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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Mon, 27 Jan 2020 08:26:03 +0100
Message-ID: <CAK8P3a2P41JjO8=GTSVL9WVEfjA_M+StH7Ons27SqSNK2JOrHg@mail.gmail.com>
Subject: Re: [PATCH v2 00/10] Rework READ_ONCE() to improve codegen
To:     Qais Yousef <qais.yousef@arm.com>
Cc:     Arvind Sankar <nivedita@alum.mit.edu>,
        Nick Desaulniers <ndesaulniers@google.com>,
        David Laight <David.Laight@aculab.com>,
        Will Deacon <will@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        "kernel-team@android.com" <kernel-team@android.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Segher Boessenkool <segher@kernel.crashing.org>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
        Peter Oberparleiter <oberpar@linux.ibm.com>,
        Masahiro Yamada <masahiroy@kernel.org>
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On Sun, Jan 26, 2020 at 2:10 AM Qais Yousef <qais.yousef@arm.com> wrote:
> On 01/23/20 14:01, Arvind Sankar wrote:
> > On Thu, Jan 23, 2020 at 10:45:08AM -0800, Nick Desaulniers wrote:
> > > On Thu, Jan 23, 2020 at 9:32 AM David Laight <David.Laight@aculab.com> wrote:
> >
> > Reposting Arnd's link
> > https://www.spinics.net/lists/linux-kbuild/msg23648.html
>
> This list seems to be x86 centric? I remember when the switch to GCC 4.6
> happened a couple or more archs had to be dropped because they lacked a newer
> compiler.

There are two architectures that already had problems last time:

- unicore32 never had any compiler that shipped with sources, only an ancient
  set of gcc binaries that already had problems building the kernel during the
  move to gcc-4.6. The maintainer said he'd work on providing support for
  modern gcc or clang, but I don't think anything came out of that.

- hexagon had an unmaintained gcc-4.5 port, but internally Qualcomm were
  already using clang to build their kernels, which should now work with the
  upstream version. I don't think there are any plans to have a more modern
  gcc.

Everything else works with mainline gcc now, openrisc and csky were the
last to get added in gcc-9.

Some of the older sub-targets (armv3, s390-g6, powerpcspe) are removed
in gcc-9, but these have a few more years before we need to worry about
them.

     Arnd