[S390] add kprobes support.

Signed-off-by: Michael Grundy <grundym@us.ibm.com>
Signed-off-by: David Wilder <dwilder@us.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 657 insertions, 0 deletions

diff --git a/arch/s390/kernel/kprobes.c b/arch/s390/kernel/kprobes.c
new file mode 100644
index 000000000000..ca28fb0b3790
--- /dev/null
+++ b/arch/s390/kernel/kprobes.c
@@ -0,0 +1,657 @@
+/*
+ *  Kernel Probes (KProbes)
+ *
+ * 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, 2006
+ *
+ * s390 port, used ppc64 as template. Mike Grundy <grundym@us.ibm.com>
+ */
+
+#include <linux/config.h>
+#include <linux/kprobes.h>
+#include <linux/ptrace.h>
+#include <linux/preempt.h>
+#include <linux/stop_machine.h>
+#include <asm/cacheflush.h>
+#include <asm/kdebug.h>
+#include <asm/sections.h>
+#include <asm/uaccess.h>
+#include <linux/module.h>
+
+DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
+DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
+
+int __kprobes arch_prepare_kprobe(struct kprobe *p)
+{
+        /* Make sure the probe isn't going on a difficult instruction */
+        if (is_prohibited_opcode((kprobe_opcode_t *) p->addr))
+                return -EINVAL;
+
+        if ((unsigned long)p->addr & 0x01) {
+                printk("Attempt to register kprobe at an unaligned address\n");
+                return -EINVAL;
+                }
+
+        /* Use the get_insn_slot() facility for correctness */
+        if (!(p->ainsn.insn = get_insn_slot()))
+                return -ENOMEM;
+
+        memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
+
+        get_instruction_type(&p->ainsn);
+        p->opcode = *p->addr;
+        return 0;
+}
+
+int __kprobes is_prohibited_opcode(kprobe_opcode_t *instruction)
+{
+        switch (*(__u8 *) instruction) {
+        case 0x0c:      /* bassm */
+        case 0x0b:      /* bsm   */
+        case 0x83:      /* diag  */
+        case 0x44:      /* ex    */
+                return -EINVAL;
+        }
+        switch (*(__u16 *) instruction) {
+        case 0x0101:    /* pr    */
+        case 0xb25a:    /* bsa   */
+        case 0xb240:    /* bakr  */
+        case 0xb258:    /* bsg   */
+        case 0xb218:    /* pc    */
+        case 0xb228:    /* pt    */
+                return -EINVAL;
+        }
+        return 0;
+}
+
+void __kprobes get_instruction_type(struct arch_specific_insn *ainsn)
+{
+        /* default fixup method */
+        ainsn->fixup = FIXUP_PSW_NORMAL;
+
+        /* save r1 operand */
+        ainsn->reg = (*ainsn->insn & 0xf0) >> 4;
+
+        /* save the instruction length (pop 5-5) in bytes */
+        switch (*(__u8 *) (ainsn->insn) >> 4) {
+        case 0:
+                ainsn->ilen = 2;
+                break;
+        case 1:
+        case 2:
+                ainsn->ilen = 4;
+                break;
+        case 3:
+                ainsn->ilen = 6;
+                break;
+        }
+
+        switch (*(__u8 *) ainsn->insn) {
+        case 0x05:      /* balr */
+        case 0x0d:      /* basr */
+                ainsn->fixup = FIXUP_RETURN_REGISTER;
+                /* if r2 = 0, no branch will be taken */
+                if ((*ainsn->insn & 0x0f) == 0)
+                        ainsn->fixup |= FIXUP_BRANCH_NOT_TAKEN;
+                break;
+        case 0x06:      /* bctr */
+        case 0x07:      /* bcr  */
+                ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
+                break;
+        case 0x45:      /* bal  */
+        case 0x4d:      /* bas  */
+                ainsn->fixup = FIXUP_RETURN_REGISTER;
+                break;
+        case 0x47:      /* bc   */
+        case 0x46:      /* bct  */
+        case 0x86:      /* bxh  */
+        case 0x87:      /* bxle */
+                ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
+                break;
+        case 0x82:      /* lpsw */
+                ainsn->fixup = FIXUP_NOT_REQUIRED;
+                break;
+        case 0xb2:      /* lpswe */
+                if (*(((__u8 *) ainsn->insn) + 1) == 0xb2) {
+                        ainsn->fixup = FIXUP_NOT_REQUIRED;
+                }
+                break;
+        case 0xa7:      /* bras */
+                if ((*ainsn->insn & 0x0f) == 0x05) {
+                        ainsn->fixup |= FIXUP_RETURN_REGISTER;
+                }
+                break;
+        case 0xc0:
+                if ((*ainsn->insn & 0x0f) == 0x00  /* larl  */
+                        || (*ainsn->insn & 0x0f) == 0x05) /* brasl */
+                ainsn->fixup |= FIXUP_RETURN_REGISTER;
