arch/powerpc/kernel/kprobes.c - arm/linux - Git at Google

 /*
  *  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, 2004
  *
  * 2002-Oct	Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
  *		Probes initial implementation ( includes contributions from
  *		Rusty Russell).
  * 2004-July	Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
  *		interface to access function arguments.
  * 2004-Nov	Ananth N Mavinakayanahalli <ananth@in.ibm.com> kprobes port
  *		for PPC64
  */

 #include <linux/kprobes.h>
 #include <linux/ptrace.h>
 #include <linux/preempt.h>
 #include <linux/module.h>
 #include <linux/kdebug.h>
 #include <linux/slab.h>
 #include <asm/cacheflush.h>
 #include <asm/sstep.h>
 #include <asm/uaccess.h>
 #include <asm/system.h>

 #ifdef CONFIG_PPC_ADV_DEBUG_REGS
 #define MSR_SINGLESTEP	(MSR_DE)
 #else
 #define MSR_SINGLESTEP	(MSR_SE)
 #endif

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

 struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};

 int __kprobes arch_prepare_kprobe(struct kprobe *p)
 {
 	int ret = 0;
 	kprobe_opcode_t insn = *p->addr;

 	if ((unsigned long)p->addr & 0x03) {
 		printk("Attempt to register kprobe at an unaligned address\n");
 		ret = -EINVAL;
 	} else if (IS_MTMSRD(insn) || IS_RFID(insn) || IS_RFI(insn)) {
 		printk("Cannot register a kprobe on rfi/rfid or mtmsr[d]\n");
 		ret = -EINVAL;
 	}

 	/* insn must be on a special executable page on ppc64.  This is
 	 * not explicitly required on ppc32 (right now), but it doesn't hurt */
 	if (!ret) {
 		p->ainsn.insn = get_insn_slot();
 		if (!p->ainsn.insn)
 			ret = -ENOMEM;
 	}

 	if (!ret) {
 		memcpy(p->ainsn.insn, p->addr,
 				MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
 		p->opcode = *p->addr;
 		flush_icache_range((unsigned long)p->ainsn.insn,
 			(unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
 	}

 	p->ainsn.boostable = 0;
 	return ret;
 }

 void __kprobes arch_arm_kprobe(struct kprobe *p)
 {
 	*p->addr = BREAKPOINT_INSTRUCTION;
 	flush_icache_range((unsigned long) p->addr,
 			   (unsigned long) p->addr + sizeof(kprobe_opcode_t));
 }

 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 {
 	*p->addr = p->opcode;
 	flush_icache_range((unsigned long) p->addr,
 			   (unsigned long) p->addr + sizeof(kprobe_opcode_t));
 }

 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 prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 {
 	/* We turn off async exceptions to ensure that the single step will
 	 * be for the instruction we have the kprobe on, if we dont its
 	 * possible we'd get the single step reported for an exception handler
 	 * like Decrementer or External Interrupt */
 	regs->msr &= ~MSR_EE;
 	regs->msr |= MSR_SINGLESTEP;
 #ifdef CONFIG_PPC_ADV_DEBUG_REGS
 	regs->msr &= ~MSR_CE;
 	mtspr(SPRN_DBCR0, mfspr(SPRN_DBCR0) | DBCR0_IC | DBCR0_IDM);
 #endif

 	/*
 	 * On powerpc we should single step on the original
 	 * instruction even if the probed insn is a trap
 	 * variant as values in regs could play a part in
 	 * if the trap is taken or not
 	 */
 	regs->nip = (unsigned long)p->ainsn.insn;
 }

 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_msr = kcb->kprobe_saved_msr;
 }

 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_msr = kcb->prev_kprobe.saved_msr;
 }

 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 				struct kprobe_ctlblk *kcb)
 {
 	__get_cpu_var(current_kprobe) = p;
 	kcb->kprobe_saved_msr = regs->msr;
 }

