aboutsummaryrefslogtreecommitdiff
path: root/src/common/linux/dump_symbols.cc
blob: 887880d26684e4c395e1d48c075994f9bf7293a8 (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
// Copyright (c) 2010 Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// Restructured in 2009 by: Jim Blandy <jimb@mozilla.com> <jimb@red-bean.com>

// dump_symbols.cc: implement google_breakpad::WriteSymbolFile:
// Find all the debugging info in a file and dump it as a Breakpad symbol file.

#include "common/linux/dump_symbols.h"

#include <assert.h>
#include <elf.h>
#include <errno.h>
#include <fcntl.h>
#include <link.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>

#include <set>
#include <string>
#include <utility>
#include <vector>

#include "common/dwarf/bytereader-inl.h"
#include "common/dwarf/dwarf2diehandler.h"
#include "common/dwarf_cfi_to_module.h"
#include "common/dwarf_cu_to_module.h"
#include "common/dwarf_line_to_module.h"
#include "common/linux/file_id.h"
#include "common/module.h"
#include "common/stabs_reader.h"
#include "common/stabs_to_module.h"

// This namespace contains helper functions.
namespace {

using google_breakpad::DwarfCFIToModule;
using google_breakpad::DwarfCUToModule;
using google_breakpad::DwarfLineToModule;
using google_breakpad::Module;
using google_breakpad::StabsToModule;

//
// FDWrapper
//
// Wrapper class to make sure opened file is closed.
//
class FDWrapper {
 public:
  explicit FDWrapper(int fd) :
    fd_(fd) {}
  ~FDWrapper() {
    if (fd_ != -1)
      close(fd_);
  }
  int get() {
    return fd_;
  }
  int release() {
    int fd = fd_;
    fd_ = -1;
    return fd;
  }
 private:
  int fd_;
};

//
// MmapWrapper
//
// Wrapper class to make sure mapped regions are unmapped.
//
class MmapWrapper {
 public:
  MmapWrapper() : is_set_(false) {}
  ~MmapWrapper() {
    assert(is_set_);
    if (base_ != NULL) {
      assert(size_ > 0);
      munmap(base_, size_);
    }
  }
  void set(void *mapped_address, size_t mapped_size) {
    is_set_ = true;
    base_ = mapped_address;
    size_ = mapped_size;
  }
  void release() {
    assert(is_set_);
    base_ = NULL;
    size_ = 0;
  }

 private:
  bool is_set_;
  void *base_;
  size_t size_;
};


// Fix offset into virtual address by adding the mapped base into offsets.
// Make life easier when want to find something by offset.
static void FixAddress(void *obj_base) {
  ElfW(Addr) base = reinterpret_cast<ElfW(Addr)>(obj_base);
  ElfW(Ehdr) *elf_header = static_cast<ElfW(Ehdr) *>(obj_base);
  elf_header->e_phoff += base;
  elf_header->e_shoff += base;
  ElfW(Shdr) *sections = reinterpret_cast<ElfW(Shdr) *>(elf_header->e_shoff);
  for (int i = 0; i < elf_header->e_shnum; ++i)
    sections[i].sh_offset += base;
}

// Find the preferred loading address of the binary.
static ElfW(Addr) GetLoadingAddress(const ElfW(Phdr) *program_headers,
                                    int nheader) {
  for (int i = 0; i < nheader; ++i) {
    const ElfW(Phdr) &header = program_headers[i];
    // For executable, it is the PT_LOAD segment with offset to zero.
    if (header.p_type == PT_LOAD &&
        header.p_offset == 0)
      return header.p_vaddr;
  }
  // For other types of ELF, return 0.
  return 0;
}

static bool IsValidElf(const ElfW(Ehdr) *elf_header) {
  return memcmp(elf_header, ELFMAG, SELFMAG) == 0;
}

static const ElfW(Shdr) *FindSectionByName(const char *name,
                                           const ElfW(Shdr) *sections,
                                           const ElfW(Shdr) *section_names,
                                           int nsection) {
  assert(name != NULL);
  assert(sections != NULL);
  assert(nsection > 0);

  int name_len = strlen(name);
  if (name_len == 0)
    return NULL;

