Android dex2oat Android逆向之dex2oat的实现解析
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简介
在Android系统5.0及以上系统开始逐渐丢弃Dalvik虚拟机，由于ART虚拟机对内存分配和回收都做了算法优化，降低了内存碎片化程度，回收时间也得以缩短，所有android系统5.0及以上都在主推ART虚拟机。在ART虚拟机中ART则会将Dex通过dex2oat工具编译得到一个ELF文件，它是一个可执行的文件。所以下面我们就针对ART的dex2oat实现进行做分析。
dex2oat介绍
Dex2oat的全称是：dalvik excutable file to optimized art file，它是一个对 android系统下的dex文件，进行编译优化的程序。通过dex2oat的编译优化，可以大大的提高android系统的启动的速度和使用手机过程的的流畅度。
dex2oat在安卓手机环境下的存放位置为/system/bin/dex2oat
dex2oat在开源系统中的路径为\art\dex2oat\dex2oat.cc。
为什么要使用dex2oat进行转换
在android系统中，Android 虚拟机可以识别到的是dex文件，App应用在使用过程中如果每次将dex文件加载进行内存，解释性执行字节码，效率就会变得非常低， 从而影响到用户在使用安卓手机的体验。通过利用dex2oat进行优化处理， 那么可以在android系统运行之前，利用合适的时机将dex文件字节码，提前转化为虚拟机上可以执行运行的机器码，后续直接从效率更高的机器码中运行，则运行阶段更加流畅，优化用户体验。
dex2oat代码
1.dex2oat类定义
class Dex2Oat {
public:
//创建函数，返回值为bool，
static bool Create(Dex2Oat** p_dex2oat,
const RuntimeOptions& runtime_options,
const CompilerOptions& compiler_options,
Compiler::Kind compiler_kind,
InstructionSet instruction_set,
InstructionSetFeatures instruction_set_features,
VerificationResults* verification_results,
DexFileToMethodInlinerMap* method_inliner_map,
size_t thread_count)
SHARED_TRYLOCK_FUNCTION(true, Locks::mutator_lock_) {
//判断参数传递进来的释放为空
CHECK(verification_results != nullptr);
CHECK(method_inliner_map != nullptr);
//用智能指针方式进行去实例化dex2oat
std::unique_ptr<Dex2Oat> dex2oat(new Dex2Oat(&compiler_options,
compiler_kind,
instruction_set,
instruction_set_features,
verification_results,
method_inliner_map,
thread_count));
if (!dex2oat->CreateRuntime(runtime_options, instruction_set)) {
*p_dex2oat = nullptr;
return false;
}
*p_dex2oat = dex2oat.release();
return true;
}
//dex2oat的虚构函数，用于释放操作。
~Dex2Oat() {
delete runtime_;
LogCompletionTime();
}
void LogCompletionTime() {
LOG(INFO) << "dex2oat took " << PrettyDuration(NanoTime() - start_ns_)
<< " (threads: " << thread_count_ << ")";
}
//从文件上获取到类名称
std::set<std::string>* ReadImageClassesFromFile(const char* image_classes_filename) {
std::unique_ptr<std::ifstream> image_classes_file(new std::ifstream(image_classes_filename,
std::ifstream::in));
if (image_classes_file.get() == nullptr) {
LOG(ERROR) << "Failed to open image classes file " << image_classes_filename;
return nullptr;
}
std::unique_ptr<std::set<std::string>> result(ReadImageClasses(*image_classes_file));
image_classes_file->close();
return result.release();
}
//读取imageclasses
std::set<std::string>* ReadImageClasses(std::istream& image_classes_stream) {
std::unique_ptr<std::set<std::string>> image_classes(new std::set<std::string>);
while (image_classes_stream.good()) {
std::string dot;
std::getline(image_classes_stream, dot);
if (StartsWith(dot, "#") || dot.empty()) {
continue;
}
std::string descriptor(DotToDescriptor(dot.c_str()));
image_classes->insert(descriptor);
}
return image_classes.release();
}
// Reads the class names (java.lang.Object) and returns a set of descriptors (Ljava/lang/Object;)
//从zip文件（apk其实就是个zip文件)读取类名称，读取到返回一个描述
std::set<std::string>* ReadImageClassesFromZip(const char* zip_filename,
const char* image_classes_filename,
std::string* error_msg) {
//通过智能指针进行打开zip压缩包，也就是apk包
std::unique_ptr<ZipArchive> zip_archive(ZipArchive::Open(zip_filename, error_msg));
//判断打开是否失败
if (zip_archive.get() == nullptr) {
return nullptr;
}
//进行遍历zip包获取zip包里面的文件信息
std::unique_ptr<ZipEntry> zip_entry(zip_archive->Find(image_classes_filename, error_msg));
if (zip_entry.get() == nullptr) {
*error_msg = StringPrintf("Failed to find '%s' within '%s': %s", image_classes_filename,
zip_filename, error_msg->c_str());
return nullptr;
}
std::unique_ptr<MemMap> image_classes_file(zip_entry->ExtractToMemMap(zip_filename,
image_classes_filename,
error_msg));
if (image_classes_file.get() == nullptr) {
*error_msg = StringPrintf("Failed to extract '%s' from '%s': %s", image_classes_filename,
zip_filename, error_msg->c_str());
return nullptr;
}
const std::string image_classes_string(reinterpret_cast<char*>(image_classes_file->Begin()),
image_classes_file->Size());
std::istringstream image_classes_stream(image_classes_string);
return ReadImageClasses(image_classes_stream);
}
bool PatchOatCode(const CompilerDriver* compiler_driver, File* oat_file,
const std::string& oat_location, std::string* error_msg) {
// We asked to include patch information but we are not making an image. We need to fix
// everything up manually.
