linux-kernel - Re: [PATCH] modpost: make KBUILD_MODPOST_WARN also configurable for external modules

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Date:   Tue, 9 Apr 2019 18:00:33 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     "Wiebe, Wladislav (Nokia - DE/Ulm)" <wladislav.wiebe@...ia.com>
Cc:     "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>,
        Jonas Gorski <jonas.gorski@...il.com>
Subject: Re: [PATCH] modpost: make KBUILD_MODPOST_WARN also configurable for
 external modules

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.


Thanks.

>
> > I suggested a desired change in the following.
> > https://patchwork.kernel.org/patch/9980691/
> >
> > I am poking Jonas Gorski
> > if he plans to send v2.
>
> I wouldn't vote for v2 based on explanation above.
>
> - Wladislav
>
> >
> >
> >> Signed-off-by: Wladislav Wiebe <wladislav.wiebe@...ia.com>
> >> ---
> >>   scripts/Makefile.modpost | 2 +-
> >>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
> >> index 6b7f354f189a..fec6ec2ffa47 100644
> >> --- a/scripts/Makefile.modpost
> >> +++ b/scripts/Makefile.modpost
> >> @@ -78,7 +78,7 @@ modpost = scripts/mod/modpost                    \
> >>    $(if $(KBUILD_EXTRA_SYMBOLS), $(patsubst %, -e %,$(KBUILD_EXTRA_SYMBOLS))) \
> >>    $(if $(KBUILD_EXTMOD),-o $(modulesymfile))      \
> >>    $(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)  \
> >> - $(if $(KBUILD_EXTMOD)$(KBUILD_MODPOST_WARN),-w)
> >> + $(if $(KBUILD_MODPOST_WARN),-w)
> >>
> >>   MODPOST_OPT=$(subst -i,-n,$(filter -i,$(MAKEFLAGS)))
> >>
> >> --
> >> 2.19.2
> >
> >
> >


--
Best Regards
Masahiro Yamada