dexlayout/compact_dex_writer.cc - platform/art - Gitiles

 /*
  * Copyright (C) 2017 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include "compact_dex_writer.h"

 #include "base/logging.h"
 #include "base/time_utils.h"
 #include "dex/compact_dex_debug_info.h"
 #include "dex/compact_dex_file.h"
 #include "dexlayout.h"

 namespace art {

 uint32_t CompactDexWriter::WriteDebugInfoOffsetTable(uint32_t offset) {
   const uint32_t start_offset = offset;
   const dex_ir::Collections& collections = header_->GetCollections();
   // Debug offsets for method indexes. 0 means no debug info.
   std::vector<uint32_t> debug_info_offsets(collections.MethodIdsSize(), 0u);

   static constexpr InvokeType invoke_types[] = {
     kDirect,
     kVirtual
   };

   for (InvokeType invoke_type : invoke_types) {
     for (const std::unique_ptr<dex_ir::ClassDef>& class_def : collections.ClassDefs()) {
       // Skip classes that are not defined in this dex file.
       dex_ir::ClassData* class_data = class_def->GetClassData();
       if (class_data == nullptr) {
         continue;
       }
       for (auto& method : *(invoke_type == InvokeType::kDirect
                                 ? class_data->DirectMethods()
                                 : class_data->VirtualMethods())) {
         const dex_ir::MethodId* method_id = method->GetMethodId();
         dex_ir::CodeItem* code_item = method->GetCodeItem();
         if (code_item != nullptr && code_item->DebugInfo() != nullptr) {
           const uint32_t debug_info_offset = code_item->DebugInfo()->GetOffset();
           const uint32_t method_idx = method_id->GetIndex();
           if (debug_info_offsets[method_idx] != 0u) {
             CHECK_EQ(debug_info_offset, debug_info_offsets[method_idx]);
           }
           debug_info_offsets[method_idx] = debug_info_offset;
         }
       }
     }
   }

   std::vector<uint8_t> data;
   debug_info_base_ = 0u;
   debug_info_offsets_table_offset_ = 0u;
   CompactDexDebugInfoOffsetTable::Build(debug_info_offsets,
                                         &data,
                                         &debug_info_base_,
                                         &debug_info_offsets_table_offset_);
   // Align the table and write it out.
   offset = RoundUp(offset, CompactDexDebugInfoOffsetTable::kAlignment);
   debug_info_offsets_pos_ = offset;
   offset += Write(data.data(), data.size(), offset);

   // Verify that the whole table decodes as expected and measure average performance.
   const bool kMeasureAndTestOutput = dex_layout_->GetOptions().verify_output_;
   if (kMeasureAndTestOutput && !debug_info_offsets.empty()) {
     uint64_t start_time = NanoTime();
     CompactDexDebugInfoOffsetTable::Accessor accessor(mem_map_->Begin() + debug_info_offsets_pos_,
                                                       debug_info_base_,
                                                       debug_info_offsets_table_offset_);

     for (size_t i = 0; i < debug_info_offsets.size(); ++i) {
       CHECK_EQ(accessor.GetDebugInfoOffset(i), debug_info_offsets[i]);
     }
     uint64_t end_time = NanoTime();
     VLOG(dex) << "Average lookup time (ns) for debug info offsets: "
               << (end_time - start_time) / debug_info_offsets.size();
   }

   return offset - start_offset;
 }

 uint32_t CompactDexWriter::WriteCodeItem(dex_ir::CodeItem* code_item,
                                          uint32_t offset,
                                          bool reserve_only) {
   DCHECK(code_item != nullptr);
   const uint32_t start_offset = offset;
   offset = RoundUp(offset, CompactDexFile::CodeItem::kAlignment);
   ProcessOffset(&offset, code_item);

