Root/samples/kprobes/jprobe_example.c

1/*
2 * Here's a sample kernel module showing the use of jprobes to dump
3 * the arguments of do_fork().
4 *
5 * For more information on theory of operation of jprobes, see
6 * Documentation/kprobes.txt
7 *
8 * Build and insert the kernel module as done in the kprobe example.
9 * You will see the trace data in /var/log/messages and on the
10 * console whenever do_fork() is invoked to create a new process.
11 * (Some messages may be suppressed if syslogd is configured to
12 * eliminate duplicate messages.)
13 */
14
15#include <linux/kernel.h>
16#include <linux/module.h>
17#include <linux/kprobes.h>
18
19/*
20 * Jumper probe for do_fork.
21 * Mirror principle enables access to arguments of the probed routine
22 * from the probe handler.
23 */
24
25/* Proxy routine having the same arguments as actual do_fork() routine */
26static long jdo_fork(unsigned long clone_flags, unsigned long stack_start,
27          struct pt_regs *regs, unsigned long stack_size,
28          int __user *parent_tidptr, int __user *child_tidptr)
29{
30    printk(KERN_INFO "jprobe: clone_flags = 0x%lx, stack_size = 0x%lx,"
31            " regs = 0x%p\n",
32           clone_flags, stack_size, regs);
33
34    /* Always end with a call to jprobe_return(). */
35    jprobe_return();
36    return 0;
37}
38
39static struct jprobe my_jprobe = {
40    .entry = jdo_fork,
41    .kp = {
42        .symbol_name = "do_fork",
43    },
44};
45
46static int __init jprobe_init(void)
47{
48    int ret;
49
50    ret = register_jprobe(&my_jprobe);
51    if (ret < 0) {
52        printk(KERN_INFO "register_jprobe failed, returned %d\n", ret);
53        return -1;
54    }
55    printk(KERN_INFO "Planted jprobe at %p, handler addr %p\n",
56           my_jprobe.kp.addr, my_jprobe.entry);
57    return 0;
58}
59
60static void __exit jprobe_exit(void)
61{
62    unregister_jprobe(&my_jprobe);
63    printk(KERN_INFO "jprobe at %p unregistered\n", my_jprobe.kp.addr);
64}
65
66module_init(jprobe_init)
67module_exit(jprobe_exit)
68MODULE_LICENSE("GPL");
69

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