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

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Message-ID: <20200608110108.GB2497@hirez.programming.kicks-ass.net>
Date:   Mon, 8 Jun 2020 13:01:08 +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>
Subject: Re: [PATCH -tip v3 1/2] kcov: Make runtime functions
 noinstr-compatible

On Mon, Jun 08, 2020 at 09:57:39AM +0200, Dmitry Vyukov wrote:

> As a crazy idea: is it possible to employ objtool (linker script?) to
> rewrite all coverage calls to nops in the noinstr section? Or relocate
> to nop function?
> What we are trying to do is very static, it _should_ have been done
> during build. We don't have means in existing _compilers_ to do this,
> but maybe we could do it elsewhere during build?...

Let me try and figure out how to make objtool actually rewrite code.