reproduce (this is a W=1 build):
        git remote add herbert-cryptodev-2.6 https://git.kernel.org/pub/scm/linux/kernel/git/herbert/cryptodev-2.6.git
        git fetch herbert-cryptodev-2.6 master
        git checkout herbert-cryptodev-2.6/master
        b4 shazam https://lore.kernel.org/r/E1qUOTQ-0020gC-0Q@formenos.hmeau.com
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 olddefconfig
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash