Android’s init is located at the root of the filesystem i.e. /init and also it uses different naming conventions than normal linux init, so its advised to first try and understand the details of android init Language, from system/core/init/readme.txt you can also check in the source code you have or click the link here.
Now, if you have a compiled source code, create a directory called exampleservice inside external folder,
$ mkdir external/exampleservice
$ cd external/exampleservice
Create an Android.mk as below,
$ vim Android.mk
LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) LOCAL_SRC_FILES := exampleservice.c LOCAL_MODULE := exampleservice LOCAL_MODULE_TAGS := debug LOCAL_SYSTEM_SHARED_LIBRARIES := libc LOCAL_SHARED_LIBRARIES := liblog include $(BUILD_EXECUTABLE)
$ cd ../../
$ make exampleservice
Once, you compiled above code, you may get a binary in out folder at out/target/product/generic/system/bin/exampleservice or you can use a command like $ find out/ -name exampleservice to find exact location.
Now, modify init.rc as below, you can also append below code to the end of init.rc
service exampleservice /system/bin/exampleservice user exampleservice group exampleservice oneshot
Boot android by pushing changed init.rc at /init.rc and exampleservice binary to /system/bin/exampleservice