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

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Date:   Tue, 27 Apr 2021 13:59:32 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        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 Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [v2] staging: rtl8723bs: avoid bogus gcc warning

On Tue, Apr 27, 2021 at 11:33 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> 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?

As I understand, this is related to
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99673

gcc-11.1.0 has now been released and it produces this warning.

        Arnd