arch/arc/kernel/kprobes.c - virt/kvm/kvm - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
  */

 #include <linux/types.h>
 #include <linux/kprobes.h>
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <linux/kdebug.h>
 #include <linux/sched.h>
 #include <linux/uaccess.h>
 #include <asm/cacheflush.h>
 #include <asm/current.h>
 #include <asm/disasm.h>

 #define MIN_STACK_SIZE(addr)	min((unsigned long)MAX_STACK_SIZE, \
 		(unsigned long)current_thread_info() + THREAD_SIZE - (addr))

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

 int __kprobes arch_prepare_kprobe(struct kprobe *p)
 {
 	/* Attempt to probe at unaligned address */
 	if ((unsigned long)p->addr & 0x01)
 		return -EINVAL;

 	/* Address should not be in exception handling code */

 	p->ainsn.is_short = is_short_instr((unsigned long)p->addr);
 	p->opcode = *p->addr;

 	return 0;
 }

 void __kprobes arch_arm_kprobe(struct kprobe *p)
 {
 	*p->addr = UNIMP_S_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)
 {
 	arch_disarm_kprobe(p);

 	/* Can we remove the kprobe in the middle of kprobe handling? */
 	if (p->ainsn.t1_addr) {
 		*(p->ainsn.t1_addr) = p->ainsn.t1_opcode;

 		flush_icache_range((unsigned long)p->ainsn.t1_addr,
 				   (unsigned long)p->ainsn.t1_addr +
 				   sizeof(kprobe_opcode_t));

 		p->ainsn.t1_addr = NULL;
 	}

 	if (p->ainsn.t2_addr) {
 		*(p->ainsn.t2_addr) = p->ainsn.t2_opcode;

 		flush_icache_range((unsigned long)p->ainsn.t2_addr,
 				   (unsigned long)p->ainsn.t2_addr +
 				   sizeof(kprobe_opcode_t));

 		p->ainsn.t2_addr = NULL;
 	}
 }

 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 {
 	kcb->prev_kprobe.kp = kprobe_running();
 	kcb->prev_kprobe.status = kcb->kprobe_status;
 }

 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;
 }

 static inline void __kprobes set_current_kprobe(struct kprobe *p)
 {
 	__this_cpu_write(current_kprobe, p);
 }

 static void __kprobes resume_execution(struct kprobe *p, unsigned long addr,
 				       struct pt_regs *regs)
 {
 	/* Remove the trap instructions inserted for single step and
 	 * restore the original instructions
 	 */
 	if (p->ainsn.t1_addr) {
 		*(p->ainsn.t1_addr) = p->ainsn.t1_opcode;

 		flush_icache_range((unsigned long)p->ainsn.t1_addr,
 				   (unsigned long)p->ainsn.t1_addr +
 				   sizeof(kprobe_opcode_t));

 		p->ainsn.t1_addr = NULL;
 	}

 	if (p->ainsn.t2_addr) {
 		*(p->ainsn.t2_addr) = p->ainsn.t2_opcode;

 		flush_icache_range((unsigned long)p->ainsn.t2_addr,
 				   (unsigned long)p->ainsn.t2_addr +
 				   sizeof(kprobe_opcode_t));

 		p->ainsn.t2_addr = NULL;
 	}

 	return;
 }

 static void __kprobes setup_singlestep(struct kprobe *p, struct pt_regs *regs)
 {
 	unsigned long next_pc;
 	unsigned long tgt_if_br = 0;
 	int is_branch;
 	unsigned long bta;

 	/* Copy the opcode back to the kprobe location and execute the
 	 * instruction. Because of this we will not be able to get into the
 	 * same kprobe until this kprobe is done
 	 */
 	*(p->addr) = p->opcode;

 	flush_icache_range((unsigned long)p->addr,
 			   (unsigned long)p->addr + sizeof(kprobe_opcode_t));

 	/* Now we insert the trap at the next location after this instruction to
 	 * single step. If it is a branch we insert the trap at possible branch
 	 * targets
 	 */

 	bta = regs->bta;

 	if (regs->status32 & 0x40) {
 		/* We are in a delay slot with the branch taken */

 		next_pc = bta & ~0x01;

 		if (!p->ainsn.is_short) {
 			if (bta & 0x01)
 				regs->blink += 2;
 			else {
 				/* Branch not taken */
 				next_pc += 2;

