[S390] fix kprobes single stepping
[linux-2.6.git] / arch / s390 / kernel / kprobes.c
1 /*
2  *  Kernel Probes (KProbes)
3  *
4  * This program is free software; you can redistribute it and/or modify
5  * it under the terms of the GNU General Public License as published by
6  * the Free Software Foundation; either version 2 of the License, or
7  * (at your option) any later version.
8  *
9  * This program is distributed in the hope that it will be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  * GNU General Public License for more details.
13  *
14  * You should have received a copy of the GNU General Public License
15  * along with this program; if not, write to the Free Software
16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17  *
18  * Copyright (C) IBM Corporation, 2002, 2006
19  *
20  * s390 port, used ppc64 as template. Mike Grundy <grundym@us.ibm.com>
21  */
22
23 #include <linux/kprobes.h>
24 #include <linux/ptrace.h>
25 #include <linux/preempt.h>
26 #include <linux/stop_machine.h>
27 #include <linux/kdebug.h>
28 #include <linux/uaccess.h>
29 #include <asm/cacheflush.h>
30 #include <asm/sections.h>
31 #include <linux/module.h>
32 #include <linux/slab.h>
33
34 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
35 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
36
37 struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
38
39 int __kprobes arch_prepare_kprobe(struct kprobe *p)
40 {
41         /* Make sure the probe isn't going on a difficult instruction */
42         if (is_prohibited_opcode((kprobe_opcode_t *) p->addr))
43                 return -EINVAL;
44
45         if ((unsigned long)p->addr & 0x01)
46                 return -EINVAL;
47
48         /* Use the get_insn_slot() facility for correctness */
49         if (!(p->ainsn.insn = get_insn_slot()))
50                 return -ENOMEM;
51
52         memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
53
54         get_instruction_type(&p->ainsn);
55         p->opcode = *p->addr;
56         return 0;
57 }
58
59 int __kprobes is_prohibited_opcode(kprobe_opcode_t *instruction)
60 {
61         switch (*(__u8 *) instruction) {
62         case 0x0c:      /* bassm */
63         case 0x0b:      /* bsm   */
64         case 0x83:      /* diag  */
65         case 0x44:      /* ex    */
66         case 0xac:      /* stnsm */
67         case 0xad:      /* stosm */
68                 return -EINVAL;
69         }
70         switch (*(__u16 *) instruction) {
71         case 0x0101:    /* pr    */
72         case 0xb25a:    /* bsa   */
73         case 0xb240:    /* bakr  */
74         case 0xb258:    /* bsg   */
75         case 0xb218:    /* pc    */
76         case 0xb228:    /* pt    */
77         case 0xb98d:    /* epsw  */
78                 return -EINVAL;
79         }
80         return 0;
81 }
82
83 void __kprobes get_instruction_type(struct arch_specific_insn *ainsn)
84 {
85         /* default fixup method */
86         ainsn->fixup = FIXUP_PSW_NORMAL;
87
88         /* save r1 operand */
89         ainsn->reg = (*ainsn->insn & 0xf0) >> 4;
90
91         /* save the instruction length (pop 5-5) in bytes */
92         switch (*(__u8 *) (ainsn->insn) >> 6) {
93         case 0:
94                 ainsn->ilen = 2;
95                 break;
96         case 1:
97         case 2:
98                 ainsn->ilen = 4;
99                 break;
100         case 3:
101                 ainsn->ilen = 6;
102                 break;
103         }
104
105         switch (*(__u8 *) ainsn->insn) {
106         case 0x05:      /* balr */
107         case 0x0d:      /* basr */
108                 ainsn->fixup = FIXUP_RETURN_REGISTER;
109                 /* if r2 = 0, no branch will be taken */
110                 if ((*ainsn->insn & 0x0f) == 0)
111                         ainsn->fixup |= FIXUP_BRANCH_NOT_TAKEN;
112                 break;
113         case 0x06:      /* bctr */
114         case 0x07:      /* bcr  */
115                 ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
116                 break;
117         case 0x45:      /* bal  */
118         case 0x4d:      /* bas  */
119                 ainsn->fixup = FIXUP_RETURN_REGISTER;
120                 break;
121         case 0x47:      /* bc   */
122         case 0x46:      /* bct  */
123         case 0x86:      /* bxh  */
124         case 0x87:      /* bxle */
125                 ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
126                 break;
127         case 0x82:      /* lpsw */
128                 ainsn->fixup = FIXUP_NOT_REQUIRED;
129                 break;
130         case 0xb2:      /* lpswe */
131                 if (*(((__u8 *) ainsn->insn) + 1) == 0xb2) {
