linux-kernel - Re: due to kconfig changes kernel config file is no longer sufficient for configuring the kernel

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Message-ID: <CAK7LNAQ5Q-DPL006UJzs-dAhMo5Cdaa9P+UAD+XL67QvPw353g@mail.gmail.com>
Date:   Mon, 3 Sep 2018 19:06:00 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Michal Suchánek <msuchanek@...e.de>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Takashi Iwai <tiwai@...e.de>, Andreas Schwab <schwab@...e.de>,
        Michal Kubecek <mkubecek@...e.cz>,
        Michal Marek <michal.lkml@...kovi.net>,
        Jonathan Corbet <corbet@....net>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ulf Magnusson <ulfalizer@...il.com>,
        Jeff Mahoney <jeffm@...e.com>,
        "Peter Zijlstra," <peterz@...radead.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Nicholas Piggin <npiggin@...il.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux-sh list <linux-sh@...r.kernel.org>,
        sparclinux <sparclinux@...r.kernel.org>,
        linux-um@...ts.infradead.org
Subject: Re: due to kconfig changes kernel config file is no longer sufficient
 for configuring the kernel

Hi,


2018-08-21 6:33 GMT+09:00 Michal Suchánek <msuchanek@...e.de>:
> Hello,
>
> On Tue, 21 Aug 2018 03:15:12 +0900
> Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:
>
>> 2018-08-07 3:07 GMT+09:00 Michal Suchánek <msuchanek@...e.de>:
>> > On Mon, 30 Jul 2018 17:02:42 +0900
>> > Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:
>> >
>> >> 2018-06-28 18:16 GMT+09:00 Michal Suchánek <msuchanek@...e.de>:
>> >> > On Wed, 27 Jun 2018 23:07:21 +0900
>> >> > Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:
>> >> >
>
>> >>
>> >>
>> >>
>> >> >>
>> >> >> out-of-tree modules are built with exactly the same
>> >> >> configuration as used for the kernel.
>> >> >
>> >> > It is not true. And that is the problem. You need the config file
>> >> > and dump of the environment passed to the make command at
>> >> > configuration time to get the exact same configuration. The
>> >> > environment is not saved anywhere, though.
>> >>
>> >>
>> >> Why dump of the environment?
>> >>
>> >>
>> >> If you are building external modules natively
>> >> your distribution provides /lib/modules/$(uname -r)/build,
>> >> which contains files enough for building external modules.
>> >>
>> >> You can pass the directory path to M=... parameter.  That's it.
>> >
>> > No, that's not it. Since passing ARCH=i386 is the de-facto standard
>> > to configure a 32bit kernel and the result of passing that was not
>> > saved you need to pass it to make as well.
>>
>>
>> If you pass ARCH= for the configuration phase,
>> you need to pass the same ARCH= in the build phase.
>>
>>
>>
>>
>> What I can suggest for you is:
>>
>>
>> $ make ARCH=i386 defconfig
>> $ make ARCH=i386
>>
>>    OR
>>
>> $ make i386_defconfig
>> $ make
>
> Maybe you missed that but I do not want to build the defconfig. I want
> to build a *particular* config which has been saved in a file
> beforehand.
>>
>> > And you need to patch a number of
>> > 3rd party build scripts that build a kernel module as part of a
>> > bigger project.
>>
>>
>> You do not need to patch a number of scripts.
>>
>> Just one liner fix.
>> Add 'export ARCH=i386' in the top level script.
>
> And that does not work because there is no toplevel script. rpm has
> three toplevel scripts - prep, build and install.


OK, I understood real problem cases.

I wrote patches to support non-interactive .config updates.

For package building like rpm, deb, etc.
the target ARCH is determined when creating a source package.
If so, it would not hurt to hard-code to record ARCH in the spec file.


> Building out-of-tree module is another toplevel script.


As I said before, the .config is not reconfigured
when building out-of-tree modules.

Out-of-tree modules are built with the .config
that has been used to build vmlinux
regardless of whether you pass ARCH=i386, ARCH=x86_64, or nothing.

If rpmbuild is given target option like 'rpmbuild --target i386 ...",
it think it makes sense to propagate it to ARCH=.


> And it does not suffice to 'export ARCH=i386'. What if it was a 64bit
> config? How do I tell?
>
> With more and more options left out of the config that depend on
> compiler features, environment variables, phase of the moon or whatnot
> you can't even tell what kind of kernel the user is running by looking
> at the config.


I added non-interactive .config update.

Please try it.




-- 
Best Regards
Masahiro Yamada