Another issue with <linux/export.h> is that it is sometimes included even when EXPORT_SYMBOL() is not used at all. Some headers (e.g. include/linux/linkage.h>) cannot be fixed for now for the reason described in the previous commit. This commit adds a warning for *.c files that include <linux/export.h> but do not use EXPORT_SYMBOL() when the kernel is built with W=1. Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>