reproduce (this is a W=1 build):
        git remote add dwmw2 git://git.infradead.org/users/dwmw2/linux
        git fetch --no-tags dwmw2 kexec-debug
        git checkout d8921caca66f0eb34be26fde01126968ebc875a3
        # 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 arch/x86/kernel/