std::unique_ptr<ElfFile> elf_file(ElfFile::Open(oat_file, PROT_READ|PROT_WRITE,
MAP_SHARED, error_msg));
if (elf_file.get() == NULL) {
LOG(ERROR) << error_msg;
return false;
}
{
ReaderMutexLock mu(Thread::Current(), *Locks::mutator_lock_);
return ElfPatcher::Patch(compiler_driver, elf_file.get(), oat_location, error_msg);
}
}
//创建一个oat文件，返回一个常量指针
const CompilerDriver* CreateOatFile(const std::string& boot_image_option,
const std::string& android_root,
bool is_host,
const std::vector<const DexFile*>& dex_files,
File* oat_file,
const std::string& oat_location,
const std::string& bitcode_filename,
bool image,
std::unique_ptr<std::set<std::string>>& image_classes,
bool dump_stats,
bool dump_passes,
TimingLogger& timings,
CumulativeLogger& compiler_phases_timings,
std::string profile_file,
SafeMap<std::string, std::string>* key_value_store) {
CHECK(key_value_store != nullptr);
// Handle and ClassLoader creation needs to come after Runtime::Create
jobject class_loader = nullptr;
//获取自身进程
Thread* self = Thread::Current();
//如果boot_image_option不为空的话，执行下面的代码
if (!boot_image_option.empty()) {
ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
std::vector<const DexFile*> class_path_files(dex_files);
OpenClassPathFiles(runtime_->GetClassPathString(), class_path_files);
ScopedObjectAccess soa(self);
//循环遍历并类文件大小，并进行dex文件进行注册
for (size_t i = 0; i < class_path_files.size(); i++) {
class_linker->RegisterDexFile(*class_path_files[i]);
}
soa.Env()->AllocObject(WellKnownClasses::dalvik_system_PathClassLoader);
ScopedLocalRef<jobject> class_loader_local(soa.Env(),
soa.Env()->AllocObject(WellKnownClasses::dalvik_system_PathClassLoader));
class_loader = soa.Env()->NewGlobalRef(class_loader_local.get());
Runtime::Current()->SetCompileTimeClassPath(class_loader, class_path_files);
}
std::unique_ptr<CompilerDriver> driver(new CompilerDriver(compiler_options_,
verification_results_,
method_inliner_map_,
compiler_kind_,
instruction_set_,
instruction_set_features_,
image,
image_classes.release(),
thread_count_,
dump_stats,
dump_passes,
&compiler_phases_timings,
profile_file));
driver->GetCompiler()->SetBitcodeFileName(*driver.get(), bitcode_filename);
driver->CompileAll(class_loader, dex_files, &timings);
TimingLogger::ScopedTiming t2("dex2oat OatWriter", &timings);
std::string image_file_location;
uint32_t image_file_location_oat_checksum = 0;
uintptr_t image_file_location_oat_data_begin = 0;
int32_t image_patch_delta = 0;
if (!driver->IsImage()) {
TimingLogger::ScopedTiming t3("Loading image checksum", &timings);
gc::space::ImageSpace* image_space = Runtime::Current()->GetHeap()->GetImageSpace();
image_file_location_oat_checksum = image_space->GetImageHeader().GetOatChecksum();
image_file_location_oat_data_begin =
reinterpret_cast<uintptr_t>(image_space->GetImageHeader().GetOatDataBegin());
image_file_location = image_space->GetImageFilename();
image_patch_delta = image_space->GetImageHeader().GetPatchDelta();
}
if (!image_file_location.empty()) {
key_value_store->Put(OatHeader::kImageLocationKey, image_file_location);
}
//oat写入操作
OatWriter oat_writer(dex_files, image_file_location_oat_checksum,
image_file_location_oat_data_begin,
image_patch_delta,
driver.get(),
&timings,
key_value_store);
t2.NewTiming("Writing ELF");
if (!driver->WriteElf(android_root, is_host, dex_files, &oat_writer, oat_file)) {
LOG(ERROR) << "Failed to write ELF file " << oat_file->GetPath();
return nullptr;
}
// Flush result to disk. Patching code will re-open the file (mmap), so ensure that our view
// of the file already made it there and won't be re-ordered with writes from PatchOat or
// image patching.
