Android系统启动之zyogte进程

image.png

目录

第一篇：Android系统启动之bootloader
第二篇：Android系统启动之Init流程(上)
第三篇：Android系统启动之Init流程(下)
第四篇：Android系统启动之init.rc文件解析过程
第五篇：Android系统启动之zyogte进程

zyogte进程

ygote进程在android系统中有着及其中要的位置.
可以说android系统中的进程都是有zygote孵化出来的, 所有应用进程都是zygote的子进程.
参考图片：

image.png

init进启动zygote服务，zygote进程再启动其他进程．
首先，分析一下zygote服务的init.rc是如何执行的.

从init.rc文件启动zyogte进程

首先我们先来看下init.rc文件:（路径为:system/core/rootdir）
其中有这么一句话:

import /init.${ro.zygote}.rc

将同目录下的init.zyogtexx.rc文件加载．

为什么是四个文件

文件	含义
init.zygote32.rc	zygote 进程对应的执行程序是 app_process (纯 32bit 模式)
init.zygote64.rc	zygote 进程对应的执行程序是 app_process64 (纯 64bit 模式)
init.zygote32_64.rc	启动两个 zygote 进程 (名为 zygote 和 zygote_secondary)，对应的执行程序分别是 app_process32 (主模式)、app_process64
init.zygote64_32.rc	启动两个 zygote 进程 (名为 zygote 和 zygote_secondary)，对应的执行程序分别是 app_process64 (主模式)、app_process32

以init.zygote64.rc为例：

service zygote /system/bin/app_process64 -Xzygote /system/bin --zygote --start-system-server
    class main
    priority -20
    user root
    group root readproc
    socket zygote stream 660 root system
    onrestart write /sys/android_power/request_state wake
    onrestart write /sys/power/state on
    onrestart restart audioserver
    onrestart restart cameraserver
    onrestart restart media
    onrestart restart netd
    onrestart restart wificond
    writepid /dev/cpuset/foreground/tasks

找到了zygote的启动设定，再来看下它的启动事件：
文件system/core/rootdir/init.rc

# It is recommended to put unnecessary data/ initialization from post-fs-data
# to start-zygote in device's init.rc to unblock zygote start.
on zygote-start && property:ro.crypto.state=unencrypted
    # A/B update verifier that marks a successful boot.
    exec_start update_verifier_nonencrypted
    start netd
    start zygote
    start zygote_secondary

on zygote-start && property:ro.crypto.state=unsupported
    # A/B update verifier that marks a successful boot.
    exec_start update_verifier_nonencrypted
    start netd
    start zygote
    start zygote_secondary

on zygote-start && property:ro.crypto.state=encrypted && property:ro.crypto.type=file
    # A/B update verifier that marks a successful boot.
    exec_start update_verifier_nonencrypted
    start netd
    start zygote
    start zygote_secondary

继续反向推理，发现zygote-start 的触发是在on late-init中：

image.png

那么late-init 在哪儿触发的呢？
在init.cpp中main函数中可以看到：

image.png

这样就启动了zyogte进程．Ｏ（∩＿∩）Ｏ哈哈～

app_process

从上文的rc文件可以知道，zyogte进程的原型是/system/bin/app_process64
代码路径为：rameworks/base/cmds/app_process

先来看下mk文件：

LOCAL_PATH:= $(call my-dir)

app_process_common_shared_libs := \
    libandroid_runtime \
    libbinder \
    libcutils \
    libdl \
    libhwbinder \
    liblog \
    libnativeloader \
    libutils \

# This is a list of libraries that need to be included in order to avoid
# bad apps. This prevents a library from having a mismatch when resolving
# new/delete from an app shared library.
# See b/21032018 for more details.
app_process_common_shared_libs += \
    libwilhelm \

app_process_common_static_libs := \
    libsigchain \

app_process_src_files := \
    app_main.cpp \

app_process_cflags := \
    -Wall -Werror -Wunused -Wunreachable-code

app_process_ldflags_32 := \
    -Wl,--version-script,art/sigchainlib/version-script32.txt -Wl,--export-dynamic
app_process_ldflags_64 := \
    -Wl,--version-script,art/sigchainlib/version-script64.txt -Wl,--export-dynamic

include $(CLEAR_VARS)

