ensure that Linux kernel is updated after a build and that busybox is not spuriously rebuilt (#397)

Makefile

@@ -179,10 +179,9 @@ endef
 define do-copy =
 	$(call do,INSTALL  ,$1 => $2',\
 		if ! cmp --quiet "$1" "$2" ; then \
-			cp -a "$1" "$2"; \
-		else  \
 			echo "$(DATE) UNCHANGED $(1:$(pwd)/%=%)" ; \
 		fi
+		cp -a "$1" "$2"; \
 	)
 	@sha256sum "$(2:$(pwd)/%=%)"
 endef
@@ -294,7 +293,7 @@ define define_module =
 
   # Target for all of the outputs, which depend on their dependent modules
   # being built, as well as this module being configured
-  $(call outputs,$1): $(build)/$($1_dir)/.build
+  $(build)/$($1_dir)/.build: $(call outputs,$1)
 
   # If any of the outputs are missing, we should force a rebuild
   # of the entire module

modules/busybox

@@ -31,6 +31,7 @@ $(initrd_tmp_dir)/bin/busybox: $(build)/$(busybox_dir)/.build
 		| tee -a $(build)/log/busybox.log \
 		$(VERBOSE_REDIRECT) \
 	)
+	@touch $< # ensure that our build file is still newer
 
 
 busybox_depends := $(musl_dep)

modules/linux

@@ -114,7 +114,7 @@ FOO := $(shell mkdir -p "$(module_initrd_lib_dir)")
 define linux_module =
 
 # Each module depends on building the Linux kernel
-$(build)/$(linux_dir)/$1: $(build)/$(BOARD)/bzImage
+$(build)/$(linux_dir)/$1: $(build)/$(linux_dir)/$(linux_output)
 
 # The cpio file will depend on every module
 $(build)/$(BOARD)/modules.cpio: $(module_initrd_lib_dir)/$(notdir $1)
@@ -141,8 +141,9 @@ $(build)/$(BOARD)/modules.cpio: $(build)/$(linux_dir)/.build
 # The output of the linux.intermediate is the bzImage in the
 # linus build directory.  We need to copy it into our board
 # specific directory for ease of locating it later.
-$(build)/$(BOARD)/bzImage: $(build)/$(linux_dir)/arch/x86/boot/bzImage
-	$(call do-copy,$<,$@)
+$(build)/$(BOARD)/bzImage: $(build)/$(linux_dir)/.build
+	$(call do-copy,$(dir $<)/$(linux_output),$@)
+	@touch $@ # force a timestamp update
 
 
 # menuconfig target allows us to easily reconfigure this Linux kernel