+                break;
+        case 0xeb:
+                if (*(((__u8 *) ainsn->insn) + 5 ) == 0x44 ||   /* bxhg  */
+                        *(((__u8 *) ainsn->insn) + 5) == 0x45) {/* bxleg */
+                        ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
+                }
+                break;
+        case 0xe3:      /* bctg */
+                if (*(((__u8 *) ainsn->insn) + 5) == 0x46) {
+                        ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
+                }
+                break;
+        }
+}
+
+static int __kprobes swap_instruction(void *aref)
+{
+        struct ins_replace_args *args = aref;
+        int err = -EFAULT;
+
+        asm volatile(
+                "0: mvc  0(2,%2),0(%3)\n"
+                "1: la   %0,0\n"
+                "2:\n"
+                EX_TABLE(0b,2b)
+                : "+d" (err), "=m" (*args->ptr)
+                : "a" (args->ptr), "a" (&args->new), "m" (args->new));
+        return err;
+}
+
+void __kprobes arch_arm_kprobe(struct kprobe *p)
+{
+        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+        unsigned long status = kcb->kprobe_status;
+        struct ins_replace_args args;
+
+        args.ptr = p->addr;
+        args.old = p->opcode;
+        args.new = BREAKPOINT_INSTRUCTION;
+
+        kcb->kprobe_status = KPROBE_SWAP_INST;
+        stop_machine_run(swap_instruction, &args, NR_CPUS);
+        kcb->kprobe_status = status;
+}
+
+void __kprobes arch_disarm_kprobe(struct kprobe *p)
+{
+        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+        unsigned long status = kcb->kprobe_status;
+        struct ins_replace_args args;
+
+        args.ptr = p->addr;
+        args.old = BREAKPOINT_INSTRUCTION;
+        args.new = p->opcode;
+
+        kcb->kprobe_status = KPROBE_SWAP_INST;
+        stop_machine_run(swap_instruction, &args, NR_CPUS);
+        kcb->kprobe_status = status;
+}
+
+void __kprobes arch_remove_kprobe(struct kprobe *p)
+{
+        mutex_lock(&kprobe_mutex);
+        free_insn_slot(p->ainsn.insn);
+        mutex_unlock(&kprobe_mutex);
+}
+
+static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
+{
+        per_cr_bits kprobe_per_regs[1];
+
+        memset(kprobe_per_regs, 0, sizeof(per_cr_bits));
+        regs->psw.addr = (unsigned long)p->ainsn.insn | PSW_ADDR_AMODE;
+
+        /* Set up the per control reg info, will pass to lctl */
+        kprobe_per_regs[0].em_instruction_fetch = 1;
+        kprobe_per_regs[0].starting_addr = (unsigned long)p->ainsn.insn;
+        kprobe_per_regs[0].ending_addr = (unsigned long)p->ainsn.insn + 1;
+
+        /* Set the PER control regs, turns on single step for this address */
+        __ctl_load(kprobe_per_regs, 9, 11);
+        regs->psw.mask |= PSW_MASK_PER;
+        regs->psw.mask &= ~(PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
+}
+
+static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
+{
+        kcb->prev_kprobe.kp = kprobe_running();
+        kcb->prev_kprobe.status = kcb->kprobe_status;
+        kcb->prev_kprobe.kprobe_saved_imask = kcb->kprobe_saved_imask;
+        memcpy(kcb->prev_kprobe.kprobe_saved_ctl, kcb->kprobe_saved_ctl,
+                                        sizeof(kcb->kprobe_saved_ctl));
+}
+
+static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
+{
+        __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
+        kcb->kprobe_status = kcb->prev_kprobe.status;
+        kcb->kprobe_saved_imask = kcb->prev_kprobe.kprobe_saved_imask;
+        memcpy(kcb->kprobe_saved_ctl, kcb->prev_kprobe.kprobe_saved_ctl,
+                                        sizeof(kcb->kprobe_saved_ctl));
+}
+
+static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
+                                                struct kprobe_ctlblk *kcb)
+{
+        __get_cpu_var(current_kprobe) = p;
+        /* Save the interrupt and per flags */
+        kcb->kprobe_saved_imask = regs->psw.mask &
+            (PSW_MASK_PER | PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
+        /* Save the control regs that govern PER */
+        __ctl_store(kcb->kprobe_saved_ctl, 9, 11);
+}
+
+/* Called with kretprobe_lock held */
+void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
+                                        struct pt_regs *regs)
+{
+        struct kretprobe_instance *ri;
+
+        if ((ri = get_free_rp_inst(rp)) != NULL) {
+                ri->rp = rp;
+                ri->task = current;
+                ri->ret_addr = (kprobe_opcode_t *) regs->gprs[14];
