AOSP - How to run an executable file with root privileges?

Question

I am creating an "embedded" system based on Android, and at the moment I am trying to introduce an update to the firmware of the audio module.
 There is a binary file that does this, but the catch is that this requires root access (it cannot access GPIO otherwise).
Thus, the problem has now shifted to providing access to the executable file (and only that executable should not do full root).
I have been doing this for several days and have tried a bunch of things without success.
Things I've already tried:

• https://stackoverflow.com/questions/535423/ ... (I did this, but still have no root. I think about it because of No setuid / setgid programs with Android 4.3 )
• Read somewhere that you can create a system service that you call and have code that requires root to run. The following is a guide to creating a system service, but it turned out that it does not have root access.

I ran out of ideas or things to try. What else can I do?

EDIT
I could not do binary startup as root, but I was able to run the shell script after loading from init.rc, where there is root access, and export / change the permissions of the specific gpio that I needed. This allowed access to it without root access, which is required later.

Answer 1

, init.rc.