kprobes: add kprobe_insn_mutex and cleanup arch_remove_kprobe()
[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 <asm/cacheflush.h>
29 #include <asm/sections.h>
30 #include <asm/uaccess.h>
31 #include <linux/module.h>
32
33 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
34 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
35
36 struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
37
38 int __kprobes arch_prepare_kprobe(struct kprobe *p)
39 {
40         /* Make sure the probe isn't going on a difficult instruction */
41         if (is_prohibited_opcode((kprobe_opcode_t *) p->addr))
42                 return -EINVAL;
43
44         if ((unsigned long)p->addr & 0x01)
45                 return -EINVAL;
46
47         /* Use the get_insn_slot() facility for correctness */
48         if (!(p->ainsn.insn = get_insn_slot()))
49                 return -ENOMEM;
50
51         memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
52
53         get_instruction_type(&p->ainsn);
54         p->opcode = *p->addr;
55         return 0;
56 }
57
58 int __kprobes is_prohibited_opcode(kprobe_opcode_t *instruction)
59 {
60         switch (*(__u8 *) instruction) {
61         case 0x0c:      /* bassm */
62         case 0x0b:      /* bsm   */
63         case 0x83:      /* diag  */
64         case 0x44:      /* ex    */
65                 return -EINVAL;
66         }
67         switch (*(__u16 *) instruction) {
68         case 0x0101:    /* pr    */
69         case 0xb25a:    /* bsa   */
70         case 0xb240:    /* bakr  */
71         case 0xb258:    /* bsg   */
72         case 0xb218:    /* pc    */
73         case 0xb228:    /* pt    */
74                 return -EINVAL;
75         }
76         return 0;
77 }
78
79 void __kprobes get_instruction_type(struct arch_specific_insn *ainsn)
80 {
81         /* default fixup method */
82         ainsn->fixup = FIXUP_PSW_NORMAL;
83
84         /* save r1 operand */
85         ainsn->reg = (*ainsn->insn & 0xf0) >> 4;
86
87         /* save the instruction length (pop 5-5) in bytes */
88         switch (*(__u8 *) (ainsn->insn) >> 6) {
89         case 0:
90                 ainsn->ilen = 2;
91                 break;
92         case 1:
93         case 2:
94                 ainsn->ilen = 4;
95                 break;
96         case 3:
97                 ainsn->ilen = 6;
98                 break;
99         }
100
101         switch (*(__u8 *) ainsn->insn) {
102         case 0x05:      /* balr */
103         case 0x0d:      /* basr */
104                 ainsn->fixup = FIXUP_RETURN_REGISTER;
105                 /* if r2 = 0, no branch will be taken */
106                 if ((*ainsn->insn & 0x0f) == 0)
107                         ainsn->fixup |= FIXUP_BRANCH_NOT_TAKEN;
108                 break;
109         case 0x06:      /* bctr */
110         case 0x07:      /* bcr  */
111                 ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
112                 break;
113         case 0x45:      /* bal  */
114         case 0x4d:      /* bas  */
115                 ainsn->fixup = FIXUP_RETURN_REGISTER;
116                 break;
117         case 0x47:      /* bc   */
118         case 0x46:      /* bct  */
119         case 0x86:      /* bxh  */
120         case 0x87:      /* bxle */
121                 ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
122                 break;
123         case 0x82:      /* lpsw */
124                 ainsn->fixup = FIXUP_NOT_REQUIRED;
125                 break;
126         case 0xb2:      /* lpswe */
127                 if (*(((__u8 *) ainsn->insn) + 1) == 0xb2) {
128                         ainsn->fixup = FIXUP_NOT_REQUIRED;
129                 }
130                 break;
131         case 0xa7:      /* bras */
132                 if ((*ainsn->insn & 0x0f) == 0x05) {
133                         ainsn->fixup |= FIXUP_RETURN_REGISTER;
134                 }
135                 break;
136         case 0xc0:
137                 if ((*ainsn->insn & 0x0f) == 0x00  /* larl  */
138                         || (*ainsn->insn & 0x0f) == 0x05) /* brasl */
139                 ainsn->fixup |= FIXUP_RETURN_REGISTER;
140                 break;
141         case 0xeb:
142                 if (*(((__u8 *) ainsn->insn) + 5 ) == 0x44 ||   /* bxhg  */
143                         *(((__u8 *) ainsn->insn) + 5) == 0x45) {/* bxleg */
144                         ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
145                 }
146                 break;
147         case 0xe3:      /* bctg */
148                 if (*(((__u8 *) ainsn->insn) + 5) == 0x46) {
149                         ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
150                 }
151                 break;
152         }
153 }
154
155 static int __kprobes swap_instruction(void *aref)
156 {
157         struct ins_replace_args *args = aref;
158         u32 *addr;
159         u32 instr;
160         int err = -EFAULT;
161
162         /*
163          * Text segment is read-only, hence we use stura to bypass dynamic
164          * address translation to exchange the instruction. Since stura
165          * always operates on four bytes, but we only want to exchange two
166          * bytes do some calculations to get things right. In addition we
167          * shall not cross any page boundaries (vmalloc area!) when writing
168          * the new instruction.
