目录
一,概述
OAT文件是一种Android私有ELF文件格式，它不仅包含有从DEX文件翻译而来的本地机器指令，还包含有原来的DEX文件内容。这使得我们无需重新编译原有的APK就可以让它正常地在ART里面运行，也就是我们不需要改变原来的APK编程接口
为了更好了弄明白oat文件的格式，目前还需要看下elf 文件格式
oat文件格式
作为Android私有的一种ELF文件，OAT文件包含有两个特殊的段oatdata和oatexec，前者包含有用来生成本地机器指令的dex文件内容，后者包含有生成的本地机器指令，它们之间的关系通过储存在oatdata段前面的oat头部描述。此外，在OAT文件的dynamic段，导出了三个符号oatdata、oatexec和oatlastword，它们的值就是用来界定oatdata段和oatexec段的起止位置的。其中，[oatdata, oatexec - 1]描述的是oatdata段的起止位置，而[oatexec, oatlastword + 3]描述的是oatexec的起止位置。要完全理解OAT的文件格式，除了要理解本文即将要分析的OAT加载过程之外，还需要掌握接下来文章分析的类和方法查找过程。
1.1 OAT是如何产生的
/Volumes/aosp/android-8.1.0_r52/frameworks/native/cmds/installd/dexopt.cpp
static void run_dex2oat(int zip_fd, int oat_fd, int input_vdex_fd, int output_vdex_fd, int image_fd,
const char* input_file_name, const char* output_file_name, int swap_fd,
const char* instruction_set, const char* compiler_filter,
bool debuggable, bool post_bootcomplete, int profile_fd, const char* class_loader_context) {
static const unsigned int MAX_INSTRUCTION_SET_LEN = 7;
if (strlen(instruction_set) >= MAX_INSTRUCTION_SET_LEN) {
ALOGE("Instruction set %s longer than max length of %d",
instruction_set, MAX_INSTRUCTION_SET_LEN);
return;
}
// Get the relative path to the input file.
const char* relative_input_file_name = get_location_from_path(input_file_name);
char dex2oat_Xms_flag[kPropertyValueMax];
bool have_dex2oat_Xms_flag = get_property("dalvik.vm.dex2oat-Xms", dex2oat_Xms_flag, NULL) > 0;
char dex2oat_Xmx_flag[kPropertyValueMax];
bool have_dex2oat_Xmx_flag = get_property("dalvik.vm.dex2oat-Xmx", dex2oat_Xmx_flag, NULL) > 0;
char dex2oat_threads_buf[kPropertyValueMax];
bool have_dex2oat_threads_flag = get_property(post_bootcomplete
? "dalvik.vm.dex2oat-threads"
: "dalvik.vm.boot-dex2oat-threads",
dex2oat_threads_buf,
NULL) > 0;
char dex2oat_threads_arg[kPropertyValueMax + 2];
if (have_dex2oat_threads_flag) {
sprintf(dex2oat_threads_arg, "-j%s", dex2oat_threads_buf);
}
char dex2oat_isa_features_key[kPropertyKeyMax];
sprintf(dex2oat_isa_features_key, "dalvik.vm.isa.%s.features", instruction_set);
char dex2oat_isa_features[kPropertyValueMax];
bool have_dex2oat_isa_features = get_property(dex2oat_isa_features_key,
dex2oat_isa_features, NULL) > 0;
char dex2oat_isa_variant_key[kPropertyKeyMax];
sprintf(dex2oat_isa_variant_key, "dalvik.vm.isa.%s.variant", instruction_set);
char dex2oat_isa_variant[kPropertyValueMax];
bool have_dex2oat_isa_variant = get_property(dex2oat_isa_variant_key,
dex2oat_isa_variant, NULL) > 0;
const char *dex2oat_norelocation = "-Xnorelocate";
bool have_dex2oat_relocation_skip_flag = false;
char dex2oat_flags[kPropertyValueMax];
int dex2oat_flags_count = get_property("dalvik.vm.dex2oat-flags",
dex2oat_flags, NULL) <= 0 ? 0 : split_count(dex2oat_flags);
ALOGV("dalvik.vm.dex2oat-flags=%s\n", dex2oat_flags);
// If we are booting without the real /data, don't spend time compiling.
char vold_decrypt[kPropertyValueMax];
bool have_vold_decrypt = get_property("vold.decrypt", vold_decrypt, "") > 0;
bool skip_compilation = (have_vold_decrypt &&
(strcmp(vold_decrypt, "trigger_restart_min_framework") == 0 ||
(strcmp(vold_decrypt, "1") == 0)));
bool generate_debug_info = property_get_bool("debug.generate-debug-info", false);
char app_image_format[kPropertyValueMax];
char image_format_arg[strlen("--image-format=") + kPropertyValueMax];
bool have_app_image_format =
image_fd >= 0 && get_property("dalvik.vm.appimageformat", app_image_format, NULL) > 0;
if (have_app_image_format) {
sprintf(image_format_arg, "--image-format=%s", app_image_format);
}
char dex2oat_large_app_threshold[kPropertyValueMax];
bool have_dex2oat_large_app_threshold =
get_property("dalvik.vm.dex2oat-very-large", dex2oat_large_app_threshold, NULL) > 0;
char dex2oat_large_app_threshold_arg[strlen("--very-large-app-threshold=") + kPropertyValueMax];
if (have_dex2oat_large_app_threshold) {
sprintf(dex2oat_large_app_threshold_arg,
"--very-large-app-threshold=%s",
dex2oat_large_app_threshold);
}
static const char* DEX2OAT_BIN = "/system/bin/dex2oat";
static const char* RUNTIME_ARG = "--runtime-arg";
static const int MAX_INT_LEN = 12; // '-'+10dig+'\0' -OR- 0x+8dig
// clang FORTIFY doesn't let us use strlen in constant array bounds, so we
// use arraysize instead.
char zip_fd_arg[arraysize("--zip-fd=") + MAX_INT_LEN];
char zip_location_arg[arraysize("--zip-location=") + PKG_PATH_MAX];
char input_vdex_fd_arg[arraysize("--input-vdex-fd=") + MAX_INT_LEN];
char output_vdex_fd_arg[arraysize("--output-vdex-fd=") + MAX_INT_LEN];
char oat_fd_arg[arraysize("--oat-fd=") + MAX_INT_LEN];
char oat_location_arg[arraysize("--oat-location=") + PKG_PATH_MAX];
char instruction_set_arg[arraysize("--instruction-set=") + MAX_INSTRUCTION_SET_LEN];
char instruction_set_variant_arg[arraysize("--instruction-set-variant=") + kPropertyValueMax];
char instruction_set_features_arg[arraysize("--instruction-set-features=") + kPropertyValueMax];
char dex2oat_Xms_arg[arraysize("-Xms") + kPropertyValueMax];
char dex2oat_Xmx_arg[arraysize("-Xmx") + kPropertyValueMax];
char dex2oat_compiler_filter_arg[arraysize("--compiler-filter=") + kPropertyValueMax];
bool have_dex2oat_swap_fd = false;
char dex2oat_swap_fd[arraysize("--swap-fd=") + MAX_INT_LEN];
bool have_dex2oat_image_fd = false;
char dex2oat_image_fd[arraysize("--app-image-fd=") + MAX_INT_LEN];
size_t class_loader_context_size = arraysize("--class-loader-context=") + PKG_PATH_MAX;
char class_loader_context_arg[class_loader_context_size];
if (class_loader_context != nullptr) {
snprintf(class_loader_context_arg, class_loader_context_size, "--class-loader-context=%s",
class_loader_context);
}
sprintf(zip_fd_arg, "--zip-fd=%d", zip_fd);
sprintf(zip_location_arg, "--zip-location=%s", relative_input_file_name);
sprintf(input_vdex_fd_arg, "--input-vdex-fd=%d", input_vdex_fd);
sprintf(output_vdex_fd_arg, "--output-vdex-fd=%d", output_vdex_fd);
sprintf(oat_fd_arg, "--oat-fd=%d", oat_fd);
sprintf(oat_location_arg, "--oat-location=%s", output_file_name);
sprintf(instruction_set_arg, "--instruction-set=%s", instruction_set);
sprintf(instruction_set_variant_arg, "--instruction-set-variant=%s", dex2oat_isa_variant);
sprintf(instruction_set_features_arg, "--instruction-set-features=%s", dex2oat_isa_features);
if (swap_fd >= 0) {
have_dex2oat_swap_fd = true;
sprintf(dex2oat_swap_fd, "--swap-fd=%d", swap_fd);
}
if (image_fd >= 0) {
have_dex2oat_image_fd = true;
sprintf(dex2oat_image_fd, "--app-image-fd=%d", image_fd);
}
if (have_dex2oat_Xms_flag) {
sprintf(dex2oat_Xms_arg, "-Xms%s", dex2oat_Xms_flag);
}
if (have_dex2oat_Xmx_flag) {
sprintf(dex2oat_Xmx_arg, "-Xmx%s", dex2oat_Xmx_flag);
}
// Compute compiler filter.
