linux-kernel - Re: [PATCH] x86/alternatives: Fix optimize

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Message-ID: <20180110203352.GS6176@hirez.programming.kicks-ass.net>
Date:   Wed, 10 Jan 2018 21:33:52 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        David Woodhouse <dwmw2@...radead.org>,
        Andi Kleen <andi@...stfloor.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Paul Turner <pjt@...gle.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Jiri Kosina <jikos@...nel.org>, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH] x86/alternatives: Fix optimize_nops() checking

On Wed, Jan 10, 2018 at 12:26:25PM -0800, Linus Torvalds wrote:
> Imagine just how crazy that would be to debug. You'd be basically
> executing insane code, and looking at the sources - or even the
> binaries - it would _look_ completely sane.

Been there done that.. we have too much self modifying code for that
not to have been needed.

Use gdb on /proc/kcore and disassemble self to see the _real_ code.

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