   CompactDexFile::CodeItem disk_code_item;
   disk_code_item.registers_size_ = code_item->RegistersSize();
   disk_code_item.ins_size_ = code_item->InsSize();
   disk_code_item.outs_size_ = code_item->OutsSize();
   disk_code_item.tries_size_ = code_item->TriesSize();
   disk_code_item.insns_size_in_code_units_ = code_item->InsnsSize();
   // Avoid using sizeof so that we don't write the fake instruction array at the end of the code
   // item.
   offset += Write(&disk_code_item,
                   OFFSETOF_MEMBER(CompactDexFile::CodeItem, insns_),
                   offset);
   // Write the instructions.
   offset += Write(code_item->Insns(), code_item->InsnsSize() * sizeof(uint16_t), offset);
   // Write the post instruction data.
   offset += WriteCodeItemPostInstructionData(code_item, offset, reserve_only);
   return offset - start_offset;
 }

 void CompactDexWriter::SortDebugInfosByMethodIndex() {
   dex_ir::Collections& collections = header_->GetCollections();
   static constexpr InvokeType invoke_types[] = {
     kDirect,
     kVirtual
   };
   std::map<const dex_ir::DebugInfoItem*, uint32_t> method_idx_map;
   for (InvokeType invoke_type : invoke_types) {
     for (std::unique_ptr<dex_ir::ClassDef>& class_def : collections.ClassDefs()) {
       // Skip classes that are not defined in this dex file.
       dex_ir::ClassData* class_data = class_def->GetClassData();
       if (class_data == nullptr) {
         continue;
       }
       for (auto& method : *(invoke_type == InvokeType::kDirect
                                 ? class_data->DirectMethods()
                                 : class_data->VirtualMethods())) {
         const dex_ir::MethodId* method_id = method->GetMethodId();
         dex_ir::CodeItem* code_item = method->GetCodeItem();
         if (code_item != nullptr && code_item->DebugInfo() != nullptr) {
           const dex_ir::DebugInfoItem* debug_item = code_item->DebugInfo();
           method_idx_map.insert(std::make_pair(debug_item, method_id->GetIndex()));
         }
       }
     }
   }
   std::sort(collections.DebugInfoItems().begin(),
             collections.DebugInfoItems().end(),
             [&](const std::unique_ptr<dex_ir::DebugInfoItem>& a,
                 const std::unique_ptr<dex_ir::DebugInfoItem>& b) {
     auto it_a = method_idx_map.find(a.get());
     auto it_b = method_idx_map.find(b.get());
     uint32_t idx_a = it_a != method_idx_map.end() ? it_a->second : 0u;
     uint32_t idx_b = it_b != method_idx_map.end() ? it_b->second : 0u;
     return idx_a < idx_b;
   });
 }

 void CompactDexWriter::WriteHeader() {
   CompactDexFile::Header header;
   CompactDexFile::WriteMagic(&header.magic_[0]);
   CompactDexFile::WriteCurrentVersion(&header.magic_[0]);
   header.checksum_ = header_->Checksum();
   std::copy_n(header_->Signature(), DexFile::kSha1DigestSize, header.signature_);
   header.file_size_ = header_->FileSize();
   // Since we are not necessarily outputting the same format as the input, avoid using the stored
   // header size.
   header.header_size_ = GetHeaderSize();
   header.endian_tag_ = header_->EndianTag();
   header.link_size_ = header_->LinkSize();
   header.link_off_ = header_->LinkOffset();
   const dex_ir::Collections& collections = header_->GetCollections();
   header.map_off_ = collections.MapListOffset();
   header.string_ids_size_ = collections.StringIdsSize();
   header.string_ids_off_ = collections.StringIdsOffset();
   header.type_ids_size_ = collections.TypeIdsSize();
   header.type_ids_off_ = collections.TypeIdsOffset();
   header.proto_ids_size_ = collections.ProtoIdsSize();
   header.proto_ids_off_ = collections.ProtoIdsOffset();
   header.field_ids_size_ = collections.FieldIdsSize();
   header.field_ids_off_ = collections.FieldIdsOffset();
   header.method_ids_size_ = collections.MethodIdsSize();
   header.method_ids_off_ = collections.MethodIdsOffset();
   header.class_defs_size_ = collections.ClassDefsSize();
   header.class_defs_off_ = collections.ClassDefsOffset();
   header.data_size_ = header_->DataSize();
   header.data_off_ = header_->DataOffset();

