/*
   * NOTE: This example is works on x86 and powerpc.
   * Here's a sample kernel module showing the use of kprobes to dump a
   * stack trace and selected registers when do_fork() is called.
   *
   * For more information on theory of operation of kprobes, see
   * Documentation/kprobes.txt
   *
   * You will see the trace data in /var/log/messages and on the console
   * whenever do_fork() is invoked to create a new process.
   */
  
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/kprobes.h>
  
  /* For each probe you need to allocate a kprobe structure */
  static struct kprobe kp = {
  	.symbol_name	= "do_fork",
  };
  
  /* kprobe pre_handler: called just before the probed instruction is executed */
  static int handler_pre(struct kprobe *p, struct pt_regs *regs)
  {
  #ifdef CONFIG_X86
  	printk(KERN_INFO "pre_handler: p->addr = 0x%p, ip = %lx,"
  			" flags = 0x%lx
  ",
  		p->addr, regs->ip, regs->flags);
  #endif
  #ifdef CONFIG_PPC
  	printk(KERN_INFO "pre_handler: p->addr = 0x%p, nip = 0x%lx,"
  			" msr = 0x%lx
  ",
  		p->addr, regs->nip, regs->msr);
  #endif
  #ifdef CONFIG_MIPS
  	printk(KERN_INFO "pre_handler: p->addr = 0x%p, epc = 0x%lx,"
  			" status = 0x%lx
  ",
  		p->addr, regs->cp0_epc, regs->cp0_status);
  #endif
  #ifdef CONFIG_TILEGX
  	printk(KERN_INFO "pre_handler: p->addr = 0x%p, pc = 0x%lx,"
  			" ex1 = 0x%lx
  ",
  		p->addr, regs->pc, regs->ex1);
  #endif
  
  	/* A dump_stack() here will give a stack backtrace */
  	return 0;
  }
  
  /* kprobe post_handler: called after the probed instruction is executed */
  static void handler_post(struct kprobe *p, struct pt_regs *regs,
  				unsigned long flags)
  {
  #ifdef CONFIG_X86
  	printk(KERN_INFO "post_handler: p->addr = 0x%p, flags = 0x%lx
  ",
  		p->addr, regs->flags);
  #endif
  #ifdef CONFIG_PPC
  	printk(KERN_INFO "post_handler: p->addr = 0x%p, msr = 0x%lx
  ",
  		p->addr, regs->msr);
  #endif
  #ifdef CONFIG_MIPS
  	printk(KERN_INFO "post_handler: p->addr = 0x%p, status = 0x%lx
  ",
  		p->addr, regs->cp0_status);
  #endif
  #ifdef CONFIG_TILEGX
  	printk(KERN_INFO "post_handler: p->addr = 0x%p, ex1 = 0x%lx
  ",
  		p->addr, regs->ex1);
  #endif
  }
  
  /*
   * fault_handler: this is called if an exception is generated for any
   * instruction within the pre- or post-handler, or when Kprobes
   * single-steps the probed instruction.
   */
  static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
  {
  	printk(KERN_INFO "fault_handler: p->addr = 0x%p, trap #%dn",
  		p->addr, trapnr);
  	/* Return 0 because we don't handle the fault. */
  	return 0;
  }
  
  static int __init kprobe_init(void)
  {
  	int ret;
  	kp.pre_handler = handler_pre;
  	kp.post_handler = handler_post;
  	kp.fault_handler = handler_fault;
  
  	ret = register_kprobe(&kp);
  	if (ret < 0) {
  		printk(KERN_INFO "register_kprobe failed, returned %d
  ", ret);
  		return ret;
  	}
  	printk(KERN_INFO "Planted kprobe at %p
  ", kp.addr);
  	return 0;
  }
  
  static void __exit kprobe_exit(void)
  {
  	unregister_kprobe(&kp);
  	printk(KERN_INFO "kprobe at %p unregistered
  ", kp.addr);
  }
  
  module_init(kprobe_init)
  module_exit(kprobe_exit)
  MODULE_LICENSE("GPL");