oat_file->Flush();
if (!driver->IsImage() && driver->GetCompilerOptions().GetIncludePatchInformation()) {
t2.NewTiming("Patching ELF");
std::string error_msg;
if (!PatchOatCode(driver.get(), oat_file, oat_location, &error_msg)) {
LOG(ERROR) << "Failed to fixup ELF file " << oat_file->GetPath() << ": " << error_msg;
return nullptr;
}
}
return driver.release();
}
//创建一个映射文件，成功返回true，失败返回false
bool CreateImageFile(const std::string& image_filename,
uintptr_t image_base,
const std::string& oat_filename,
const std::string& oat_location,
const CompilerDriver& compiler)
LOCKS_EXCLUDED(Locks::mutator_lock_) {
uintptr_t oat_data_begin;
{
// ImageWriter is scoped so it can free memory before doing FixupElf
ImageWriter image_writer(compiler);
if (!image_writer.Write(image_filename, image_base, oat_filename, oat_location)) {
LOG(ERROR) << "Failed to create image file " << image_filename;
return false;
}
oat_data_begin = image_writer.GetOatDataBegin();
}
std::unique_ptr<File> oat_file(OS::OpenFileReadWrite(oat_filename.c_str()));
if (oat_file.get() == nullptr) {
PLOG(ERROR) << "Failed to open ELF file: " << oat_filename;
return false;
}
if (!ElfFixup::Fixup(oat_file.get(), oat_data_begin)) {
LOG(ERROR) << "Failed to fixup ELF file " << oat_file->GetPath();
return false;
}
return true;
}
private:
//定义一个显示的dex2oat构造函数
explicit Dex2Oat(const CompilerOptions* compiler_options,
Compiler::Kind compiler_kind,
InstructionSet instruction_set,
InstructionSetFeatures instruction_set_features,
VerificationResults* verification_results,
DexFileToMethodInlinerMap* method_inliner_map,
size_t thread_count)
: compiler_options_(compiler_options),
compiler_kind_(compiler_kind),
instruction_set_(instruction_set),
instruction_set_features_(instruction_set_features),
verification_results_(verification_results),
method_inliner_map_(method_inliner_map),
runtime_(nullptr),
thread_count_(thread_count),
start_ns_(NanoTime()) {
CHECK(compiler_options != nullptr);
CHECK(verification_results != nullptr);
CHECK(method_inliner_map != nullptr);
}
bool CreateRuntime(const RuntimeOptions& runtime_options, InstructionSet instruction_set)
SHARED_TRYLOCK_FUNCTION(true, Locks::mutator_lock_) {
if (!Runtime::Create(runtime_options, false)) {
LOG(ERROR) << "Failed to create runtime";
return false;
}
Runtime* runtime = Runtime::Current();
runtime->SetInstructionSet(instruction_set);
for (int i = 0; i < Runtime::kLastCalleeSaveType; i++) {
Runtime::CalleeSaveType type = Runtime::CalleeSaveType(i);
if (!runtime->HasCalleeSaveMethod(type)) {
runtime->SetCalleeSaveMethod(runtime->CreateCalleeSaveMethod(type), type);
}
}
runtime->GetClassLinker()->FixupDexCaches(runtime->GetResolutionMethod());
runtime->GetClassLinker()->RunRootClinits();
runtime_ = runtime;
return true;
}
// Appends to dex_files any elements of class_path that it doesn't already
// contain. This will open those dex files as necessary.
static void OpenClassPathFiles(const std::string& class_path,
std::vector<const DexFile*>& dex_files) {
//通过定义l的vector向量的字符串
std::vector<std::string> parsed;
Split(class_path, ':', parsed);
// Take Locks::mutator_lock_ so that lock ordering on the ClassLinker::dex_lock_ is maintained.
ScopedObjectAccess soa(Thread::Current());
for (size_t i = 0; i < parsed.size(); ++i) {
//判断是否包含dex文件
if (DexFilesContains(dex_files, parsed[i])) {
continue;
}
std::string error_msg;
//判断是否可以打得开dex文件
if (!DexFile::Open(parsed[i].c_str(), parsed[i].c_str(), &error_msg, &dex_files)) {
LOG(WARNING) << "Failed to open dex file '" << parsed[i] << "': " << error_msg;
}
}
}
//如果dex文件有指定位置的话，那么就返回为true
static bool DexFilesContains(const std::vector<const DexFile*>& dex_files,
const std::string& location) {
//循环变量dex文件的大小，并进行判断location是否相等。
for (size_t i = 0; i < dex_files.size(); ++i) {
if (dex_files[i]->GetLocation() == location) {
return true;
}
}
return false;
}
//定义了个四个常量
const CompilerOptions* const compiler_options_;
const Compiler::Kind compiler_kind_;
const InstructionSet instruction_set_;
const InstructionSetFeatures instruction_set_features_;
VerificationResults* const verification_results_;
DexFileToMethodInlinerMap* const method_inliner_map_;
Runtime* runtime_;
size_t thread_count_;
uint64_t start_ns_;
DISALLOW_IMPLICIT_CONSTRUCTORS(Dex2Oat);
};
2.OpenDexFiles函数定义
//OpenDexFiles打开dex文件，成功返回dex文件的大小
static size_t OpenDexFiles(const std::vector<const char*>& dex_filenames,
const std::vector<const char*>& dex_locations,
std::vector<const DexFile*>& dex_files) {
size_t failure_count = 0;
//循环遍历dex文件的大小。
for (size_t i = 0; i < dex_filenames.size(); i++) {
const char* dex_filename = dex_filenames[i];
const char* dex_location = dex_locations[i];
ATRACE_BEGIN(StringPrintf("Opening dex file '%s'", dex_filenames[i]).c_str());
std::string error_msg;
//判断文件是否存在，
if (!OS::FileExists(dex_filename)) {
LOG(WARNING) << "Skipping non-existent dex file '" << dex_filename << "'";
continue;
}
//真正的打开操作还是调用底层的open函数实现的。
if (!DexFile::Open(dex_filename, dex_location, &error_msg, &dex_files)) {
LOG(WARNING) << "Failed to open .dex from file '" << dex_filename << "': " << error_msg;
++failure_count;
}
ATRACE_END();
}
return failure_count;
}
3.dex2oat入口函数定义
下面dex2oat函数的整个流程
做一个arm上的workaround。
构造Dex2oat对象
处理命令行参数
判断对于文件是否有写的权限
打印命令行参数
判断dex2oat的setup是否完成
根据是否image分别调用CompileImage或CompileApp的处理
//dex2oat两次参数通过控制窗口方式进行输入确
static int dex2oat(int argc, char** argv) {
#if defined(__linux__) && defined(__arm__)
//定义变量
int major, minor;
//定义获取主机信息结构体
struct utsname uts;
//调用uname判断是否可以显示系统信息
if (uname(&uts) != -1 &&
sscanf(uts.release, "%d.%d", &major, &minor) == 2 &&
((major < 3) || ((major == 3) && (minor < 4)))) {
// Kernels before 3.4 don't handle the ASLR well and we can run out of address
// space (http://b/13564922). Work around the issue by inhibiting further mmap() randomization.
