arch/tile/kernel/kprobes.c - linux - Git at Google

 /*
  * arch/tile/kernel/kprobes.c
  * Kprobes on TILE-Gx
  *
  * Some portions copied from the MIPS version.
  *
  * Copyright (C) IBM Corporation, 2002, 2004
  * Copyright 2006 Sony Corp.
  * Copyright 2010 Cavium Networks
  *
  * Copyright 2012 Tilera Corporation. All Rights Reserved.
  *
  *   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, version 2.
  *
  *   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, GOOD TITLE or
  *   NON INFRINGEMENT.  See the GNU General Public License for
  *   more details.
  */

 #include <linux/kprobes.h>
 #include <linux/kdebug.h>
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/uaccess.h>
 #include <asm/cacheflush.h>

 #include <arch/opcode.h>

 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);

 tile_bundle_bits breakpoint_insn = TILEGX_BPT_BUNDLE;
 tile_bundle_bits breakpoint2_insn = TILEGX_BPT_BUNDLE | DIE_SSTEPBP;

 /*
  * Check whether instruction is branch or jump, or if executing it
  * has different results depending on where it is executed (e.g. lnk).
  */
 static int __kprobes insn_has_control(kprobe_opcode_t insn)
 {
 	if (get_Mode(insn) != 0) {   /* Y-format bundle */
 		if (get_Opcode_Y1(insn) != RRR_1_OPCODE_Y1 ||
 		    get_RRROpcodeExtension_Y1(insn) != UNARY_RRR_1_OPCODE_Y1)
 			return 0;

 		switch (get_UnaryOpcodeExtension_Y1(insn)) {
 		case JALRP_UNARY_OPCODE_Y1:
 		case JALR_UNARY_OPCODE_Y1:
 		case JRP_UNARY_OPCODE_Y1:
 		case JR_UNARY_OPCODE_Y1:
 		case LNK_UNARY_OPCODE_Y1:
 			return 1;
 		default:
 			return 0;
 		}
 	}

 	switch (get_Opcode_X1(insn)) {
 	case BRANCH_OPCODE_X1:	/* branch instructions */
 	case JUMP_OPCODE_X1:	/* jump instructions: j and jal */
 		return 1;

 	case RRR_0_OPCODE_X1:   /* other jump instructions */
 		if (get_RRROpcodeExtension_X1(insn) != UNARY_RRR_0_OPCODE_X1)
 			return 0;
 		switch (get_UnaryOpcodeExtension_X1(insn)) {
 		case JALRP_UNARY_OPCODE_X1:
 		case JALR_UNARY_OPCODE_X1:
 		case JRP_UNARY_OPCODE_X1:
 		case JR_UNARY_OPCODE_X1:
 		case LNK_UNARY_OPCODE_X1:
 			return 1;
 		default:
 			return 0;
 		}
 	default:
 		return 0;
 	}
 }

 int __kprobes arch_prepare_kprobe(struct kprobe *p)
 {
 	unsigned long addr = (unsigned long)p->addr;

 	if (addr & (sizeof(kprobe_opcode_t) - 1))
 		return -EINVAL;

 	if (insn_has_control(*p->addr)) {
 		pr_notice("Kprobes for control instructions are not supported\n");
 		return -EINVAL;
 	}

 	/* insn: must be on special executable page on tile. */
 	p->ainsn.insn = get_insn_slot();
 	if (!p->ainsn.insn)
 		return -ENOMEM;

 	/*
 	 * In the kprobe->ainsn.insn[] array we store the original
 	 * instruction at index zero and a break trap instruction at
 	 * index one.
 	 */
 	memcpy(&p->ainsn.insn[0], p->addr, sizeof(kprobe_opcode_t));
 	p->ainsn.insn[1] = breakpoint2_insn;
 	p->opcode = *p->addr;

 	return 0;
 }

 void __kprobes arch_arm_kprobe(struct kprobe *p)
 {
 	unsigned long addr_wr;

 	/* Operate on writable kernel text mapping. */
 	addr_wr = ktext_writable_addr(p->addr);

 	if (probe_kernel_write((void *)addr_wr, &breakpoint_insn,
 		sizeof(breakpoint_insn)))
 		pr_err("%s: failed to enable kprobe\n", __func__);

 	smp_wmb();
 	flush_insn_slot(p);
 }

 void __kprobes arch_disarm_kprobe(struct kprobe *kp)
 {
 	unsigned long addr_wr;

 	/* Operate on writable kernel text mapping. */
 	addr_wr = ktext_writable_addr(kp->addr);

 	if (probe_kernel_write((void *)addr_wr, &kp->opcode,
 		sizeof(kp->opcode)))
 		pr_err("%s: failed to enable kprobe\n", __func__);

 	smp_wmb();
 	flush_insn_slot(kp);
 }

 void __kprobes arch_remove_kprobe(struct kprobe *p)
 {
 	if (p->ainsn.insn) {
 		free_insn_slot(p->ainsn.insn, 0);
 		p->ainsn.insn = NULL;
 	}
 }

 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.saved_pc = kcb->kprobe_saved_pc;
 }

 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 {
 	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 	kcb->kprobe_status = kcb->prev_kprobe.status;
 	kcb->kprobe_saved_pc = kcb->prev_kprobe.saved_pc;
 }

 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 			struct kprobe_ctlblk *kcb)
 {
 	__this_cpu_write(current_kprobe, p);
 	kcb->kprobe_saved_pc = regs->pc;
 }

 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 {
 	/* Single step inline if the instruction is a break. */
 	if (p->opcode == breakpoint_insn ||
 	    p->opcode == breakpoint2_insn)
 		regs->pc = (unsigned long)p->addr;
 	else
 		regs->pc = (unsigned long)&p->ainsn.insn[0];
 }

 static int __kprobes kprobe_handler(struct pt_regs *regs)
 {
 	struct kprobe *p;
 	int ret = 0;
 	kprobe_opcode_t *addr;
 	struct kprobe_ctlblk *kcb;

 	addr = (kprobe_opcode_t *)regs->pc;

 	/*
 	 * 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[0] == breakpoint_insn) {
 				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 {
 			if (*addr != breakpoint_insn) {
 				/*
 				 * The breakpoint instruction was removed by
 				 * another cpu right after we hit, no further
 				 * handling of this interrupt is appropriate.
 				 */
 				ret = 1;
 				goto no_kprobe;
 			}
 			p = __this_cpu_read(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_insn) {
 			/*
 			 * 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;
 	}

 	set_current_kprobe(p, regs, kcb);
 	kcb->kprobe_status = KPROBE_HIT_ACTIVE;

 	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;
 }

 /*
  * Called after single-stepping.  p->addr is the address of the
  * instruction that has been replaced by the breakpoint. 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.
  *
  * This function prepares to return from the post-single-step
  * breakpoint trap.
  */
 static void __kprobes resume_execution(struct kprobe *p,
 				       struct pt_regs *regs,
 				       struct kprobe_ctlblk *kcb)
 {
 	unsigned long orig_pc = kcb->kprobe_saved_pc;
 	regs->pc = orig_pc + 8;
 }

 static inline int 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, kcb);

 	/* 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();

 	return 1;
 }

 static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 {
 	struct kprobe *cur = kprobe_running();
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

 	if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
 		return 1;

 	if (kcb->kprobe_status & KPROBE_HIT_SS) {
 		/*
 		 * We are here because the instruction being single
 		 * stepped caused a page fault. We reset the current
 		 * kprobe and the ip points back to the probe address
 		 * and allow the page fault handler to continue as a
 		 * normal page fault.
 		 */
 		resume_execution(cur, regs, kcb);
 		reset_current_kprobe();
 		preempt_enable_no_resched();
 	}
 	return 0;
 }

 /*
  * Wrapper routine 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_BREAK:
 		if (kprobe_handler(args->regs))
 			ret = NOTIFY_STOP;
 		break;
 	case DIE_SSTEPBP:
 		if (post_kprobe_handler(args->regs))
 			ret = NOTIFY_STOP;
 		break;
 	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);
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

 	kcb->jprobe_saved_regs = *regs;
 	kcb->jprobe_saved_sp = regs->sp;

 	memcpy(kcb->jprobes_stack, (void *)kcb->jprobe_saved_sp,
 	       MIN_JPROBES_STACK_SIZE(kcb->jprobe_saved_sp));

 	regs->pc = (unsigned long)(jp->entry);

 	return 1;
 }

 /* Defined in the inline asm below. */
 void jprobe_return_end(void);

 void __kprobes jprobe_return(void)
 {
 	asm volatile(
 		"bpt\n\t"
 		".globl jprobe_return_end\n"
 		"jprobe_return_end:\n");
 }

