linux-kernel - RE: [Intel-wired-lan] [PATCH] [v2] ethernet: ice: avoid gcc-9 integer overflow warning

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Date:   Tue, 28 Feb 2023 07:53:05 +0000
From:   "Buvaneswaran, Sujai" <sujai.buvaneswaran@...el.com>
To:     Arnd Bergmann <arnd@...nel.org>,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Eric Dumazet" <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Martyna Szapar-Mudlaw <martyna.szapar-mudlaw@...ux.intel.com>
CC:     Lu Wei <luwei32@...wei.com>, Arnd Bergmann <arnd@...db.de>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>
Subject: RE: [Intel-wired-lan] [PATCH] [v2] ethernet: ice: avoid gcc-9 integer
 overflow warning

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@...osl.org> On Behalf Of
> Arnd Bergmann
> Sent: Tuesday, February 14, 2023 8:56 PM
> To: Brandeburg, Jesse <jesse.brandeburg@...el.com>; Nguyen, Anthony L
> <anthony.l.nguyen@...el.com>; David S. Miller <davem@...emloft.net>;
> Eric Dumazet <edumazet@...gle.com>; Jakub Kicinski <kuba@...nel.org>;
> Paolo Abeni <pabeni@...hat.com>; Martyna Szapar-Mudlaw
> <martyna.szapar-mudlaw@...ux.intel.com>
> Cc: Lu Wei <luwei32@...wei.com>; Arnd Bergmann <arnd@...db.de>;
> netdev@...r.kernel.org; linux-kernel@...r.kernel.org; intel-wired-
> lan@...ts.osuosl.org
> Subject: [Intel-wired-lan] [PATCH] [v2] ethernet: ice: avoid gcc-9 integer
> overflow warning
> 
> From: Arnd Bergmann <arnd@...db.de>
> 
> With older compilers like gcc-9, the calculation of the vlan priority field
> causes a false-positive warning from the byteswap:
> 
> In file included from drivers/net/ethernet/intel/ice/ice_tc_lib.c:4:
> drivers/net/ethernet/intel/ice/ice_tc_lib.c: In function 'ice_parse_cls_flower':
> include/uapi/linux/swab.h:15:15: error: integer overflow in expression
> '(int)(short unsigned int)((int)match.key-><U67c8>.<U6698>.vlan_priority <<
> 13) & 57344 & 255' of type 'int' results in '0' [-Werror=overflow]
>    15 |  (((__u16)(x) & (__u16)0x00ffU) << 8) |   \
>       |   ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
> include/uapi/linux/swab.h:106:2: note: in expansion of macro
> '___constant_swab16'
>   106 |  ___constant_swab16(x) :   \
>       |  ^~~~~~~~~~~~~~~~~~
> include/uapi/linux/byteorder/little_endian.h:42:43: note: in expansion of
> macro '__swab16'
>    42 | #define __cpu_to_be16(x) ((__force __be16)__swab16((x)))
>       |                                           ^~~~~~~~
> include/linux/byteorder/generic.h:96:21: note: in expansion of macro
> '__cpu_to_be16'
>    96 | #define cpu_to_be16 __cpu_to_be16
>       |                     ^~~~~~~~~~~~~
> drivers/net/ethernet/intel/ice/ice_tc_lib.c:1458:5: note: in expansion of
> macro 'cpu_to_be16'
>  1458 |     cpu_to_be16((match.key->vlan_priority <<
>       |     ^~~~~~~~~~~
> 
> After a change to be16_encode_bits(), the code becomes more readable to
> both people and compilers, which avoids the warning.
> 
> Fixes: 34800178b302 ("ice: Add support for VLAN priority filters in
> switchdev")
> Suggested-by: Alexander Lobakin <alexandr.lobakin@...el.com>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> v2: use be16_encode_bits() instead of a temporary variable.
> ---
>  drivers/net/ethernet/intel/ice/ice_tc_lib.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 

Tested-by: Sujai Buvaneswaran <sujai.buvaneswaran@...el.com>