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

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