linux-kernel - Re: [PATCH v3] x86/entry: emit a symbol for register restoring thunk

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Message-ID: <20210112114725.GA13086@zn.tnic>
Date:   Tue, 12 Jan 2021 12:47:25 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Fāng-ruì Sòng <maskray@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>, X86 ML <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH v3] x86/entry: emit a symbol for register restoring thunk

On Mon, Jan 11, 2021 at 05:13:16PM -0800, Nick Desaulniers wrote:
> Unconditionally. See
> https://sourceware.org/pipermail/binutils/2021-January/114700.html
> where that flag was rejected and the optimization was adopted as the
> optimization was obvious to GNU binutils developers. So I suspect this
> will become a problem for GNU binutils users as well after the latest
> release that contains
> https://sourceware.org/pipermail/binutils/attachments/20210105/75dd4a9d/attachment-0001.bin.

Aha, thanks for this.

> I can clean that up in v5; The section symbols were not generated then
> stripped; they were simply never generated.

I'd appreciate a more verbose writeup explaining why this is being done,
but written for outsiders who are not necessarily toolchain developers.
So that it is clear months/years from now why this was done. Something
structured like this maybe:

  Problem is A.

  It happens because of B.

  Fix it by doing C.

  (Potentially do D).

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette