linux-kernel - Re: [PATCH -tip v3 1/2] kcov: Make runtime functions noinstr-compatible

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Message-ID: <20200612113401.GC2554@hirez.programming.kicks-ass.net>
Date:   Fri, 12 Jun 2020 13:34:01 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Marco Elver <elver@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH -tip v3 1/2] kcov: Make runtime functions
 noinstr-compatible

On Thu, Jun 11, 2020 at 11:58:12PM +0200, Peter Zijlstra wrote:
> On Thu, Jun 11, 2020 at 11:55:38PM +0200, Peter Zijlstra wrote:
> > I'll have to dig around a little more to see if I can't get rid of the
> > relocation entirely. Also, I need to steal better arch_nop_insn() from
> > the kernel :-)

Oh, I just realized that recordmcount does exactly this same thing, so I
checked what that does to the relocation, and it turns out, it does the
same thing I did. They change the relocation type to R_*_NONE too.

So I suppose that's all right then.

I suppose I ought to go look at the recordmcount to objtool patches to
see if there's anything to share there.