Getting ready

Since we need to add our code to the Linux sources, let's go into the directory where all sources are located. On my system, I use the Projects/ldddc/linux/ path located in my home directory. Here is what the kernel sources look like:

$ cd Projects/ldddc/linux/
$ ls
arch        Documentation  Kbuild       mm               scripts   virt
block       drivers        Kconfig      modules.builtin  security  vmlinux
built-in.a  firmware       kernel       modules.order    sound     vmlinux.o
certs       fs             lib          Module.symvers   stNXtP40
COPYING     include        LICENSES     net System.map
CREDITS     init           MAINTAINERS  README tools
crypto      ipc            Makefile     samples usr

Now, we need to set the environment variables, ARCH and CROSS_COMPILE, as follows in order to be able to cross-compile code for the ESPRESSObin:

$ export ARCH=arm64
$ export CROSS_COMPILE=aarch64-linux-gnu-

So, if we try to execute a make command as follows, the system should start compiling the kernel as usual:

$ make Image dtbs modules
  CALL scripts/checksyscalls.sh
...

At this point, kernel sources and the compiling environment are ready.