   // Compact dex specific flags.
   header.debug_info_offsets_pos_ = debug_info_offsets_pos_;
   header.debug_info_offsets_table_offset_ = debug_info_offsets_table_offset_;
   header.debug_info_base_ = debug_info_base_;
   header.feature_flags_ = 0u;
   // In cases where apps are converted to cdex during install, maintain feature flags so that
   // the verifier correctly verifies apps that aren't targetting default methods.
   if (header_->SupportDefaultMethods()) {
     header.feature_flags_ |= static_cast<uint32_t>(CompactDexFile::FeatureFlags::kDefaultMethods);
   }
   UNUSED(Write(reinterpret_cast<uint8_t*>(&header), sizeof(header), 0u));
 }

 size_t CompactDexWriter::GetHeaderSize() const {
   return sizeof(CompactDexFile::Header);
 }

 void CompactDexWriter::WriteMemMap() {
   // Starting offset is right after the header.
   uint32_t offset = GetHeaderSize();

   dex_ir::Collections& collection = header_->GetCollections();

   // Based on: https://source.android.com/devices/tech/dalvik/dex-format
   // Since the offsets may not be calculated already, the writing must be done in the correct order.
   const uint32_t string_ids_offset = offset;
   offset += WriteStringIds(offset, /*reserve_only*/ true);
   offset += WriteTypeIds(offset);
   const uint32_t proto_ids_offset = offset;
   offset += WriteProtoIds(offset, /*reserve_only*/ true);
   offset += WriteFieldIds(offset);
   offset += WriteMethodIds(offset);
   const uint32_t class_defs_offset = offset;
   offset += WriteClassDefs(offset, /*reserve_only*/ true);
   const uint32_t call_site_ids_offset = offset;
   offset += WriteCallSiteIds(offset, /*reserve_only*/ true);
   offset += WriteMethodHandles(offset);

   uint32_t data_offset_ = 0u;
   if (compute_offsets_) {
     // Data section.
     offset = RoundUp(offset, kDataSectionAlignment);
     data_offset_ = offset;
   }

   // Write code item first to minimize the space required for encoded methods.
   // For cdex, the code items don't depend on the debug info.
   offset += WriteCodeItems(offset, /*reserve_only*/ false);

   // Sort the debug infos by method index order, this reduces size by ~0.1% by reducing the size of
   // the debug info offset table.
   SortDebugInfosByMethodIndex();
   offset += WriteDebugInfoItems(offset);

   offset += WriteEncodedArrays(offset);
   offset += WriteAnnotations(offset);
   offset += WriteAnnotationSets(offset);
   offset += WriteAnnotationSetRefs(offset);
   offset += WriteAnnotationsDirectories(offset);
   offset += WriteTypeLists(offset);
   offset += WriteClassDatas(offset);
   offset += WriteStringDatas(offset);

   // Write delayed id sections that depend on data sections.
   WriteStringIds(string_ids_offset, /*reserve_only*/ false);
   WriteProtoIds(proto_ids_offset, /*reserve_only*/ false);
   WriteClassDefs(class_defs_offset, /*reserve_only*/ false);
   WriteCallSiteIds(call_site_ids_offset, /*reserve_only*/ false);

   // Write the map list.
   if (compute_offsets_) {
     offset = RoundUp(offset, SectionAlignment(DexFile::kDexTypeMapList));
     collection.SetMapListOffset(offset);
   } else {
     offset = collection.MapListOffset();
   }
   offset += GenerateAndWriteMapItems(offset);
   offset = RoundUp(offset, kDataSectionAlignment);

   // Map items are included in the data section.
   if (compute_offsets_) {
     header_->SetDataSize(offset - data_offset_);
     if (header_->DataSize() != 0) {
       // Offset must be zero when the size is zero.
       header_->SetDataOffset(data_offset_);
     } else {
       header_->SetDataOffset(0u);
     }
   }

   // Write link data if it exists.
   const std::vector<uint8_t>& link_data = collection.LinkData();
   if (link_data.size() > 0) {
     CHECK_EQ(header_->LinkSize(), static_cast<uint32_t>(link_data.size()));
     if (compute_offsets_) {
       header_->SetLinkOffset(offset);
     }
     offset += Write(&link_data[0], link_data.size(), header_->LinkOffset());
   }

   // Write debug info offset table last to make dex file verifier happy.
   offset += WriteDebugInfoOffsetTable(offset);

   // Write header last.
   if (compute_offsets_) {
     header_->SetFileSize(offset);
   }
   WriteHeader();

   if (dex_layout_->GetOptions().update_checksum_) {
     header_->SetChecksum(DexFile::CalculateChecksum(mem_map_->Begin(), offset));
     // Rewrite the header with the calculated checksum.
     WriteHeader();
   }
 }