169          */
170         addr = (u32 *)((unsigned long)args->ptr & -4UL);
171         if ((unsigned long)args->ptr & 2)
172                 instr = ((*addr) & 0xffff0000) | args->new;
173         else
174                 instr = ((*addr) & 0x0000ffff) | args->new << 16;
175
176         asm volatile(
177                 "       lra     %1,0(%1)\n"
178                 "0:     stura   %2,%1\n"
179                 "1:     la      %0,0\n"
180                 "2:\n"
181                 EX_TABLE(0b,2b)
182                 : "+d" (err)
183                 : "a" (addr), "d" (instr)
184                 : "memory", "cc");
185
186         return err;
187 }
188
189 void __kprobes arch_arm_kprobe(struct kprobe *p)
190 {
191         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
192         unsigned long status = kcb->kprobe_status;
193         struct ins_replace_args args;
194
195         args.ptr = p->addr;
196         args.old = p->opcode;
197         args.new = BREAKPOINT_INSTRUCTION;
198
199         kcb->kprobe_status = KPROBE_SWAP_INST;
200         stop_machine(swap_instruction, &args, NULL);
201         kcb->kprobe_status = status;
202 }
203
204 void __kprobes arch_disarm_kprobe(struct kprobe *p)
205 {
206         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
207         unsigned long status = kcb->kprobe_status;
208         struct ins_replace_args args;
209
210         args.ptr = p->addr;
211         args.old = BREAKPOINT_INSTRUCTION;
212         args.new = p->opcode;
213
214         kcb->kprobe_status = KPROBE_SWAP_INST;
215         stop_machine(swap_instruction, &args, NULL);
216         kcb->kprobe_status = status;
217 }
218
219 void __kprobes arch_remove_kprobe(struct kprobe *p)
220 {
221         if (p->ainsn.insn) {
222                 free_insn_slot(p->ainsn.insn, 0);
223                 p->ainsn.insn = NULL;
224         }
225 }
226
227 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
228 {
229         per_cr_bits kprobe_per_regs[1];
230
231         memset(kprobe_per_regs, 0, sizeof(per_cr_bits));
232         regs->psw.addr = (unsigned long)p->ainsn.insn | PSW_ADDR_AMODE;
233
234         /* Set up the per control reg info, will pass to lctl */
235         kprobe_per_regs[0].em_instruction_fetch = 1;
236         kprobe_per_regs[0].starting_addr = (unsigned long)p->ainsn.insn;
237         kprobe_per_regs[0].ending_addr = (unsigned long)p->ainsn.insn + 1;
238
239         /* Set the PER control regs, turns on single step for this address */
240         __ctl_load(kprobe_per_regs, 9, 11);
241         regs->psw.mask |= PSW_MASK_PER;
242         regs->psw.mask &= ~(PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
243 }
244
245 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
246 {
247         kcb->prev_kprobe.kp = kprobe_running();
248         kcb->prev_kprobe.status = kcb->kprobe_status;
249         kcb->prev_kprobe.kprobe_saved_imask = kcb->kprobe_saved_imask;
250         memcpy(kcb->prev_kprobe.kprobe_saved_ctl, kcb->kprobe_saved_ctl,
251                                         sizeof(kcb->kprobe_saved_ctl));
252 }
253
254 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
255 {
256         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
257         kcb->kprobe_status = kcb->prev_kprobe.status;
258         kcb->kprobe_saved_imask = kcb->prev_kprobe.kprobe_saved_imask;
259         memcpy(kcb->kprobe_saved_ctl, kcb->prev_kprobe.kprobe_saved_ctl,
260                                         sizeof(kcb->kprobe_saved_ctl));
261 }
262
263 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
264                                                 struct kprobe_ctlblk *kcb)
265 {
266         __get_cpu_var(current_kprobe) = p;
267         /* Save the interrupt and per flags */
268         kcb->kprobe_saved_imask = regs->psw.mask &
269             (PSW_MASK_PER | PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
270         /* Save the control regs that govern PER */
271         __ctl_store(kcb->kprobe_saved_ctl, 9, 11);
272 }
273
274 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
275                                         struct pt_regs *regs)
276 {
277         ri->ret_addr = (kprobe_opcode_t *) regs->gprs[14];
278
279         /* Replace the return addr with trampoline addr */
280         regs->gprs[14] = (unsigned long)&kretprobe_trampoline;
281 }
282
283 static int __kprobes kprobe_handler(struct pt_regs *regs)
284 {
285         struct kprobe *p;
286         int ret = 0;
287         unsigned long *addr = (unsigned long *)
288                 ((regs->psw.addr & PSW_ADDR_INSN) - 2);
289         struct kprobe_ctlblk *kcb;
290
291         /*
292          * We don't want to be preempted for the entire
293          * duration of kprobe processing
294          */
295         preempt_disable();
296         kcb = get_kprobe_ctlblk();
297
298         /* Check we're not actually recursing */
299         if (kprobe_running()) {
300                 p = get_kprobe(addr);
301                 if (p) {
302                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
303                             *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
304                                 regs->psw.mask &= ~PSW_MASK_PER;
305                                 regs->psw.mask |= kcb->kprobe_saved_imask;
306                                 goto no_kprobe;
307                         }
308                         /* We have reentered the kprobe_handler(), since
309                          * another probe was hit while within the handler.
310                          * We here save the original kprobes variables and
311                          * just single step on the instruction of the new probe
312                          * without calling any user handlers.
313                          */
314                         save_previous_kprobe(kcb);
315                         set_current_kprobe(p, regs, kcb);
316                         kprobes_inc_nmissed_count(p);
317                         prepare_singlestep(p, regs);
318                         kcb->kprobe_status = KPROBE_REENTER;
319                         return 1;
320                 } else {
321                         p = __get_cpu_var(current_kprobe);
322                         if (p->break_handler && p->break_handler(p, regs)) {
323                                 goto ss_probe;
324                         }
325                 }
326                 goto no_kprobe;
327         }
328
329         p = get_kprobe(addr);
330         if (!p)
331                 /*
332                  * No kprobe at this address. The fault has not been
333                  * caused by a kprobe breakpoint. The race of breakpoint
334                  * vs. kprobe remove does not exist because on s390 we
335                  * use stop_machine to arm/disarm the breakpoints.
336                  */
337                 goto no_kprobe;
338
339         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
340         set_current_kprobe(p, regs, kcb);
341         if (p->pre_handler && p->pre_handler(p, regs))
342                 /* handler has already set things up, so skip ss setup */
343                 return 1;
344
345 ss_probe:
346         prepare_singlestep(p, regs);
347         kcb->kprobe_status = KPROBE_HIT_SS;
348         return 1;
349
350 no_kprobe:
351         preempt_enable_no_resched();
352         return ret;
353 }
354
355 /*
356  * Function return probe trampoline:
357  *      - init_kprobes() establishes a probepoint here
358  *      - When the probed function returns, this probe
359  *              causes the handlers to fire
360  */
361 static void __used kretprobe_trampoline_holder(void)
362 {
363         asm volatile(".global kretprobe_trampoline\n"
364                      "kretprobe_trampoline: bcr 0,0\n");
365 }
366
367 /*
368  * Called when the probe at kretprobe trampoline is hit
369  */
370 static int __kprobes trampoline_probe_handler(struct kprobe *p,
371                                               struct pt_regs *regs)
372 {
373         struct kretprobe_instance *ri = NULL;
374         struct hlist_head *head, empty_rp;
375         struct hlist_node *node, *tmp;
376         unsigned long flags, orig_ret_address = 0;
377         unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
378
379         INIT_HLIST_HEAD(&empty_rp);
380         kretprobe_hash_lock(current, &head, &flags);
381
382         /*
383          * It is possible to have multiple instances associated with a given
384          * task either because an multiple functions in the call path
385          * have a return probe installed on them, and/or more then one return
386          * return probe was registered for a target function.