  // Find the end of the section name section, to make sure that
  // comparisons don't run off the end of the section.
  const char *names_end =
    reinterpret_cast<char*>(section_names->sh_offset + section_names->sh_size);

  for (int i = 0; i < nsection; ++i) {
    const char *section_name =
      reinterpret_cast<char*>(section_names->sh_offset + sections[i].sh_name);
    if (names_end - section_name >= name_len + 1 &&
        strcmp(name, section_name) == 0) {
      if (sections[i].sh_type == SHT_NOBITS) {
        fprintf(stderr,
                "Section %s found, but ignored because type=SHT_NOBITS.\n",
                name);
        return NULL;
      }
      return sections + i;
    }
  }
  return NULL;
}

static bool LoadStabs(const ElfW(Ehdr) *elf_header,
                      const ElfW(Shdr) *stab_section,
                      const ElfW(Shdr) *stabstr_section,
                      const bool big_endian,
                      Module *module) {
  // A callback object to handle data from the STABS reader.
  StabsToModule handler(module);
  // Find the addresses of the STABS data, and create a STABS reader object.
  // On Linux, STABS entries always have 32-bit values, regardless of the
  // address size of the architecture whose code they're describing, and
  // the strings are always "unitized".
  uint8_t *stabs = reinterpret_cast<uint8_t *>(stab_section->sh_offset);
  uint8_t *stabstr = reinterpret_cast<uint8_t *>(stabstr_section->sh_offset);
  google_breakpad::StabsReader reader(stabs, stab_section->sh_size,
                                      stabstr, stabstr_section->sh_size,
                                      big_endian, 4, true, &handler);
  // Read the STABS data, and do post-processing.
  if (!reader.Process())
    return false;
  handler.Finalize();
  return true;
}

// A line-to-module loader that accepts line number info parsed by
// dwarf2reader::LineInfo and populates a Module and a line vector
// with the results.
class DumperLineToModule: public DwarfCUToModule::LineToModuleFunctor {
 public:
  // Create a line-to-module converter using BYTE_READER.
  explicit DumperLineToModule(dwarf2reader::ByteReader *byte_reader)
      : byte_reader_(byte_reader) { }
  void operator()(const char *program, uint64 length,
                  Module *module, vector<Module::Line> *lines) {
    DwarfLineToModule handler(module, lines);
    dwarf2reader::LineInfo parser(program, length, byte_reader_, &handler);
    parser.Start();
  }
 private:
  dwarf2reader::ByteReader *byte_reader_;
};

static bool LoadDwarf(const string &dwarf_filename,
                      const ElfW(Ehdr) *elf_header,
                      const bool big_endian,
                      Module *module) {
  const dwarf2reader::Endianness endianness = big_endian ?
      dwarf2reader::ENDIANNESS_BIG : dwarf2reader::ENDIANNESS_LITTLE;
  dwarf2reader::ByteReader byte_reader(endianness);

  // Construct a context for this file.
  DwarfCUToModule::FileContext file_context(dwarf_filename, module);

  // Build a map of the ELF file's sections.
  const ElfW(Shdr) *sections
      = reinterpret_cast<ElfW(Shdr) *>(elf_header->e_shoff);
  int num_sections = elf_header->e_shnum;
  const ElfW(Shdr) *section_names = sections + elf_header->e_shstrndx;
  for (int i = 0; i < num_sections; i++) {
    const ElfW(Shdr) *section = &sections[i];
    string name = reinterpret_cast<const char *>(section_names->sh_offset
                                                 + section->sh_name);
    const char *contents = reinterpret_cast<const char *>(section->sh_offset);
    uint64 length = section->sh_size;
    file_context.section_map[name] = std::make_pair(contents, length);
  }

