linux-kernel - Re: [PATCH 4/4] kbuild: refactor module BTF rule

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Date:   Tue, 17 Oct 2023 14:58:04 +0200
From:   Nicolas Schier <n.schier@....de>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>
Subject: Re: [PATCH 4/4] kbuild: refactor module BTF rule

On Tue, Oct 17, 2023 at 07:37:42PM +0900, Masahiro Yamada wrote:
> newer_prereqs_except and if_changed_except are ugly hacks of the
> newer_prereqs and if_changed in scripts/Kbuild.include.

newer-prereqs

> 
> Remove.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
> 
>  scripts/Makefile.modfinal | 23 +++++------------------
>  1 file changed, 5 insertions(+), 18 deletions(-)
> 
> diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
> index 9fd7a26e4fe9..6ab10dba05c7 100644
> --- a/scripts/Makefile.modfinal
> +++ b/scripts/Makefile.modfinal
> @@ -19,6 +19,9 @@ vmlinux :=
>  ifdef CONFIG_DEBUG_INFO_BTF_MODULES
>  ifneq ($(wildcard vmlinux),)
>  vmlinux := vmlinux
> +cmd_btf = ; \

while reading, I stumpled over this semicolon, but probably it's a good
reminder that cmd_btf is only a cmd extension.

> +	LLVM_OBJCOPY="$(OBJCOPY)" $(PAHOLE) -J $(PAHOLE_FLAGS) --btf_base vmlinux $@; \
> +	$(RESOLVE_BTFIDS) -b vmlinux $@
>  else
>  $(warning Skipping BTF generation due to unavailability of vmlinux)
>  endif
> @@ -41,27 +44,11 @@ quiet_cmd_ld_ko_o = LD [M]  $@
>        cmd_ld_ko_o +=							\
>  	$(LD) -r $(KBUILD_LDFLAGS)					\
>  		$(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE)		\
> -		-T scripts/module.lds -o $@ $(filter %.o, $^)
> +		-T scripts/module.lds -o $@ $(filter %.o, $^)		\
> +	$(cmd_btf)
>  
> -quiet_cmd_btf_ko = BTF [M] $@
> -      cmd_btf_ko = 							\
> -		LLVM_OBJCOPY="$(OBJCOPY)" $(PAHOLE) -J $(PAHOLE_FLAGS) --btf_base vmlinux $@; \
> -		$(RESOLVE_BTFIDS) -b vmlinux $@
> -
> -# Same as newer-prereqs, but allows to exclude specified extra dependencies
> -newer_prereqs_except = $(filter-out $(PHONY) $(1),$?)
> -
> -# Same as if_changed, but allows to exclude specified extra dependencies
> -if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check),      \
> -	$(cmd);                                                              \
> -	printf '%s\n' 'savedcmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:)
> -
> -# Re-generate module BTFs if either module's .ko or vmlinux changed
>  %.ko: %.o %.mod.o scripts/module.lds $(vmlinux) FORCE
>  	+$(call if_changed_except,ld_ko_o,vmlinux)

This should probably be:

  +$(call if_changed,ld_ko_o)


> -ifdef vmlinux
> -	+$(if $(newer-prereqs),$(call cmd,btf_ko))
> -endif
>  
>  targets += $(modules:%.o=%.ko) $(modules:%.o=%.mod.o)
>  
> -- 
> 2.40.1
>