reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git/commit/?id=85ea4fc216f7e8eb4a97a6fa417bfe78d679fb1a
        git remote add mhiramat https://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git
        git fetch --no-tags mhiramat topic/fprobe-on-fgraph
        git checkout 85ea4fc216f7e8eb4a97a6fa417bfe78d679fb1a
        # 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 drivers/base/regmap/ kernel/