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

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Date:   Thu, 7 Apr 2022 21:39:16 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Nick Desaulniers' <ndesaulniers@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>
CC:     "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
        "linux-kernel@...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

From: Nick Desaulniers
> Sent: 07 April 2022 18:59
> 
> 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?

I think I'd do:
single-no-ko := $(filter-out $(single-ko), $(MAKECMDGOALS))
single-no-ko += $(patsubst %.ko, %.o, $(single-ko))
single-no-ko += $(patsubst %.ko, %.mod, $(single-ko))

Although you can use the simpler SYSV make suffix substitution syntax:
single-no-ko += $(single-ko:.ko=.o) $(single-ko:.ko=.mod)

	David

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