bool have_dex2oat_compiler_filter_flag = false;
if (skip_compilation) {
strcpy(dex2oat_compiler_filter_arg, "--compiler-filter=extract");
have_dex2oat_compiler_filter_flag = true;
have_dex2oat_relocation_skip_flag = true;
} else if (compiler_filter != nullptr) {
if (strlen(compiler_filter) + strlen("--compiler-filter=") <
arraysize(dex2oat_compiler_filter_arg)) {
sprintf(dex2oat_compiler_filter_arg, "--compiler-filter=%s", compiler_filter);
have_dex2oat_compiler_filter_flag = true;
} else {
ALOGW("Compiler filter name '%s' is too large (max characters is %zu)",
compiler_filter,
kPropertyValueMax);
}
}
if (!have_dex2oat_compiler_filter_flag) {
char dex2oat_compiler_filter_flag[kPropertyValueMax];
have_dex2oat_compiler_filter_flag = get_property("dalvik.vm.dex2oat-filter",
dex2oat_compiler_filter_flag, NULL) > 0;
if (have_dex2oat_compiler_filter_flag) {
sprintf(dex2oat_compiler_filter_arg,
"--compiler-filter=%s",
dex2oat_compiler_filter_flag);
}
}
// Check whether all apps should be compiled debuggable.
if (!debuggable) {
char prop_buf[kPropertyValueMax];
debuggable =
(get_property("dalvik.vm.always_debuggable", prop_buf, "0") > 0) &&
(prop_buf[0] == '1');
}
char profile_arg[strlen("--profile-file-fd=") + MAX_INT_LEN];
if (profile_fd != -1) {
sprintf(profile_arg, "--profile-file-fd=%d", profile_fd);
}
// Get the directory of the apk to pass as a base classpath directory.
char base_dir[arraysize("--classpath-dir=") + PKG_PATH_MAX];
std::string apk_dir(input_file_name);
unsigned long dir_index = apk_dir.rfind('/');
bool has_base_dir = dir_index != std::string::npos;
if (has_base_dir) {
apk_dir = apk_dir.substr(0, dir_index);
sprintf(base_dir, "--classpath-dir=%s", apk_dir.c_str());
}
ALOGV("Running %s in=%s out=%s\n", DEX2OAT_BIN, relative_input_file_name, output_file_name);
const char* argv[9 // program name, mandatory arguments and the final NULL
+ (have_dex2oat_isa_variant ? 1 : 0)
+ (have_dex2oat_isa_features ? 1 : 0)
+ (have_dex2oat_Xms_flag ? 2 : 0)
+ (have_dex2oat_Xmx_flag ? 2 : 0)
+ (have_dex2oat_compiler_filter_flag ? 1 : 0)
+ (have_dex2oat_threads_flag ? 1 : 0)
+ (have_dex2oat_swap_fd ? 1 : 0)
+ (have_dex2oat_image_fd ? 1 : 0)
+ (have_dex2oat_relocation_skip_flag ? 2 : 0)
+ (generate_debug_info ? 1 : 0)
+ (debuggable ? 1 : 0)
+ (have_app_image_format ? 1 : 0)
+ dex2oat_flags_count
+ (profile_fd == -1 ? 0 : 1)
+ (class_loader_context != nullptr ? 1 : 0)
+ (has_base_dir ? 1 : 0)
+ (have_dex2oat_large_app_threshold ? 1 : 0)];
int i = 0;
argv[i++] = DEX2OAT_BIN;
argv[i++] = zip_fd_arg;
argv[i++] = zip_location_arg;
argv[i++] = input_vdex_fd_arg;
argv[i++] = output_vdex_fd_arg;
argv[i++] = oat_fd_arg;
argv[i++] = oat_location_arg;
argv[i++] = instruction_set_arg;
if (have_dex2oat_isa_variant) {
argv[i++] = instruction_set_variant_arg;
}
if (have_dex2oat_isa_features) {
argv[i++] = instruction_set_features_arg;
}
if (have_dex2oat_Xms_flag) {
argv[i++] = RUNTIME_ARG;
argv[i++] = dex2oat_Xms_arg;
}
if (have_dex2oat_Xmx_flag) {
argv[i++] = RUNTIME_ARG;
argv[i++] = dex2oat_Xmx_arg;
}
if (have_dex2oat_compiler_filter_flag) {
argv[i++] = dex2oat_compiler_filter_arg;
}
if (have_dex2oat_threads_flag) {
argv[i++] = dex2oat_threads_arg;
}
if (have_dex2oat_swap_fd) {
argv[i++] = dex2oat_swap_fd;
}
if (have_dex2oat_image_fd) {
argv[i++] = dex2oat_image_fd;
}
if (generate_debug_info) {
argv[i++] = "--generate-debug-info";
}
if (debuggable) {
argv[i++] = "--debuggable";
}
if (have_app_image_format) {
argv[i++] = image_format_arg;
}
if (have_dex2oat_large_app_threshold) {
argv[i++] = dex2oat_large_app_threshold_arg;
}
if (dex2oat_flags_count) {
i += split(dex2oat_flags, argv + i);
}
if (have_dex2oat_relocation_skip_flag) {
argv[i++] = RUNTIME_ARG;
argv[i++] = dex2oat_norelocation;
}
if (profile_fd != -1) {
argv[i++] = profile_arg;
}
if (has_base_dir) {
argv[i++] = base_dir;
}
if (class_loader_context != nullptr) {
argv[i++] = class_loader_context_arg;
}
// Do not add after dex2oat_flags, they should override others for debugging.