 }  // namespace art
	/*
	* Copyright (C) 2017 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#include "compact_dex_writer.h"

	#include "base/logging.h"
	#include "base/time_utils.h"
	#include "dex/compact_dex_debug_info.h"
	#include "dex/compact_dex_file.h"
	#include "dexlayout.h"

	namespace art {

	uint32_t CompactDexWriter::WriteDebugInfoOffsetTable(uint32_t offset) {
	const uint32_t start_offset = offset;
	const dex_ir::Collections& collections = header_->GetCollections();
	// Debug offsets for method indexes. 0 means no debug info.
	std::vector<uint32_t> debug_info_offsets(collections.MethodIdsSize(), 0u);

	static constexpr InvokeType invoke_types[] = {
	kDirect,
	kVirtual
	};

	for (InvokeType invoke_type : invoke_types) {
	for (const std::unique_ptr<dex_ir::ClassDef>& class_def : collections.ClassDefs()) {
	// Skip classes that are not defined in this dex file.
	dex_ir::ClassData* class_data = class_def->GetClassData();
	if (class_data == nullptr) {
	continue;
	}
	for (auto& method : *(invoke_type == InvokeType::kDirect
	? class_data->DirectMethods()
	: class_data->VirtualMethods())) {
	const dex_ir::MethodId* method_id = method->GetMethodId();
	dex_ir::CodeItem* code_item = method->GetCodeItem();
	if (code_item != nullptr && code_item->DebugInfo() != nullptr) {
	const uint32_t debug_info_offset = code_item->DebugInfo()->GetOffset();
	const uint32_t method_idx = method_id->GetIndex();
	if (debug_info_offsets[method_idx] != 0u) {
	CHECK_EQ(debug_info_offset, debug_info_offsets[method_idx]);
	}
	debug_info_offsets[method_idx] = debug_info_offset;
	}
	}
	}
	}

	std::vector<uint8_t> data;
	debug_info_base_ = 0u;
	debug_info_offsets_table_offset_ = 0u;
	CompactDexDebugInfoOffsetTable::Build(debug_info_offsets,
	&data,
	&debug_info_base_,
	&debug_info_offsets_table_offset_);
	// Align the table and write it out.
	offset = RoundUp(offset, CompactDexDebugInfoOffsetTable::kAlignment);
	debug_info_offsets_pos_ = offset;
	offset += Write(data.data(), data.size(), offset);

	// Verify that the whole table decodes as expected and measure average performance.
	const bool kMeasureAndTestOutput = dex_layout_->GetOptions().verify_output_;
	if (kMeasureAndTestOutput && !debug_info_offsets.empty()) {
	uint64_t start_time = NanoTime();
	CompactDexDebugInfoOffsetTable::Accessor accessor(mem_map_->Begin() + debug_info_offsets_pos_,
	debug_info_base_,
	debug_info_offsets_table_offset_);

	for (size_t i = 0; i < debug_info_offsets.size(); ++i) {
	CHECK_EQ(accessor.GetDebugInfoOffset(i), debug_info_offsets[i]);
	}
	uint64_t end_time = NanoTime();
	VLOG(dex) << "Average lookup time (ns) for debug info offsets: "
	<< (end_time - start_time) / debug_info_offsets.size();
	}

	return offset - start_offset;
	}

	uint32_t CompactDexWriter::WriteCodeItem(dex_ir::CodeItem* code_item,
	uint32_t offset,
	bool reserve_only) {
	DCHECK(code_item != nullptr);
	const uint32_t start_offset = offset;
	offset = RoundUp(offset, CompactDexFile::CodeItem::kAlignment);
	ProcessOffset(&offset, code_item);

