linux-kernel - Re: Clang arm64 build is broken

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Message-ID: <CAKwvOdkedxmstRytbWeYU8Pj9ahgWOe7rODJJ8BDtRzUroQeXw@mail.gmail.com>
Date:   Mon, 14 May 2018 09:24:45 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     marc.zyngier@....com, Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        LKML <linux-kernel@...r.kernel.org>,
        Kostya Serebryany <kcc@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        christoffer.dall@....com,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: Clang arm64 build is broken

On Fri, Apr 20, 2018 at 7:59 AM Andrey Konovalov <andreyknvl@...gle.com>
wrote:
> On Fri, Apr 20, 2018 at 10:13 AM, Marc Zyngier <marc.zyngier@....com>
wrote:
> >> The issue is that
> >> clang doesn't know about the "S" asm constraint. I reported this to
> >> clang [2], and hopefully this will get fixed. In the meantime, would
> >> it possible to work around using the "S" constraint in the kernel?
> >
> > I have no idea, I've never used clang to build the kernel. Clang isn't
> > really supported to build the arm64 kernel anyway (as you mention
> > below), and working around clang deficiencies would mean that we leave
> > with the workaround forever. I'd rather enable clang once it is at
> > feature parity with GCC.

> The fact that there are some existing issues with building arm64
> kernel with clang doesn't sound like a good justification for adding
> new issues :)

> However in this case I do believe that this is more of a bug in clang
> that should be fixed.

Just to follow up with this thread;

Support for "S" constraints is being (re-)added to Clang in:
https://reviews.llvm.org/D46745

-- 
Thanks,
~Nick Desaulniers