 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 {
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

 	if (regs->pc >= (unsigned long)jprobe_return &&
 	    regs->pc <= (unsigned long)jprobe_return_end) {
 		*regs = kcb->jprobe_saved_regs;
 		memcpy((void *)kcb->jprobe_saved_sp, kcb->jprobes_stack,
 		       MIN_JPROBES_STACK_SIZE(kcb->jprobe_saved_sp));
 		preempt_enable_no_resched();

 		return 1;
 	}
 	return 0;
 }

 /*
  * Function return probe trampoline:
  * - init_kprobes() establishes a probepoint here
  * - When the probed function returns, this probe causes the
  *   handlers to fire
  */
 static void __used kretprobe_trampoline_holder(void)
 {
 	asm volatile(
 		"nop\n\t"
 		".global kretprobe_trampoline\n"
 		"kretprobe_trampoline:\n\t"
 		"nop\n\t"
 		: : : "memory");
 }

 void kretprobe_trampoline(void);

 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 				      struct pt_regs *regs)
 {
 	ri->ret_addr = (kprobe_opcode_t *) regs->lr;

 	/* Replace the return addr with trampoline addr */
 	regs->lr = (unsigned long)kretprobe_trampoline;
 }

 /*
  * Called when the probe at kretprobe trampoline is hit.
  */
 static int __kprobes trampoline_probe_handler(struct kprobe *p,
 						struct pt_regs *regs)
 {
 	struct kretprobe_instance *ri = NULL;
 	struct hlist_head *head, empty_rp;
 	struct hlist_node *tmp;
 	unsigned long flags, orig_ret_address = 0;
 	unsigned long trampoline_address = (unsigned long)kretprobe_trampoline;

 	INIT_HLIST_HEAD(&empty_rp);
 	kretprobe_hash_lock(current, &head, &flags);

 	/*
 	 * It is possible to have multiple instances associated with a given
 	 * task either because multiple functions in the call path have
 	 * a return probe installed on them, and/or more than 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, 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, &empty_rp);

 		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;
 		}
 	}

 	kretprobe_assert(ri, orig_ret_address, trampoline_address);
 	instruction_pointer(regs) = orig_ret_address;

 	reset_current_kprobe();
 	kretprobe_hash_unlock(current, &flags);
 	preempt_enable_no_resched();

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

 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 {
 	if (p->addr == (kprobe_opcode_t *)kretprobe_trampoline)
 		return 1;

 	return 0;
 }

 static struct kprobe trampoline_p = {
 	.addr = (kprobe_opcode_t *)kretprobe_trampoline,
 	.pre_handler = trampoline_probe_handler
 };

 int __init arch_init_kprobes(void)
 {
 	register_kprobe(&trampoline_p);
 	return 0;
 }
	/*
	* arch/tile/kernel/kprobes.c
	* Kprobes on TILE-Gx
	*
	* Some portions copied from the MIPS version.
	*
	* Copyright (C) IBM Corporation, 2002, 2004
	* Copyright 2006 Sony Corp.
	* Copyright 2010 Cavium Networks
	*
	* Copyright 2012 Tilera Corporation. All Rights Reserved.
	*
	* 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, version 2.
	*
	* 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, GOOD TITLE or
	* NON INFRINGEMENT. See the GNU General Public License for
	* more details.
	*/

	#include <linux/kprobes.h>
	#include <linux/kdebug.h>
	#include <linux/module.h>
	#include <linux/slab.h>
	#include <linux/uaccess.h>
	#include <asm/cacheflush.h>

	#include <arch/opcode.h>

	DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
	DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);

	tile_bundle_bits breakpoint_insn = TILEGX_BPT_BUNDLE;
	tile_bundle_bits breakpoint2_insn = TILEGX_BPT_BUNDLE \| DIE_SSTEPBP;

	/*
	* Check whether instruction is branch or jump, or if executing it
	* has different results depending on where it is executed (e.g. lnk).
	*/
	static int __kprobes insn_has_control(kprobe_opcode_t insn)
	{
	if (get_Mode(insn) != 0) { /* Y-format bundle */
	if (get_Opcode_Y1(insn) != RRR_1_OPCODE_Y1 \|\|
	get_RRROpcodeExtension_Y1(insn) != UNARY_RRR_1_OPCODE_Y1)
	return 0;

	switch (get_UnaryOpcodeExtension_Y1(insn)) {
	case JALRP_UNARY_OPCODE_Y1:
	case JALR_UNARY_OPCODE_Y1:
	case JRP_UNARY_OPCODE_Y1:
	case JR_UNARY_OPCODE_Y1:
	case LNK_UNARY_OPCODE_Y1:
	return 1;
	default:
	return 0;
	}
	}

	switch (get_Opcode_X1(insn)) {
	case BRANCH_OPCODE_X1: /* branch instructions */
	case JUMP_OPCODE_X1: /* jump instructions: j and jal */
	return 1;

