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

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  *  Kernel Probes (KProbes)
  *  arch/mips/kernel/kprobes.c
  *
  *  Copyright 2006 Sony Corp.
  *  Copyright 2010 Cavium Networks
  *
  *  Some portions copied from the powerpc version.
  *
  *   Copyright (C) IBM Corporation, 2002, 2004
  */

 #include <linux/kprobes.h>
 #include <linux/preempt.h>
 #include <linux/uaccess.h>
 #include <linux/kdebug.h>
 #include <linux/slab.h>

 #include <asm/ptrace.h>
 #include <asm/branch.h>
 #include <asm/break.h>

 #include "probes-common.h"

 static const union mips_instruction breakpoint_insn = {
 	.b_format = {
 		.opcode = spec_op,
 		.code = BRK_KPROBE_BP,
 		.func = break_op
 	}
 };

 static const union mips_instruction breakpoint2_insn = {
 	.b_format = {
 		.opcode = spec_op,
 		.code = BRK_KPROBE_SSTEPBP,
 		.func = break_op
 	}
 };

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

 static int __kprobes insn_has_delayslot(union mips_instruction insn)
 {
 	return __insn_has_delay_slot(insn);
 }

 /*
  * insn_has_ll_or_sc function checks whether instruction is ll or sc
  * one; putting breakpoint on top of atomic ll/sc pair is bad idea;
  * so we need to prevent it and refuse kprobes insertion for such
  * instructions; cannot do much about breakpoint in the middle of
  * ll/sc pair; it is upto user to avoid those places
  */
 static int __kprobes insn_has_ll_or_sc(union mips_instruction insn)
 {
 	int ret = 0;

 	switch (insn.i_format.opcode) {
 	case ll_op:
 	case lld_op:
 	case sc_op:
 	case scd_op:
 		ret = 1;
 		break;
 	default:
 		break;
 	}
 	return ret;
 }

 int __kprobes arch_prepare_kprobe(struct kprobe *p)
 {
 	union mips_instruction insn;
 	union mips_instruction prev_insn;
 	int ret = 0;

 	insn = p->addr[0];

 	if (insn_has_ll_or_sc(insn)) {
 		pr_notice("Kprobes for ll and sc instructions are not"
 			  "supported\n");
 		ret = -EINVAL;
 		goto out;
 	}

 	if (copy_from_kernel_nofault(&prev_insn, p->addr - 1,
 			sizeof(mips_instruction)) == 0 &&
 	    insn_has_delayslot(prev_insn)) {
 		pr_notice("Kprobes for branch delayslot are not supported\n");
 		ret = -EINVAL;
 		goto out;
 	}

 	if (__insn_is_compact_branch(insn)) {
 		pr_notice("Kprobes for compact branches are not supported\n");
 		ret = -EINVAL;
 		goto out;
 	}

 	/* insn: must be on special executable page on mips. */
 	p->ainsn.insn = get_insn_slot();
 	if (!p->ainsn.insn) {
 		ret = -ENOMEM;
 		goto out;
 	}

 	/*
 	 * In the kprobe->ainsn.insn[] array we store the original
 	 * instruction at index zero and a break trap instruction at
 	 * index one.
 	 *
 	 * On MIPS arch if the instruction at probed address is a
 	 * branch instruction, we need to execute the instruction at
 	 * Branch Delayslot (BD) at the time of probe hit. As MIPS also
 	 * doesn't have single stepping support, the BD instruction can
 	 * not be executed in-line and it would be executed on SSOL slot
 	 * using a normal breakpoint instruction in the next slot.
 	 * So, read the instruction and save it for later execution.
 	 */
 	if (insn_has_delayslot(insn))
 		memcpy(&p->ainsn.insn[0], p->addr + 1, sizeof(kprobe_opcode_t));
 	else
 		memcpy(&p->ainsn.insn[0], p->addr, sizeof(kprobe_opcode_t));

 	p->ainsn.insn[1] = breakpoint2_insn;
 	p->opcode = *p->addr;

 out:
 	return ret;
 }

 void __kprobes arch_arm_kprobe(struct kprobe *p)
 {
 	*p->addr = breakpoint_insn;
 	flush_insn_slot(p);
 }

 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 {
 	*p->addr = p->opcode;
 	flush_insn_slot(p);
 }