argv[i] = NULL;
execv(DEX2OAT_BIN, (char * const *)argv);
ALOGE("execv(%s) failed: %s\n", DEX2OAT_BIN, strerror(errno));
}其中，参数zip_fd和oat_fd都是打开文件描述符，指向的分别是正在安装的APK文件和要生成的OAT文件。OAT文件的生成过程主要就是涉及到将包含在APK里面的classes.dex文件的DEX字节码翻译成本地机器指令。这相当于是编写一个输入文件为DEX、输出文件为OAT的编译器
当我们选择了ART运行时时，Zygote进程在启动的过程中，会调用libart.so里面的函数JNI_CreateJavaVM来创建一个ART
/Volumes/aosp/android-8.1.0_r52/art/runtime/java_vm_ext.cc
extern "C" jint JNI_CreateJavaVM(JavaVM** p_vm, JNIEnv** p_env, void* vm_args) {
ScopedTrace trace(__FUNCTION__);
const JavaVMInitArgs* args = static_cast<JavaVMInitArgs*>(vm_args);
if (JavaVMExt::IsBadJniVersion(args->version)) {
LOG(ERROR) << "Bad JNI version passed to CreateJavaVM: " << args->version;
return JNI_EVERSION;
}
RuntimeOptions options;
for (int i = 0; i < args->nOptions; ++i) {
JavaVMOption* option = &args->options[i];
options.push_back(std::make_pair(std::string(option->optionString), option->extraInfo));
}
bool ignore_unrecognized = args->ignoreUnrecognized;
if (!Runtime::Create(options, ignore_unrecognized)) {
return JNI_ERR;
}
// Initialize native loader. This step makes sure we have
// everything set up before we start using JNI.
android::InitializeNativeLoader();
Runtime* runtime = Runtime::Current();
bool started = runtime->Start();
if (!started) {
delete Thread::Current()->GetJniEnv();
delete runtime->GetJavaVM();
LOG(WARNING) << "CreateJavaVM failed";
return JNI_ERR;
}
*p_env = Thread::Current()->GetJniEnv();
*p_vm = runtime->GetJavaVM();
return JNI_OK;
}参数vm_args用作ART虚拟机的启动参数，它被转换为一个JavaVMInitArgs对象后，再按照Key-Value的组织形式保存一个Options向量中，并且以该向量作为参数传递给Runtime类的静态成员函数Create。
Runtime类的静态成员函数Create负责在进程中创建一个ART虚拟机。创建成功后，就调用Runtime类的另外一个静态成员函数Start启动该ART虚拟机。注意，这个创建ART虚拟的动作只会在Zygote进程中执行，SystemServer系统进程以及Android应用程序进程的ART虚拟机都是直接从Zygote进程fork出来共享的。这与Dalvik虚拟机的创建方式是完全一样的。
接下来我们就重点分析Runtime类的静态成员函数Create，它的实现如下所示
/Volumes/aosp/android-8.1.0_r52/art/runtime/runtime.cc
bool Runtime::Create(RuntimeArgumentMap&& runtime_options) {
// TODO: acquire a static mutex on Runtime to avoid racing.
if (Runtime::instance_ != nullptr) {
return false;
}
instance_ = new Runtime;
Locks::SetClientCallback(IsSafeToCallAbort);
if (!instance_->Init(std::move(runtime_options))) {
// TODO: Currently deleting the instance will abort the runtime on destruction. Now This will
// leak memory, instead. Fix the destructor. b/19100793.
// delete instance_;
instance_ = nullptr;
return false;
}
return true;
}instance_是Runtime类的静态成员变量，它指向进程中的一个Runtime单例。这个Runtime单例描述的就是当前进程的ART虚拟机实例。
函数首先判断当前进程是否已经创建有一个ART虚拟机实例了。如果有的话，函数就立即返回。否则的话，就创建一个ART虚拟机实例，并且保存在Runtime类的静态成员变量instance_中，最后调用Runtime类的成员函数Init对该新创建的ART虚拟机进行初始化。
Runtime类的成员函数Init的实现如下所示：
bool Runtime::Init(RuntimeArgumentMap&& runtime_options_in) {
// (b/30160149): protect subprocesses from modifications to LD_LIBRARY_PATH, etc.
