Copy Crashpad into the Chrome tree instead of importing it via DEPS

third_party/crashpad/crashpad/snapshot/mac/mach_o_image_reader.cc

Index: third_party/crashpad/crashpad/snapshot/mac/mach_o_image_reader.cc
diff --git a/third_party/crashpad/crashpad/snapshot/mac/mach_o_image_reader.cc b/third_party/crashpad/crashpad/snapshot/mac/mach_o_image_reader.cc
new file mode 100644
index 0000000000000000000000000000000000000000..09b7ffeb29983c4a7a7f21fe3b77df052db023d2
--- /dev/null
+++ b/third_party/crashpad/crashpad/snapshot/mac/mach_o_image_reader.cc
@@ -0,0 +1,724 @@
+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "snapshot/mac/mach_o_image_reader.h"
+
+#include <mach-o/loader.h>
+#include <mach-o/nlist.h>
+#include <string.h>
+
+#include <limits>
+#include <vector>
+#include <utility>
+
+#include "base/logging.h"
+#include "base/strings/stringprintf.h"
+#include "client/crashpad_info.h"
+#include "snapshot/mac/mach_o_image_segment_reader.h"
+#include "snapshot/mac/mach_o_image_symbol_table_reader.h"
+#include "snapshot/mac/process_reader.h"
+#include "util/mac/checked_mach_address_range.h"
+#include "util/misc/implicit_cast.h"
+
+namespace {
+
+const uint32_t kInvalidSegmentIndex = std::numeric_limits<uint32_t>::max();
+
+}  // namespace
+
+namespace crashpad {
+
+MachOImageReader::MachOImageReader()
+    : segments_(),
+      segment_map_(),
+      module_name_(),
+      module_info_(),
+      dylinker_name_(),
+      uuid_(),
+      address_(0),
+      size_(0),
+      slide_(0),
+      source_version_(0),
+      symtab_command_(),
+      dysymtab_command_(),
+      symbol_table_(),
+      id_dylib_command_(),
+      process_reader_(nullptr),
+      file_type_(0),
+      initialized_(),
+      symbol_table_initialized_() {
+}
+
+MachOImageReader::~MachOImageReader() {
+}
+
+bool MachOImageReader::Initialize(ProcessReader* process_reader,
+                                  mach_vm_address_t address,
+                                  const std::string& name) {
+  INITIALIZATION_STATE_SET_INITIALIZING(initialized_);
+
+  process_reader_ = process_reader;
+  address_ = address;
+  module_name_ = name;
+
+  module_info_ =
+      base::StringPrintf(", module %s, address 0x%llx", name.c_str(), address);
+
+  process_types::mach_header mach_header;
+  if (!mach_header.Read(process_reader, address)) {
+    LOG(WARNING) << "could not read mach_header" << module_info_;
+    return false;
+  }
+
+  const bool is_64_bit = process_reader->Is64Bit();
+  const uint32_t kExpectedMagic = is_64_bit ? MH_MAGIC_64 : MH_MAGIC;
+  if (mach_header.magic != kExpectedMagic) {
+    LOG(WARNING) << base::StringPrintf("unexpected mach_header::magic 0x%08x",
+                                       mach_header.magic) << module_info_;
+    return false;
+  }
+
+  switch (mach_header.filetype) {
+    case MH_EXECUTE:
+    case MH_DYLIB:
+    case MH_DYLINKER:
+    case MH_BUNDLE:
+      file_type_ = mach_header.filetype;
+      break;
+    default:
+      LOG(WARNING) << base::StringPrintf(
+                          "unexpected mach_header::filetype 0x%08x",
+                          mach_header.filetype) << module_info_;
+      return false;
+  }
+
+  const uint32_t kExpectedSegmentCommand =
+      is_64_bit ? LC_SEGMENT_64 : LC_SEGMENT;
+  const uint32_t kUnexpectedSegmentCommand =
+      is_64_bit ? LC_SEGMENT : LC_SEGMENT_64;
+
+  const struct {
+    // Which method to call when encountering a load command matching |command|.
+    bool (MachOImageReader::*function)(mach_vm_address_t, const std::string&);
+
+    // The minimum size that may be allotted to store the load command.
+    size_t size;
+
+    // The load command to match.
+    uint32_t command;
+
+    // True if the load command must not appear more than one time.
