reproduce (this is a W=1 build):
        git checkout v6.9
        b4 shazam https://lore.kernel.org/r/20240523113638.1196299-1-asmadeus@codewreck.org
        # 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 fs/9p/