reproduce:
        # apt-get install sparse
        # sparse version: v0.6.4-61-g09411a7a-dirty
        # https://git.kernel.org/pub/scm/linux/kernel/git/netfilter/nf.git/commit/?id=6099505cd2a2652bbb4156582a22feb6d651b6d6
        git remote add netfilter-nf git://git.kernel.org/pub/scm/linux/kernel/git/netfilter/nf.git
        git fetch --no-tags netfilter-nf testing
        git checkout 6099505cd2a2652bbb4156582a22feb6d651b6d6
        # 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 net/netfilter/