	CompactDexFile::CodeItem disk_code_item;
	disk_code_item.registers_size_ = code_item->RegistersSize();
	disk_code_item.ins_size_ = code_item->InsSize();
	disk_code_item.outs_size_ = code_item->OutsSize();
	disk_code_item.tries_size_ = code_item->TriesSize();
	disk_code_item.insns_size_in_code_units_ = code_item->InsnsSize();
	// Avoid using sizeof so that we don't write the fake instruction array at the end of the code
	// item.
	offset += Write(&disk_code_item,
	OFFSETOF_MEMBER(CompactDexFile::CodeItem, insns_),
	offset);
	// Write the instructions.
	offset += Write(code_item->Insns(), code_item->InsnsSize() * sizeof(uint16_t), offset);
	// Write the post instruction data.
	offset += WriteCodeItemPostInstructionData(code_item, offset, reserve_only);
	return offset - start_offset;
	}

	void CompactDexWriter::SortDebugInfosByMethodIndex() {
	dex_ir::Collections& collections = header_->GetCollections();
	static constexpr InvokeType invoke_types[] = {
	kDirect,
	kVirtual
	};
	std::map<const dex_ir::DebugInfoItem*, uint32_t> method_idx_map;
	for (InvokeType invoke_type : invoke_types) {
	for (std::unique_ptr<dex_ir::ClassDef>& class_def : collections.ClassDefs()) {
	// Skip classes that are not defined in this dex file.
	dex_ir::ClassData* class_data = class_def->GetClassData();
	if (class_data == nullptr) {
	continue;
	}
	for (auto& method : *(invoke_type == InvokeType::kDirect
	? class_data->DirectMethods()
	: class_data->VirtualMethods())) {
	const dex_ir::MethodId* method_id = method->GetMethodId();
	dex_ir::CodeItem* code_item = method->GetCodeItem();
	if (code_item != nullptr && code_item->DebugInfo() != nullptr) {
	const dex_ir::DebugInfoItem* debug_item = code_item->DebugInfo();
	method_idx_map.insert(std::make_pair(debug_item, method_id->GetIndex()));
	}
	}
	}
	}
	std::sort(collections.DebugInfoItems().begin(),
	collections.DebugInfoItems().end(),
	[&](const std::unique_ptr<dex_ir::DebugInfoItem>& a,
	const std::unique_ptr<dex_ir::DebugInfoItem>& b) {
	auto it_a = method_idx_map.find(a.get());
	auto it_b = method_idx_map.find(b.get());
	uint32_t idx_a = it_a != method_idx_map.end() ? it_a->second : 0u;
	uint32_t idx_b = it_b != method_idx_map.end() ? it_b->second : 0u;
	return idx_a < idx_b;
	});
	}

	void CompactDexWriter::WriteHeader() {
	CompactDexFile::Header header;
	CompactDexFile::WriteMagic(&header.magic_[0]);
	CompactDexFile::WriteCurrentVersion(&header.magic_[0]);
	header.checksum_ = header_->Checksum();
	std::copy_n(header_->Signature(), DexFile::kSha1DigestSize, header.signature_);
	header.file_size_ = header_->FileSize();
	// Since we are not necessarily outputting the same format as the input, avoid using the stored
	// header size.
	header.header_size_ = GetHeaderSize();
	header.endian_tag_ = header_->EndianTag();
	header.link_size_ = header_->LinkSize();
	header.link_off_ = header_->LinkOffset();
	const dex_ir::Collections& collections = header_->GetCollections();
	header.map_off_ = collections.MapListOffset();
	header.string_ids_size_ = collections.StringIdsSize();
	header.string_ids_off_ = collections.StringIdsOffset();
	header.type_ids_size_ = collections.TypeIdsSize();
	header.type_ids_off_ = collections.TypeIdsOffset();
	header.proto_ids_size_ = collections.ProtoIdsSize();
	header.proto_ids_off_ = collections.ProtoIdsOffset();
	header.field_ids_size_ = collections.FieldIdsSize();
	header.field_ids_off_ = collections.FieldIdsOffset();
	header.method_ids_size_ = collections.MethodIdsSize();
	header.method_ids_off_ = collections.MethodIdsOffset();
	header.class_defs_size_ = collections.ClassDefsSize();
	header.class_defs_off_ = collections.ClassDefsOffset();
	header.data_size_ = header_->DataSize();
	header.data_off_ = header_->DataOffset();

