linux-kernel - Re: [PATCH] [v2] staging: rtl8723bs: avoid bogus gcc warning

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Date:   Tue, 27 Apr 2021 11:32:29 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Fabio Aiuto <fabioaiuto83@...il.com>,
        Ross Schmidt <ross.schm.dev@...il.com>,
        Marco Cesati <marcocesati@...il.com>,
        Johannes Berg <johannes.berg@...el.com>,
        Ivan Safonov <insafonov@...il.com>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [v2] staging: rtl8723bs: avoid bogus gcc warning

On Thu, Apr 22, 2021 at 05:26:19PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> gcc gets confused by some of the type casts and produces an
> apparently senseless warning about an out-of-bound memcpy to
> an unrelated array in the same structure:
> 
> drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c: In function 'rtw_cfg80211_ap_set_encryption':
> cc1: error: writing 8 bytes into a region of size 0 [-Werror=stringop-overflow=]
> In file included from drivers/staging/rtl8723bs/include/drv_types.h:32,
>                  from drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c:10:
> drivers/staging/rtl8723bs/include/rtw_security.h:98:15: note: at offset [184, 4264] into destination object 'dot11AuthAlgrthm' of size 4
>    98 |         u32   dot11AuthAlgrthm;         /*  802.11 auth, could be open, shared, 8021x and authswitch */
>       |               ^~~~~~~~~~~~~~~~
> cc1: error: writing 8 bytes into a region of size 0 [-Werror=stringop-overflow=]
> drivers/staging/rtl8723bs/include/rtw_security.h:98:15: note: at offset [264, 4344] into destination object 'dot11AuthAlgrthm' of size 4
> 
> This is a known gcc bug, and the patch here is only a workaround,
> but the approach of using a temporary variable to hold a pointer
> to the key also improves readability in addition to avoiding the
> warning, so overall this should still help.

What version of gcc causes this?  Should this go into 5.13-final and be
backported?  Or is this only showing up on "unreleased" versions of gcc
and it is safe to wait until 5.14?

thanks,

greg k-h