linux-kernel - Re: [bpf-next PATCH v2 3/4] kbuild: skip module BTF with one-time check for vmlinux

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Date:   Thu, 19 Oct 2023 10:17:29 +0200
From:   Jiri Olsa <olsajiri@...il.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nicolas Schier <n.schier@....de>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>, bpf@...r.kernel.org
Subject: Re: [bpf-next PATCH v2 3/4] kbuild: skip module BTF with one-time
 check for vmlinux

On Thu, Oct 19, 2023 at 12:19:49AM +0900, Masahiro Yamada wrote:
> When CONFIG_DEBUG_INFO_BTF_MODULES is enabled, vmlinux presence is
> checked in every module build, resulting in repetitive warning
> messages if vmlinux is missing.
> 
> Check vmlinux and print a warning just once.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> Reviewed-by: Nicolas Schier <n.schier@....de>

lgtm

Acked-by: Jiri Olsa <jolsa@...nel.org>

jirka

> ---
> 
> (no changes since v1)
> 
>  scripts/Makefile.modfinal | 19 ++++++++++++-------
>  1 file changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
> index 8568d256d6fb..9fd7a26e4fe9 100644
> --- a/scripts/Makefile.modfinal
> +++ b/scripts/Makefile.modfinal
> @@ -14,6 +14,15 @@ include $(srctree)/scripts/Makefile.lib
>  
>  # find all modules listed in modules.order
>  modules := $(call read-file, $(MODORDER))
> +vmlinux :=
> +
> +ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +ifneq ($(wildcard vmlinux),)
> +vmlinux := vmlinux
> +else
> +$(warning Skipping BTF generation due to unavailability of vmlinux)
> +endif
> +endif
>  
>  __modfinal: $(modules:%.o=%.ko)
>  	@:
> @@ -36,12 +45,8 @@ quiet_cmd_ld_ko_o = LD [M]  $@
>  
>  quiet_cmd_btf_ko = BTF [M] $@
>        cmd_btf_ko = 							\
> -	if [ ! -f vmlinux ]; then					\
> -		printf "Skipping BTF generation for %s due to unavailability of vmlinux\n" $@ 1>&2; \
> -	else								\
>  		LLVM_OBJCOPY="$(OBJCOPY)" $(PAHOLE) -J $(PAHOLE_FLAGS) --btf_base vmlinux $@; \
> -		$(RESOLVE_BTFIDS) -b vmlinux $@; 			\
> -	fi;
> +		$(RESOLVE_BTFIDS) -b vmlinux $@
>  
>  # Same as newer-prereqs, but allows to exclude specified extra dependencies
>  newer_prereqs_except = $(filter-out $(PHONY) $(1),$?)
> @@ -52,9 +57,9 @@ if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check),      \
>  	printf '%s\n' 'savedcmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:)
>  
>  # Re-generate module BTFs if either module's .ko or vmlinux changed
> -%.ko: %.o %.mod.o scripts/module.lds $(and $(CONFIG_DEBUG_INFO_BTF_MODULES),$(KBUILD_BUILTIN),vmlinux) FORCE
> +%.ko: %.o %.mod.o scripts/module.lds $(vmlinux) FORCE
>  	+$(call if_changed_except,ld_ko_o,vmlinux)
> -ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +ifdef vmlinux
>  	+$(if $(newer-prereqs),$(call cmd,btf_ko))
>  endif
>  
> -- 
> 2.40.1
> 
>