 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 save_previous_kprobe(struct kprobe_ctlblk *kcb)
 {
 	kcb->prev_kprobe.kp = kprobe_running();
 	kcb->prev_kprobe.status = kcb->kprobe_status;
 	kcb->prev_kprobe.old_SR = kcb->kprobe_old_SR;
 	kcb->prev_kprobe.saved_SR = kcb->kprobe_saved_SR;
 	kcb->prev_kprobe.saved_epc = kcb->kprobe_saved_epc;
 }

 static void 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_old_SR = kcb->prev_kprobe.old_SR;
 	kcb->kprobe_saved_SR = kcb->prev_kprobe.saved_SR;
 	kcb->kprobe_saved_epc = kcb->prev_kprobe.saved_epc;
 }

 static void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 			       struct kprobe_ctlblk *kcb)
 {
 	__this_cpu_write(current_kprobe, p);
 	kcb->kprobe_saved_SR = kcb->kprobe_old_SR = (regs->cp0_status & ST0_IE);
 	kcb->kprobe_saved_epc = regs->cp0_epc;
 }

 /**
  * evaluate_branch_instrucion -
  *
  * Evaluate the branch instruction at probed address during probe hit. The
  * result of evaluation would be the updated epc. The insturction in delayslot
  * would actually be single stepped using a normal breakpoint) on SSOL slot.
  *
  * The result is also saved in the kprobe control block for later use,
  * in case we need to execute the delayslot instruction. The latter will be
  * false for NOP instruction in dealyslot and the branch-likely instructions
  * when the branch is taken. And for those cases we set a flag as
  * SKIP_DELAYSLOT in the kprobe control block
  */
 static int evaluate_branch_instruction(struct kprobe *p, struct pt_regs *regs,
 					struct kprobe_ctlblk *kcb)
 {
 	union mips_instruction insn = p->opcode;
 	long epc;
 	int ret = 0;

 	epc = regs->cp0_epc;
 	if (epc & 3)
 		goto unaligned;

 	if (p->ainsn.insn->word == 0)
 		kcb->flags |= SKIP_DELAYSLOT;
 	else
 		kcb->flags &= ~SKIP_DELAYSLOT;

 	ret = __compute_return_epc_for_insn(regs, insn);
 	if (ret < 0)
 		return ret;

 	if (ret == BRANCH_LIKELY_TAKEN)
 		kcb->flags |= SKIP_DELAYSLOT;

 	kcb->target_epc = regs->cp0_epc;

 	return 0;

 unaligned:
 	pr_notice("%s: unaligned epc - sending SIGBUS.\n", current->comm);
 	force_sig(SIGBUS);
 	return -EFAULT;

 }

 static void prepare_singlestep(struct kprobe *p, struct pt_regs *regs,
 						struct kprobe_ctlblk *kcb)
 {
 	int ret = 0;

 	regs->cp0_status &= ~ST0_IE;

 	/* single step inline if the instruction is a break */
 	if (p->opcode.word == breakpoint_insn.word ||
 	    p->opcode.word == breakpoint2_insn.word)
 		regs->cp0_epc = (unsigned long)p->addr;
 	else if (insn_has_delayslot(p->opcode)) {
 		ret = evaluate_branch_instruction(p, regs, kcb);
 		if (ret < 0) {
 			pr_notice("Kprobes: Error in evaluating branch\n");
 			return;
 		}
 	}
 	regs->cp0_epc = (unsigned long)&p->ainsn.insn[0];
 }

 /*
  * Called after single-stepping.  p->addr is the address of the
  * instruction whose first byte has been replaced by the "break 0"
  * 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.
  *
  * This function prepares to return from the post-single-step
  * breakpoint trap. In case of branch instructions, the target
  * epc to be restored.
  */
 static void __kprobes resume_execution(struct kprobe *p,
 				       struct pt_regs *regs,
 				       struct kprobe_ctlblk *kcb)
 {
 	if (insn_has_delayslot(p->opcode))
 		regs->cp0_epc = kcb->target_epc;
 	else {
 		unsigned long orig_epc = kcb->kprobe_saved_epc;
 		regs->cp0_epc = orig_epc + 4;
 	}
 }

 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->cp0_epc;

