剖析 Android ART Runtime (4) – patchoat

if (has_cache && ChecksumsMatch(system_filename.c_str(), cache_filename.c_str())) {
          // We already have a relocated version
          image_filename = &cache_filename;
          relocated_version_used = true;
        } else {
          // We cannot have a relocated version, Relocate the system one and use it.

          std::string reason;
          bool success;

          // Check whether we are allowed to relocate.
          if (!can_compile) {
            reason = "Image dex2oat disabled by -Xnoimage-dex2oat.";
            success = false;
          } else if (!ImageCreationAllowed(is_global_cache, &reason)) {
            // Whether we can write to the cache.
            success = false;
          } else {
            // Try to relocate.
            success = RelocateImage(image_location, cache_filename.c_str(), image_isa, &reason);
          }
          // ...
        }

static int32_t ChooseRelocationOffsetDelta(int32_t min_delta, int32_t max_delta) {
  CHECK_ALIGNED(min_delta, kPageSize);
  CHECK_ALIGNED(max_delta, kPageSize);
  CHECK_LT(min_delta, max_delta);

  std::default_random_engine generator;
  generator.seed(NanoTime() * getpid());
  std::uniform_int_distribution<int32_t> distribution(min_delta, max_delta);
  int32_t r = distribution(generator);
  if (r % 2 == 0) {
    r = RoundUp(r, kPageSize);
  } else {
    r = RoundDown(r, kPageSize);
  }
  CHECK_LE(min_delta, r);
  CHECK_GE(max_delta, r);
  CHECK_ALIGNED(r, kPageSize);
  return r;
}

// Relocate the image at image_location to dest_filename and relocate it by a random amount.
static bool RelocateImage(const char* image_location, const char* dest_filename,
                               InstructionSet isa, std::string* error_msg) {
  // We should clean up so we are more likely to have room for the image.
  if (Runtime::Current()->IsZygote()) {
    LOG(INFO) << "Pruning dalvik-cache since we are relocating an image and will need to recompile";
    PruneDalvikCache(isa);
  }

  std::string patchoat(Runtime::Current()->GetPatchoatExecutable());

  std::string input_image_location_arg("--input-image-location=");
  input_image_location_arg += image_location;

  std::string output_image_filename_arg("--output-image-file=");
  output_image_filename_arg += dest_filename;

  std::string input_oat_location_arg("--input-oat-location=");
  input_oat_location_arg += ImageHeader::GetOatLocationFromImageLocation(image_location);

  std::string output_oat_filename_arg("--output-oat-file=");
  output_oat_filename_arg += ImageHeader::GetOatLocationFromImageLocation(dest_filename);

  std::string instruction_set_arg("--instruction-set=");
  instruction_set_arg += GetInstructionSetString(isa);

  std::string base_offset_arg("--base-offset-delta=");
  StringAppendF(&base_offset_arg, "%d", ChooseRelocationOffsetDelta(ART_BASE_ADDRESS_MIN_DELTA,
                                                                    ART_BASE_ADDRESS_MAX_DELTA));
  // ...
  return Exec(argv, error_msg);
}

  if (have_image_files && have_oat_files) {
    TimingLogger::ScopedTiming pt("patch image and oat", &timings);
    ret = PatchOat::Patch(input_oat.get(), input_image_location, base_delta,
                          output_oat.get(), output_image.get(), isa, &timings,
                          output_oat_fd >= 0,  // was it opened from FD?
                          new_oat_out);
    // The order here doesn't matter. If the first one is successfully saved and the second one
    // erased, ImageSpace will still detect a problem and not use the files.
    ret = ret && FinishFile(output_image.get(), ret);
    ret = ret && FinishFile(output_oat.get(), ret);
  } else if (have_oat_files) {
    TimingLogger::ScopedTiming pt("patch oat", &timings);
    ret = PatchOat::Patch(input_oat.get(), base_delta, output_oat.get(), &timings,
                          output_oat_fd >= 0,  // was it opened from FD?
                          new_oat_out);
    ret = ret && FinishFile(output_oat.get(), ret);
  } else if (have_image_files) {
    TimingLogger::ScopedTiming pt("patch image", &timings);
    ret = PatchOat::Patch(input_image_location, base_delta, output_image.get(), isa, &timings);
    ret = ret && FinishFile(output_image.get(), ret);
  } else {
    CHECK(false);
    ret = true;
  }

  if (is_oat_pic >= ERROR_FIRST) {
    // Error logged by IsOatPic
    return false;
  } else if (is_oat_pic == PIC) {
    // Do not need to do ELF-file patching. Create a symlink and skip the ELF patching.
    if (!ReplaceOatFileWithSymlink(input_oat->GetPath(),
                                   output_oat->GetPath(),
                                   output_oat_opened_from_fd,
                                   new_oat_out)) {
      // Errors already logged by above call.
      return false;
    }
    // Don't patch the OAT, since we just symlinked it. Image still needs patching.
    skip_patching_oat = true;
  } else {
    CHECK(is_oat_pic == NOT_PIC);
  }

