[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);
+}