There is a regression new to 4.15 that happens in a rather common workflow which results in the frustrating situation where the user has clearly disabled UNWINDER_ORC in their ".config" file, and yet they still get the immediate false error saying they need libelf-dev since "CONFIG_UNWINDER_ORC=y" is still set, and hence they can not build. The regression requires UNWINDER_ORC=y (now the default in commit fc72ae40e303) followed by the user subsequently disabling it, which is common if the user doesn't have libelf-dev and doesn't care about ORC. This happens because the recently added test in the top level Makefile assumes that ,config data will be mapped into include/config/auto.conf either by the end user running "make oldconfig" or the Makefile itself detecting that "silentoldconfig" should be run. As the simple reproducer below shows, this clearly does not happen as expected. Note that the test for CONFIG_STACK_VALIDATION and libelf-dev in the same place in the Makefile is broken in the same way, but since it is a warning and not an error, nobody cared about the bogus false positives. Since there is no way I'm going to debug Makefile stuff on Christmas Day, I figured that I should at least report it intstead. The work around is to save your .config and run a "make distclean" or manually clobber the stale include/config/auto.conf or similar. But a frustrated user wouldn't know that w/o the root cause... --------------------- reproducer ------------------------ paul@gw:~/git/linux-head$ git describe v4.15-rc5 paul@gw:~/git/linux-head$ make distclean paul@gw:~/git/linux-head$ make defconfig HOSTCC scripts/basic/fixdep HOSTCC scripts/kconfig/conf.o SHIPPED scripts/kconfig/zconf.tab.c SHIPPED scripts/kconfig/zconf.lex.c HOSTCC scripts/kconfig/zconf.tab.o HOSTLD scripts/kconfig/conf *** Default configuration is based on 'x86_64_defconfig' # # configuration written to .config # paul@gw:~/git/linux-head$ make scripts/kconfig/conf --silentoldconfig Kconfig Makefile:926: *** "Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel". Stop. paul@gw:~/git/linux-head$ vi .config # disable ORC in favour of FRAME_POINTER paul@gw:~/git/linux-head$ make oldconfig scripts/kconfig/conf --oldconfig Kconfig # # configuration written to .config # paul@gw:~/git/linux-head$ grep UNWINDER .config # CONFIG_UNWINDER_ORC is not set CONFIG_UNWINDER_FRAME_POINTER=y paul@gw:~/git/linux-head$ make Makefile:926: *** "Cannot generate ORC metadata for CONFIG_UNWINDER_ORC=y, please install libelf-dev, libelf-devel or elfutils-libelf-devel". Stop. paul@gw:~/git/linux-head$ ls -l .config include/config/auto.conf -rw-rw-r-- 1 paul paul 115953 Dec 25 22:48 .config -rw-rw-r-- 1 paul paul 33069 Dec 25 22:46 include/config/auto.conf paul@gw:~/git/linux-head$ grep UNWINDER include/config/auto.conf CONFIG_UNWINDER_ORC=y paul@gw:~/git/linux-head$ --------------------- reproducer ------------------------ -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html