linux-kernel - Re: [PATCH v3 5/7] kbuild: unify two modpost invocations

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Date:   Wed, 28 Sep 2022 21:59:16 +0200
From:   Nicolas Schier <nicolas@...sle.eu>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH v3 5/7] kbuild: unify two modpost invocations

On Sun, 25 Sep 2022 03:19:13 +0900 Masahiro Yamada wrote:
> 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@...nel.org>
> ---
> 
> (no changes since v1)
> 
>  Makefile                  | 30 ++++++++++---
>  scripts/Makefile.modfinal |  2 +-
>  scripts/Makefile.modpost  | 93 ++++++++++++---------------------------
>  scripts/link-vmlinux.sh   |  3 --
>  4 files changed, 53 insertions(+), 75 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index b5dfb54b1993..cf9d7b1d8c14 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1152,7 +1152,7 @@ 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
> @@ -1428,7 +1428,13 @@ 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
> @@ -1741,8 +1747,12 @@ 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)
> @@ -1773,6 +1783,11 @@ 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:
> @@ -1792,16 +1807,19 @@ 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

PHONY += single_modules

Reviewed-by: Nicolas Schier <nicolas@...sle.eu>

> -single_modpost: $(single-no-ko) modules_prepare
> +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))
> diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
> index 35100e981f4a..a3cf9e3647c9 100644
> --- a/scripts/Makefile.modfinal
> +++ b/scripts/Makefile.modfinal
> @@ -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))
> diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
> index 04ad00917b2f..2daf760eeb25 100644
> --- a/scripts/Makefile.modpost
> +++ b/scripts/Makefile.modpost
> @@ -32,9 +32,6 @@
>  # Step 4 is solely used to allow module versioning in external modules,
>  # where the CRC of each module is retrieved from the Module.symvers file.
>  
> -# KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
> -# This is solely useful to speed up test compiles
> -
>  PHONY := __modpost
>  __modpost:
>  
> @@ -45,24 +42,23 @@ MODPOST = scripts/mod/modpost								\
>  	$(if $(CONFIG_MODVERSIONS),-m)							\
>  	$(if $(CONFIG_MODULE_SRCVERSION_ALL),-a)					\
>  	$(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)					\
> +	$(if $(KBUILD_NSDEPS),-d $(MODULES_NSDEPS))					\
> +	$(if $(CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS)$(KBUILD_NSDEPS),-N)	\
>  	-o $@
>  
> -ifdef MODPOST_VMLINUX
> -
> -quiet_cmd_modpost = MODPOST $@
> -      cmd_modpost = $(MODPOST) $<
> -
> -vmlinux.symvers: vmlinux.o
> -	$(call cmd,modpost)
> +# 'make -i -k' ignores compile errors, and builds as many modules as possible.
> +ifneq ($(findstring i,$(filter-out --%,$(MAKEFLAGS))),)
> +MODPOST += -n
> +endif
>  
> -__modpost: vmlinux.symvers
> +ifeq ($(KBUILD_EXTMOD),)
>  
>  # Generate the list of in-tree objects in vmlinux
>  # ---------------------------------------------------------------------------
>  
>  # This is used to retrieve symbol versions generated by genksyms.
>  ifdef CONFIG_MODVERSIONS
> -vmlinux.symvers: .vmlinux.objs
> +vmlinux.symvers Module.symvers: .vmlinux.objs
>  endif
>  
>  # Ignore libgcc.a
> @@ -83,24 +79,12 @@ targets += .vmlinux.objs
>  .vmlinux.objs: $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS) FORCE
>  	$(call if_changed,vmlinux_objs)
>  
> -else
> -
> -ifeq ($(KBUILD_EXTMOD),)
> -
> -input-symdump := vmlinux.symvers
> -output-symdump := modules-only.symvers
> -
> -quiet_cmd_cat = GEN     $@
> -      cmd_cat = cat $(real-prereqs) > $@
> -
> -ifneq ($(wildcard vmlinux.symvers),)
> -
> -__modpost: Module.symvers