 				/* next pc is taken from bta after executing the
 				 * delay slot instruction
 				 */
 				regs->bta += 2;
 			}
 		}

 		is_branch = 0;
 	} else
 		is_branch =
 		    disasm_next_pc((unsigned long)p->addr, regs,
 			(struct callee_regs *) current->thread.callee_reg,
 			&next_pc, &tgt_if_br);

 	p->ainsn.t1_addr = (kprobe_opcode_t *) next_pc;
 	p->ainsn.t1_opcode = *(p->ainsn.t1_addr);
 	*(p->ainsn.t1_addr) = TRAP_S_2_INSTRUCTION;

 	flush_icache_range((unsigned long)p->ainsn.t1_addr,
 			   (unsigned long)p->ainsn.t1_addr +
 			   sizeof(kprobe_opcode_t));

 	if (is_branch) {
 		p->ainsn.t2_addr = (kprobe_opcode_t *) tgt_if_br;
 		p->ainsn.t2_opcode = *(p->ainsn.t2_addr);
 		*(p->ainsn.t2_addr) = TRAP_S_2_INSTRUCTION;

 		flush_icache_range((unsigned long)p->ainsn.t2_addr,
 				   (unsigned long)p->ainsn.t2_addr +
 				   sizeof(kprobe_opcode_t));
 	}
 }

 int __kprobes arc_kprobe_handler(unsigned long addr, struct pt_regs *regs)
 {
 	struct kprobe *p;
 	struct kprobe_ctlblk *kcb;

 	preempt_disable();

 	kcb = get_kprobe_ctlblk();
 	p = get_kprobe((unsigned long *)addr);

 	if (p) {
 		/*
 		 * We have reentered the kprobe_handler, since another kprobe
 		 * was hit while within the handler, we save the original
 		 * kprobes and single step on the instruction of the new probe
 		 * without calling any user handlers to avoid recursive
 		 * kprobes.
 		 */
 		if (kprobe_running()) {
 			save_previous_kprobe(kcb);
 			set_current_kprobe(p);
 			kprobes_inc_nmissed_count(p);
 			setup_singlestep(p, regs);
 			kcb->kprobe_status = KPROBE_REENTER;
 			return 1;
 		}

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

 		/* If we have no pre-handler or it returned 0, we continue with
 		 * normal processing. If we have a pre-handler and it returned
 		 * non-zero - which means user handler setup registers to exit
 		 * to another instruction, we must skip the single stepping.
 		 */
 		if (!p->pre_handler || !p->pre_handler(p, regs)) {
 			setup_singlestep(p, regs);
 			kcb->kprobe_status = KPROBE_HIT_SS;
 		} else {
 			reset_current_kprobe();
 			preempt_enable_no_resched();
 		}

 		return 1;
 	}

 	/* no_kprobe: */
 	preempt_enable_no_resched();
 	return 0;
 }

 static int __kprobes arc_post_kprobe_handler(unsigned long addr,
 					 struct pt_regs *regs)
 {
 	struct kprobe *cur = kprobe_running();
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

 	if (!cur)
 		return 0;

 	resume_execution(cur, addr, regs);

 	/* Rearm the kprobe */
 	arch_arm_kprobe(cur);

 	/*
 	 * When we return from trap instruction we go to the next instruction
 	 * We restored the actual instruction in resume_exectuiont and we to
 	 * return to the same address and execute it
 	 */
 	regs->ret = addr;

 	if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
 		kcb->kprobe_status = KPROBE_HIT_SSDONE;
 		cur->post_handler(cur, regs, 0);
 	}

 	if (kcb->kprobe_status == KPROBE_REENTER) {
 		restore_previous_kprobe(kcb);
 		goto out;
 	}

 	reset_current_kprobe();

 out:
 	preempt_enable_no_resched();
 	return 1;
 }

 /*
  * Fault can be for the instruction being single stepped or for the
  * pre/post handlers in the module.
  * This is applicable for applications like user probes, where we have the
  * probe in user space and the handlers in the kernel
  */

