Call All-subdir-makefiles and call all-makefiles-under,$ (Local_path) differences

Call All-subdir-makefiles and call all-makefiles-under,$ (Local_path) are different when writing android.mk files.

The former indicates that "there are no files that need to be compiled in the current directory, please Shangzi the directory in Depth", which is a prescribed notation that tells the compiler to continue to recursive to the depths of the directory. The latter, literally, should also be the same meaning. However, consider a scenario in which you:

If there are files in the current directory that need to be compiled, and there are subdirectories in the current directory, there are files in the subdirectory that need to be compiled. The android.mk in the current directory, in addition to the statement that compiles the files in the current directory, also contains statements that tell the compiler to continue to the subdirectory after compiling the files in the current directory. Here's a question, how do you write the statement later? Is it call all-subdir-makefiles or call all-makefiles-under,$ (Local_path)? In my experiment here, writing the former is not possible, the compiler will not go into the subdirectory compilation after compiling the files in the current directory. And in the latter case, we can meet our expectations.

Local_path: = $ (call My-dir)
include $ (call all-makefiles-under,$ (Local_path))