summaryrefslogtreecommitdiff
path: root/absl/debugging/symbolize_elf.inc
blob: ae75cd4153d25b3363c484e3d5ba32a9970de5a8 (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
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
// Copyright 2018 The Abseil Authors.
//
// 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
//
//      https://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.

// This library provides Symbolize() function that symbolizes program
// counters to their corresponding symbol names on linux platforms.
// This library has a minimal implementation of an ELF symbol table
// reader (i.e. it doesn't depend on libelf, etc.).
//
// The algorithm used in Symbolize() is as follows.
//
//   1. Go through a list of maps in /proc/self/maps and find the map
//   containing the program counter.
//
//   2. Open the mapped file and find a regular symbol table inside.
//   Iterate over symbols in the symbol table and look for the symbol
//   containing the program counter.  If such a symbol is found,
//   obtain the symbol name, and demangle the symbol if possible.
//   If the symbol isn't found in the regular symbol table (binary is
//   stripped), try the same thing with a dynamic symbol table.
//
// Note that Symbolize() is originally implemented to be used in
// signal handlers, hence it doesn't use malloc() and other unsafe
// operations.  It should be both thread-safe and async-signal-safe.
//
// Implementation note:
//
// We don't use heaps but only use stacks.  We want to reduce the
// stack consumption so that the symbolizer can run on small stacks.
//
// Here are some numbers collected with GCC 4.1.0 on x86:
// - sizeof(Elf32_Sym)  = 16
// - sizeof(Elf32_Shdr) = 40
// - sizeof(Elf64_Sym)  = 24
// - sizeof(Elf64_Shdr) = 64
//
// This implementation is intended to be async-signal-safe but uses some
// functions which are not guaranteed to be so, such as memchr() and
// memmove().  We assume they are async-signal-safe.

#include <dlfcn.h>
#include <elf.h>
#include <fcntl.h>
#include <link.h>  // For ElfW() macro.
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#include <algorithm>
#include <array>
#include <atomic>
#include <cerrno>
#include <cinttypes>
#include <climits>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>

#include "absl/base/casts.h"
#include "absl/base/dynamic_annotations.h"
#include "absl/base/internal/low_level_alloc.h"
#include "absl/base/internal/raw_logging.h"
#include "absl/base/internal/spinlock.h"
#include "absl/base/port.h"
#include "absl/debugging/internal/demangle.h"
#include "absl/debugging/internal/vdso_support.h"
#include "absl/strings/string_view.h"

#if defined(__FreeBSD__) && !defined(ElfW)
#define ElfW(x) __ElfN(x)
#endif

namespace absl {
ABSL_NAMESPACE_BEGIN

// Value of argv[0]. Used by MaybeInitializeObjFile().
static char *argv0_value = nullptr;

void InitializeSymbolizer(const char *argv0) {
#ifdef ABSL_HAVE_VDSO_SUPPORT
  // We need to make sure VDSOSupport::Init() is called before any setuid or
  // chroot calls, so InitializeSymbolizer() should be called very early in the
  // life of a program.
  absl::debugging_internal::VDSOSupport::Init();
#endif
  if (argv0_value != nullptr) {
    free(argv0_value);
    argv0_value = nullptr;
  }
  if (argv0 != nullptr && argv0[0] != '\0') {
    argv0_value = strdup(argv0);
  }
}

namespace debugging_internal {
namespace {

// Re-runs fn until it doesn't cause EINTR.
#define NO_INTR(fn) \
  do {              \
  } while ((fn) < 0 && errno == EINTR)

// On Linux, ELF_ST_* are defined in <linux/elf.h>.  To make this portable
// we define our own ELF_ST_BIND and ELF_ST_TYPE if not available.
#ifndef ELF_ST_BIND
#define ELF_ST_BIND(info) (((unsigned char)(info)) >> 4)
#endif

#ifndef ELF_ST_TYPE
#define ELF_ST_TYPE(info) (((unsigned char)(info)) & 0xF)
#endif

// Some platforms use a special .opd section to store function pointers.
const char kOpdSectionName[] = ".opd";

#if (defined(__powerpc__) && !(_CALL_ELF > 1)) || defined(__ia64)
// Use opd section for function descriptors on these platforms, the function
// address is the first word of the descriptor.
enum { kPlatformUsesOPDSections = 1 };
#else  // not PPC or IA64
enum { kPlatformUsesOPDSections = 0 };
#endif

// This works for PowerPC & IA64 only.  A function descriptor consist of two
// pointers and the first one is the function's entry.
const size_t kFunctionDescriptorSize = sizeof(void *) * 2;

const int kMaxDecorators = 10;  // Seems like a reasonable upper limit.

struct InstalledSymbolDecorator {
  SymbolDecorator fn;
  void *arg;
  int ticket;
};

int g_num_decorators;
InstalledSymbolDecorator g_decorators[kMaxDecorators];

struct FileMappingHint {
  const void *start;
  const void *end;
  uint64_t offset;
  const char *filename;
};

// Protects g_decorators.
// We are using SpinLock and not a Mutex here, because we may be called
// from inside Mutex::Lock itself, and it prohibits recursive calls.
// This happens in e.g. base/stacktrace_syscall_unittest.
// Moreover, we are using only TryLock(), if the decorator list
// is being modified (is busy), we skip all decorators, and possibly
// loose some info. Sorry, that's the best we could do.
ABSL_CONST_INIT absl::base_internal::SpinLock g_decorators_mu(
    absl::kConstInit, absl::base_internal::SCHEDULE_KERNEL_ONLY);

const int kMaxFileMappingHints = 8;
int g_num_file_mapping_hints;
FileMappingHint g_file_mapping_hints[kMaxFileMappingHints];
// Protects g_file_mapping_hints.
ABSL_CONST_INIT absl::base_internal::SpinLock g_file_mapping_mu(
    absl::kConstInit, absl::base_internal::SCHEDULE_KERNEL_ONLY);

// Async-signal-safe function to zero a buffer.
// memset() is not guaranteed to be async-signal-safe.
static void SafeMemZero(void* p, size_t size) {
  unsigned char *c = static_cast<unsigned char *>(p);
  while (size--) {
    *c++ = 0;
  }
}

struct ObjFile {
  ObjFile()
      : filename(nullptr),
        start_addr(nullptr),
        end_addr(nullptr),
        offset(0),
        fd(-1),
        elf_type(-1) {
    SafeMemZero(&elf_header, sizeof(elf_header));
    SafeMemZero(&phdr[0], sizeof(phdr));
  }

  char *filename;
  const void *start_addr;
  const void *end_addr;
  uint64_t offset;

  // The following fields are initialized on the first access to the
  // object file.
  int fd;
  int elf_type;
  ElfW(Ehdr) elf_header;

  // PT_LOAD program header describing executable code.
  // Normally we expect just one, but SWIFT binaries have two.
  // CUDA binaries have 3 (see cr/473913254 description).
  std::array<ElfW(Phdr), 4> phdr;
};

// Build 4-way associative cache for symbols. Within each cache line, symbols
// are replaced in LRU order.
enum {
  ASSOCIATIVITY = 4,
};
struct SymbolCacheLine {
  const void *pc[ASSOCIATIVITY];
  char *name[ASSOCIATIVITY];

  // age[i] is incremented when a line is accessed. it's reset to zero if the
  // i'th entry is read.
  uint32_t age[ASSOCIATIVITY];
};

// ---------------------------------------------------------------
// An async-signal-safe arena for LowLevelAlloc
static std::atomic<base_internal::LowLevelAlloc::Arena *> g_sig_safe_arena;

static base_internal::LowLevelAlloc::Arena *SigSafeArena() {
  return g_sig_safe_arena.load(std::memory_order_acquire);
}

static void InitSigSafeArena() {
  if (SigSafeArena() == nullptr) {
    base_internal::LowLevelAlloc::Arena *new_arena =
        base_internal::LowLevelAlloc::NewArena(
            base_internal::LowLevelAlloc::kAsyncSignalSafe);
    base_internal::LowLevelAlloc::Arena *old_value = nullptr;
    if (!g_sig_safe_arena.compare_exchange_strong(old_value, new_arena,
                                                  std::memory_order_release,
                                                  std::memory_order_relaxed)) {
      // We lost a race to allocate an arena; deallocate.
      base_internal::LowLevelAlloc::DeleteArena(new_arena);
    }
  }
}

// ---------------------------------------------------------------
// An AddrMap is a vector of ObjFile, using SigSafeArena() for allocation.

class AddrMap {
 public:
  AddrMap() : size_(0), allocated_(0), obj_(nullptr) {}
  ~AddrMap() { base_internal::LowLevelAlloc::Free(obj_); }
  size_t Size() const { return size_; }
  ObjFile *At(size_t i) { return &obj_[i]; }
  ObjFile *Add();
  void Clear();

 private:
  size_t size_;       // count of valid elements (<= allocated_)
  size_t allocated_;  // count of allocated elements
  ObjFile *obj_;      // array of allocated_ elements
  AddrMap(const AddrMap &) = delete;
  AddrMap &operator=(const AddrMap &) = delete;
};

void AddrMap::Clear() {
  for (size_t i = 0; i != size_; i++) {
    At(i)->~ObjFile();
  }
  size_ = 0;
}

ObjFile *AddrMap::Add() {
  if (size_ == allocated_) {
    size_t new_allocated = allocated_ * 2 + 50;
    ObjFile *new_obj_ =
        static_cast<ObjFile *>(base_internal::LowLevelAlloc::AllocWithArena(
            new_allocated * sizeof(*new_obj_), SigSafeArena()));
    if (obj_) {
      memcpy(new_obj_, obj_, allocated_ * sizeof(*new_obj_));
      base_internal::LowLevelAlloc::Free(obj_);
    }
    obj_ = new_obj_;
    allocated_ = new_allocated;
  }
  return new (&obj_[size_++]) ObjFile;
}

class CachingFile {
 public:
  // Setup reader for fd that uses buf[0, buf_size-1] as a cache.
  CachingFile(int fd, char *buf, size_t buf_size)
      : fd_(fd),
        cache_(buf),
        cache_size_(buf_size),
        cache_start_(0),
        cache_limit_(0) {}

  int fd() const { return fd_; }
  ssize_t ReadFromOffset(void *buf, size_t count, off_t offset);
  bool ReadFromOffsetExact(void *buf, size_t count, off_t offset);

 private:
  // Bytes [cache_start_, cache_limit_-1] from fd_ are stored in
  // a prefix of cache_[0, cache_size_-1].
  int fd_;
  char *cache_;
  size_t cache_size_;
  off_t cache_start_;
  off_t cache_limit_;
};

// ---------------------------------------------------------------

enum FindSymbolResult { SYMBOL_NOT_FOUND = 1, SYMBOL_TRUNCATED, SYMBOL_FOUND };

class Symbolizer {
 public:
  Symbolizer();
  ~Symbolizer();
  const char *GetSymbol(const void *const pc);

 private:
  char *CopyString(const char *s) {
    size_t len = strlen(s);
    char *dst = static_cast<char *>(
        base_internal::LowLevelAlloc::AllocWithArena(len + 1, SigSafeArena()));
    ABSL_RAW_CHECK(dst != nullptr, "out of memory");
    memcpy(dst, s, len + 1);
    return dst;
  }
  ObjFile *FindObjFile(const void *const start,
                       size_t size) ABSL_ATTRIBUTE_NOINLINE;
  static bool RegisterObjFile(const char *filename,
                              const void *const start_addr,
                              const void *const end_addr, uint64_t offset,
                              void *arg);
  SymbolCacheLine *GetCacheLine(const void *const pc);
  const char *FindSymbolInCache(const void *const pc);
  const char *InsertSymbolInCache(const void *const pc, const char *name);
  void AgeSymbols(SymbolCacheLine *line);
  void ClearAddrMap();
  FindSymbolResult GetSymbolFromObjectFile(const ObjFile &obj,
                                           const void *const pc,
                                           const ptrdiff_t relocation,
                                           char *out, size_t out_size,
                                           char *tmp_buf, size_t tmp_buf_size);
  const char *GetUncachedSymbol(const void *pc);

  enum {
    SYMBOL_BUF_SIZE = 3072,
    TMP_BUF_SIZE = 1024,
    SYMBOL_CACHE_LINES = 128,
    FILE_CACHE_SIZE = 8192,
  };

  AddrMap addr_map_;

  bool ok_;
  bool addr_map_read_;

  char symbol_buf_[SYMBOL_BUF_SIZE];
  char file_cache_[FILE_CACHE_SIZE];

  // tmp_buf_ will be used to store arrays of ElfW(Shdr) and ElfW(Sym)
  // so we ensure that tmp_buf_ is properly aligned to store either.
  alignas(16) char tmp_buf_[TMP_BUF_SIZE];
  static_assert(alignof(ElfW(Shdr)) <= 16,
                "alignment of tmp buf too small for Shdr");
  static_assert(alignof(ElfW(Sym)) <= 16,
                "alignment of tmp buf too small for Sym");

  SymbolCacheLine symbol_cache_[SYMBOL_CACHE_LINES];
};

static std::atomic<Symbolizer *> g_cached_symbolizer;

}  // namespace

static size_t SymbolizerSize() {
#if defined(__wasm__) || defined(__asmjs__)
  auto pagesize = static_cast<size_t>(getpagesize());
#else
  auto pagesize = static_cast<size_t>(sysconf(_SC_PAGESIZE));
#endif
  return ((sizeof(Symbolizer) - 1) / pagesize + 1) * pagesize;
}

// Return (and set null) g_cached_symbolized_state if it is not null.
// Otherwise return a new symbolizer.
static Symbolizer *AllocateSymbolizer() {
  InitSigSafeArena();
  Symbolizer *symbolizer =
      g_cached_symbolizer.exchange(nullptr, std::memory_order_acquire);
  if (symbolizer != nullptr) {
    return symbolizer;
  }
  return new (base_internal::LowLevelAlloc::AllocWithArena(
      SymbolizerSize(), SigSafeArena())) Symbolizer();
}

// Set g_cached_symbolize_state to s if it is null, otherwise
// delete s.
static void FreeSymbolizer(Symbolizer *s) {
  Symbolizer *old_cached_symbolizer = nullptr;
  if (!g_cached_symbolizer.compare_exchange_strong(old_cached_symbolizer, s,
                                                   std::memory_order_release,
                                                   std::memory_order_relaxed)) {
    s->~Symbolizer();
    base_internal::LowLevelAlloc::Free(s);
  }
}

Symbolizer::Symbolizer() : ok_(true), addr_map_read_(false) {
  for (SymbolCacheLine &symbol_cache_line : symbol_cache_) {
    for (size_t j = 0; j < ABSL_ARRAYSIZE(symbol_cache_line.name); ++j) {
      symbol_cache_line.pc[j] = nullptr;
      symbol_cache_line.name[j] = nullptr;
      symbol_cache_line.age[j] = 0;
    }
  }
}

Symbolizer::~Symbolizer() {
  for (SymbolCacheLine &symbol_cache_line : symbol_cache_) {
    for (char *s : symbol_cache_line.name) {
      base_internal::LowLevelAlloc::Free(s);
    }
  }
  ClearAddrMap();
}

// We don't use assert() since it's not guaranteed to be
// async-signal-safe.  Instead we define a minimal assertion
// macro. So far, we don't need pretty printing for __FILE__, etc.
#define SAFE_ASSERT(expr) ((expr) ? static_cast<void>(0) : abort())

// Read up to "count" bytes from file descriptor "fd" into the buffer
// starting at "buf" while handling short reads and EINTR.  On
// success, return the number of bytes read.  Otherwise, return -1.
static ssize_t ReadPersistent(int fd, void *buf, size_t count) {
  SAFE_ASSERT(fd >= 0);
  SAFE_ASSERT(count <= SSIZE_MAX);
  char *buf0 = reinterpret_cast<char *>(buf);
  size_t num_bytes = 0;
  while (num_bytes < count) {
    ssize_t len;
    NO_INTR(len = read(fd, buf0 + num_bytes, count - num_bytes));
    if (len < 0) {  // There was an error other than EINTR.
      ABSL_RAW_LOG(WARNING, "read failed: errno=%d", errno);
      return -1;
    }
    if (len == 0) {  // Reached EOF.
      break;
    }
    num_bytes += static_cast<size_t>(len);
  }
  SAFE_ASSERT(num_bytes <= count);
  return static_cast<ssize_t>(num_bytes);
}

// Read up to "count" bytes from "offset" into the buffer starting at "buf",
// while handling short reads and EINTR.  On success, return the number of bytes
// read.  Otherwise, return -1.
ssize_t CachingFile::ReadFromOffset(void *buf, size_t count, off_t offset) {
  char *dst = static_cast<char *>(buf);
  size_t read = 0;
  while (read < count) {
    // Look in cache first.
    if (offset >= cache_start_ && offset < cache_limit_) {
      const char *hit_start = &cache_[offset - cache_start_];
      const size_t n =
          std::min(count - read, static_cast<size_t>(cache_limit_ - offset));
      memcpy(dst, hit_start, n);
      dst += n;
      read += static_cast<size_t>(n);
      offset += static_cast<off_t>(n);
      continue;
    }

    cache_start_ = 0;
    cache_limit_ = 0;
    ssize_t n = pread(fd_, cache_, cache_size_, offset);
    if (n < 0) {
      if (errno == EINTR) {
        continue;
      }
      ABSL_RAW_LOG(WARNING, "read failed: errno=%d", errno);
      return -1;
    }
    if (n == 0) {  // Reached EOF.
      break;
    }

    cache_start_ = offset;
    cache_limit_ = offset + static_cast<off_t>(n);
    // Next iteration will copy from cache into dst.
  }
  return static_cast<ssize_t>(read);
}

// Try reading exactly "count" bytes from "offset" bytes into the buffer
// starting at "buf" while handling short reads and EINTR.  On success, return
// true. Otherwise, return false.
bool CachingFile::ReadFromOffsetExact(void *buf, size_t count, off_t offset) {
  ssize_t len = ReadFromOffset(buf, count, offset);
  return len >= 0 && static_cast<size_t>(len) == count;
}

// Returns elf_header.e_type if the file pointed by fd is an ELF binary.
static int FileGetElfType(CachingFile *file) {
  ElfW(Ehdr) elf_header;
  if (!file->ReadFromOffsetExact(&elf_header, sizeof(elf_header), 0)) {
    return -1;
  }
  if (memcmp(elf_header.e_ident, ELFMAG, SELFMAG) != 0) {
    return -1;
  }
  return elf_header.e_type;
}

// Read the section headers in the given ELF binary, and if a section
// of the specified type is found, set the output to this section header
// and return true.  Otherwise, return false.
// To keep stack consumption low, we would like this function to not get
// inlined.
static ABSL_ATTRIBUTE_NOINLINE bool GetSectionHeaderByType(
    CachingFile *file, ElfW(Half) sh_num, const off_t sh_offset,
    ElfW(Word) type, ElfW(Shdr) * out, char *tmp_buf, size_t tmp_buf_size) {
  ElfW(Shdr) *buf = reinterpret_cast<ElfW(Shdr) *>(tmp_buf);
  const size_t buf_entries = tmp_buf_size / sizeof(buf[0]);
  const size_t buf_bytes = buf_entries * sizeof(buf[0]);

  for (size_t i = 0; static_cast<int>(i) < sh_num;) {
    const size_t num_bytes_left =
        (static_cast<size_t>(sh_num) - i) * sizeof(buf[0]);
    const size_t num_bytes_to_read =
        (buf_bytes > num_bytes_left) ? num_bytes_left : buf_bytes;
    const off_t offset = sh_offset + static_cast<off_t>(i * sizeof(buf[0]));
    const ssize_t len = file->ReadFromOffset(buf, num_bytes_to_read, offset);
    if (len < 0) {
      ABSL_RAW_LOG(
          WARNING,
          "Reading %zu bytes from offset %ju returned %zd which is negative.",
          num_bytes_to_read, static_cast<intmax_t>(offset), len);
      return false;
    }
    if (static_cast<size_t>(len) % sizeof(buf[0]) != 0) {
      ABSL_RAW_LOG(
          WARNING,
          "Reading %zu bytes from offset %jd returned %zd which is not a "
          "multiple of %zu.",
          num_bytes_to_read, static_cast<intmax_t>(offset), len,
          sizeof(buf[0]));
      return false;
    }
    const size_t num_headers_in_buf = static_cast<size_t>(len) / sizeof(buf[0]);
    SAFE_ASSERT(num_headers_in_buf <= buf_entries);
    for (size_t j = 0; j < num_headers_in_buf; ++j) {
      if (buf[j].sh_type == type) {
        *out = buf[j];
        return true;
      }
    }
    i += num_headers_in_buf;
  }
  return false;
}

// There is no particular reason to limit section name to 63 characters,
// but there has (as yet) been no need for anything longer either.
const int kMaxSectionNameLen = 64;

// Small cache to use for miscellaneous file reads.
const int kSmallFileCacheSize = 100;

bool ForEachSection(int fd,
                    const std::function<bool(absl::string_view name,
                                             const ElfW(Shdr) &)> &callback) {
  char buf[kSmallFileCacheSize];
  CachingFile file(fd, buf, sizeof(buf));

  ElfW(Ehdr) elf_header;
  if (!file.ReadFromOffsetExact(&elf_header, sizeof(elf_header), 0)) {
    return false;
  }

  // Technically it can be larger, but in practice this never happens.
  if (elf_header.e_shentsize != sizeof(ElfW(Shdr))) {
    return false;
  }

  ElfW(Shdr) shstrtab;
  off_t shstrtab_offset = static_cast<off_t>(elf_header.e_shoff) +
                          elf_header.e_shentsize * elf_header.e_shstrndx;
  if (!file.ReadFromOffsetExact(&shstrtab, sizeof(shstrtab), shstrtab_offset)) {
    return false;
  }

  for (int i = 0; i < elf_header.e_shnum; ++i) {
    ElfW(Shdr) out;
    off_t section_header_offset =
        static_cast<off_t>(elf_header.e_shoff) + elf_header.e_shentsize * i;
    if (!file.ReadFromOffsetExact(&out, sizeof(out), section_header_offset)) {
      return false;
    }
    off_t name_offset = static_cast<off_t>(shstrtab.sh_offset) + out.sh_name;
    char header_name[kMaxSectionNameLen];
    ssize_t n_read =
        file.ReadFromOffset(&header_name, kMaxSectionNameLen, name_offset);
    if (n_read < 0) {
      return false;
    } else if (n_read > kMaxSectionNameLen) {
      // Long read?
      return false;
    }

    absl::string_view name(header_name,
                           strnlen(header_name, static_cast<size_t>(n_read)));
    if (!callback(name, out)) {
      break;
    }
  }
  return true;
}

// name_len should include terminating '\0'.
bool GetSectionHeaderByName(int fd, const char *name, size_t name_len,
                            ElfW(Shdr) * out) {
  char header_name[kMaxSectionNameLen];
  if (sizeof(header_name) < name_len) {
    ABSL_RAW_LOG(WARNING,
                 "Section name '%s' is too long (%zu); "
                 "section will not be found (even if present).",
                 name, name_len);
    // No point in even trying.
    return false;
  }

  char buf[kSmallFileCacheSize];
  CachingFile file(fd, buf, sizeof(buf));
  ElfW(Ehdr) elf_header;
  if (!file.ReadFromOffsetExact(&elf_header, sizeof(elf_header), 0)) {
    return false;
  }

  // Technically it can be larger, but in practice this never happens.
  if (elf_header.e_shentsize != sizeof(ElfW(Shdr))) {
    return false;
  }

  ElfW(Shdr) shstrtab;
  off_t shstrtab_offset = static_cast<off_t>(elf_header.e_shoff) +
                          elf_header.e_shentsize * elf_header.e_shstrndx;
  if (!file.ReadFromOffsetExact(&shstrtab, sizeof(shstrtab), shstrtab_offset)) {
    return false;
  }

  for (int i = 0; i < elf_header.e_shnum; ++i) {
    off_t section_header_offset =
        static_cast<off_t>(elf_header.e_shoff) + elf_header.e_shentsize * i;
    if (!file.ReadFromOffsetExact(out, sizeof(*out), section_header_offset)) {
      return false;
    }
    off_t name_offset = static_cast<off_t>(shstrtab.sh_offset) + out->sh_name;
    ssize_t n_read = file.ReadFromOffset(&header_name, name_len, name_offset);
    if (n_read < 0) {
      return false;
    } else if (static_cast<size_t>(n_read) != name_len) {
      // Short read -- name could be at end of file.
      continue;
    }
    if (memcmp(header_name, name, name_len) == 0) {
      return true;
    }
  }
  return false;
}

// Compare symbols at in the same address.
// Return true if we should pick symbol1.
static bool ShouldPickFirstSymbol(const ElfW(Sym) & symbol1,
                                  const ElfW(Sym) & symbol2) {
  // If one of the symbols is weak and the other is not, pick the one
  // this is not a weak symbol.
  char bind1 = ELF_ST_BIND(symbol1.st_info);
  char bind2 = ELF_ST_BIND(symbol1.st_info);
  if (bind1 == STB_WEAK && bind2 != STB_WEAK) return false;
  if (bind2 == STB_WEAK && bind1 != STB_WEAK) return true;

  // If one of the symbols has zero size and the other is not, pick the
  // one that has non-zero size.
  if (symbol1.st_size != 0 && symbol2.st_size == 0) {
    return true;
  }
  if (symbol1.st_size == 0 && symbol2.st_size != 0) {
    return false;
  }

  // If one of the symbols has no type and the other is not, pick the
  // one that has a type.
  char type1 = ELF_ST_TYPE(symbol1.st_info);
  char type2 = ELF_ST_TYPE(symbol1.st_info);
  if (type1 != STT_NOTYPE && type2 == STT_NOTYPE) {
    return true;
  }
  if (type1 == STT_NOTYPE && type2 != STT_NOTYPE) {
    return false;
  }

  // Pick the first one, if we still cannot decide.
  return true;
}

// Return true if an address is inside a section.
static bool InSection(const void *address, ptrdiff_t relocation,
                      const ElfW(Shdr) * section) {
  const char *start = reinterpret_cast<const char *>(
      section->sh_addr + static_cast<ElfW(Addr)>(relocation));
  size_t size = static_cast<size_t>(section->sh_size);
  return start <= address && address < (start + size);
}

static const char *ComputeOffset(const char *base, ptrdiff_t offset) {
  // Note: cast to intptr_t to avoid undefined behavior when base evaluates to
  // zero and offset is non-zero.
  return reinterpret_cast<const char *>(reinterpret_cast<intptr_t>(base) +
                                        offset);
}

// Read a symbol table and look for the symbol containing the
// pc. Iterate over symbols in a symbol table and look for the symbol
// containing "pc".  If the symbol is found, and its name fits in
// out_size, the name is written into out and SYMBOL_FOUND is returned.
// If the name does not fit, truncated name is written into out,
// and SYMBOL_TRUNCATED is returned. Out is NUL-terminated.
// If the symbol is not found, SYMBOL_NOT_FOUND is returned;
// To keep stack consumption low, we would like this function to not get
// inlined.
static ABSL_ATTRIBUTE_NOINLINE FindSymbolResult FindSymbol(
    const void *const pc, CachingFile *file, char *out, size_t out_size,
    ptrdiff_t relocation, const ElfW(Shdr) * strtab, const ElfW(Shdr) * symtab,
    const ElfW(Shdr) * opd, char *tmp_buf, size_t tmp_buf_size) {
  if (symtab == nullptr) {
    return SYMBOL_NOT_FOUND;
  }

  // Read multiple symbols at once to save read() calls.
  ElfW(Sym) *buf = reinterpret_cast<ElfW(Sym) *>(tmp_buf);
  const size_t buf_entries = tmp_buf_size / sizeof(buf[0]);

  const size_t num_symbols = symtab->sh_size / symtab->sh_entsize;

  // On platforms using an .opd section (PowerPC & IA64), a function symbol
  // has the address of a function descriptor, which contains the real
  // starting address.  However, we do not always want to use the real
  // starting address because we sometimes want to symbolize a function
  // pointer into the .opd section, e.g. FindSymbol(&foo,...).
  const bool pc_in_opd = kPlatformUsesOPDSections && opd != nullptr &&
                         InSection(pc, relocation, opd);
  const bool deref_function_descriptor_pointer =
      kPlatformUsesOPDSections && opd != nullptr && !pc_in_opd;

  ElfW(Sym) best_match;
  SafeMemZero(&best_match, sizeof(best_match));
  bool found_match = false;
  for (size_t i = 0; i < num_symbols;) {
    off_t offset =
        static_cast<off_t>(symtab->sh_offset + i * symtab->sh_entsize);
    const size_t num_remaining_symbols = num_symbols - i;
    const size_t entries_in_chunk =
        std::min(num_remaining_symbols, buf_entries);
    const size_t bytes_in_chunk = entries_in_chunk * sizeof(buf[0]);
    const ssize_t len = file->ReadFromOffset(buf, bytes_in_chunk, offset);
    SAFE_ASSERT(len >= 0);
    SAFE_ASSERT(static_cast<size_t>(len) % sizeof(buf[0]) == 0);
    const size_t num_symbols_in_buf = static_cast<size_t>(len) / sizeof(buf[0]);
    SAFE_ASSERT(num_symbols_in_buf <= entries_in_chunk);
    for (size_t j = 0; j < num_symbols_in_buf; ++j) {
      const ElfW(Sym) &symbol = buf[j];

      // For a DSO, a symbol address is relocated by the loading address.
      // We keep the original address for opd redirection below.
      const char *const original_start_address =
          reinterpret_cast<const char *>(symbol.st_value);
      const char *start_address =
          ComputeOffset(original_start_address, relocation);

#ifdef __arm__
      // ARM functions are always aligned to multiples of two bytes; the
      // lowest-order bit in start_address is ignored by the CPU and indicates
      // whether the function contains ARM (0) or Thumb (1) code. We don't care
      // about what encoding is being used; we just want the real start address
      // of the function.
      start_address = reinterpret_cast<const char *>(
          reinterpret_cast<uintptr_t>(start_address) & ~1u);
#endif

      if (deref_function_descriptor_pointer &&
          InSection(original_start_address, /*relocation=*/0, opd)) {
        // The opd section is mapped into memory.  Just dereference
        // start_address to get the first double word, which points to the
        // function entry.
        start_address = *reinterpret_cast<const char *const *>(start_address);
      }

      // If pc is inside the .opd section, it points to a function descriptor.
      const size_t size = pc_in_opd ? kFunctionDescriptorSize : symbol.st_size;
      const void *const end_address =
          ComputeOffset(start_address, static_cast<ptrdiff_t>(size));
      if (symbol.st_value != 0 &&  // Skip null value symbols.
          symbol.st_shndx != 0 &&  // Skip undefined symbols.
#ifdef STT_TLS
          ELF_ST_TYPE(symbol.st_info) != STT_TLS &&  // Skip thread-local data.
#endif                                               // STT_TLS
          ((start_address <= pc && pc < end_address) ||
           (start_address == pc && pc == end_address))) {
        if (!found_match || ShouldPickFirstSymbol(symbol, best_match)) {
          found_match = true;
          best_match = symbol;
        }
      }
    }
    i += num_symbols_in_buf;
  }

  if (found_match) {
    const off_t off =
        static_cast<off_t>(strtab->sh_offset) + best_match.st_name;
    const ssize_t n_read = file->ReadFromOffset(out, out_size, off);
    if (n_read <= 0) {
      // This should never happen.
      ABSL_RAW_LOG(WARNING,
                   "Unable to read from fd %d at offset %lld: n_read = %zd",
                   file->fd(), static_cast<long long>(off), n_read);
      return SYMBOL_NOT_FOUND;
    }
    ABSL_RAW_CHECK(static_cast<size_t>(n_read) <= out_size,
                   "ReadFromOffset read too much data.");

