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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Fri, 8 Apr 2022 09:37:37 +0900
Message-ID: <CAK7LNASJKMqfaifGA9r_cYqgkVgL6OPCfjFZCGN4mZwxW_rZvw@mail.gmail.com>
Subject: Re: [PATCH 6/7] kbuild: make *.mod not depend on *.o
To:     David Laight <David.Laight@aculab.com>
Cc:     Nick Desaulniers <ndesaulniers@google.com>,
        "linux-kbuild@vger.kernel.org" <linux-kbuild@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Michal Marek <michal.lkml@markovi.net>
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On Fri, Apr 8, 2022 at 6:39 AM David Laight <David.Laight@aculab.com> wrote:
>
> From: Nick Desaulniers
> > Sent: 07 April 2022 18:59
> >
> > On Wed, Apr 6, 2022 at 8:31 AM Masahiro Yamada <masahiroy@kernel.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@kernel.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?


Yes.

Kbuild can build a module individually.

    make  foo/bar/baz.ko

(but modpost check does not work well)

To do this, Kbuild needs to descend to
the directory and generate
foo/bar/baz.o  and  foo/bar/baz.mod.

Previously, foo/bar/baz.o was generated as a
prerequisite of foo/bar/baz.mod, but now we
need to request Kbuild to generate both of them.


> 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)


Right.   I tend to use $(patsubst ), but
in some places, shorter SYSV syntax is used.
I admit inconsistency.


>
>         David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)


-- 
Best Regards
Masahiro Yamada