	case RRR_0_OPCODE_X1: /* other jump instructions */
	if (get_RRROpcodeExtension_X1(insn) != UNARY_RRR_0_OPCODE_X1)
	return 0;
	switch (get_UnaryOpcodeExtension_X1(insn)) {
	case JALRP_UNARY_OPCODE_X1:
	case JALR_UNARY_OPCODE_X1:
	case JRP_UNARY_OPCODE_X1:
	case JR_UNARY_OPCODE_X1:
	case LNK_UNARY_OPCODE_X1:
	return 1;
	default:
	return 0;
	}
	default:
	return 0;
	}
	}

	int __kprobes arch_prepare_kprobe(struct kprobe *p)
	{
	unsigned long addr = (unsigned long)p->addr;

	if (addr & (sizeof(kprobe_opcode_t) - 1))
	return -EINVAL;

	if (insn_has_control(*p->addr)) {
	pr_notice("Kprobes for control instructions are not supported\n");
	return -EINVAL;
	}

	/* insn: must be on special executable page on tile. */
	p->ainsn.insn = get_insn_slot();
	if (!p->ainsn.insn)
	return -ENOMEM;

	/*
	* In the kprobe->ainsn.insn[] array we store the original
	* instruction at index zero and a break trap instruction at
	* index one.
	*/
	memcpy(&p->ainsn.insn[0], p->addr, sizeof(kprobe_opcode_t));
	p->ainsn.insn[1] = breakpoint2_insn;
	p->opcode = *p->addr;

	return 0;
	}

	void __kprobes arch_arm_kprobe(struct kprobe *p)
	{
	unsigned long addr_wr;

	/* Operate on writable kernel text mapping. */
	addr_wr = ktext_writable_addr(p->addr);

	if (probe_kernel_write((void *)addr_wr, &breakpoint_insn,
	sizeof(breakpoint_insn)))
	pr_err("%s: failed to enable kprobe\n", __func__);

	smp_wmb();
	flush_insn_slot(p);
	}

	void __kprobes arch_disarm_kprobe(struct kprobe *kp)
	{
	unsigned long addr_wr;

	/* Operate on writable kernel text mapping. */
	addr_wr = ktext_writable_addr(kp->addr);

	if (probe_kernel_write((void *)addr_wr, &kp->opcode,
	sizeof(kp->opcode)))
	pr_err("%s: failed to enable kprobe\n", __func__);

	smp_wmb();
	flush_insn_slot(kp);
	}

	void __kprobes arch_remove_kprobe(struct kprobe *p)
	{
	if (p->ainsn.insn) {
	free_insn_slot(p->ainsn.insn, 0);
	p->ainsn.insn = NULL;
	}
	}

	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.saved_pc = kcb->kprobe_saved_pc;
	}

	static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
	{
	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
	kcb->kprobe_status = kcb->prev_kprobe.status;
	kcb->kprobe_saved_pc = kcb->prev_kprobe.saved_pc;
	}

	static void __kprobes set_current_kprobe(struct kprobe p, struct pt_regs regs,
	struct kprobe_ctlblk *kcb)
	{
	__this_cpu_write(current_kprobe, p);
	kcb->kprobe_saved_pc = regs->pc;
	}

	static void __kprobes prepare_singlestep(struct kprobe p, struct pt_regs regs)
	{
	/* Single step inline if the instruction is a break. */
	if (p->opcode == breakpoint_insn \|\|
	p->opcode == breakpoint2_insn)
	regs->pc = (unsigned long)p->addr;
	else
	regs->pc = (unsigned long)&p->ainsn.insn[0];
	}

	static int __kprobes kprobe_handler(struct pt_regs *regs)
	{
	struct kprobe *p;
	int ret = 0;
	kprobe_opcode_t *addr;
	struct kprobe_ctlblk *kcb;

	addr = (kprobe_opcode_t *)regs->pc;

	/*
	* 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[0] == breakpoint_insn) {
	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 {
	if (*addr != breakpoint_insn) {
	/*
	* The breakpoint instruction was removed by
	* another cpu right after we hit, no further
	* handling of this interrupt is appropriate.
	*/
	ret = 1;
	goto no_kprobe;
	}
	p = __this_cpu_read(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_insn) {
	/*
	* 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;
	}

	set_current_kprobe(p, regs, kcb);
	kcb->kprobe_status = KPROBE_HIT_ACTIVE;

