cregit-Linux how code gets into the kernel

Release 4.10 samples/kprobes/kretprobe_example.c

Directory: samples/kprobes
 * kretprobe_example.c
 * Here's a sample kernel module showing the use of return probes to
 * report the return value and total time taken for probed function
 * to run.
 * usage: insmod kretprobe_example.ko func=<func_name>
 * If no func_name is specified, _do_fork is instrumented
 * For more information on theory of operation of kretprobes, see
 * Documentation/kprobes.txt
 * Build and insert the kernel module as done in the kprobe example.
 * You will see the trace data in /var/log/messages and on the console
 * whenever the probed function returns. (Some messages may be suppressed
 * if syslogd is configured to eliminate duplicate messages.)

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/kprobes.h>
#include <linux/ktime.h>
#include <linux/limits.h>
#include <linux/sched.h>

static char func_name[NAME_MAX] = "_do_fork";
module_param_string(func, func_name, NAME_MAX, S_IRUGO);
MODULE_PARM_DESC(func, "Function to kretprobe; this module will report the"
			" function's execution time");

/* per-instance private data */

struct my_data {
ktime_t entry_stamp;

/* Here we use the entry_hanlder to timestamp function entry */

static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs) { struct my_data *data; if (!current->mm) return 1; /* Skip kernel threads */ data = (struct my_data *)ri->data; data->entry_stamp = ktime_get(); return 0; }


ananth n. mavinakayanahalliananth n. mavinakayanahalli53100.00%1100.00%

/* * Return-probe handler: Log the return value and duration. Duration may turn * out to be zero consistently, depending upon the granularity of time * accounting on the platform. */
static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs) { unsigned long retval = regs_return_value(regs); struct my_data *data = (struct my_data *)ri->data; s64 delta; ktime_t now; now = ktime_get(); delta = ktime_to_ns(ktime_sub(now, data->entry_stamp)); pr_info("%s returned %lu and took %lld ns to execute\n", func_name, retval, (long long)delta); return 0; }


ananth n. mavinakayanahalliananth n. mavinakayanahalli7895.12%133.33%
huang shijiehuang shijie44.88%266.67%

static struct kretprobe my_kretprobe = { .handler = ret_handler, .entry_handler = entry_handler, .data_size = sizeof(struct my_data), /* Probe up to 20 instances concurrently. */ .maxactive = 20, };
static int __init kretprobe_init(void) { int ret; = func_name; ret = register_kretprobe(&my_kretprobe); if (ret < 0) { pr_err("register_kretprobe failed, returned %d\n", ret); return -1; } pr_info("Planted return probe at %s: %p\n",,; return 0; }


ananth n. mavinakayanahalliananth n. mavinakayanahalli6597.01%150.00%
huang shijiehuang shijie22.99%150.00%

static void __exit kretprobe_exit(void) { unregister_kretprobe(&my_kretprobe); pr_info("kretprobe at %p unregistered\n",; /* nmissed > 0 suggests that maxactive was set too low. */ pr_info("Missed probing %d instances of %s\n", my_kretprobe.nmissed,; }


ananth n. mavinakayanahalliananth n. mavinakayanahalli4095.24%150.00%
huang shijiehuang shijie24.76%150.00%

module_init(kretprobe_init) module_exit(kretprobe_exit) MODULE_LICENSE("GPL");

Overall Contributors

ananth n. mavinakayanahalliananth n. mavinakayanahalli33496.25%120.00%
huang shijiehuang shijie82.31%240.00%
alexey dobriyanalexey dobriyan30.86%120.00%
petr mladekpetr mladek20.58%120.00%
Directory: samples/kprobes
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