bool OatFileBase::Setup(const char* abs_dex_location, std::string* error_msg) {
  if (!GetOatHeader().IsValid()) {
    std::string cause = GetOatHeader().GetValidationErrorMessage();
    *error_msg = StringPrintf("Invalid oat header for '%s': %s",
                              GetLocation().c_str(),
                              cause.c_str());
    return false;
  }
  PointerSize pointer_size = GetInstructionSetPointerSize(GetOatHeader().GetInstructionSet());
  size_t key_value_store_size =
      (Size() >= sizeof(OatHeader)) ? GetOatHeader().GetKeyValueStoreSize() : 0u;
  if (Size() < sizeof(OatHeader) + key_value_store_size) {
    *error_msg = StringPrintf("In oat file '%s' found truncated OatHeader, "
                                  "size = %zu < %zu + %zu",
                              GetLocation().c_str(),
                              Size(),
                              sizeof(OatHeader),
                              key_value_store_size);
    return false;
  }

  size_t oat_dex_files_offset = GetOatHeader().GetOatDexFilesOffset();
  if (oat_dex_files_offset < GetOatHeader().GetHeaderSize() || oat_dex_files_offset > Size()) {
    *error_msg = StringPrintf("In oat file '%s' found invalid oat dex files offset: "
                                  "%zu is not in [%zu, %zu]",
                              GetLocation().c_str(),
                              oat_dex_files_offset,
                              GetOatHeader().GetHeaderSize(),
                              Size());
    return false;
  }
  const uint8_t* oat = Begin() + oat_dex_files_offset;  // Jump to the OatDexFile records.//oat指针跳到OatDexFile去

  DCHECK_GE(static_cast<size_t>(pointer_size), alignof(GcRoot<mirror::Object>));
  if (!IsAligned<kPageSize>(bss_begin_) ||
      !IsAlignedParam(bss_methods_, static_cast<size_t>(pointer_size)) ||
      !IsAlignedParam(bss_roots_, static_cast<size_t>(pointer_size)) ||
      !IsAligned<alignof(GcRoot<mirror::Object>)>(bss_end_)) {
    *error_msg = StringPrintf("In oat file '%s' found unaligned bss symbol(s): "
                                  "begin = %p, methods_ = %p, roots = %p, end = %p",
                              GetLocation().c_str(),
                              bss_begin_,
                              bss_methods_,
                              bss_roots_,
                              bss_end_);
    return false;
  }

  if ((bss_methods_ != nullptr && (bss_methods_ < bss_begin_ || bss_methods_ > bss_end_)) ||
      (bss_roots_ != nullptr && (bss_roots_ < bss_begin_ || bss_roots_ > bss_end_)) ||
      (bss_methods_ != nullptr && bss_roots_ != nullptr && bss_methods_ > bss_roots_)) {
    *error_msg = StringPrintf("In oat file '%s' found bss symbol(s) outside .bss or unordered: "
                                  "begin = %p, methods_ = %p, roots = %p, end = %p",
                              GetLocation().c_str(),
                              bss_begin_,
                              bss_methods_,
                              bss_roots_,
                              bss_end_);
    return false;
  }

  uint8_t* after_arrays = (bss_methods_ != nullptr) ? bss_methods_ : bss_roots_;  // May be null.
  uint8_t* dex_cache_arrays = (bss_begin_ == after_arrays) ? nullptr : bss_begin_;
  uint8_t* dex_cache_arrays_end =
      (bss_begin_ == after_arrays) ? nullptr : (after_arrays != nullptr) ? after_arrays : bss_end_;
  DCHECK_EQ(dex_cache_arrays != nullptr, dex_cache_arrays_end != nullptr);
  uint32_t dex_file_count = GetOatHeader().GetDexFileCount();//获得dex_file_count
  oat_dex_files_storage_.reserve(dex_file_count);
  for (size_t i = 0; i < dex_file_count; i++) {
    uint32_t dex_file_location_size;
    if (UNLIKELY(!ReadOatDexFileData(*this, &oat, &dex_file_location_size))) //循环通过ReadOatDexFileData函数读取dex_file_location_size并调整oat指针
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu truncated after dex file "
                                    "location size",
                                GetLocation().c_str(),
                                i);
      return false;
    }
    if (UNLIKELY(dex_file_location_size == 0U)) {
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu with empty location name",
                                GetLocation().c_str(),
                                i);
      return false;
    }
    if (UNLIKELY(static_cast<size_t>(End() - oat) < dex_file_location_size)) {
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu with truncated dex file "
                                    "location",
                                GetLocation().c_str(),
                                i);
      return false;
    }
    const char* dex_file_location_data = reinterpret_cast<const char*>(oat);
    oat += dex_file_location_size;

