60 | ktime_t now; | |
| 61 | ||
| 62 | now = ktime_get(); | |
| 63 | delta = ktime_to_ns(ktime_sub(now, data->entry_stamp)); | |
| 64 | printk(KERN_INFO "%s returned %d and took %lld ns to execute\n", | |
| 65 | func_name, retval, (long long)delta); | |
| 66 | return 0; | |
| 67 | } | |
| 68 | ||
| 69 | static struct kretprobe my_kretprobe = { | |
| 70 | .handler = ret_handler, | |
| 71 | .entry_handler = entry_handler, | |
| 72 | .data_size = sizeof(struct my_data), | |
| 73 | /* Probe up to 20 instances concurrently. */ | |
| 74 | .maxactive = 20, | |
| 75 | }; | |
| 76 | ||
| 77 | static int __init kretprobe_init(void) | |
| 78 | { | |
| 79 | int ret; | |
| 80 | ||
| 81 | my_kretprobe.kp.symbol_name = func_name; | |
| 82 | ret = register_kretprobe(&my_kretprobe); | |
| 83 | if (ret < 0) { | |
| 84 | printk(KERN_INFO "register_kretprobe failed, returned %d\n", | |
| 85 | ret); | |
| 86 | return -1; | |
| 87 | } | |
| 88 | printk(KERN_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 | printk(KERN_INFO "kretprobe at %p unregistered\n", | |
| 97 | my_kretprobe.kp.addr); | |
| 98 | ||
| 99 | /* nmissed > 0 suggests that maxactive was set too low. */ | |
| 100 | printk(KERN_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"); |