  PatchOat p(isa, elf.release(), image.release(), ispc->GetLiveBitmap(), ispc->GetMemMap(),
             delta, timings);
  t.NewTiming("Patching files");
  if (!skip_patching_oat && !p.PatchElf()) {
    LOG(ERROR) << "Failed to patch oat file " << input_oat->GetPath();
    return false;
  }
  if (!p.PatchImage()) {
    LOG(ERROR) << "Failed to patch image file " << input_image->GetPath();
    return false;
  }

  t.NewTiming("Writing files");
  if (!skip_patching_oat && !p.WriteElf(output_oat)) {
    LOG(ERROR) << "Failed to write oat file " << input_oat->GetPath();
    return false;
  }
  if (!p.WriteImage(output_image)) {
    LOG(ERROR) << "Failed to write image file " << input_image->GetPath();
    return false;
  }

// 为了方便阅读，部分代码已删除
template <typename ElfFileImpl>
bool PatchOat::PatchElf(ElfFileImpl* oat_file) {
  oat_file->ApplyOatPatchesTo(".text", delta_);

  PatchOatHeader<ElfFileImpl>(oat_file);

  for (unsigned int i = 0; i < oat_file->GetProgramHeaderNum(); ++i) {
    auto hdr = oat_file->GetProgramHeader(i);
    if (hdr->p_type == PT_LOAD && hdr->p_vaddr == 0u) {
      need_boot_oat_fixup = false;
      break;
    }
  }
  if (!need_boot_oat_fixup) {
    // This is an app oat file that can be loaded at an arbitrary address in memory.
    // Boot image references were patched above and there's nothing else to do.
    return true;
  }

  // This is a boot oat file that's loaded at a particular address and we need
  // to patch all absolute addresses, starting with ELF program headers.

  // Fixup Phdr's
  oat_file->FixupProgramHeaders(delta_);

  // Fixup Shdr's
  oat_file->FixupSectionHeaders(delta_);

  oat_file->FixupDynamic(delta_);

  // Fixup dynsym
  oat_file->FixupSymbols(delta_, true);

  // Fixup symtab
  oat_file->FixupSymbols(delta_, false);

  oat_file->FixupDebugSections(delta_);

template <typename ElfTypes>
bool ElfFileImpl<ElfTypes>::ApplyOatPatchesTo(
    const char* target_section_name, Elf_Addr delta) {
  auto target_section = FindSectionByName(target_section_name);
  if (target_section == nullptr) {
    return true;
  }
  std::string patches_name = target_section_name + std::string(".oat_patches");
  auto patches_section = FindSectionByName(patches_name.c_str());
  if (patches_section == nullptr) {
    LOG(ERROR) << patches_name << " section not found.";
    return false;
  }
  if (patches_section->sh_type != SHT_OAT_PATCH) {
    LOG(ERROR) << "Unexpected type of " << patches_name;
    return false;
  }
  ApplyOatPatches(
      Begin() + patches_section->sh_offset,
      Begin() + patches_section->sh_offset + patches_section->sh_size,
      delta,
      Begin() + target_section->sh_offset,
      Begin() + target_section->sh_offset + target_section->sh_size);
  return true;
}

// Apply LEB128 encoded patches to given section.
template <typename ElfTypes>
void ElfFileImpl<ElfTypes>::ApplyOatPatches(
    const uint8_t* patches, const uint8_t* patches_end, Elf_Addr delta,
    uint8_t* to_patch, const uint8_t* to_patch_end) {
  typedef __attribute__((__aligned__(1))) Elf_Addr UnalignedAddress;
  while (patches < patches_end) {
    to_patch += DecodeUnsignedLeb128(&patches);
    DCHECK_LE(patches, patches_end) << "Unexpected end of patch list.";
    DCHECK_LT(to_patch, to_patch_end) << "Patch past the end of section.";
    *reinterpret_cast<UnalignedAddress*>(to_patch) += delta;
  }
}

void Mir2Lir::InstallLiteralPools() {
// ...
  data_lir = code_literal_list_;
  while (data_lir != nullptr) {
    uint32_t target_method_idx = data_lir->operands[0];
    const DexFile* target_dex_file = UnwrapPointer<DexFile>(data_lir->operands[1]);
    patches_.push_back(LinkerPatch::CodePatch(code_buffer_.size(),
                                              target_dex_file, target_method_idx));
    PushUnpatchedReference(&code_buffer_);
    data_lir = NEXT_LIR(data_lir);
  }
// ...
}

void ArmMir2Lir::InstallLiteralPools() {
  patches_.reserve(call_method_insns_.size() + dex_cache_access_insns_.size());

