From b2c88554912267483baf8b4f5ae0a1bff529f6a3 Mon Sep 17 00:00:00 2001
From: Masahiro Yamada <masahiroy@kernel.org>
Date: Mon, 1 Jun 2020 14:57:00 +0900
Subject: 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>
---
 Makefile | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

(limited to 'Makefile')

diff --git a/Makefile b/Makefile
index 24cf37c21cba..b0bbf8453b66 100644
--- a/Makefile
+++ b/Makefile
@@ -1066,6 +1066,10 @@ vmlinux-alldirs	:= $(sort $(vmlinux-dirs) Documentation \
 		     $(patsubst %/,%,$(filter %/, $(core-) \
 			$(drivers-) $(libs-))))
 
+subdir-modorder := $(addsuffix modules.order,$(filter %/, \
+			$(core-y) $(core-m) $(libs-y) $(libs-m) \
+			$(drivers-y) $(drivers-m)))
+
 build-dirs	:= $(vmlinux-dirs)
 clean-dirs	:= $(vmlinux-alldirs)
 
@@ -1124,7 +1128,7 @@ targets := vmlinux
 
 # The actual objects are generated when descending,
 # make sure no implicit rule kicks in
-$(sort $(vmlinux-deps)): descend ;
+$(sort $(vmlinux-deps) $(subdir-modorder)): descend ;
 
 filechk_kernel.release = \
 	echo "$(KERNELVERSION)$$($(CONFIG_SHELL) $(srctree)/scripts/setlocalversion $(srctree))"
@@ -1345,8 +1349,12 @@ PHONY += modules_check
 modules_check: modules.order
 	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/modules-check.sh $<
 
-modules.order: descend
-	$(Q)$(AWK) '!x[$$0]++' $(addsuffix /$@, $(build-dirs)) > $@
+cmd_modules_order = $(AWK) '!x[$$0]++' $(real-prereqs) > $@
+
+modules.order: $(subdir-modorder) FORCE
+	$(call if_changed,modules_order)
+
+targets += modules.order
 
 # Target to prepare building external modules
 PHONY += modules_prepare
-- 
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