The StartUps: Android Runtime

The Zygote Process starts the Android Runtime with the following command.
The code for this is at frameworks/base/core/jni/AndroidRuntime.cpp

runtime.start("com.android.internal.os.ZygoteInit", args, zygote);

This involves starting the virtual machine and calling the "static void main(String[] args)" method of ZygoteInit. Event Log for Boot Progrsess Start is printed here.
Steps:

Check is /system/ directory is available

Initialize Jni_invocation

jni_invocation.Init(NULL);
    -Jni_invocation: adds a layer of indirection for applications using the JNI invocation API to allow the JNI implementation to be selected dynamically. Apps can specify a specific implementation to be used by calling InitJniInvocation. 
    If this is not done, the library will chosen based on the value of Android system property "persist.sys.dalvik.vm.lib"(say libart.so, libdvm.so or libartd.so) on the device, and otherwise fall back to a hard-coded default implementation ("libart.so").

StartVM

startVm(&mJavaVM, &env, zygote)
     Get The Java VM init properties from the dalvik.vm.xxx system properties and initialize Java VM.
     We can call jni methods once this call succeeds
            JNI_CreateJavaVM(pJavaVM, pEnv, &initArgs)
       @/art/runtime/java_vm_ext.cc -> JNI_CreateJavaVM
Runtime* runtime = Runtime::Current();
runtime->Start();
pEnv = Thread::Current()->GetJniEnv();
pJavaVM = runtime->GetJavaVM();
   pEnv is per Thread & pJavaVM is per process

Register all native android functions.

startReg(env) 
This registers all Native system services like
       register_com_android_internal_os_RuntimeInit
register_android_os_SystemClock
register_android_os_Process
register_android_view_Surface
register_android_graphics_Camera
register_android_view_InputChannel
etc...

Finally call the main() of the "startClass", In our case this is ZygoteInit
 jmethodID startMeth = env->GetStaticMethodID(startClass, "main", "([Ljava/lang/String;)V");
 env->CallStaticVoidMethod(startClass, startMeth, strArray);