  // PC-relative calls to methods.
  for (LIR* p : call_method_insns_) {
    DCHECK_EQ(p->opcode, kThumb2Bl);
    uint32_t target_method_idx = p->operands[1];
    const DexFile* target_dex_file = UnwrapPointer<DexFile>(p->operands[2]);
    patches_.push_back(LinkerPatch::RelativeCodePatch(p->offset,
                                                      target_dex_file, target_method_idx));
  }
}

LIR* ArmMir2Lir::GenCallInsn(const MirMethodLoweringInfo& method_info) {
  LIR* call_insn;
  if (method_info.FastPath() && ArmUseRelativeCall(cu_, method_info.GetTargetMethod()) &&
      (method_info.GetSharpType() == kDirect || method_info.GetSharpType() == kStatic) &&
      method_info.DirectCode() == static_cast<uintptr_t>(-1)) {
    call_insn = CallWithLinkerFixup(method_info.GetTargetMethod(), method_info.GetSharpType());
  } else {
    call_insn = OpReg(kOpBlx, TargetPtrReg(kInvokeTgt));
  }
  return call_insn;
}

  std::unique_ptr<RawSection> text_oat_patches(new RawSection(
      ".text.oat_patches", SHT_OAT_PATCH));
  if (compiler_driver_->GetCompilerOptions().GetIncludePatchInformation()) {
    // Note that ElfWriter::Fixup will be called regardless and therefore
    // we need to include oat_patches for debug sections unconditionally.
    EncodeOatPatches(oat_writer->GetAbsolutePatchLocations(),
                     text_oat_patches->GetBuffer());
    builder->RegisterSection(text_oat_patches.get());
  }

bool PatchOat::PatchImage() {
  ImageHeader* image_header = reinterpret_cast<ImageHeader*>(image_->Begin());
  CHECK_GT(image_->Size(), sizeof(ImageHeader));
  // These are the roots from the original file.
  auto* img_roots = image_header->GetImageRoots();
  image_header->RelocateImage(delta_);

  PatchArtFields(image_header);
  PatchArtMethods(image_header);
  PatchInternedStrings(image_header);
  // Patch dex file int/long arrays which point to ArtFields.
  PatchDexFileArrays(img_roots);

  VisitObject(img_roots);
  if (!image_header->IsValid()) {
    LOG(ERROR) << "reloction renders image header invalid";
    return false;
  }

  {
    TimingLogger::ScopedTiming t("Walk Bitmap", timings_);
    // Walk the bitmap.
    WriterMutexLock mu(Thread::Current(), *Locks::heap_bitmap_lock_);
    bitmap_->Walk(PatchOat::BitmapCallback, this);
  }
  return true;
}

void PatchOat::PatchArtMethods(const ImageHeader* image_header) {
  const auto& section = image_header->GetMethodsSection();
  const size_t pointer_size = InstructionSetPointerSize(isa_);
  size_t method_size = ArtMethod::ObjectSize(pointer_size);
  for (size_t pos = 0; pos < section.Size(); pos += method_size) {
    auto* src = reinterpret_cast<ArtMethod*>(heap_->Begin() + section.Offset() + pos);
    auto* dest = RelocatedCopyOf(src);
    FixupMethod(src, dest);
  }
}

void PatchOat::FixupMethod(ArtMethod* object, ArtMethod* copy) {
  const size_t pointer_size = InstructionSetPointerSize(isa_);
  copy->CopyFrom(object, pointer_size);
  // Just update the entry points if it looks like we should.
  // TODO: sanity check all the pointers' values
  copy->SetDeclaringClass(RelocatedAddressOfPointer(object->GetDeclaringClass()));
  copy->SetDexCacheResolvedMethods(RelocatedAddressOfPointer(object->GetDexCacheResolvedMethods()));
  copy->SetDexCacheResolvedTypes(RelocatedAddressOfPointer(object->GetDexCacheResolvedTypes()));
  copy->SetEntryPointFromQuickCompiledCodePtrSize(RelocatedAddressOfPointer(
      object->GetEntryPointFromQuickCompiledCodePtrSize(pointer_size)), pointer_size);
  copy->SetEntryPointFromInterpreterPtrSize(RelocatedAddressOfPointer(
      object->GetEntryPointFromInterpreterPtrSize(pointer_size)), pointer_size);
  copy->SetEntryPointFromJniPtrSize(RelocatedAddressOfPointer(
      object->GetEntryPointFromJniPtrSize(pointer_size)), pointer_size);
}