Merge master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6

[linux/fpc-iii.git] / kernel / kprobes.c

/*
 *  Kernel Probes (KProbes)
 *  kernel/kprobes.c
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright (C) IBM Corporation, 2002, 2004
 *
 * 2002-Oct     Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
 *              Probes initial implementation (includes suggestions from
 *              Rusty Russell).
 * 2004-Aug     Updated by Prasanna S Panchamukhi <prasanna@in.ibm.com> with
 *              hlists and exceptions notifier as suggested by Andi Kleen.
 * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
 *              interface to access function arguments.
 * 2004-Sep     Prasanna S Panchamukhi <prasanna@in.ibm.com> Changed Kprobes
 *              exceptions notifier to be first on the priority list.
 * 2005-May     Hien Nguyen <hien@us.ibm.com>, Jim Keniston
 *              <jkenisto@us.ibm.com> and Prasanna S Panchamukhi
 *              <prasanna@in.ibm.com> added function-return probes.
 */
#include <linux/kprobes.h>
#include <linux/hash.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/moduleloader.h>
#include <linux/kallsyms.h>
#include <linux/freezer.h>
#include <asm-generic/sections.h>
#include <asm/cacheflush.h>
#include <asm/errno.h>
#include <asm/kdebug.h>

#define KPROBE_HASH_BITS 6
#define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS)


/*
 * Some oddball architectures like 64bit powerpc have function descriptors
 * so this must be overridable.
 */
#ifndef kprobe_lookup_name
#define kprobe_lookup_name(name, addr) \
        addr = ((kprobe_opcode_t *)(kallsyms_lookup_name(name)))
#endif

static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];
static atomic_t kprobe_count;

DEFINE_MUTEX(kprobe_mutex);             /* Protects kprobe_table */
DEFINE_SPINLOCK(kretprobe_lock);        /* Protects kretprobe_inst_table */
static DEFINE_PER_CPU(struct kprobe *, kprobe_instance) = NULL;

static struct notifier_block kprobe_page_fault_nb = {
        .notifier_call = kprobe_exceptions_notify,
        .priority = 0x7fffffff /* we need to notified first */
};

#ifdef __ARCH_WANT_KPROBES_INSN_SLOT
/*
 * kprobe->ainsn.insn points to the copy of the instruction to be
 * single-stepped. x86_64, POWER4 and above have no-exec support and
 * stepping on the instruction on a vmalloced/kmalloced/data page
 * is a recipe for disaster
 */
#define INSNS_PER_PAGE  (PAGE_SIZE/(MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))

struct kprobe_insn_page {
        struct hlist_node hlist;
        kprobe_opcode_t *insns;         /* Page of instruction slots */
        char slot_used[INSNS_PER_PAGE];
        int nused;
        int ngarbage;
};

enum kprobe_slot_state {
        SLOT_CLEAN = 0,
        SLOT_DIRTY = 1,
        SLOT_USED = 2,
};

static struct hlist_head kprobe_insn_pages;
static int kprobe_garbage_slots;
static int collect_garbage_slots(void);

static int __kprobes check_safety(void)
{
        int ret = 0;
#if defined(CONFIG_PREEMPT) && defined(CONFIG_PM)
        ret = freeze_processes();
        if (ret == 0) {
                struct task_struct *p, *q;
                do_each_thread(p, q) {
                        if (p != current && p->state == TASK_RUNNING &&
                            p->pid != 0) {
                                printk("Check failed: %s is running\n",p->comm);
                                ret = -1;
                                goto loop_end;
                        }
                } while_each_thread(p, q);
        }
loop_end:
        thaw_processes();
#else
        synchronize_sched();
#endif
        return ret;
}

/**
 * get_insn_slot() - Find a slot on an executable page for an instruction.
 * We allocate an executable page if there's no room on existing ones.
 */
kprobe_opcode_t __kprobes *get_insn_slot(void)
{
        struct kprobe_insn_page *kip;
        struct hlist_node *pos;

      retry:
        hlist_for_each(pos, &kprobe_insn_pages) {
                kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
                if (kip->nused < INSNS_PER_PAGE) {
                        int i;
                        for (i = 0; i < INSNS_PER_PAGE; i++) {
                                if (kip->slot_used[i] == SLOT_CLEAN) {
                                        kip->slot_used[i] = SLOT_USED;
                                        kip->nused++;
                                        return kip->insns + (i * MAX_INSN_SIZE);
                                }
                        }
                        /* Surprise!  No unused slots.  Fix kip->nused. */
                        kip->nused = INSNS_PER_PAGE;
                }
        }

