arch/arm/kernel/kprobes.c

   1 /*
   2  * arch/arm/kernel/kprobes.c
   3  *
   4  * Kprobes on ARM
   5  *
   6  * Abhishek Sagar <sagar.abhishek@gmail.com>
   7  * Copyright (C) 2006, 2007 Motorola Inc.
   8  *
   9  * Nicolas Pitre <nico@marvell.com>
  10  * Copyright (C) 2007 Marvell Ltd.
  11  *
  12  * This program is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License version 2 as
  14  * published by the Free Software Foundation.
  15  *
  16  * This program is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  19  * General Public License for more details.
  20  */
  21
  22 #include <linux/kernel.h>
  23 #include <linux/kprobes.h>
  24 #include <linux/module.h>
  25 #include <linux/slab.h>
  26 #include <linux/stop_machine.h>
  27 #include <linux/stringify.h>
  28 #include <asm/traps.h>
  29 #include <asm/cacheflush.h>
  30
  31 #include "kprobes.h"
  32 #include "patch.h"
  33
  34 #define MIN_STACK_SIZE(addr)                            \
  35         min((unsigned long)MAX_STACK_SIZE,              \
  36             (unsigned long)current_thread_info() + THREAD_START_SP - (addr))
  37
  38 #define flush_insns(addr, size)                         \
  39         flush_icache_range((unsigned long)(addr),       \
  40                            (unsigned long)(addr) +      \
  41                            (size))
  42
  43 /* Used as a marker in ARM_pc to note when we're in a jprobe. */
  44 #define JPROBE_MAGIC_ADDR               0xffffffff
  45
  46 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  47 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  48
  49
  50 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  51 {
  52         kprobe_opcode_t insn;
  53         kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
  54         unsigned long addr = (unsigned long)p->addr;
  55         bool thumb;
  56         kprobe_decode_insn_t *decode_insn;
  57         int is;
  58
  59         if (in_exception_text(addr))
  60                 return -EINVAL;
  61
  62 #ifdef CONFIG_THUMB2_KERNEL
  63         thumb = true;
  64         addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
  65         insn = ((u16 *)addr)[0];
  66         if (is_wide_instruction(insn)) {
  67                 insn <<= 16;
  68                 insn |= ((u16 *)addr)[1];
  69                 decode_insn = thumb32_kprobe_decode_insn;
  70         } else
  71                 decode_insn = thumb16_kprobe_decode_insn;
  72 #else /* !CONFIG_THUMB2_KERNEL */
  73         thumb = false;
  74         if (addr & 0x3)
  75                 return -EINVAL;
  76         insn = *p->addr;
  77         decode_insn = arm_kprobe_decode_insn;
  78 #endif
  79
  80         p->opcode = insn;
  81         p->ainsn.insn = tmp_insn;
  82
  83         switch ((*decode_insn)(insn, &p->ainsn)) {
  84         case INSN_REJECTED:     /* not supported */
  85                 return -EINVAL;
  86
  87         case INSN_GOOD:         /* instruction uses slot */
  88                 p->ainsn.insn = get_insn_slot();
  89                 if (!p->ainsn.insn)
  90                         return -ENOMEM;
  91                 for (is = 0; is < MAX_INSN_SIZE; ++is)
  92                         p->ainsn.insn[is] = tmp_insn[is];
  93                 flush_insns(p->ainsn.insn,
  94                                 sizeof(p->ainsn.insn[0]) * MAX_INSN_SIZE);
  95                 p->ainsn.insn_fn = (kprobe_insn_fn_t *)
  96                                         ((uintptr_t)p->ainsn.insn | thumb);
  97                 break;
  98
  99         case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */
 100                 p->ainsn.insn = NULL;
 101                 break;
 102         }
 103
 104         return 0;
 105 }
 106
 107 void __kprobes arch_arm_kprobe(struct kprobe *p)
 108 {
 109         unsigned int brkp;
 110         void *addr;
 111
 112         if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
 113                 /* Remove any Thumb flag */
 114                 addr = (void *)((uintptr_t)p->addr & ~1);
 115
 116                 if (is_wide_instruction(p->opcode))
 117                         brkp = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION;
 118                 else
 119                         brkp = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION;
 120         } else {
 121                 kprobe_opcode_t insn = p->opcode;
 122
 123                 addr = p->addr;
 124                 brkp = KPROBE_ARM_BREAKPOINT_INSTRUCTION;
 125
 126                 if (insn >= 0xe0000000)
 127                         brkp |= 0xe0000000;  /* Unconditional instruction */
 128                 else
 129                         brkp |= insn & 0xf0000000;  /* Copy condition from insn */
 130         }
 131
 132         patch_text(addr, brkp);
 133 }
 134
 135 /*
 136  * The actual disarming is done here on each CPU and synchronized using
 137  * stop_machine. This synchronization is necessary on SMP to avoid removing
 138  * a probe between the moment the 'Undefined Instruction' exception is raised
 139  * and the moment the exception handler reads the faulting instruction from
 140  * memory. It is also needed to atomically set the two half-words of a 32-bit
 141  * Thumb breakpoint.
