linux-kernel - Re: [PATCH] x86/asm: Fix inline asm call constraints for GCC 4.4

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Date:   Fri, 29 Sep 2017 08:29:35 -0700
From:   Arnd Bergmann <arnd@...db.de>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        kernel test robot <xiaolong.ye@...el.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Alexander Potapenko <glider@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dmitriy Vyukov <dvyukov@...gle.com>,
        Miguel Bernal Marin <miguel.bernal.marin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, LKP <lkp@...org>
Subject: Re: [PATCH] x86/asm: Fix inline asm call constraints for GCC 4.4

On Fri, Sep 29, 2017 at 12:51 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>
>> On Thu, Sep 28, 2017 at 2:58 PM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>> The kernel test robot report looked to be ignored as a "gcc-4.4 is too
>> old to worry about" thing. [...]
>
> No, and sorry if my first reply grumbling about how old GCC 4.4 is sounded that
> way! We have to live with compiler bugs no matter how old the compiler is, the
> release cycles are decoupled to such a degree and external tooling propagates with
> such high latencies that that's the only sane thing to do.
>
> We also officially support GCC 3.2 and later compilers. Had this regression not
> been resolved within a week or so I was fully ready to queue up a revert commit,
> no questions asked.

FWIW, we had a discussion about which compiler versions actually still work
earlier this year: We concluded that gcc-4.0 and earlier have been broken
for a while without anyone caring. gcc-4.1 support is kept working in certain
configurations primarily due to Geert using it for build testing, but my tests
across multiple architectures showed that gcc-4.3 is needed on most
other architectures already. Some architectures need  even newer ones, and
some features need compiler support that was added much later of course.

         Arnd