        /* If there are any garbage slots, collect it and try again. */
        if (kprobe_garbage_slots && collect_garbage_slots() == 0) {
                goto retry;
        }
        /* All out of space.  Need to allocate a new page. Use slot 0. */
        kip = kmalloc(sizeof(struct kprobe_insn_page), GFP_KERNEL);
        if (!kip) {
                return NULL;
        }

        /*
         * Use module_alloc so this page is within +/- 2GB of where the
         * kernel image and loaded module images reside. This is required
         * so x86_64 can correctly handle the %rip-relative fixups.
         */
        kip->insns = module_alloc(PAGE_SIZE);
        if (!kip->insns) {
                kfree(kip);
                return NULL;
        }
        INIT_HLIST_NODE(&kip->hlist);
        hlist_add_head(&kip->hlist, &kprobe_insn_pages);
        memset(kip->slot_used, SLOT_CLEAN, INSNS_PER_PAGE);
        kip->slot_used[0] = SLOT_USED;
        kip->nused = 1;
        kip->ngarbage = 0;
        return kip->insns;
}

/* Return 1 if all garbages are collected, otherwise 0. */
static int __kprobes collect_one_slot(struct kprobe_insn_page *kip, int idx)
{
        kip->slot_used[idx] = SLOT_CLEAN;
        kip->nused--;
        if (kip->nused == 0) {
                /*
                 * Page is no longer in use.  Free it unless
                 * it's the last one.  We keep the last one
                 * so as not to have to set it up again the
                 * next time somebody inserts a probe.
                 */
                hlist_del(&kip->hlist);
                if (hlist_empty(&kprobe_insn_pages)) {
                        INIT_HLIST_NODE(&kip->hlist);
                        hlist_add_head(&kip->hlist,
                                       &kprobe_insn_pages);
                } else {
                        module_free(NULL, kip->insns);
                        kfree(kip);
                }
                return 1;
        }
        return 0;
}

static int __kprobes collect_garbage_slots(void)
{
        struct kprobe_insn_page *kip;
        struct hlist_node *pos, *next;

        /* Ensure no-one is preepmted on the garbages */
        if (check_safety() != 0)
                return -EAGAIN;

        hlist_for_each_safe(pos, next, &kprobe_insn_pages) {
                int i;
                kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
                if (kip->ngarbage == 0)
                        continue;
                kip->ngarbage = 0;      /* we will collect all garbages */
                for (i = 0; i < INSNS_PER_PAGE; i++) {
                        if (kip->slot_used[i] == SLOT_DIRTY &&
                            collect_one_slot(kip, i))
                                break;
                }
        }
        kprobe_garbage_slots = 0;
        return 0;
}

void __kprobes free_insn_slot(kprobe_opcode_t * slot, int dirty)
{
        struct kprobe_insn_page *kip;
        struct hlist_node *pos;

        hlist_for_each(pos, &kprobe_insn_pages) {
                kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
                if (kip->insns <= slot &&
                    slot < kip->insns + (INSNS_PER_PAGE * MAX_INSN_SIZE)) {
                        int i = (slot - kip->insns) / MAX_INSN_SIZE;
                        if (dirty) {
                                kip->slot_used[i] = SLOT_DIRTY;
                                kip->ngarbage++;
                        } else {
                                collect_one_slot(kip, i);
                        }
                        break;
                }
        }
        if (dirty && (++kprobe_garbage_slots > INSNS_PER_PAGE)) {
                collect_garbage_slots();
        }
}
#endif

/* We have preemption disabled.. so it is safe to use __ versions */
static inline void set_kprobe_instance(struct kprobe *kp)
{
        __get_cpu_var(kprobe_instance) = kp;
}

static inline void reset_kprobe_instance(void)
{
        __get_cpu_var(kprobe_instance) = NULL;
}

/*
 * This routine is called either:
 *      - under the kprobe_mutex - during kprobe_[un]register()
 *                              OR
 *      - with preemption disabled - from arch/xxx/kernel/kprobes.c
 */
struct kprobe __kprobes *get_kprobe(void *addr)
{
        struct hlist_head *head;
        struct hlist_node *node;
        struct kprobe *p;

        head = &kprobe_table[hash_ptr(addr, KPROBE_HASH_BITS)];
        hlist_for_each_entry_rcu(p, node, head, hlist) {
                if (p->addr == addr)
                        return p;
        }
        return NULL;
}