 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned long trapnr)
 {
 	struct kprobe *cur = kprobe_running();
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

 	switch (kcb->kprobe_status) {
 	case KPROBE_HIT_SS:
 	case KPROBE_REENTER:
 		/*
 		 * We are here because the instruction being single stepped
 		 * caused the fault. We reset the current kprobe and allow the
 		 * exception handler as if it is regular exception. In our
 		 * case it doesn't matter because the system will be halted
 		 */
 		resume_execution(cur, (unsigned long)cur->addr, regs);

 		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 are here because the instructions in the pre/post handler
 		 * caused the fault.
 		 */

 		/* We increment the nmissed count for accounting,
 		 * we can also use npre/npostfault count for accounting
 		 * 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 (fixup_exception(regs))
 			return 1;

 		/*
 		 * fixup_exception() could not handle it,
 		 * Let do_page_fault() fix it.
 		 */
 		break;

 	default:
 		break;
 	}
 	return 0;
 }

 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 				       unsigned long val, void *data)
 {
 	struct die_args *args = data;
 	unsigned long addr = args->err;
 	int ret = NOTIFY_DONE;

 	switch (val) {
 	case DIE_IERR:
 		if (arc_kprobe_handler(addr, args->regs))
 			return NOTIFY_STOP;
 		break;

 	case DIE_TRAP:
 		if (arc_post_kprobe_handler(addr, args->regs))
 			return NOTIFY_STOP;
 		break;

 	default:
 		break;
 	}

 	return ret;
 }

 static void __used kretprobe_trampoline_holder(void)
 {
 	__asm__ __volatile__(".global kretprobe_trampoline\n"
 			     "kretprobe_trampoline:\n" "nop\n");
 }

 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 				      struct pt_regs *regs)
 {

 	ri->ret_addr = (kprobe_opcode_t *) regs->blink;

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

 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 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, 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->ret = orig_ret_address;

 	kretprobe_hash_unlock(current, &flags);

 	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 the kprobe handler
 	 * that we don't want the post_handler to run
 	 */
 	return 1;
 }

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

 int __init arch_init_kprobes(void)
 {
 	/* Registering the trampoline code for the kret probe */
 	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;
 }

 void trap_is_kprobe(unsigned long address, struct pt_regs *regs)
 {
 	notify_die(DIE_TRAP, "kprobe_trap", regs, address, 0, SIGTRAP);
 }
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
	*/

	#include <linux/types.h>
	#include <linux/kprobes.h>
	#include <linux/slab.h>
	#include <linux/module.h>
	#include <linux/kdebug.h>
	#include <linux/sched.h>
	#include <linux/uaccess.h>
	#include <asm/cacheflush.h>
	#include <asm/current.h>
	#include <asm/disasm.h>

	#define MIN_STACK_SIZE(addr) min((unsigned long)MAX_STACK_SIZE, \
	(unsigned long)current_thread_info() + THREAD_SIZE - (addr))

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

	int __kprobes arch_prepare_kprobe(struct kprobe *p)
	{
	/* Attempt to probe at unaligned address */
	if ((unsigned long)p->addr & 0x01)
	return -EINVAL;

	/* Address should not be in exception handling code */

	p->ainsn.is_short = is_short_instr((unsigned long)p->addr);
	p->opcode = *p->addr;

	return 0;
	}

	void __kprobes arch_arm_kprobe(struct kprobe *p)
	{
	*p->addr = UNIMP_S_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)
	{
	arch_disarm_kprobe(p);

	/* Can we remove the kprobe in the middle of kprobe handling? */
	if (p->ainsn.t1_addr) {
	*(p->ainsn.t1_addr) = p->ainsn.t1_opcode;

	flush_icache_range((unsigned long)p->ainsn.t1_addr,
	(unsigned long)p->ainsn.t1_addr +
	sizeof(kprobe_opcode_t));

	p->ainsn.t1_addr = NULL;
	}

	if (p->ainsn.t2_addr) {
	*(p->ainsn.t2_addr) = p->ainsn.t2_opcode;

	flush_icache_range((unsigned long)p->ainsn.t2_addr,
	(unsigned long)p->ainsn.t2_addr +
	sizeof(kprobe_opcode_t));

	p->ainsn.t2_addr = NULL;
	}
	}

	static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
	{
	kcb->prev_kprobe.kp = kprobe_running();
	kcb->prev_kprobe.status = kcb->kprobe_status;
	}

