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, 14 insertions, 13 deletions

diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 748e44d5a1e3..e598b07e6de4 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -32,27 +32,29 @@ obj-m := $(filter-out $(obj-y),$(obj-m))
 # Filter out objects already built-in
 lib-y := $(filter-out $(obj-y), $(sort $(lib-y) $(lib-m)))
 
-# Determine modorder.
-# Unfortunately, we don't have information about ordering between -y
-# and -m subdirs.  Just put -y's first.
-ifdef need-modorder
-modorder	:= $(patsubst %/,%/modules.order, $(filter %/, $(obj-y)) $(obj-m:.o=.ko))
-endif
-
 # Subdirectories we need to descend into
 subdir-ym := $(sort $(subdir-y) $(subdir-m) \
 			$(patsubst %/,%, $(filter %/, $(obj-y) $(obj-m))))
 
-# Handle objects in subdirs
-# ---------------------------------------------------------------------------
-# o if we encounter foo/ in $(obj-y), replace it by foo/built-in.a
-# o if we encounter foo/ in $(obj-m), remove it from $(obj-m)
+# Handle objects in subdirs:
+# - If we encounter foo/ in $(obj-y), replace it by foo/built-in.a and
+#   foo/modules.order
+# - If we encounter foo/ in $(obj-m), replace it by foo/modules.order
+#
+# Generate modules.order to determine modorder. Unfortunately, we don't have
+# information about ordering between -y and -m subdirs. Just put -y's first.
+
+ifdef need-modorder
+obj-m := $(patsubst %/,%/modules.order, $(filter %/, $(obj-y)) $(obj-m))
+else
+obj-m := $(filter-out %/, $(obj-m))
+endif
+
 ifdef need-builtin
 obj-y		:= $(patsubst %/, %/built-in.a, $(obj-y))
 else
 obj-y		:= $(filter-out %/, $(obj-y))
 endif
-obj-m		:= $(filter-out %/, $(obj-m))
 
 # If $(foo-objs), $(foo-y), $(foo-m), or $(foo-) exists, foo.o is a composite object
 multi-used-y := $(sort $(foreach m,$(obj-y), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y)) $($(m:.o=-))), $(m))))
@@ -81,7 +83,6 @@ endif
 extra-y		:= $(addprefix $(obj)/,$(extra-y))
 always-y	:= $(addprefix $(obj)/,$(always-y))
 targets		:= $(addprefix $(obj)/,$(targets))
-modorder	:= $(addprefix $(obj)/,$(modorder))
 obj-m		:= $(addprefix $(obj)/,$(obj-m))
 lib-y		:= $(addprefix $(obj)/,$(lib-y))
 real-obj-y	:= $(addprefix $(obj)/,$(real-obj-y))