 142  */
 143 int __kprobes __arch_disarm_kprobe(void *p)
 144 {
 145         struct kprobe *kp = p;
 146         void *addr = (void *)((uintptr_t)kp->addr & ~1);
 147
 148         __patch_text(addr, kp->opcode);
 149
 150         return 0;
 151 }
 152
 153 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 154 {
 155         stop_machine(__arch_disarm_kprobe, p, cpu_online_mask);
 156 }
 157
 158 void __kprobes arch_remove_kprobe(struct kprobe *p)
 159 {
 160         if (p->ainsn.insn) {
 161                 free_insn_slot(p->ainsn.insn, 0);
 162                 p->ainsn.insn = NULL;
 163         }
 164 }
 165
 166 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 167 {
 168         kcb->prev_kprobe.kp = kprobe_running();
 169         kcb->prev_kprobe.status = kcb->kprobe_status;
 170 }
 171
 172 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 173 {
 174         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 175         kcb->kprobe_status = kcb->prev_kprobe.status;
 176 }
 177
 178 static void __kprobes set_current_kprobe(struct kprobe *p)
 179 {
 180         __this_cpu_write(current_kprobe, p);
 181 }
 182
 183 static void __kprobes
 184 singlestep_skip(struct kprobe *p, struct pt_regs *regs)
 185 {
 186 #ifdef CONFIG_THUMB2_KERNEL
 187         regs->ARM_cpsr = it_advance(regs->ARM_cpsr);
 188         if (is_wide_instruction(p->opcode))
 189                 regs->ARM_pc += 4;
 190         else
 191                 regs->ARM_pc += 2;
 192 #else
 193         regs->ARM_pc += 4;
 194 #endif
 195 }
 196
 197 static inline void __kprobes
 198 singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb)
 199 {
 200         p->ainsn.insn_singlestep(p, regs);
 201 }
 202
 203 /*
 204  * Called with IRQs disabled. IRQs must remain disabled from that point
 205  * all the way until processing this kprobe is complete.  The current
 206  * kprobes implementation cannot process more than one nested level of
 207  * kprobe, and that level is reserved for user kprobe handlers, so we can't
 208  * risk encountering a new kprobe in an interrupt handler.
 209  */
 210 void __kprobes kprobe_handler(struct pt_regs *regs)
 211 {
 212         struct kprobe *p, *cur;
 213         struct kprobe_ctlblk *kcb;
 214
 215         kcb = get_kprobe_ctlblk();
 216         cur = kprobe_running();
 217
 218 #ifdef CONFIG_THUMB2_KERNEL
 219         /*
 220          * First look for a probe which was registered using an address with
 221          * bit 0 set, this is the usual situation for pointers to Thumb code.
 222          * If not found, fallback to looking for one with bit 0 clear.
 223          */
 224         p = get_kprobe((kprobe_opcode_t *)(regs->ARM_pc | 1));
 225         if (!p)
 226                 p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
 227
 228 #else /* ! CONFIG_THUMB2_KERNEL */
 229         p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
 230 #endif
 231
 232         if (p) {
 233                 if (cur) {
 234                         /* Kprobe is pending, so we're recursing. */
 235                         switch (kcb->kprobe_status) {
 236                         case KPROBE_HIT_ACTIVE:
 237                         case KPROBE_HIT_SSDONE:
 238                                 /* A pre- or post-handler probe got us here. */
 239                                 kprobes_inc_nmissed_count(p);
 240                                 save_previous_kprobe(kcb);
 241                                 set_current_kprobe(p);
 242                                 kcb->kprobe_status = KPROBE_REENTER;
 243                                 singlestep(p, regs, kcb);
 244                                 restore_previous_kprobe(kcb);
 245                                 break;
 246                         default:
 247                                 /* impossible cases */
 248                                 BUG();
 249                         }
 250                 } else if (p->ainsn.insn_check_cc(regs->ARM_cpsr)) {
 251                         /* Probe hit and conditional execution check ok. */
 252                         set_current_kprobe(p);
 253                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 254
 255                         /*
 256                          * If we have no pre-handler or it returned 0, we
 257                          * continue with normal processing.  If we have a
 258                          * pre-handler and it returned non-zero, it prepped
 259                          * for calling the break_handler below on re-entry,
 260                          * so get out doing nothing more here.
