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

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Message-ID: <77e11884-f520-d983-3d33-ccc3043ba604@nokia.com>
Date:   Mon, 8 Apr 2019 08:02:46 +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 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. 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 :-)


> 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
> 
> 
>