text: /*
   *  Kernel Probes (KProbes)
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
   *
   * Copyright (C) IBM Corporation, 2002, 2006
   *
   * s390 port, used ppc64 as template. Mike Grundy <grundym@us.ibm.com>
   */
  
  #include <linux/kprobes.h>
  #include <linux/ptrace.h>
  #include <linux/preempt.h>
  #include <linux/stop_machine.h>
  #include <linux/kdebug.h>
  #include <asm/cacheflush.h>
  #include <asm/sections.h>
  #include <asm/uaccess.h>
  #include <linux/module.h>
  
  DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  
  int __kprobes arch_prepare_kprobe(struct kprobe *p)
  {
  	/* Make sure the probe isn't going on a difficult instruction */
  	if (is_prohibited_opcode((kprobe_opcode_t *) p->addr))
  		return -EINVAL;
  
  	if ((unsigned long)p->addr & 0x01) {
  		printk("Attempt to register kprobe at an unaligned address\n");
  		return -EINVAL;
  		}
  
  	/* Use the get_insn_slot() facility for correctness */
  	if (!(p->ainsn.insn = get_insn_slot()))
  		return -ENOMEM;
  
  	memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
  
  	get_instruction_type(&p->ainsn);
  	p->opcode = *p->addr;
  	return 0;
  }
  
  int __kprobes is_prohibited_opcode(kprobe_opcode_t *instruction)
  {
  	switch (*(__u8 *) instruction) {
  	case 0x0c:	/* bassm */
  	case 0x0b:	/* bsm	 */
  	case 0x83:	/* diag  */
  	case 0x44:	/* ex	 */
  		return -EINVAL;
  	}
  	switch (*(__u16 *) instruction) {
  	case 0x0101:	/* pr	 */
  	case 0xb25a:	/* bsa	 */
  	case 0xb240:	/* bakr  */
  	case 0xb258:	/* bsg	 */
  	case 0xb218:	/* pc	 */
  	case 0xb228:	/* pt	 */
  		return -EINVAL;
  	}
  	return 0;
  }
  
  void __kprobes get_instruction_type(struct arch_specific_insn *ainsn)
  {
  	/* default fixup method */
  	ainsn->fixup = FIXUP_PSW_NORMAL;
  
  	/* save r1 operand */
  	ainsn->reg = (*ainsn->insn & 0xf0) >> 4;
  
  	/* save the instruction length (pop 5-5) in bytes */
  	switch (*(__u8 *) (ainsn->insn) >> 4) {
  	case 0:
  		ainsn->ilen = 2;
  		break;
  	case 1:
  	case 2:
  		ainsn->ilen = 4;
  		break;
  	case 3:
  		ainsn->ilen = 6;
  		break;
  	}
  
  	switch (*(__u8 *) ainsn->insn) {
  	case 0x05:	/* balr	*/
  	case 0x0d:	/* basr */
  		ainsn->fixup = FIXUP_RETURN_REGISTER;
  		/* if r2 = 0, no branch will be taken */
  		if ((*ainsn->insn & 0x0f) == 0)
  			ainsn->fixup |= FIXUP_BRANCH_NOT_TAKEN;
  		break;
  	case 0x06:	/* bctr	*/
  	case 0x07:	/* bcr	*/
  		ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
  		break;
  	case 0x45:	/* bal	*/
  	case 0x4d:	/* bas	*/
  		ainsn->fixup = FIXUP_RETURN_REGISTER;
  		break;
  	case 0x47:	/* bc	*/
  	case 0x46:	/* bct	*/
  	case 0x86:	/* bxh	*/
  	case 0x87:	/* bxle	*/
  		ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
  		break;
  	case 0x82:	/* lpsw	*/
  		ainsn->fixup = FIXUP_NOT_REQUIRED;
  		break;
  	case 0xb2:	/* lpswe */
  		if (*(((__u8 *) ainsn->insn) + 1) == 0xb2) {
  			ainsn->fixup = FIXUP_NOT_REQUIRED;
  		}
  		break;
  	case 0xa7:	/* bras	*/
  		if ((*ainsn->insn & 0x0f) == 0x05) {
  			ainsn->fixup |= FIXUP_RETURN_REGISTER;
  		}
  		break;
  	case 0xc0:
  		if ((*ainsn->insn & 0x0f) == 0x00  /* larl  */
  			|| (*ainsn->insn & 0x0f) == 0x05) /* brasl */
  		ainsn->fixup |= FIXUP_RETURN_REGISTER;
  		break;
  	case 0xeb:
  		if (*(((__u8 *) ainsn->insn) + 5 ) == 0x44 ||	/* bxhg  */
  			*(((__u8 *) ainsn->insn) + 5) == 0x45) {/* bxleg */
  			ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
  		}
  		break;
  	case 0xe3:	/* bctg	*/
  		if (*(((__u8 *) ainsn->insn) + 5) == 0x46) {
  			ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
  		}
  		break;
  	}
  }
  
