Dynamically Generating Dalvik Bytecode into a running Dalvik/Android application

Question

This question has been asked(and answered) many times about dynamically generating and loading java bytecodes at runtime into a running Dalvik VM, but is there any way to lo

Answer 1

If inside any C or C++ program, you want to load and call into the DEX classes, you can see how the Dalvik VM is started, inside the AndroidRuntime - for example frameworks/base/cmds/app_process/app_main.cpp:

status_t app_init(const char* className, int argc, const char* const argv[])
{
    LOGV("Entered app_init()!\n");

    AndroidRuntime* jr = AndroidRuntime::getRuntime();
    jr->callMain(className, argc, argv);

    LOGV("Exiting app_init()!\n");
    return NO_ERROR;
}

As "jr" AndroidRuntime is already started, callMain() will be called:

status_t AndroidRuntime::callMain(
    const char* className, int argc, const char* const argv[])
{
    JNIEnv* env;
    jclass clazz;
    jmethodID methodId;

    LOGD("Calling main entry %s", className);

    env = getJNIEnv();
    if (env == NULL)
        return UNKNOWN_ERROR;

    clazz = findClass(env, className);
    if (clazz == NULL) {
        LOGE("ERROR: could not find class '%s'\n", className);
        return UNKNOWN_ERROR;
    }

    methodId = env->GetStaticMethodID(clazz, "main", "([Ljava/lang/String;)V");
    if (methodId == NULL) {
        LOGE("ERROR: could not find method %s.main(String[])\n", className);
        return UNKNOWN_ERROR;
    }
<...>
    env->CallStaticVoidMethod(clazz, methodId, strArray);
    return NO_ERROR;
}

From above, we can see how the DEX classes' codes are loaded and CallStaticVoidMethod() will start interpreting the DEX codes.