    std::string dex_file_location = ResolveRelativeEncodedDexLocation(
        abs_dex_location,
        std::string(dex_file_location_data, dex_file_location_size));

    uint32_t dex_file_checksum;
    if (UNLIKELY(!ReadOatDexFileData(*this, &oat, &dex_file_checksum))) {//通过ReadOatDexFileData函数读取dex_file_checksum并调整oat指针
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu for '%s' truncated after "
                                    "dex file checksum",
                                GetLocation().c_str(),
                                i,
                                dex_file_location.c_str());
      return false;
    }

    uint32_t dex_file_offset;
    if (UNLIKELY(!ReadOatDexFileData(*this, &oat, &dex_file_offset))) {//通过ReadOatDexFileData函数读取dex_file_offset并调整oat指针
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu for '%s' truncated "
                                    "after dex file offsets",
                                GetLocation().c_str(),
                                i,
                                dex_file_location.c_str());
      return false;
    }
    if (UNLIKELY(dex_file_offset == 0U)) {
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu for '%s' with zero dex "
                                    "file offset",
                                GetLocation().c_str(),
                                i,
                                dex_file_location.c_str());
      return false;
    }
    if (UNLIKELY(dex_file_offset > DexSize())) {
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu for '%s' with dex file "
                                    "offset %u > %zu",
                                GetLocation().c_str(),
                                i,
                                dex_file_location.c_str(),
                                dex_file_offset,
                                DexSize());
      return false;
    }
    if (UNLIKELY(DexSize() - dex_file_offset < sizeof(DexFile::Header))) {
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu for '%s' with dex file "
                                    "offset %u of %zu but the size of dex file header is %zu",
                                GetLocation().c_str(),
                                i,
                                dex_file_location.c_str(),
                                dex_file_offset,
                                DexSize(),
                                sizeof(DexFile::Header));
      return false;
    }

    const uint8_t* dex_file_pointer = DexBegin() + dex_file_offset;
    if (UNLIKELY(!DexFile::IsMagicValid(dex_file_pointer))) {
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu for '%s' with invalid "
                                    "dex file magic '%s'",
                                GetLocation().c_str(),
                                i,
                                dex_file_location.c_str(),
                                dex_file_pointer);
      return false;
    }
    if (UNLIKELY(!DexFile::IsVersionValid(dex_file_pointer))) {
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu for '%s' with invalid "
                                    "dex file version '%s'",
                                GetLocation().c_str(),
                                i,
                                dex_file_location.c_str(),
                                dex_file_pointer);
      return false;
    }
    const DexFile::Header* header = reinterpret_cast<const DexFile::Header*>(dex_file_pointer);
    if (DexSize() - dex_file_offset < header->file_size_) {
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu for '%s' with dex file "
                                    "offset %u and size %u truncated at %zu",
                                GetLocation().c_str(),
                                i,
                                dex_file_location.c_str(),
                                dex_file_offset,
                                header->file_size_,
                                DexSize());
      return false;
    }

    uint32_t class_offsets_offset;
    if (UNLIKELY(!ReadOatDexFileData(*this, &oat, &class_offsets_offset))) {//通过ReadOatDexFileData函数读取class_offsets_offset并调整oat指针
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu for '%s' truncated "
                                    "after class offsets offset",
                                GetLocation().c_str(),
                                i,
                                dex_file_location.c_str());
      return false;
    }
    if (UNLIKELY(class_offsets_offset > Size()) ||
        UNLIKELY((Size() - class_offsets_offset) / sizeof(uint32_t) < header->class_defs_size_)) {
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu for '%s' with truncated "
                                    "class offsets, offset %u of %zu, class defs %u",
                                GetLocation().c_str(),
                                i,
                                dex_file_location.c_str(),
                                class_offsets_offset,
                                Size(),
                                header->class_defs_size_);
      return false;
    }
    if (UNLIKELY(!IsAligned<alignof(uint32_t)>(class_offsets_offset))) {
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu for '%s' with unaligned "
                                    "class offsets, offset %u",
                                GetLocation().c_str(),
                                i,
                                dex_file_location.c_str(),
                                class_offsets_offset);
      return false;
    }
    const uint32_t* class_offsets_pointer =
        reinterpret_cast<const uint32_t*>(Begin() + class_offsets_offset);

    uint32_t lookup_table_offset;
    if (UNLIKELY(!ReadOatDexFileData(*this, &oat, &lookup_table_offset))) {//通过ReadOatDexFileData函数读取lookup_table_offset并调整oat指针,lookup_table用于加速类的查找
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zd for '%s' truncated "
                                    "after lookup table offset",
                                GetLocation().c_str(),
                                i,
                                dex_file_location.c_str());
      return false;
    }
    const uint8_t* lookup_table_data = lookup_table_offset != 0u
        ? Begin() + lookup_table_offset
        : nullptr;
    if (lookup_table_offset != 0u &&
        (UNLIKELY(lookup_table_offset > Size()) ||
            UNLIKELY(Size() - lookup_table_offset <
                     TypeLookupTable::RawDataLength(header->class_defs_size_)))) {
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu for '%s' with truncated "
                                    "type lookup table, offset %u of %zu, class defs %u",
                                GetLocation().c_str(),
                                i,
                                dex_file_location.c_str(),
                                lookup_table_offset,
                                Size(),
                                header->class_defs_size_);
      return false;
    }

    uint32_t dex_layout_sections_offset;
    if (UNLIKELY(!ReadOatDexFileData(*this, &oat, &dex_layout_sections_offset))) {//通过ReadOatDexFileData函数读取dex_layout_sections_offset并调整oat指针
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zd for '%s' truncated "
                                    "after dex layout sections offset",
                                GetLocation().c_str(),
                                i,
                                dex_file_location.c_str());
      return false;
    }
    const DexLayoutSections* const dex_layout_sections = dex_layout_sections_offset != 0
        ? reinterpret_cast<const DexLayoutSections*>(Begin() + dex_layout_sections_offset)
        : nullptr;

    uint32_t method_bss_mapping_offset;
    if (UNLIKELY(!ReadOatDexFileData(*this, &oat, &method_bss_mapping_offset))) {//通过ReadOatDexFileData函数读取method_bss_mapping_offset并调整oat指针
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zd for '%s' truncated "
                                    "after method bss mapping offset",
                                GetLocation().c_str(),
                                i,
                                dex_file_location.c_str());
      return false;
    }
    const bool readable_method_bss_mapping_size =
        method_bss_mapping_offset != 0u &&
        method_bss_mapping_offset <= Size() &&
        IsAligned<alignof(MethodBssMapping)>(method_bss_mapping_offset) &&
        Size() - method_bss_mapping_offset >= MethodBssMapping::ComputeSize(0);
    const MethodBssMapping* method_bss_mapping = readable_method_bss_mapping_size
        ? reinterpret_cast<const MethodBssMapping*>(Begin() + method_bss_mapping_offset)
        : nullptr;
    if (method_bss_mapping_offset != 0u &&
        (UNLIKELY(method_bss_mapping == nullptr) ||
            UNLIKELY(method_bss_mapping->size() == 0u) ||
            UNLIKELY(Size() - method_bss_mapping_offset <
                     MethodBssMapping::ComputeSize(method_bss_mapping->size())))) {
      *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu for '%s' with unaligned or "
                                    " truncated method bss mapping, offset %u of %zu, length %zu",
                                GetLocation().c_str(),
                                i,
                                dex_file_location.c_str(),
                                method_bss_mapping_offset,
                                Size(),
                                method_bss_mapping != nullptr ? method_bss_mapping->size() : 0u);
      return false;
    }
    if (kIsDebugBuild && method_bss_mapping != nullptr) {
      const MethodBssMappingEntry* prev_entry = nullptr;
      for (const MethodBssMappingEntry& entry : *method_bss_mapping) {
        CHECK_ALIGNED_PARAM(entry.bss_offset, static_cast<size_t>(pointer_size));
        CHECK_LT(entry.bss_offset, BssSize());
        CHECK_LE(POPCOUNT(entry.index_mask) * static_cast<size_t>(pointer_size),  entry.bss_offset);
        size_t index_mask_span = (entry.index_mask != 0u) ? 16u - CTZ(entry.index_mask) : 0u;
        CHECK_LE(index_mask_span, entry.method_index);
        if (prev_entry != nullptr) {
          CHECK_LT(prev_entry->method_index, entry.method_index - index_mask_span);
        }
        prev_entry = &entry;
      }
      CHECK_LT(prev_entry->method_index,
               reinterpret_cast<const DexFile::Header*>(dex_file_pointer)->method_ids_size_);
    }