LOCAL_SRC_FILES:= $(app_process_src_files)

LOCAL_LDFLAGS_32 := $(app_process_ldflags_32)
LOCAL_LDFLAGS_64 := $(app_process_ldflags_64)

LOCAL_SHARED_LIBRARIES := $(app_process_common_shared_libs)

LOCAL_WHOLE_STATIC_LIBRARIES := $(app_process_common_static_libs)

LOCAL_MODULE:= app_process
LOCAL_MULTILIB := both
LOCAL_MODULE_STEM_32 := app_process32
LOCAL_MODULE_STEM_64 := app_process64

LOCAL_CFLAGS += $(app_process_cflags)

# In SANITIZE_LITE mode, we create the sanitized binary in a separate location (but reuse
# the same module). Using the same module also works around an issue with make: binaries
# that depend on sanitized libraries will be relinked, even if they set LOCAL_SANITIZE := never.
#
# Also pull in the asanwrapper helper.
ifeq ($(SANITIZE_LITE),true)
LOCAL_MODULE_PATH := $(TARGET_OUT_EXECUTABLES)/asan
LOCAL_REQUIRED_MODULES := asanwrapper
endif

include $(BUILD_EXECUTABLE)

# Create a symlink from app_process to app_process32 or 64
# depending on the target configuration.
ifneq ($(SANITIZE_LITE),true)
include  $(BUILD_SYSTEM)/executable_prefer_symlink.mk
endif

从Android.mk文件可以看出，app_process程序的来源就是文件app_main.cpp.

代码文件app_main.cpp就是zyogte进程的源码．

zyogte进程功能解析

zyogte进程大致有两个功能：

1. zygote模式，也就是初始化zygote进程.
2. application模式，也就是启动普通应用程序.

下面来分析一下app_main源文件的main函数：

int main(int argc, char* const argv[])
{
//*******************************************************************
//                       解析参数
//*******************************************************************
    if (!LOG_NDEBUG) {
      String8 argv_String;
      for (int i = 0; i < argc; ++i) {
        argv_String.append("\"");
        argv_String.append(argv[i]);
        argv_String.append("\" ");
      }
      ALOGV("app_process main with argv: %s", argv_String.string());
    }

    AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv));
    // Process command line arguments
    // ignore argv[0]
    argc--;
    argv++;

    // Everything up to '--' or first non '-' arg goes to the vm.
    //
    // The first argument after the VM args is the "parent dir", which
    // is currently unused.
    //
    // After the parent dir, we expect one or more the following internal
    // arguments :
    //
    // --zygote : Start in zygote mode
    // --start-system-server : Start the system server.
    // --application : Start in application (stand alone, non zygote) mode.
    // --nice-name : The nice name for this process.
    //
    // For non zygote starts, these arguments will be followed by
    // the main class name. All remaining arguments are passed to
    // the main method of this class.
    //
    // For zygote starts, all remaining arguments are passed to the zygote.
    // main function.
    //
    // Note that we must copy argument string values since we will rewrite the
    // entire argument block when we apply the nice name to argv0.
    //
    // As an exception to the above rule, anything in "spaced commands"
    // goes to the vm even though it has a space in it.
    const char* spaced_commands[] = { "-cp", "-classpath" };
    // Allow "spaced commands" to be succeeded by exactly 1 argument (regardless of -s).
    bool known_command = false;

    int i;
    for (i = 0; i < argc; i++) {
        if (known_command == true) {
          runtime.addOption(strdup(argv[i]));
          ALOGV("app_process main add known option '%s'", argv[i]);
          known_command = false;
          continue;
        }

        for (int j = 0;
             j < static_cast<int>(sizeof(spaced_commands) / sizeof(spaced_commands[0]));
             ++j) {
          if (strcmp(argv[i], spaced_commands[j]) == 0) {
            known_command = true;
            ALOGV("app_process main found known command '%s'", argv[i]);
          }
        }

        if (argv[i][0] != '-') {
            break;
        }
        if (argv[i][1] == '-' && argv[i][2] == 0) {
            ++i; // Skip --.
            break;
        }

        runtime.addOption(strdup(argv[i]));
        ALOGV("app_process main add option '%s'", argv[i]);
    }
//*******************************************************************
//                       根据参数选择模式
//　1.--zygote                 zygote模式
// 2.--start-system-server　   启动一个系统服务（app模式）
//　3.--application            启动application（app模式）
// 4.--nice-name=             修改名字（app模式）
//*******************************************************************
    // Parse runtime arguments.  Stop at first unrecognized option.
    bool zygote = false;
    bool startSystemServer = false;
    bool application = false;
    String8 niceName;
    String8 className;