    // strtab->sh_offset points into .strtab-like section that contains
    // NUL-terminated strings: '\0foo\0barbaz\0...".
    //
    // sh_offset+st_name points to the start of symbol name, but we don't know
    // how long the symbol is, so we try to read as much as we have space for,
    // and usually over-read (i.e. there is a NUL somewhere before n_read).
    if (memchr(out, '\0', static_cast<size_t>(n_read)) == nullptr) {
      // Either out_size was too small (n_read == out_size and no NUL), or
      // we tried to read past the EOF (n_read < out_size) and .strtab is
      // corrupt (missing terminating NUL; should never happen for valid ELF).
      out[n_read - 1] = '\0';
      return SYMBOL_TRUNCATED;
    }
    return SYMBOL_FOUND;
  }

  return SYMBOL_NOT_FOUND;
}

// Get the symbol name of "pc" from the file pointed by "fd".  Process
// both regular and dynamic symbol tables if necessary.
// See FindSymbol() comment for description of return value.
FindSymbolResult Symbolizer::GetSymbolFromObjectFile(
    const ObjFile &obj, const void *const pc, const ptrdiff_t relocation,
    char *out, size_t out_size, char *tmp_buf, size_t tmp_buf_size) {
  ElfW(Shdr) symtab;
  ElfW(Shdr) strtab;
  ElfW(Shdr) opd;
  ElfW(Shdr) *opd_ptr = nullptr;

  // On platforms using an .opd sections for function descriptor, read
  // the section header.  The .opd section is in data segment and should be
  // loaded but we check that it is mapped just to be extra careful.
  if (kPlatformUsesOPDSections) {
    if (GetSectionHeaderByName(obj.fd, kOpdSectionName,
                               sizeof(kOpdSectionName) - 1, &opd) &&
        FindObjFile(reinterpret_cast<const char *>(opd.sh_addr) + relocation,
                    opd.sh_size) != nullptr) {
      opd_ptr = &opd;
    } else {
      return SYMBOL_NOT_FOUND;
    }
  }

  CachingFile file(obj.fd, file_cache_, sizeof(file_cache_));

  // Consult a regular symbol table, then fall back to the dynamic symbol table.
  for (const auto symbol_table_type : {SHT_SYMTAB, SHT_DYNSYM}) {
    if (!GetSectionHeaderByType(&file, obj.elf_header.e_shnum,
                                static_cast<off_t>(obj.elf_header.e_shoff),
                                static_cast<ElfW(Word)>(symbol_table_type),
                                &symtab, tmp_buf, tmp_buf_size)) {
      continue;
    }
    if (!file.ReadFromOffsetExact(
            &strtab, sizeof(strtab),
            static_cast<off_t>(obj.elf_header.e_shoff +
                               symtab.sh_link * sizeof(symtab)))) {
      continue;
    }
    const FindSymbolResult rc =
        FindSymbol(pc, &file, out, out_size, relocation, &strtab, &symtab,
                   opd_ptr, tmp_buf, tmp_buf_size);
    if (rc != SYMBOL_NOT_FOUND) {
      return rc;
    }
  }

  return SYMBOL_NOT_FOUND;
}

namespace {
// Thin wrapper around a file descriptor so that the file descriptor
// gets closed for sure.
class FileDescriptor {
 public:
  explicit FileDescriptor(int fd) : fd_(fd) {}
  FileDescriptor(const FileDescriptor &) = delete;
  FileDescriptor &operator=(const FileDescriptor &) = delete;

  ~FileDescriptor() {
    if (fd_ >= 0) {
      close(fd_);
    }
  }

  int get() const { return fd_; }

 private:
  const int fd_;
};

// Helper class for reading lines from file.
//
// Note: we don't use ProcMapsIterator since the object is big (it has
// a 5k array member) and uses async-unsafe functions such as sscanf()
// and snprintf().
class LineReader {
 public:
  explicit LineReader(int fd, char *buf, size_t buf_len)
      : fd_(fd),
        buf_len_(buf_len),
        buf_(buf),
        bol_(buf),
        eol_(buf),
        eod_(buf) {}

  LineReader(const LineReader &) = delete;
  LineReader &operator=(const LineReader &) = delete;

  // Read '\n'-terminated line from file.  On success, modify "bol"
  // and "eol", then return true.  Otherwise, return false.
  //
  // Note: if the last line doesn't end with '\n', the line will be
  // dropped.  It's an intentional behavior to make the code simple.
  bool ReadLine(const char **bol, const char **eol) {
    if (BufferIsEmpty()) {  // First time.
      const ssize_t num_bytes = ReadPersistent(fd_, buf_, buf_len_);
      if (num_bytes <= 0) {  // EOF or error.
        return false;
      }
      eod_ = buf_ + num_bytes;
      bol_ = buf_;
    } else {
      bol_ = eol_ + 1;            // Advance to the next line in the buffer.
      SAFE_ASSERT(bol_ <= eod_);  // "bol_" can point to "eod_".
      if (!HasCompleteLine()) {
        const auto incomplete_line_length = static_cast<size_t>(eod_ - bol_);
        // Move the trailing incomplete line to the beginning.
        memmove(buf_, bol_, incomplete_line_length);
        // Read text from file and append it.
        char *const append_pos = buf_ + incomplete_line_length;
        const size_t capacity_left = buf_len_ - incomplete_line_length;
        const ssize_t num_bytes =
            ReadPersistent(fd_, append_pos, capacity_left);
        if (num_bytes <= 0) {  // EOF or error.
          return false;
        }
        eod_ = append_pos + num_bytes;
        bol_ = buf_;
      }
    }
    eol_ = FindLineFeed();
    if (eol_ == nullptr) {  // '\n' not found.  Malformed line.
      return false;
    }
    *eol_ = '\0';  // Replace '\n' with '\0'.

    *bol = bol_;
    *eol = eol_;
    return true;
  }

 private:
  char *FindLineFeed() const {
    return reinterpret_cast<char *>(
        memchr(bol_, '\n', static_cast<size_t>(eod_ - bol_)));
  }

  bool BufferIsEmpty() const { return buf_ == eod_; }

  bool HasCompleteLine() const {
    return !BufferIsEmpty() && FindLineFeed() != nullptr;
  }

  const int fd_;
  const size_t buf_len_;
  char *const buf_;
  char *bol_;
  char *eol_;
  const char *eod_;  // End of data in "buf_".
};
}  // namespace

// Place the hex number read from "start" into "*hex".  The pointer to
// the first non-hex character or "end" is returned.
static const char *GetHex(const char *start, const char *end,
                          uint64_t *const value) {
  uint64_t hex = 0;
  const char *p;
  for (p = start; p < end; ++p) {
    int ch = *p;
    if ((ch >= '0' && ch <= '9') || (ch >= 'A' && ch <= 'F') ||
        (ch >= 'a' && ch <= 'f')) {
      hex = (hex << 4) |
            static_cast<uint64_t>(ch < 'A' ? ch - '0' : (ch & 0xF) + 9);
    } else {  // Encountered the first non-hex character.
      break;
    }
  }
  SAFE_ASSERT(p <= end);
  *value = hex;
  return p;
}

static const char *GetHex(const char *start, const char *end,
                          const void **const addr) {
  uint64_t hex = 0;
  const char *p = GetHex(start, end, &hex);
  *addr = reinterpret_cast<void *>(hex);
  return p;
}

// Normally we are only interested in "r?x" maps.
// On the PowerPC, function pointers point to descriptors in the .opd
// section.  The descriptors themselves are not executable code, so
// we need to relax the check below to "r??".
static bool ShouldUseMapping(const char *const flags) {
  return flags[0] == 'r' && (kPlatformUsesOPDSections || flags[2] == 'x');
}

// Read /proc/self/maps and run "callback" for each mmapped file found.  If
// "callback" returns false, stop scanning and return true. Else continue
// scanning /proc/self/maps. Return true if no parse error is found.
static ABSL_ATTRIBUTE_NOINLINE bool ReadAddrMap(
    bool (*callback)(const char *filename, const void *const start_addr,
                     const void *const end_addr, uint64_t offset, void *arg),
    void *arg, void *tmp_buf, size_t tmp_buf_size) {
  // Use /proc/self/task/<pid>/maps instead of /proc/self/maps. The latter
  // requires kernel to stop all threads, and is significantly slower when there
  // are 1000s of threads.
  char maps_path[80];
  snprintf(maps_path, sizeof(maps_path), "/proc/self/task/%d/maps", getpid());

  int maps_fd;
  NO_INTR(maps_fd = open(maps_path, O_RDONLY));
  FileDescriptor wrapped_maps_fd(maps_fd);
  if (wrapped_maps_fd.get() < 0) {
    ABSL_RAW_LOG(WARNING, "%s: errno=%d", maps_path, errno);
    return false;
  }

  // Iterate over maps and look for the map containing the pc.  Then
  // look into the symbol tables inside.
  LineReader reader(wrapped_maps_fd.get(), static_cast<char *>(tmp_buf),
                    tmp_buf_size);
  while (true) {
    const char *cursor;
    const char *eol;
    if (!reader.ReadLine(&cursor, &eol)) {  // EOF or malformed line.
      break;
    }

    const char *line = cursor;
    const void *start_address;
    // Start parsing line in /proc/self/maps.  Here is an example:
    //
    // 08048000-0804c000 r-xp 00000000 08:01 2142121    /bin/cat
    //
    // We want start address (08048000), end address (0804c000), flags
    // (r-xp) and file name (/bin/cat).

