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

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Date:   Thu, 19 Oct 2023 00:16:16 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Nicolas Schier <nicolas@...sle.eu>
Subject: Re: [PATCH 4/4] kbuild: refactor module BTF rule

On Tue, Oct 17, 2023 at 9:58 PM Nicolas Schier <n.schier@....de> wrote:
>
> 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

Yes.


>
> >
> > 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.


A semicolon is needed as a command separator, but
the trailing semicolon after the last command.

I usually prepend a semicolon to conditional commands.


>
> > +     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)


Right. Thanks for catching it.


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



-- 
Best Regards
Masahiro Yamada