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

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

 static int __kprobes kprobe_handler(struct pt_regs *regs)
 {
 	struct kprobe *p;
 	int ret = 0;
 	unsigned int *addr = (unsigned int *)regs->nip;
 	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) {
 			kprobe_opcode_t insn = *p->ainsn.insn;
 			if (kcb->kprobe_status == KPROBE_HIT_SS &&
 					is_trap(insn)) {
 				/* Turn off 'trace' bits */
 				regs->msr &= ~MSR_SINGLESTEP;
 				regs->msr |= kcb->kprobe_saved_msr;
 				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);
 			kcb->kprobe_saved_msr = regs->msr;
 			kprobes_inc_nmissed_count(p);
 			prepare_singlestep(p, regs);
 			kcb->kprobe_status = KPROBE_REENTER;
 			return 1;
 		} else {
 			if (*addr != BREAKPOINT_INSTRUCTION) {
 				/* If trap variant, then it belongs not to us */
 				kprobe_opcode_t cur_insn = *addr;
 				if (is_trap(cur_insn))
 		       			goto no_kprobe;
 				/* 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_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) {
 			/*
 			 * PowerPC has multiple variants of the "trap"
 			 * instruction. If the current instruction is a
 			 * trap variant, it could belong to someone else
 			 */
 			kprobe_opcode_t cur_insn = *addr;
 			if (is_trap(cur_insn))
 		       		goto no_kprobe;
 			/*
 			 * 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:
 	if (p->ainsn.boostable >= 0) {
 		unsigned int insn = *p->ainsn.insn;

 		/* regs->nip is also adjusted if emulate_step returns 1 */
 		ret = emulate_step(regs, insn);
 		if (ret > 0) {
 			/*
 			 * Once this instruction has been boosted
 			 * successfully, set the boostable flag
 			 */
 			if (unlikely(p->ainsn.boostable == 0))
 				p->ainsn.boostable = 1;

 			if (p->post_handler)
 				p->post_handler(p, regs, 0);

 			kcb->kprobe_status = KPROBE_HIT_SSDONE;
 			reset_current_kprobe();
 			preempt_enable_no_resched();
 			return 1;
 		} else if (ret < 0) {
 			/*
 			 * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
 			 * So, we should never get here... but, its still
 			 * good to catch them, just in case...
 			 */
 			printk("Can't step on instruction %x\n", insn);
 			BUG();
 		} else if (ret == 0)
 			/* This instruction can't be boosted */
 			p->ainsn.boostable = -1;
 	}
 	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
  */
 static void __used kretprobe_trampoline_holder(void)
 {
 	asm volatile(".global kretprobe_trampoline\n"
 			"kretprobe_trampoline:\n"
 			"nop\n");
 }

 /*
  * 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 *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 an 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, 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, &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);
 	regs->nip = orig_ret_address;

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

 	hlist_for_each_entry_safe(ri, node, 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;
 }

 /*
  * 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)
 {
 	int ret;
 	unsigned int insn = *p->ainsn.insn;

 	regs->nip = (unsigned long)p->addr;
 	ret = emulate_step(regs, insn);
 	if (ret == 0)
 		regs->nip = (unsigned long)p->addr + 4;
 }

 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;

 	/* make sure we got here for instruction we have a kprobe on */
 	if (((unsigned long)cur->ainsn.insn + 4) != regs->nip)
 		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);
 	regs->msr |= kcb->kprobe_saved_msr;

 	/*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, msr
 	 * will have DE/SE set, in which case, continue the remaining processing
 	 * of do_debug, as if this is not a probe hit.
 	 */
 	if (regs->msr & MSR_SINGLESTEP)
 		return 0;

 	return 1;
 }

 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_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->nip = (unsigned long)cur->addr;
 		regs->msr &= ~MSR_SINGLESTEP; /* Turn off 'trace' bits */
 		regs->msr |= kcb->kprobe_saved_msr;
 		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.
 		 */
 		if ((entry = search_exception_tables(regs->nip)) != NULL) {
 			regs->nip = entry->fixup;
 			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;

 	if (args->regs && user_mode(args->regs))
 		return ret;

 	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;
 	default:
 		break;
 	}
 	return ret;
 }

 #ifdef CONFIG_PPC64
 unsigned long arch_deref_entry_point(void *entry)
 {
 	return ((func_descr_t *)entry)->entry;
 }
 #endif

 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();

 	memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));

 	/* setup return addr to the jprobe handler routine */
 	regs->nip = arch_deref_entry_point(jp->entry);
 #ifdef CONFIG_PPC64
 	regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
 #endif

 	return 1;
 }

 void __used __kprobes jprobe_return(void)
 {
 	asm volatile("trap" ::: "memory");
 }

 static void __used __kprobes jprobe_return_end(void)
 {
 };

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

 	/*
 	 * FIXME - we should ideally be validating that we got here 'cos
 	 * of the "trap" in jprobe_return() above, before restoring the
 	 * saved regs...
 	 */
 	memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
 	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);
 }

