kprobe_example.c

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/*
 * 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\n",
        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\n",
        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\n",
        p->addr, regs->cp0_epc, regs->cp0_status);
#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\n",
        p->addr, regs->flags);
#endif
#ifdef CONFIG_PPC
    printk(KERN_INFO "post_handler: p->addr = 0x%p, msr = 0x%lx\n",
        p->addr, regs->msr);
#endif
#ifdef CONFIG_MIPS
    printk(KERN_INFO "post_handler: p->addr = 0x%p, status = 0x%lx\n",
        p->addr, regs->cp0_status);
#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\n", ret);
        return ret;
    }
    printk(KERN_INFO "Planted kprobe at %p\n", kp.addr);
    return 0;
}

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

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