    ++i;  // Skip unused "parent dir" argument.
    while (i < argc) {
        const char* arg = argv[i++];
        if (strcmp(arg, "--zygote") == 0) {
            zygote = true;
            niceName = ZYGOTE_NICE_NAME;
        } else if (strcmp(arg, "--start-system-server") == 0) {
            startSystemServer = true;
        } else if (strcmp(arg, "--application") == 0) {
            application = true;
        } else if (strncmp(arg, "--nice-name=", 12) == 0) {
            niceName.setTo(arg + 12);
        } else if (strncmp(arg, "--", 2) != 0) {
            className.setTo(arg);
            break;
        } else {
            --i;
            break;
        }
    }

    Vector<String8> args;
//*******************************************************************
//                       application模式
//*******************************************************************
    if (!className.isEmpty()) {
        // We're not in zygote mode, the only argument we need to pass
        // to RuntimeInit is the application argument.
        //
        // The Remainder of args get passed to startup class main(). Make
        // copies of them before we overwrite them with the process name.
        args.add(application ? String8("application") : String8("tool"));
        runtime.setClassNameAndArgs(className, argc - i, argv + i);

        if (!LOG_NDEBUG) {
          String8 restOfArgs;
          char* const* argv_new = argv + i;
          int argc_new = argc - i;
          for (int k = 0; k < argc_new; ++k) {
            restOfArgs.append("\"");
            restOfArgs.append(argv_new[k]);
            restOfArgs.append("\" ");
          }
          ALOGV("Class name = %s, args = %s", className.string(), restOfArgs.string());
        }
    } else {
//*******************************************************************
//                       zygote模式
//*******************************************************************
        // We're in zygote mode.
        maybeCreateDalvikCache();

        if (startSystemServer) {
            args.add(String8("start-system-server"));
        }

        char prop[PROP_VALUE_MAX];
        if (property_get(ABI_LIST_PROPERTY, prop, NULL) == 0) {
            LOG_ALWAYS_FATAL("app_process: Unable to determine ABI list from property %s.",
                ABI_LIST_PROPERTY);
            return 11;
        }

        String8 abiFlag("--abi-list=");
        abiFlag.append(prop);
        args.add(abiFlag);

        // In zygote mode, pass all remaining arguments to the zygote
        // main() method.
        for (; i < argc; ++i) {
            args.add(String8(argv[i]));
        }
    }

    if (!niceName.isEmpty()) {
        runtime.setArgv0(niceName.string(), true /* setProcName */);
    }

    if (zygote) {
        runtime.start("com.android.internal.os.ZygoteInit", args, zygote);
    } else if (className) {
        runtime.start("com.android.internal.os.RuntimeInit", args, zygote);
    } else {
        fprintf(stderr, "Error: no class name or --zygote supplied.\n");
        app_usage();
        LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied.");
    }
}

加了一点注释Ｏ（∩＿∩）Ｏ哈哈～
代码最后的runtime.start函数，就是要启动虚拟机了.

  if (zygote) {
//zygote模式
        runtime.start("com.android.internal.os.ZygoteInit", args, zygote);
    } else if (className) {
//app模式
        runtime.start("com.android.internal.os.RuntimeInit", args, zygote);
    } else {
        fprintf(stderr, "Error: no class name or --zygote supplied.\n");
        app_usage();
        LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied.");
    }

runtime是AndroidRuntime类的对象．
这个类的实现在文件：frameworks/base/core/jni/AndroidRuntime.cpp中：

AndroidRuntime类

start函数中主要分为两部

1. 初始化jni
2. 启动虚拟机
   代码：

oid AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote)
{

    ...

