linux-kernel - Re: [PATCH] Raise the minimum GCC version to 5.2

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Date:   Mon, 3 May 2021 13:35:30 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Joe Perches <joe@...ches.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Corbet <corbet@....net>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Paul Mackerras <paulus@...ba.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Will Deacon <will@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] Raise the minimum GCC version to 5.2

On Mon, May 3, 2021 at 12:32 AM Matthew Wilcox <willy@...radead.org> wrote:
> On Sun, May 02, 2021 at 02:08:31PM -0700, Linus Torvalds wrote:
> > What is relevant is what version of gcc various distributions actually
> > have reasonably easily available, and how old and relevant the
> > distributions are. We did decide that (just as an example) RHEL 7 was
> > too old to worry about when we updated the gcc version requirement
> > last time.
> >
> > Last year, Arnd and Kirill (maybe others were involved too) made a
> > list of distros and older gcc versions. But I don't think anybody
> > actually _maintains_ such a list. It would be perhaps interesting to
> > have some way to check what compiler versions are being offered by
> > different distros.
>
> fwiw, Debian 9 aka Stretch released June 2017 had gcc 6.3
> Debian 10 aka Buster released June 2019 had gcc 7.4 *and* 8.3.
> Debian 8 aka Jessie had gcc-4.8.4 and gcc-4.9.2.
>
> So do we care about people who haven't bothered to upgrade userspace
> since 2017?  If so, we can't go past 4.9.

I would argue that we shouldn't care about distros that are officially
end-of-life. Jessie support ended last July according to the official
Debian pages at https://wiki.debian.org/LTS.

It's a little harder for distros that are still officially supported, like the
RHEL7 case that Linus mentioned, Debian Stretch (gcc-6.3),
Slackware 14.2 (gcc-5.3), or Ubuntu 18.04 (gcc-7.3). For any of
these you could make the argument one way or the other: either
say we care as long as the distro cares, or the users that want
to build their own kernels can be reasonably expected to either
upgrade their distro or install a newer compiler manually.

Looking at the Debian case specifically, I see these numbers
from https://popcon.debian.org/:

testing/unstable: 16730
buster/stable: 113881
stretch/oldstable: 39147
jessie/oldoldstable: 19286

Assuming the numbers of users that installed popcon are
proportional to the actual number of users, that's still a large
chunk of people running stretch or older. Presumably,
these users are actually less likely to build their own kernels.

       Arnd