int old_personality = personality(0xffffffff);
if ((old_personality & ADDR_NO_RANDOMIZE) == 0) {
int new_personality = personality(old_personality | ADDR_NO_RANDOMIZE);
if (new_personality == -1) {
LOG(WARNING) << "personality(. | ADDR_NO_RANDOMIZE) failed.";
}
}
}
#endif
//参数传递赋值到全局变量
original_argc = argc;
original_argv = argv;
//打印程序执行时间
TimingLogger timings("compiler", false, false);
CumulativeLogger compiler_phases_timings("compilation times");
InitLogging(argv);
// Skip over argv[0].
argv++;
argc--;
if (argc == 0) {
Usage("No arguments specified");
}
//到这里为止前面都是进行初始化及环境操作，真正的dex2oat功能在后面代码实现。
//定义一系列的向量，字符串，常量为后面代码使用
std::vector<const char*> dex_filenames;
std::vector<const char*> dex_locations;
int zip_fd = -1;
std::string zip_location;
std::string oat_filename;
std::string oat_symbols;
std::string oat_location;
int oat_fd = -1;
std::string bitcode_filename;
const char* image_classes_zip_filename = nullptr;
const char* image_classes_filename = nullptr;
std::string image_filename;
std::string boot_image_filename;
uintptr_t image_base = 0;
std::string android_root;
std::vector<const char*> runtime_args;
int thread_count = sysconf(_SC_NPROCESSORS_CONF);
Compiler::Kind compiler_kind = kUsePortableCompiler
? Compiler::kPortable
: Compiler::kQuick;
const char* compiler_filter_string = nullptr;
int huge_method_threshold = CompilerOptions::kDefaultHugeMethodThreshold;
int large_method_threshold = CompilerOptions::kDefaultLargeMethodThreshold;
int small_method_threshold = CompilerOptions::kDefaultSmallMethodThreshold;
int tiny_method_threshold = CompilerOptions::kDefaultTinyMethodThreshold;
int num_dex_methods_threshold = CompilerOptions::kDefaultNumDexMethodsThreshold;
//从构建中获取默认的指令功能集。
InstructionSetFeatures instruction_set_features =
ParseFeatureList(Runtime::GetDefaultInstructionSetFeatures());
InstructionSet instruction_set = kRuntimeISA;
// 配置文件的定义使用
std::string profile_file;
double top_k_profile_threshold = CompilerOptions::kDefaultTopKProfileThreshold;
bool is_host = false;
bool dump_stats = false;
bool dump_timing = false;
bool dump_passes = false;
bool include_patch_information = CompilerOptions::kDefaultIncludePatchInformation;
bool include_debug_symbols = kIsDebugBuild;
bool dump_slow_timing = kIsDebugBuild;
bool watch_dog_enabled = true;
bool generate_gdb_information = kIsDebugBuild;
// Checks are all explicit until we know the architecture.
bool implicit_null_checks = false;
bool implicit_so_checks = false;
bool implicit_suspend_checks = false;
//下面主要代码通过一系列进行执行打印命令行操作。
//统计用户输入的参数总和
for (int i = 0; i < argc; i++) {
const StringPiece option(argv[i]);
const bool log_options = false;
if (log_options) {
LOG(INFO) << "dex2oat: option[" << i << "]=" << argv[i];
}
//判断字符串是否包含
if (option.starts_with("--dex-file=")) {
//将dex文件名称数据传入vector里面
dex_filenames.push_back(option.substr(strlen("--dex-file=")).data());
} else if (option.starts_with("--dex-location=")) {
dex_locations.push_back(option.substr(strlen("--dex-location=")).data());
}
//判断是否是zip文件，并对zip文件操作，并对字符串信息进行截取
else if (option.starts_with("--zip-fd=")) {
const char* zip_fd_str = option.substr(strlen("--zip-fd=")).data();
if (!ParseInt(zip_fd_str, &zip_fd)) {
Usage("Failed to parse --zip-fd argument '%s' as an integer", zip_fd_str);
}
if (zip_fd < 0) {
Usage("--zip-fd passed a negative value %d", zip_fd);
}
} else if (option.starts_with("--zip-location=")) {
zip_location = option.substr(strlen("--zip-location=")).data();
} else if (option.starts_with("--oat-file=")) {
oat_filename = option.substr(strlen("--oat-file=")).data();
} else if (option.starts_with("--oat-symbols=")) {
oat_symbols = option.substr(strlen("--oat-symbols=")).data();
} else if (option.starts_with("--oat-fd=")) {
const char* oat_fd_str = option.substr(strlen("--oat-fd=")).data();
if (!ParseInt(oat_fd_str, &oat_fd)) {
Usage("Failed to parse --oat-fd argument '%s' as an integer", oat_fd_str);
}
if (oat_fd < 0) {
Usage("--oat-fd passed a negative value %d", oat_fd);
}
} else if (option == "--watch-dog") {
watch_dog_enabled = true;
} else if (option == "--no-watch-dog") {
watch_dog_enabled = false;
} else if (option == "--gen-gdb-info") {
generate_gdb_information = true;
// Debug symbols are needed for gdb information.