    // Read start address.
    cursor = GetHex(cursor, eol, &start_address);
    if (cursor == eol || *cursor != '-') {
      ABSL_RAW_LOG(WARNING, "Corrupt /proc/self/maps line: %s", line);
      return false;
    }
    ++cursor;  // Skip '-'.

    // Read end address.
    const void *end_address;
    cursor = GetHex(cursor, eol, &end_address);
    if (cursor == eol || *cursor != ' ') {
      ABSL_RAW_LOG(WARNING, "Corrupt /proc/self/maps line: %s", line);
      return false;
    }
    ++cursor;  // Skip ' '.

    // Read flags.  Skip flags until we encounter a space or eol.
    const char *const flags_start = cursor;
    while (cursor < eol && *cursor != ' ') {
      ++cursor;
    }
    // We expect at least four letters for flags (ex. "r-xp").
    if (cursor == eol || cursor < flags_start + 4) {
      ABSL_RAW_LOG(WARNING, "Corrupt /proc/self/maps: %s", line);
      return false;
    }

    // Check flags.
    if (!ShouldUseMapping(flags_start)) {
      continue;  // We skip this map.
    }
    ++cursor;  // Skip ' '.

    // Read file offset.
    uint64_t offset;
    cursor = GetHex(cursor, eol, &offset);
    ++cursor;  // Skip ' '.

    // Skip to file name.  "cursor" now points to dev.  We need to skip at least
    // two spaces for dev and inode.
    int num_spaces = 0;
    while (cursor < eol) {
      if (*cursor == ' ') {
        ++num_spaces;
      } else if (num_spaces >= 2) {
        // The first non-space character after  skipping two spaces
        // is the beginning of the file name.
        break;
      }
      ++cursor;
    }

    // Check whether this entry corresponds to our hint table for the true
    // filename.
    bool hinted =
        GetFileMappingHint(&start_address, &end_address, &offset, &cursor);
    if (!hinted && (cursor == eol || cursor[0] == '[')) {
      // not an object file, typically [vdso] or [vsyscall]
      continue;
    }
    if (!callback(cursor, start_address, end_address, offset, arg)) break;
  }
  return true;
}

// Find the objfile mapped in address region containing [addr, addr + len).
ObjFile *Symbolizer::FindObjFile(const void *const addr, size_t len) {
  for (int i = 0; i < 2; ++i) {
    if (!ok_) return nullptr;

    // Read /proc/self/maps if necessary
    if (!addr_map_read_) {
      addr_map_read_ = true;
      if (!ReadAddrMap(RegisterObjFile, this, tmp_buf_, TMP_BUF_SIZE)) {
        ok_ = false;
        return nullptr;
      }
    }

    size_t lo = 0;
    size_t hi = addr_map_.Size();
    while (lo < hi) {
      size_t mid = (lo + hi) / 2;
      if (addr < addr_map_.At(mid)->end_addr) {
        hi = mid;
      } else {
        lo = mid + 1;
      }
    }
    if (lo != addr_map_.Size()) {
      ObjFile *obj = addr_map_.At(lo);
      SAFE_ASSERT(obj->end_addr > addr);
      if (addr >= obj->start_addr &&
          reinterpret_cast<const char *>(addr) + len <= obj->end_addr)
        return obj;
    }

    // The address mapping may have changed since it was last read.  Retry.
    ClearAddrMap();
  }
  return nullptr;
}

void Symbolizer::ClearAddrMap() {
  for (size_t i = 0; i != addr_map_.Size(); i++) {
    ObjFile *o = addr_map_.At(i);
    base_internal::LowLevelAlloc::Free(o->filename);
    if (o->fd >= 0) {
      close(o->fd);
    }
  }
  addr_map_.Clear();
  addr_map_read_ = false;
}

// Callback for ReadAddrMap to register objfiles in an in-memory table.
bool Symbolizer::RegisterObjFile(const char *filename,
                                 const void *const start_addr,
                                 const void *const end_addr, uint64_t offset,
                                 void *arg) {
  Symbolizer *impl = static_cast<Symbolizer *>(arg);

  // Files are supposed to be added in the increasing address order.  Make
  // sure that's the case.
  size_t addr_map_size = impl->addr_map_.Size();
  if (addr_map_size != 0) {
    ObjFile *old = impl->addr_map_.At(addr_map_size - 1);
    if (old->end_addr > end_addr) {
      ABSL_RAW_LOG(ERROR,
                   "Unsorted addr map entry: 0x%" PRIxPTR ": %s <-> 0x%" PRIxPTR
                   ": %s",
                   reinterpret_cast<uintptr_t>(end_addr), filename,
                   reinterpret_cast<uintptr_t>(old->end_addr), old->filename);
      return true;
    } else if (old->end_addr == end_addr) {
      // The same entry appears twice. This sometimes happens for [vdso].
      if (old->start_addr != start_addr ||
          strcmp(old->filename, filename) != 0) {
        ABSL_RAW_LOG(ERROR,
                     "Duplicate addr 0x%" PRIxPTR ": %s <-> 0x%" PRIxPTR ": %s",
                     reinterpret_cast<uintptr_t>(end_addr), filename,
                     reinterpret_cast<uintptr_t>(old->end_addr), old->filename);
      }
      return true;
    } else if (old->end_addr == start_addr &&
               reinterpret_cast<uintptr_t>(old->start_addr) - old->offset ==
                   reinterpret_cast<uintptr_t>(start_addr) - offset &&
               strcmp(old->filename, filename) == 0) {
      // Two contiguous map entries that span a contiguous region of the file,
      // perhaps because some part of the file was mlock()ed. Combine them.
      old->end_addr = end_addr;
      return true;
    }
  }
  ObjFile *obj = impl->addr_map_.Add();
  obj->filename = impl->CopyString(filename);
  obj->start_addr = start_addr;
  obj->end_addr = end_addr;
  obj->offset = offset;
  obj->elf_type = -1;  // filled on demand
  obj->fd = -1;        // opened on demand
  return true;
}

// This function wraps the Demangle function to provide an interface
// where the input symbol is demangled in-place.
// To keep stack consumption low, we would like this function to not
// get inlined.
static ABSL_ATTRIBUTE_NOINLINE void DemangleInplace(char *out, size_t out_size,
                                                    char *tmp_buf,
                                                    size_t tmp_buf_size) {
  if (Demangle(out, tmp_buf, tmp_buf_size)) {
    // Demangling succeeded. Copy to out if the space allows.
    size_t len = strlen(tmp_buf);
    if (len + 1 <= out_size) {  // +1 for '\0'.
      SAFE_ASSERT(len < tmp_buf_size);
      memmove(out, tmp_buf, len + 1);
    }
  }
}

SymbolCacheLine *Symbolizer::GetCacheLine(const void *const pc) {
  uintptr_t pc0 = reinterpret_cast<uintptr_t>(pc);
  pc0 >>= 3;  // drop the low 3 bits