// Take a snapshot of the environment at the time the runtime was created, for use by Exec, etc.
env_snapshot_.TakeSnapshot();
RuntimeArgumentMap runtime_options(std::move(runtime_options_in));
ScopedTrace trace(__FUNCTION__);
CHECK_EQ(sysconf(_SC_PAGE_SIZE), kPageSize);
MemMap::Init();
// Try to reserve a dedicated fault page. This is allocated for clobbered registers and sentinels.
// If we cannot reserve it, log a warning.
// Note: We allocate this first to have a good chance of grabbing the page. The address (0xebad..)
// is out-of-the-way enough that it should not collide with boot image mapping.
// Note: Don't request an error message. That will lead to a maps dump in the case of failure,
// leading to logspam.
{
constexpr uintptr_t kSentinelAddr =
RoundDown(static_cast<uintptr_t>(Context::kBadGprBase), kPageSize);
protected_fault_page_.reset(MemMap::MapAnonymous("Sentinel fault page",
reinterpret_cast<uint8_t*>(kSentinelAddr),
kPageSize,
PROT_NONE,
/* low_4g */ true,
/* reuse */ false,
/* error_msg */ nullptr));
if (protected_fault_page_ == nullptr) {
LOG(WARNING) << "Could not reserve sentinel fault page";
} else if (reinterpret_cast<uintptr_t>(protected_fault_page_->Begin()) != kSentinelAddr) {
LOG(WARNING) << "Could not reserve sentinel fault page at the right address.";
protected_fault_page_.reset();
}
}
using Opt = RuntimeArgumentMap;
VLOG(startup) << "Runtime::Init -verbose:startup enabled";
QuasiAtomic::Startup();
oat_file_manager_ = new OatFileManager;
Thread::SetSensitiveThreadHook(runtime_options.GetOrDefault(Opt::HookIsSensitiveThread));
Monitor::Init(runtime_options.GetOrDefault(Opt::LockProfThreshold),
runtime_options.GetOrDefault(Opt::StackDumpLockProfThreshold));
boot_class_path_string_ = runtime_options.ReleaseOrDefault(Opt::BootClassPath);
class_path_string_ = runtime_options.ReleaseOrDefault(Opt::ClassPath);
properties_ = runtime_options.ReleaseOrDefault(Opt::PropertiesList);
compiler_callbacks_ = runtime_options.GetOrDefault(Opt::CompilerCallbacksPtr);
patchoat_executable_ = runtime_options.ReleaseOrDefault(Opt::PatchOat);
must_relocate_ = runtime_options.GetOrDefault(Opt::Relocate);
is_zygote_ = runtime_options.Exists(Opt::Zygote);
is_explicit_gc_disabled_ = runtime_options.Exists(Opt::DisableExplicitGC);
dex2oat_enabled_ = runtime_options.GetOrDefault(Opt::Dex2Oat);
image_dex2oat_enabled_ = runtime_options.GetOrDefault(Opt::ImageDex2Oat);
dump_native_stack_on_sig_quit_ = runtime_options.GetOrDefault(Opt::DumpNativeStackOnSigQuit);
vfprintf_ = runtime_options.GetOrDefault(Opt::HookVfprintf);
exit_ = runtime_options.GetOrDefault(Opt::HookExit);
abort_ = runtime_options.GetOrDefault(Opt::HookAbort);
default_stack_size_ = runtime_options.GetOrDefault(Opt::StackSize);
use_tombstoned_traces_ = runtime_options.GetOrDefault(Opt::UseTombstonedTraces);
#if !defined(ART_TARGET_ANDROID)
CHECK(!use_tombstoned_traces_)
<< "-Xusetombstonedtraces is only supported in an Android environment";
#endif
stack_trace_file_ = runtime_options.ReleaseOrDefault(Opt::StackTraceFile);
compiler_executable_ = runtime_options.ReleaseOrDefault(Opt::Compiler);
compiler_options_ = runtime_options.ReleaseOrDefault(Opt::CompilerOptions);
for (StringPiece option : Runtime::Current()->GetCompilerOptions()) {
if (option.starts_with("--debuggable")) {
SetJavaDebuggable(true);
break;
}
}
image_compiler_options_ = runtime_options.ReleaseOrDefault(Opt::ImageCompilerOptions);
image_location_ = runtime_options.GetOrDefault(Opt::Image);
max_spins_before_thin_lock_inflation_ =
runtime_options.GetOrDefault(Opt::MaxSpinsBeforeThinLockInflation);
monitor_list_ = new MonitorList;
monitor_pool_ = MonitorPool::Create();
thread_list_ = new ThreadList(runtime_options.GetOrDefault(Opt::ThreadSuspendTimeout));
intern_table_ = new InternTable;
verify_ = runtime_options.GetOrDefault(Opt::Verify);
allow_dex_file_fallback_ = !runtime_options.Exists(Opt::NoDexFileFallback);
no_sig_chain_ = runtime_options.Exists(Opt::NoSigChain);
force_native_bridge_ = runtime_options.Exists(Opt::ForceNativeBridge);
Split(runtime_options.GetOrDefault(Opt::CpuAbiList), ',', &cpu_abilist_);
fingerprint_ = runtime_options.ReleaseOrDefault(Opt::Fingerprint);
if (runtime_options.GetOrDefault(Opt::Interpret)) {
GetInstrumentation()->ForceInterpretOnly();
}
zygote_max_failed_boots_ = runtime_options.GetOrDefault(Opt::ZygoteMaxFailedBoots);
experimental_flags_ = runtime_options.GetOrDefault(Opt::Experimental);
is_low_memory_mode_ = runtime_options.Exists(Opt::LowMemoryMode);
madvise_random_access_ = runtime_options.GetOrDefault(Opt::MadviseRandomAccess);
plugins_ = runtime_options.ReleaseOrDefault(Opt::Plugins);
agents_ = runtime_options.ReleaseOrDefault(Opt::AgentPath);
// TODO Add back in -agentlib
// for (auto lib : runtime_options.ReleaseOrDefault(Opt::AgentLib)) {
// agents_.push_back(lib);
// }
float foreground_heap_growth_multiplier;
if (is_low_memory_mode_ && !runtime_options.Exists(Opt::ForegroundHeapGrowthMultiplier)) {
// If low memory mode, use 1.0 as the multiplier by default.