+    bool singleton;
+  } kLoadCommandReaders[] = {
+    {
+      &MachOImageReader::ReadSegmentCommand,
+      process_types::segment_command::ExpectedSize(process_reader),
+      kExpectedSegmentCommand,
+      false,
+    },
+    {
+      &MachOImageReader::ReadSymTabCommand,
+      process_types::symtab_command::ExpectedSize(process_reader),
+      LC_SYMTAB,
+      true,
+    },
+    {
+      &MachOImageReader::ReadDySymTabCommand,
+      process_types::symtab_command::ExpectedSize(process_reader),
+      LC_DYSYMTAB,
+      true,
+    },
+    {
+      &MachOImageReader::ReadIdDylibCommand,
+      process_types::dylib_command::ExpectedSize(process_reader),
+      LC_ID_DYLIB,
+      true,
+    },
+    {
+      &MachOImageReader::ReadDylinkerCommand,
+      process_types::dylinker_command::ExpectedSize(process_reader),
+      LC_LOAD_DYLINKER,
+      true,
+    },
+    {
+      &MachOImageReader::ReadDylinkerCommand,
+      process_types::dylinker_command::ExpectedSize(process_reader),
+      LC_ID_DYLINKER,
+      true,
+    },
+    {
+      &MachOImageReader::ReadUUIDCommand,
+      process_types::uuid_command::ExpectedSize(process_reader),
+      LC_UUID,
+      true,
+    },
+    {
+      &MachOImageReader::ReadSourceVersionCommand,
+      process_types::source_version_command::ExpectedSize(process_reader),
+      LC_SOURCE_VERSION,
+      true,
+    },
+
+    // When reading a 64-bit process, no 32-bit segment commands should be
+    // present, and vice-versa.
+    {
+      &MachOImageReader::ReadUnexpectedCommand,
+      process_types::load_command::ExpectedSize(process_reader),
+      kUnexpectedSegmentCommand,
+      false,
+    },
+  };
+
+  // This vector is parallel to the kLoadCommandReaders array, and tracks
+  // whether a singleton load command matching the |command| field has been
+  // found yet.
+  std::vector<uint32_t> singleton_indices(arraysize(kLoadCommandReaders),
+                                          kInvalidSegmentIndex);
+
+  size_t offset = mach_header.Size();
+  const mach_vm_address_t kLoadCommandAddressLimit =
+      address + offset + mach_header.sizeofcmds;
+
+  for (uint32_t load_command_index = 0;
+       load_command_index < mach_header.ncmds;
+       ++load_command_index) {
+    mach_vm_address_t load_command_address = address + offset;
+    std::string load_command_info = base::StringPrintf(", load command %u/%u%s",
+                                                       load_command_index,
+                                                       mach_header.ncmds,
+                                                       module_info_.c_str());
+
+    process_types::load_command load_command;
+
+    // Make sure that the basic load command structure doesn’t overflow the
+    // space allotted for load commands.
+    if (load_command_address + load_command.ExpectedSize(process_reader) >
+            kLoadCommandAddressLimit) {
+      LOG(WARNING) << base::StringPrintf(
+                          "load_command at 0x%llx exceeds sizeofcmds 0x%x",
+                          load_command_address,
+                          mach_header.sizeofcmds) << load_command_info;
+      return false;
+    }
+
+    if (!load_command.Read(process_reader, load_command_address)) {
+      LOG(WARNING) << "could not read load_command" << load_command_info;
+      return false;
+    }
+
+    load_command_info = base::StringPrintf(", load command 0x%x %u/%u%s",
+                                           load_command.cmd,
+                                           load_command_index,
+                                           mach_header.ncmds,
+                                           module_info_.c_str());
+
+    // Now that the load command’s stated size is known, make sure that it
+    // doesn’t overflow the space allotted for load commands.
+    if (load_command_address + load_command.cmdsize >
+            kLoadCommandAddressLimit) {
+      LOG(WARNING)
+          << base::StringPrintf(
+                 "load_command at 0x%llx cmdsize 0x%x exceeds sizeofcmds 0x%x",
+                 load_command_address,
+                 load_command.cmdsize,
+                 mach_header.sizeofcmds) << load_command_info;
+      return false;
+    }
+
+    for (size_t reader_index = 0;
+         reader_index < arraysize(kLoadCommandReaders);
+         ++reader_index) {
+      if (load_command.cmd != kLoadCommandReaders[reader_index].command) {
+        continue;
+      }
+
+      if (load_command.cmdsize < kLoadCommandReaders[reader_index].size) {
+        LOG(WARNING) << base::StringPrintf(
+                            "load command cmdsize 0x%x insufficient for 0x%zx",
+                            load_command.cmdsize,
+                            kLoadCommandReaders[reader_index].size)
+                     << load_command_info;
+        return false;
+      }
+
+      if (kLoadCommandReaders[reader_index].singleton) {
+        if (singleton_indices[reader_index] != kInvalidSegmentIndex) {
+          LOG(WARNING) << "duplicate load command at "
+                       << singleton_indices[reader_index] << load_command_info;
+          return false;
+        }
+
+        singleton_indices[reader_index] = load_command_index;
+      }
+
+      if (!((this)->*(kLoadCommandReaders[reader_index].function))(
+              load_command_address, load_command_info)) {
+        return false;
+      }
+
+      break;
+    }
+
+    offset += load_command.cmdsize;
+  }
+
+  // Now that the slide is known, push it into the segments.
+  for (MachOImageSegmentReader* segment : segments_) {
+    segment->SetSlide(slide_);
+
+    // This was already checked for the unslid values while the segments were
+    // read, but now it’s possible to check the slid values too. The individual
+    // sections don’t need to be checked because they were verified to be
+    // contained within their respective segments when the segments were read.
+    mach_vm_address_t slid_segment_address = segment->Address();
+    mach_vm_size_t slid_segment_size = segment->Size();
+    CheckedMachAddressRange slid_segment_range(
+        process_reader_->Is64Bit(), slid_segment_address, slid_segment_size);
+    if (!slid_segment_range.IsValid()) {
+      LOG(WARNING) << base::StringPrintf(
+                          "invalid slid segment range 0x%llx + 0x%llx, "
+                          "segment ",
+                          slid_segment_address,
+                          slid_segment_size) << segment->Name() << module_info_;
+      return false;
+    }
+  }
+
+  if (!segment_map_.count(SEG_TEXT)) {
+    // The __TEXT segment is required. Even a module with no executable code
+    // will have a __TEXT segment encompassing the Mach-O header and load
+    // commands. Without a __TEXT segment, |size_| will not have been computed.
+    LOG(WARNING) << "no " SEG_TEXT " segment" << module_info_;
+    return false;
+  }
+
+  if (mach_header.filetype == MH_DYLIB && !id_dylib_command_) {
+    // This doesn’t render a module unusable, it’s just weird and worth noting.
+    LOG(INFO) << "no LC_ID_DYLIB" << module_info_;
+  }
+
+  INITIALIZATION_STATE_SET_VALID(initialized_);
+  return true;
+}
+
+const MachOImageSegmentReader* MachOImageReader::GetSegmentByName(
+    const std::string& segment_name) const {
+  INITIALIZATION_STATE_DCHECK_VALID(initialized_);
+
+  const auto& iterator = segment_map_.find(segment_name);
+  if (iterator == segment_map_.end()) {
+    return nullptr;
+  }
+
+  const MachOImageSegmentReader* segment = segments_[iterator->second];
+  return segment;
+}
+
+const process_types::section* MachOImageReader::GetSectionByName(
+    const std::string& segment_name,
+    const std::string& section_name,
+    mach_vm_address_t* address) const {
+  INITIALIZATION_STATE_DCHECK_VALID(initialized_);
+
+  const MachOImageSegmentReader* segment = GetSegmentByName(segment_name);
+  if (!segment) {
+    return nullptr;
+  }
+
+  return segment->GetSectionByName(section_name, address);
+}
+
+const process_types::section* MachOImageReader::GetSectionAtIndex(
+    size_t index,
+    const MachOImageSegmentReader** containing_segment,
+    mach_vm_address_t* address) const {
+  INITIALIZATION_STATE_DCHECK_VALID(initialized_);
+
+  static_assert(NO_SECT == 0, "NO_SECT must be zero");
+  if (index == NO_SECT) {
+    LOG(WARNING) << "section index " << index << " out of range";
+    return nullptr;
+  }
+
+  // Switch to a more comfortable 0-based index.
