reproduce (this is a W=1 build):
        git remote add drm-tip https://gitlab.freedesktop.org/drm/tip.git
        git fetch --no-tags drm-tip drm-tip
        git checkout f8363c190f6fe6cffebc8733c2375330112327f9

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=um olddefconfig
        make W=1 O=build_dir ARCH=um SHELL=/bin/bash