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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Thu, 27 Oct 2022 23:31:49 +0900
Message-ID: <CAK7LNARfKkiNSUfZAqDQd15O8NAhpX13dHDuGn3OPL_b_F_92g@mail.gmail.com>
Subject: Re: [PATCH 3/5] Kconfig.debug: disable CONFIG_FRAME_WARN for KMSAN by default
To:     Alexander Potapenko <glider@google.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        linux-kbuild@vger.kernel.org
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On Tue, Oct 25, 2022 at 6:22 AM Alexander Potapenko <glider@google.com> wrote:
>
> KMSAN adds a lot of instrumentation to the code, which results in
> increased stack usage (up to 2048 bytes and more in some cases).
> It's hard to predict how big the stack frames can be, so we disable
> the warnings for KMSAN instead.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Masahiro Yamada <masahiroy@kernel.org>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: linux-kbuild@vger.kernel.org
> Link: https://github.com/google/kmsan/issues/89
> Signed-off-by: Alexander Potapenko <glider@google.com>
> ---
>  lib/Kconfig.debug | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 3fc7abffc7aa2..29280072dc0e4 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -400,8 +400,9 @@ config FRAME_WARN
>         default 1536 if (!64BIT && XTENSA)
>         default 1024 if !64BIT
>         default 2048 if 64BIT
> +       default 0 if KMSAN


This is wrong.

Kconfig picks up the first default entry which has
true 'if' condition.


Since (!64BIT || 64BIT) covers all the possible cases,
this patch is just adding dead code.


>         help
> -         Tell gcc to warn at build time for stack frames larger than this.
> +         Tell the compiler to warn at build time for stack frames larger than this.
>           Setting this too low will cause a lot of warnings.
>           Setting it to 0 disables the warning.
>
> --
> 2.38.0.135.g90850a2211-goog
>


-- 
Best Regards
Masahiro Yamada