linux-kernel - Re: [PATCH 6/7] kbuild: make *.mod not depend on *.o

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Date:   Thu, 7 Apr 2022 10:59:21 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Michal Marek <michal.lkml@...kovi.net>
Subject: Re: [PATCH 6/7] kbuild: make *.mod not depend on *.o

On Wed, Apr 6, 2022 at 8:31 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> The dependency
>
>     $(obj)/%.mod: $(obj)/%$(mod-prelink-ext).o
>
> ... exists because *.mod files previously contained undefined symbols,
> which are computed from *.o files when CONFIG_TRIM_UNUSED_KSYMS=y.
>
> Now that the undefined symbols are put into separate *.usyms files,
> there is no reason to make *.mod depend on *.o files.
>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
>
>  Makefile               | 3 ++-
>  scripts/Makefile.build | 5 ++---
>  2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 82ee893909e9..e915aacd02b0 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1792,7 +1792,8 @@ ifdef single-build
>
>  # .ko is special because modpost is needed
>  single-ko := $(sort $(filter %.ko, $(MAKECMDGOALS)))
> -single-no-ko := $(sort $(patsubst %.ko,%.mod, $(MAKECMDGOALS)))
> +single-no-ko := $(filter-out $(single-ko), $(MAKECMDGOALS)) \
> +               $(foreach x, o mod, $(patsubst %.ko, %.$x, $(single-ko)))

I'm on board with this patch, and the overall goal with the series. My
brain is having a hard time parsing `o mod` though. Can you walk me
through that? Are those targets for .o and .mod files, respectively?

>
>  $(single-ko): single_modpost
>         @:
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index f7a30f378e20..3da731cf6978 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -85,7 +85,7 @@ ifdef need-builtin
>  targets-for-builtin += $(obj)/built-in.a
>  endif
>
> -targets-for-modules := $(foreach x, mod $(if $(CONFIG_TRIM_UNUSED_KSYMS), usyms), \
> +targets-for-modules := $(foreach x, o mod $(if $(CONFIG_TRIM_UNUSED_KSYMS), usyms), \
>                                 $(patsubst %.o, %.$x, $(filter %.o, $(obj-m))))
>
>  ifneq ($(CONFIG_LTO_CLANG)$(CONFIG_X86_KERNEL_IBT),)
> @@ -306,7 +306,7 @@ endif
>  cmd_mod = echo $(addprefix $(obj)/, $(call real-search, $*.o, .o, -objs -y -m)) | \
>         $(AWK) -v RS='( |\n)' '!x[$$0]++' > $@
>
> -$(obj)/%.mod: $(obj)/%$(mod-prelink-ext).o FORCE
> +$(obj)/%.mod: FORCE
>         $(call if_changed,mod)
>
>  # List module undefined symbols
> @@ -469,7 +469,6 @@ $(multi-obj-m): FORCE
>         $(call if_changed,link_multi-m)
>  $(call multi_depend, $(multi-obj-m), .o, -objs -y -m)
>
> -targets += $(multi-obj-m)
>  targets := $(filter-out $(PHONY), $(targets))
>
>  # Add intermediate targets:
> --
> 2.32.0
>


-- 
Thanks,
~Nick Desaulniers