linux-kernel - Re: [RFC] x86/retpoline: Add clang support for 64-bit builds

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Message-ID: <1517950341.3677.27.camel@woodhou.se>
Date:   Tue, 06 Feb 2018 20:52:21 +0000
From:   David Woodhouse <david@...dhou.se>
To:     Guenter Roeck <linux@...ck-us.net>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>, gnomes@...rguk.ukuu.org.uk,
        Rik van Riel <riel@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>, thomas.lendacky@....com,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jiri Kosina <jikos@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Hansen <dave.hansen@...el.com>,
        Kees Cook <keescook@...gle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Paul Turner <pjt@...gle.com>
Subject: Re: [RFC] x86/retpoline: Add clang support for 64-bit builds

On Tue, 2018-02-06 at 12:32 -0800, Guenter Roeck wrote:
> 
> > 
> Feedback, anyone ?
> 
> I understand that there is no love for the ABI differences between clang
> and gcc, but that doesn't help me. Even if the patch is unacceptable
> as-is, I would like to have some feedback to get an idea if I am on the
> right track, and what I would have to change to at least move into the
> right direction.

I'm going for just a comprehensive NACK. If they fix clang so that at
least the thunk symbols __x86_indirect_thunk_\reg are compatible, then
we could tolerate command line differences. Otherwise, just no.

Unless you really fancy trying to do some kind of alias hack in modules
so that they link to the external thunk by its proper name, even when
built with clang? I reserve the right to hate that too.

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