linux-kernel - Re: Toolchain-dependent config options

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Date:   Thu, 14 Jan 2021 12:55:26 +0100
From:   Bernd Petrovitsch <bernd@...rovitsch.priv.at>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Toolchain-dependent config options

Hi all!

On Thu, 2021-01-14 at 13:56 +0900, Masahiro Yamada wrote:
> On Thu, Jan 14, 2021 at 7:21 AM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
[...]
> > If I copy a config with CONFIG_GCC_PLUGINS to another system which
> > doesn't have the gcc-plugin-devel package, it gets silently disabled by
> > "make olddefconfig".
> > 
> > I've seen multiple cases lately where this is causing confusion.  I
> > suspect the problem is getting worse with recent added support for a
> > variety of toolchains and toolchain-dependent features.
> > 
> > Would it be possible to have an error (or at least a warning) in this
> > case?
> > 
> > For example, a "depends-error" which triggers an error if its failure
> > would disable a feature?
[...]
> We disable any feature that is unsupported by the compiler in use.
> 
> Conventionally, we did that in the top Makefile
> by using $(call cc-option, ) macro or by running some scripts.
> 
> Recently, we are moving such compiler tests to the Kconfig stage.
> 
> Anyway, we disable unsupported features so any combination
> of CONFIG options builds successfully.
> This will ease randconfg and allmodconfig tests.

For options of $CC, that makes sense since there are different
compilers and lots of versions of them out there.

> A lot of people and CI systems are running allmodconfig tests
> for various architectures and toolchains.

Isn't some kind of defying (or more killing) the usefulness
of regression compile runs if one does `make allmodconfig`
and some (lots?) of stuff gets automatically configured
out just because some
-dev(|el) package is missing?

Aren't there some kernel-build meta packages for various
distributions out there that pull all necessary in?

> Introducing the build breakage is annoying.

Yes, update/install the necessary package to fix it.

MfG,
	Bernd
-- 
Bernd Petrovitsch                  Email : bernd@...rovitsch.priv.at
There is no cloud, just other people computers. - FSFE
                     LUGA : http://www.luga.at