How to create new directories and move .o files to it while compiling a kernel module from multiple directories/files

Question

I'm trying to build a kernel module from files in multiple directories. I want to place the resulting .o files in new directories, created corresponding to each source directories.

For example, if my sources are A/a1.c , A/a2.c , B/bc ; I want the .o files to go to A/new-dir/a1.o A/new-dir/a2.o B/new-dir/bo and so on.

My current Makefile is like this:

obj-m += foo.o

lavya-objs := lavya_module1.o  lavya_module2.o

lavya-objs += $(A_DIR)/a1.o $(A_DIR)/a2.o $(B_DIR)/b.o 


all: 

        make -C $KERNEL_PATH  M=$(PWD) modules

and it creates .o files in the same directories as the corresponding .c files. Is it possible to modify the Makefile to insert a new directory in each of the source directories and move the .o files there instead? How can it be done?

Many Thanks!

Answer 1

The main kernel Makefile tells of two ways of placing output elsewhere (not like you ask, but it could be useful). Look for KBUILD_OUTPUT (can be set as an environment variable or as O=where/to/put to make).

Answer 2

Yes you can do it in makefile like below

obj-m += foo.o

lavya-objs := lavya_module1.o  lavya_module2.o

lavya-objs += $(A_DIR)/a1.o $(A_DIR)/a2.o $(B_DIR)/b.o 


all: 
    make -C $KERNEL_PATH  M=$(PWD) modules
    mkdir -p $(A_DIR)/objs && mv $(A_DIR)/*.o $(A_DIR)/objs/
    mkdir -p $(B_DIR)/objs && mv $(B_DIR)/*.o $(B_DIR)/objs/