linux-kernel - Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64

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Message-ID: <CAHk-=whNKuuhS9DTYx_ta_yDt4x2mLjtAgWgLE=gXEQrvz_vNg@mail.gmail.com>
Date:   Thu, 29 Nov 2018 09:54:26 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Lutomirski <luto@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, mhiramat@...nel.org,
        jbaron@...mai.com, Jiri Kosina <jkosina@...e.cz>,
        David.Laight@...lab.com, bp@...en8.de, julia@...com,
        jeyu@...nel.org, Peter Anvin <hpa@...or.com>
Subject: Re: [PATCH v2 4/4] x86/static_call: Add inline static call
 implementation for x86-64

On Thu, Nov 29, 2018 at 9:50 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
>  - corrupt random registers because we "know" they aren't in use

Just to clarify: I think that's a completely unacceptable model.

We already have lots of special calling conventions, including ones
that do not have any call-clobbered registers at all, because we have
special magic calls in inline asm.

Some of those might be prime material for doing static calls (ie PV-op
stuff, where the native model does *not* change any registers).

So no. Don't do ugly hacks like that.

               Linus