reproduce (this is a W=1 build):
        git remote add trace https://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace
        git fetch trace for-next
        git checkout trace/for-next
        b4 shazam https://lore.kernel.org/r/175826135058.101165.7219957344129610147.stgit@devnote2
        # 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 kernel/