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* Copyright (C) 2012 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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include "elf_writer_quick.h"
#include <unordered_map>
#include <unordered_set>
#include "base/logging.h"
#include "base/unix_file/fd_file.h"
#include "compiled_method.h"
#include "dex_file-inl.h"
#include "driver/compiler_driver.h"
#include "driver/compiler_options.h"
#include "elf_builder.h"
#include "elf_file.h"
#include "elf_utils.h"
#include "elf_writer_debug.h"
#include "globals.h"
#include "leb128.h"
#include "oat.h"
#include "oat_writer.h"
#include "utils.h"
namespace art {
template <typename ElfTypes>
bool ElfWriterQuick<ElfTypes>::Create(File* elf_file,
OatWriter* oat_writer,
const std::vector<const DexFile*>& dex_files,
const std::string& android_root,
bool is_host,
const CompilerDriver& driver) {
ElfWriterQuick elf_writer(driver, elf_file);
return elf_writer.Write(oat_writer, dex_files, android_root, is_host);
template <typename ElfTypes>
static void WriteDebugSymbols(ElfBuilder<ElfTypes>* builder, OatWriter* oat_writer);
// Encode patch locations in .oat_patches format.
template <typename ElfTypes>
void ElfWriterQuick<ElfTypes>::EncodeOatPatches(
const OatWriter::PatchLocationsMap& sections,
std::vector<uint8_t>* buffer) {
for (const auto& section : sections) {
const std::string& name = section.first;
std::vector<uintptr_t>* locations = section.second.get();
std::sort(locations->begin(), locations->end());
// Reserve buffer space - guess 2 bytes per ULEB128.
buffer->reserve(buffer->size() + name.size() + locations->size() * 2);
// Write null-terminated section name.
const uint8_t* name_data = reinterpret_cast<const uint8_t*>(name.c_str());
buffer->insert(buffer->end(), name_data, name_data + name.size() + 1);
// Write placeholder for data length.
size_t length_pos = buffer->size();
EncodeUnsignedLeb128(buffer, UINT32_MAX);
// Write LEB128 encoded list of advances (deltas between consequtive addresses).
size_t data_pos = buffer->size();
uintptr_t address = 0; // relative to start of section.
for (uintptr_t location : *locations) {
DCHECK_LT(location - address, UINT32_MAX) << "Large gap between patch locations";
EncodeUnsignedLeb128(buffer, location - address);
address = location;
// Update length.
UpdateUnsignedLeb128(buffer->data() + length_pos, buffer->size() - data_pos);
buffer->push_back(0); // End of sections.
class RodataWriter FINAL : public CodeOutput {
explicit RodataWriter(OatWriter* oat_writer) : oat_writer_(oat_writer) {}
bool Write(OutputStream* out) OVERRIDE {
return oat_writer_->WriteRodata(out);
OatWriter* oat_writer_;
class TextWriter FINAL : public CodeOutput {
explicit TextWriter(OatWriter* oat_writer) : oat_writer_(oat_writer) {}
bool Write(OutputStream* out) OVERRIDE {
return oat_writer_->WriteCode(out);
OatWriter* oat_writer_;
enum PatchResult {
kAbsoluteAddress, // Absolute memory location.
kPointerRelativeAddress, // Offset relative to the location of the pointer.
kSectionRelativeAddress, // Offset relative to start of containing section.
// Patch memory addresses within a buffer.
// It assumes that the unpatched addresses are offsets relative to base_address.
// (which generally means method's low_pc relative to the start of .text)
template <typename Elf_Addr, typename Address, PatchResult kPatchResult>
static void Patch(const std::vector<uintptr_t>& patch_locations,
Elf_Addr buffer_address, Elf_Addr base_address,
std::vector<uint8_t>* buffer) {
for (uintptr_t location : patch_locations) {
typedef __attribute__((__aligned__(1))) Address UnalignedAddress;
auto* to_patch = reinterpret_cast<UnalignedAddress*>(buffer->data() + location);
switch (kPatchResult) {
case kAbsoluteAddress:
*to_patch = (base_address + *to_patch);
case kPointerRelativeAddress:
*to_patch = (base_address + *to_patch) - (buffer_address + location);
case kSectionRelativeAddress:
*to_patch = (base_address + *to_patch) - buffer_address;
template <typename ElfTypes>
bool ElfWriterQuick<ElfTypes>::Write(
OatWriter* oat_writer,
const std::vector<const DexFile*>& dex_files_unused ATTRIBUTE_UNUSED,
const std::string& android_root_unused ATTRIBUTE_UNUSED,
bool is_host_unused ATTRIBUTE_UNUSED) {
using Elf_Addr = typename ElfTypes::Addr;
const InstructionSet isa = compiler_driver_->GetInstructionSet();
// Setup the builder with the main OAT sections (.rodata .text .bss).
const size_t rodata_size = oat_writer->GetOatHeader().GetExecutableOffset();
const size_t text_size = oat_writer->GetSize() - rodata_size;
const size_t bss_size = oat_writer->GetBssSize();
RodataWriter rodata_writer(oat_writer);
TextWriter text_writer(oat_writer);
std::unique_ptr<ElfBuilder<ElfTypes>> builder(new ElfBuilder<ElfTypes>(
isa, rodata_size, &rodata_writer, text_size, &text_writer, bss_size));
// Add debug sections.