foreground_heap_growth_multiplier = 1.0f;
} else {
foreground_heap_growth_multiplier =
runtime_options.GetOrDefault(Opt::ForegroundHeapGrowthMultiplier) +
kExtraDefaultHeapGrowthMultiplier;
}
XGcOption xgc_option = runtime_options.GetOrDefault(Opt::GcOption);
heap_ = new gc::Heap(runtime_options.GetOrDefault(Opt::MemoryInitialSize),
runtime_options.GetOrDefault(Opt::HeapGrowthLimit),
runtime_options.GetOrDefault(Opt::HeapMinFree),
runtime_options.GetOrDefault(Opt::HeapMaxFree),
runtime_options.GetOrDefault(Opt::HeapTargetUtilization),
foreground_heap_growth_multiplier,
runtime_options.GetOrDefault(Opt::MemoryMaximumSize),
runtime_options.GetOrDefault(Opt::NonMovingSpaceCapacity),
runtime_options.GetOrDefault(Opt::Image),
runtime_options.GetOrDefault(Opt::ImageInstructionSet),
// Override the collector type to CC if the read barrier config.
kUseReadBarrier ? gc::kCollectorTypeCC : xgc_option.collector_type_,
kUseReadBarrier ? BackgroundGcOption(gc::kCollectorTypeCCBackground)
: runtime_options.GetOrDefault(Opt::BackgroundGc),
runtime_options.GetOrDefault(Opt::LargeObjectSpace),
runtime_options.GetOrDefault(Opt::LargeObjectThreshold),
runtime_options.GetOrDefault(Opt::ParallelGCThreads),
runtime_options.GetOrDefault(Opt::ConcGCThreads),
runtime_options.Exists(Opt::LowMemoryMode),
runtime_options.GetOrDefault(Opt::LongPauseLogThreshold),
runtime_options.GetOrDefault(Opt::LongGCLogThreshold),
runtime_options.Exists(Opt::IgnoreMaxFootprint),
runtime_options.GetOrDefault(Opt::UseTLAB),
xgc_option.verify_pre_gc_heap_,
xgc_option.verify_pre_sweeping_heap_,
xgc_option.verify_post_gc_heap_,
xgc_option.verify_pre_gc_rosalloc_,
xgc_option.verify_pre_sweeping_rosalloc_,
xgc_option.verify_post_gc_rosalloc_,
xgc_option.gcstress_,
xgc_option.measure_,
runtime_options.GetOrDefault(Opt::EnableHSpaceCompactForOOM),
runtime_options.GetOrDefault(Opt::HSpaceCompactForOOMMinIntervalsMs));
if (!heap_->HasBootImageSpace() && !allow_dex_file_fallback_) {
LOG(ERROR) << "Dex file fallback disabled, cannot continue without image.";
return false;
}
dump_gc_performance_on_shutdown_ = runtime_options.Exists(Opt::DumpGCPerformanceOnShutdown);
if (runtime_options.Exists(Opt::JdwpOptions)) {
Dbg::ConfigureJdwp(runtime_options.GetOrDefault(Opt::JdwpOptions));
}
callbacks_->AddThreadLifecycleCallback(Dbg::GetThreadLifecycleCallback());
callbacks_->AddClassLoadCallback(Dbg::GetClassLoadCallback());
jit_options_.reset(jit::JitOptions::CreateFromRuntimeArguments(runtime_options));
if (IsAotCompiler()) {
// If we are already the compiler at this point, we must be dex2oat. Don't create the jit in
// this case.