    uint8_t* current_dex_cache_arrays = nullptr;
    if (dex_cache_arrays != nullptr) {
      // All DexCache types except for CallSite have their instance counts in the
      // DexFile header. For CallSites, we need to read the info from the MapList.
	  //对于CallSites，必须从MapList中读取，他不存储在header中
      const DexFile::MapItem* call_sites_item = nullptr;
      if (!FindDexFileMapItem(DexBegin(),                                           //通过FindDexFileMapItem读取call_sites_item并解析
                              DexEnd(),
                              DexFile::MapItemType::kDexTypeCallSiteIdItem,
                              &call_sites_item)) {
        *error_msg = StringPrintf("In oat file '%s' could not read data from truncated DexFile map",
                                  GetLocation().c_str());
        return false;
      }
      size_t num_call_sites = call_sites_item == nullptr ? 0 : call_sites_item->size_;
      DexCacheArraysLayout layout(pointer_size, *header, num_call_sites);
      if (layout.Size() != 0u) {
        if (static_cast<size_t>(dex_cache_arrays_end - dex_cache_arrays) < layout.Size()) {
          *error_msg = StringPrintf("In oat file '%s' found OatDexFile #%zu for '%s' with "
                                        "truncated dex cache arrays, %zu < %zu.",
                                    GetLocation().c_str(),
                                    i,
                                    dex_file_location.c_str(),
                                    static_cast<size_t>(dex_cache_arrays_end - dex_cache_arrays),
                                    layout.Size());
          return false;
        }
        current_dex_cache_arrays = dex_cache_arrays;
        dex_cache_arrays += layout.Size();
      }
    }

    std::string canonical_location = DexFile::GetDexCanonicalLocation(dex_file_location.c_str());

    // Create the OatDexFile and add it to the owning container.
    OatDexFile* oat_dex_file = new OatDexFile(this,                                 //根据上面ReadOatDexFileData和FindDexFileMapItem获得的信息构建oat_dex_file
                                              dex_file_location,
                                              canonical_location,
                                              dex_file_checksum,
                                              dex_file_pointer,
                                              lookup_table_data,
                                              method_bss_mapping,
                                              class_offsets_pointer,
                                              current_dex_cache_arrays,
                                              dex_layout_sections);
    oat_dex_files_storage_.push_back(oat_dex_file);

    // Add the location and canonical location (if different) to the oat_dex_files_ table.
    StringPiece key(oat_dex_file->GetDexFileLocation());
    oat_dex_files_.Put(key, oat_dex_file);
    if (canonical_location != dex_file_location) {
      StringPiece canonical_key(oat_dex_file->GetCanonicalDexFileLocation());
      oat_dex_files_.Put(canonical_key, oat_dex_file);
    }
  }

  if (dex_cache_arrays != dex_cache_arrays_end) {
    // We expect the bss section to be either empty (dex_cache_arrays and bss_end_
    // both null) or contain just the dex cache arrays and optionally some GC roots.
    *error_msg = StringPrintf("In oat file '%s' found unexpected bss size bigger by %zu bytes.",
                              GetLocation().c_str(),
                              static_cast<size_t>(bss_end_ - dex_cache_arrays));
    return false;
  }
  return true;
}