+  size_t local_index = index - 1;
+
+  for (const MachOImageSegmentReader* segment : segments_) {
+    size_t nsects = segment->nsects();
+    if (local_index < nsects) {
+      const process_types::section* section =
+          segment->GetSectionAtIndex(local_index, address);
+
+      if (containing_segment) {
+        *containing_segment = segment;
+      }
+
+      return section;
+    }
+
+    local_index -= nsects;
+  }
+
+  LOG(WARNING) << "section index " << index << " out of range";
+  return nullptr;
+}
+
+bool MachOImageReader::LookUpExternalDefinedSymbol(
+    const std::string& name,
+    mach_vm_address_t* value) const {
+  INITIALIZATION_STATE_DCHECK_VALID(initialized_);
+
+  if (symbol_table_initialized_.is_uninitialized()) {
+    InitializeSymbolTable();
+  }
+
+  if (!symbol_table_initialized_.is_valid() || !symbol_table_) {
+    return false;
+  }
+
+  const MachOImageSymbolTableReader::SymbolInformation* symbol_info =
+      symbol_table_->LookUpExternalDefinedSymbol(name);
+  if (!symbol_info) {
+    return false;
+  }
+
+  if (symbol_info->section == NO_SECT) {
+    // This is an absolute (N_ABS) symbol, which requires no further validation
+    // or processing.
+    *value = symbol_info->value;
+    return true;
+  }
+
+  // This is a symbol defined in a particular section, so make sure that it’s
+  // valid for that section and fix it up for any “slide” as needed.
+
+  mach_vm_address_t section_address;
+  const MachOImageSegmentReader* segment;
+  const process_types::section* section =
+      GetSectionAtIndex(symbol_info->section, &segment, &section_address);
+  if (!section) {
+    return false;
+  }
+
+  mach_vm_address_t slid_value =
+      symbol_info->value + (segment->SegmentSlides() ? slide_ : 0);
+
+  // The __mh_execute_header (_MH_EXECUTE_SYM) symbol is weird. In
+  // position-independent executables, it shows up in the symbol table as a
+  // symbol in section 1, although it’s not really in that section. It points to
+  // the mach_header[_64], which is the beginning of the __TEXT segment, and the
+  // __text section normally begins after the load commands in the __TEXT
+  // segment. The range check below will fail for this symbol, because it’s not
+  // really in the section it claims to be in. See Xcode 5.1
+  // ld64-236.3/src/ld/OutputFile.cpp ld::tool::OutputFile::buildSymbolTable().
+  // There, ld takes symbols that refer to anything in the mach_header[_64] and
+  // marks them as being in section 1. Here, section 1 is treated in this same
+  // special way as long as it’s in the __TEXT segment that begins at the start
+  // of the image, which is normally the case, and as long as the symbol’s value
+  // is the base of the image.
+  //
+  // This only happens for PIE executables, because __mh_execute_header needs
+  // to slide. In non-PIE executables, __mh_execute_header is an absolute
+  // symbol.
+  CheckedMachAddressRange section_range(
+      process_reader_->Is64Bit(), section_address, section->size);
+  if (!section_range.ContainsValue(slid_value) &&
+      !(symbol_info->section == 1 && segment->Name() == SEG_TEXT &&
+        slid_value == Address())) {
+    std::string section_name_full =
+        MachOImageSegmentReader::SegmentAndSectionNameString(section->segname,
+                                                             section->sectname);
+    LOG(WARNING) << base::StringPrintf(
+                        "symbol %s (0x%llx) outside of section %s (0x%llx + "
+                        "0x%llx)",
+                        name.c_str(),
+                        slid_value,
+                        section_name_full.c_str(),
+                        section_address,
+                        section->size) << module_info_;
+    return false;
+  }
+
+  *value = slid_value;
+  return true;
+}
+
+uint32_t MachOImageReader::DylibVersion() const {
+  INITIALIZATION_STATE_DCHECK_VALID(initialized_);
+  DCHECK_EQ(FileType(), implicit_cast<uint32_t>(MH_DYLIB));
+
+  if (id_dylib_command_) {
+    return id_dylib_command_->dylib_current_version;
+  }
+
+  // In case this was a weird dylib without an LC_ID_DYLIB command.
