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 */
18static struct kprobe kp = {
19	.symbol_name	= "do_fork",
20};
21
22/* kprobe pre_handler: called just before the probed instruction is executed */
23static 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#ifdef CONFIG_MIPS
36	printk(KERN_INFO "pre_handler: p->addr = 0x%p, epc = 0x%lx,"
37			" status = 0x%lx\n",
38		p->addr, regs->cp0_epc, regs->cp0_status);
39#endif
40#ifdef CONFIG_TILEGX
41	printk(KERN_INFO "pre_handler: p->addr = 0x%p, pc = 0x%lx,"
42			" ex1 = 0x%lx\n",
43		p->addr, regs->pc, regs->ex1);
44#endif
45
46	/* A dump_stack() here will give a stack backtrace */
47	return 0;
48}
49
50/* kprobe post_handler: called after the probed instruction is executed */
51static void handler_post(struct kprobe *p, struct pt_regs *regs,
52				unsigned long flags)
53{
54#ifdef CONFIG_X86
55	printk(KERN_INFO "post_handler: p->addr = 0x%p, flags = 0x%lx\n",
56		p->addr, regs->flags);
57#endif
58#ifdef CONFIG_PPC
59	printk(KERN_INFO "post_handler: p->addr = 0x%p, msr = 0x%lx\n",
60		p->addr, regs->msr);
61#endif
62#ifdef CONFIG_MIPS
63	printk(KERN_INFO "post_handler: p->addr = 0x%p, status = 0x%lx\n",
64		p->addr, regs->cp0_status);
65#endif
66#ifdef CONFIG_TILEGX
67	printk(KERN_INFO "post_handler: p->addr = 0x%p, ex1 = 0x%lx\n",
68		p->addr, regs->ex1);
69#endif
70}
71
72/*
73 * fault_handler: this is called if an exception is generated for any
74 * instruction within the pre- or post-handler, or when Kprobes
75 * single-steps the probed instruction.
76 */
77static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
78{
79	printk(KERN_INFO "fault_handler: p->addr = 0x%p, trap #%dn",
80		p->addr, trapnr);
81	/* Return 0 because we don't handle the fault. */
82	return 0;
83}
84
85static int __init kprobe_init(void)
86{
87	int ret;
88	kp.pre_handler = handler_pre;
89	kp.post_handler = handler_post;
90	kp.fault_handler = handler_fault;
91
92	ret = register_kprobe(&kp);
93	if (ret < 0) {
94		printk(KERN_INFO "register_kprobe failed, returned %d\n", ret);
95		return ret;
96	}
97	printk(KERN_INFO "Planted kprobe at %p\n", kp.addr);
98	return 0;
99}
100
101static void __exit kprobe_exit(void)
102{
103	unregister_kprobe(&kp);
104	printk(KERN_INFO "kprobe at %p unregistered\n", kp.addr);
105}
106
107module_init(kprobe_init)
108module_exit(kprobe_exit)
109MODULE_LICENSE("GPL");
110