[dpdk-dev] [EXT] Re: [PATCH v10] ethdev: add HIGIG2 key field to flow API

[Olivier Matz]

On Wed, Oct 23, 2019 at 11:43:58AM +0000, Kiran Kumar Kokkilagadda wrote:
> > -----Original Message-----
> > From: Olivier Matz <olivier.matz at 6wind.com>
> > Sent: Wednesday, October 23, 2019 5:09 PM
> > To: Raslan Darawsheh <rasland at mellanox.com>
> > Cc: Ferruh Yigit <ferruh.yigit at intel.com>; Kiran Kumar Kokkilagadda
> > <kirankumark at marvell.com>; Adrien Mazarguil
> > <adrien.mazarguil at 6wind.com>; Wenzhuo Lu <wenzhuo.lu at intel.com>;
> > Jingjing Wu <jingjing.wu at intel.com>; Bernard Iremonger
> > <bernard.iremonger at intel.com>; John McNamara
> > <john.mcnamara at intel.com>; Marko Kovacevic <marko.kovacevic at intel.com>;
> > Thomas Monjalon <thomas at monjalon.net>; Andrew Rybchenko
> > <arybchenko at solarflare.com>; dev at dpdk.org; ajit.khaparde at broadcom.com
> > Subject: [EXT] Re: [dpdk-dev] [PATCH v10] ethdev: add HIGIG2 key field to flow
> > API
> > 
> > External Email
> > 
> > ----------------------------------------------------------------------
> > Hi,
> > 
> > 
> > 
> > On Wed, Oct 23, 2019 at 10:50:52AM +0000, Raslan Darawsheh wrote:
> > 
> > > Hi,
> > 
> > >
> > 
> > > This patch broke the compilation of MLX5 PMD in debug mode:
> > 
> > >
> > 
> > >                  from /root/dpdk/x86_64-native-linux-
> > gcc/include/rte_ethdev_driver.h:18,
> > 
> > >                  from /root/dpdk/drivers/net/mlx5/mlx5_mp.c:11:
> > 
> > > /root/dpdk/x86_64-native-linux-gcc/include/rte_higig.h:112:2: error: type of
> > bit-field 'opcode' is a GCC extension [-Werror=pedantic]
> > 
> > >   uint16_t opcode:3;
> > 
> > >   ^
> > 
> > > /root/dpdk/x86_64-native-linux-gcc/include/rte_higig.h:113:2: error: type of
> > bit-field 'resv1' is a GCC extension [-Werror=pedantic]
> > 
> > >   uint16_t resv1:2;
> > 
> > >   ^
> > 
> > > /root/dpdk/x86_64-native-linux-gcc/include/rte_higig.h:114:2: error: type of
> > bit-field 'src_t' is a GCC extension [-Werror=pedantic]
> > 
> > >   uint16_t src_t:1;
> > 
> > >   ^
> > 
> > > /root/dpdk/x86_64-native-linux-gcc/include/rte_higig.h:115:2: error: type of
> > bit-field 'pfm' is a GCC extension [-Werror=pedantic]
> > 
> > >   uint16_t pfm:2;
> > 
> > >   ^
> > 
> > > /root/dpdk/x86_64-native-linux-gcc/include/rte_higig.h:116:2: error: type of
> > bit-field 'resv2' is a GCC extension [-Werror=pedantic]
> > 
> > >   uint16_t resv2:5;
> > 
> > >   ^
> > 
> > > /root/dpdk/x86_64-native-linux-gcc/include/rte_higig.h:117:2: error: type of
> > bit-field 'hdr_ext_len' is a GCC extension [-Werror=pedantic]
> > 
> > >   uint16_t hdr_ext_len:3;
> > 
> > >
> > 
> > > and this is with gcc 4.8.5
> > 
> > 
> > 
> > From https://urldefense.proofpoint.com/v2/url?u=https-
> > 3A__stackoverflow.com_questions_10906238_warning-2Dwhen-2Dusing-
> > 2Dbitfield-2Dwith-2Dunsigned-
> > 2Dchar&d=DwIBAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=owEKckYY4FTmil1Z6oBUR
> > wkTThyuRbLAY9LdfiaT6HA&m=GZ-
> > 6cngPycaUlGJT20VEOf9oTcp5PMwk7j1JV1vAQfs&s=SCg5yVPS4zZa8GSn9bl_eUtI
> > vBmoDzi35PspWUttIUY&e=
> > 
> > it seems that it is allowed in c99, so I guess it's a gcc 4.8 bug.
> > 
> > 
> > 
> > Adding __extension__ above the struct solves the warnings, I suggest to
> > 
> > add it.
> 
> /**
>  *
>  * higig2 ppt type1 header.
>  */
> RTE_STD_C11
> struct rte_higig2_ppt_type1 {
>         uint16_t classification;
>         uint16_t resv;
>         uint16_t vid;
> #if RTE_BYTE_ORDER == RTE_LITTLE_ENDIAN
>         uint16_t opcode:3;
>         uint16_t resv1:2;
>         uint16_t src_t:1;
>         uint16_t pfm:2;
>         uint16_t resv2:5;
>         uint16_t hdr_ext_len:3;
> #elif RTE_BYTE_ORDER == RTE_BIG_ENDIAN
>         uint16_t pfm:2;
>         uint16_t src_t:1;
>         uint16_t resv1:2;
>         uint16_t opcode:3;
>         uint16_t hdr_ext_len:3;
>         uint16_t resv2:5;
> #endif
> };
> 
> I have already added it. RTE_STD_C11 , this is a macro for __extension__. 
> /** C extension macro for environments lacking C11 features. */
> #if !defined(__STDC_VERSION__) || __STDC_VERSION__ < 201112L
> #define RTE_STD_C11 __extension__
> #else
> #define RTE_STD_C11
> #endif

The __extension__ is only added if compiled for < c11.
But there is apparently a problem with gcc-4.8: even in c11, it does
not support bitfields on u16. See: https://godbolt.org/z/hRIbgg

On gcc-4.9, the problem disappeared: https://godbolt.org/z/kkzz9v

So as a workaround, using __extension__ should work, probably with a short
explanation.