reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git/commit/?id=533c20b062d7c25cbcbadb31e3ecb95a08ddb877
        git remote add trace https://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace
        git fetch --no-tags trace ftrace/for-next
        git checkout 533c20b062d7c25cbcbadb31e3ecb95a08ddb877
        # 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