linux-kernel - Re: include/linux/fortify-string.h:52:29: warning: '__builtin_strcpy' source argument is the same as destination

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Message-ID: <202311301409.F2AFF5DA1@keescook>
Date:   Thu, 30 Nov 2023 14:11:54 -0800
From:   Kees Cook <keescook@...omium.org>
To:     kernel test robot <lkp@...el.com>
Cc:     oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: include/linux/fortify-string.h:52:29: warning:
 '__builtin_strcpy' source argument is the same as destination

On Thu, Nov 30, 2023 at 12:02:50PM +0800, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   3b47bc037bd44f142ac09848e8d3ecccc726be99
> commit: ba38961a069b0d8d03b53218a6c29d737577d448 um: Enable FORTIFY_SOURCE
> date:   1 year, 3 months ago
> config: um-randconfig-r034-20230830 (https://download.01.org/0day-ci/archive/20231130/202311301039.7i51bZCz-lkp@intel.com/config)
> compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231130/202311301039.7i51bZCz-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202311301039.7i51bZCz-lkp@intel.com/
> 
> [...]
>    kernel/kallsyms.c: In function '__sprint_symbol.isra.0':
> >> include/linux/fortify-string.h:52:29: warning: '__builtin_strcpy' source argument is the same as destination [-Wrestrict]
>       52 | #define __underlying_strcpy __builtin_strcpy
>          |                             ^
>    include/linux/fortify-string.h:567:10: note: in expansion of macro '__underlying_strcpy'
>      567 |   return __underlying_strcpy(p, q);
>          |          ^~~~~~~~~~~~~~~~~~~

The only strcpy() in __sprint_symbol() is:

	if (name != buffer)
		strcpy(buffer, name);

Which is explicitly not the same address...

This appears to be a GCC 9 false positive, maybe?

-- 
Kees Cook