// If runtime_options doesn't have UseJIT set to true then CreateFromRuntimeArguments returns
// null and we don't create the jit.
jit_options_->SetUseJitCompilation(false);
jit_options_->SetSaveProfilingInfo(false);
}
// Use MemMap arena pool for jit, malloc otherwise. Malloc arenas are faster to allocate but
// can't be trimmed as easily.
const bool use_malloc = IsAotCompiler();
arena_pool_.reset(new ArenaPool(use_malloc, /* low_4gb */ false));
jit_arena_pool_.reset(
new ArenaPool(/* use_malloc */ false, /* low_4gb */ false, "CompilerMetadata"));
if (IsAotCompiler() && Is64BitInstructionSet(kRuntimeISA)) {
// 4gb, no malloc. Explanation in header.
low_4gb_arena_pool_.reset(new ArenaPool(/* use_malloc */ false, /* low_4gb */ true));
}
linear_alloc_.reset(CreateLinearAlloc());
BlockSignals();
InitPlatformSignalHandlers();
// Change the implicit checks flags based on runtime architecture.
switch (kRuntimeISA) {
case kArm:
case kThumb2:
case kX86:
case kArm64:
case kX86_64:
case kMips:
case kMips64:
implicit_null_checks_ = true;
// Installing stack protection does not play well with valgrind.
implicit_so_checks_ = !(RUNNING_ON_MEMORY_TOOL && kMemoryToolIsValgrind);
break;
default:
// Keep the defaults.
break;
}
if (!no_sig_chain_) {
// Dex2Oat's Runtime does not need the signal chain or the fault handler.
if (implicit_null_checks_ || implicit_so_checks_ || implicit_suspend_checks_) {
fault_manager.Init();
// These need to be in a specific order. The null point check handler must be
// after the suspend check and stack overflow check handlers.
//
// Note: the instances attach themselves to the fault manager and are handled by it. The manager
// will delete the instance on Shutdown().
if (implicit_suspend_checks_) {
new SuspensionHandler(&fault_manager);
}
if (implicit_so_checks_) {
new StackOverflowHandler(&fault_manager);
}
if (implicit_null_checks_) {
new NullPointerHandler(&fault_manager);
}
if (kEnableJavaStackTraceHandler) {
new JavaStackTraceHandler(&fault_manager);
}
}
}
std::string error_msg;
java_vm_ = JavaVMExt::Create(this, runtime_options, &error_msg);
if (java_vm_.get() == nullptr) {
LOG(ERROR) << "Could not initialize JavaVMExt: " << error_msg;
return false;
}
// Add the JniEnv handler.
// TODO Refactor this stuff.
java_vm_->AddEnvironmentHook(JNIEnvExt::GetEnvHandler);
Thread::Startup();
// ClassLinker needs an attached thread, but we can't fully attach a thread without creating
// objects. We can't supply a thread group yet; it will be fixed later. Since we are the main
// thread, we do not get a java peer.
Thread* self = Thread::Attach("main", false, nullptr, false);
CHECK_EQ(self->GetThreadId(), ThreadList::kMainThreadId);
CHECK(self != nullptr);
self->SetCanCallIntoJava(!IsAotCompiler());
// Set us to runnable so tools using a runtime can allocate and GC by default
self->TransitionFromSuspendedToRunnable();
// Now we're attached, we can take the heap locks and validate the heap.
GetHeap()->EnableObjectValidation();
CHECK_GE(GetHeap()->GetContinuousSpaces().size(), 1U);
if (UNLIKELY(IsAotCompiler())) {
class_linker_ = new AotClassLinker(intern_table_);
} else {
class_linker_ = new ClassLinker(intern_table_);
}
if (GetHeap()->HasBootImageSpace()) {
bool result = class_linker_->InitFromBootImage(&error_msg);
if (!result) {
LOG(ERROR) << "Could not initialize from image: " << error_msg;
return false;
}
if (kIsDebugBuild) {
for (auto image_space : GetHeap()->GetBootImageSpaces()) {
image_space->VerifyImageAllocations();
}
}
if (boot_class_path_string_.empty()) {
// The bootclasspath is not explicitly specified: construct it from the loaded dex files.
const std::vector<const DexFile*>& boot_class_path = GetClassLinker()->GetBootClassPath();
std::vector<std::string> dex_locations;
dex_locations.reserve(boot_class_path.size());
for (const DexFile* dex_file : boot_class_path) {
dex_locations.push_back(dex_file->GetLocation());
}
boot_class_path_string_ = android::base::Join(dex_locations, ':');
}
{
ScopedTrace trace2("AddImageStringsToTable");
GetInternTable()->AddImagesStringsToTable(heap_->GetBootImageSpaces());
}
if (IsJavaDebuggable()) {
// Now that we have loaded the boot image, deoptimize its methods if we are running
// debuggable, as the code may have been compiled non-debuggable.