132                         ainsn->fixup = FIXUP_NOT_REQUIRED;
133                 }
134                 break;
135         case 0xa7:      /* bras */
136                 if ((*ainsn->insn & 0x0f) == 0x05) {
137                         ainsn->fixup |= FIXUP_RETURN_REGISTER;
138                 }
139                 break;
140         case 0xc0:
141                 if ((*ainsn->insn & 0x0f) == 0x00  /* larl  */
142                         || (*ainsn->insn & 0x0f) == 0x05) /* brasl */
143                 ainsn->fixup |= FIXUP_RETURN_REGISTER;
144                 break;
145         case 0xeb:
146                 if (*(((__u8 *) ainsn->insn) + 5 ) == 0x44 ||   /* bxhg  */
147                         *(((__u8 *) ainsn->insn) + 5) == 0x45) {/* bxleg */
148                         ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
149                 }
150                 break;
151         case 0xe3:      /* bctg */
152                 if (*(((__u8 *) ainsn->insn) + 5) == 0x46) {
153                         ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
154                 }
155                 break;
156         }
157 }
158
159 static int __kprobes swap_instruction(void *aref)
160 {
161         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
162         unsigned long status = kcb->kprobe_status;
163         struct ins_replace_args *args = aref;
164         int rc;
165
166         kcb->kprobe_status = KPROBE_SWAP_INST;
167         rc = probe_kernel_write(args->ptr, &args->new, sizeof(args->new));
168         kcb->kprobe_status = status;
169         return rc;
170 }
171
172 void __kprobes arch_arm_kprobe(struct kprobe *p)
173 {
174         struct ins_replace_args args;
175
176         args.ptr = p->addr;
177         args.old = p->opcode;
178         args.new = BREAKPOINT_INSTRUCTION;
179         stop_machine(swap_instruction, &args, NULL);
180 }
181
182 void __kprobes arch_disarm_kprobe(struct kprobe *p)
183 {
184         struct ins_replace_args args;
185
186         args.ptr = p->addr;
187         args.old = BREAKPOINT_INSTRUCTION;
188         args.new = p->opcode;
189         stop_machine(swap_instruction, &args, NULL);
190 }
191
192 void __kprobes arch_remove_kprobe(struct kprobe *p)
193 {
194         if (p->ainsn.insn) {
195                 free_insn_slot(p->ainsn.insn, 0);
196                 p->ainsn.insn = NULL;
197         }
198 }
199
200 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
201 {
202         per_cr_bits kprobe_per_regs[1];
203
204         memset(kprobe_per_regs, 0, sizeof(per_cr_bits));
205         regs->psw.addr = (unsigned long)p->ainsn.insn | PSW_ADDR_AMODE;
206
207         /* Set up the per control reg info, will pass to lctl */
208         kprobe_per_regs[0].em_instruction_fetch = 1;
209         kprobe_per_regs[0].starting_addr = (unsigned long)p->ainsn.insn;
210         kprobe_per_regs[0].ending_addr = (unsigned long)p->ainsn.insn + 1;
211
212         /* Set the PER control regs, turns on single step for this address */
213         __ctl_load(kprobe_per_regs, 9, 11);
214         regs->psw.mask |= PSW_MASK_PER;
215         regs->psw.mask &= ~(PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
216 }
217
218 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
219 {
220         kcb->prev_kprobe.kp = kprobe_running();
221         kcb->prev_kprobe.status = kcb->kprobe_status;
222         kcb->prev_kprobe.kprobe_saved_imask = kcb->kprobe_saved_imask;
223         memcpy(kcb->prev_kprobe.kprobe_saved_ctl, kcb->kprobe_saved_ctl,
224                                         sizeof(kcb->kprobe_saved_ctl));
225 }
226
227 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
228 {
229         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
230         kcb->kprobe_status = kcb->prev_kprobe.status;
231         kcb->kprobe_saved_imask = kcb->prev_kprobe.kprobe_saved_imask;
232         memcpy(kcb->kprobe_saved_ctl, kcb->prev_kprobe.kprobe_saved_ctl,
233                                         sizeof(kcb->kprobe_saved_ctl));
234 }
235
236 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
237                                                 struct kprobe_ctlblk *kcb)
238 {
239         __get_cpu_var(current_kprobe) = p;
240         /* Save the interrupt and per flags */
241         kcb->kprobe_saved_imask = regs->psw.mask &
242             (PSW_MASK_PER | PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
243         /* Save the control regs that govern PER */
244         __ctl_store(kcb->kprobe_saved_ctl, 9, 11);
245 }
246
247 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
248                                         struct pt_regs *regs)
249 {
