summaryrefslogtreecommitdiffstats
path: root/libbacktrace/BacktraceOffline.cpp
blob: 0a2f5a31f1f4ffbd36a382f39a645de82b9ab435 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "BacktraceOffline.h"

extern "C" {
#define UNW_REMOTE_ONLY
#include <dwarf.h>
}

#include <pthread.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <ucontext.h>
#include <unistd.h>

#include <memory>
#include <mutex>
#include <string>
#include <vector>

#include <android-base/file.h>
#include <android-base/macros.h>
#include <backtrace/Backtrace.h>
#include <backtrace/BacktraceMap.h>
#include <ziparchive/zip_archive.h>

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wunused-parameter"

#include <llvm/ADT/StringRef.h>
#include <llvm/Object/Binary.h>
#include <llvm/Object/ELFObjectFile.h>
#include <llvm/Object/ObjectFile.h>

#pragma clang diagnostic pop

#include "BacktraceLog.h"

struct EhFrame {
  uint64_t hdr_vaddr;
  uint64_t vaddr;
  uint64_t fde_table_offset;
  uintptr_t min_func_vaddr;
  std::vector<uint8_t> hdr_data;
  std::vector<uint8_t> data;
};

struct ArmIdxEntry {
  uint32_t func_offset;
  uint32_t value;
};

struct ArmExidx {
  uint64_t exidx_vaddr;
  uint64_t extab_vaddr;
  std::vector<ArmIdxEntry> exidx_data;
  std::vector<uint8_t> extab_data;
  // There is a one-to-one map from exidx_data.func_offset to func_vaddr_array.
  std::vector<uint32_t> func_vaddr_array;
};

struct DebugFrameInfo {
  bool has_arm_exidx;
  bool has_eh_frame;
  bool has_debug_frame;
  bool has_gnu_debugdata;

  EhFrame eh_frame;
  ArmExidx arm_exidx;

  uint64_t min_vaddr;
  uint64_t text_end_vaddr;

  DebugFrameInfo() : has_arm_exidx(false), has_eh_frame(false),
      has_debug_frame(false), has_gnu_debugdata(false) { }
};

void Space::Clear() {
  start = 0;
  end = 0;
  data = nullptr;
}

size_t Space::Read(uint64_t addr, uint8_t* buffer, size_t size) {
  if (addr >= start && addr < end) {
    size_t read_size = std::min(size, static_cast<size_t>(end - addr));
    memcpy(buffer, data + (addr - start), read_size);
    return read_size;
  }
  return 0;
}

static int FindProcInfo(unw_addr_space_t addr_space, unw_word_t ip, unw_proc_info* proc_info,
                        int need_unwind_info, void* arg) {
  BacktraceOffline* backtrace = reinterpret_cast<BacktraceOffline*>(arg);
  bool result = backtrace->FindProcInfo(addr_space, ip, proc_info, need_unwind_info);
  return result ? 0 : -UNW_EINVAL;
}

static void PutUnwindInfo(unw_addr_space_t, unw_proc_info_t*, void*) {
}

static int GetDynInfoListAddr(unw_addr_space_t, unw_word_t*, void*) {
  return -UNW_ENOINFO;
}

static int AccessMem(unw_addr_space_t, unw_word_t addr, unw_word_t* value, int write, void* arg) {
  if (write == 1) {
    return -UNW_EINVAL;
  }
  BacktraceOffline* backtrace = reinterpret_cast<BacktraceOffline*>(arg);
  *value = 0;
  size_t read_size = backtrace->Read(addr, reinterpret_cast<uint8_t*>(value), sizeof(unw_word_t));
  // Strictly we should check if read_size matches sizeof(unw_word_t), but it is possible in
  // .eh_frame_hdr that the section can end at a position not aligned in sizeof(unw_word_t), and
  // we should permit the read at the end of the section.
  return (read_size > 0u ? 0 : -UNW_EINVAL);
}

static int AccessReg(unw_addr_space_t, unw_regnum_t unwind_reg, unw_word_t* value, int write,
                     void* arg) {
  if (write == 1) {
    return -UNW_EINVAL;
  }
  BacktraceOffline* backtrace = reinterpret_cast<BacktraceOffline*>(arg);
  uint64_t reg_value;
  bool result = backtrace->ReadReg(unwind_reg, &reg_value);
  if (result) {
    *value = static_cast<unw_word_t>(reg_value);
  }
  return result ? 0 : -UNW_EINVAL;
}

