[Buildroot] Cross-compiling out-of-tree kernel modules and user-space apps

[Mason]

Hello,

I use buildroot to generate kernel + rootfs image for an ARM
platform, typically cross-compiled with the Linaro toolchain.

I also have a large body of software in a separate repo
(outside of the BR tree) with its own build system.
This repo includes kernel modules, user-space libraries
and apps, which need to be cross-compiled and built on
top of the rootfs generated by BR.

Therefore, I would need to pass some information from BR
to the separate build system, such as

- ARCH
- CROSS_COMPILE
- location of the cross-toolchain, to add to the PATH
- location of the sysroot

What is the best way to do this?

I tried a post-image script, but I didn't see ARCH or
CROSS_COMPILE in the env or as arguments.

Regards.