250         ri->ret_addr = (kprobe_opcode_t *) regs->gprs[14];
251
252         /* Replace the return addr with trampoline addr */
253         regs->gprs[14] = (unsigned long)&kretprobe_trampoline;
254 }
255
256 static int __kprobes kprobe_handler(struct pt_regs *regs)
257 {
258         struct kprobe *p;
259         int ret = 0;
260         unsigned long *addr = (unsigned long *)
261                 ((regs->psw.addr & PSW_ADDR_INSN) - 2);
262         struct kprobe_ctlblk *kcb;
263
264         /*
265          * We don't want to be preempted for the entire
266          * duration of kprobe processing
267          */
268         preempt_disable();
269         kcb = get_kprobe_ctlblk();
270
271         /* Check we're not actually recursing */
272         if (kprobe_running()) {
273                 p = get_kprobe(addr);
274                 if (p) {
275                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
276                             *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
277                                 regs->psw.mask &= ~PSW_MASK_PER;
278                                 regs->psw.mask |= kcb->kprobe_saved_imask;
279                                 goto no_kprobe;
280                         }
281                         /* We have reentered the kprobe_handler(), since
282                          * another probe was hit while within the handler.
283                          * We here save the original kprobes variables and
284                          * just single step on the instruction of the new probe
285                          * without calling any user handlers.
286                          */
287                         save_previous_kprobe(kcb);
288                         set_current_kprobe(p, regs, kcb);
289                         kprobes_inc_nmissed_count(p);
290                         prepare_singlestep(p, regs);
291                         kcb->kprobe_status = KPROBE_REENTER;
292                         return 1;
293                 } else {
294                         p = __get_cpu_var(current_kprobe);
295                         if (p->break_handler && p->break_handler(p, regs)) {
296                                 goto ss_probe;
297                         }
298                 }
299                 goto no_kprobe;
300         }
301
302         p = get_kprobe(addr);
303         if (!p)
304                 /*
305                  * No kprobe at this address. The fault has not been
306                  * caused by a kprobe breakpoint. The race of breakpoint
307                  * vs. kprobe remove does not exist because on s390 we
308                  * use stop_machine to arm/disarm the breakpoints.
309                  */
310                 goto no_kprobe;
311
312         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
313         set_current_kprobe(p, regs, kcb);
314         if (p->pre_handler && p->pre_handler(p, regs))
315                 /* handler has already set things up, so skip ss setup */
316                 return 1;
317
318 ss_probe:
319         if (regs->psw.mask & (PSW_MASK_PER | PSW_MASK_IO))
320                 local_irq_disable();
321         prepare_singlestep(p, regs);
322         kcb->kprobe_status = KPROBE_HIT_SS;
323         return 1;
324
325 no_kprobe:
326         preempt_enable_no_resched();
327         return ret;
328 }
329
330 /*
331  * Function return probe trampoline:
332  *      - init_kprobes() establishes a probepoint here
333  *      - When the probed function returns, this probe
334  *              causes the handlers to fire
335  */
336 static void __used kretprobe_trampoline_holder(void)
337 {
338         asm volatile(".global kretprobe_trampoline\n"
339                      "kretprobe_trampoline: bcr 0,0\n");
340 }
341
342 /*
343  * Called when the probe at kretprobe trampoline is hit
344  */
345 static int __kprobes trampoline_probe_handler(struct kprobe *p,
346                                               struct pt_regs *regs)
347 {
348         struct kretprobe_instance *ri = NULL;
349         struct hlist_head *head, empty_rp;
350         struct hlist_node *node, *tmp;
351         unsigned long flags, orig_ret_address = 0;
352         unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
353
354         INIT_HLIST_HEAD(&empty_rp);
355         kretprobe_hash_lock(current, &head, &flags);
356
357         /*
358          * It is possible to have multiple instances associated with a given
359          * task either because an multiple functions in the call path
360          * have a return probe installed on them, and/or more than one return
361          * return probe was registered for a target function.
