reproduce:
        # apt-get install sparse
        # sparse version: v0.6.4-66-g0196afe1
        # https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/commit/?id=9b98f162cf0788f36f3bba230c4baf56af057450
        git remote add peterz-queue https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git
        git fetch --no-tags peterz-queue perf/pmu-unregister
        git checkout 9b98f162cf0788f36f3bba230c4baf56af057450
        # 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=i386 olddefconfig
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=i386 SHELL=/bin/bash kernel/events/