+
+                /* Replace the return addr with trampoline addr */
+                regs->gprs[14] = (unsigned long)&kretprobe_trampoline;
+
+                add_rp_inst(ri);
+        } else {
+                rp->nmissed++;
+        }
+}
+
+static int __kprobes kprobe_handler(struct pt_regs *regs)
+{
+        struct kprobe *p;
+        int ret = 0;
+        unsigned long *addr = (unsigned long *)
+                ((regs->psw.addr & PSW_ADDR_INSN) - 2);
+        struct kprobe_ctlblk *kcb;
+
+        /*
+         * We don't want to be preempted for the entire
+         * duration of kprobe processing
+         */
+        preempt_disable();
+        kcb = get_kprobe_ctlblk();
+
+        /* Check we're not actually recursing */
+        if (kprobe_running()) {
+                p = get_kprobe(addr);
+                if (p) {
+                        if (kcb->kprobe_status == KPROBE_HIT_SS &&
+                            *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
+                                regs->psw.mask &= ~PSW_MASK_PER;
+                                regs->psw.mask |= kcb->kprobe_saved_imask;
+                                goto no_kprobe;
+                        }
+                        /* We have reentered the kprobe_handler(), since
+                         * another probe was hit while within the handler.
+                         * We here save the original kprobes variables and
+                         * just single step on the instruction of the new probe
+                         * without calling any user handlers.
+                         */
+                        save_previous_kprobe(kcb);
+                        set_current_kprobe(p, regs, kcb);
+                        kprobes_inc_nmissed_count(p);
+                        prepare_singlestep(p, regs);
+                        kcb->kprobe_status = KPROBE_REENTER;
+                        return 1;
+                } else {
+                        p = __get_cpu_var(current_kprobe);
+                        if (p->break_handler && p->break_handler(p, regs)) {
+                                goto ss_probe;
+                        }
+                }
+                goto no_kprobe;
+        }
+
+        p = get_kprobe(addr);
+        if (!p) {
+                if (*addr != BREAKPOINT_INSTRUCTION) {
+                        /*
+                         * The breakpoint instruction was removed right
+                         * after we hit it.  Another cpu has removed
+                         * either a probepoint or a debugger breakpoint
+                         * at this address.  In either case, no further
+                         * handling of this interrupt is appropriate.
+                         *
+                         */
+                        ret = 1;
+                }
+                /* Not one of ours: let kernel handle it */
+                goto no_kprobe;
+        }
+
+        kcb->kprobe_status = KPROBE_HIT_ACTIVE;
+        set_current_kprobe(p, regs, kcb);
+        if (p->pre_handler && p->pre_handler(p, regs))
+                /* handler has already set things up, so skip ss setup */
+                return 1;
+
+ss_probe:
+        prepare_singlestep(p, regs);
+        kcb->kprobe_status = KPROBE_HIT_SS;
+        return 1;
+
+no_kprobe:
+        preempt_enable_no_resched();
+        return ret;
+}
+
+/*
+ * Function return probe trampoline:
+ *      - init_kprobes() establishes a probepoint here
+ *      - When the probed function returns, this probe
+ *              causes the handlers to fire
+ */
+void __kprobes kretprobe_trampoline_holder(void)
+{
+        asm volatile(".global kretprobe_trampoline\n"
+                     "kretprobe_trampoline: bcr 0,0\n");
+}
+
+/*
+ * Called when the probe at kretprobe trampoline is hit
+ */
+int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
+{
+        struct kretprobe_instance *ri = NULL;
+        struct hlist_head *head;
+        struct hlist_node *node, *tmp;
+        unsigned long flags, orig_ret_address = 0;
+        unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
+
+        spin_lock_irqsave(&kretprobe_lock, flags);
+        head = kretprobe_inst_table_head(current);
+
+        /*
+         * It is possible to have multiple instances associated with a given
+         * task either because an multiple functions in the call path
+         * have a return probe installed on them, and/or more then one return
+         * return probe was registered for a target function.