static int AccessFpReg(unw_addr_space_t, unw_regnum_t, unw_fpreg_t*, int, void*) {
  return -UNW_EINVAL;
}

static int Resume(unw_addr_space_t, unw_cursor_t*, void*) {
  return -UNW_EINVAL;
}

static int GetProcName(unw_addr_space_t, unw_word_t, char*, size_t, unw_word_t*, void*) {
  return -UNW_EINVAL;
}

static unw_accessors_t accessors = {
    .find_proc_info = FindProcInfo,
    .put_unwind_info = PutUnwindInfo,
    .get_dyn_info_list_addr = GetDynInfoListAddr,
    .access_mem = AccessMem,
    .access_reg = AccessReg,
    .access_fpreg = AccessFpReg,
    .resume = Resume,
    .get_proc_name = GetProcName,
};

bool BacktraceOffline::Unwind(size_t num_ignore_frames, ucontext_t* context) {
  if (context == nullptr) {
    BACK_LOGW("The context is needed for offline backtracing.");
    error_ = BACKTRACE_UNWIND_ERROR_NO_CONTEXT;
    return false;
  }
  context_ = context;
  error_ = BACKTRACE_UNWIND_NO_ERROR;

  unw_addr_space_t addr_space = unw_create_addr_space(&accessors, 0);
  unw_cursor_t cursor;
  int ret = unw_init_remote(&cursor, addr_space, this);
  if (ret != 0) {
    BACK_LOGW("unw_init_remote failed %d", ret);
    unw_destroy_addr_space(addr_space);
    error_ = BACKTRACE_UNWIND_ERROR_SETUP_FAILED;
    return false;
  }
  size_t num_frames = 0;
  do {
    unw_word_t pc;
    ret = unw_get_reg(&cursor, UNW_REG_IP, &pc);
    if (ret < 0) {
      BACK_LOGW("Failed to read IP %d", ret);
      break;
    }
    unw_word_t sp;
    ret = unw_get_reg(&cursor, UNW_REG_SP, &sp);
    if (ret < 0) {
      BACK_LOGW("Failed to read SP %d", ret);
      break;
    }

    if (num_ignore_frames == 0) {
      frames_.resize(num_frames + 1);
      backtrace_frame_data_t* frame = &frames_[num_frames];
      frame->num = num_frames;
      frame->pc = static_cast<uintptr_t>(pc);
      frame->sp = static_cast<uintptr_t>(sp);
      frame->stack_size = 0;

      if (num_frames > 0) {
        backtrace_frame_data_t* prev = &frames_[num_frames - 1];
        prev->stack_size = frame->sp - prev->sp;
      }
      frame->func_name = GetFunctionName(frame->pc, &frame->func_offset);
      FillInMap(frame->pc, &frame->map);
      num_frames++;
    } else {
      num_ignore_frames--;
    }
    ret = unw_step(&cursor);
  } while (ret > 0 && num_frames < MAX_BACKTRACE_FRAMES);

  unw_destroy_addr_space(addr_space);
  context_ = nullptr;
  return true;
}

bool BacktraceOffline::ReadWord(uintptr_t ptr, word_t* out_value) {
  size_t bytes_read = Read(ptr, reinterpret_cast<uint8_t*>(out_value), sizeof(word_t));
  return bytes_read == sizeof(word_t);
}

size_t BacktraceOffline::Read(uintptr_t addr, uint8_t* buffer, size_t bytes) {
  // Normally, libunwind needs stack information and call frame information to do remote unwinding.
  // If call frame information is stored in .debug_frame, libunwind can read it from file
  // by itself. If call frame information is stored in .eh_frame, we need to provide data in
  // .eh_frame/.eh_frame_hdr sections.
  // The order of readings below doesn't matter, as the spaces don't overlap with each other.
  size_t read_size = eh_frame_hdr_space_.Read(addr, buffer, bytes);
  if (read_size != 0) {
    return read_size;
  }
  read_size = eh_frame_space_.Read(addr, buffer, bytes);
  if (read_size != 0) {
    return read_size;
  }
  read_size = arm_exidx_space_.Read(addr, buffer, bytes);
  if (read_size != 0) {
    return read_size;
  }
  read_size = arm_extab_space_.Read(addr, buffer, bytes);
  if (read_size != 0) {
    return read_size;
  }
  read_size = stack_space_.Read(addr, buffer, bytes);
  return read_size;
}

