Eudyptula Challenge Task 01

[me storage]

Hi i every one i am new to linux kernel programming .I am participating in
Eudyptula Challenge .Recently i submitted my solutions to Task 01 but i
gives me reply like the below

"Please read the requirements for the Makefile and allow the module to be
built against any kernel source tree on the filesystem, not just those
kernels that happened to be installed in /lib/ at some point in time."

And my make file is like this

ifneq ($(KERNELRELEASE),)
     obj-m += helloworld.o
 else
 default:
       make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
 clean:
       make -C /lib/modules/$(shell uname -r)/bulid M=$(PWD) clean
 end


So can any please tell me how to allow the module to be built against any
kernel source tree on the filesystem?
or can any one pleae tell me what does it mean?
Thank you
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