include_debug_symbols = true;
} else if (option == "--no-gen-gdb-info") {
generate_gdb_information = false;
} else if (option.starts_with("-j")) {
const char* thread_count_str = option.substr(strlen("-j")).data();
if (!ParseInt(thread_count_str, &thread_count)) {
Usage("Failed to parse -j argument '%s' as an integer", thread_count_str);
}
} else if (option.starts_with("--oat-location=")) {
oat_location = option.substr(strlen("--oat-location=")).data();
} else if (option.starts_with("--bitcode=")) {
bitcode_filename = option.substr(strlen("--bitcode=")).data();
} else if (option.starts_with("--image=")) {
image_filename = option.substr(strlen("--image=")).data();
} else if (option.starts_with("--image-classes=")) {
image_classes_filename = option.substr(strlen("--image-classes=")).data();
} else if (option.starts_with("--image-classes-zip=")) {
image_classes_zip_filename = option.substr(strlen("--image-classes-zip=")).data();
} else if (option.starts_with("--base=")) {
const char* image_base_str = option.substr(strlen("--base=")).data();
char* end;
image_base = strtoul(image_base_str, &end, 16);
if (end == image_base_str || *end != '\0') {
Usage("Failed to parse hexadecimal value for option %s", option.data());
}
} else if (option.starts_with("--boot-image=")) {
boot_image_filename = option.substr(strlen("--boot-image=")).data();
} else if (option.starts_with("--android-root=")) {
android_root = option.substr(strlen("--android-root=")).data();
}
else if (option.starts_with("--instruction-set=")) {
StringPiece instruction_set_str = option.substr(strlen("--instruction-set=")).data();
if (instruction_set_str == "arm") {
instruction_set = kThumb2;
} else if (instruction_set_str == "arm64") {
instruction_set = kArm64;
} else if (instruction_set_str == "mips") {
instruction_set = kMips;
} else if (instruction_set_str == "x86") {
instruction_set = kX86;
} else if (instruction_set_str == "x86_64") {
instruction_set = kX86_64;
}
} else if (option.starts_with("--instruction-set-features=")) {
StringPiece str = option.substr(strlen("--instruction-set-features=")).data();
instruction_set_features = ParseFeatureList(str.as_string());
} else if (option.starts_with("--compiler-backend=")) {
StringPiece backend_str = option.substr(strlen("--compiler-backend=")).data();
if (backend_str == "Quick") {
compiler_kind = Compiler::kQuick;
} else if (backend_str == "Optimizing") {
compiler_kind = Compiler::kOptimizing;
} else if (backend_str == "Portable") {
compiler_kind = Compiler::kPortable;
}
} else if (option.starts_with("--compiler-filter=")) {
compiler_filter_string = option.substr(strlen("--compiler-filter=")).data();
} else if (option.starts_with("--huge-method-max=")) {
const char* threshold = option.substr(strlen("--huge-method-max=")).data();
if (!ParseInt(threshold, &huge_method_threshold)) {
Usage("Failed to parse --huge-method-max '%s' as an integer", threshold);
}
if (huge_method_threshold < 0) {
Usage("--huge-method-max passed a negative value %s", huge_method_threshold);
}
} else if (option.starts_with("--large-method-max=")) {
const char* threshold = option.substr(strlen("--large-method-max=")).data();
if (!ParseInt(threshold, &large_method_threshold)) {
Usage("Failed to parse --large-method-max '%s' as an integer", threshold);
}
if (large_method_threshold < 0) {
Usage("--large-method-max passed a negative value %s", large_method_threshold);
}
} else if (option.starts_with("--small-method-max=")) {
const char* threshold = option.substr(strlen("--small-method-max=")).data();
if (!ParseInt(threshold, &small_method_threshold)) {
Usage("Failed to parse --small-method-max '%s' as an integer", threshold);
}
if (small_method_threshold < 0) {
Usage("--small-method-max passed a negative value %s", small_method_threshold);
}
} else if (option.starts_with("--tiny-method-max=")) {
const char* threshold = option.substr(strlen("--tiny-method-max=")).data();
if (!ParseInt(threshold, &tiny_method_threshold)) {
Usage("Failed to parse --tiny-method-max '%s' as an integer", threshold);
}
if (tiny_method_threshold < 0) {
Usage("--tiny-method-max passed a negative value %s", tiny_method_threshold);
}
} else if (option.starts_with("--num-dex-methods=")) {
const char* threshold = option.substr(strlen("--num-dex-methods=")).data();
if (!ParseInt(threshold, &num_dex_methods_threshold)) {
Usage("Failed to parse --num-dex-methods '%s' as an integer", threshold);
}
if (num_dex_methods_threshold < 0) {
Usage("--num-dex-methods passed a negative value %s", num_dex_methods_threshold);
}
} else if (option == "--host") {
is_host = true;
} else if (option == "--runtime-arg") {
if (++i >= argc) {
Usage("Missing required argument for --runtime-arg");
}
if (log_options) {
LOG(INFO) << "dex2oat: option[" << i << "]=" << argv[i];
}
runtime_args.push_back(argv[i]);
} else if (option == "--dump-timing") {
dump_timing = true;
} else if (option == "--dump-passes") {
dump_passes = true;
} else if (option == "--dump-stats") {
dump_stats = true;
} else if (option == "--include-debug-symbols" || option == "--no-strip-symbols") {
include_debug_symbols = true;
} else if (option == "--no-include-debug-symbols" || option == "--strip-symbols") {
include_debug_symbols = false;
generate_gdb_information = false; // Depends on debug symbols, see above.