+         *
+         * We can handle this because:
+         *     - instances are always inserted at the head of the list
+         *     - when multiple return probes are registered for the same
+         *       function, the first instance's ret_addr will point to the
+         *       real return address, and all the rest will point to
+         *       kretprobe_trampoline
+         */
+        hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
+                if (ri->task != current)
+                        /* another task is sharing our hash bucket */
+                        continue;
+
+                if (ri->rp && ri->rp->handler)
+                        ri->rp->handler(ri, regs);
+
+                orig_ret_address = (unsigned long)ri->ret_addr;
+                recycle_rp_inst(ri);
+
+                if (orig_ret_address != trampoline_address) {
+                        /*
+                         * This is the real return address. Any other
+                         * instances associated with this task are for
+                         * other calls deeper on the call stack
+                         */
+                        break;
+                }
+        }
+        BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
+        regs->psw.addr = orig_ret_address | PSW_ADDR_AMODE;
+
+        reset_current_kprobe();
+        spin_unlock_irqrestore(&kretprobe_lock, flags);
+        preempt_enable_no_resched();
+
+        /*
+         * By returning a non-zero value, we are telling
+         * kprobe_handler() that we don't want the post_handler
+         * to run (and have re-enabled preemption)
+         */
+        return 1;
+}
+
+/*
+ * Called after single-stepping.  p->addr is the address of the
+ * instruction whose first byte has been replaced by the "breakpoint"
+ * instruction.  To avoid the SMP problems that can occur when we
+ * temporarily put back the original opcode to single-step, we
+ * single-stepped a copy of the instruction.  The address of this
+ * copy is p->ainsn.insn.
+ */
+static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
+{
+        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+        regs->psw.addr &= PSW_ADDR_INSN;
+
+        if (p->ainsn.fixup & FIXUP_PSW_NORMAL)
+                regs->psw.addr = (unsigned long)p->addr +
+                                ((unsigned long)regs->psw.addr -
+                                 (unsigned long)p->ainsn.insn);
+
+        if (p->ainsn.fixup & FIXUP_BRANCH_NOT_TAKEN)
+                if ((unsigned long)regs->psw.addr -
+                    (unsigned long)p->ainsn.insn == p->ainsn.ilen)
+                        regs->psw.addr = (unsigned long)p->addr + p->ainsn.ilen;
+
+        if (p->ainsn.fixup & FIXUP_RETURN_REGISTER)
+                regs->gprs[p->ainsn.reg] = ((unsigned long)p->addr +
+                                                (regs->gprs[p->ainsn.reg] -
+                                                (unsigned long)p->ainsn.insn))
+                                                | PSW_ADDR_AMODE;
+
+        regs->psw.addr |= PSW_ADDR_AMODE;
+        /* turn off PER mode */
+        regs->psw.mask &= ~PSW_MASK_PER;
+        /* Restore the original per control regs */
+        __ctl_load(kcb->kprobe_saved_ctl, 9, 11);
+        regs->psw.mask |= kcb->kprobe_saved_imask;
+}
+
+static int __kprobes post_kprobe_handler(struct pt_regs *regs)
+{
+        struct kprobe *cur = kprobe_running();
+        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+        if (!cur)
+                return 0;
+
+        if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
+                kcb->kprobe_status = KPROBE_HIT_SSDONE;
+                cur->post_handler(cur, regs, 0);
+        }
+
+        resume_execution(cur, regs);
+
+        /*Restore back the original saved kprobes variables and continue. */
+        if (kcb->kprobe_status == KPROBE_REENTER) {
+                restore_previous_kprobe(kcb);
+                goto out;
+        }
+        reset_current_kprobe();
+out:
+        preempt_enable_no_resched();
+
+        /*
+         * if somebody else is singlestepping across a probe point, psw mask
+         * will have PER set, in which case, continue the remaining processing
+         * of do_single_step, as if this is not a probe hit.
+         */
+        if (regs->psw.mask & PSW_MASK_PER) {
+                return 0;
+        }
+
+        return 1;
+}
+
+static int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
+{
+        struct kprobe *cur = kprobe_running();
+        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+        const struct exception_table_entry *entry;
+
+        switch(kcb->kprobe_status) {
+        case KPROBE_SWAP_INST:
+                /* We are here because the instruction replacement failed */
+                return 0;
+        case KPROBE_HIT_SS:
+        case KPROBE_REENTER:
+                /*
+                 * We are here because the instruction being single
+                 * stepped caused a page fault. We reset the current
+                 * kprobe and the nip points back to the probe address
+                 * and allow the page fault handler to continue as a
+                 * normal page fault.
