cregit-Linux how code gets into the kernel

Release 4.7 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; }

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ananth n. mavinakayanahalliananth n. mavinakayanahalli53100.00%1100.00%
Total53100.00%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) { int 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)); printk(KERN_INFO "%s returned %d and took %lld ns to execute\n", func_name, retval, (long long)delta); return 0; }

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ananth n. mavinakayanahalliananth n. mavinakayanahalli82100.00%1100.00%
Total82100.00%1100.00%

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; my_kretprobe.kp.symbol_name = func_name; ret = register_kretprobe(&my_kretprobe); if (ret < 0) { printk(KERN_INFO "register_kretprobe failed, returned %d\n", ret); return -1; } printk(KERN_INFO "Planted return probe at %s: %p\n", my_kretprobe.kp.symbol_name, my_kretprobe.kp.addr); return 0; }

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ananth n. mavinakayanahalliananth n. mavinakayanahalli69100.00%1100.00%
Total69100.00%1100.00%


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

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ananth n. mavinakayanahalliananth n. mavinakayanahalli44100.00%1100.00%
Total44100.00%1100.00%

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

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ananth n. mavinakayanahalliananth n. mavinakayanahalli34698.58%133.33%
alexey dobriyanalexey dobriyan30.85%133.33%
petr mladekpetr mladek20.57%133.33%
Total351100.00%3100.00%
Directory: samples/kprobes
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