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From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Tue, 4 May 2021 16:25:09 +0300
Message-ID: <CAHp75VdE9h9=CpzX094iJ52HR6Sz+f-qGfCt6YHfSPpG2Lb4-w@mail.gmail.com>
Subject: Re: [PATCH] Raise the minimum GCC version to 5.2
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Segher Boessenkool <segher@kernel.crashing.org>,
        Joe Perches <joe@perches.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
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        Paul Walmsley <paul.walmsley@sifive.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Miguel Ojeda <ojeda@kernel.org>,
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On Mon, May 3, 2021 at 12:29 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Mon, May 3, 2021 at 9:35 AM Alexander Dahl <ada@thorsis.com> wrote:
> >
> > Desktops and servers are all nice, however I just want to make you
> > aware, there are embedded users forced to stick to older cross
> > toolchains for different reasons as well, e.g. in industrial
> > environment. :-)
> >
> > This is no show stopper for us, I just wanted to let you be aware.
>
> Can you be more specific about what scenarios you are thinking of,
> what the motivations are for using an old compiler with a new kernel
> on embedded systems, and what you think a realistic maximum
> time would be between compiler updates?
>
> One scenario that I've seen previously is where user space and
> kernel are built together as a source based distribution (OE, buildroot,
> openwrt, ...), and the compiler is picked to match the original sources
> of the user space because that is best tested, but the same compiler
> then gets used to build the kernel as well because that is the default
> in the build environment.
>
> There are two problems I see with this logic:
>
> - Running the latest kernel to avoid security problems is of course
>   a good idea, but if one runs that with ten year old user space that
>   is never updated, the system is likely to end up just as insecure.
>   Not all bugs are in the kernel.
>
> - The same logic that applies to ancient user space staying with
>   an ancient compiler (it's better tested in this combination) also
>   applies to the kernel: running the latest kernel on an old compiler
>   is something that few people test, and tends to run into more bugs
>   than using the compiler that other developers used to test that
>   kernel.

I understand that you are talking about embedded, but it you stuck
with a distro (esp. LTS one, like CentOS 7.x), you have gcc 4.8.5
there for everything, but they have got security updates. Seems if you
are with a distro you have to stick with its kernel with all pros and
cons of such an approach.


-- 
With Best Regards,
Andy Shevchenko