 261                          */
 262                         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 263                                 kcb->kprobe_status = KPROBE_HIT_SS;
 264                                 singlestep(p, regs, kcb);
 265                                 if (p->post_handler) {
 266                                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 267                                         p->post_handler(p, regs, 0);
 268                                 }
 269                                 reset_current_kprobe();
 270                         }
 271                 } else {
 272                         /*
 273                          * Probe hit but conditional execution check failed,
 274                          * so just skip the instruction and continue as if
 275                          * nothing had happened.
 276                          */
 277                         singlestep_skip(p, regs);
 278                 }
 279         } else if (cur) {
 280                 /* We probably hit a jprobe.  Call its break handler. */
 281                 if (cur->break_handler && cur->break_handler(cur, regs)) {
 282                         kcb->kprobe_status = KPROBE_HIT_SS;
 283                         singlestep(cur, regs, kcb);
 284                         if (cur->post_handler) {
 285                                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 286                                 cur->post_handler(cur, regs, 0);
 287                         }
 288                 }
 289                 reset_current_kprobe();
 290         } else {
 291                 /*
 292                  * The probe was removed and a race is in progress.
 293                  * There is nothing we can do about it.  Let's restart
 294                  * the instruction.  By the time we can restart, the
 295                  * real instruction will be there.
 296                  */
 297         }
 298 }
 299
 300 static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
 301 {
 302         unsigned long flags;
 303         local_irq_save(flags);
 304         kprobe_handler(regs);
 305         local_irq_restore(flags);
 306         return 0;
 307 }
 308
 309 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 310 {
 311         struct kprobe *cur = kprobe_running();
 312         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 313
 314         switch (kcb->kprobe_status) {
 315         case KPROBE_HIT_SS:
 316         case KPROBE_REENTER:
 317                 /*
 318                  * We are here because the instruction being single
 319                  * stepped caused a page fault. We reset the current
 320                  * kprobe and the PC to point back to the probe address
 321                  * and allow the page fault handler to continue as a
 322                  * normal page fault.
 323                  */
 324                 regs->ARM_pc = (long)cur->addr;
 325                 if (kcb->kprobe_status == KPROBE_REENTER) {
 326                         restore_previous_kprobe(kcb);
 327                 } else {
 328                         reset_current_kprobe();
 329                 }
 330                 break;
 331
 332         case KPROBE_HIT_ACTIVE:
 333         case KPROBE_HIT_SSDONE:
 334                 /*
 335                  * We increment the nmissed count for accounting,
 336                  * we can also use npre/npostfault count for accounting
 337                  * these specific fault cases.
 338                  */
 339                 kprobes_inc_nmissed_count(cur);
 340
 341                 /*
 342                  * We come here because instructions in the pre/post
 343                  * handler caused the page_fault, this could happen
 344                  * if handler tries to access user space by
 345                  * copy_from_user(), get_user() etc. Let the
 346                  * user-specified handler try to fix it.
 347                  */
 348                 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
 349                         return 1;
 350                 break;
 351
 352         default:
 353                 break;
 354         }
 355
 356         return 0;
 357 }
 358
 359 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 360                                        unsigned long val, void *data)
 361 {
 362         /*
 363          * notify_die() is currently never called on ARM,
 364          * so this callback is currently empty.
 365          */
 366         return NOTIFY_DONE;
 367 }
 368
 369 /*
 370  * When a retprobed function returns, trampoline_handler() is called,
 371  * calling the kretprobe's handler. We construct a struct pt_regs to
 372  * give a view of registers r0-r11 to the user return-handler.  This is
 373  * not a complete pt_regs structure, but that should be plenty sufficient
 374  * for kretprobe handlers which should normally be interested in r0 only
 375  * anyway.
