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kbuild: unify two modpost invocations

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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>
This commit is contained in:
Masahiro Yamada
2022-09-25 03:19:13 +09:00
parent 9c5a0ac3c3
commit f73edc8951
4 changed files with 54 additions and 76 deletions
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2
scripts/Makefile.modfinal
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@@ -55,7 +55,7 @@ if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check), \
printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:)
# Re-generate module BTFs if either module's .ko or vmlinux changed
$(modules): %.ko: %.o %.mod.o scripts/module.lds $(if $(KBUILD_BUILTIN),vmlinux) FORCE
$(modules): %.ko: %.o %.mod.o scripts/module.lds $(and $(CONFIG_DEBUG_INFO_BTF_MODULES),$(KBUILD_BUILTIN),vmlinux) FORCE
+$(call if_changed_except,ld_ko_o,vmlinux)
ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+$(if $(newer-prereqs),$(call cmd,btf_ko))