} else if (option.starts_with("--profile-file=")) {
profile_file = option.substr(strlen("--profile-file=")).data();
VLOG(compiler) << "dex2oat: profile file is " << profile_file;
} else if (option == "--no-profile-file") {
// No profile
} else if (option.starts_with("--top-k-profile-threshold=")) {
ParseDouble(option.data(), '=', 0.0, 100.0, &top_k_profile_threshold);
} else if (option == "--print-pass-names") {
PassDriverMEOpts::PrintPassNames();
} else if (option.starts_with("--disable-passes=")) {
std::string disable_passes = option.substr(strlen("--disable-passes=")).data();
PassDriverMEOpts::CreateDefaultPassList(disable_passes);
} else if (option.starts_with("--print-passes=")) {
std::string print_passes = option.substr(strlen("--print-passes=")).data();
PassDriverMEOpts::SetPrintPassList(print_passes);
} else if (option == "--print-all-passes") {
PassDriverMEOpts::SetPrintAllPasses();
} else if (option.starts_with("--dump-cfg-passes=")) {
std::string dump_passes = option.substr(strlen("--dump-cfg-passes=")).data();
PassDriverMEOpts::SetDumpPassList(dump_passes);
} else if (option == "--include-patch-information") {
include_patch_information = true;
} else if (option == "--no-include-patch-information") {
include_patch_information = false;
} else {
Usage("Unknown argument %s", option.data());
}
}
//判断oat文件是否存在
if (oat_filename.empty() && oat_fd == -1) {
Usage("Output must be supplied with either --oat-file or --oat-fd");
}
if (!oat_filename.empty() && oat_fd != -1) {
Usage("--oat-file should not be used with --oat-fd");
}
//判断oat符号表是否为空
if (!oat_symbols.empty() && oat_fd != -1) {
Usage("--oat-symbols should not be used with --oat-fd");
}
if (!oat_symbols.empty() && is_host) {
Usage("--oat-symbols should not be used with --host");
}
if (oat_fd != -1 && !image_filename.empty()) {
Usage("--oat-fd should not be used with --image");
}
//判断android_root是否为空
if (android_root.empty()) {
const char* android_root_env_var = getenv("ANDROID_ROOT");
if (android_root_env_var == nullptr) {
Usage("--android-root unspecified and ANDROID_ROOT not set");
}
android_root += android_root_env_var;
}
bool image = (!image_filename.empty());
if (!image && boot_image_filename.empty()) {
boot_image_filename += android_root;
boot_image_filename += "/framework/boot.art";
}
std::string boot_image_option;
if (!boot_image_filename.empty()) {
boot_image_option += "-Ximage:";
boot_image_option += boot_image_filename;
}
if (image_classes_filename != nullptr && !image) {
Usage("--image-classes should only be used with --image");
}
if (image_classes_filename != nullptr && !boot_image_option.empty()) {
Usage("--image-classes should not be used with --boot-image");
}
if (image_classes_zip_filename != nullptr && image_classes_filename == nullptr) {
Usage("--image-classes-zip should be used with --image-classes");
}
if (dex_filenames.empty() && zip_fd == -1) {
Usage("Input must be supplied with either --dex-file or --zip-fd");
}
if (!dex_filenames.empty() && zip_fd != -1) {
Usage("--dex-file should not be used with --zip-fd");
}
if (!dex_filenames.empty() && !zip_location.empty()) {
Usage("--dex-file should not be used with --zip-location");
}
if (dex_locations.empty()) {
for (size_t i = 0; i < dex_filenames.size(); i++) {
dex_locations.push_back(dex_filenames[i]);
}
} else if (dex_locations.size() != dex_filenames.size()) {
Usage("--dex-location arguments do not match --dex-file arguments");
}
if (zip_fd != -1 && zip_location.empty()) {
Usage("--zip-location should be supplied with --zip-fd");
}
if (boot_image_option.empty()) {
if (image_base == 0) {
Usage("Non-zero --base not specified");
}
}
std::string oat_stripped(oat_filename);
std::string oat_unstripped;
if (!oat_symbols.empty()) {
oat_unstripped += oat_symbols;
} else {
oat_unstripped += oat_filename;
}
if (compiler_filter_string == nullptr) {
if (instruction_set == kMips64) {
// TODO: fix compiler for Mips64.
compiler_filter_string = "interpret-only";
} else if (image) {
compiler_filter_string = "speed";
} else {
#if ART_SMALL_MODE
compiler_filter_string = "interpret-only";
#else
compiler_filter_string = "speed";
#endif
}
}
CHECK(compiler_filter_string != nullptr);
CompilerOptions::CompilerFilter compiler_filter = CompilerOptions::kDefaultCompilerFilter;
if (strcmp(compiler_filter_string, "verify-none") == 0) {
compiler_filter = CompilerOptions::kVerifyNone;
} else if (strcmp(compiler_filter_string, "interpret-only") == 0) {
compiler_filter = CompilerOptions::kInterpretOnly;
} else if (strcmp(compiler_filter_string, "space") == 0) {
compiler_filter = CompilerOptions::kSpace;
} else if (strcmp(compiler_filter_string, "balanced") == 0) {
compiler_filter = CompilerOptions::kBalanced;
} else if (strcmp(compiler_filter_string, "speed") == 0) {
compiler_filter = CompilerOptions::kSpeed;
} else if (strcmp(compiler_filter_string, "everything") == 0) {
compiler_filter = CompilerOptions::kEverything;
} else {
Usage("Unknown --compiler-filter value %s", compiler_filter_string);
}
// Set the compilation target's implicit checks options.
switch (instruction_set) {
case kArm:
case kThumb2:
case kArm64:
case kX86:
case kX86_64:
implicit_null_checks = true;
implicit_so_checks = true;
break;
default:
// Defaults are correct.