/*
 * Aggregate handlers for multiple kprobes support - these handlers
 * take care of invoking the individual kprobe handlers on p->list
 */
static int __kprobes aggr_pre_handler(struct kprobe *p, struct pt_regs *regs)
{
        struct kprobe *kp;

        list_for_each_entry_rcu(kp, &p->list, list) {
                if (kp->pre_handler) {
                        set_kprobe_instance(kp);
                        if (kp->pre_handler(kp, regs))
                                return 1;
                }
                reset_kprobe_instance();
        }
        return 0;
}

static void __kprobes aggr_post_handler(struct kprobe *p, struct pt_regs *regs,
                                        unsigned long flags)
{
        struct kprobe *kp;

        list_for_each_entry_rcu(kp, &p->list, list) {
                if (kp->post_handler) {
                        set_kprobe_instance(kp);
                        kp->post_handler(kp, regs, flags);
                        reset_kprobe_instance();
                }
        }
        return;
}

static int __kprobes aggr_fault_handler(struct kprobe *p, struct pt_regs *regs,
                                        int trapnr)
{
        struct kprobe *cur = __get_cpu_var(kprobe_instance);

        /*
         * if we faulted "during" the execution of a user specified
         * probe handler, invoke just that probe's fault handler
         */
        if (cur && cur->fault_handler) {
                if (cur->fault_handler(cur, regs, trapnr))
                        return 1;
        }
        return 0;
}

static int __kprobes aggr_break_handler(struct kprobe *p, struct pt_regs *regs)
{
        struct kprobe *cur = __get_cpu_var(kprobe_instance);
        int ret = 0;

        if (cur && cur->break_handler) {
                if (cur->break_handler(cur, regs))
                        ret = 1;
        }
        reset_kprobe_instance();
        return ret;
}

/* Walks the list and increments nmissed count for multiprobe case */
void __kprobes kprobes_inc_nmissed_count(struct kprobe *p)
{
        struct kprobe *kp;
        if (p->pre_handler != aggr_pre_handler) {
                p->nmissed++;
        } else {
                list_for_each_entry_rcu(kp, &p->list, list)
                        kp->nmissed++;
        }
        return;
}

/* Called with kretprobe_lock held */
struct kretprobe_instance __kprobes *get_free_rp_inst(struct kretprobe *rp)
{
        struct hlist_node *node;
        struct kretprobe_instance *ri;
        hlist_for_each_entry(ri, node, &rp->free_instances, uflist)
                return ri;
        return NULL;
}

/* Called with kretprobe_lock held */
static struct kretprobe_instance __kprobes *get_used_rp_inst(struct kretprobe
                                                              *rp)
{
        struct hlist_node *node;
        struct kretprobe_instance *ri;
        hlist_for_each_entry(ri, node, &rp->used_instances, uflist)
                return ri;
        return NULL;
}

/* Called with kretprobe_lock held */
void __kprobes add_rp_inst(struct kretprobe_instance *ri)
{
        /*
         * Remove rp inst off the free list -
         * Add it back when probed function returns
         */
        hlist_del(&ri->uflist);

        /* Add rp inst onto table */
        INIT_HLIST_NODE(&ri->hlist);
        hlist_add_head(&ri->hlist,
                        &kretprobe_inst_table[hash_ptr(ri->task, KPROBE_HASH_BITS)]);

        /* Also add this rp inst to the used list. */
        INIT_HLIST_NODE(&ri->uflist);
        hlist_add_head(&ri->uflist, &ri->rp->used_instances);
}

/* Called with kretprobe_lock held */
void __kprobes recycle_rp_inst(struct kretprobe_instance *ri,
                                struct hlist_head *head)
{
        /* remove rp inst off the rprobe_inst_table */
        hlist_del(&ri->hlist);
        if (ri->rp) {
                /* remove rp inst off the used list */
                hlist_del(&ri->uflist);
                /* put rp inst back onto the free list */
                INIT_HLIST_NODE(&ri->uflist);
                hlist_add_head(&ri->uflist, &ri->rp->free_instances);
        } else
                /* Unregistering */
                hlist_add_head(&ri->hlist, head);
}

struct hlist_head __kprobes *kretprobe_inst_table_head(struct task_struct *tsk)
{
        return &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)];
}