  static int __kprobes swap_instruction(void *aref)
  {
  	struct ins_replace_args *args = aref;
  	u32 *addr;
  	u32 instr;
  	int err = -EFAULT;
  
  	/*
  	 * Text segment is read-only, hence we use stura to bypass dynamic
  	 * address translation to exchange the instruction. Since stura
  	 * always operates on four bytes, but we only want to exchange two
  	 * bytes do some calculations to get things right. In addition we
  	 * shall not cross any page boundaries (vmalloc area!) when writing
  	 * the new instruction.
  	 */
  	addr = (u32 *)((unsigned long)args->ptr & -4UL);
  	if ((unsigned long)args->ptr & 2)
  		instr = ((*addr) & 0xffff0000) | args->new;
  	else
  		instr = ((*addr) & 0x0000ffff) | args->new << 16;
  
  	asm volatile(
  		"	lra	%1,0(%1)\n"
  		"0:	stura	%2,%1\n"
  		"1:	la	%0,0\n"
  		"2:\n"
  		EX_TABLE(0b,2b)
  		: "+d" (err)
  		: "a" (addr), "d" (instr)
  		: "memory", "cc");
  
  	return err;
  }
  
  void __kprobes arch_arm_kprobe(struct kprobe *p)
  {
  	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  	unsigned long status = kcb->kprobe_status;
  	struct ins_replace_args args;
  
  	args.ptr = p->addr;
  	args.old = p->opcode;
  	args.new = BREAKPOINT_INSTRUCTION;
  
  	kcb->kprobe_status = KPROBE_SWAP_INST;
  	stop_machine_run(swap_instruction, &args, NR_CPUS);
  	kcb->kprobe_status = status;
  }
  
  void __kprobes arch_disarm_kprobe(struct kprobe *p)
  {
  	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  	unsigned long status = kcb->kprobe_status;
  	struct ins_replace_args args;
  
  	args.ptr = p->addr;
  	args.old = BREAKPOINT_INSTRUCTION;
  	args.new = p->opcode;
  
  	kcb->kprobe_status = KPROBE_SWAP_INST;
  	stop_machine_run(swap_instruction, &args, NR_CPUS);
  	kcb->kprobe_status = status;
  }
  
  void __kprobes arch_remove_kprobe(struct kprobe *p)
  {
  	mutex_lock(&kprobe_mutex);
  	free_insn_slot(p->ainsn.insn, 0);
  	mutex_unlock(&kprobe_mutex);
  }
  
  static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
  {
  	per_cr_bits kprobe_per_regs[1];
  
  	memset(kprobe_per_regs, 0, sizeof(per_cr_bits));
  	regs->psw.addr = (unsigned long)p->ainsn.insn | PSW_ADDR_AMODE;
  
  	/* Set up the per control reg info, will pass to lctl */
  	kprobe_per_regs[0].em_instruction_fetch = 1;
  	kprobe_per_regs[0].starting_addr = (unsigned long)p->ainsn.insn;
  	kprobe_per_regs[0].ending_addr = (unsigned long)p->ainsn.insn + 1;
  
