linux-kernel - Re: [PATCH 3/3] Kconfig.debug: Provide a little extra FRAME

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Date:   Fri, 25 Nov 2022 11:05:25 +0100
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Lee Jones" <lee@...nel.org>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Nathan Chancellor" <nathan@...nel.org>,
        "Maarten Lankhorst" <maarten.lankhorst@...ux.intel.com>,
        mripard@...nel.org, "Thomas Zimmermann" <tzimmermann@...e.de>,
        "Dave Airlie" <airlied@...il.com>,
        "Daniel Vetter" <daniel@...ll.ch>,
        "Nick Desaulniers" <ndesaulniers@...gle.com>,
        "Tom Rix" <trix@...hat.com>,
        "Harry Wentland" <harry.wentland@....com>,
        "Leo Li" <sunpeng.li@....com>,
        "Rodrigo Siqueira" <Rodrigo.Siqueira@....com>,
        "Alex Deucher" <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        Xinhui.Pan@....com
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 3/3] Kconfig.debug: Provide a little extra FRAME_WARN leeway when
 KASAN is enabled

On Fri, Nov 25, 2022, at 10:25, Lee Jones wrote:
> When enabled, KASAN enlarges function's stack-frames.  Pushing quite a
> few over the current threshold.  This can mainly be seen on 32-bit
> architectures where the present limit (when !GCC) is a lowly
> 1024-Bytes.
>
> Signed-off-by: Lee Jones <lee@...nel.org>

Acked-by: Arnd Bergmann <arnd@...db.de>

If this affects only clang but not gcc, I wonder if we could
limit the scope and keep the 1024 byte limit on gcc builds.

> ---
>  lib/Kconfig.debug | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index c3c0b077ade33..82d475168db95 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -399,6 +399,7 @@ config FRAME_WARN
>  	default 2048 if GCC_PLUGIN_LATENT_ENTROPY

This is actually a related bug that we should fix: allmodconfig
with gcc turns on GCC_PLUGIN_LATENT_ENTROPY, so the limit
ends up being way too high. I think we need to either ensure
that allmodconfig turns off the latent entropy plugin,
or that the limit gets lowered again to something that is
not any higher than the KASAN limit.

     Arnd