/*
 * This function is called from finish_task_switch when task tk becomes dead,
 * so that we can recycle any function-return probe instances associated
 * with this task. These left over instances represent probed functions
 * that have been called but will never return.
 */
void __kprobes kprobe_flush_task(struct task_struct *tk)
{
        struct kretprobe_instance *ri;
        struct hlist_head *head, empty_rp;
        struct hlist_node *node, *tmp;
        unsigned long flags = 0;

        INIT_HLIST_HEAD(&empty_rp);
        spin_lock_irqsave(&kretprobe_lock, flags);
        head = kretprobe_inst_table_head(tk);
        hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
                if (ri->task == tk)
                        recycle_rp_inst(ri, &empty_rp);
        }
        spin_unlock_irqrestore(&kretprobe_lock, flags);

        hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
                hlist_del(&ri->hlist);
                kfree(ri);
        }
}

static inline void free_rp_inst(struct kretprobe *rp)
{
        struct kretprobe_instance *ri;
        while ((ri = get_free_rp_inst(rp)) != NULL) {
                hlist_del(&ri->uflist);
                kfree(ri);
        }
}

/*
 * Keep all fields in the kprobe consistent
 */
static inline void copy_kprobe(struct kprobe *old_p, struct kprobe *p)
{
        memcpy(&p->opcode, &old_p->opcode, sizeof(kprobe_opcode_t));
        memcpy(&p->ainsn, &old_p->ainsn, sizeof(struct arch_specific_insn));
}

/*
* Add the new probe to old_p->list. Fail if this is the
* second jprobe at the address - two jprobes can't coexist
*/
static int __kprobes add_new_kprobe(struct kprobe *old_p, struct kprobe *p)
{
        if (p->break_handler) {
                if (old_p->break_handler)
                        return -EEXIST;
                list_add_tail_rcu(&p->list, &old_p->list);
                old_p->break_handler = aggr_break_handler;
        } else
                list_add_rcu(&p->list, &old_p->list);
        if (p->post_handler && !old_p->post_handler)
                old_p->post_handler = aggr_post_handler;
        return 0;
}

/*
 * Fill in the required fields of the "manager kprobe". Replace the
 * earlier kprobe in the hlist with the manager kprobe
 */
static inline void add_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
{
        copy_kprobe(p, ap);
        flush_insn_slot(ap);
        ap->addr = p->addr;
        ap->pre_handler = aggr_pre_handler;
        ap->fault_handler = aggr_fault_handler;
        if (p->post_handler)
                ap->post_handler = aggr_post_handler;
        if (p->break_handler)
                ap->break_handler = aggr_break_handler;

        INIT_LIST_HEAD(&ap->list);
        list_add_rcu(&p->list, &ap->list);

        hlist_replace_rcu(&p->hlist, &ap->hlist);
}

/*
 * This is the second or subsequent kprobe at the address - handle
 * the intricacies
 */
static int __kprobes register_aggr_kprobe(struct kprobe *old_p,
                                          struct kprobe *p)
{
        int ret = 0;
        struct kprobe *ap;

        if (old_p->pre_handler == aggr_pre_handler) {
                copy_kprobe(old_p, p);
                ret = add_new_kprobe(old_p, p);
        } else {
                ap = kzalloc(sizeof(struct kprobe), GFP_KERNEL);
                if (!ap)
                        return -ENOMEM;
                add_aggr_kprobe(ap, old_p);
                copy_kprobe(ap, p);
                ret = add_new_kprobe(ap, p);
        }
        return ret;
}

static int __kprobes in_kprobes_functions(unsigned long addr)
{
        if (addr >= (unsigned long)__kprobes_text_start
                && addr < (unsigned long)__kprobes_text_end)
                return -EINVAL;
        return 0;
}

static int __kprobes __register_kprobe(struct kprobe *p,
        unsigned long called_from)
{
        int ret = 0;
        struct kprobe *old_p;
        struct module *probed_mod;

