linux/samples/kprobes/jprobe_example.c
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   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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