  // Shuffle bits.
  pc0 ^= (pc0 >> 6) ^ (pc0 >> 12) ^ (pc0 >> 18);
  return &symbol_cache_[pc0 % SYMBOL_CACHE_LINES];
}

void Symbolizer::AgeSymbols(SymbolCacheLine *line) {
  for (uint32_t &age : line->age) {
    ++age;
  }
}

const char *Symbolizer::FindSymbolInCache(const void *const pc) {
  if (pc == nullptr) return nullptr;

  SymbolCacheLine *line = GetCacheLine(pc);
  for (size_t i = 0; i < ABSL_ARRAYSIZE(line->pc); ++i) {
    if (line->pc[i] == pc) {
      AgeSymbols(line);
      line->age[i] = 0;
      return line->name[i];
    }
  }
  return nullptr;
}

const char *Symbolizer::InsertSymbolInCache(const void *const pc,
                                            const char *name) {
  SAFE_ASSERT(pc != nullptr);

  SymbolCacheLine *line = GetCacheLine(pc);
  uint32_t max_age = 0;
  size_t oldest_index = 0;
  bool found_oldest_index = false;
  for (size_t i = 0; i < ABSL_ARRAYSIZE(line->pc); ++i) {
    if (line->pc[i] == nullptr) {
      AgeSymbols(line);
      line->pc[i] = pc;
      line->name[i] = CopyString(name);
      line->age[i] = 0;
      return line->name[i];
    }
    if (line->age[i] >= max_age) {
      max_age = line->age[i];
      oldest_index = i;
      found_oldest_index = true;
    }
  }

  AgeSymbols(line);
  ABSL_RAW_CHECK(found_oldest_index, "Corrupt cache");
  base_internal::LowLevelAlloc::Free(line->name[oldest_index]);
  line->pc[oldest_index] = pc;
  line->name[oldest_index] = CopyString(name);
  line->age[oldest_index] = 0;
  return line->name[oldest_index];
}

static void MaybeOpenFdFromSelfExe(ObjFile *obj) {
  if (memcmp(obj->start_addr, ELFMAG, SELFMAG) != 0) {
    return;
  }
  int fd = open("/proc/self/exe", O_RDONLY);
  if (fd == -1) {
    return;
  }
  // Verify that contents of /proc/self/exe matches in-memory image of
  // the binary. This can fail if the "deleted" binary is in fact not
  // the main executable, or for binaries that have the first PT_LOAD
  // segment smaller than 4K. We do it in four steps so that the
  // buffer is smaller and we don't consume too much stack space.
  const char *mem = reinterpret_cast<const char *>(obj->start_addr);
  for (int i = 0; i < 4; ++i) {
    char buf[1024];
    ssize_t n = read(fd, buf, sizeof(buf));
    if (n != sizeof(buf) || memcmp(buf, mem, sizeof(buf)) != 0) {
      close(fd);
      return;
    }
    mem += sizeof(buf);
  }
  obj->fd = fd;
}

static bool MaybeInitializeObjFile(ObjFile *obj) {
  if (obj->fd < 0) {
    obj->fd = open(obj->filename, O_RDONLY);

    if (obj->fd < 0) {
      // Getting /proc/self/exe here means that we were hinted.
      if (strcmp(obj->filename, "/proc/self/exe") == 0) {
        // /proc/self/exe may be inaccessible (due to setuid, etc.), so try
        // accessing the binary via argv0.
        if (argv0_value != nullptr) {
          obj->fd = open(argv0_value, O_RDONLY);
        }
      } else {
        MaybeOpenFdFromSelfExe(obj);
      }
    }

    if (obj->fd < 0) {
      ABSL_RAW_LOG(WARNING, "%s: open failed: errno=%d", obj->filename, errno);
      return false;
    }

    char buf[kSmallFileCacheSize];
    CachingFile file(obj->fd, buf, sizeof(buf));

    obj->elf_type = FileGetElfType(&file);
    if (obj->elf_type < 0) {
      ABSL_RAW_LOG(WARNING, "%s: wrong elf type: %d", obj->filename,
                   obj->elf_type);
      return false;
    }

    if (!file.ReadFromOffsetExact(&obj->elf_header, sizeof(obj->elf_header),
                                  0)) {
      ABSL_RAW_LOG(WARNING, "%s: failed to read elf header", obj->filename);
      return false;
    }
    const int phnum = obj->elf_header.e_phnum;
    const int phentsize = obj->elf_header.e_phentsize;
    auto phoff = static_cast<off_t>(obj->elf_header.e_phoff);
    size_t num_interesting_load_segments = 0;
    for (int j = 0; j < phnum; j++) {
      ElfW(Phdr) phdr;
      if (!file.ReadFromOffsetExact(&phdr, sizeof(phdr), phoff)) {
        ABSL_RAW_LOG(WARNING, "%s: failed to read program header %d",
                     obj->filename, j);
        return false;
      }
      phoff += phentsize;

#if defined(__powerpc__) && !(_CALL_ELF > 1)
      // On the PowerPC ELF v1 ABI, function pointers actually point to function
      // descriptors. These descriptors are stored in an .opd section, which is
      // mapped read-only. We thus need to look at all readable segments, not
      // just the executable ones.
      constexpr int interesting = PF_R;
#else
      constexpr int interesting = PF_X | PF_R;
#endif

      if (phdr.p_type != PT_LOAD
          || (phdr.p_flags & interesting) != interesting) {
        // Not a LOAD segment, not executable code, and not a function
        // descriptor.
        continue;
      }
      if (num_interesting_load_segments < obj->phdr.size()) {
        memcpy(&obj->phdr[num_interesting_load_segments++], &phdr, sizeof(phdr));
      } else {
        ABSL_RAW_LOG(
            WARNING, "%s: too many interesting LOAD segments: %zu >= %zu",
            obj->filename, num_interesting_load_segments, obj->phdr.size());
        break;
      }
    }
    if (num_interesting_load_segments == 0) {
      // This object has no interesting LOAD segments. That's unexpected.
      ABSL_RAW_LOG(WARNING, "%s: no interesting LOAD segments", obj->filename);
      return false;
    }
  }
  return true;
}

// The implementation of our symbolization routine.  If it
// successfully finds the symbol containing "pc" and obtains the
// symbol name, returns pointer to that symbol. Otherwise, returns nullptr.
// If any symbol decorators have been installed via InstallSymbolDecorator(),
// they are called here as well.
// To keep stack consumption low, we would like this function to not
// get inlined.
const char *Symbolizer::GetUncachedSymbol(const void *pc) {
  ObjFile *const obj = FindObjFile(pc, 1);
  ptrdiff_t relocation = 0;
  int fd = -1;
  if (obj != nullptr) {
    if (MaybeInitializeObjFile(obj)) {
      const size_t start_addr = reinterpret_cast<size_t>(obj->start_addr);
      if (obj->elf_type == ET_DYN && start_addr >= obj->offset) {
        // This object was relocated.
        //
        // For obj->offset > 0, adjust the relocation since a mapping at offset
        // X in the file will have a start address of [true relocation]+X.
        relocation = static_cast<ptrdiff_t>(start_addr - obj->offset);