    /* start the virtual machine */
//**********************************************
//                   初始化JNI
//***********************************************
    JniInvocation jni_invocation;
    jni_invocation.Init(NULL);
    JNIEnv* env;
//**********************************************
//                  启动虚拟机
//***********************************************
    if (startVm(&mJavaVM, &env, zygote) != 0) {
        return;
    }
    onVmCreated(env);
    ... 
}

启动虚拟机

/*
 * Start the Dalvik Virtual Machine.
 *
 * Various arguments, most determined by system properties, are passed in.
 * The "mOptions" vector is updated.
 *
 * CAUTION: when adding options in here, be careful not to put the
 * char buffer inside a nested scope.  Adding the buffer to the
 * options using mOptions.add() does not copy the buffer, so if the
 * buffer goes out of scope the option may be overwritten.  It's best
 * to put the buffer at the top of the function so that it is more
 * unlikely that someone will surround it in a scope at a later time
 * and thus introduce a bug.
 *
 * Returns 0 on success.
 */
int AndroidRuntime::startVm(JavaVM** pJavaVM, JNIEnv** pEnv, bool zygote)
{
    JavaVMInitArgs initArgs;
    char propBuf[PROPERTY_VALUE_MAX];
    char stackTraceFileBuf[sizeof("-Xstacktracefile:")-1 + PROPERTY_VALUE_MAX];
    char jniOptsBuf[sizeof("-Xjniopts:")-1 + PROPERTY_VALUE_MAX];
    char heapstartsizeOptsBuf[sizeof("-Xms")-1 + PROPERTY_VALUE_MAX];
    char heapsizeOptsBuf[sizeof("-Xmx")-1 + PROPERTY_VALUE_MAX];
    char heapgrowthlimitOptsBuf[sizeof("-XX:HeapGrowthLimit=")-1 + PROPERTY_VALUE_MAX];
    char heapminfreeOptsBuf[sizeof("-XX:HeapMinFree=")-1 + PROPERTY_VALUE_MAX];
    char heapmaxfreeOptsBuf[sizeof("-XX:HeapMaxFree=")-1 + PROPERTY_VALUE_MAX];
    char usejitOptsBuf[sizeof("-Xusejit:")-1 + PROPERTY_VALUE_MAX];
    char jitmaxsizeOptsBuf[sizeof("-Xjitmaxsize:")-1 + PROPERTY_VALUE_MAX];
    char jitinitialsizeOptsBuf[sizeof("-Xjitinitialsize:")-1 + PROPERTY_VALUE_MAX];
    char jitthresholdOptsBuf[sizeof("-Xjitthreshold:")-1 + PROPERTY_VALUE_MAX];
    char useJitProfilesOptsBuf[sizeof("-Xjitsaveprofilinginfo:")-1 + PROPERTY_VALUE_MAX];
    char jitprithreadweightOptBuf[sizeof("-Xjitprithreadweight:")-1 + PROPERTY_VALUE_MAX];
    char jittransitionweightOptBuf[sizeof("-Xjittransitionweight:")-1 + PROPERTY_VALUE_MAX];
    char gctypeOptsBuf[sizeof("-Xgc:")-1 + PROPERTY_VALUE_MAX];
    char backgroundgcOptsBuf[sizeof("-XX:BackgroundGC=")-1 + PROPERTY_VALUE_MAX];
    char heaptargetutilizationOptsBuf[sizeof("-XX:HeapTargetUtilization=")-1 + PROPERTY_VALUE_MAX];
    char cachePruneBuf[sizeof("-Xzygote-max-boot-retry=")-1 + PROPERTY_VALUE_MAX];
    char dex2oatXmsImageFlagsBuf[sizeof("-Xms")-1 + PROPERTY_VALUE_MAX];
    char dex2oatXmxImageFlagsBuf[sizeof("-Xmx")-1 + PROPERTY_VALUE_MAX];
    char dex2oatXmsFlagsBuf[sizeof("-Xms")-1 + PROPERTY_VALUE_MAX];
    char dex2oatXmxFlagsBuf[sizeof("-Xmx")-1 + PROPERTY_VALUE_MAX];
    char dex2oatCompilerFilterBuf[sizeof("--compiler-filter=")-1 + PROPERTY_VALUE_MAX];
    char dex2oatImageCompilerFilterBuf[sizeof("--compiler-filter=")-1 + PROPERTY_VALUE_MAX];
    char dex2oatThreadsBuf[sizeof("-j")-1 + PROPERTY_VALUE_MAX];
    char dex2oatThreadsImageBuf[sizeof("-j")-1 + PROPERTY_VALUE_MAX];
    char dex2oat_isa_variant_key[PROPERTY_KEY_MAX];
    char dex2oat_isa_variant[sizeof("--instruction-set-variant=") -1 + PROPERTY_VALUE_MAX];
    char dex2oat_isa_features_key[PROPERTY_KEY_MAX];
    char dex2oat_isa_features[sizeof("--instruction-set-features=") -1 + PROPERTY_VALUE_MAX];
    char dex2oatFlagsBuf[PROPERTY_VALUE_MAX];
    char dex2oatImageFlagsBuf[PROPERTY_VALUE_MAX];
    char extraOptsBuf[PROPERTY_VALUE_MAX];
    char voldDecryptBuf[PROPERTY_VALUE_MAX];
    enum {
      kEMDefault,
      kEMIntPortable,
      kEMIntFast,
      kEMJitCompiler,
    } executionMode = kEMDefault;
    char localeOption[sizeof("-Duser.locale=") + PROPERTY_VALUE_MAX];
    char lockProfThresholdBuf[sizeof("-Xlockprofthreshold:")-1 + PROPERTY_VALUE_MAX];
    char nativeBridgeLibrary[sizeof("-XX:NativeBridge=") + PROPERTY_VALUE_MAX];
    char cpuAbiListBuf[sizeof("--cpu-abilist=") + PROPERTY_VALUE_MAX];
    char methodTraceFileBuf[sizeof("-Xmethod-trace-file:") + PROPERTY_VALUE_MAX];
    char methodTraceFileSizeBuf[sizeof("-Xmethod-trace-file-size:") + PROPERTY_VALUE_MAX];
    char fingerprintBuf[sizeof("-Xfingerprint:") + PROPERTY_VALUE_MAX];