  // Parse all the compilation units in the .debug_info section.
  DumperLineToModule line_to_module(&byte_reader);
  std::pair<const char *, uint64> debug_info_section
      = file_context.section_map[".debug_info"];
  // We should never have been called if the file doesn't have a
  // .debug_info section.
  assert(debug_info_section.first);
  uint64 debug_info_length = debug_info_section.second;
  for (uint64 offset = 0; offset < debug_info_length;) {
    // Make a handler for the root DIE that populates MODULE with the
    // data we find.
    DwarfCUToModule::WarningReporter reporter(dwarf_filename, offset);
    DwarfCUToModule root_handler(&file_context, &line_to_module, &reporter);
    // Make a Dwarf2Handler that drives our DIEHandler.
    dwarf2reader::DIEDispatcher die_dispatcher(&root_handler);
    // Make a DWARF parser for the compilation unit at OFFSET.
    dwarf2reader::CompilationUnit reader(file_context.section_map,
                                         offset,
                                         &byte_reader,
                                         &die_dispatcher);
    // Process the entire compilation unit; get the offset of the next.
    offset += reader.Start();
  }
  return true;
}

// Fill REGISTER_NAMES with the register names appropriate to the
// machine architecture given in HEADER, indexed by the register
// numbers used in DWARF call frame information. Return true on
// success, or false if we don't recognize HEADER's machine
// architecture.
static bool DwarfCFIRegisterNames(const ElfW(Ehdr) *elf_header,
                                  vector<string> *register_names) {
  switch (elf_header->e_machine) {
    case EM_386:
      *register_names = DwarfCFIToModule::RegisterNames::I386();
      return true;
    case EM_ARM:
      *register_names = DwarfCFIToModule::RegisterNames::ARM();
      return true;
    case EM_X86_64:
      *register_names = DwarfCFIToModule::RegisterNames::X86_64();
      return true;
    default:
      return false;
  }
}

static bool LoadDwarfCFI(const string &dwarf_filename,
                         const ElfW(Ehdr) *elf_header,
                         const char *section_name,
                         const ElfW(Shdr) *section,
                         const bool eh_frame,
                         const ElfW(Shdr) *got_section,
                         const ElfW(Shdr) *text_section,
                         const bool big_endian,
                         Module *module) {
  // Find the appropriate set of register names for this file's
  // architecture.
  vector<string> register_names;
  if (!DwarfCFIRegisterNames(elf_header, &register_names)) {
    fprintf(stderr, "%s: unrecognized ELF machine architecture '%d';"
            " cannot convert DWARF call frame information\n",
            dwarf_filename.c_str(), elf_header->e_machine);
    return false;
  }

  const dwarf2reader::Endianness endianness = big_endian ?
      dwarf2reader::ENDIANNESS_BIG : dwarf2reader::ENDIANNESS_LITTLE;

  // Find the call frame information and its size.
  const char *cfi = reinterpret_cast<const char *>(section->sh_offset);
  size_t cfi_size = section->sh_size;

  // Plug together the parser, handler, and their entourages.
  DwarfCFIToModule::Reporter module_reporter(dwarf_filename, section_name);
  DwarfCFIToModule handler(module, register_names, &module_reporter);
  dwarf2reader::ByteReader byte_reader(endianness);
  // Since we're using the ElfW macro, we're not actually capable of
  // processing both ELF32 and ELF64 files with the same program; that
  // would take a bit more work. But this will work out well enough.
  if (elf_header->e_ident[EI_CLASS] == ELFCLASS32)
    byte_reader.SetAddressSize(4);
  else if (elf_header->e_ident[EI_CLASS] == ELFCLASS64)
    byte_reader.SetAddressSize(8);
  else {
    fprintf(stderr, "%s: bad file class in ELF header: %d\n",
            dwarf_filename.c_str(), elf_header->e_ident[EI_CLASS]);
    return false;
  }
  // Provide the base addresses for .eh_frame encoded pointers, if
  // possible.
  byte_reader.SetCFIDataBase(section->sh_addr, cfi);
  if (got_section)
    byte_reader.SetDataBase(got_section->sh_addr);
  if (text_section)
    byte_reader.SetTextBase(text_section->sh_addr);