        // Note: some binaries have multiple LOAD segments that can contain
        // function pointers. We must find the right one.
        ElfW(Phdr) *phdr = nullptr;
        for (size_t j = 0; j < obj->phdr.size(); j++) {
          ElfW(Phdr) &p = obj->phdr[j];
          if (p.p_type != PT_LOAD) {
            // We only expect PT_LOADs. This must be PT_NULL that we didn't
            // write over (i.e. we exhausted all interesting PT_LOADs).
            ABSL_RAW_CHECK(p.p_type == PT_NULL, "unexpected p_type");
            break;
          }
          if (pc < reinterpret_cast<void *>(start_addr + p.p_vaddr + p.p_memsz)) {
            phdr = &p;
            break;
          }
        }
        if (phdr == nullptr) {
          // That's unexpected. Hope for the best.
          ABSL_RAW_LOG(
              WARNING,
              "%s: unable to find LOAD segment for pc: %p, start_addr: %zx",
              obj->filename, pc, start_addr);
        } else {
          // Adjust relocation in case phdr.p_vaddr != 0.
          // This happens for binaries linked with `lld --rosegment`, and for
          // binaries linked with BFD `ld -z separate-code`.
          relocation -= phdr->p_vaddr - phdr->p_offset;
        }
      }

      fd = obj->fd;
      if (GetSymbolFromObjectFile(*obj, pc, relocation, symbol_buf_,
                                  sizeof(symbol_buf_), tmp_buf_,
                                  sizeof(tmp_buf_)) == SYMBOL_FOUND) {
        // Only try to demangle the symbol name if it fit into symbol_buf_.
        DemangleInplace(symbol_buf_, sizeof(symbol_buf_), tmp_buf_,
                        sizeof(tmp_buf_));
      }
    }
  } else {
#if ABSL_HAVE_VDSO_SUPPORT
    VDSOSupport vdso;
    if (vdso.IsPresent()) {
      VDSOSupport::SymbolInfo symbol_info;
      if (vdso.LookupSymbolByAddress(pc, &symbol_info)) {
        // All VDSO symbols are known to be short.
        size_t len = strlen(symbol_info.name);
        ABSL_RAW_CHECK(len + 1 < sizeof(symbol_buf_),
                       "VDSO symbol unexpectedly long");
        memcpy(symbol_buf_, symbol_info.name, len + 1);
      }
    }
#endif
  }

  if (g_decorators_mu.TryLock()) {
    if (g_num_decorators > 0) {
      SymbolDecoratorArgs decorator_args = {
          pc,       relocation,       fd,     symbol_buf_, sizeof(symbol_buf_),
          tmp_buf_, sizeof(tmp_buf_), nullptr};
      for (int i = 0; i < g_num_decorators; ++i) {
        decorator_args.arg = g_decorators[i].arg;
        g_decorators[i].fn(&decorator_args);
      }
    }
    g_decorators_mu.Unlock();
  }
  if (symbol_buf_[0] == '\0') {
    return nullptr;
  }
  symbol_buf_[sizeof(symbol_buf_) - 1] = '\0';  // Paranoia.
  return InsertSymbolInCache(pc, symbol_buf_);
}

const char *Symbolizer::GetSymbol(const void *pc) {
  const char *entry = FindSymbolInCache(pc);
  if (entry != nullptr) {
    return entry;
  }
  symbol_buf_[0] = '\0';

#ifdef __hppa__
  {
    // In some contexts (e.g., return addresses), PA-RISC uses the lowest two
    // bits of the address to indicate the privilege level. Clear those bits
    // before trying to symbolize.
    const auto pc_bits = reinterpret_cast<uintptr_t>(pc);
    const auto address = pc_bits & ~0x3;
    entry = GetUncachedSymbol(reinterpret_cast<const void *>(address));
    if (entry != nullptr) {
      return entry;
    }

    // In some contexts, PA-RISC also uses bit 1 of the address to indicate that
    // this is a cross-DSO function pointer. Such function pointers actually
    // point to a procedure label, a struct whose first 32-bit (pointer) element
    // actually points to the function text. With no symbol found for this
    // address so far, try interpreting it as a cross-DSO function pointer and
    // see how that goes.
    if (pc_bits & 0x2) {
      return GetUncachedSymbol(*reinterpret_cast<const void *const *>(address));
    }

    return nullptr;
  }
#else
  return GetUncachedSymbol(pc);
#endif
}

bool RemoveAllSymbolDecorators(void) {
  if (!g_decorators_mu.TryLock()) {
    // Someone else is using decorators. Get out.
    return false;
  }
  g_num_decorators = 0;
  g_decorators_mu.Unlock();
  return true;
}

bool RemoveSymbolDecorator(int ticket) {
  if (!g_decorators_mu.TryLock()) {
    // Someone else is using decorators. Get out.
    return false;
  }
  for (int i = 0; i < g_num_decorators; ++i) {
    if (g_decorators[i].ticket == ticket) {
      while (i < g_num_decorators - 1) {
        g_decorators[i] = g_decorators[i + 1];
        ++i;
      }
      g_num_decorators = i;
      break;
    }
  }
  g_decorators_mu.Unlock();
  return true;  // Decorator is known to be removed.
}

int InstallSymbolDecorator(SymbolDecorator decorator, void *arg) {
  static int ticket = 0;

  if (!g_decorators_mu.TryLock()) {
    // Someone else is using decorators. Get out.
    return -2;
  }
  int ret = ticket;
  if (g_num_decorators >= kMaxDecorators) {
    ret = -1;
  } else {
    g_decorators[g_num_decorators] = {decorator, arg, ticket++};
    ++g_num_decorators;
  }
  g_decorators_mu.Unlock();
  return ret;
}

bool RegisterFileMappingHint(const void *start, const void *end, uint64_t offset,
                             const char *filename) {
  SAFE_ASSERT(start <= end);
  SAFE_ASSERT(filename != nullptr);

  InitSigSafeArena();

  if (!g_file_mapping_mu.TryLock()) {
    return false;
  }

  bool ret = true;
  if (g_num_file_mapping_hints >= kMaxFileMappingHints) {
    ret = false;
  } else {
    // TODO(ckennelly): Move this into a string copy routine.
    size_t len = strlen(filename);
    char *dst = static_cast<char *>(
        base_internal::LowLevelAlloc::AllocWithArena(len + 1, SigSafeArena()));
    ABSL_RAW_CHECK(dst != nullptr, "out of memory");
    memcpy(dst, filename, len + 1);

    auto &hint = g_file_mapping_hints[g_num_file_mapping_hints++];
    hint.start = start;
    hint.end = end;
    hint.offset = offset;
    hint.filename = dst;
  }

  g_file_mapping_mu.Unlock();
  return ret;
}

bool GetFileMappingHint(const void **start, const void **end, uint64_t *offset,
                        const char **filename) {
  if (!g_file_mapping_mu.TryLock()) {
    return false;
  }
  bool found = false;
  for (int i = 0; i < g_num_file_mapping_hints; i++) {
    if (g_file_mapping_hints[i].start <= *start &&
        *end <= g_file_mapping_hints[i].end) {
      // We assume that the start_address for the mapping is the base
      // address of the ELF section, but when [start_address,end_address) is
      // not strictly equal to [hint.start, hint.end), that assumption is
      // invalid.
      //
      // This uses the hint's start address (even though hint.start is not
      // necessarily equal to start_address) to ensure the correct
      // relocation is computed later.
      *start = g_file_mapping_hints[i].start;
      *end = g_file_mapping_hints[i].end;
      *offset = g_file_mapping_hints[i].offset;
      *filename = g_file_mapping_hints[i].filename;
      found = true;
      break;
    }
  }
  g_file_mapping_mu.Unlock();
  return found;
}

}  // namespace debugging_internal

bool Symbolize(const void *pc, char *out, int out_size) {
  // Symbolization is very slow under tsan.
  ABSL_ANNOTATE_IGNORE_READS_AND_WRITES_BEGIN();
  SAFE_ASSERT(out_size >= 0);
  debugging_internal::Symbolizer *s = debugging_internal::AllocateSymbolizer();
  const char *name = s->GetSymbol(pc);
  bool ok = false;
  if (name != nullptr && out_size > 0) {
    strncpy(out, name, static_cast<size_t>(out_size));
    ok = true;
    if (out[static_cast<size_t>(out_size) - 1] != '\0') {
      // strncpy() does not '\0' terminate when it truncates.  Do so, with
      // trailing ellipsis.
      static constexpr char kEllipsis[] = "...";
      size_t ellipsis_size =
          std::min(strlen(kEllipsis), static_cast<size_t>(out_size) - 1);
      memcpy(out + static_cast<size_t>(out_size) - ellipsis_size - 1, kEllipsis,
             ellipsis_size);
      out[static_cast<size_t>(out_size) - 1] = '\0';
    }
  }
  debugging_internal::FreeSymbolizer(s);
  ABSL_ANNOTATE_IGNORE_READS_AND_WRITES_END();
  return ok;
}

ABSL_NAMESPACE_END
}  // namespace absl

extern "C" bool AbslInternalGetFileMappingHint(const void **start,
                                               const void **end, uint64_t *offset,
                                               const char **filename) {
  return absl::debugging_internal::GetFileMappingHint(start, end, offset,
                                                      filename);
}