reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # https://git.kernel.org/pub/scm/linux/kernel/git/cip/linux-cip.git/commit/?id=438c470eb865a5d5812922e93245a3412733fd87
        git remote add cip https://git.kernel.org/pub/scm/linux/kernel/git/cip/linux-cip.git
        git fetch --no-tags cip linux-4.4.y-st-rt
        git checkout 438c470eb865a5d5812922e93245a3412733fd87
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-7.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=mips olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-7.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=mips SHELL=/bin/bash fs/proc/ kernel/trace/