bool BacktraceOffline::FindProcInfo(unw_addr_space_t addr_space, uint64_t ip,
                                    unw_proc_info_t* proc_info, int need_unwind_info) {
  backtrace_map_t map;
  FillInMap(ip, &map);
  if (!BacktraceMap::IsValid(map)) {
    return false;
  }
  const std::string& filename = map.name;
  DebugFrameInfo* debug_frame = GetDebugFrameInFile(filename);
  if (debug_frame == nullptr) {
    return false;
  }

  eh_frame_hdr_space_.Clear();
  eh_frame_space_.Clear();
  arm_exidx_space_.Clear();
  arm_extab_space_.Clear();

  // vaddr in the elf file.
  uint64_t ip_vaddr = ip - map.start + debug_frame->min_vaddr;

  // The unwind info can come from .ARM.exidx or .eh_frame, or .debug_frame/.gnu_debugdata.
  // First check .eh_frame/.debug_frame, then check .ARM.exidx. Because .eh_frame/.debug_frame has
  // function range for each entry, by matching ip address with the function range, we know exactly
  // whether the ip address hits an entry. But .ARM.exidx doesn't have function range for each
  // entry, it thinks that an ip address hits an entry when (entry.addr <= ip < next_entry.addr).
  // To prevent ip addresses hit in .eh_frame/.debug_frame being regarded as addresses hit in
  // .ARM.exidx, we need to check .eh_frame/.debug_frame first.
  if (debug_frame->has_eh_frame) {
    if (ip_vaddr >= debug_frame->eh_frame.min_func_vaddr &&
        ip_vaddr < debug_frame->text_end_vaddr) {
      // Prepare eh_frame_hdr space and eh_frame space.
      eh_frame_hdr_space_.start = ip - ip_vaddr + debug_frame->eh_frame.hdr_vaddr;
      eh_frame_hdr_space_.end =
          eh_frame_hdr_space_.start + debug_frame->eh_frame.hdr_data.size();
      eh_frame_hdr_space_.data = debug_frame->eh_frame.hdr_data.data();
      eh_frame_space_.start = ip - ip_vaddr + debug_frame->eh_frame.vaddr;
      eh_frame_space_.end = eh_frame_space_.start + debug_frame->eh_frame.data.size();
      eh_frame_space_.data = debug_frame->eh_frame.data.data();

      unw_dyn_info di;
      memset(&di, '\0', sizeof(di));
      di.start_ip = map.start;
      di.end_ip = map.end;
      di.format = UNW_INFO_FORMAT_REMOTE_TABLE;
      di.u.rti.name_ptr = 0;
      di.u.rti.segbase = eh_frame_hdr_space_.start;
      di.u.rti.table_data =
          eh_frame_hdr_space_.start + debug_frame->eh_frame.fde_table_offset;
      di.u.rti.table_len = (eh_frame_hdr_space_.end - di.u.rti.table_data) / sizeof(unw_word_t);
      // TODO: Do it ourselves is more efficient than calling this function.
      int ret = dwarf_search_unwind_table(addr_space, ip, &di, proc_info, need_unwind_info, this);
      if (ret == 0) {
        return true;
      }
    }
  }
  if (debug_frame->has_debug_frame || debug_frame->has_gnu_debugdata) {
    unw_dyn_info_t di;
    unw_word_t segbase = map.start - map.offset;
    // TODO: http://b/32916571
    // TODO: Do it ourselves is more efficient than calling libunwind functions.
    int found = dwarf_find_debug_frame(0, &di, ip, segbase, filename.c_str(), map.start, map.end);
    if (found == 1) {
      int ret = dwarf_search_unwind_table(addr_space, ip, &di, proc_info, need_unwind_info, this);
      if (ret == 0) {
        return true;
      }
    }
  }