        /*
         * If we have a symbol_name argument look it up,
         * and add it to the address.  That way the addr
         * field can either be global or relative to a symbol.
         */
        if (p->symbol_name) {
                if (p->addr)
                        return -EINVAL;
                kprobe_lookup_name(p->symbol_name, p->addr);
        }

        if (!p->addr)
                return -EINVAL;
        p->addr = (kprobe_opcode_t *)(((char *)p->addr)+ p->offset);

        if ((!kernel_text_address((unsigned long) p->addr)) ||
                in_kprobes_functions((unsigned long) p->addr))
                return -EINVAL;

        p->mod_refcounted = 0;
        /* Check are we probing a module */
        if ((probed_mod = module_text_address((unsigned long) p->addr))) {
                struct module *calling_mod = module_text_address(called_from);
                /* We must allow modules to probe themself and
                 * in this case avoid incrementing the module refcount,
                 * so as to allow unloading of self probing modules.
                 */
                if (calling_mod && (calling_mod != probed_mod)) {
                        if (unlikely(!try_module_get(probed_mod)))
                                return -EINVAL;
                        p->mod_refcounted = 1;
                } else
                        probed_mod = NULL;
        }

        p->nmissed = 0;
        mutex_lock(&kprobe_mutex);
        old_p = get_kprobe(p->addr);
        if (old_p) {
                ret = register_aggr_kprobe(old_p, p);
                if (!ret)
                        atomic_inc(&kprobe_count);
                goto out;
        }

        if ((ret = arch_prepare_kprobe(p)) != 0)
                goto out;

        INIT_HLIST_NODE(&p->hlist);
        hlist_add_head_rcu(&p->hlist,
                       &kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);

        if (atomic_add_return(1, &kprobe_count) == \
                                (ARCH_INACTIVE_KPROBE_COUNT + 1))
                register_page_fault_notifier(&kprobe_page_fault_nb);

        arch_arm_kprobe(p);

out:
        mutex_unlock(&kprobe_mutex);

        if (ret && probed_mod)
                module_put(probed_mod);
        return ret;
}

int __kprobes register_kprobe(struct kprobe *p)
{
        return __register_kprobe(p,
                (unsigned long)__builtin_return_address(0));
}

void __kprobes unregister_kprobe(struct kprobe *p)
{
        struct module *mod;
        struct kprobe *old_p, *list_p;
        int cleanup_p;

        mutex_lock(&kprobe_mutex);
        old_p = get_kprobe(p->addr);
        if (unlikely(!old_p)) {
                mutex_unlock(&kprobe_mutex);
                return;
        }
        if (p != old_p) {
                list_for_each_entry_rcu(list_p, &old_p->list, list)
                        if (list_p == p)
                        /* kprobe p is a valid probe */
                                goto valid_p;
                mutex_unlock(&kprobe_mutex);
                return;
        }
valid_p:
        if ((old_p == p) || ((old_p->pre_handler == aggr_pre_handler) &&
                (p->list.next == &old_p->list) &&
                (p->list.prev == &old_p->list))) {
                /* Only probe on the hash list */
                arch_disarm_kprobe(p);
                hlist_del_rcu(&old_p->hlist);
                cleanup_p = 1;
        } else {
                list_del_rcu(&p->list);
                cleanup_p = 0;
        }

        mutex_unlock(&kprobe_mutex);

        synchronize_sched();
        if (p->mod_refcounted &&
            (mod = module_text_address((unsigned long)p->addr)))
                module_put(mod);

        if (cleanup_p) {
                if (p != old_p) {
                        list_del_rcu(&p->list);
                        kfree(old_p);
                }
                arch_remove_kprobe(p);
        } else {
                mutex_lock(&kprobe_mutex);
                if (p->break_handler)
                        old_p->break_handler = NULL;
                if (p->post_handler){
                        list_for_each_entry_rcu(list_p, &old_p->list, list){
                                if (list_p->post_handler){
                                        cleanup_p = 2;
                                        break;
                                }
                        }
                        if (cleanup_p == 0)
                                old_p->post_handler = NULL;
                }
                mutex_unlock(&kprobe_mutex);
        }