  dwarf2reader::CallFrameInfo::Reporter dwarf_reporter(dwarf_filename,
                                                       section_name);
  dwarf2reader::CallFrameInfo parser(cfi, cfi_size,
                                     &byte_reader, &handler, &dwarf_reporter,
                                     eh_frame);
  parser.Start();
  return true;
}

bool LoadELF(const std::string &obj_file, MmapWrapper* map_wrapper,
             ElfW(Ehdr) **elf_header) {
  int obj_fd = open(obj_file.c_str(), O_RDONLY);
  if (obj_fd < 0) {
    fprintf(stderr, "Failed to open ELF file '%s': %s\n",
            obj_file.c_str(), strerror(errno));
    return false;
  }
  FDWrapper obj_fd_wrapper(obj_fd);
  struct stat st;
  if (fstat(obj_fd, &st) != 0 && st.st_size <= 0) {
    fprintf(stderr, "Unable to fstat ELF file '%s': %s\n",
            obj_file.c_str(), strerror(errno));
    return false;
  }
  void *obj_base = mmap(NULL, st.st_size,
                        PROT_READ | PROT_WRITE, MAP_PRIVATE, obj_fd, 0);
  if (obj_base == MAP_FAILED) {
    fprintf(stderr, "Failed to mmap ELF file '%s': %s\n",
            obj_file.c_str(), strerror(errno));
    return false;
  }
  map_wrapper->set(obj_base, st.st_size);
  *elf_header = reinterpret_cast<ElfW(Ehdr) *>(obj_base);
  if (!IsValidElf(*elf_header)) {
    fprintf(stderr, "Not a valid ELF file: %s\n", obj_file.c_str());
    return false;
  }
  return true;
}

// Get the endianness of ELF_HEADER. If it's invalid, return false.
bool ElfEndianness(const ElfW(Ehdr) *elf_header, bool *big_endian) {
  if (elf_header->e_ident[EI_DATA] == ELFDATA2LSB) {
    *big_endian = false;
    return true;
  }
  if (elf_header->e_ident[EI_DATA] == ELFDATA2MSB) {
    *big_endian = true;
    return true;
  }

  fprintf(stderr, "bad data encoding in ELF header: %d\n",
          elf_header->e_ident[EI_DATA]);
  return false;
}

// Read the .gnu_debuglink and get the debug file name. If anything goes
// wrong, return an empty string.
static std::string ReadDebugLink(const ElfW(Shdr) *debuglink_section,
                                 const std::string &obj_file,
                                 const std::string &debug_dir) {
  char *debuglink = reinterpret_cast<char *>(debuglink_section->sh_offset);
  size_t debuglink_len = strlen(debuglink) + 5;  // '\0' + CRC32.
  debuglink_len = 4 * ((debuglink_len + 3) / 4);  // Round to nearest 4 bytes.

  // Sanity check.
  if (debuglink_len != debuglink_section->sh_size) {
    fprintf(stderr, "Mismatched .gnu_debuglink string / section size: "
            "%zx %zx\n", debuglink_len, debuglink_section->sh_size);
    return "";
  }

  std::string debuglink_path = debug_dir + "/" + debuglink;
  int debuglink_fd = open(debuglink_path.c_str(), O_RDONLY);
  if (debuglink_fd < 0) {
    fprintf(stderr, "Failed to open debug ELF file '%s' for '%s': %s\n",
            debuglink_path.c_str(), obj_file.c_str(), strerror(errno));
    return "";
  }
  FDWrapper debuglink_fd_wrapper(debuglink_fd);
  // TODO(thestig) check the CRC-32 at the end of the .gnu_debuglink
  // section.

