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

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Message-ID: <CAHk-=whhCBvjXtRiFM2JEZ4XyBmuPprvdo5tpPVBqUhkRszxiQ@mail.gmail.com>
Date:   Mon, 11 May 2020 11:24:07 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        David Woodhouse <dwmw2@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Dmitry Golovin <dima@...ovin.in>,
        Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] x86: support i386 with Clang

On Mon, May 11, 2020 at 11:12 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Would using "__builtin_choose_expr()" be able to avoid this whole issue?

We actually have a fair amount of "pick expression based on size", so
with a few helper macros we could make the code look better than the
case statements too.

Something (ENTIRELY UNTESTED!) like the attached patch, perhaps?

NOTE! I only converted one single use to that "pick_size_xyz()" model.
If this actually works for clang too, we could do the others.

I guess I should just test it, since I have that clang tree.

                  Linus

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