cross-compile kernel module for buildroot system

Hi
I'm trying to follow the linux kernel development from bootlin.. But I'm using a different board (specifically the Orange PI Zero 3) and using buildroot for my system image.

I can crosscompile C *applications* succesfully using the generated toolchain from buildroot from `~/buildroot/output/host/bin`; by running `aarch64-linux-gcc -o hello hello.c`.

Now I need to cross-compile kernel modules in this course.. They have provided the following `Makefile`:

ifneq ($(KERNELRELEASE),)
obj-m := hello_version.o
else
KDIR := $(HOME)/linux-kernel-labs/src/linux
all:
	$(MAKE) -C $(KDIR) M=$$PWD

clean:
	$(MAKE) -C $(KDIR) M=$$PWD clean
endif

I realise I need to adjust `KDIR` variable according to my situation (buildroot). Where does buildroot provide this?

Thank you in advance!

Okay found it (source: https://blog.billvanleeuwen.ca/writi...lack-buildroot). It's in ~/buildroot/output/build/linux-custom