 376  */
 377 void __naked __kprobes kretprobe_trampoline(void)
 378 {
 379         __asm__ __volatile__ (
 380                 "stmdb  sp!, {r0 - r11}         \n\t"
 381                 "mov    r0, sp                  \n\t"
 382                 "bl     trampoline_handler      \n\t"
 383                 "mov    lr, r0                  \n\t"
 384                 "ldmia  sp!, {r0 - r11}         \n\t"
 385 #ifdef CONFIG_THUMB2_KERNEL
 386                 "bx     lr                      \n\t"
 387 #else
 388                 "mov    pc, lr                  \n\t"
 389 #endif
 390                 : : : "memory");
 391 }
 392
 393 /* Called from kretprobe_trampoline */
 394 static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
 395 {
 396         struct kretprobe_instance *ri = NULL;
 397         struct hlist_head *head, empty_rp;
 398         struct hlist_node *tmp;
 399         unsigned long flags, orig_ret_address = 0;
 400         unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
 401
 402         INIT_HLIST_HEAD(&empty_rp);
 403         kretprobe_hash_lock(current, &head, &flags);
 404
 405         /*
 406          * It is possible to have multiple instances associated with a given
 407          * task either because multiple functions in the call path have
 408          * a return probe installed on them, and/or more than one return
 409          * probe was registered for a target function.
 410          *
 411          * We can handle this because:
 412          *     - instances are always inserted at the head of the list
 413          *     - when multiple return probes are registered for the same
 414          *       function, the first instance's ret_addr will point to the
 415          *       real return address, and all the rest will point to
 416          *       kretprobe_trampoline
 417          */
 418         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 419                 if (ri->task != current)
 420                         /* another task is sharing our hash bucket */
 421                         continue;
 422
 423                 if (ri->rp && ri->rp->handler) {
 424                         __this_cpu_write(current_kprobe, &ri->rp->kp);
 425                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 426                         ri->rp->handler(ri, regs);
 427                         __this_cpu_write(current_kprobe, NULL);
 428                 }
 429
 430                 orig_ret_address = (unsigned long)ri->ret_addr;
 431                 recycle_rp_inst(ri, &empty_rp);
 432
 433                 if (orig_ret_address != trampoline_address)
 434                         /*
 435                          * This is the real return address. Any other
 436                          * instances associated with this task are for
 437                          * other calls deeper on the call stack
 438                          */
 439                         break;
 440         }
 441
 442         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 443         kretprobe_hash_unlock(current, &flags);
 444
 445         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
 446                 hlist_del(&ri->hlist);
 447                 kfree(ri);
 448         }
 449
 450         return (void *)orig_ret_address;
 451 }
 452
 453 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 454                                       struct pt_regs *regs)
 455 {
 456         ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
 457
 458         /* Replace the return addr with trampoline addr. */
 459         regs->ARM_lr = (unsigned long)&kretprobe_trampoline;
 460 }
 461
 462 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 463 {
 464         struct jprobe *jp = container_of(p, struct jprobe, kp);
 465         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 466         long sp_addr = regs->ARM_sp;
 467         long cpsr;
 468
 469         kcb->jprobe_saved_regs = *regs;
 470         memcpy(kcb->jprobes_stack, (void *)sp_addr, MIN_STACK_SIZE(sp_addr));
 471         regs->ARM_pc = (long)jp->entry;
 472
 473         cpsr = regs->ARM_cpsr | PSR_I_BIT;
 474 #ifdef CONFIG_THUMB2_KERNEL
 475         /* Set correct Thumb state in cpsr */
 476         if (regs->ARM_pc & 1)
 477                 cpsr |= PSR_T_BIT;
 478         else
 479                 cpsr &= ~PSR_T_BIT;
 480 #endif
 481         regs->ARM_cpsr = cpsr;
 482
 483         preempt_disable();
 484         return 1;
 485 }
 486
 487 void __kprobes jprobe_return(void)
 488 {
 489         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 490
 491         __asm__ __volatile__ (
 492                 /*
 493                  * Setup an empty pt_regs. Fill SP and PC fields as
 494                  * they're needed by longjmp_break_handler.
 495                  *
 496                  * We allocate some slack between the original SP and start of
 497                  * our fabricated regs. To be precise we want to have worst case
 498                  * covered which is STMFD with all 16 regs so we allocate 2 *
 499                  * sizeof(struct_pt_regs)).
 500                  *
 501                  * This is to prevent any simulated instruction from writing
 502                  * over the regs when they are accessing the stack.
 503                  */
 504 #ifdef CONFIG_THUMB2_KERNEL
 505                 "sub    r0, %0, %1              \n\t"
 506                 "mov    sp, r0                  \n\t"
 507 #else
 508                 "sub    sp, %0, %1              \n\t"
 509 #endif
 510                 "ldr    r0, ="__stringify(JPROBE_MAGIC_ADDR)"\n\t"
 511                 "str    %0, [sp, %2]            \n\t"
 512                 "str    r0, [sp, %3]            \n\t"
 513                 "mov    r0, sp                  \n\t"
 514                 "bl     kprobe_handler          \n\t"
 515
 516                 /*
 517                  * Return to the context saved by setjmp_pre_handler
 518                  * and restored by longjmp_break_handler.
