samples/kprobes/kprobe_example.c

   1 /*
   2  * NOTE: This example is works on x86 and powerpc.
   3  * Here's a sample kernel module showing the use of kprobes to dump a
   4  * stack trace and selected registers when do_fork() is called.
   5  *
   6  * For more information on theory of operation of kprobes, see
   7  * Documentation/kprobes.txt
   8  *
   9  * You will see the trace data in /var/log/messages and on the console
  10  * whenever do_fork() is invoked to create a new process.
  11  */
  12
  13 #include <linux/kernel.h>
  14 #include <linux/module.h>
  15 #include <linux/kprobes.h>
  16
  17 /* For each probe you need to allocate a kprobe structure */
  18 static struct kprobe kp = {
  19         .symbol_name    = "do_fork",
  20 };
  21
  22 /* kprobe pre_handler: called just before the probed instruction is executed */
  23 static int handler_pre(struct kprobe *p, struct pt_regs *regs)
  24 {
  25 #ifdef CONFIG_X86
  26         printk(KERN_INFO "pre_handler: p->addr = 0x%p, ip = %lx,"
  27                         " flags = 0x%lx\n",
  28                 p->addr, regs->ip, regs->flags);
  29 #endif
  30 #ifdef CONFIG_PPC
  31         printk(KERN_INFO "pre_handler: p->addr = 0x%p, nip = 0x%lx,"
  32                         " msr = 0x%lx\n",
  33                 p->addr, regs->nip, regs->msr);
  34 #endif
  35
  36         /* A dump_stack() here will give a stack backtrace */
  37         return 0;
  38 }
  39
  40 /* kprobe post_handler: called after the probed instruction is executed */
  41 static void handler_post(struct kprobe *p, struct pt_regs *regs,
  42                                 unsigned long flags)
  43 {
  44 #ifdef CONFIG_X86
  45         printk(KERN_INFO "post_handler: p->addr = 0x%p, flags = 0x%lx\n",
  46                 p->addr, regs->flags);
  47 #endif
  48 #ifdef CONFIG_PPC
  49         printk(KERN_INFO "post_handler: p->addr = 0x%p, msr = 0x%lx\n",
  50                 p->addr, regs->msr);
  51 #endif
  52 }
  53
  54 /*
  55  * fault_handler: this is called if an exception is generated for any
  56  * instruction within the pre- or post-handler, or when Kprobes
  57  * single-steps the probed instruction.
  58  */
  59 static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
  60 {
  61         printk(KERN_INFO "fault_handler: p->addr = 0x%p, trap #%dn",
  62                 p->addr, trapnr);
  63         /* Return 0 because we don't handle the fault. */
  64         return 0;
  65 }
  66
  67 static int __init kprobe_init(void)
  68 {
  69         int ret;
  70         kp.pre_handler = handler_pre;
  71         kp.post_handler = handler_post;
  72         kp.fault_handler = handler_fault;
  73
  74         ret = register_kprobe(&kp);
  75         if (ret < 0) {
  76                 printk(KERN_INFO "register_kprobe failed, returned %d\n", ret);
  77                 return ret;
  78         }
  79         printk(KERN_INFO "Planted kprobe at %p\n", kp.addr);
  80         return 0;
  81 }
  82
  83 static void __exit kprobe_exit(void)
  84 {
  85         unregister_kprobe(&kp);
  86         printk(KERN_INFO "kprobe at %p unregistered\n", kp.addr);
  87 }
  88
  89 module_init(kprobe_init)
  90 module_exit(kprobe_exit)
  91 MODULE_LICENSE("GPL");