  if (debug_frame->has_arm_exidx) {
    auto& func_vaddrs = debug_frame->arm_exidx.func_vaddr_array;
    if (ip_vaddr >= func_vaddrs[0] && ip_vaddr < debug_frame->text_end_vaddr) {
      // Use binary search to find the correct function.
      auto it = std::upper_bound(func_vaddrs.begin(), func_vaddrs.end(),
                                 static_cast<uint32_t>(ip_vaddr));
      if (it != func_vaddrs.begin()) {
        --it;
        // Found the exidx entry.
        size_t index = it - func_vaddrs.begin();
        proc_info->start_ip = *it;
        proc_info->format = UNW_INFO_FORMAT_ARM_EXIDX;
        proc_info->unwind_info = reinterpret_cast<void*>(
            static_cast<uintptr_t>(index * sizeof(ArmIdxEntry) +
                                   debug_frame->arm_exidx.exidx_vaddr +
                                   debug_frame->min_vaddr));
        eh_frame_hdr_space_.Clear();
        eh_frame_space_.Clear();
        // Prepare arm_exidx space and arm_extab space.
        arm_exidx_space_.start = debug_frame->min_vaddr + debug_frame->arm_exidx.exidx_vaddr;
        arm_exidx_space_.end = arm_exidx_space_.start +
            debug_frame->arm_exidx.exidx_data.size() * sizeof(ArmIdxEntry);
        arm_exidx_space_.data = reinterpret_cast<const uint8_t*>(
            debug_frame->arm_exidx.exidx_data.data());

        arm_extab_space_.start = debug_frame->min_vaddr + debug_frame->arm_exidx.extab_vaddr;
        arm_extab_space_.end = arm_extab_space_.start +
            debug_frame->arm_exidx.extab_data.size();
        arm_extab_space_.data = debug_frame->arm_exidx.extab_data.data();
        return true;
      }
    }
  }
  return false;
}

