kbuild: update modules.order only when contained modules are updated

Make modules.order depend on $(obj-m), and use if_changed to build it.
This will avoid unneeded update of modules.order, which will be useful
to optimize the modpost stage.

Currently, the second pass of modpost is always invoked. By checking the
timestamp of modules.order, we can avoid the unneeded modpost.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

1 files changed, 13 insertions, 8 deletions

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index a1f09bec8c70..2e8810b7e5ed 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -71,7 +71,7 @@ endif
 
 # subdir-builtin and subdir-modorder may contain duplications. Use $(sort ...)
 subdir-builtin := $(sort $(filter %/built-in.a, $(real-obj-y)))
-subdir-modorder := $(sort $(filter %/modules.order, $(modorder)))
+subdir-modorder := $(sort $(filter %/modules.order, $(obj-m)))
 
 targets-for-builtin := $(extra-y)
 
@@ -83,8 +83,7 @@ ifdef need-builtin
 targets-for-builtin += $(obj)/built-in.a
 endif
 
-targets-for-modules := $(obj-m)
-targets-for-modules += $(patsubst %.o, %.mod, $(obj-m))
+targets-for-modules := $(patsubst %.o, %.mod, $(filter %.o, $(obj-m)))
 
 ifdef need-modorder
 targets-for-modules += $(obj)/modules.order
@@ -361,8 +360,9 @@ endif
 $(obj)/%.o: $(src)/%.S $(objtool_dep) FORCE
 	$(call if_changed_rule,as_o_S)
 
-targets += $(filter-out $(subdir-builtin), $(real-obj-y)) $(real-obj-m) $(lib-y)
-targets += $(always-y) $(MAKECMDGOALS)
+targets += $(filter-out $(subdir-builtin), $(real-obj-y))
+targets += $(filter-out $(subdir-modorder), $(real-obj-m))
+targets += $(lib-y) $(always-y) $(MAKECMDGOALS)
 
 # Linker scripts preprocessor (.lds.S -> .lds)
 # ---------------------------------------------------------------------------
@@ -404,11 +404,16 @@ $(obj)/built-in.a: $(real-obj-y) FORCE
 #
 # Create commands to either record .ko file or cat modules.order from
 # a subdirectory
-$(obj)/modules.order: $(subdir-modorder) FORCE
-	$(Q){ $(foreach m, $(modorder), \
-	$(if $(filter $^, $m), cat $m, echo $m);) :; } \
+# Add $(obj-m) as the prerequisite to avoid updating the timestamp of
+# modules.order unless contained modules are updated.
+
+cmd_modules_order = { $(foreach m, $(real-prereqs), \
+	$(if $(filter %/modules.order, $m), cat $m, echo $(patsubst %.o,%.ko,$m));) :; } \
 	| $(AWK) '!x[$$0]++' - > $@
 
+$(obj)/modules.order: $(obj-m) FORCE
+	$(call if_changed,modules_order)
+
 #
 # Rule to compile a set of .o files into one .a file (with symbol table)
 #