  return debuglink_path;
}

//
// LoadSymbolsInfo
//
// Holds the state between the two calls to LoadSymbols() in case we have to
// follow the .gnu_debuglink section and load debug information from a
// different file.
//
class LoadSymbolsInfo {
 public:
  explicit LoadSymbolsInfo(const std::string &dbg_dir) :
    debug_dir_(dbg_dir),
    has_loading_addr_(false) {}

  // Keeps track of which sections have been loaded so we don't accidentally
  // load it twice from two different files.
  void LoadedSection(const std::string &section) {
    if (loaded_sections_.count(section) == 0) {
      loaded_sections_.insert(section);
    } else {
      fprintf(stderr, "Section %s has already been loaded.\n",
              section.c_str());
    }
  }

  // We expect the ELF file and linked debug file to have the same preferred
  // loading address.
  void set_loading_addr(ElfW(Addr) addr, const std::string &filename) {
    if (!has_loading_addr_) {
      loading_addr_ = addr;
      loaded_file_ = filename;
      return;
    }

    if (addr != loading_addr_) {
      fprintf(stderr,
              "ELF file '%s' and debug ELF file '%s' "
              "have different load addresses.\n",
              loaded_file_.c_str(), filename.c_str());
      assert(false);
    }
  }

  // Setters and getters
  const std::string &debug_dir() const {
    return debug_dir_;
  }

  std::string debuglink_file() const {
    return debuglink_file_;
  }
  void set_debuglink_file(std::string file) {
    debuglink_file_ = file;
  }

 private:
  const std::string &debug_dir_;  // Directory with the debug ELF file.

  std::string debuglink_file_;  // Full path to the debug ELF file.

  bool has_loading_addr_;  // Indicate if LOADING_ADDR_ is valid.

  ElfW(Addr) loading_addr_;  // Saves the preferred loading address from the
                             // first call to LoadSymbols().

  std::string loaded_file_;  // Name of the file loaded from the first call to
                             // LoadSymbols().

  std::set<std::string> loaded_sections_;  // Tracks the Loaded ELF sections
                                           // between calls to LoadSymbols().
};

static bool LoadSymbols(const std::string &obj_file,
                        const bool big_endian,
                        ElfW(Ehdr) *elf_header,
                        const bool read_gnu_debug_link,
                        LoadSymbolsInfo *info,
                        Module *module) {
  // Translate all offsets in section headers into address.
  FixAddress(elf_header);
  ElfW(Addr) loading_addr = GetLoadingAddress(
      reinterpret_cast<ElfW(Phdr) *>(elf_header->e_phoff),
      elf_header->e_phnum);
  module->SetLoadAddress(loading_addr);
  info->set_loading_addr(loading_addr, obj_file);

  const ElfW(Shdr) *sections =
      reinterpret_cast<ElfW(Shdr) *>(elf_header->e_shoff);
  const ElfW(Shdr) *section_names = sections + elf_header->e_shstrndx;
  bool found_debug_info_section = false;

  // Look for STABS debugging information, and load it if present.
  const ElfW(Shdr) *stab_section
      = FindSectionByName(".stab", sections, section_names,
                          elf_header->e_shnum);
  if (stab_section) {
    const ElfW(Shdr) *stabstr_section = stab_section->sh_link + sections;
    if (stabstr_section) {
      found_debug_info_section = true;
      info->LoadedSection(".stab");
      if (!LoadStabs(elf_header, stab_section, stabstr_section, big_endian,
                     module)) {
        fprintf(stderr, "%s: \".stab\" section found, but failed to load STABS"
                " debugging information\n", obj_file.c_str());
      }
    }
  }

