reproduce:
        # apt-get install sparse
        # sparse version: v0.6.4-66-g0196afe1
        # https://github.com/brauner/linux/commit/df0177575e5e6cc90351b898384103bc4d14aa80
        git remote add brauner-github https://github.com/brauner/linux.git
        git fetch --no-tags brauner-github work.cred
        git checkout df0177575e5e6cc90351b898384103bc4d14aa80
        # 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=x86_64 olddefconfig
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=x86_64 SHELL=/bin/bash fs/overlayfs/