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

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Message-ID: <82f5a922-1dd8-50b5-551c-33aa6d9e1192@nokia.com>
Date:   Wed, 10 Apr 2019 09:27:07 +0000
From:   "Wiebe, Wladislav (Nokia - DE/Ulm)" <wladislav.wiebe@...ia.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.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 09.04.2019 11:00, Masahiro Yamada 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.


Ok, I've posted v2:
https://lore.kernel.org/patchwork/patch/1059985/


Thanks!

- Wladislav



> 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
>