+  return 0;
+}
+
+void MachOImageReader::UUID(crashpad::UUID* uuid) const {
+  INITIALIZATION_STATE_DCHECK_VALID(initialized_);
+  memcpy(uuid, &uuid_, sizeof(uuid_));
+}
+
+bool MachOImageReader::GetCrashpadInfo(
+    process_types::CrashpadInfo* crashpad_info) const {
+  INITIALIZATION_STATE_DCHECK_VALID(initialized_);
+
+  mach_vm_address_t crashpad_info_address;
+  const process_types::section* crashpad_info_section =
+      GetSectionByName(SEG_DATA, "__crashpad_info", &crashpad_info_address);
+  if (!crashpad_info_section) {
+    return false;
+  }
+
+  if (crashpad_info_section->size <
+      crashpad_info->ExpectedSize(process_reader_)) {
+    LOG(WARNING) << "small crashpad info section size "
+                 << crashpad_info_section->size << module_info_;
+    return false;
+  }
+
+  if (!crashpad_info->Read(process_reader_, crashpad_info_address)) {
+    LOG(WARNING) << "could not read crashpad info" << module_info_;
+    return false;
+  }
+
+  if (crashpad_info->signature != CrashpadInfo::kSignature ||
+      crashpad_info->size != crashpad_info_section->size ||
+      crashpad_info->version < 1) {
+    LOG(WARNING) << "unexpected crashpad info data" << module_info_;
+    return false;
+  }
+
+  return true;
+}
+
+template <typename T>
+bool MachOImageReader::ReadLoadCommand(mach_vm_address_t load_command_address,
+                                       const std::string& load_command_info,
+                                       uint32_t expected_load_command_id,
+                                       T* load_command) {
+  if (!load_command->Read(process_reader_, load_command_address)) {
+    LOG(WARNING) << "could not read load command" << load_command_info;
+    return false;
+  }
+
+  DCHECK_GE(load_command->cmdsize, load_command->Size());
+  DCHECK_EQ(load_command->cmd, expected_load_command_id);
+  return true;
+}
+
+bool MachOImageReader::ReadSegmentCommand(
+    mach_vm_address_t load_command_address,
+    const std::string& load_command_info) {
+  MachOImageSegmentReader* segment = new MachOImageSegmentReader();
+  size_t segment_index = segments_.size();
+  segments_.push_back(segment);  // Takes ownership.
+
+  if (!segment->Initialize(process_reader_,
+                           load_command_address,
+                           load_command_info,
+                           module_name_,
+                           file_type_)) {
+    segments_.pop_back();
+    return false;
+  }
+
+  // At this point, the segment itself is considered valid, but if one of the
+  // next checks fails, it will render the module invalid. If any of the next
+  // checks fail, this method should return false, but it doesn’t need to bother
+  // removing the segment from segments_. The segment will be properly released
+  // when the image is destroyed, and the image won’t be usable because
+  // initialization won’t have completed. Most importantly, leaving the segment
+  // in segments_ means that no other structures (such as perhaps segment_map_)
+  // become inconsistent or require cleanup.
+
+  const std::string segment_name = segment->Name();
+  const auto insert_result =
+      segment_map_.insert(std::make_pair(segment_name, segment_index));
+  if (!insert_result.second) {
+    LOG(WARNING) << base::StringPrintf("duplicate %s segment at %zu and %zu",
+                                       segment_name.c_str(),
+                                       insert_result.first->second,
+                                       segment_index) << load_command_info;
+    return false;
+  }
+
+  mach_vm_size_t vmsize = segment->vmsize();
+
+  if (segment_name == SEG_TEXT) {
+    if (vmsize == 0) {
+      LOG(WARNING) << "zero-sized " SEG_TEXT " segment" << load_command_info;
+      return false;
+    }
+
+    mach_vm_size_t fileoff = segment->fileoff();
+    if (fileoff != 0) {
+      LOG(WARNING) << base::StringPrintf(
+                          SEG_TEXT " segment has unexpected fileoff 0x%llx",
+                          fileoff) << load_command_info;
+      return false;
+    }
+
+    size_ = vmsize;
+
+    // The slide is computed as the difference between the __TEXT segment’s
+    // preferred and actual load addresses. This is the same way that dyld
+    // computes slide. See 10.9.2 dyld-239.4/src/dyldInitialization.cpp
+    // slideOfMainExecutable().
