How do I integrate a system app on Android 9

I've been creating a system app on a debug board used Android 9.
The app and dpendenced JAR using ServiceManager looked build-successfully.

But, after written the system.img and restarted,
the device is shutdown automatically and transition to Android Recovery Screen.

What do I have to do to build system apps correctly on Android 9?

My app is like this.

/system/priv-app/SampServiceApp/SampServiceApp.apk, /oat
/system/framework/com.android.sampservice.jar, /oat
/system/etc/permissions/com.android.sampservice.xml

almost the same as this example. (I don't want to use system_server if possible)
https://devarea.com/aosp-creating-a-system-service/

but, only difference is ...
added "LOCAL_PRIVATE_PLATFORM_APIS" insted of "LOCAL_SDK_VERSION"
in Android.mk for SampServiceApp.apk (to compile & link successfully)

# LOCAL_SDK_VERSION := current    
LOCAL_PRIVATE_PLATFORM_APIS := true

And also, I tried to update this xml. (https://source.android.google.cn/devices/tech/config/perms-whitelist)

/etc/permissions/privapp-permissions-platform.xml

but, this python scripts output no entries.

$ development/tools/privapp_permissions/privapp_permissions.py

↓↓ the result
<?xml version="1.0" encoding="utf-8"?>
<permissions>
</permissions>

Thank you in advance for your cooperation.

Solution

Oka, To build your application like system you should: To define mk file. It should be something like that:

 include $(CLEAR_VARS)

LOCAL_SRC_FILES := $(call all-java-files-under, app/src/main/java) $(call all-Iaidl-files-under, app/src/main/aidl)
LOCAL_AIDL_INCLUDES := \
    $(LOCAL_PATH)/app/src/main/aidl \
    $(CAR_BROADCASTRADIO_SUPPORTLIB_PATH)/src

LOCAL_PACKAGE_NAME := YOUR_MODULE_NAME
LOCAL_OVERRIDES_PACKAGES := IF YOU OVERRIDE AOSP PACKAGE
LOCAL_PRIVATE_PLATFORM_APIS := true

LOCAL_CERTIFICATE := platform
LOCAL_MANIFEST_FILE := /app/src/main/AndroidManifest.xml

LOCAL_PROGUARD_ENABLED := disabled

LOCAL_DEX_PREOPT := false

include $(BUILD_PACKAGE)

include $(CLEAR_VARS)

Sure, you can use bp file instead of mk.

Include LOCAL_PACKAGE_NAME into device/path_to_your_lunch_target.

/etc/permissions/privapp-permissions-platform.xml

The file is about only permissions. Here you can define any permission that may be required for your application. You can define your own manifest for your application, but don't forget to include it to build.

What about crash. It is a very strange behaviour. Could you plz share dmesg and logcat?