reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git/commit/?id=d83c23ec2a39f1ae346bbce351cb004be5c58c1e
        git remote add mhiramat https://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git
        git fetch --no-tags mhiramat topic/wprobe-v2
        git checkout d83c23ec2a39f1ae346bbce351cb004be5c58c1e

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash kernel/trace/