    bool checkJni = false;
    property_get("dalvik.vm.checkjni", propBuf, "");
    if (strcmp(propBuf, "true") == 0) {
        checkJni = true;
    } else if (strcmp(propBuf, "false") != 0) {
        /* property is neither true nor false; fall back on kernel parameter */
        property_get("ro.kernel.android.checkjni", propBuf, "");
        if (propBuf[0] == '1') {
            checkJni = true;
        }
    }
    ALOGV("CheckJNI is %s\n", checkJni ? "ON" : "OFF");
    if (checkJni) {
        /* extended JNI checking */
        addOption("-Xcheck:jni");

        /* with -Xcheck:jni, this provides a JNI function call trace */
        //addOption("-verbose:jni");
    }

    property_get("dalvik.vm.execution-mode", propBuf, "");
    if (strcmp(propBuf, "int:portable") == 0) {
        executionMode = kEMIntPortable;
    } else if (strcmp(propBuf, "int:fast") == 0) {
        executionMode = kEMIntFast;
    } else if (strcmp(propBuf, "int:jit") == 0) {
        executionMode = kEMJitCompiler;
    }

    parseRuntimeOption("dalvik.vm.stack-trace-file", stackTraceFileBuf, "-Xstacktracefile:");

    strcpy(jniOptsBuf, "-Xjniopts:");
    if (parseRuntimeOption("dalvik.vm.jniopts", jniOptsBuf, "-Xjniopts:")) {
        ALOGI("JNI options: '%s'\n", jniOptsBuf);
    }

    /* route exit() to our handler */
    addOption("exit", (void*) runtime_exit);

    /* route fprintf() to our handler */
    addOption("vfprintf", (void*) runtime_vfprintf);

    /* register the framework-specific "is sensitive thread" hook */
    addOption("sensitiveThread", (void*) runtime_isSensitiveThread);

    /* enable verbose; standard options are { jni, gc, class } */
    //addOption("-verbose:jni");
    addOption("-verbose:gc");
    //addOption("-verbose:class");

