/*
 * NOTE: This example is designed to check that the kprobe reentry work.
 *
 * For more information on theory of operation of kprobes, see
 * Documentation/kprobes.txt
 *
 */

#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",
};

static struct kprobe kp_re = {
	.symbol_name	= "int_sqrt",
};

static unsigned long y=0;
static unsigned long z=0;

/* kprobe pre_handler: called just before the probed instruction is executed */
static int handler_pre(struct kprobe *p, struct pt_regs *regs)
{
  /* call another function that is instrumented with a kprobe to
     ensure that reentry works */
  unsigned long x=1764;
  y = int_sqrt(x);
  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)
{
  return;
}

/* kprobe pre_handler: called just before the probed instruction is executed */
static int handler_pre_re(struct kprobe *p, struct pt_regs *regs)
{
  /* if reentry is working as expected this code may not be executed */
  z = 0xdeadbeef;
  return 0;
}

/* kprobe post_handler: called after the probed instruction is executed */
static void handler_post_re(struct kprobe *p, struct pt_regs *regs,
				unsigned long flags)
{
  return;
}

/*
 * 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\n", ret);
		return ret;
	}
	printk(KERN_INFO "Planted kprobe at %p\n", kp.addr);

	kp_re.pre_handler = handler_pre_re;
	kp_re.post_handler = handler_post_re;
	kp_re.fault_handler = handler_fault;

	ret = register_kprobe(&kp_re);
	if (ret < 0) {
		printk(KERN_INFO "register_kprobe failed, returned %d\n", ret);
		return ret;
	}
	printk(KERN_INFO "Planted kprobe at %p\n", kp_re.addr);
	return 0;
}

static void __exit kprobe_exit(void)
{
	unregister_kprobe(&kp);
	printk(KERN_INFO "kprobe at %p unregistered\n", kp.addr);
	unregister_kprobe(&kp_re);
	printk(KERN_INFO "kprobe at %p unregistered\n", kp_re.addr);
	printk(KERN_INFO "y = %ld\n", y);
	printk(KERN_INFO "z = %lx\n", z);
}

module_init(kprobe_init)
module_exit(kprobe_exit)
MODULE_LICENSE("GPL");