	// Compact dex specific flags.
	header.debug_info_offsets_pos_ = debug_info_offsets_pos_;
	header.debug_info_offsets_table_offset_ = debug_info_offsets_table_offset_;
	header.debug_info_base_ = debug_info_base_;
	header.feature_flags_ = 0u;
	// In cases where apps are converted to cdex during install, maintain feature flags so that
	// the verifier correctly verifies apps that aren't targetting default methods.
	if (header_->SupportDefaultMethods()) {
	header.feature_flags_ \|= static_cast<uint32_t>(CompactDexFile::FeatureFlags::kDefaultMethods);
	}
	UNUSED(Write(reinterpret_cast<uint8_t*>(&header), sizeof(header), 0u));
	}

	size_t CompactDexWriter::GetHeaderSize() const {
	return sizeof(CompactDexFile::Header);
	}

	void CompactDexWriter::WriteMemMap() {
	// Starting offset is right after the header.
	uint32_t offset = GetHeaderSize();

	dex_ir::Collections& collection = header_->GetCollections();

	// Based on: https://source.android.com/devices/tech/dalvik/dex-format
	// Since the offsets may not be calculated already, the writing must be done in the correct order.
	const uint32_t string_ids_offset = offset;
	offset += WriteStringIds(offset, /reserve_only/ true);
	offset += WriteTypeIds(offset);
	const uint32_t proto_ids_offset = offset;
	offset += WriteProtoIds(offset, /reserve_only/ true);
	offset += WriteFieldIds(offset);
	offset += WriteMethodIds(offset);
	const uint32_t class_defs_offset = offset;
	offset += WriteClassDefs(offset, /reserve_only/ true);
	const uint32_t call_site_ids_offset = offset;
	offset += WriteCallSiteIds(offset, /reserve_only/ true);
	offset += WriteMethodHandles(offset);

	uint32_t data_offset_ = 0u;
	if (compute_offsets_) {
	// Data section.
	offset = RoundUp(offset, kDataSectionAlignment);
	data_offset_ = offset;
	}

	// Write code item first to minimize the space required for encoded methods.
	// For cdex, the code items don't depend on the debug info.
	offset += WriteCodeItems(offset, /reserve_only/ false);

	// Sort the debug infos by method index order, this reduces size by ~0.1% by reducing the size of
	// the debug info offset table.
	SortDebugInfosByMethodIndex();
	offset += WriteDebugInfoItems(offset);

	offset += WriteEncodedArrays(offset);
	offset += WriteAnnotations(offset);
	offset += WriteAnnotationSets(offset);
	offset += WriteAnnotationSetRefs(offset);
	offset += WriteAnnotationsDirectories(offset);
	offset += WriteTypeLists(offset);
	offset += WriteClassDatas(offset);
	offset += WriteStringDatas(offset);

	// Write delayed id sections that depend on data sections.
	WriteStringIds(string_ids_offset, /reserve_only/ false);
	WriteProtoIds(proto_ids_offset, /reserve_only/ false);
	WriteClassDefs(class_defs_offset, /reserve_only/ false);
	WriteCallSiteIds(call_site_ids_offset, /reserve_only/ false);

	// Write the map list.
	if (compute_offsets_) {
	offset = RoundUp(offset, SectionAlignment(DexFile::kDexTypeMapList));
	collection.SetMapListOffset(offset);
	} else {
	offset = collection.MapListOffset();
	}
	offset += GenerateAndWriteMapItems(offset);
	offset = RoundUp(offset, kDataSectionAlignment);

	// Map items are included in the data section.
	if (compute_offsets_) {
	header_->SetDataSize(offset - data_offset_);
	if (header_->DataSize() != 0) {
	// Offset must be zero when the size is zero.
	header_->SetDataOffset(data_offset_);
	} else {
	header_->SetDataOffset(0u);
	}
	}

	// Write link data if it exists.
	const std::vector<uint8_t>& link_data = collection.LinkData();
	if (link_data.size() > 0) {
	CHECK_EQ(header_->LinkSize(), static_cast<uint32_t>(link_data.size()));
	if (compute_offsets_) {
	header_->SetLinkOffset(offset);
	}
	offset += Write(&link_data[0], link_data.size(), header_->LinkOffset());
	}

	// Write debug info offset table last to make dex file verifier happy.
	offset += WriteDebugInfoOffsetTable(offset);

	// Write header last.
	if (compute_offsets_) {
	header_->SetFileSize(offset);
	}
	WriteHeader();

	if (dex_layout_->GetOptions().update_checksum_) {
	header_->SetChecksum(DexFile::CalculateChecksum(mem_map_->Begin(), offset));
	// Rewrite the header with the calculated checksum.
	WriteHeader();
	}
	}

	} // namespace art