 519                  */
 520 #ifdef CONFIG_THUMB2_KERNEL
 521                 "ldr    lr, [sp, %2]            \n\t" /* lr = saved sp */
 522                 "ldrd   r0, r1, [sp, %5]        \n\t" /* r0,r1 = saved lr,pc */
 523                 "ldr    r2, [sp, %4]            \n\t" /* r2 = saved psr */
 524                 "stmdb  lr!, {r0, r1, r2}       \n\t" /* push saved lr and */
 525                                                       /* rfe context */
 526                 "ldmia  sp, {r0 - r12}          \n\t"
 527                 "mov    sp, lr                  \n\t"
 528                 "ldr    lr, [sp], #4            \n\t"
 529                 "rfeia  sp!                     \n\t"
 530 #else
 531                 "ldr    r0, [sp, %4]            \n\t"
 532                 "msr    cpsr_cxsf, r0           \n\t"
 533                 "ldmia  sp, {r0 - pc}           \n\t"
 534 #endif
 535                 :
 536                 : "r" (kcb->jprobe_saved_regs.ARM_sp),
 537                   "I" (sizeof(struct pt_regs) * 2),
 538                   "J" (offsetof(struct pt_regs, ARM_sp)),
 539                   "J" (offsetof(struct pt_regs, ARM_pc)),
 540                   "J" (offsetof(struct pt_regs, ARM_cpsr)),
 541                   "J" (offsetof(struct pt_regs, ARM_lr))
 542                 : "memory", "cc");
 543 }
 544
 545 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 546 {
 547         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 548         long stack_addr = kcb->jprobe_saved_regs.ARM_sp;
 549         long orig_sp = regs->ARM_sp;
 550         struct jprobe *jp = container_of(p, struct jprobe, kp);
 551
 552         if (regs->ARM_pc == JPROBE_MAGIC_ADDR) {
 553                 if (orig_sp != stack_addr) {
 554                         struct pt_regs *saved_regs =
 555                                 (struct pt_regs *)kcb->jprobe_saved_regs.ARM_sp;
 556                         printk("current sp %lx does not match saved sp %lx\n",
 557                                orig_sp, stack_addr);
 558                         printk("Saved registers for jprobe %p\n", jp);
 559                         show_regs(saved_regs);
 560                         printk("Current registers\n");
 561                         show_regs(regs);
 562                         BUG();
 563                 }
 564                 *regs = kcb->jprobe_saved_regs;
 565                 memcpy((void *)stack_addr, kcb->jprobes_stack,
 566                        MIN_STACK_SIZE(stack_addr));
 567                 preempt_enable_no_resched();
 568                 return 1;
 569         }
 570         return 0;
 571 }
 572
 573 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 574 {
 575         return 0;
 576 }
 577
 578 #ifdef CONFIG_THUMB2_KERNEL
 579
 580 static struct undef_hook kprobes_thumb16_break_hook = {
 581         .instr_mask     = 0xffff,
 582         .instr_val      = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION,
 583         .cpsr_mask      = MODE_MASK,
 584         .cpsr_val       = SVC_MODE,
 585         .fn             = kprobe_trap_handler,
 586 };
 587
 588 static struct undef_hook kprobes_thumb32_break_hook = {
 589         .instr_mask     = 0xffffffff,
 590         .instr_val      = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION,
 591         .cpsr_mask      = MODE_MASK,
 592         .cpsr_val       = SVC_MODE,
 593         .fn             = kprobe_trap_handler,
 594 };
 595
 596 #else  /* !CONFIG_THUMB2_KERNEL */
 597
 598 static struct undef_hook kprobes_arm_break_hook = {
 599         .instr_mask     = 0x0fffffff,
 600         .instr_val      = KPROBE_ARM_BREAKPOINT_INSTRUCTION,
 601         .cpsr_mask      = MODE_MASK,
 602         .cpsr_val       = SVC_MODE,
 603         .fn             = kprobe_trap_handler,
 604 };
 605
 606 #endif /* !CONFIG_THUMB2_KERNEL */
 607
 608 int __init arch_init_kprobes()
 609 {
 610         arm_kprobe_decode_init();
 611 #ifdef CONFIG_THUMB2_KERNEL
 612         register_undef_hook(&kprobes_thumb16_break_hook);
 613         register_undef_hook(&kprobes_thumb32_break_hook);
 614 #else
 615         register_undef_hook(&kprobes_arm_break_hook);
 616 #endif
 617         return 0;
 618 }