Subject: Re: default 0 if KASAN expression not working in kbuild
To: Nikolay Borisov <n.borisov.lkml@gmail.com>,
        linux-kbuild@vger.kernel.org
References: <e8e7205e-17f4-1d2c-f6d1-bd741b65e032@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>, yann.morin.1998@free.fr
From: Michal Marek <mmarek@suse.com>
Message-ID: <8c63bae0-79fb-4594-125a-7e5d76e0c603@suse.com>
Date: Mon, 19 Dec 2016 11:57:23 +0100
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On 2016-12-15 19:09, Nikolay Borisov wrote:
> Hello,
> 
> I was doing some kasan-related debugging and when I enabled it I started
> getting warnings for large stackframes. So CONFIG_FRAME_WARN has :
> 
> int "Warn for stack frames larger than (needs gcc 4.4)"
>     range 0 8192
>     default 0 if KASAN
>     default 2048 if GCC_PLUGIN_LATENT_ENTROPY
>     default 1024 if !64BIT
>     default 2048 if 64BIT
> 
> This means that frame_warns should effectively be disabled when kasan is
> enabled. However in my case this is not the situation.
> http://sprunge.us/FiGf here is the config file. It does have
> CONFIG_KASAN=y and CONFIG_FRAME_WARN=1024 . And even this is erroneous
> since it's a 64bit kernel, so it should be 2k. I haven't manually set
> the limit to 1k either.

I guess the problem is that it's an option with a propt, so deviating
from the default value is legitimate. And most likely the
value is computed during menuconfig startup and a subsequent change of
CONFIG_KASAN does not change it (because 2048 or 1048 are also valid).

Michal