362          *
363          * We can handle this because:
364          *     - instances are always inserted at the head of the list
365          *     - when multiple return probes are registered for the same
366          *       function, the first instance's ret_addr will point to the
367          *       real return address, and all the rest will point to
368          *       kretprobe_trampoline
369          */
370         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
371                 if (ri->task != current)
372                         /* another task is sharing our hash bucket */
373                         continue;
374
375                 if (ri->rp && ri->rp->handler)
376                         ri->rp->handler(ri, regs);
377
378                 orig_ret_address = (unsigned long)ri->ret_addr;
379                 recycle_rp_inst(ri, &empty_rp);
380
381                 if (orig_ret_address != trampoline_address) {
382                         /*
383                          * This is the real return address. Any other
384                          * instances associated with this task are for
385                          * other calls deeper on the call stack
386                          */
387                         break;
388                 }
389         }
390         kretprobe_assert(ri, orig_ret_address, trampoline_address);
391         regs->psw.addr = orig_ret_address | PSW_ADDR_AMODE;
392
393         reset_current_kprobe();
394         kretprobe_hash_unlock(current, &flags);
395         preempt_enable_no_resched();
396
397         hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
398                 hlist_del(&ri->hlist);
399                 kfree(ri);
400         }
401         /*
402          * By returning a non-zero value, we are telling
403          * kprobe_handler() that we don't want the post_handler
404          * to run (and have re-enabled preemption)
405          */
406         return 1;
407 }
408
409 /*
410  * Called after single-stepping.  p->addr is the address of the
411  * instruction whose first byte has been replaced by the "breakpoint"
412  * instruction.  To avoid the SMP problems that can occur when we
413  * temporarily put back the original opcode to single-step, we
414  * single-stepped a copy of the instruction.  The address of this
415  * copy is p->ainsn.insn.
416  */
417 static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
418 {
419         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
420
421         regs->psw.addr &= PSW_ADDR_INSN;
422
423         if (p->ainsn.fixup & FIXUP_PSW_NORMAL)
424                 regs->psw.addr = (unsigned long)p->addr +
425                                 ((unsigned long)regs->psw.addr -
426                                  (unsigned long)p->ainsn.insn);
427
428         if (p->ainsn.fixup & FIXUP_BRANCH_NOT_TAKEN)
429                 if ((unsigned long)regs->psw.addr -
430                     (unsigned long)p->ainsn.insn == p->ainsn.ilen)
431                         regs->psw.addr = (unsigned long)p->addr + p->ainsn.ilen;
432
433         if (p->ainsn.fixup & FIXUP_RETURN_REGISTER)
434                 regs->gprs[p->ainsn.reg] = ((unsigned long)p->addr +
435                                                 (regs->gprs[p->ainsn.reg] -
436                                                 (unsigned long)p->ainsn.insn))
437                                                 | PSW_ADDR_AMODE;
438
439         regs->psw.addr |= PSW_ADDR_AMODE;
440         /* turn off PER mode */
441         regs->psw.mask &= ~PSW_MASK_PER;
442         /* Restore the original per control regs */
443         __ctl_load(kcb->kprobe_saved_ctl, 9, 11);
444         regs->psw.mask |= kcb->kprobe_saved_imask;
445 }
446
447 static int __kprobes post_kprobe_handler(struct pt_regs *regs)
448 {
449         struct kprobe *cur = kprobe_running();
450         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
451
452         if (!cur)
453                 return 0;
454
455         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
456                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
457                 cur->post_handler(cur, regs, 0);
458         }
459
460         resume_execution(cur, regs);
461
462         /*Restore back the original saved kprobes variables and continue. */
463         if (kcb->kprobe_status == KPROBE_REENTER) {
464                 restore_previous_kprobe(kcb);
465                 goto out;
466         }
467         reset_current_kprobe();
468         if (regs->psw.mask & (PSW_MASK_PER | PSW_MASK_IO))
469                 local_irq_enable();
470 out:
471         preempt_enable_no_resched();
472
473         /*
474          * if somebody else is singlestepping across a probe point, psw mask
475          * will have PER set, in which case, continue the remaining processing
476          * of do_single_step, as if this is not a probe hit.
477          */
478         if (regs->psw.mask & PSW_MASK_PER) {
479                 return 0;
480         }
481
482         return 1;
483 }
484
485 int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
486 {
487         struct kprobe *cur = kprobe_running();
488         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
489         const struct exception_table_entry *entry;
490
491         switch(kcb->kprobe_status) {
492         case KPROBE_SWAP_INST:
493                 /* We are here because the instruction replacement failed */
494                 return 0;
495         case KPROBE_HIT_SS:
496         case KPROBE_REENTER:
497                 /*
498                  * We are here because the instruction being single
499                  * stepped caused a page fault. We reset the current
500                  * kprobe and the nip points back to the probe address
501                  * and allow the page fault handler to continue as a
502                  * normal page fault.
