reproduce:
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # apt-get install sparse
        # sparse version: v0.6.4-52-g1cf3d98c-dirty
        # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fdf68acccfc6af9497c34ee411d89af13b6516ed
        git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
        git fetch --no-tags linus master
        git checkout fdf68acccfc6af9497c34ee411d89af13b6516ed
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        ~/lkp-tests/kbuild/make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=riscv olddefconfig
        ~/lkp-tests/kbuild/make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=riscv SHELL=/bin/bash arch/riscv/kernel/