+                 */
+                regs->psw.addr = (unsigned long)cur->addr | PSW_ADDR_AMODE;
+                regs->psw.mask &= ~PSW_MASK_PER;
+                regs->psw.mask |= kcb->kprobe_saved_imask;
+                if (kcb->kprobe_status == KPROBE_REENTER)
+                        restore_previous_kprobe(kcb);
+                else
+                        reset_current_kprobe();
+                preempt_enable_no_resched();
+                break;
+        case KPROBE_HIT_ACTIVE:
+        case KPROBE_HIT_SSDONE:
+                /*
+                 * We increment the nmissed count for accounting,
+                 * we can also use npre/npostfault count for accouting
+                 * these specific fault cases.
+                 */
+                kprobes_inc_nmissed_count(cur);
+
+                /*
+                 * We come here because instructions in the pre/post
+                 * handler caused the page_fault, this could happen
+                 * if handler tries to access user space by
+                 * copy_from_user(), get_user() etc. Let the
+                 * user-specified handler try to fix it first.
+                 */
+                if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
+                        return 1;
+
+                /*
+                 * In case the user-specified fault handler returned
+                 * zero, try to fix up.
+                 */
+                entry = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
+                if (entry) {
+                        regs->psw.addr = entry->fixup | PSW_ADDR_AMODE;
+                        return 1;
+                }
+
+                /*
+                 * fixup_exception() could not handle it,
+                 * Let do_page_fault() fix it.
+                 */
+                break;
+        default:
+                break;
+        }
+        return 0;
+}
+
+/*
+ * Wrapper routine to for handling exceptions.
+ */
+int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
+                                       unsigned long val, void *data)
+{
+        struct die_args *args = (struct die_args *)data;
+        int ret = NOTIFY_DONE;
+
+        switch (val) {
+        case DIE_BPT:
+                if (kprobe_handler(args->regs))
+                        ret = NOTIFY_STOP;
+                break;
+        case DIE_SSTEP:
+                if (post_kprobe_handler(args->regs))
+                        ret = NOTIFY_STOP;
+                break;
+        case DIE_TRAP:
+        case DIE_PAGE_FAULT:
+                /* kprobe_running() needs smp_processor_id() */
+                preempt_disable();
+                if (kprobe_running() &&
+                    kprobe_fault_handler(args->regs, args->trapnr))
+                        ret = NOTIFY_STOP;
+                preempt_enable();
+                break;
+        default:
+                break;
+        }
+        return ret;
+}
+
+int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
+{
+        struct jprobe *jp = container_of(p, struct jprobe, kp);
+        unsigned long addr;
+        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+        memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
+
+        /* setup return addr to the jprobe handler routine */
+        regs->psw.addr = (unsigned long)(jp->entry) | PSW_ADDR_AMODE;
+
+        /* r14 is the function return address */
+        kcb->jprobe_saved_r14 = (unsigned long)regs->gprs[14];
+        /* r15 is the stack pointer */
+        kcb->jprobe_saved_r15 = (unsigned long)regs->gprs[15];
+        addr = (unsigned long)kcb->jprobe_saved_r15;
+
+        memcpy(kcb->jprobes_stack, (kprobe_opcode_t *) addr,
+               MIN_STACK_SIZE(addr));
+        return 1;
+}
+
+void __kprobes jprobe_return(void)
+{
+        asm volatile(".word 0x0002");
+}
+
+void __kprobes jprobe_return_end(void)
+{
+        asm volatile("bcr 0,0");
+}
+
+int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
+{
+        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+        unsigned long stack_addr = (unsigned long)(kcb->jprobe_saved_r15);
+
+        /* Put the regs back */
+        memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
+        /* put the stack back */
+        memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
+               MIN_STACK_SIZE(stack_addr));
+        preempt_enable_no_resched();
+        return 1;
+}
+
+static struct kprobe trampoline_p = {
+        .addr = (kprobe_opcode_t *) & kretprobe_trampoline,
+        .pre_handler = trampoline_probe_handler
+};
+
+int __init arch_init_kprobes(void)
+{
+        return register_kprobe(&trampoline_p);
+}