387          *
388          * We can handle this because:
389          *     - instances are always inserted at the head of the list
390          *     - when multiple return probes are registered for the same
391          *       function, the first instance's ret_addr will point to the
392          *       real return address, and all the rest will point to
393          *       kretprobe_trampoline
394          */
395         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
396                 if (ri->task != current)
397                         /* another task is sharing our hash bucket */
398                         continue;
399
400                 if (ri->rp && ri->rp->handler)
401                         ri->rp->handler(ri, regs);
402
403                 orig_ret_address = (unsigned long)ri->ret_addr;
404                 recycle_rp_inst(ri, &empty_rp);
405
406                 if (orig_ret_address != trampoline_address) {
407                         /*
408                          * This is the real return address. Any other
409                          * instances associated with this task are for
410                          * other calls deeper on the call stack
411                          */
412                         break;
413                 }
414         }
415         kretprobe_assert(ri, orig_ret_address, trampoline_address);
416         regs->psw.addr = orig_ret_address | PSW_ADDR_AMODE;
417
418         reset_current_kprobe();
419         kretprobe_hash_unlock(current, &flags);
420         preempt_enable_no_resched();
421
422         hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
423                 hlist_del(&ri->hlist);
424                 kfree(ri);
425         }
426         /*
427          * By returning a non-zero value, we are telling
428          * kprobe_handler() that we don't want the post_handler
429          * to run (and have re-enabled preemption)
430          */
431         return 1;
432 }
433
434 /*
435  * Called after single-stepping.  p->addr is the address of the
436  * instruction whose first byte has been replaced by the "breakpoint"
437  * instruction.  To avoid the SMP problems that can occur when we
438  * temporarily put back the original opcode to single-step, we
439  * single-stepped a copy of the instruction.  The address of this
440  * copy is p->ainsn.insn.
441  */
442 static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
443 {
444         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
445
446         regs->psw.addr &= PSW_ADDR_INSN;
447
448         if (p->ainsn.fixup & FIXUP_PSW_NORMAL)
449                 regs->psw.addr = (unsigned long)p->addr +
450                                 ((unsigned long)regs->psw.addr -
451                                  (unsigned long)p->ainsn.insn);
452
453         if (p->ainsn.fixup & FIXUP_BRANCH_NOT_TAKEN)
454                 if ((unsigned long)regs->psw.addr -
455                     (unsigned long)p->ainsn.insn == p->ainsn.ilen)
456                         regs->psw.addr = (unsigned long)p->addr + p->ainsn.ilen;
457
458         if (p->ainsn.fixup & FIXUP_RETURN_REGISTER)
459                 regs->gprs[p->ainsn.reg] = ((unsigned long)p->addr +
460                                                 (regs->gprs[p->ainsn.reg] -
461                                                 (unsigned long)p->ainsn.insn))
462                                                 | PSW_ADDR_AMODE;
463
464         regs->psw.addr |= PSW_ADDR_AMODE;
465         /* turn off PER mode */
466         regs->psw.mask &= ~PSW_MASK_PER;
467         /* Restore the original per control regs */
468         __ctl_load(kcb->kprobe_saved_ctl, 9, 11);
469         regs->psw.mask |= kcb->kprobe_saved_imask;
470 }
471
472 static int __kprobes post_kprobe_handler(struct pt_regs *regs)
473 {
474         struct kprobe *cur = kprobe_running();
475         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
476
477         if (!cur)
478                 return 0;
479
480         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
481                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
482                 cur->post_handler(cur, regs, 0);
483         }
484
485         resume_execution(cur, regs);
486
487         /*Restore back the original saved kprobes variables and continue. */
488         if (kcb->kprobe_status == KPROBE_REENTER) {
489                 restore_previous_kprobe(kcb);
490                 goto out;
491         }
492         reset_current_kprobe();
493 out:
494         preempt_enable_no_resched();
495
496         /*
497          * if somebody else is singlestepping across a probe point, psw mask
498          * will have PER set, in which case, continue the remaining processing
499          * of do_single_step, as if this is not a probe hit.
500          */
501         if (regs->psw.mask & PSW_MASK_PER) {
502                 return 0;
503         }
504
505         return 1;
506 }
507
508 int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
509 {
510         struct kprobe *cur = kprobe_running();
511         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
512         const struct exception_table_entry *entry;
513
514         switch(kcb->kprobe_status) {
515         case KPROBE_SWAP_INST:
516                 /* We are here because the instruction replacement failed */
517                 return 0;
518         case KPROBE_HIT_SS:
519         case KPROBE_REENTER:
520                 /*
521                  * We are here because the instruction being single
522                  * stepped caused a page fault. We reset the current
523                  * kprobe and the nip points back to the probe address
524                  * and allow the page fault handler to continue as a
525                  * normal page fault.