  	/* Set the PER control regs, turns on single step for this address */
  	__ctl_load(kprobe_per_regs, 9, 11);
  	regs->psw.mask |= PSW_MASK_PER;
  	regs->psw.mask &= ~(PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
  }
  
  static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
  {
  	kcb->prev_kprobe.kp = kprobe_running();
  	kcb->prev_kprobe.status = kcb->kprobe_status;
  	kcb->prev_kprobe.kprobe_saved_imask = kcb->kprobe_saved_imask;
  	memcpy(kcb->prev_kprobe.kprobe_saved_ctl, kcb->kprobe_saved_ctl,
  					sizeof(kcb->kprobe_saved_ctl));
  }
  
  static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
  {
  	__get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
  	kcb->kprobe_status = kcb->prev_kprobe.status;
  	kcb->kprobe_saved_imask = kcb->prev_kprobe.kprobe_saved_imask;
  	memcpy(kcb->kprobe_saved_ctl, kcb->prev_kprobe.kprobe_saved_ctl,
  					sizeof(kcb->kprobe_saved_ctl));
  }
  
  static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
  						struct kprobe_ctlblk *kcb)
  {
  	__get_cpu_var(current_kprobe) = p;
  	/* Save the interrupt and per flags */
  	kcb->kprobe_saved_imask = regs->psw.mask &
  	    (PSW_MASK_PER | PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
  	/* Save the control regs that govern PER */
  	__ctl_store(kcb->kprobe_saved_ctl, 9, 11);
  }
  
  /* Called with kretprobe_lock held */
  void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
  					struct pt_regs *regs)
  {
  	ri->ret_addr = (kprobe_opcode_t *) regs->gprs[14];
  
  	/* Replace the return addr with trampoline addr */
  	regs->gprs[14] = (unsigned long)&kretprobe_trampoline;
  }
  
  static int __kprobes kprobe_handler(struct pt_regs *regs)
  {
  	struct kprobe *p;
  	int ret = 0;
  	unsigned long *addr = (unsigned long *)
  		((regs->psw.addr & PSW_ADDR_INSN) - 2);
  	struct kprobe_ctlblk *kcb;
  
  	/*
  	 * We don't want to be preempted for the entire
  	 * duration of kprobe processing
  	 */
  	preempt_disable();
  	kcb = get_kprobe_ctlblk();
  
  	/* Check we're not actually recursing */
  	if (kprobe_running()) {
  		p = get_kprobe(addr);
  		if (p) {
  			if (kcb->kprobe_status == KPROBE_HIT_SS &&
  			    *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
  				regs->psw.mask &= ~PSW_MASK_PER;
  				regs->psw.mask |= kcb->kprobe_saved_imask;
  				goto no_kprobe;
  			}
  			/* We have reentered the kprobe_handler(), since
  			 * another probe was hit while within the handler.
  			 * We here save the original kprobes variables and
  			 * just single step on the instruction of the new probe
  			 * without calling any user handlers.
  			 */
  			save_previous_kprobe(kcb);
  			set_current_kprobe(p, regs, kcb);
  			kprobes_inc_nmissed_count(p);
  			prepare_singlestep(p, regs);
  			kcb->kprobe_status = KPROBE_REENTER;
  			return 1;
  		} else {
  			p = __get_cpu_var(current_kprobe);
  			if (p->break_handler && p->break_handler(p, regs)) {
  				goto ss_probe;
  			}
  		}
  		goto no_kprobe;
  	}
  
  	p = get_kprobe(addr);
  	if (!p)
  		/*
  		 * No kprobe at this address. The fault has not been
  		 * caused by a kprobe breakpoint. The race of breakpoint
  		 * vs. kprobe remove does not exist because on s390 we
  		 * use stop_machine_run to arm/disarm the breakpoints.
  		 */
  		goto no_kprobe;
  
  	kcb->kprobe_status = KPROBE_HIT_ACTIVE;
  	set_current_kprobe(p, regs, kcb);
  	if (p->pre_handler && p->pre_handler(p, regs))
  		/* handler has already set things up, so skip ss setup */
  		return 1;
  
  ss_probe:
  	prepare_singlestep(p, regs);
  	kcb->kprobe_status = KPROBE_HIT_SS;
  	return 1;
  
  no_kprobe:
  	preempt_enable_no_resched();
  	return ret;
  }
  
  /*
   * Function return probe trampoline:
   *	- init_kprobes() establishes a probepoint here
   *	- When the probed function returns, this probe
   *		causes the handlers to fire
   */
  void kretprobe_trampoline_holder(void)
  {
  	asm volatile(".global kretprobe_trampoline\n"
  		     "kretprobe_trampoline: bcr 0,0\n");
  }
  