  // Look for DWARF debugging information, and load it if present.
  const ElfW(Shdr) *dwarf_section
      = FindSectionByName(".debug_info", sections, section_names,
                          elf_header->e_shnum);
  if (dwarf_section) {
    found_debug_info_section = true;
    info->LoadedSection(".debug_info");
    if (!LoadDwarf(obj_file, elf_header, big_endian, module))
      fprintf(stderr, "%s: \".debug_info\" section found, but failed to load "
              "DWARF debugging information\n", obj_file.c_str());
  }

  // Dwarf Call Frame Information (CFI) is actually independent from
  // the other DWARF debugging information, and can be used alone.
  const ElfW(Shdr) *dwarf_cfi_section =
      FindSectionByName(".debug_frame", sections, section_names,
                          elf_header->e_shnum);
  if (dwarf_cfi_section) {
    // Ignore the return value of this function; even without call frame
    // information, the other debugging information could be perfectly
    // useful.
    info->LoadedSection(".debug_frame");
    LoadDwarfCFI(obj_file, elf_header, ".debug_frame",
                 dwarf_cfi_section, false, 0, 0, big_endian, module);
  }

  // Linux C++ exception handling information can also provide
  // unwinding data.
  const ElfW(Shdr) *eh_frame_section =
      FindSectionByName(".eh_frame", sections, section_names,
                        elf_header->e_shnum);
  if (eh_frame_section) {
    // Pointers in .eh_frame data may be relative to the base addresses of
    // certain sections. Provide those sections if present.
    const ElfW(Shdr) *got_section =
      FindSectionByName(".got", sections, section_names, elf_header->e_shnum);
    const ElfW(Shdr) *text_section =
      FindSectionByName(".text", sections, section_names,
                        elf_header->e_shnum);
    info->LoadedSection(".eh_frame");
    // As above, ignore the return value of this function.
    LoadDwarfCFI(obj_file, elf_header, ".eh_frame", eh_frame_section, true,
                 got_section, text_section, big_endian, module);
  }

  if (!found_debug_info_section) {
    fprintf(stderr, "%s: file contains no debugging information"
            " (no \".stab\" or \".debug_info\" sections)\n",
            obj_file.c_str());

    // Failed, but maybe we can find a .gnu_debuglink section?
    if (read_gnu_debug_link) {
      const ElfW(Shdr) *gnu_debuglink_section
          = FindSectionByName(".gnu_debuglink", sections, section_names,
                              elf_header->e_shnum);
      if (gnu_debuglink_section) {
        if (!info->debug_dir().empty()) {
          std::string debuglink_file =
              ReadDebugLink(gnu_debuglink_section, obj_file, info->debug_dir());
          info->set_debuglink_file(debuglink_file);
        } else {
          fprintf(stderr, ".gnu_debuglink section found in '%s', "
                  "but no debug path specified.\n", obj_file.c_str());
        }
      } else {
        fprintf(stderr, "%s does not contain a .gnu_debuglink section.\n",
                obj_file.c_str());
      }
    }
    return false;
  }

  return true;
}

// Return the breakpad symbol file identifier for the architecture of
// ELF_HEADER.
const char *ElfArchitecture(const ElfW(Ehdr) *elf_header) {
  ElfW(Half) arch = elf_header->e_machine;
  switch (arch) {
    case EM_386:        return "x86";
    case EM_ARM:        return "arm";
    case EM_MIPS:       return "mips";
    case EM_PPC64:      return "ppc64";
    case EM_PPC:        return "ppc";
    case EM_S390:       return "s390";
    case EM_SPARC:      return "sparc";
    case EM_SPARCV9:    return "sparcv9";
    case EM_X86_64:     return "x86_64";
    default: return NULL;
  }
}

