reproduce (this is a W=1 build):
        # https://github.com/jgunthorpe/linux/commit/4391e88cc4f62e532f2c1aee1012ac4b4d0e71bf
        git remote add jgunthorpe https://github.com/jgunthorpe/linux
        git fetch --no-tags jgunthorpe pr/4
        git checkout 4391e88cc4f62e532f2c1aee1012ac4b4d0e71bf
        # 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