526                  */
527                 regs->psw.addr = (unsigned long)cur->addr | PSW_ADDR_AMODE;
528                 regs->psw.mask &= ~PSW_MASK_PER;
529                 regs->psw.mask |= kcb->kprobe_saved_imask;
530                 if (kcb->kprobe_status == KPROBE_REENTER)
531                         restore_previous_kprobe(kcb);
532                 else
533                         reset_current_kprobe();
534                 preempt_enable_no_resched();
535                 break;
536         case KPROBE_HIT_ACTIVE:
537         case KPROBE_HIT_SSDONE:
538                 /*
539                  * We increment the nmissed count for accounting,
540                  * we can also use npre/npostfault count for accouting
541                  * these specific fault cases.
542                  */
543                 kprobes_inc_nmissed_count(cur);
544
545                 /*
546                  * We come here because instructions in the pre/post
547                  * handler caused the page_fault, this could happen
548                  * if handler tries to access user space by
549                  * copy_from_user(), get_user() etc. Let the
550                  * user-specified handler try to fix it first.
551                  */
552                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
553                         return 1;
554
555                 /*
556                  * In case the user-specified fault handler returned
557                  * zero, try to fix up.
558                  */
559                 entry = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
560                 if (entry) {
561                         regs->psw.addr = entry->fixup | PSW_ADDR_AMODE;
562                         return 1;
563                 }
564
565                 /*
566                  * fixup_exception() could not handle it,
567                  * Let do_page_fault() fix it.
568                  */
569                 break;
570         default:
571                 break;
572         }
573         return 0;
574 }
575
576 /*
577  * Wrapper routine to for handling exceptions.
578  */
579 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
580                                        unsigned long val, void *data)
581 {
582         struct die_args *args = (struct die_args *)data;
583         int ret = NOTIFY_DONE;
584
585         switch (val) {
586         case DIE_BPT:
587                 if (kprobe_handler(args->regs))
588                         ret = NOTIFY_STOP;
589                 break;
590         case DIE_SSTEP:
591                 if (post_kprobe_handler(args->regs))
592                         ret = NOTIFY_STOP;
593                 break;
594         case DIE_TRAP:
595                 /* kprobe_running() needs smp_processor_id() */
596                 preempt_disable();
597                 if (kprobe_running() &&
598                     kprobe_fault_handler(args->regs, args->trapnr))
599                         ret = NOTIFY_STOP;
600                 preempt_enable();
601                 break;
602         default:
603                 break;
604         }
605         return ret;
606 }
607
608 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
609 {
610         struct jprobe *jp = container_of(p, struct jprobe, kp);
611         unsigned long addr;
612         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
613
614         memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
615
616         /* setup return addr to the jprobe handler routine */
617         regs->psw.addr = (unsigned long)(jp->entry) | PSW_ADDR_AMODE;
618
619         /* r14 is the function return address */
620         kcb->jprobe_saved_r14 = (unsigned long)regs->gprs[14];
621         /* r15 is the stack pointer */
622         kcb->jprobe_saved_r15 = (unsigned long)regs->gprs[15];
623         addr = (unsigned long)kcb->jprobe_saved_r15;
624
625         memcpy(kcb->jprobes_stack, (kprobe_opcode_t *) addr,
626                MIN_STACK_SIZE(addr));
627         return 1;
628 }
629
630 void __kprobes jprobe_return(void)
631 {
632         asm volatile(".word 0x0002");
633 }
634
635 void __kprobes jprobe_return_end(void)
636 {
637         asm volatile("bcr 0,0");
638 }
639
640 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
641 {
642         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
643         unsigned long stack_addr = (unsigned long)(kcb->jprobe_saved_r15);
644
645         /* Put the regs back */
646         memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
647         /* put the stack back */
648         memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
649                MIN_STACK_SIZE(stack_addr));
650         preempt_enable_no_resched();
651         return 1;
652 }
653
654 static struct kprobe trampoline_p = {
655         .addr = (kprobe_opcode_t *) & kretprobe_trampoline,
656         .pre_handler = trampoline_probe_handler
657 };
658
659 int __init arch_init_kprobes(void)
660 {
661         return register_kprobe(&trampoline_p);
662 }
663
664 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
665 {
666         if (p->addr == (kprobe_opcode_t *) & kretprobe_trampoline)
667                 return 1;
668         return 0;
669 }