how to compile a kernel module

Question

I\'m trying to compile a simple hello world module following this guide and I\'m confused about what the Makefile is actually doing.

obj-m += hello-1.o

all:
            


        

Answer 1

To compile kernel module, the make command you normally need is in this form:

make -C /lib/modules/3.16.0-70-generic/build M=/home/test/ldd3/hello modules

in which, -C means switching to another path.

/lib/modules/3.16.0-70-generic/

is the path to the kernel in used, and

/home/test/ldd3/hello

is where the source of your module resides.

what does the M=$(PWD) modules do?

So as I said M=$(PWD) is simply a shell variable that stores the current path to your kernel module. make needs to store this as it switches to the kernel build path.