bool BacktraceOffline::ReadReg(size_t reg, uint64_t* value) {
  bool result = true;
#if defined(__arm__)
  switch (reg) {
    case UNW_ARM_R0:
      *value = context_->uc_mcontext.arm_r0;
      break;
    case UNW_ARM_R1:
      *value = context_->uc_mcontext.arm_r1;
      break;
    case UNW_ARM_R2:
      *value = context_->uc_mcontext.arm_r2;
      break;
    case UNW_ARM_R3:
      *value = context_->uc_mcontext.arm_r3;
      break;
    case UNW_ARM_R4:
      *value = context_->uc_mcontext.arm_r4;
      break;
    case UNW_ARM_R5:
      *value = context_->uc_mcontext.arm_r5;
      break;
    case UNW_ARM_R6:
      *value = context_->uc_mcontext.arm_r6;
      break;
    case UNW_ARM_R7:
      *value = context_->uc_mcontext.arm_r7;
      break;
    case UNW_ARM_R8:
      *value = context_->uc_mcontext.arm_r8;
      break;
    case UNW_ARM_R9:
      *value = context_->uc_mcontext.arm_r9;
      break;
    case UNW_ARM_R10:
      *value = context_->uc_mcontext.arm_r10;
      break;
    case UNW_ARM_R11:
      *value = context_->uc_mcontext.arm_fp;
      break;
    case UNW_ARM_R12:
      *value = context_->uc_mcontext.arm_ip;
      break;
    case UNW_ARM_R13:
      *value = context_->uc_mcontext.arm_sp;
      break;
    case UNW_ARM_R14:
      *value = context_->uc_mcontext.arm_lr;
      break;
    case UNW_ARM_R15:
      *value = context_->uc_mcontext.arm_pc;
      break;
    default:
      result = false;
  }
#elif defined(__aarch64__)
  if (reg <= UNW_AARCH64_PC) {
    *value = context_->uc_mcontext.regs[reg];
  } else {
    result = false;
  }
#elif defined(__x86_64__)
  switch (reg) {
    case UNW_X86_64_R8:
      *value = context_->uc_mcontext.gregs[REG_R8];
      break;
    case UNW_X86_64_R9:
      *value = context_->uc_mcontext.gregs[REG_R9];
      break;
    case UNW_X86_64_R10:
      *value = context_->uc_mcontext.gregs[REG_R10];
      break;
    case UNW_X86_64_R11:
      *value = context_->uc_mcontext.gregs[REG_R11];
      break;
    case UNW_X86_64_R12:
      *value = context_->uc_mcontext.gregs[REG_R12];
      break;
    case UNW_X86_64_R13:
      *value = context_->uc_mcontext.gregs[REG_R13];
      break;
    case UNW_X86_64_R14:
      *value = context_->uc_mcontext.gregs[REG_R14];
      break;
    case UNW_X86_64_R15:
      *value = context_->uc_mcontext.gregs[REG_R15];
      break;
    case UNW_X86_64_RDI:
      *value = context_->uc_mcontext.gregs[REG_RDI];
      break;
    case UNW_X86_64_RSI:
      *value = context_->uc_mcontext.gregs[REG_RSI];
      break;
    case UNW_X86_64_RBP:
      *value = context_->uc_mcontext.gregs[REG_RBP];
      break;
    case UNW_X86_64_RBX:
      *value = context_->uc_mcontext.gregs[REG_RBX];
      break;
    case UNW_X86_64_RDX:
      *value = context_->uc_mcontext.gregs[REG_RDX];
      break;
    case UNW_X86_64_RAX:
      *value = context_->uc_mcontext.gregs[REG_RAX];
      break;
    case UNW_X86_64_RCX:
      *value = context_->uc_mcontext.gregs[REG_RCX];
      break;
    case UNW_X86_64_RSP:
      *value = context_->uc_mcontext.gregs[REG_RSP];
      break;
    case UNW_X86_64_RIP:
      *value = context_->uc_mcontext.gregs[REG_RIP];
      break;
    default:
      result = false;
  }
#elif defined(__i386__)
  switch (reg) {
    case UNW_X86_GS:
      *value = context_->uc_mcontext.gregs[REG_GS];
      break;
    case UNW_X86_FS:
      *value = context_->uc_mcontext.gregs[REG_FS];
      break;
    case UNW_X86_ES:
      *value = context_->uc_mcontext.gregs[REG_ES];
      break;
    case UNW_X86_DS:
      *value = context_->uc_mcontext.gregs[REG_DS];
      break;
    case UNW_X86_EAX:
      *value = context_->uc_mcontext.gregs[REG_EAX];
      break;
    case UNW_X86_EBX:
      *value = context_->uc_mcontext.gregs[REG_EBX];
      break;
    case UNW_X86_ECX:
      *value = context_->uc_mcontext.gregs[REG_ECX];
      break;
    case UNW_X86_EDX:
      *value = context_->uc_mcontext.gregs[REG_EDX];
      break;
    case UNW_X86_ESI:
      *value = context_->uc_mcontext.gregs[REG_ESI];
      break;
    case UNW_X86_EDI:
      *value = context_->uc_mcontext.gregs[REG_EDI];
      break;
    case UNW_X86_EBP:
      *value = context_->uc_mcontext.gregs[REG_EBP];
      break;
    case UNW_X86_EIP:
      *value = context_->uc_mcontext.gregs[REG_EIP];
      break;
    case UNW_X86_ESP:
      *value = context_->uc_mcontext.gregs[REG_ESP];
      break;
    case UNW_X86_TRAPNO:
      *value = context_->uc_mcontext.gregs[REG_TRAPNO];
      break;
    case UNW_X86_CS:
      *value = context_->uc_mcontext.gregs[REG_CS];
      break;
    case UNW_X86_EFLAGS:
      *value = context_->uc_mcontext.gregs[REG_EFL];
      break;
    case UNW_X86_SS:
      *value = context_->uc_mcontext.gregs[REG_SS];
      break;
    default:
      result = false;
  }
#else
  UNUSED(reg);
  UNUSED(value);
  result = false;
#endif
  return result;
}

std::string BacktraceOffline::GetFunctionNameRaw(uintptr_t, uintptr_t* offset) {
  // We don't have enough information to support this. And it is expensive.
  *offset = 0;
  return "";
}

static std::mutex g_lock;
static std::unordered_map<std::string, std::unique_ptr<DebugFrameInfo>>* g_debug_frames = nullptr;

static DebugFrameInfo* ReadDebugFrameFromFile(const std::string& filename);