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

 	return 0;
 }
	/*
	* 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, 2004
	*
	* 2002-Oct Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
	* Probes initial implementation ( includes contributions from
	* Rusty Russell).
	* 2004-July Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
	* interface to access function arguments.
	* 2004-Nov Ananth N Mavinakayanahalli <ananth@in.ibm.com> kprobes port
	* for PPC64
	*/

	#include <linux/kprobes.h>
	#include <linux/ptrace.h>
	#include <linux/preempt.h>
	#include <linux/module.h>
	#include <linux/kdebug.h>
	#include <linux/slab.h>
	#include <asm/cacheflush.h>
	#include <asm/sstep.h>
	#include <asm/uaccess.h>
	#include <asm/system.h>

	#ifdef CONFIG_PPC_ADV_DEBUG_REGS
	#define MSR_SINGLESTEP (MSR_DE)
	#else
	#define MSR_SINGLESTEP (MSR_SE)
	#endif

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

	struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};

	int __kprobes arch_prepare_kprobe(struct kprobe *p)
	{
	int ret = 0;
	kprobe_opcode_t insn = *p->addr;

	if ((unsigned long)p->addr & 0x03) {
	printk("Attempt to register kprobe at an unaligned address\n");
	ret = -EINVAL;
	} else if (IS_MTMSRD(insn) \|\| IS_RFID(insn) \|\| IS_RFI(insn)) {
	printk("Cannot register a kprobe on rfi/rfid or mtmsr[d]\n");
	ret = -EINVAL;
	}

	/* insn must be on a special executable page on ppc64. This is
	* not explicitly required on ppc32 (right now), but it doesn't hurt */
	if (!ret) {
	p->ainsn.insn = get_insn_slot();
	if (!p->ainsn.insn)
	ret = -ENOMEM;
	}

	if (!ret) {
	memcpy(p->ainsn.insn, p->addr,
	MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
	p->opcode = *p->addr;
	flush_icache_range((unsigned long)p->ainsn.insn,
	(unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
	}

	p->ainsn.boostable = 0;
	return ret;
	}

	void __kprobes arch_arm_kprobe(struct kprobe *p)
	{
	*p->addr = BREAKPOINT_INSTRUCTION;
	flush_icache_range((unsigned long) p->addr,
	(unsigned long) p->addr + sizeof(kprobe_opcode_t));
	}

	void __kprobes arch_disarm_kprobe(struct kprobe *p)
	{
	*p->addr = p->opcode;
	flush_icache_range((unsigned long) p->addr,
	(unsigned long) p->addr + sizeof(kprobe_opcode_t));
	}

	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 prepare_singlestep(struct kprobe p, struct pt_regs regs)
	{
	/* We turn off async exceptions to ensure that the single step will
	* be for the instruction we have the kprobe on, if we dont its
	* possible we'd get the single step reported for an exception handler
	* like Decrementer or External Interrupt */
	regs->msr &= ~MSR_EE;
	regs->msr \|= MSR_SINGLESTEP;
	#ifdef CONFIG_PPC_ADV_DEBUG_REGS
	regs->msr &= ~MSR_CE;
	mtspr(SPRN_DBCR0, mfspr(SPRN_DBCR0) \| DBCR0_IC \| DBCR0_IDM);
	#endif

	/*
	* On powerpc we should single step on the original
	* instruction even if the probed insn is a trap
	* variant as values in regs could play a part in
	* if the trap is taken or not
	*/
	regs->nip = (unsigned long)p->ainsn.insn;
	}

	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_msr = kcb->kprobe_saved_msr;
	}

	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_msr = kcb->prev_kprobe.saved_msr;
	}

	static void __kprobes set_current_kprobe(struct kprobe p, struct pt_regs regs,
	struct kprobe_ctlblk *kcb)
	{
	__get_cpu_var(current_kprobe) = p;
	kcb->kprobe_saved_msr = regs->msr;
	}