    /*
     * The default starting and maximum size of the heap.  Larger
     * values should be specified in a product property override.
     */
    parseRuntimeOption("dalvik.vm.heapstartsize", heapstartsizeOptsBuf, "-Xms", "4m");
    parseRuntimeOption("dalvik.vm.heapsize", heapsizeOptsBuf, "-Xmx", "16m");

    parseRuntimeOption("dalvik.vm.heapgrowthlimit", heapgrowthlimitOptsBuf, "-XX:HeapGrowthLimit=");
    parseRuntimeOption("dalvik.vm.heapminfree", heapminfreeOptsBuf, "-XX:HeapMinFree=");
    parseRuntimeOption("dalvik.vm.heapmaxfree", heapmaxfreeOptsBuf, "-XX:HeapMaxFree=");
    parseRuntimeOption("dalvik.vm.heaptargetutilization",
                       heaptargetutilizationOptsBuf,
                       "-XX:HeapTargetUtilization=");

    /*
     * JIT related options.
     */
    parseRuntimeOption("dalvik.vm.usejit", usejitOptsBuf, "-Xusejit:");
    parseRuntimeOption("dalvik.vm.jitmaxsize", jitmaxsizeOptsBuf, "-Xjitmaxsize:");
    parseRuntimeOption("dalvik.vm.jitinitialsize", jitinitialsizeOptsBuf, "-Xjitinitialsize:");
    parseRuntimeOption("dalvik.vm.jitthreshold", jitthresholdOptsBuf, "-Xjitthreshold:");
    property_get("dalvik.vm.usejitprofiles", useJitProfilesOptsBuf, "");
    if (strcmp(useJitProfilesOptsBuf, "true") == 0) {
        addOption("-Xjitsaveprofilinginfo");
    }

    parseRuntimeOption("dalvik.vm.jitprithreadweight",
                       jitprithreadweightOptBuf,
                       "-Xjitprithreadweight:");

    parseRuntimeOption("dalvik.vm.jittransitionweight",
                       jittransitionweightOptBuf,
                       "-Xjittransitionweight:");

    property_get("ro.config.low_ram", propBuf, "");
    if (strcmp(propBuf, "true") == 0) {
      addOption("-XX:LowMemoryMode");
    }

    parseRuntimeOption("dalvik.vm.gctype", gctypeOptsBuf, "-Xgc:");
    parseRuntimeOption("dalvik.vm.backgroundgctype", backgroundgcOptsBuf, "-XX:BackgroundGC=");

    /*
     * Enable debugging only for apps forked from zygote.
     * Set suspend=y to pause during VM init and use android ADB transport.
     */
    if (zygote) {
      addOption("-agentlib:jdwp=transport=dt_android_adb,suspend=n,server=y");
    }

    parseRuntimeOption("dalvik.vm.lockprof.threshold",
                       lockProfThresholdBuf,
                       "-Xlockprofthreshold:");

    if (executionMode == kEMIntPortable) {
        addOption("-Xint:portable");
    } else if (executionMode == kEMIntFast) {
        addOption("-Xint:fast");
    } else if (executionMode == kEMJitCompiler) {
        addOption("-Xint:jit");
    }

    // If we are booting without the real /data, don't spend time compiling.
    property_get("vold.decrypt", voldDecryptBuf, "");
    bool skip_compilation = ((strcmp(voldDecryptBuf, "trigger_restart_min_framework") == 0) ||
                             (strcmp(voldDecryptBuf, "1") == 0));

    // Extra options for boot.art/boot.oat image generation.
    parseCompilerRuntimeOption("dalvik.vm.image-dex2oat-Xms", dex2oatXmsImageFlagsBuf,
                               "-Xms", "-Ximage-compiler-option");
    parseCompilerRuntimeOption("dalvik.vm.image-dex2oat-Xmx", dex2oatXmxImageFlagsBuf,
                               "-Xmx", "-Ximage-compiler-option");
    if (skip_compilation) {
        addOption("-Ximage-compiler-option");
        addOption("--compiler-filter=assume-verified");
    } else {
        parseCompilerOption("dalvik.vm.image-dex2oat-filter", dex2oatImageCompilerFilterBuf,
                            "--compiler-filter=", "-Ximage-compiler-option");
    }