break;
}
std::unique_ptr<CompilerOptions> compiler_options(new CompilerOptions(compiler_filter,
huge_method_threshold,
large_method_threshold,
small_method_threshold,
tiny_method_threshold,
num_dex_methods_threshold,
generate_gdb_information,
include_patch_information,
top_k_profile_threshold,
include_debug_symbols,
implicit_null_checks,
implicit_so_checks,
implicit_suspend_checks
#ifdef ART_SEA_IR_MODE
, compiler_options.sea_ir_ =
true;
#endif
)); // NOLINT(whitespace/parens)
// Done with usage checks, enable watchdog if requested
WatchDog watch_dog(watch_dog_enabled);
// Check early that the result of compilation can be written
std::unique_ptr<File> oat_file;
bool create_file = !oat_unstripped.empty(); // as opposed to using open file descriptor
if (create_file) {
oat_file.reset(OS::CreateEmptyFile(oat_unstripped.c_str()));
if (oat_location.empty()) {
oat_location = oat_filename;
}
} else {
oat_file.reset(new File(oat_fd, oat_location));
oat_file->DisableAutoClose();
oat_file->SetLength(0);
}
if (oat_file.get() == nullptr) {
PLOG(ERROR) << "Failed to create oat file: " << oat_location;
return EXIT_FAILURE;
}
if (create_file && fchmod(oat_file->Fd(), 0644) != 0) {
PLOG(ERROR) << "Failed to make oat file world readable: " << oat_location;
return EXIT_FAILURE;
}
//开始真正的执行dex2oat工作了
timings.StartTiming("dex2oat Setup");
LOG(INFO) << CommandLine();
RuntimeOptions runtime_options;
std::vector<const DexFile*> boot_class_path;
art::MemMap::Init(); // For ZipEntry::ExtractToMemMap.
if (boot_image_option.empty()) {
//打开zip文件中的dex文件
size_t failure_count = OpenDexFiles(dex_filenames, dex_locations, boot_class_path);
if (failure_count > 0) {
LOG(ERROR) << "Failed to open some dex files: " << failure_count;
return EXIT_FAILURE;
}
runtime_options.push_back(std::make_pair("bootclasspath", &boot_class_path));
} else {
runtime_options.push_back(std::make_pair(boot_image_option.c_str(), nullptr));
}
for (size_t i = 0; i < runtime_args.size(); i++) {
runtime_options.push_back(std::make_pair(runtime_args[i], nullptr));
}
std::unique_ptr<VerificationResults> verification_results(new VerificationResults(
compiler_options.get()));
DexFileToMethodInlinerMap method_inliner_map;
QuickCompilerCallbacks callbacks(verification_results.get(), &method_inliner_map);
runtime_options.push_back(std::make_pair("compilercallbacks", &callbacks));
runtime_options.push_back(
std::make_pair("imageinstructionset",
reinterpret_cast<const void*>(GetInstructionSetString(instruction_set))));
Dex2Oat* p_dex2oat;
//创建一个dex2oat
if (!Dex2Oat::Create(&p_dex2oat,
runtime_options,
*compiler_options,
compiler_kind,
instruction_set,
instruction_set_features,
verification_results.get(),
&method_inliner_map,
thread_count)) {
LOG(ERROR) << "Failed to create dex2oat";
return EXIT_FAILURE;
}
std::unique_ptr<Dex2Oat> dex2oat(p_dex2oat);
Thread* self = Thread::Current();
self->TransitionFromRunnableToSuspended(kNative);
WellKnownClasses::Init(self->GetJniEnv());
// If --image-classes was specified, calculate the full list of classes to include in the image
std::unique_ptr<std::set<std::string>> image_classes(nullptr);
if (image_classes_filename != nullptr) {
std::string error_msg;
if (image_classes_zip_filename != nullptr) {
image_classes.reset(dex2oat->ReadImageClassesFromZip(image_classes_zip_filename,
image_classes_filename,
&error_msg));
} else {
image_classes.reset(dex2oat->ReadImageClassesFromFile(image_classes_filename));
}
if (image_classes.get() == nullptr) {
LOG(ERROR) << "Failed to create list of image classes from '" << image_classes_filename <<
"': " << error_msg;
return EXIT_FAILURE;
}
} else if (image) {
image_classes.reset(new std::set<std::string>);
}
std::vector<const DexFile*> dex_files;
if (boot_image_option.empty()) {
dex_files = Runtime::Current()->GetClassLinker()->GetBootClassPath();
} else {
if (dex_filenames.empty()) {
ATRACE_BEGIN("Opening zip archive from file descriptor");
std::string error_msg;
std::unique_ptr<ZipArchive> zip_archive(ZipArchive::OpenFromFd(zip_fd, zip_location.c_str(),
&error_msg));
if (zip_archive.get() == nullptr) {
LOG(ERROR) << "Failed to open zip from file descriptor for '" << zip_location << "': "
<< error_msg;
return EXIT_FAILURE;
}
if (!DexFile::OpenFromZip(*zip_archive.get(), zip_location, &error_msg, &dex_files)) {
LOG(ERROR) << "Failed to open dex from file descriptor for zip file '" << zip_location
<< "': " << error_msg;
return EXIT_FAILURE;
}
ATRACE_END();
} else {
size_t failure_count = OpenDexFiles(dex_filenames, dex_locations, dex_files);
if (failure_count > 0) {
LOG(ERROR) << "Failed to open some dex files: " << failure_count;
return EXIT_FAILURE;
}
}
const bool kSaveDexInput = false;
if (kSaveDexInput) {
for (size_t i = 0; i < dex_files.size(); ++i) {
const DexFile* dex_file = dex_files[i];
std::string tmp_file_name(StringPrintf("/data/local/tmp/dex2oat.%d.%zd.dex", getpid(), i));
std::unique_ptr<File> tmp_file(OS::CreateEmptyFile(tmp_file_name.c_str()));
if (tmp_file.get() == nullptr) {
PLOG(ERROR) << "Failed to open file " << tmp_file_name
<< ". Try: adb shell chmod 777 /data/local/tmp";
continue;
}
//进行对dex文件写入操作
tmp_file->WriteFully(dex_file->Begin(), dex_file->Size());
LOG(INFO) << "Wrote input to " << tmp_file_name;
}
}
}
// Ensure opened dex files are writable for dex-to-dex transformations.
