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Date:   Fri, 12 Apr 2019 10:52:20 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Jonas Gorski <jonas.gorski@...il.com>
Cc:     "Wiebe, Wladislav (Nokia - DE/Ulm)" <wladislav.wiebe@...ia.com>,
        "michal.lkml@...kovi.net" <michal.lkml@...kovi.net>,
        "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] modpost: make KBUILD_MODPOST_WARN also configurable for
 external modules

On Tue, Apr 9, 2019 at 7:31 PM Jonas Gorski <jonas.gorski@...il.com> wrote:
>
> Hi,
>
> 本当に申し訳ありません, I got sidetracked and completely forgot about it. I
> actually still have my old tree with the suggested changes for v2.
>
> On Tue, 9 Apr 2019 at 11:01, Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
> >
> > Hi.
> >
> > On Mon, Apr 8, 2019 at 5:03 PM Wiebe, Wladislav (Nokia - DE/Ulm)
> > <wladislav.wiebe@...ia.com> wrote:
> > >
> > > Hi!
> > >
> > > On 07.04.2019 11:04, Masahiro Yamada wrote:
> > > > (+CC Jonas Gorski)
> > > >
> > > >
> > > > On Tue, Mar 26, 2019 at 6:58 PM Wiebe, Wladislav (Nokia - DE/Ulm)
> > > > <wladislav.wiebe@...ia.com> wrote:
> > > >>
> > > >> Commit ea837f1c0503 ("kbuild: make modpost processing configurable")
> > > >> was intended to give KBUILD_MODPOST_WARN flexibility to be configurable.
> > > >> Right now KBUILD_MODPOST_WARN gets just ignored when KBUILD_EXTMOD is
> > > >> set which happens per default when building modules out of the tree.
> > > >>
> > > >> This change gives the opportunity to define module build behaving also
> > > >> in case of out of tree builds and default will become exit on error.
> > > >> Errors which can be detected by the build should be trapped out of the box
> > > >> there, unless somebody wants to notice broken stuff later at runtime.
> > > >
> > > > If an external module refers to a symbol
> > > > provided by another external module,
> > > > this patch will turn the warning into the error by default,
> > > > which is probably a bad idea.
> > >
> > > Indeed, exactly this should happen. You should fix your external module
> > > dependencies by providing their symbols. Please use e.g.
> > > KBUILD_EXTRA_SYMBOLS instead of converting errors to warning and hoping
> > > that things will work.
> >
> > I know this option.
> > What I want to say is, this patch changes the behavior, and
> > may annoy some people.
> >
> > > Or how do you want to make sure module A still
> > > delivers all symbols needed by module B after an update/changes?
> > > Manually comparing the logs after an update or waiting until it turns
> > > out broken during run-time? I wouldn't say this is a good idea :-)
> >
> > OK, so the commit log should record both the behavior change
> > and workarounds.
> >
> > - If an external module being built refers to symbols
> >   in another external module, Kbuild previously showed a warning,
> >   but going forward it will turn it into an error.
> >
> > - To work around this, you should pass a symbol table via KBUILD_EXTRA_SYMBOLS,
> >   or KBUILD_EXTRA_SYMBOLS=1 to turn the error into a warning.
>
> This sounds like a good middle ground. When you do the effort of
> setting KBUILD_EXTRA_SYMBOLS, you are likely interested in proper
> dependency resolution and being notified if it fails.
>
> I would probably still use KBUILD_MODPOST_WARN=0 to force the warnings
> as errors, to have it as the central switch for the behaviour. So the
> behaviour would then become
>
> - If KBUILD_MODPOST_WARN is set to any value, set -w accordingly
> - else, set -w only when building for an external module and
> KBUILD_EXTRA_SYMBOLS is empty
>
> or
>
> ifdef KBUILD_MODPOST_WARN
>     KBUILD_MODPOST_WARN:=$(filter-out 0,$(KBUILD_MODPOST_WARN))
> else
>     KBUILD_MODPOST_WARN:=$(if $(KBUILD_EXTMOD),$(if $(KBUILD_EXTRA_SYMBOLS),,1))
> endif


Sorry, I think this is too complicated.

I applied this since it is simple.
https://patchwork.kernel.org/patch/10895465/



-- 
Best Regards
Masahiro Yamada

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