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References: <20211201152604.3984495-1-elver@google.com>
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From:   Marco Elver <elver@google.com>
Date:   Thu, 9 Dec 2021 11:00:00 +0100
Message-ID: <CANpmjNPaKMsgfDo5PE_dX794otFXbJvGubxG44C8-QL66UVaUw@mail.gmail.com>
Subject: Re: [PATCH] kcov: fix generic Kconfig dependencies if ARCH_WANTS_NO_INSTR
To:     elver@google.com, Andrew Morton <akpm@linux-foundation.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, kasan-dev@googlegroups.com,
        Peter Zijlstra <peterz@infradead.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        linux-arm-kernel@lists.infradead.org
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On Wed, 1 Dec 2021 at 16:26, Marco Elver <elver@google.com> wrote:
[...]
> At the time of 0f1441b44e823, we didn't yet have ARCH_WANTS_NO_INSTR,
> but now we can move the Kconfig dependency checks to the generic KCOV
> option. KCOV will be available if:
>
>         - architecture does not care about noinstr, OR
>         - we have objtool support (like on x86), OR
>         - GCC is 12.0 or newer, OR
>         - Clang is 13.0 or newer.
>
> Signed-off-by: Marco Elver <elver@google.com>

I think this is good to pick up. Even though it has an x86 change in
it, I think kcov changes go through -mm. Andrew, x86 maintainers, any
preference?

With the conclusion from [1], I think we decided it's better to take
this now, given we discovered KCOV already appears broken on arm64
(likely due to noinstr) and e.g. syzbot disables it on arm64.

[1] https://lkml.kernel.org/r/Yae+6clmwHox7CHN@FVFF77S0Q05N

Thanks,
-- Marco