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

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Date:   Fri, 24 Jul 2020 15:22:03 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
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 3:56 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> 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.
>

Again thank you for your feedback.

Unsure if people are aware of the different behaviours and results.

That's why I keep the same make line with and without "defconfig".

Unfortunately, I had no opportunity to test the patchset :-(.

For testing I had done:
$ MAKE_OPTS="..."
$ ARCH=x86 make V=1 -j3 $MAKE_OPTS i386_defconfig (whereas V=1 and -j3
can be dropped of course)
$ ARCH=x86 make V=1 -j3 $MAKE_OPTS

Side-note:
How wonderful my patch "x86/defconfigs: Remove CONFIG_CRYPTO_AES_586
from i386_defconfig" landed in <tip.git#x86/build>.

- Sedat -

[1] https://git.kernel.org/tip/tip/c/6526b12de07588253a52577f42ec99fc7ca26a1f