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

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

	static int __kprobes kprobe_handler(struct pt_regs *regs)
	{
	struct kprobe *p;
	int ret = 0;
	unsigned int addr = (unsigned int )regs->nip;
	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) {
	kprobe_opcode_t insn = *p->ainsn.insn;
	if (kcb->kprobe_status == KPROBE_HIT_SS &&
	is_trap(insn)) {
	/* Turn off 'trace' bits */
	regs->msr &= ~MSR_SINGLESTEP;
	regs->msr \|= kcb->kprobe_saved_msr;
	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);
	kcb->kprobe_saved_msr = regs->msr;
	kprobes_inc_nmissed_count(p);
	prepare_singlestep(p, regs);
	kcb->kprobe_status = KPROBE_REENTER;
	return 1;
	} else {
	if (*addr != BREAKPOINT_INSTRUCTION) {
	/* If trap variant, then it belongs not to us */
	kprobe_opcode_t cur_insn = *addr;
	if (is_trap(cur_insn))
	goto no_kprobe;
	/* 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_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) {
	/*
	* PowerPC has multiple variants of the "trap"
	* instruction. If the current instruction is a
	* trap variant, it could belong to someone else
	*/
	kprobe_opcode_t cur_insn = *addr;
	if (is_trap(cur_insn))
	goto no_kprobe;
	/*
	* 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:
	if (p->ainsn.boostable >= 0) {
	unsigned int insn = *p->ainsn.insn;

	/* regs->nip is also adjusted if emulate_step returns 1 */
	ret = emulate_step(regs, insn);
	if (ret > 0) {
	/*
	* Once this instruction has been boosted
	* successfully, set the boostable flag
	*/
	if (unlikely(p->ainsn.boostable == 0))
	p->ainsn.boostable = 1;

	if (p->post_handler)
	p->post_handler(p, regs, 0);

	kcb->kprobe_status = KPROBE_HIT_SSDONE;
	reset_current_kprobe();
	preempt_enable_no_resched();
	return 1;
	} else if (ret < 0) {
	/*
	* We don't allow kprobes on mtmsr(d)/rfi(d), etc.
	* So, we should never get here... but, its still
	* good to catch them, just in case...
	*/
	printk("Can't step on instruction %x\n", insn);
	BUG();
	} else if (ret == 0)
	/* This instruction can't be boosted */
	p->ainsn.boostable = -1;
	}
	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
	*/
	static void __used kretprobe_trampoline_holder(void)
	{
	asm volatile(".global kretprobe_trampoline\n"
	"kretprobe_trampoline:\n"
	"nop\n");
	}

	/*
	* 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 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 an 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, 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, &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);
	regs->nip = orig_ret_address;

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

	hlist_for_each_entry_safe(ri, node, 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;
	}

	/*
	* 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)
	{
	int ret;
	unsigned int insn = *p->ainsn.insn;

	regs->nip = (unsigned long)p->addr;
	ret = emulate_step(regs, insn);
	if (ret == 0)
	regs->nip = (unsigned long)p->addr + 4;
	}

	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;

	/* make sure we got here for instruction we have a kprobe on */
	if (((unsigned long)cur->ainsn.insn + 4) != regs->nip)
	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);
	regs->msr \|= kcb->kprobe_saved_msr;

	/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, msr
	* will have DE/SE set, in which case, continue the remaining processing
	* of do_debug, as if this is not a probe hit.
	*/
	if (regs->msr & MSR_SINGLESTEP)
	return 0;

	return 1;
	}

	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_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->nip = (unsigned long)cur->addr;
	regs->msr &= ~MSR_SINGLESTEP; /* Turn off 'trace' bits */
	regs->msr \|= kcb->kprobe_saved_msr;
	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.
	*/
	if ((entry = search_exception_tables(regs->nip)) != NULL) {
	regs->nip = entry->fixup;
	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;

	if (args->regs && user_mode(args->regs))
	return ret;

	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;
	default:
	break;
	}
	return ret;
	}

	#ifdef CONFIG_PPC64
	unsigned long arch_deref_entry_point(void *entry)
	{
	return ((func_descr_t *)entry)->entry;
	}
	#endif

	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();

	memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));

	/* setup return addr to the jprobe handler routine */
	regs->nip = arch_deref_entry_point(jp->entry);
	#ifdef CONFIG_PPC64
	regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
	#endif

	return 1;
	}

	void __used __kprobes jprobe_return(void)
	{
	asm volatile("trap" ::: "memory");
	}

	static void __used __kprobes jprobe_return_end(void)
	{
	};

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

	/*
	* FIXME - we should ideally be validating that we got here 'cos
	* of the "trap" in jprobe_return() above, before restoring the
	* saved regs...
	*/
	memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
	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);
	}

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

	return 0;
	}