	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;
	}

	static inline void __kprobes set_current_kprobe(struct kprobe *p)
	{
	__this_cpu_write(current_kprobe, p);
	}

	static void __kprobes resume_execution(struct kprobe *p, unsigned long addr,
	struct pt_regs *regs)
	{
	/* Remove the trap instructions inserted for single step and
	* restore the original instructions
	*/
	if (p->ainsn.t1_addr) {
	*(p->ainsn.t1_addr) = p->ainsn.t1_opcode;

	flush_icache_range((unsigned long)p->ainsn.t1_addr,
	(unsigned long)p->ainsn.t1_addr +
	sizeof(kprobe_opcode_t));

	p->ainsn.t1_addr = NULL;
	}

	if (p->ainsn.t2_addr) {
	*(p->ainsn.t2_addr) = p->ainsn.t2_opcode;

	flush_icache_range((unsigned long)p->ainsn.t2_addr,
	(unsigned long)p->ainsn.t2_addr +
	sizeof(kprobe_opcode_t));

	p->ainsn.t2_addr = NULL;
	}

	return;
	}

	static void __kprobes setup_singlestep(struct kprobe p, struct pt_regs regs)
	{
	unsigned long next_pc;
	unsigned long tgt_if_br = 0;
	int is_branch;
	unsigned long bta;

	/* Copy the opcode back to the kprobe location and execute the
	* instruction. Because of this we will not be able to get into the
	* same kprobe until this kprobe is done
	*/
	*(p->addr) = p->opcode;

	flush_icache_range((unsigned long)p->addr,
	(unsigned long)p->addr + sizeof(kprobe_opcode_t));

	/* Now we insert the trap at the next location after this instruction to
	* single step. If it is a branch we insert the trap at possible branch
	* targets
	*/

	bta = regs->bta;

	if (regs->status32 & 0x40) {
	/* We are in a delay slot with the branch taken */

	next_pc = bta & ~0x01;

	if (!p->ainsn.is_short) {
	if (bta & 0x01)
	regs->blink += 2;
	else {
	/* Branch not taken */
	next_pc += 2;

	/* next pc is taken from bta after executing the
	* delay slot instruction
	*/
	regs->bta += 2;
	}
	}

	is_branch = 0;
	} else
	is_branch =
	disasm_next_pc((unsigned long)p->addr, regs,
	(struct callee_regs *) current->thread.callee_reg,
	&next_pc, &tgt_if_br);

	p->ainsn.t1_addr = (kprobe_opcode_t *) next_pc;
	p->ainsn.t1_opcode = *(p->ainsn.t1_addr);
	*(p->ainsn.t1_addr) = TRAP_S_2_INSTRUCTION;

	flush_icache_range((unsigned long)p->ainsn.t1_addr,
	(unsigned long)p->ainsn.t1_addr +
	sizeof(kprobe_opcode_t));

	if (is_branch) {
	p->ainsn.t2_addr = (kprobe_opcode_t *) tgt_if_br;
	p->ainsn.t2_opcode = *(p->ainsn.t2_addr);
	*(p->ainsn.t2_addr) = TRAP_S_2_INSTRUCTION;

	flush_icache_range((unsigned long)p->ainsn.t2_addr,
	(unsigned long)p->ainsn.t2_addr +
	sizeof(kprobe_opcode_t));
	}
	}

	int __kprobes arc_kprobe_handler(unsigned long addr, struct pt_regs *regs)
	{
	struct kprobe *p;
	struct kprobe_ctlblk *kcb;

	preempt_disable();

	kcb = get_kprobe_ctlblk();
	p = get_kprobe((unsigned long *)addr);

	if (p) {
	/*
	* We have reentered the kprobe_handler, since another kprobe
	* was hit while within the handler, we save the original
	* kprobes and single step on the instruction of the new probe
	* without calling any user handlers to avoid recursive
	* kprobes.
	*/
	if (kprobe_running()) {
	save_previous_kprobe(kcb);
	set_current_kprobe(p);
	kprobes_inc_nmissed_count(p);
	setup_singlestep(p, regs);
	kcb->kprobe_status = KPROBE_REENTER;
	return 1;
	}