  /*
   * Called when the probe at kretprobe trampoline is hit
   */
  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);
  	spin_lock_irqsave(&kretprobe_lock, flags);
  	head = kretprobe_inst_table_head(current);
  
  	/*
  	 * It is possible to have multiple instances associated with a given
  	 * task either because an multiple functions in the call path
  	 * have a return probe installed on them, and/or more then one return
  	 * return probe was registered for a target function.
  	 *
  	 * We can handle this because:
  	 *     - instances are always inserted at the head of the list
  	 *     - when multiple return probes are registered for the same
  	 *	 function, the first instance's ret_addr will point to the
  	 *	 real return address, and all the rest will point to
  	 *	 kretprobe_trampoline
  	 */
  	hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
  		if (ri->task != current)
  			/* another task is sharing our hash bucket */
  			continue;
  
  		if (ri->rp && ri->rp->handler)
  			ri->rp->handler(ri, regs);
  
  		orig_ret_address = (unsigned long)ri->ret_addr;
  		recycle_rp_inst(ri, &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->psw.addr = orig_ret_address | PSW_ADDR_AMODE;
  
  	reset_current_kprobe();
  	spin_unlock_irqrestore(&kretprobe_lock, 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)
  {
  	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  
  	regs->psw.addr &= PSW_ADDR_INSN;
  
  	if (p->ainsn.fixup & FIXUP_PSW_NORMAL)
  		regs->psw.addr = (unsigned long)p->addr +
  				((unsigned long)regs->psw.addr -
  				 (unsigned long)p->ainsn.insn);
  
  	if (p->ainsn.fixup & FIXUP_BRANCH_NOT_TAKEN)
  		if ((unsigned long)regs->psw.addr -
  		    (unsigned long)p->ainsn.insn == p->ainsn.ilen)
  			regs->psw.addr = (unsigned long)p->addr + p->ainsn.ilen;
  
  	if (p->ainsn.fixup & FIXUP_RETURN_REGISTER)
  		regs->gprs[p->ainsn.reg] = ((unsigned long)p->addr +
  						(regs->gprs[p->ainsn.reg] -
  						(unsigned long)p->ainsn.insn))
  						| PSW_ADDR_AMODE;
  
  	regs->psw.addr |= PSW_ADDR_AMODE;
  	/* turn off PER mode */
  	regs->psw.mask &= ~PSW_MASK_PER;
  	/* Restore the original per control regs */
  	__ctl_load(kcb->kprobe_saved_ctl, 9, 11);
  	regs->psw.mask |= kcb->kprobe_saved_imask;
  }
  
  static int __kprobes post_kprobe_handler(struct pt_regs *regs)
  {
  	struct kprobe *cur = kprobe_running();
  	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  
  	if (!cur)
  		return 0;
  
  	if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
  		kcb->kprobe_status = KPROBE_HIT_SSDONE;
  		cur->post_handler(cur, regs, 0);
  	}
  
  	resume_execution(cur, regs);
  
  	/*Restore back the original saved kprobes variables and continue. */
  	if (kcb->kprobe_status == KPROBE_REENTER) {
  		restore_previous_kprobe(kcb);
  		goto out;
  	}
  	reset_current_kprobe();
  out:
  	preempt_enable_no_resched();
  
  	/*
  	 * if somebody else is singlestepping across a probe point, psw mask
  	 * will have PER set, in which case, continue the remaining processing
  	 * of do_single_step, as if this is not a probe hit.
  	 */
  	if (regs->psw.mask & PSW_MASK_PER) {
  		return 0;
  	}
  
  	return 1;
  }
  
  int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
  {
  	struct kprobe *cur = kprobe_running();
  	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  	const struct exception_table_entry *entry;
  
