linux-kernel - Re: [PATCH v3 11/11] x86: support i386 with Clang

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Message-ID: <CAK8P3a0gFG8z_qdY2gPm5p7kjpj8xq-APyazk390FpHUJiZ7Hw@mail.gmail.com>
Date:   Thu, 23 Jul 2020 15:55:55 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Sedat Dilek <sedat.dilek@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Dmitry Golovin <dima@...ovin.in>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v3 11/11] x86: support i386 with Clang

On Thu, Jul 23, 2020 at 3:14 PM Sedat Dilek <sedat.dilek@...il.com> wrote:
> What happens when there is no CONFIG_64BIT line?
> There exist explicit checks for (and "inverse") of CONFIG_64BIT like
> "ifdef" and "ifndef" or any "defined(...)" and its opposite?
> I remember I have seen checks for it in x86 tree.

As long as you consistently pass ARCH=i386 when running 'make',
nothing bad happens, as ARCH=i386 just hides that option.

If you run "make ARCH=i386 defconfig" followed by "make olddefconfig"
(without ARCH=i386) on a non-i386 machine, the absence of that
CONFIG_64BIT line will lead to the kernel going back to a 64-bit
configuration.

    Arnd