From mboxrd@z Thu Jan  1 00:00:00 1970
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752888AbeAJUtk (ORCPT <rfc822;ralf@linux-mips.org> + 1 other);
        Wed, 10 Jan 2018 15:49:40 -0500
Received: from mail-io0-f177.google.com ([209.85.223.177]:46358 "EHLO
        mail-io0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751794AbeAJUtj (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 10 Jan 2018 15:49:39 -0500
X-Google-Smtp-Source: ACJfBos6euT8Uss/ahsNX1qBwnXl1jLf8BNKL+Dfxk00Em971pni0mm0wMUUYj9bALmNuUVjlPKF9/SAWeBZzZmELjo=
MIME-Version: 1.0
In-Reply-To: <20180110203352.GS6176@hirez.programming.kicks-ass.net>
References: <20180110003139.10531-1-andi@firstfloor.org> <CA+55aFzyVFEUKaLpqxfwh5E9QFgMjzr+wVoYGxqTHVDkGcFkOw@mail.gmail.com>
 <1515568506.22302.72.camel@infradead.org> <1515578735.22302.91.camel@infradead.org>
 <20180110112815.mgciyf5acwacphkq@pd.tnic> <CA+55aFz=yU7Q87ooyokssaFEGBx8BL+Vzs=4z+OOzvg-K5tfbA@mail.gmail.com>
 <alpine.DEB.2.20.1801102053120.1919@nanos> <20180110201532.5jnji6ypfl6slzvb@treble>
 <CA+55aFzMzBwtfO1e=eC6oCx9mMMXPoRko0FvKKJrriUGqyQtEg@mail.gmail.com> <20180110203352.GS6176@hirez.programming.kicks-ass.net>
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 10 Jan 2018 12:49:37 -0800
X-Google-Sender-Auth: NlysSYVQaMVwByFj1vFsNqdUt4E
Message-ID: <CA+55aFw_KWncsY0x=_BnEKkZz3dFUm921ppu0HbGk8e2sBwiAA@mail.gmail.com>
Subject: Re: [PATCH] x86/alternatives: Fix optimize_nops() checking
To: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>,
        David Woodhouse <dwmw2@infradead.org>,
        Andi Kleen <andi@firstfloor.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Paul Turner <pjt@google.com>,
        Andrew Lutomirski <luto@kernel.org>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linux-foundation.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Jiri Kosina <jikos@kernel.org>, Andi Kleen <ak@linux.intel.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Return-Path: <linux-kernel-owner@vger.kernel.org>

On Wed, Jan 10, 2018 at 12:33 PM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> Use gdb on /proc/kcore and disassemble self to see the _real_ code.

Yes, because that works so well when you get these random reports of
crazy behavior that simply doesn't ever trigger on any machine you
have.

> But yes, tricky stuff. Not arguing we need relocations in alternatives,
> just saying debugging them (and static keys and others) is great fun.

Yes. It's definitely a good challenge, and can be _very_ satisfying
when you then finally figure it out.

I'm not sure it's worth the pain before that point, though.

So I think we should strive to make our alternatives code just catch
some of the more subtle errors early instead.

           Linus