From f73edc8951b2de515b5ecc8a357ccd47dd41077e Mon Sep 17 00:00:00 2001
From: Masahiro Yamada <masahiroy@kernel.org>
Date: Sun, 25 Sep 2022 03:19:13 +0900
Subject: kbuild: unify two modpost invocations

Currently, modpost is executed twice; first for vmlinux, second
for modules.

This commit merges them.

Current build flow
==================

  1) build obj-y and obj-m objects
    2) link vmlinux.o
      3) modpost for vmlinux
        4) link vmlinux
          5) modpost for modules
            6) link modules (*.ko)

The build steps 1) through 6) are serialized, that is, modules are
built after vmlinux. You do not get benefits of parallel builds when
scripts/link-vmlinux.sh is being run.

New build flow
==============

  1) build obj-y and obj-m objects
    2) link vmlinux.o
      3) modpost for vmlinux and modules
        4a) link vmlinux
        4b) link modules (*.ko)

In the new build flow, modpost is invoked just once.

vmlinux and modules are built in parallel. One exception is
CONFIG_DEBUG_INFO_BTF_MODULES=y, where modules depend on vmlinux.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
---
 Makefile | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)

(limited to 'Makefile')

diff --git a/Makefile b/Makefile
index 21c41a03d98d..41ab27601bb4 100644
--- a/Makefile
+++ b/Makefile
@@ -1150,7 +1150,7 @@ cmd_link-vmlinux =                                                 \
 	$(CONFIG_SHELL) $< "$(LD)" "$(KBUILD_LDFLAGS)" "$(LDFLAGS_vmlinux)";    \
 	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
 
-vmlinux: scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) FORCE
+vmlinux: scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) modpost FORCE
 	+$(call if_changed_dep,link-vmlinux)
 
 targets := vmlinux
@@ -1426,7 +1426,13 @@ endif
 # Build modules
 #
 
-modules: $(if $(KBUILD_BUILTIN),vmlinux) modules_prepare
+# *.ko are usually independent of vmlinux, but CONFIG_DEBUG_INFOBTF_MODULES
+# is an exception.
+ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+modules: vmlinux
+endif
+
+modules: modules_prepare
 
 # Target to prepare building external modules
 modules_prepare: prepare
@@ -1739,8 +1745,12 @@ ifdef CONFIG_MODULES
 $(MODORDER): $(build-dir)
 	@:
 
-modules: modules_check
-	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost
+# KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
+# This is solely useful to speed up test compiles.
+modules: modpost
+ifneq ($(KBUILD_MODPOST_NOFINAL),1)
+	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modfinal
+endif
 
 PHONY += modules_check
 modules_check: $(MODORDER)
@@ -1771,6 +1781,11 @@ KBUILD_MODULES :=
 
 endif # CONFIG_MODULES
 
+PHONY += modpost
+modpost: $(if $(single-build),, $(if $(KBUILD_BUILTIN), vmlinux.o)) \
+	 $(if $(KBUILD_MODULES), modules_check)
+	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost
+
 # Single targets
 # ---------------------------------------------------------------------------
 # To build individual files in subdirectories, you can do like this:
@@ -1790,16 +1805,19 @@ single-ko := $(sort $(filter %.ko, $(MAKECMDGOALS)))
 single-no-ko := $(filter-out $(single-ko), $(MAKECMDGOALS)) \
 		$(foreach x, o mod, $(patsubst %.ko, %.$x, $(single-ko)))
 
-$(single-ko): single_modpost
+$(single-ko): single_modules
 	@:
 $(single-no-ko): $(build-dir)
 	@:
 
 # Remove MODORDER when done because it is not the real one.
-PHONY += single_modpost
-single_modpost: $(single-no-ko) modules_prepare
+PHONY += single_modules
+single_modules: $(single-no-ko) modules_prepare
 	$(Q){ $(foreach m, $(single-ko), echo $(extmod_prefix)$m;) } > $(MODORDER)
 	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost
+ifneq ($(KBUILD_MODPOST_NOFINAL),1)
+	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modfinal
+endif
 	$(Q)rm -f $(MODORDER)
 
 single-goals := $(addprefix $(build-dir)/, $(single-no-ko))
-- 
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