DebugFrameInfo* BacktraceOffline::GetDebugFrameInFile(const std::string& filename) {
  if (cache_file_) {
    std::lock_guard<std::mutex> lock(g_lock);
    if (g_debug_frames != nullptr) {
      auto it = g_debug_frames->find(filename);
      if (it != g_debug_frames->end()) {
        return it->second.get();
      }
    }
  }
  DebugFrameInfo* debug_frame = ReadDebugFrameFromFile(filename);
  if (cache_file_) {
    std::lock_guard<std::mutex> lock(g_lock);
    if (g_debug_frames == nullptr) {
      g_debug_frames = new std::unordered_map<std::string, std::unique_ptr<DebugFrameInfo>>;
    }
    auto pair = g_debug_frames->emplace(filename, std::unique_ptr<DebugFrameInfo>(debug_frame));
    if (!pair.second) {
      debug_frame = pair.first->second.get();
    }
  }
  return debug_frame;
}

static bool OmitEncodedValue(uint8_t encode, const uint8_t*& p) {
  if (encode == DW_EH_PE_omit) {
    return 0;
  }
  uint8_t format = encode & 0x0f;
  switch (format) {
    case DW_EH_PE_ptr:
      p += sizeof(unw_word_t);
      break;
    case DW_EH_PE_uleb128:
    case DW_EH_PE_sleb128:
      while ((*p & 0x80) != 0) {
        ++p;
      }
      ++p;
      break;
    case DW_EH_PE_udata2:
    case DW_EH_PE_sdata2:
      p += 2;
      break;
    case DW_EH_PE_udata4:
    case DW_EH_PE_sdata4:
      p += 4;
      break;
    case DW_EH_PE_udata8:
    case DW_EH_PE_sdata8:
      p += 8;
      break;
    default:
      return false;
  }
  return true;
}

static bool GetFdeTableOffsetInEhFrameHdr(const std::vector<uint8_t>& data,
                                          uint64_t* table_offset_in_eh_frame_hdr) {
  const uint8_t* p = data.data();
  const uint8_t* end = p + data.size();
  if (p + 4 > end) {
    return false;
  }
  uint8_t version = *p++;
  if (version != 1) {
    return false;
  }
  uint8_t eh_frame_ptr_encode = *p++;
  uint8_t fde_count_encode = *p++;
  uint8_t fde_table_encode = *p++;

  if (fde_table_encode != (DW_EH_PE_datarel | DW_EH_PE_sdata4)) {
    return false;
  }

  if (!OmitEncodedValue(eh_frame_ptr_encode, p) || !OmitEncodedValue(fde_count_encode, p)) {
    return false;
  }
  if (p >= end) {
    return false;
  }
  *table_offset_in_eh_frame_hdr = p - data.data();
  return true;
}

template <class ELFT>
DebugFrameInfo* ReadDebugFrameFromELFFile(const llvm::object::ELFFile<ELFT>* elf) {
  DebugFrameInfo* result = new DebugFrameInfo;
  result->text_end_vaddr = std::numeric_limits<uint64_t>::max();

  bool has_eh_frame_hdr = false;
  bool has_eh_frame = false;

  for (auto it = elf->section_begin(); it != elf->section_end(); ++it) {
    llvm::ErrorOr<llvm::StringRef> name = elf->getSectionName(&*it);
    if (name) {
      std::string s = name.get();
      if (s == ".debug_frame") {
        result->has_debug_frame = true;
      } else if (s == ".gnu_debugdata") {
        result->has_gnu_debugdata = true;
      } else if (s == ".eh_frame_hdr") {
        result->eh_frame.hdr_vaddr = it->sh_addr;
        llvm::ErrorOr<llvm::ArrayRef<uint8_t>> data = elf->getSectionContents(&*it);
        if (data) {
          result->eh_frame.hdr_data.insert(result->eh_frame.hdr_data.end(),
              data->data(), data->data() + data->size());

