kbuild: consistently decide when to rebuild a target

Consistently decide when to rebuild a target across all of
if_changed, if_changed_dep, if_changed_rule.
PHONY targets are now treated alike (ignored) for all targets

While add it make Kbuild.include almost readable by factoring out a few
bits to some common variables and reuse this in Makefile.build.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

scripts/Kbuild.include

@@ -7,10 +7,14 @@ squote  := '
 empty   :=
 space   := $(empty) $(empty)
 
+###
+# Name of target with a '.' as filename prefix. foo/bar.o => foo/.bar.o
+dot-target = $(dir $@).$(notdir $@)
+
 ###
 # The temporary file to save gcc -MD generated dependencies must not
 # contain a comma
-depfile = $(subst $(comma),_,$(@D)/.$(@F).d)
+depfile = $(subst $(comma),_,$(dot-target).d)
 
 ###
 # filename of target with directory and extension stripped
@@ -119,40 +123,44 @@ objectify = $(foreach o,$(1),$(if $(filter /%,$(o)),$(o),$(obj)/$(o)))
 ifneq ($(KBUILD_NOCMDDEP),1)
 # Check if both arguments has same arguments. Result in empty string if equal
 # User may override this check using make KBUILD_NOCMDDEP=1
-arg-check = $(strip $(filter-out $(1), $(2)) $(filter-out $(2), $(1)) )
+arg-check = $(strip $(filter-out $(cmd_$(1)), $(cmd_$@)) \
+                    $(filter-out $(cmd_$@),   $(cmd_$(1))) )
 endif
 
 # echo command. Short version is $(quiet) equals quiet, otherwise full command
 echo-cmd = $(if $($(quiet)cmd_$(1)), \
 	echo '  $(call escsq,$($(quiet)cmd_$(1)))';)
 
+# >'< substitution is for echo to work,
+# >$< substitution to preserve $ when reloading .cmd file
+# note: when using inline perl scripts [perl -e '...$$t=1;...']
+# in $(cmd_xxx) double $$ your perl vars
 make-cmd = $(subst \#,\\\#,$(subst $$,$$$$,$(call escsq,$(cmd_$(1)))))
 
-# function to only execute the passed command if necessary
-# >'< substitution is for echo to work, >$< substitution to preserve $ when reloading .cmd file
-# note: when using inline perl scripts [perl -e '...$$t=1;...'] in $(cmd_xxx) double $$ your perl vars
+# Find any prerequisites that is newer than target or that does not exist.
+# PHONY targets skipped in both cases.
+any-prereq = $(filter-out $(PHONY),$?) $(filter-out $(PHONY) $(wildcard $^),$^)
+
+# Execute command if command has changed or prerequisitei(s) are updated
 #
-if_changed = $(if $(strip $(filter-out $(PHONY),$?)          \
-		$(call arg-check, $(cmd_$(1)), $(cmd_$@)) ), \
+if_changed = $(if $(strip $(any-prereq) $(arg-check)),                       \
 	@set -e;                                                             \
 	$(echo-cmd) $(cmd_$(1));                                             \
-	echo 'cmd_$@ := $(make-cmd)' > $(@D)/.$(@F).cmd)
+	echo 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd)
 
 # execute the command and also postprocess generated .d dependencies
 # file
-if_changed_dep = $(if $(strip $(filter-out $(PHONY),$?)  \
-		$(filter-out FORCE $(wildcard $^),$^)    \
-	$(call arg-check, $(cmd_$(1)), $(cmd_$@)) ),     \
+if_changed_dep = $(if $(strip $(any-prereq) $(arg-check) ),                  \
 	@set -e;                                                             \
 	$(echo-cmd) $(cmd_$(1));                                             \
-	scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(@D)/.$(@F).tmp; \
+	scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).tmp;\
 	rm -f $(depfile);                                                    \
-	mv -f $(@D)/.$(@F).tmp $(@D)/.$(@F).cmd)
+	mv -f $(dot-target).tmp $(dot-target).cmd)
 
 # Usage: $(call if_changed_rule,foo)
 # will check if $(cmd_foo) changed, or any of the prequisites changed,
 # and if so will execute $(rule_foo)
-if_changed_rule = $(if $(strip $(filter-out $(PHONY),$?)            \
-			$(call arg-check, $(cmd_$(1)), $(cmd_$@)) ),\
+if_changed_rule = $(if $(strip $(any-prereq) $(arg-check) ),                 \
 	@set -e;                                                             \
 	$(rule_$(1)))
+

scripts/Makefile.build

@@ -191,9 +191,10 @@ define rule_cc_o_c
 	$(call echo-cmd,checksrc) $(cmd_checksrc)			  \
 	$(call echo-cmd,cc_o_c) $(cmd_cc_o_c);				  \
 	$(cmd_modversions)						  \
-	scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,cc_o_c)' > $(@D)/.$(@F).tmp;  \
+	scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,cc_o_c)' >    \
+	                                              $(dot-target).tmp;  \
 	rm -f $(depfile);						  \
-	mv -f $(@D)/.$(@F).tmp $(@D)/.$(@F).cmd
+	mv -f $(dot-target).tmp $(dot-target).cmd
 endef
 
 # Built-in and composite module parts

usr/Makefile

@@ -3,6 +3,8 @@
 #
 
 klibcdirs:;
+PHONY += klibcdirs
+
 
 # Generate builtin.o based on initramfs_data.o
 obj-y := initramfs_data.o