// They are stack allocated here (in the same scope as the builder),
// but they are registred with the builder only if they are used.
using RawSection = typename ElfBuilder<ElfTypes>::RawSection;
const auto* text = builder->GetText();
const bool is64bit = Is64BitInstructionSet(isa);
RawSection eh_frame(".eh_frame", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, kPageSize, 0,
is64bit ? Patch<Elf_Addr, uint64_t, kPointerRelativeAddress> :
Patch<Elf_Addr, uint32_t, kPointerRelativeAddress>,
RawSection eh_frame_hdr(".eh_frame_hdr", SHT_PROGBITS, SHF_ALLOC, nullptr, 0, 4, 0,
Patch<Elf_Addr, uint32_t, kSectionRelativeAddress>, text);
RawSection debug_info(".debug_info", SHT_PROGBITS, 0, nullptr, 0, 1, 0,
Patch<Elf_Addr, uint32_t, kAbsoluteAddress>, text);
RawSection debug_abbrev(".debug_abbrev", SHT_PROGBITS, 0, nullptr, 0, 1, 0);
RawSection debug_str(".debug_str", SHT_PROGBITS, 0, nullptr, 0, 1, 0);
RawSection debug_line(".debug_line", SHT_PROGBITS, 0, nullptr, 0, 1, 0,
Patch<Elf_Addr, uint32_t, kAbsoluteAddress>, text);
if (!oat_writer->GetMethodDebugInfo().empty()) {
if (compiler_driver_->GetCompilerOptions().GetIncludeCFI()) {
compiler_driver_, oat_writer, dwarf::DW_EH_PE_pcrel,
eh_frame.GetBuffer(), eh_frame.GetPatchLocations(),
eh_frame_hdr.GetBuffer(), eh_frame_hdr.GetPatchLocations());
if (compiler_driver_->GetCompilerOptions().GetIncludeDebugSymbols()) {
// Add methods to .symtab.
WriteDebugSymbols(builder.get(), oat_writer);
// Generate DWARF .debug_* sections.
compiler_driver_, oat_writer,
debug_info.GetBuffer(), debug_info.GetPatchLocations(),
debug_line.GetBuffer(), debug_line.GetPatchLocations());
*oat_writer->GetAbsolutePatchLocationsFor(".debug_info") =
*oat_writer->GetAbsolutePatchLocationsFor(".debug_line") =
// Add relocation section.
RawSection oat_patches(".oat_patches", SHT_OAT_PATCH, 0, nullptr, 0, 1, 0);
if (compiler_driver_->GetCompilerOptions().GetIncludePatchInformation() ||
// ElfWriter::Fixup will be called regardless and it needs to be able
// to patch debug sections so we have to include patches for them.
compiler_driver_->GetCompilerOptions().GetIncludeDebugSymbols()) {
EncodeOatPatches(oat_writer->GetAbsolutePatchLocations(), oat_patches.GetBuffer());
return builder->Write(elf_file_);
template <typename ElfTypes>
static void WriteDebugSymbols(ElfBuilder<ElfTypes>* builder, OatWriter* oat_writer) {
const std::vector<OatWriter::DebugInfo>& method_info = oat_writer->GetMethodDebugInfo();
// Find all addresses (low_pc) which contain deduped methods.
// The first instance of method is not marked deduped_, but the rest is.
std::unordered_set<uint32_t> deduped_addresses;
for (auto it = method_info.begin(); it != method_info.end(); ++it) {
if (it->deduped_) {
auto* symtab = builder->GetSymtab();
for (auto it = method_info.begin(); it != method_info.end(); ++it) {
if (it->deduped_) {
continue; // Add symbol only for the first instance.
std::string name = PrettyMethod(it->dex_method_index_, *it->dex_file_, true);
if (deduped_addresses.find(it->low_pc_) != deduped_addresses.end()) {
name += " [DEDUPED]";
uint32_t low_pc = it->low_pc_;
// Add in code delta, e.g., thumb bit 0 for Thumb2 code.
low_pc += it->compiled_method_->CodeDelta();
symtab->AddSymbol(name, builder->GetText(), low_pc,
true, it->high_pc_ - it->low_pc_, STB_GLOBAL, STT_FUNC);
// Conforming to aaelf, add $t mapping symbol to indicate start of a sequence of thumb2
// instructions, so that disassembler tools can correctly disassemble.
if (it->compiled_method_->GetInstructionSet() == kThumb2) {
symtab->AddSymbol("$t", builder->GetText(), it->low_pc_ & ~1, true,
// Explicit instantiations
template class ElfWriterQuick<ElfTypes32>;
template class ElfWriterQuick<ElfTypes64>;
} // namespace art