          uint64_t fde_table_offset;
          if (GetFdeTableOffsetInEhFrameHdr(result->eh_frame.hdr_data,
                                             &fde_table_offset)) {
            result->eh_frame.fde_table_offset = fde_table_offset;
            // Make sure we have at least one entry in fde_table.
            if (fde_table_offset + 2 * sizeof(int32_t) <= data->size()) {
              intptr_t eh_frame_hdr_vaddr = it->sh_addr;
              int32_t sdata;
              uint8_t* p = result->eh_frame.hdr_data.data() + fde_table_offset;
              memcpy(&sdata, p, sizeof(sdata));
              result->eh_frame.min_func_vaddr = eh_frame_hdr_vaddr + sdata;
              has_eh_frame_hdr = true;
            }
          }
        }
      } else if (s == ".eh_frame") {
        result->eh_frame.vaddr = it->sh_addr;
        llvm::ErrorOr<llvm::ArrayRef<uint8_t>> data = elf->getSectionContents(&*it);
        if (data) {
          result->eh_frame.data.insert(result->eh_frame.data.end(),
                                                data->data(), data->data() + data->size());
          has_eh_frame = true;
        }
      } else if (s == ".ARM.exidx") {
        result->arm_exidx.exidx_vaddr = it->sh_addr;
        llvm::ErrorOr<llvm::ArrayRef<uint8_t>> data = elf->getSectionContents(&*it);
        if (data) {
          size_t entry_count = data->size() / sizeof(ArmIdxEntry);
          result->arm_exidx.exidx_data.resize(entry_count);
          memcpy(result->arm_exidx.exidx_data.data(), data->data(),
                 entry_count * sizeof(ArmIdxEntry));
          if (entry_count > 0u) {
            // Change IdxEntry.func_offset into vaddr.
            result->arm_exidx.func_vaddr_array.reserve(entry_count);
            uint32_t vaddr = it->sh_addr;
            for (auto& entry : result->arm_exidx.exidx_data) {
              uint32_t func_offset = entry.func_offset + vaddr;
              // Clear bit 31 for the prel31 offset.
              // Arm sets bit 0 to mark it as thumb code, remove the flag.
              result->arm_exidx.func_vaddr_array.push_back(
                  func_offset & 0x7ffffffe);
              vaddr += 8;
            }
            result->has_arm_exidx = true;
          }
        }
      } else if (s == ".ARM.extab") {
        result->arm_exidx.extab_vaddr = it->sh_addr;
        llvm::ErrorOr<llvm::ArrayRef<uint8_t>> data = elf->getSectionContents(&*it);
        if (data) {
          result->arm_exidx.extab_data.insert(result->arm_exidx.extab_data.end(),
                                              data->data(), data->data() + data->size());
        }
      } else if (s == ".text") {
        result->text_end_vaddr = it->sh_addr + it->sh_size;
      }
    }
  }

  if (has_eh_frame_hdr && has_eh_frame) {
    result->has_eh_frame = true;
  }

  result->min_vaddr = std::numeric_limits<uint64_t>::max();
  for (auto it = elf->program_header_begin(); it != elf->program_header_end(); ++it) {
    if ((it->p_type == llvm::ELF::PT_LOAD) && (it->p_flags & llvm::ELF::PF_X)) {
      if (it->p_vaddr < result->min_vaddr) {
        result->min_vaddr = it->p_vaddr;
      }
    }
  }
  if (!result->has_eh_frame && !result->has_arm_exidx && !result->has_debug_frame &&
      !result->has_gnu_debugdata) {
    delete result;
    return nullptr;
  }
  return result;
}

static bool IsValidElfPath(const std::string& filename) {
  static const char elf_magic[] = {0x7f, 'E', 'L', 'F'};

  struct stat st;
  if (stat(filename.c_str(), &st) != 0 || !S_ISREG(st.st_mode)) {
    return false;
  }
  FILE* fp = fopen(filename.c_str(), "reb");
  if (fp == nullptr) {
    return false;
  }
  char buf[4];
  if (fread(buf, 4, 1, fp) != 1) {
    fclose(fp);
    return false;
  }
  fclose(fp);
  return memcmp(buf, elf_magic, 4) == 0;
}

static bool IsValidApkPath(const std::string& apk_path) {
  static const char zip_preamble[] = {0x50, 0x4b, 0x03, 0x04};
  struct stat st;
  if (stat(apk_path.c_str(), &st) != 0 || !S_ISREG(st.st_mode)) {
    return false;
  }
  FILE* fp = fopen(apk_path.c_str(), "reb");
  if (fp == nullptr) {
    return false;
  }
  char buf[4];
  if (fread(buf, 4, 1, fp) != 1) {
    fclose(fp);
    return false;
  }
  fclose(fp);
  return memcmp(buf, zip_preamble, 4) == 0;
}

class ScopedZiparchiveHandle {
 public:
  explicit ScopedZiparchiveHandle(ZipArchiveHandle handle) : handle_(handle) {
  }

