Generates kernel module headers from linux source.

This is based on the arch linux script which performs the same task. We expand it to better handle cross-compiling to other architectures.

usage: gen_mod_headers [target dir] [linux source dir] [objects dir] <arch> <x-compile-prefix> <customcc>

Ensure .config and Module.symvers are in the objects directory (this can be the same as the source directory.) If you don't have Module.symvers, you can generate it with a kernel build.

If you want to cross-compile, ensure you have the appropriate cross-compile version of gcc available. Google 'linaro cross compile' if you need to get hold of one. Then specify the arch, and the prefix of the cross-compiler as shown above.

If you're generating a typical x86 on x86 build, you can simply run something like:

./gen_mod_headers /tmp/headers ~/kerndev/kernels/linux ~/kerndev/linux-obj

Where /tmp/headers is the desired output directory, ~/kerndev/kernels/linux is your linux source code dir, and ~/kerndev/linux-obj contains .config and Module.symvers.

For cross compile you need to specify architecture and the prefix for your cross-compiler binaries, e.g.:

./gen_mod_headers /tmp/headers ~/kerndev/kernels/linux-arm ~/kerndev/linux-arm-obj arm arm-linux-gnueabihf-

IMPORTANT: Note that the script will generate headers that can only be used to compile modules on the target architecture.

If you need to use a specific custom cross-compiler when building binaries in the scripts/ directory, set customcc accordingly.

Typically an external module will expect these header files to be in /lib/modules/$(uname -r)/build, however you can typically override this with a parameter in the module's Makefile like KERNELDIR or similar, e.g. make KERNELDIR=/tmp/headers. You will need to check the module's Makefile to see if they provide an optional argument like:

KERNELDIR ?= /lib/modules/$(shell uname -r)/build

The ?= here means it's optional and can be overridden as described. If this is not set it isn't too difficult to make whatever variable is pointing at /lib/modules/$(uname -r)/build optional using ?= so you can override it.