 	/*
 	 * 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->word == breakpoint_insn.word) {
 				regs->cp0_status &= ~ST0_IE;
 				regs->cp0_status |= kcb->kprobe_saved_SR;
 				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);
 			kcb->kprobe_status = KPROBE_REENTER;
 			if (kcb->flags & SKIP_DELAYSLOT) {
 				resume_execution(p, regs, kcb);
 				restore_previous_kprobe(kcb);
 				preempt_enable_no_resched();
 			}
 			return 1;
 		} else if (addr->word != breakpoint_insn.word) {
 			/*
 			 * 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 = get_kprobe(addr);
 	if (!p) {
 		if (addr->word != breakpoint_insn.word) {
 			/*
 			 * 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 */
 		reset_current_kprobe();
 		preempt_enable_no_resched();
 		return 1;
 	}

 	prepare_singlestep(p, regs, kcb);
 	if (kcb->flags & SKIP_DELAYSLOT) {
 		kcb->kprobe_status = KPROBE_HIT_SSDONE;
 		if (p->post_handler)
 			p->post_handler(p, regs, 0);
 		resume_execution(p, regs, kcb);
 		preempt_enable_no_resched();
 	} else
 		kcb->kprobe_status = KPROBE_HIT_SS;

 	return 1;

 no_kprobe:
 	preempt_enable_no_resched();
 	return ret;

 }

 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);

 	regs->cp0_status |= kcb->kprobe_saved_SR;

 	/* 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;
 }

 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) {
 		resume_execution(cur, regs, kcb);
 		regs->cp0_status |= kcb->kprobe_old_SR;

 		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;
 }

 /*
  * 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(
 		".set push\n\t"
 		/* Keep the assembler from reordering and placing JR here. */
 		".set noreorder\n\t"
 		"nop\n\t"
 		".global kretprobe_trampoline\n"
 		"kretprobe_trampoline:\n\t"
 		"nop\n\t"
 		".set pop"
 		: : : "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->regs[31];
 	ri->fp = NULL;

 	/* Replace the return addr with trampoline addr */
 	regs->regs[31] = (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)
 {
 	instruction_pointer(regs) = __kretprobe_trampoline_handler(regs,
 						kretprobe_trampoline, NULL);
 	/*
 	 * 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)
 {
 	return register_kprobe(&trampoline_p);
 }
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* Kernel Probes (KProbes)
	* arch/mips/kernel/kprobes.c
	*
	* Copyright 2006 Sony Corp.
	* Copyright 2010 Cavium Networks
	*
	* Some portions copied from the powerpc version.
	*
	* Copyright (C) IBM Corporation, 2002, 2004
	*/

	#include <linux/kprobes.h>
	#include <linux/preempt.h>
	#include <linux/uaccess.h>
	#include <linux/kdebug.h>
	#include <linux/slab.h>

	#include <asm/ptrace.h>
	#include <asm/branch.h>
	#include <asm/break.h>

	#include "probes-common.h"

	static const union mips_instruction breakpoint_insn = {
	.b_format = {
	.opcode = spec_op,
	.code = BRK_KPROBE_BP,
	.func = break_op
	}
	};

	static const union mips_instruction breakpoint2_insn = {
	.b_format = {
	.opcode = spec_op,
	.code = BRK_KPROBE_SSTEPBP,
	.func = break_op
	}
	};

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

	static int __kprobes insn_has_delayslot(union mips_instruction insn)
	{
	return __insn_has_delay_slot(insn);
	}

	/*
	* insn_has_ll_or_sc function checks whether instruction is ll or sc
	* one; putting breakpoint on top of atomic ll/sc pair is bad idea;
	* so we need to prevent it and refuse kprobes insertion for such
	* instructions; cannot do much about breakpoint in the middle of
	* ll/sc pair; it is upto user to avoid those places
	*/
	static int __kprobes insn_has_ll_or_sc(union mips_instruction insn)
	{
	int ret = 0;

	switch (insn.i_format.opcode) {
	case ll_op:
	case lld_op:
	case sc_op:
	case scd_op:
	ret = 1;
	break;
	default:
	break;
	}
	return ret;
	}

	int __kprobes arch_prepare_kprobe(struct kprobe *p)
	{
	union mips_instruction insn;
	union mips_instruction prev_insn;
	int ret = 0;

