linux-kernel - Re: [PATCH] gcov,x86: Mark GCOV broken for x86

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Message-ID: <CAKwvOd=PYrMnNOu060T3Z26RJriNXqu3iM85Daink4-BN__2sQ@mail.gmail.com>
Date:   Mon, 14 Jun 2021 09:05:04 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Johannes Berg <johannes.berg@...el.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Marco Elver <elver@...gle.com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH] gcov,x86: Mark GCOV broken for x86

On Mon, Jun 14, 2021 at 3:17 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
>
> As recently discovered, there is no function attribute to disable the
> -fprofile-generate instrumentation. As such, GCOV is fundamentally
> incompatible with architectures that rely on 'noinstr' for correctness.

Is there context for comment, or is this patch meant as a joke?

>
> Until such time as that compilers have added a function attribute to
> disable this instrumentation, mark GCOV as broken.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  arch/x86/Kconfig    | 2 +-
>  kernel/gcov/Kconfig | 4 ++++
>  2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 86dae426798b..c0f8c9d4c31a 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -75,7 +75,7 @@ config X86
>         select ARCH_HAS_FAST_MULTIPLIER
>         select ARCH_HAS_FILTER_PGPROT
>         select ARCH_HAS_FORTIFY_SOURCE
> -       select ARCH_HAS_GCOV_PROFILE_ALL
> +       select ARCH_HAS_GCOV_BROKEN
>         select ARCH_HAS_KCOV                    if X86_64 && STACK_VALIDATION
>         select ARCH_HAS_MEM_ENCRYPT
>         select ARCH_HAS_MEMBARRIER_SYNC_CORE
> diff --git a/kernel/gcov/Kconfig b/kernel/gcov/Kconfig
> index 58f87a3092f3..74b028a66ebe 100644
> --- a/kernel/gcov/Kconfig
> +++ b/kernel/gcov/Kconfig
> @@ -1,10 +1,14 @@
>  # SPDX-License-Identifier: GPL-2.0-only
>  menu "GCOV-based kernel profiling"
>
> +config ARCH_HAS_GCOV_BROKEN
> +       def_bool n
> +
>  config GCOV_KERNEL
>         bool "Enable gcov-based kernel profiling"
>         depends on DEBUG_FS
>         depends on !CC_IS_CLANG || CLANG_VERSION >= 110000
> +       depends on !ARCH_HAS_GCOV_BROKEN
>         select CONSTRUCTORS
>         default n
>         help



-- 
Thanks,
~Nick Desaulniers