503                  */
504                 regs->psw.addr = (unsigned long)cur->addr | PSW_ADDR_AMODE;
505                 regs->psw.mask &= ~PSW_MASK_PER;
506                 regs->psw.mask |= kcb->kprobe_saved_imask;
507                 if (kcb->kprobe_status == KPROBE_REENTER)
508                         restore_previous_kprobe(kcb);
509                 else {
510                         reset_current_kprobe();
511                         if (regs->psw.mask & (PSW_MASK_PER | PSW_MASK_IO))
512                                 local_irq_enable();
513                 }
514                 preempt_enable_no_resched();
515                 break;
516         case KPROBE_HIT_ACTIVE:
517         case KPROBE_HIT_SSDONE:
518                 /*
519                  * We increment the nmissed count for accounting,
520                  * we can also use npre/npostfault count for accouting
521                  * these specific fault cases.
522                  */
523                 kprobes_inc_nmissed_count(cur);
524
525                 /*
526                  * We come here because instructions in the pre/post
527                  * handler caused the page_fault, this could happen
528                  * if handler tries to access user space by
529                  * copy_from_user(), get_user() etc. Let the
530                  * user-specified handler try to fix it first.
531                  */
532                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
533                         return 1;
534
535                 /*
536                  * In case the user-specified fault handler returned
537                  * zero, try to fix up.
538                  */
539                 entry = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
540                 if (entry) {
541                         regs->psw.addr = entry->fixup | PSW_ADDR_AMODE;
542                         return 1;
543                 }
544
545                 /*
546                  * fixup_exception() could not handle it,
547                  * Let do_page_fault() fix it.
548                  */
549                 break;
550         default:
551                 break;
552         }
553         return 0;
554 }
555
556 /*
557  * Wrapper routine to for handling exceptions.
558  */
559 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
560                                        unsigned long val, void *data)
561 {
562         struct die_args *args = (struct die_args *)data;
563         int ret = NOTIFY_DONE;
564
565         switch (val) {
566         case DIE_BPT:
567                 if (kprobe_handler(args->regs))
568                         ret = NOTIFY_STOP;
569                 break;
570         case DIE_SSTEP:
571                 if (post_kprobe_handler(args->regs))
572                         ret = NOTIFY_STOP;
573                 break;
574         case DIE_TRAP:
575                 /* kprobe_running() needs smp_processor_id() */
576                 preempt_disable();
577                 if (kprobe_running() &&
578                     kprobe_fault_handler(args->regs, args->trapnr))
579                         ret = NOTIFY_STOP;
580                 preempt_enable();
581                 break;
582         default:
583                 break;
584         }
585         return ret;
586 }
587
588 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
589 {
590         struct jprobe *jp = container_of(p, struct jprobe, kp);
591         unsigned long addr;
592         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
593
594         memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
595
596         /* setup return addr to the jprobe handler routine */
597         regs->psw.addr = (unsigned long)(jp->entry) | PSW_ADDR_AMODE;
598
599         /* r14 is the function return address */
600         kcb->jprobe_saved_r14 = (unsigned long)regs->gprs[14];
601         /* r15 is the stack pointer */
602         kcb->jprobe_saved_r15 = (unsigned long)regs->gprs[15];
603         addr = (unsigned long)kcb->jprobe_saved_r15;
604
605         memcpy(kcb->jprobes_stack, (kprobe_opcode_t *) addr,
606                MIN_STACK_SIZE(addr));
607         return 1;
608 }
609
610 void __kprobes jprobe_return(void)
611 {
612         asm volatile(".word 0x0002");
613 }
614
615 void __kprobes jprobe_return_end(void)
616 {
617         asm volatile("bcr 0,0");
618 }
619
620 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
621 {
622         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
623         unsigned long stack_addr = (unsigned long)(kcb->jprobe_saved_r15);
624
625         /* Put the regs back */
626         memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
627         /* put the stack back */
628         memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
629                MIN_STACK_SIZE(stack_addr));
630         preempt_enable_no_resched();
631         return 1;
632 }
633
634 static struct kprobe trampoline_p = {
635         .addr = (kprobe_opcode_t *) & kretprobe_trampoline,
636         .pre_handler = trampoline_probe_handler
637 };
638
639 int __init arch_init_kprobes(void)
640 {
641         return register_kprobe(&trampoline_p);
642 }
643
644 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
645 {
646         if (p->addr == (kprobe_opcode_t *) & kretprobe_trampoline)
647                 return 1;
648         return 0;
649 }