// Format the Elf file identifier in IDENTIFIER as a UUID with the
// dashes removed.
std::string FormatIdentifier(unsigned char identifier[16]) {
  char identifier_str[40];
  google_breakpad::FileID::ConvertIdentifierToString(
      identifier,
      identifier_str,
      sizeof(identifier_str));
  std::string id_no_dash;
  for (int i = 0; identifier_str[i] != '\0'; ++i)
    if (identifier_str[i] != '-')
      id_no_dash += identifier_str[i];
  // Add an extra "0" by the end.  PDB files on Windows have an 'age'
  // number appended to the end of the file identifier; this isn't
  // really used or necessary on other platforms, but let's preserve
  // the pattern.
  id_no_dash += '0';
  return id_no_dash;
}

// Return the non-directory portion of FILENAME: the portion after the
// last slash, or the whole filename if there are no slashes.
std::string BaseFileName(const std::string &filename) {
  // Lots of copies!  basename's behavior is less than ideal.
  char *c_filename = strdup(filename.c_str());
  std::string base = basename(c_filename);
  free(c_filename);
  return base;
}

}  // namespace

namespace google_breakpad {

bool WriteSymbolFile(const std::string &obj_file,
                     const std::string &debug_dir, FILE *sym_file) {
  MmapWrapper map_wrapper;
  ElfW(Ehdr) *elf_header = NULL;
  if (!LoadELF(obj_file, &map_wrapper, &elf_header))
    return false;

  unsigned char identifier[16];
  google_breakpad::FileID file_id(obj_file.c_str());
  if (!file_id.ElfFileIdentifierFromMappedFile(elf_header, identifier)) {
    fprintf(stderr, "%s: unable to generate file identifier\n",
            obj_file.c_str());
    return false;
  }

  const char *architecture = ElfArchitecture(elf_header);
  if (!architecture) {
    fprintf(stderr, "%s: unrecognized ELF machine architecture: %d\n",
            obj_file.c_str(), elf_header->e_machine);
    return false;
  }

  // Figure out what endianness this file is.
  bool big_endian;
  if (!ElfEndianness(elf_header, &big_endian))
    return false;

  std::string name = BaseFileName(obj_file);
  std::string os = "Linux";
  std::string id = FormatIdentifier(identifier);

  LoadSymbolsInfo info(debug_dir);
  Module module(name, os, architecture, id);
  if (!LoadSymbols(obj_file, big_endian, elf_header, true, &info, &module)) {
    const std::string debuglink_file = info.debuglink_file();
    if (debuglink_file.empty())
      return false;

    // Load debuglink ELF file.
    fprintf(stderr, "Found debugging info in %s\n", debuglink_file.c_str());
    MmapWrapper debug_map_wrapper;
    ElfW(Ehdr) *debug_elf_header = NULL;
    if (!LoadELF(debuglink_file, &debug_map_wrapper, &debug_elf_header))
      return false;
    // Sanity checks to make sure everything matches up.
    const char *debug_architecture = ElfArchitecture(debug_elf_header);
    if (!debug_architecture) {
      fprintf(stderr, "%s: unrecognized ELF machine architecture: %d\n",
              debuglink_file.c_str(), debug_elf_header->e_machine);
      return false;
    }
    if (strcmp(architecture, debug_architecture)) {
      fprintf(stderr, "%s with ELF machine architecture %s does not match "
              "%s with ELF architecture %s\n",
              debuglink_file.c_str(), debug_architecture,
              obj_file.c_str(), architecture);
      return false;
    }

    bool debug_big_endian;
    if (!ElfEndianness(debug_elf_header, &debug_big_endian))
      return false;
    if (debug_big_endian != big_endian) {
      fprintf(stderr, "%s and %s does not match in endianness\n",
              obj_file.c_str(), debuglink_file.c_str());
      return false;
    }

    if (!LoadSymbols(debuglink_file, debug_big_endian, debug_elf_header,
                     false, &info, &module)) {
      return false;
    }
  }
  if (!module.Write(sym_file))
    return false;

  return true;
}

}  // namespace google_breakpad