	insn = p->addr[0];

	if (insn_has_ll_or_sc(insn)) {
	pr_notice("Kprobes for ll and sc instructions are not"
	"supported\n");
	ret = -EINVAL;
	goto out;
	}

	if (copy_from_kernel_nofault(&prev_insn, p->addr - 1,
	sizeof(mips_instruction)) == 0 &&
	insn_has_delayslot(prev_insn)) {
	pr_notice("Kprobes for branch delayslot are not supported\n");
	ret = -EINVAL;
	goto out;
	}

	if (__insn_is_compact_branch(insn)) {
	pr_notice("Kprobes for compact branches are not supported\n");
	ret = -EINVAL;
	goto out;
	}

	/* insn: must be on special executable page on mips. */
	p->ainsn.insn = get_insn_slot();
	if (!p->ainsn.insn) {
	ret = -ENOMEM;
	goto out;
	}

	/*
	* In the kprobe->ainsn.insn[] array we store the original
	* instruction at index zero and a break trap instruction at
	* index one.
	*
	* On MIPS arch if the instruction at probed address is a
	* branch instruction, we need to execute the instruction at
	* Branch Delayslot (BD) at the time of probe hit. As MIPS also
	* doesn't have single stepping support, the BD instruction can
	* not be executed in-line and it would be executed on SSOL slot
	* using a normal breakpoint instruction in the next slot.
	* So, read the instruction and save it for later execution.
	*/
	if (insn_has_delayslot(insn))
	memcpy(&p->ainsn.insn[0], p->addr + 1, sizeof(kprobe_opcode_t));
	else
	memcpy(&p->ainsn.insn[0], p->addr, sizeof(kprobe_opcode_t));

	p->ainsn.insn[1] = breakpoint2_insn;
	p->opcode = *p->addr;

	out:
	return ret;
	}

	void __kprobes arch_arm_kprobe(struct kprobe *p)
	{
	*p->addr = breakpoint_insn;
	flush_insn_slot(p);
	}

	void __kprobes arch_disarm_kprobe(struct kprobe *p)
	{
	*p->addr = p->opcode;
	flush_insn_slot(p);
	}

	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 save_previous_kprobe(struct kprobe_ctlblk *kcb)
	{
	kcb->prev_kprobe.kp = kprobe_running();
	kcb->prev_kprobe.status = kcb->kprobe_status;
	kcb->prev_kprobe.old_SR = kcb->kprobe_old_SR;
	kcb->prev_kprobe.saved_SR = kcb->kprobe_saved_SR;
	kcb->prev_kprobe.saved_epc = kcb->kprobe_saved_epc;
	}

	static void 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_old_SR = kcb->prev_kprobe.old_SR;
	kcb->kprobe_saved_SR = kcb->prev_kprobe.saved_SR;
	kcb->kprobe_saved_epc = kcb->prev_kprobe.saved_epc;
	}

	static void set_current_kprobe(struct kprobe p, struct pt_regs regs,
	struct kprobe_ctlblk *kcb)
	{
	__this_cpu_write(current_kprobe, p);
	kcb->kprobe_saved_SR = kcb->kprobe_old_SR = (regs->cp0_status & ST0_IE);
	kcb->kprobe_saved_epc = regs->cp0_epc;
	}

	/**
	* evaluate_branch_instrucion -
	*
	* Evaluate the branch instruction at probed address during probe hit. The
	* result of evaluation would be the updated epc. The insturction in delayslot
	* would actually be single stepped using a normal breakpoint) on SSOL slot.
	*
	* The result is also saved in the kprobe control block for later use,
	* in case we need to execute the delayslot instruction. The latter will be
	* false for NOP instruction in dealyslot and the branch-likely instructions
	* when the branch is taken. And for those cases we set a flag as
	* SKIP_DELAYSLOT in the kprobe control block
	*/
	static int evaluate_branch_instruction(struct kprobe p, struct pt_regs regs,
	struct kprobe_ctlblk *kcb)
	{
	union mips_instruction insn = p->opcode;
	long epc;
	int ret = 0;

	epc = regs->cp0_epc;
	if (epc & 3)
	goto unaligned;

	if (p->ainsn.insn->word == 0)
	kcb->flags \|= SKIP_DELAYSLOT;
	else
	kcb->flags &= ~SKIP_DELAYSLOT;

	ret = __compute_return_epc_for_insn(regs, insn);
	if (ret < 0)
	return ret;

	if (ret == BRANCH_LIKELY_TAKEN)
	kcb->flags \|= SKIP_DELAYSLOT;

	kcb->target_epc = regs->cp0_epc;

	return 0;

	unaligned:
	pr_notice("%s: unaligned epc - sending SIGBUS.\n", current->comm);
	force_sig(SIGBUS);
	return -EFAULT;