  	switch(kcb->kprobe_status) {
  	case KPROBE_SWAP_INST:
  		/* We are here because the instruction replacement failed */
  		return 0;
  	case KPROBE_HIT_SS:
  	case KPROBE_REENTER:
  		/*
  		 * We are here because the instruction being single
  		 * stepped caused a page fault. We reset the current
  		 * kprobe and the nip points back to the probe address
  		 * and allow the page fault handler to continue as a
  		 * normal page fault.
  		 */
  		regs->psw.addr = (unsigned long)cur->addr | PSW_ADDR_AMODE;
  		regs->psw.mask &= ~PSW_MASK_PER;
  		regs->psw.mask |= kcb->kprobe_saved_imask;
  		if (kcb->kprobe_status == KPROBE_REENTER)
  			restore_previous_kprobe(kcb);
  		else
  			reset_current_kprobe();
  		preempt_enable_no_resched();
  		break;
  	case KPROBE_HIT_ACTIVE:
  	case KPROBE_HIT_SSDONE:
  		/*
  		 * We increment the nmissed count for accounting,
  		 * we can also use npre/npostfault count for accouting
  		 * these specific fault cases.
  		 */
  		kprobes_inc_nmissed_count(cur);
  
  		/*
  		 * We come here because instructions in the pre/post
  		 * handler caused the page_fault, this could happen
  		 * if handler tries to access user space by
  		 * copy_from_user(), get_user() etc. Let the
  		 * user-specified handler try to fix it first.
  		 */
  		if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
  			return 1;
  
  		/*
  		 * In case the user-specified fault handler returned
  		 * zero, try to fix up.
  		 */
  		entry = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
  		if (entry) {
  			regs->psw.addr = entry->fixup | PSW_ADDR_AMODE;
  			return 1;
  		}
  
  		/*
  		 * fixup_exception() could not handle it,
  		 * Let do_page_fault() fix it.
  		 */
  		break;
  	default:
  		break;
  	}
  	return 0;
  }
  
  /*
   * Wrapper routine to for handling exceptions.
   */
  int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
  				       unsigned long val, void *data)
  {
  	struct die_args *args = (struct die_args *)data;
  	int ret = NOTIFY_DONE;
  
  	switch (val) {
  	case DIE_BPT:
  		if (kprobe_handler(args->regs))
  			ret = NOTIFY_STOP;
  		break;
  	case DIE_SSTEP:
  		if (post_kprobe_handler(args->regs))
  			ret = NOTIFY_STOP;
  		break;
  	case DIE_TRAP:
  		/* kprobe_running() needs smp_processor_id() */
  		preempt_disable();
  		if (kprobe_running() &&
  		    kprobe_fault_handler(args->regs, args->trapnr))
  			ret = NOTIFY_STOP;
  		preempt_enable();
  		break;
  	default:
  		break;
  	}
  	return ret;
  }
  
  int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
  {
  	struct jprobe *jp = container_of(p, struct jprobe, kp);
  	unsigned long addr;
  	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  
  	memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
  
  	/* setup return addr to the jprobe handler routine */
  	regs->psw.addr = (unsigned long)(jp->entry) | PSW_ADDR_AMODE;
  
  	/* r14 is the function return address */
  	kcb->jprobe_saved_r14 = (unsigned long)regs->gprs[14];
  	/* r15 is the stack pointer */
  	kcb->jprobe_saved_r15 = (unsigned long)regs->gprs[15];
  	addr = (unsigned long)kcb->jprobe_saved_r15;
  
  	memcpy(kcb->jprobes_stack, (kprobe_opcode_t *) addr,
  	       MIN_STACK_SIZE(addr));
  	return 1;
  }
  
  void __kprobes jprobe_return(void)
  {
  	asm volatile(".word 0x0002");
  }
  
  void __kprobes jprobe_return_end(void)
  {
  	asm volatile("bcr 0,0");
  }
  
  int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
  {
  	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  	unsigned long stack_addr = (unsigned long)(kcb->jprobe_saved_r15);
  
  	/* Put the regs back */
  	memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
  	/* put the stack back */
  	memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
  	       MIN_STACK_SIZE(stack_addr));
  	preempt_enable_no_resched();
  	return 1;
  }
  
  static struct kprobe trampoline_p = {
  	.addr = (kprobe_opcode_t *) & kretprobe_trampoline,
  	.pre_handler = trampoline_probe_handler
  };
  
  int __init arch_init_kprobes(void)
  {
  	return register_kprobe(&trampoline_p);
  }
  
  int __kprobes arch_trampoline_kprobe(struct kprobe *p)
  {
  	if (p->addr == (kprobe_opcode_t *) & kretprobe_trampoline)
  		return 1;
  	return 0;
  }
  