+    slide_ = address_ - segment->vmaddr();
+  }
+
+  return true;
+}
+
+bool MachOImageReader::ReadSymTabCommand(mach_vm_address_t load_command_address,
+                                         const std::string& load_command_info) {
+  symtab_command_.reset(new process_types::symtab_command());
+  return ReadLoadCommand(load_command_address,
+                         load_command_info,
+                         LC_SYMTAB,
+                         symtab_command_.get());
+}
+
+bool MachOImageReader::ReadDySymTabCommand(
+    mach_vm_address_t load_command_address,
+    const std::string& load_command_info) {
+  dysymtab_command_.reset(new process_types::dysymtab_command());
+  return ReadLoadCommand(load_command_address,
+                         load_command_info,
+                         LC_DYSYMTAB,
+                         dysymtab_command_.get());
+}
+
+bool MachOImageReader::ReadIdDylibCommand(
+    mach_vm_address_t load_command_address,
+    const std::string& load_command_info) {
+  if (file_type_ != MH_DYLIB) {
+    LOG(WARNING) << base::StringPrintf(
+                        "LC_ID_DYLIB inappropriate in non-dylib file type 0x%x",
+                        file_type_) << load_command_info;
+    return false;
+  }
+
+  DCHECK(!id_dylib_command_);
+  id_dylib_command_.reset(new process_types::dylib_command());
+  return ReadLoadCommand(load_command_address,
+                         load_command_info,
+                         LC_ID_DYLIB,
+                         id_dylib_command_.get());
+}
+
+bool MachOImageReader::ReadDylinkerCommand(
+    mach_vm_address_t load_command_address,
+    const std::string& load_command_info) {
+  if (file_type_ != MH_EXECUTE && file_type_ != MH_DYLINKER) {
+    LOG(WARNING) << base::StringPrintf(
+                        "LC_LOAD_DYLINKER/LC_ID_DYLINKER inappropriate in file "
+                        "type 0x%x",
+                        file_type_) << load_command_info;
+    return false;
+  }
+
+  const uint32_t kExpectedCommand =
+      file_type_ == MH_DYLINKER ? LC_ID_DYLINKER : LC_LOAD_DYLINKER;
+  process_types::dylinker_command dylinker_command;
+  if (!ReadLoadCommand(load_command_address,
+                       load_command_info,
+                       kExpectedCommand,
+                       &dylinker_command)) {
+    return false;
+  }
+
+  if (!process_reader_->Memory()->ReadCStringSizeLimited(
+          load_command_address + dylinker_command.name,
+          dylinker_command.cmdsize - dylinker_command.name,
+          &dylinker_name_)) {
+    LOG(WARNING) << "could not read dylinker_command name" << load_command_info;
+    return false;
+  }
+
+  return true;
+}
+
+bool MachOImageReader::ReadUUIDCommand(mach_vm_address_t load_command_address,
+                                       const std::string& load_command_info) {
+  process_types::uuid_command uuid_command;
+  if (!ReadLoadCommand(
+          load_command_address, load_command_info, LC_UUID, &uuid_command)) {
+    return false;
+  }
+
+  uuid_.InitializeFromBytes(uuid_command.uuid);
+  return true;
+}
+
+bool MachOImageReader::ReadSourceVersionCommand(
+    mach_vm_address_t load_command_address,
+    const std::string& load_command_info) {
+  process_types::source_version_command source_version_command;
+  if (!ReadLoadCommand(load_command_address,
+                       load_command_info,
+                       LC_SOURCE_VERSION,
+                       &source_version_command)) {
+    return false;
+  }
+
+  source_version_ = source_version_command.version;
+  return true;
+}
+
+bool MachOImageReader::ReadUnexpectedCommand(
+    mach_vm_address_t load_command_address,
+    const std::string& load_command_info) {
+  LOG(WARNING) << "unexpected load command" << load_command_info;
+  return false;
+}
+
+void MachOImageReader::InitializeSymbolTable() const {
+  DCHECK(symbol_table_initialized_.is_uninitialized());
+  symbol_table_initialized_.set_invalid();
+
+  if (!symtab_command_) {
+    // It’s technically valid for there to be no LC_SYMTAB, and in that case,
+    // any symbol lookups should fail. Mark the symbol table as valid, and
+    // LookUpExternalDefinedSymbol() will understand what it means when this is
+    // valid but symbol_table_ is not present.
+    symbol_table_initialized_.set_valid();
+    return;
+  }
+
+  // Find the __LINKEDIT segment. Technically, the symbol table can be in any
+  // mapped segment, but by convention, it’s in the one named __LINKEDIT.
+  const MachOImageSegmentReader* linkedit_segment =
+      GetSegmentByName(SEG_LINKEDIT);
+  if (!linkedit_segment) {
+    LOG(WARNING) << "no " SEG_LINKEDIT " segment";
+    return;
+  }
+
+  symbol_table_.reset(new MachOImageSymbolTableReader());
+  if (!symbol_table_->Initialize(process_reader_,
+                                 symtab_command_.get(),
+                                 dysymtab_command_.get(),
+                                 linkedit_segment,
+                                 module_info_)) {
+    symbol_table_.reset();
+    return;
+  }
+
+  symbol_table_initialized_.set_valid();
+}
+
+}  // namespace crashpad