	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;
	}

	/*
	* Called after single-stepping. p->addr is the address of the
	* instruction that has been replaced by the breakpoint. 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.
	*
	* This function prepares to return from the post-single-step
	* breakpoint trap.
	*/
	static void __kprobes resume_execution(struct kprobe *p,
	struct pt_regs *regs,
	struct kprobe_ctlblk *kcb)
	{
	unsigned long orig_pc = kcb->kprobe_saved_pc;
	regs->pc = orig_pc + 8;
	}

	static inline int 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, kcb);

	/* 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();

	return 1;
	}

	static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
	{
	struct kprobe *cur = kprobe_running();
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
	return 1;

	if (kcb->kprobe_status & KPROBE_HIT_SS) {
	/*
	* We are here because the instruction being single
	* stepped caused a page fault. We reset the current
	* kprobe and the ip points back to the probe address
	* and allow the page fault handler to continue as a
	* normal page fault.
	*/
	resume_execution(cur, regs, kcb);
	reset_current_kprobe();
	preempt_enable_no_resched();
	}
	return 0;
	}

	/*
	* Wrapper routine 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_BREAK:
	if (kprobe_handler(args->regs))
	ret = NOTIFY_STOP;
	break;
	case DIE_SSTEPBP:
	if (post_kprobe_handler(args->regs))
	ret = NOTIFY_STOP;
	break;
	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);
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	kcb->jprobe_saved_regs = *regs;
	kcb->jprobe_saved_sp = regs->sp;

	memcpy(kcb->jprobes_stack, (void *)kcb->jprobe_saved_sp,
	MIN_JPROBES_STACK_SIZE(kcb->jprobe_saved_sp));

	regs->pc = (unsigned long)(jp->entry);

	return 1;
	}

	/* Defined in the inline asm below. */
	void jprobe_return_end(void);

	void __kprobes jprobe_return(void)
	{
	asm volatile(
	"bpt\n\t"
	".globl jprobe_return_end\n"
	"jprobe_return_end:\n");
	}

	int __kprobes longjmp_break_handler(struct kprobe p, struct pt_regs regs)
	{
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	if (regs->pc >= (unsigned long)jprobe_return &&
	regs->pc <= (unsigned long)jprobe_return_end) {
	*regs = kcb->jprobe_saved_regs;
	memcpy((void *)kcb->jprobe_saved_sp, kcb->jprobes_stack,
	MIN_JPROBES_STACK_SIZE(kcb->jprobe_saved_sp));
	preempt_enable_no_resched();

	return 1;
	}
	return 0;
	}

	/*
	* Function return probe trampoline:
	* - init_kprobes() establishes a probepoint here
	* - When the probed function returns, this probe causes the
	* handlers to fire
	*/
	static void __used kretprobe_trampoline_holder(void)
	{
	asm volatile(
	"nop\n\t"
	".global kretprobe_trampoline\n"
	"kretprobe_trampoline:\n\t"
	"nop\n\t"
	: : : "memory");
	}

	void kretprobe_trampoline(void);

	void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
	struct pt_regs *regs)
	{
	ri->ret_addr = (kprobe_opcode_t *) regs->lr;

	/* Replace the return addr with trampoline addr */
	regs->lr = (unsigned long)kretprobe_trampoline;
	}

	/*
	* Called when the probe at kretprobe trampoline is hit.
	*/
	static int __kprobes trampoline_probe_handler(struct kprobe *p,
	struct pt_regs *regs)
	{
	struct kretprobe_instance *ri = NULL;
	struct hlist_head *head, empty_rp;
	struct hlist_node *tmp;
	unsigned long flags, orig_ret_address = 0;
	unsigned long trampoline_address = (unsigned long)kretprobe_trampoline;

	INIT_HLIST_HEAD(&empty_rp);
	kretprobe_hash_lock(current, &head, &flags);

	/*
	* It is possible to have multiple instances associated with a given
	* task either because multiple functions in the call path have
	* a return probe installed on them, and/or more than 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, 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, &empty_rp);

	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;
	}
	}

	kretprobe_assert(ri, orig_ret_address, trampoline_address);
	instruction_pointer(regs) = orig_ret_address;

	reset_current_kprobe();
	kretprobe_hash_unlock(current, &flags);
	preempt_enable_no_resched();

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

	int __kprobes arch_trampoline_kprobe(struct kprobe *p)
	{
	if (p->addr == (kprobe_opcode_t *)kretprobe_trampoline)
	return 1;

	return 0;
	}

	static struct kprobe trampoline_p = {
	.addr = (kprobe_opcode_t *)kretprobe_trampoline,
	.pre_handler = trampoline_probe_handler
	};

	int __init arch_init_kprobes(void)
	{
	register_kprobe(&trampoline_p);
	return 0;
	}