DeoptimizeBootImage();
}
} else {
std::vector<std::string> dex_filenames;
Split(boot_class_path_string_, ':', &dex_filenames);
std::vector<std::string> dex_locations;
if (!runtime_options.Exists(Opt::BootClassPathLocations)) {
dex_locations = dex_filenames;
} else {
dex_locations = runtime_options.GetOrDefault(Opt::BootClassPathLocations);
CHECK_EQ(dex_filenames.size(), dex_locations.size());
}
std::vector<std::unique_ptr<const DexFile>> boot_class_path;
if (runtime_options.Exists(Opt::BootClassPathDexList)) {
boot_class_path.swap(*runtime_options.GetOrDefault(Opt::BootClassPathDexList));
} else {
OpenDexFiles(dex_filenames,
dex_locations,
runtime_options.GetOrDefault(Opt::Image),
&boot_class_path);
}
instruction_set_ = runtime_options.GetOrDefault(Opt::ImageInstructionSet);
if (!class_linker_->InitWithoutImage(std::move(boot_class_path), &error_msg)) {
LOG(ERROR) << "Could not initialize without image: " << error_msg;
return false;
}
// TODO: Should we move the following to InitWithoutImage?
SetInstructionSet(instruction_set_);
for (uint32_t i = 0; i < kCalleeSaveSize; i++) {
CalleeSaveType type = CalleeSaveType(i);
if (!HasCalleeSaveMethod(type)) {
SetCalleeSaveMethod(CreateCalleeSaveMethod(), type);
}
}
}
CHECK(class_linker_ != nullptr);
verifier::MethodVerifier::Init();
if (runtime_options.Exists(Opt::MethodTrace)) {
trace_config_.reset(new TraceConfig());
trace_config_->trace_file = runtime_options.ReleaseOrDefault(Opt::MethodTraceFile);
trace_config_->trace_file_size = runtime_options.ReleaseOrDefault(Opt::MethodTraceFileSize);
trace_config_->trace_mode = Trace::TraceMode::kMethodTracing;
trace_config_->trace_output_mode = runtime_options.Exists(Opt::MethodTraceStreaming) ?
Trace::TraceOutputMode::kStreaming :
Trace::TraceOutputMode::kFile;
}
// TODO: move this to just be an Trace::Start argument
Trace::SetDefaultClockSource(runtime_options.GetOrDefault(Opt::ProfileClock));
// Pre-allocate an OutOfMemoryError for the double-OOME case.
self->ThrowNewException("Ljava/lang/OutOfMemoryError;",
"OutOfMemoryError thrown while trying to throw OutOfMemoryError; "
"no stack trace available");
pre_allocated_OutOfMemoryError_ = GcRoot<mirror::Throwable>....
......}
创建好ART虚拟机堆后，Runtime类的成员函数Init接着又创建了一个JavaVMExt实例。这个JavaVMExt实例最终是要返回给调用者的，使得调用者可以通过该JavaVMExt实例来和ART虚拟机交互。再接下来，Runtime类的成员函数Init通过Thread类的成员函数Attach将当前线程作为ART虚拟机的主线程，使得当前线程可以调用ART虚拟机提供的JNI接口
Runtime类的成员函数GetHeap返回的便是当前ART虚拟机的堆，也就是前面创建的ART虚拟机堆。通过调用Heap类的成员函数GetContinuousSpaces可以获得堆里面的连续空间列表。如果这个列表的第一个连续空间是一个Image空间，那么就调用ClassLinker类的静态成员函数CreateFromImage来创建一个ClassLinker对象。否则的话，上述ClassLinker对象就要通过ClassLinker类的另外一个静态成员函数CreateFromCompiler来创建。创建出来的ClassLinker对象是后面ART虚拟机加载加载Java类时要用到的。
后面我们分析ART虚拟机的垃圾收集机制时会看到，ART虚拟机的堆包含有三个连续空间和一个不连续空间。三个连续空间分别用来分配不同的对象。当第一个连续空间不是Image空间时，就表明当前进程不是Zygote进程，而是安装应用程序时启动的一个dex2oat进程。安装应用程序时启动的dex2oat进程也会在内部创建一个ART虚拟机，不过这个ART虚拟机是用来将DEX字节码编译成本地机器指令的，而Zygote进程创建的ART虚拟机是用来运行应用程序的。
接下来我们主要分析ParsedOptions类的静态成员函数Create和ART虚拟机堆Heap的构造函数，以便可以了解ART虚拟机的启动参数解析过程和ART虚拟机的堆创建过程。
Heap类的构造函数的