    // Make sure there is a preloaded-classes file.
    if (!hasFile("/system/etc/preloaded-classes")) {
        ALOGE("Missing preloaded-classes file, /system/etc/preloaded-classes not found: %s\n",
              strerror(errno));
        return -1;
    }
    addOption("-Ximage-compiler-option");
    addOption("--image-classes=/system/etc/preloaded-classes");

    // If there is a compiled-classes file, push it.
    if (hasFile("/system/etc/compiled-classes")) {
        addOption("-Ximage-compiler-option");
        addOption("--compiled-classes=/system/etc/compiled-classes");
    }

    property_get("dalvik.vm.image-dex2oat-flags", dex2oatImageFlagsBuf, "");
    parseExtraOpts(dex2oatImageFlagsBuf, "-Ximage-compiler-option");

    // Extra options for DexClassLoader.
    parseCompilerRuntimeOption("dalvik.vm.dex2oat-Xms", dex2oatXmsFlagsBuf,
                               "-Xms", "-Xcompiler-option");
    parseCompilerRuntimeOption("dalvik.vm.dex2oat-Xmx", dex2oatXmxFlagsBuf,
                               "-Xmx", "-Xcompiler-option");
    if (skip_compilation) {
        addOption("-Xcompiler-option");
        addOption("--compiler-filter=assume-verified");

        // We skip compilation when a minimal runtime is brought up for decryption. In that case
        // /data is temporarily backed by a tmpfs, which is usually small.
        // If the system image contains prebuilts, they will be relocated into the tmpfs. In this
        // specific situation it is acceptable to *not* relocate and run out of the prebuilts
        // directly instead.
        addOption("--runtime-arg");
        addOption("-Xnorelocate");
    } else {
        parseCompilerOption("dalvik.vm.dex2oat-filter", dex2oatCompilerFilterBuf,
                            "--compiler-filter=", "-Xcompiler-option");
    }
    parseCompilerOption("dalvik.vm.dex2oat-threads", dex2oatThreadsBuf, "-j", "-Xcompiler-option");
    parseCompilerOption("dalvik.vm.image-dex2oat-threads", dex2oatThreadsImageBuf, "-j",
                        "-Ximage-compiler-option");

    // The runtime will compile a boot image, when necessary, not using installd. Thus, we need to
    // pass the instruction-set-features/variant as an image-compiler-option.
    // TODO: Find a better way for the instruction-set.
#if defined(__arm__)
    constexpr const char* instruction_set = "arm";
#elif defined(__aarch64__)
    constexpr const char* instruction_set = "arm64";
#elif defined(__mips__) && !defined(__LP64__)
    constexpr const char* instruction_set = "mips";
#elif defined(__mips__) && defined(__LP64__)
    constexpr const char* instruction_set = "mips64";
#elif defined(__i386__)
    constexpr const char* instruction_set = "x86";
#elif defined(__x86_64__)
    constexpr const char* instruction_set = "x86_64";
#else
    constexpr const char* instruction_set = "unknown";
#endif
    // Note: it is OK to reuse the buffer, as the values are exactly the same between
    //       * compiler-option, used for runtime compilation (DexClassLoader)
    //       * image-compiler-option, used for boot-image compilation on device

    // Copy the variant.
    sprintf(dex2oat_isa_variant_key, "dalvik.vm.isa.%s.variant", instruction_set);
    parseCompilerOption(dex2oat_isa_variant_key, dex2oat_isa_variant,
                        "--instruction-set-variant=", "-Ximage-compiler-option");
    parseCompilerOption(dex2oat_isa_variant_key, dex2oat_isa_variant,
                        "--instruction-set-variant=", "-Xcompiler-option");
    // Copy the features.
    sprintf(dex2oat_isa_features_key, "dalvik.vm.isa.%s.features", instruction_set);
    parseCompilerOption(dex2oat_isa_features_key, dex2oat_isa_features,
                        "--instruction-set-features=", "-Ximage-compiler-option");
    parseCompilerOption(dex2oat_isa_features_key, dex2oat_isa_features,
                        "--instruction-set-features=", "-Xcompiler-option");


    property_get("dalvik.vm.dex2oat-flags", dex2oatFlagsBuf, "");
    parseExtraOpts(dex2oatFlagsBuf, "-Xcompiler-option");

