"No rule to make target .../.config, needed by .../.built" error

For Developers
1

I'm trying to build a hello_world kernel module following this guide.
Here is the source code (some blank spaces should be hard tab):

Makefile:

#Kernel module example

include $(TOPDIR)/rules.mk
include $(INCLUDE_DIR)/kernel.mk

PKG_NAME:=example
PKG_RELEASE:=1

include $(INCLUDE_DIR)/package.mk

EXTRA_KCONFIG:= \
   CONFIG_BUTTON_HOTPLUG=m
EXTRA_CFLAGS:= \
   $(patsubst CONFIG_%, -DCONFIG_%=1, $(patsubst %=m,%,$(filter %=m,$(EXTRA_KCONFIG)))) \
   $(patsubst CONFIG_%, -DCONFIG_%=1, $(patsubst %=y,%,$(filter %=y,$(EXTRA_KCONFIG)))) \

MAKE_OPTS:=$(KERNEL_MAKE_FLAGS) \
   SUBDIRS="$(PKG_BUILD_DIR)" \
   EXTRA_CFLAGS="$(EXTRA_CFLAGS)" \
   CONFIG_EXAMPLE=m

define KernelPackage/example
   SUBMENU:=Other modules
   TITLE:=Support Module for example
   FILES:=$(PKG_BUILD_DIR)/example.ko
   AUTOLOAD:=$(call AutoLoad,81,example) 
   KCONFIG:=
endef

define Build/Prepare
   mkdir -p $(PKG_BUILD_DIR)/
   $(CP) -R ./src/* $(PKG_BUILD_DIR)/
endef

define Build/Compile
$(MAKE) -C "$(LINUX_DIR)" $(MAKE_OPTS) modules
endef

$(eval $(call KernelPackage,example))

src/Makefile

obj-${CONFIG_EXAMPLE}	+= example.o

src/Kconfig

config EXAMPLE
	tristate "Just a example"
	help
	This is a example, for debugging kernel model.
	If unsure, say N.

src/example.c

#include <linux/module.h>
#include <linux/version.h>
#include <linux/kmod.h>

#define DRV_NAME "example"

static int __init example_init(void)
{
	printk("hello example openwrt\n");
	return 0;
}

static void __exit example_exit(void)
{
	printk("hello example openwrt exit\n");
}

module_init(example_init);
module_exit(example_exit);

MODULE_AUTHOR("hello world");
MODULE_DESCRIPTION("example driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:" DRV_NAME);

After menuconfig , complied the toolchain and updated and installed my custom feeds, I tap:

chn@chn-PC:~/router/openwrt$ make package/example/compile V=sc

(under home/chn/router/openwrt is openwrt source code)
It says:

make[2]: *** No rule to make target '/home/chn/router/openwrt/build_dir/target-mips_24kc_musl/linux-ar71xx_nand/linux-4.9.124/.config', needed by '/home/chn/router/openwrt/build_dir/target-mips_24kc_musl/linux-ar71xx_nand/example/.built'.  Stop.

Who can please tell me how to correct the error?
THANKS very much!:smile:

2

I have solved the problom by myself. Just select Build the Openwrt SDK and Package the Openwrt-based Toolchain in make menuconfig, then make -j 9. Wait after all done, my package can be build without error.
But, why it works ?
programmer-problems

3

This only works if you also did select (m,*) your module via menuconfig. This means packages are only build if they exist in the .config aka have been selected, even if you directly try to compile them.