> -Module.symvers: vmlinux.symvers modules-only.symvers FORCE
> -	$(call if_changed,cat)
> -
> -targets += Module.symvers
> +vmlinux.o-if-present := $(wildcard vmlinux.o)
> +output-symdump := vmlinux.symvers
>  
> +ifdef KBUILD_MODULES
> +output-symdump := $(if $(vmlinux.o-if-present), Module.symvers, modules-only.symvers)
> +missing-input := $(filter-out $(vmlinux.o-if-present),vmlinux.o)
>  endif
>  
>  else
> @@ -112,56 +96,35 @@ src := $(obj)
>  # Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
>  include $(or $(wildcard $(src)/Kbuild), $(src)/Makefile)
>  
> -# modpost option for external modules
> -MODPOST += -e
> -
> -input-symdump := Module.symvers $(KBUILD_EXTRA_SYMBOLS)
> +module.symvers-if-present := $(wildcard Module.symvers)
>  output-symdump := $(KBUILD_EXTMOD)/Module.symvers
> +missing-input := $(filter-out $(module.symvers-if-present), Module.symvers)
>  
> -endif
> -
> -existing-input-symdump := $(wildcard $(input-symdump))
> -
> -# modpost options for modules (both in-kernel and external)
> -MODPOST += \
> -	$(addprefix -i ,$(existing-input-symdump)) \
> -	$(if $(KBUILD_NSDEPS),-d $(MODULES_NSDEPS)) \
> -	$(if $(CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS)$(KBUILD_NSDEPS),-N)
> -
> -# 'make -i -k' ignores compile errors, and builds as many modules as possible.
> -ifneq ($(findstring i,$(filter-out --%,$(MAKEFLAGS))),)
> -MODPOST += -n
> -endif
> +MODPOST += -e $(addprefix -i ,$(module.symvers-if-present) $(KBUILD_EXTRA_SYMBOLS))
>  
> -# Clear VPATH to not search for *.symvers in $(srctree). Check only $(objtree).
> -VPATH :=
> -$(input-symdump):
> -	@echo >&2 'WARNING: Symbol version dump "$@" is missing.'
> -	@echo >&2 '         Modules may not have dependencies or modversions.'
> -	@echo >&2 '         You may get many unresolved symbol warnings.'
> +endif # ($(KBUILD_EXTMOD),)
>  
> -# KBUILD_MODPOST_WARN can be set to avoid error out in case of undefined symbols
> -ifneq ($(KBUILD_MODPOST_WARN)$(filter-out $(existing-input-symdump), $(input-symdump)),)
> +ifneq ($(KBUILD_MODPOST_WARN)$(missing-input),)
>  MODPOST += -w
>  endif
>  
> +modorder-if-needed := $(if $(KBUILD_MODULES), $(MODORDER))
> +
>  # Read out modules.order to pass in modpost.
>  # Otherwise, allmodconfig would fail with "Argument list too long".
>  quiet_cmd_modpost = MODPOST $@
> -      cmd_modpost = sed 's/ko$$/o/' $< | $(MODPOST) -T -
> -
> -$(output-symdump): $(MODORDER) $(input-symdump) FORCE
> -	$(call if_changed,modpost)
> +      cmd_modpost = \
> +	$(if $(missing-input), \
> +		echo >&2 "WARNING: $(missing-input) is missing."; \
> +		echo >&2 "         Modules may not have dependencies or modversions."; \
> +		echo >&2 "         You may get many unresolved symbol warnings.";) \
> +	sed 's/ko$$/o/' $(or $(modorder-if-needed), /dev/null) | $(MODPOST) $(vmlinux.o-if-present) -T -
>  
>  targets += $(output-symdump)
> +$(output-symdump): $(modorder-if-needed) $(vmlinux.o-if-present) $(moudle.symvers-if-present) FORCE
> +	$(call if_changed,modpost)
>  
>  __modpost: $(output-symdump)
> -ifneq ($(KBUILD_MODPOST_NOFINAL),1)
> -	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modfinal
> -endif
> -
> -endif
> -
>  PHONY += FORCE
>  FORCE:
>  
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index 07486f90d5e2..6a197d8a88ac 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -214,9 +214,6 @@ if [ "$1" = "clean" ]; then
>  	exit 0
>  fi
>  
> -# modpost vmlinux.o to check for section mismatches
> -${MAKE} -f "${srctree}/scripts/Makefile.modpost" MODPOST_VMLINUX=1
> -
>  info MODINFO modules.builtin.modinfo
>  ${OBJCOPY} -j .modinfo -O binary vmlinux.o modules.builtin.modinfo
>  info GEN modules.builtin
> -- 
> 2.34.1

-- 
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