    /* extra options; parse this late so it overrides others */
    property_get("dalvik.vm.extra-opts", extraOptsBuf, "");
    parseExtraOpts(extraOptsBuf, NULL);

    /* Set the properties for locale */
    {
        strcpy(localeOption, "-Duser.locale=");
        const std::string locale = readLocale();
        strncat(localeOption, locale.c_str(), PROPERTY_VALUE_MAX);
        addOption(localeOption);
    }

    // Trace files are stored in /data/misc/trace which is writable only in debug mode.
    property_get("ro.debuggable", propBuf, "0");
    if (strcmp(propBuf, "1") == 0) {
        property_get("dalvik.vm.method-trace", propBuf, "false");
        if (strcmp(propBuf, "true") == 0) {
            addOption("-Xmethod-trace");
            parseRuntimeOption("dalvik.vm.method-trace-file",
                               methodTraceFileBuf,
                               "-Xmethod-trace-file:");
            parseRuntimeOption("dalvik.vm.method-trace-file-siz",
                               methodTraceFileSizeBuf,
                               "-Xmethod-trace-file-size:");
            property_get("dalvik.vm.method-trace-stream", propBuf, "false");
            if (strcmp(propBuf, "true") == 0) {
                addOption("-Xmethod-trace-stream");
            }
        }
    }

    // Native bridge library. "0" means that native bridge is disabled.
    property_get("ro.dalvik.vm.native.bridge", propBuf, "");
    if (propBuf[0] == '\0') {
        ALOGW("ro.dalvik.vm.native.bridge is not expected to be empty");
    } else if (strcmp(propBuf, "0") != 0) {
        snprintf(nativeBridgeLibrary, sizeof("-XX:NativeBridge=") + PROPERTY_VALUE_MAX,
                 "-XX:NativeBridge=%s", propBuf);
        addOption(nativeBridgeLibrary);
    }

#if defined(__LP64__)
    const char* cpu_abilist_property_name = "ro.product.cpu.abilist64";
#else
    const char* cpu_abilist_property_name = "ro.product.cpu.abilist32";
#endif  // defined(__LP64__)
    property_get(cpu_abilist_property_name, propBuf, "");
    if (propBuf[0] == '\0') {
        ALOGE("%s is not expected to be empty", cpu_abilist_property_name);
        return -1;
    }
    snprintf(cpuAbiListBuf, sizeof(cpuAbiListBuf), "--cpu-abilist=%s", propBuf);
    addOption(cpuAbiListBuf);

    // Dalvik-cache pruning counter.
    parseRuntimeOption("dalvik.vm.zygote.max-boot-retry", cachePruneBuf,
                       "-Xzygote-max-boot-retry=");

    /*
     * When running with debug.generate-debug-info, add --generate-debug-info to
     * the compiler options so that the boot image, if it is compiled on device,
     * will include native debugging information.
     */
    property_get("debug.generate-debug-info", propBuf, "");
    if (strcmp(propBuf, "true") == 0) {
        addOption("-Xcompiler-option");
        addOption("--generate-debug-info");
        addOption("-Ximage-compiler-option");
        addOption("--generate-debug-info");
    }

    /*
     * Retrieve the build fingerprint and provide it to the runtime. That way, ANR dumps will
     * contain the fingerprint and can be parsed.
     */
    parseRuntimeOption("ro.build.fingerprint", fingerprintBuf, "-Xfingerprint:");

    initArgs.version = JNI_VERSION_1_4;
    initArgs.options = mOptions.editArray();
    initArgs.nOptions = mOptions.size();
    initArgs.ignoreUnrecognized = JNI_FALSE;

    /*
     * Initialize the VM.
     *
     * The JavaVM* is essentially per-process, and the JNIEnv* is per-thread.
     * If this call succeeds, the VM is ready, and we can start issuing
     * JNI calls.
     */
    if (JNI_CreateJavaVM(pJavaVM, pEnv, &initArgs) < 0) {
        ALOGE("JNI_CreateJavaVM failed\n");
        return -1;
    }

    return 0;
}

源码还是挺多的．．．要消化一下．Ｏ（∩＿∩）Ｏ哈哈～

参考

android7.0启动zygote进程
(连载)Android 8.0 : Android系统启动流程之zygote进程(一)