  ~ScopedZiparchiveHandle() {
    CloseArchive(handle_);
  }

 private:
  ZipArchiveHandle handle_;
};

llvm::object::OwningBinary<llvm::object::Binary> OpenEmbeddedElfFile(const std::string& filename) {
  llvm::object::OwningBinary<llvm::object::Binary> nothing;
  size_t pos = filename.find("!/");
  if (pos == std::string::npos) {
    return nothing;
  }
  std::string apk_file = filename.substr(0, pos);
  std::string elf_file = filename.substr(pos + 2);
  if (!IsValidApkPath(apk_file)) {
    BACK_LOGW("%s is not a valid apk file", apk_file.c_str());
    return nothing;
  }
  ZipArchiveHandle handle;
  int32_t ret_code = OpenArchive(apk_file.c_str(), &handle);
  if (ret_code != 0) {
    CloseArchive(handle);
    BACK_LOGW("failed to open archive %s: %s", apk_file.c_str(), ErrorCodeString(ret_code));
    return nothing;
  }
  ScopedZiparchiveHandle scoped_handle(handle);
  ZipEntry zentry;
  ret_code = FindEntry(handle, ZipString(elf_file.c_str()), &zentry);
  if (ret_code != 0) {
    BACK_LOGW("failed to find %s in %s: %s", elf_file.c_str(), apk_file.c_str(),
              ErrorCodeString(ret_code));
    return nothing;
  }
  if (zentry.method != kCompressStored || zentry.compressed_length != zentry.uncompressed_length) {
    BACK_LOGW("%s is compressed in %s, which doesn't support running directly", elf_file.c_str(),
              apk_file.c_str());
    return nothing;
  }
  auto buffer_or_err = llvm::MemoryBuffer::getOpenFileSlice(GetFileDescriptor(handle), apk_file,
                                                            zentry.uncompressed_length,
                                                            zentry.offset);
  if (!buffer_or_err) {
    BACK_LOGW("failed to read %s in %s: %s", elf_file.c_str(), apk_file.c_str(),
              buffer_or_err.getError().message().c_str());
    return nothing;
  }
  auto binary_or_err = llvm::object::createBinary(buffer_or_err.get()->getMemBufferRef());
  if (!binary_or_err) {
    BACK_LOGW("failed to create binary for %s in %s: %s", elf_file.c_str(), apk_file.c_str(),
              llvm::toString(binary_or_err.takeError()).c_str());
    return nothing;
  }
  return llvm::object::OwningBinary<llvm::object::Binary>(std::move(binary_or_err.get()),
                                                          std::move(buffer_or_err.get()));
}

static DebugFrameInfo* ReadDebugFrameFromFile(const std::string& filename) {
  llvm::object::OwningBinary<llvm::object::Binary> owning_binary;
  if (filename.find("!/") != std::string::npos) {
    owning_binary = OpenEmbeddedElfFile(filename);
  } else {
    if (!IsValidElfPath(filename)) {
      return nullptr;
    }
    auto binary_or_err = llvm::object::createBinary(llvm::StringRef(filename));
    if (!binary_or_err) {
      return nullptr;
    }
    owning_binary = std::move(binary_or_err.get());
  }
  llvm::object::Binary* binary = owning_binary.getBinary();
  auto obj = llvm::dyn_cast<llvm::object::ObjectFile>(binary);
  if (obj == nullptr) {
    return nullptr;
  }
  if (auto elf = llvm::dyn_cast<llvm::object::ELF32LEObjectFile>(obj)) {
    return ReadDebugFrameFromELFFile(elf->getELFFile());
  }
  if (auto elf = llvm::dyn_cast<llvm::object::ELF64LEObjectFile>(obj)) {
    return ReadDebugFrameFromELFFile(elf->getELFFile());
  }
  return nullptr;
}

Backtrace* Backtrace::CreateOffline(pid_t pid, pid_t tid, BacktraceMap* map,
                                    const backtrace_stackinfo_t& stack, bool cache_file) {
  return new BacktraceOffline(pid, tid, map, stack, cache_file);
}