reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?id=3c74955937520e6aabc0ec921b1bfe01734c6abc
        git remote add kees https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git
        git fetch --no-tags kees for-next/hardening
        git checkout 3c74955937520e6aabc0ec921b1bfe01734c6abc
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # pip install -r Documentation/sphinx/requirements.txt
        make htmldocs