Compiling out-of-tree kernel module against any kernel source tree on the filesystem - linux

Question

I am trying to compile a module against any source tree on the file system but I am having trouble with the Makefile. This was the original Makefile I had against the kernel specified:
obj-m += new-mod.o
all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
clean:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
This Makefile would compile correctly, but goal is to have it compile against any source tree. I have tried just:
obj-m += new-mod.o
I thought that "all:" is assumed but I get error:
make: *** No targets. Stop.
I have also added:
all:
to the Makefile with no difference except for error message:
make: Nothing to be done for `all'
I have tried a lot of documentation but no luck. I would greatly appreciate any help.

Answer 1

goal is to have it compile against any source tree
ya you can do it providing a compiled source-code path
just replace make -C /lib/modules/$(shell uname -r)/build M=$PWD modules
with this
make -C <path-to-compiled-src-code> M=$PWD modules
make -C /home/vinay/linux-3.9 M=$PWD modules
try below makefile
Makefile –
# if KERNELRELEASE is defined, we've been invoked from the
# kernel build system and can use its language.
ifneq (${KERNELRELEASE},)
obj-m := new-mod.o
# Otherwise we were called directly from the command line.
# Invoke the kernel build system.
else
KERNEL_SOURCE := /usr/src/linux
PWD := $(shell pwd)
default:
${MAKE} -C ${KERNEL_SOURCE} SUBDIRS=${PWD} modules
clean:
${MAKE} -C ${KERNEL_SOURCE} SUBDIRS=${PWD} clean
endif
In above you can change KERNEL_SOURCE := /usr/src/linux-->to.--> your sr-code KERNEL_SOURCE := <path to compiled-src-code>
for further info find below liks
while building kernel modules why do we need /lib/modules?
A simple program on linux device driver
How to make a built-in device driver in linux

Answer 2

Build against your custom kernel source ( not the one that is installed),
You can use following steps.
1.download kernel from kernel.org (tar)
2.Extract
3.make x86_64_defconfig
4.make prepare
5.make modules_prepare
Now you have to change Makefile to point to kernel source you had downloaded and extracted. Something similar mentioned in example by Vinay Answer.
Just remember you cannot insmod this module as kernel running and module built is for different kernel.