reproduce:
        # apt-get install sparse
        # sparse version: v0.6.4-66-g0196afe1
        # https://github.com/isilence/linux/commit/72118a096b5f2056c9fa57009c90c7d7ecd2e208
        git remote add isilence https://github.com/isilence/linux
        git fetch --no-tags isilence zcrx/v9-wip
        git checkout 72118a096b5f2056c9fa57009c90c7d7ecd2e208
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=um olddefconfig
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=um SHELL=/bin/bash drivers/net/