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

	/* If we have no pre-handler or it returned 0, we continue with
	* normal processing. If we have a pre-handler and it returned
	* non-zero - which means user handler setup registers to exit
	* to another instruction, we must skip the single stepping.
	*/
	if (!p->pre_handler \|\| !p->pre_handler(p, regs)) {
	setup_singlestep(p, regs);
	kcb->kprobe_status = KPROBE_HIT_SS;
	} else {
	reset_current_kprobe();
	preempt_enable_no_resched();
	}

	return 1;
	}

	/* no_kprobe: */
	preempt_enable_no_resched();
	return 0;
	}

	static int __kprobes arc_post_kprobe_handler(unsigned long addr,
	struct pt_regs *regs)
	{
	struct kprobe *cur = kprobe_running();
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	if (!cur)
	return 0;

	resume_execution(cur, addr, regs);

	/* Rearm the kprobe */
	arch_arm_kprobe(cur);

	/*
	* When we return from trap instruction we go to the next instruction
	* We restored the actual instruction in resume_exectuiont and we to
	* return to the same address and execute it
	*/
	regs->ret = addr;

	if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
	kcb->kprobe_status = KPROBE_HIT_SSDONE;
	cur->post_handler(cur, regs, 0);
	}

	if (kcb->kprobe_status == KPROBE_REENTER) {
	restore_previous_kprobe(kcb);
	goto out;
	}

	reset_current_kprobe();

	out:
	preempt_enable_no_resched();
	return 1;
	}

	/*
	* Fault can be for the instruction being single stepped or for the
	* pre/post handlers in the module.
	* This is applicable for applications like user probes, where we have the
	* probe in user space and the handlers in the kernel
	*/

	int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned long trapnr)
	{
	struct kprobe *cur = kprobe_running();
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	switch (kcb->kprobe_status) {
	case KPROBE_HIT_SS:
	case KPROBE_REENTER:
	/*
	* We are here because the instruction being single stepped
	* caused the fault. We reset the current kprobe and allow the
	* exception handler as if it is regular exception. In our
	* case it doesn't matter because the system will be halted
	*/
	resume_execution(cur, (unsigned long)cur->addr, regs);

	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 are here because the instructions in the pre/post handler
	* caused the fault.
	*/

	/* We increment the nmissed count for accounting,
	* we can also use npre/npostfault count for accounting
	* 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 (fixup_exception(regs))
	return 1;

	/*
	* fixup_exception() could not handle it,
	* Let do_page_fault() fix it.
	*/
	break;

	default:
	break;
	}
	return 0;
	}

	int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
	unsigned long val, void *data)
	{
	struct die_args *args = data;
	unsigned long addr = args->err;
	int ret = NOTIFY_DONE;

	switch (val) {
	case DIE_IERR:
	if (arc_kprobe_handler(addr, args->regs))
	return NOTIFY_STOP;
	break;

	case DIE_TRAP:
	if (arc_post_kprobe_handler(addr, args->regs))
	return NOTIFY_STOP;
	break;

	default:
	break;
	}

	return ret;
	}

	static void __used kretprobe_trampoline_holder(void)
	{
	__asm__ __volatile__(".global kretprobe_trampoline\n"
	"kretprobe_trampoline:\n" "nop\n");
	}

	void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
	struct pt_regs *regs)
	{

	ri->ret_addr = (kprobe_opcode_t *) regs->blink;

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

	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 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, 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->ret = orig_ret_address;

	kretprobe_hash_unlock(current, &flags);

	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 the kprobe handler
	* that we don't want the post_handler to run
	*/
	return 1;
	}

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

	int __init arch_init_kprobes(void)
	{
	/* Registering the trampoline code for the kret probe */
	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;
	}

	void trap_is_kprobe(unsigned long address, struct pt_regs *regs)
	{
	notify_die(DIE_TRAP, "kprobe_trap", regs, address, 0, SIGTRAP);
	}