        /* Call unregister_page_fault_notifier()
         * if no probes are active
         */
        mutex_lock(&kprobe_mutex);
        if (atomic_add_return(-1, &kprobe_count) == \
                                ARCH_INACTIVE_KPROBE_COUNT)
                unregister_page_fault_notifier(&kprobe_page_fault_nb);
        mutex_unlock(&kprobe_mutex);
        return;
}

static struct notifier_block kprobe_exceptions_nb = {
        .notifier_call = kprobe_exceptions_notify,
        .priority = 0x7fffffff /* we need to be notified first */
};


int __kprobes register_jprobe(struct jprobe *jp)
{
        /* Todo: Verify probepoint is a function entry point */
        jp->kp.pre_handler = setjmp_pre_handler;
        jp->kp.break_handler = longjmp_break_handler;

        return __register_kprobe(&jp->kp,
                (unsigned long)__builtin_return_address(0));
}

void __kprobes unregister_jprobe(struct jprobe *jp)
{
        unregister_kprobe(&jp->kp);
}

#ifdef ARCH_SUPPORTS_KRETPROBES

/*
 * This kprobe pre_handler is registered with every kretprobe. When probe
 * hits it will set up the return probe.
 */
static int __kprobes pre_handler_kretprobe(struct kprobe *p,
                                           struct pt_regs *regs)
{
        struct kretprobe *rp = container_of(p, struct kretprobe, kp);
        unsigned long flags = 0;

        /*TODO: consider to only swap the RA after the last pre_handler fired */
        spin_lock_irqsave(&kretprobe_lock, flags);
        arch_prepare_kretprobe(rp, regs);
        spin_unlock_irqrestore(&kretprobe_lock, flags);
        return 0;
}

int __kprobes register_kretprobe(struct kretprobe *rp)
{
        int ret = 0;
        struct kretprobe_instance *inst;
        int i;

        rp->kp.pre_handler = pre_handler_kretprobe;
        rp->kp.post_handler = NULL;
        rp->kp.fault_handler = NULL;
        rp->kp.break_handler = NULL;

        /* Pre-allocate memory for max kretprobe instances */
        if (rp->maxactive <= 0) {
#ifdef CONFIG_PREEMPT
                rp->maxactive = max(10, 2 * NR_CPUS);
#else
                rp->maxactive = NR_CPUS;
#endif
        }
        INIT_HLIST_HEAD(&rp->used_instances);
        INIT_HLIST_HEAD(&rp->free_instances);
        for (i = 0; i < rp->maxactive; i++) {
                inst = kmalloc(sizeof(struct kretprobe_instance), GFP_KERNEL);
                if (inst == NULL) {
                        free_rp_inst(rp);
                        return -ENOMEM;
                }
                INIT_HLIST_NODE(&inst->uflist);
                hlist_add_head(&inst->uflist, &rp->free_instances);
        }

        rp->nmissed = 0;
        /* Establish function entry probe point */
        if ((ret = __register_kprobe(&rp->kp,
                (unsigned long)__builtin_return_address(0))) != 0)
                free_rp_inst(rp);
        return ret;
}

#else /* ARCH_SUPPORTS_KRETPROBES */

int __kprobes register_kretprobe(struct kretprobe *rp)
{
        return -ENOSYS;
}

#endif /* ARCH_SUPPORTS_KRETPROBES */

void __kprobes unregister_kretprobe(struct kretprobe *rp)
{
        unsigned long flags;
        struct kretprobe_instance *ri;

        unregister_kprobe(&rp->kp);
        /* No race here */
        spin_lock_irqsave(&kretprobe_lock, flags);
        while ((ri = get_used_rp_inst(rp)) != NULL) {
                ri->rp = NULL;
                hlist_del(&ri->uflist);
        }
        spin_unlock_irqrestore(&kretprobe_lock, flags);
        free_rp_inst(rp);
}

static int __init init_kprobes(void)
{
        int i, err = 0;

        /* FIXME allocate the probe table, currently defined statically */
        /* initialize all list heads */
        for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
                INIT_HLIST_HEAD(&kprobe_table[i]);
                INIT_HLIST_HEAD(&kretprobe_inst_table[i]);
        }
        atomic_set(&kprobe_count, 0);

        err = arch_init_kprobes();
        if (!err)
                err = register_die_notifier(&kprobe_exceptions_nb);

        return err;
}

__initcall(init_kprobes);

EXPORT_SYMBOL_GPL(register_kprobe);
EXPORT_SYMBOL_GPL(unregister_kprobe);
EXPORT_SYMBOL_GPL(register_jprobe);
EXPORT_SYMBOL_GPL(unregister_jprobe);
EXPORT_SYMBOL_GPL(jprobe_return);
EXPORT_SYMBOL_GPL(register_kretprobe);
EXPORT_SYMBOL_GPL(unregister_kretprobe);