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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Thu, 23 Jul 2020 15:55:55 +0200
Message-ID: <CAK8P3a0gFG8z_qdY2gPm5p7kjpj8xq-APyazk390FpHUJiZ7Hw@mail.gmail.com>
Subject: Re: [PATCH v3 11/11] x86: support i386 with Clang
To:     Sedat Dilek <sedat.dilek@gmail.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dennis Zhou <dennis@kernel.org>, Tejun Heo <tj@kernel.org>,
        Christoph Lameter <cl@linux.com>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Clang-Built-Linux ML <clang-built-linux@googlegroups.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Dmitry Golovin <dima@golovin.in>,
        Linus Torvalds <torvalds@linux-foundation.org>
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On Thu, Jul 23, 2020 at 3:14 PM Sedat Dilek <sedat.dilek@gmail.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