Differences between call all-subdir-makefiles and call all-makefiles-under, $ (local_path) in Android. mk

When writing an android. mk file, call all-subdir-makefiles and call all-makefiles-under, $ (local_path) are different.

The former indicates that "there is no file to be compiled in the current directory, please go deep into the subdirectory", which is a required way to tell the compiler to continue recursion in the directory. The latter can be understood literally in the same way. However, consider the following situation:

If there are files in the current directory that need to be compiled, and there are subdirectories in the current directory, and files in the subdirectories need to be compiled, then the android in the current directory. in addition to the statements used to compile files in the current directory, MK also contains statements that tell the compiler to continue to penetrate into the subdirectory after compiling the files in the current directory. Here is a question. How can I write the following statement? Is it call all-subdir-makefiles, or call all-makefiles-under, $ (local_path? After my experiment, writing the former won't work. The compiler will not compile the files in the current directory into the subdirectory after compilation. The latter can meet our expectations.