for (const auto& dex_file : dex_files) {
if (!dex_file->EnableWrite()) {
PLOG(ERROR) << "Failed to make .dex file writeable '" << dex_file->GetLocation() << "'\n";
}
}
if (!image && compiler_options->IsCompilationEnabled()) {
size_t num_methods = 0;
for (size_t i = 0; i != dex_files.size(); ++i) {
const DexFile* dex_file = dex_files[i];
CHECK(dex_file != nullptr);
num_methods += dex_file->NumMethodIds();
}
if (num_methods <= compiler_options->GetNumDexMethodsThreshold()) {
compiler_options->SetCompilerFilter(CompilerOptions::kSpeed);
VLOG(compiler) << "Below method threshold, compiling anyways";
}
}
// Fill some values into the key-value store for the oat header.
std::unique_ptr<SafeMap<std::string, std::string> > key_value_store(
new SafeMap<std::string, std::string>());
// Insert some compiler things.
std::ostringstream oss;
for (int i = 0; i < argc; ++i) {
if (i > 0) {
oss << ' ';
}
oss << argv[i];
}
key_value_store->Put(OatHeader::kDex2OatCmdLineKey, oss.str());
oss.str(""); // Reset.
oss << kRuntimeISA;
key_value_store->Put(OatHeader::kDex2OatHostKey, oss.str());
//编译dex文件功能，主要将dex文件转换我oat文件
std::unique_ptr<const CompilerDriver> compiler(dex2oat->CreateOatFile(boot_image_option,
android_root,
is_host,
dex_files,
oat_file.get(),
oat_location,
bitcode_filename,
image,
image_classes,
dump_stats,
dump_passes,
timings,
compiler_phases_timings,
profile_file,
key_value_store.get()));
if (compiler.get() == nullptr) {
LOG(ERROR) << "Failed to create oat file: " << oat_location;
return EXIT_FAILURE;
}
VLOG(compiler) << "Oat file written successfully (unstripped): " << oat_location;
if (image) {
//打印运行时间日志
TimingLogger::ScopedTiming t("dex2oat ImageWriter", &timings);
//创建一个oat映射文件
bool image_creation_success = dex2oat->CreateImageFile(image_filename,
image_base,
oat_unstripped,
oat_location,
*compiler.get());
if (!image_creation_success) {
return EXIT_FAILURE;
}
VLOG(compiler) << "Image written successfully: " << image_filename;
}
if (is_host) {
timings.EndTiming();
if (dump_timing || (dump_slow_timing && timings.GetTotalNs() > MsToNs(1000))) {
LOG(INFO) << Dumpable<TimingLogger>(timings);
}
if (dump_passes) {
LOG(INFO) << Dumpable<CumulativeLogger>(*compiler.get()->GetTimingsLogger());
}
return EXIT_SUCCESS;
}
if (oat_unstripped != oat_stripped) {
//记录程序执行时间
TimingLogger::ScopedTiming t("dex2oat OatFile copy", &timings);
oat_file.reset();
//用智能指针方式进行打开读取文件
std::unique_ptr<File> in(OS::OpenFileForReading(oat_unstripped.c_str()));
std::unique_ptr<File> out(OS::CreateEmptyFile(oat_stripped.c_str()));
size_t buffer_size = 8192;
std::unique_ptr<uint8_t> buffer(new uint8_t[buffer_size]);
while (true) {
int bytes_read = TEMP_FAILURE_RETRY(read(in->Fd(), buffer.get(), buffer_size));
if (bytes_read <= 0) {
break;
}
bool write_ok = out->WriteFully(buffer.get(), bytes_read);
CHECK(write_ok);
}
oat_file.reset(out.release());
VLOG(compiler) << "Oat file copied successfully (stripped): " << oat_stripped;
}
#if ART_USE_PORTABLE_COMPILER // We currently only generate symbols on Portable
if (!compiler_options.GetIncludeDebugSymbols()) {
timings.NewSplit("dex2oat ElfStripper");
// Strip unneeded sections for target
off_t seek_actual = lseek(oat_file->Fd(), 0, SEEK_SET);
CHECK_EQ(0, seek_actual);
std::string error_msg;
CHECK(ElfStripper::Strip(oat_file.get(), &error_msg)) << error_msg;
// 成功的编译成oat文件
VLOG(compiler) << "Oat file written successfully (stripped): " << oat_location;
} else {
VLOG(compiler) << "Oat file written successfully without stripping: " << oat_location;
}
#endif // ART_USE_PORTABLE_COMPILER
timings.EndTiming();
if (dump_timing || (dump_slow_timing && timings.GetTotalNs() > MsToNs(1000))) {
LOG(INFO) << Dumpable<TimingLogger>(timings);
}
if (dump_passes) {
LOG(INFO) << Dumpable<CumulativeLogger>(compiler_phases_timings);
}
if (!kIsDebugBuild && (RUNNING_ON_VALGRIND == 0)) {
dex2oat->LogCompletionTime();
exit(EXIT_SUCCESS);
}
return EXIT_SUCCESS;
} // NOLINT(readability/fn_size)
} // namespace art
总结
基于以上的分析，我们可以指定dex2oat在我们现在android系统运行过程中占据很重要的地位，因为app安装，手机屏幕滑动，系统启动等等都需要和dex2oat打交道，同时dex2oat在加壳和脱壳方面应用场景，在脱壳方面通过修改dex2oat代码可以进行更好的脱壳。
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