	}

	static void prepare_singlestep(struct kprobe p, struct pt_regs regs,
	struct kprobe_ctlblk *kcb)
	{
	int ret = 0;

	regs->cp0_status &= ~ST0_IE;

	/* single step inline if the instruction is a break */
	if (p->opcode.word == breakpoint_insn.word \|\|
	p->opcode.word == breakpoint2_insn.word)
	regs->cp0_epc = (unsigned long)p->addr;
	else if (insn_has_delayslot(p->opcode)) {
	ret = evaluate_branch_instruction(p, regs, kcb);
	if (ret < 0) {
	pr_notice("Kprobes: Error in evaluating branch\n");
	return;
	}
	}
	regs->cp0_epc = (unsigned long)&p->ainsn.insn[0];
	}

	/*
	* Called after single-stepping. p->addr is the address of the
	* instruction whose first byte has been replaced by the "break 0"
	* 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.
	*
	* This function prepares to return from the post-single-step
	* breakpoint trap. In case of branch instructions, the target
	* epc to be restored.
	*/
	static void __kprobes resume_execution(struct kprobe *p,
	struct pt_regs *regs,
	struct kprobe_ctlblk *kcb)
	{
	if (insn_has_delayslot(p->opcode))
	regs->cp0_epc = kcb->target_epc;
	else {
	unsigned long orig_epc = kcb->kprobe_saved_epc;
	regs->cp0_epc = orig_epc + 4;
	}
	}

	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->cp0_epc;

	/*
	* 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->word == breakpoint_insn.word) {
	regs->cp0_status &= ~ST0_IE;
	regs->cp0_status \|= kcb->kprobe_saved_SR;
	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);
	kcb->kprobe_status = KPROBE_REENTER;
	if (kcb->flags & SKIP_DELAYSLOT) {
	resume_execution(p, regs, kcb);
	restore_previous_kprobe(kcb);
	preempt_enable_no_resched();
	}
	return 1;
	} else if (addr->word != breakpoint_insn.word) {
	/*
	* 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 = get_kprobe(addr);
	if (!p) {
	if (addr->word != breakpoint_insn.word) {
	/*
	* 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 */
	reset_current_kprobe();
	preempt_enable_no_resched();
	return 1;
	}

	prepare_singlestep(p, regs, kcb);
	if (kcb->flags & SKIP_DELAYSLOT) {
	kcb->kprobe_status = KPROBE_HIT_SSDONE;
	if (p->post_handler)
	p->post_handler(p, regs, 0);
	resume_execution(p, regs, kcb);
	preempt_enable_no_resched();
	} else
	kcb->kprobe_status = KPROBE_HIT_SS;

	return 1;

	no_kprobe:
	preempt_enable_no_resched();
	return ret;

	}

	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);

	regs->cp0_status \|= kcb->kprobe_saved_SR;

	/* 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;
	}

	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) {
	resume_execution(cur, regs, kcb);
	regs->cp0_status \|= kcb->kprobe_old_SR;

	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;
	}

	/*
	* 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(
	".set push\n\t"
	/* Keep the assembler from reordering and placing JR here. */
	".set noreorder\n\t"
	"nop\n\t"
	".global kretprobe_trampoline\n"
	"kretprobe_trampoline:\n\t"
	"nop\n\t"
	".set pop"
	: : : "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->regs[31];
	ri->fp = NULL;

	/* Replace the return addr with trampoline addr */
	regs->regs[31] = (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)
	{
	instruction_pointer(regs) = __kretprobe_trampoline_handler(regs,
	kretprobe_trampoline, NULL);
	/*
	* 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)
	{
	return register_kprobe(&trampoline_p);
	}