reproduce:
        # apt-get install sparse
        # sparse version: v0.6.4-66-g0196afe1
        git remote add dwmw2 git://git.infradead.org/users/dwmw2/linux
        git fetch --no-tags dwmw2 vmclock
        git checkout dea92ae21f9df74ad8784ae0f343724f74f20b0e
        # 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 drivers/ptp/