patches for DPDK stable branches
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From: Ferruh Yigit <ferruh.yigit@intel.com>
To: Gavin Hu <Gavin.Hu@arm.com>, "dev@dpdk.org" <dev@dpdk.org>
Cc: nd <nd@arm.com>,
	"david.marchand@redhat.com" <david.marchand@redhat.com>,
	 "thomas@monjalon.net" <thomas@monjalon.net>,
	"ktraynor@redhat.com" <ktraynor@redhat.com>,
	"jerinj@marvell.com" <jerinj@marvell.com>,
	Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
	Ruifeng Wang <Ruifeng.Wang@arm.com>,
	Phil Yang <Phil.Yang@arm.com>, Joyce Kong <Joyce.Kong@arm.com>,
	"stable@dpdk.org" <stable@dpdk.org>,
	Olivier MATZ <olivier.matz@6wind.com>,
	Konstantin Ananyev <konstantin.ananyev@intel.com>,
	Andrew Rybchenko <arybchenko@solarflare.com>
Subject: Re: [dpdk-stable] [dpdk-dev] [PATCH v2] mbuf: replace zero-length marker with unnamed union
Date: Mon, 9 Mar 2020 11:29:56 +0000
Message-ID: <dffb4554-4719-8838-3001-eebdf7228c48@intel.com> (raw)
In-Reply-To: <VI1PR08MB53761D519B18A133E05F082A8FFE0@VI1PR08MB5376.eurprd08.prod.outlook.com>

On 3/9/2020 9:45 AM, Gavin Hu wrote:
> Hi Ferruh,
> 
>> -----Original Message-----
>> From: Ferruh Yigit <ferruh.yigit@intel.com>
>> Sent: Monday, March 9, 2020 4:55 PM
>> To: Gavin Hu <Gavin.Hu@arm.com>; dev@dpdk.org
>> Cc: nd <nd@arm.com>; david.marchand@redhat.com; thomas@monjalon.net;
>> ktraynor@redhat.com; jerinj@marvell.com; Honnappa Nagarahalli
>> <Honnappa.Nagarahalli@arm.com>; Ruifeng Wang
>> <Ruifeng.Wang@arm.com>; Phil Yang <Phil.Yang@arm.com>; Joyce Kong
>> <Joyce.Kong@arm.com>; stable@dpdk.org; Olivier MATZ
>> <olivier.matz@6wind.com>; Konstantin Ananyev
>> <konstantin.ananyev@intel.com>; Andrew Rybchenko
>> <arybchenko@solarflare.com>
>> Subject: Re: [dpdk-dev] [PATCH v2] mbuf: replace zero-length marker with
>> unnamed union
>>
>> On 3/7/2020 3:56 PM, Gavin Hu wrote:
>>> Declaring zero-length arrays in other contexts, including as interior
>>> members of structure objects or as non-member objects, is discouraged.
>>> Accessing elements of zero-length arrays declared in such contexts is
>>> undefined and may be diagnosed.[1]
>>>
>>> Fix by using unnamed union and struct.
>>>
>>> https://bugs.dpdk.org/show_bug.cgi?id=396
>>>
>>> Bugzilla ID: 396
>>>
>>> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
>>>
>>> Fixes: 3e6181b07038 ("mbuf: use structure marker from EAL")
>>> Cc: stable@dpdk.org
>>>
>>> Signed-off-by: Gavin Hu <gavin.hu@arm.com>
>>> ---
>>> v2:
>>> * change 'uint64_t rearm_data' to 'uint_64_t rearm_data[1]' to fix
>>>   the SFC PMD compiling error on x86. <Kevin Traynor>
>>> ---
>>>  lib/librte_mbuf/rte_mbuf_core.h | 54 +++++++++++++++++++--------------
>>>  1 file changed, 32 insertions(+), 22 deletions(-)
>>>
>>> diff --git a/lib/librte_mbuf/rte_mbuf_core.h
>> b/lib/librte_mbuf/rte_mbuf_core.h
>>> index b9a59c879..34cb152e2 100644
>>> --- a/lib/librte_mbuf/rte_mbuf_core.h
>>> +++ b/lib/librte_mbuf/rte_mbuf_core.h
>>> @@ -480,31 +480,41 @@ struct rte_mbuf {
>>>  		rte_iova_t buf_physaddr; /**< deprecated */
>>>  	} __rte_aligned(sizeof(rte_iova_t));
>>>
>>> -	/* next 8 bytes are initialised on RX descriptor rearm */
>>> -	RTE_MARKER64 rearm_data;
>>> -	uint16_t data_off;
>>> -
>>> -	/**
>>> -	 * Reference counter. Its size should at least equal to the size
>>> -	 * of port field (16 bits), to support zero-copy broadcast.
>>> -	 * It should only be accessed using the following functions:
>>> -	 * rte_mbuf_refcnt_update(), rte_mbuf_refcnt_read(), and
>>> -	 * rte_mbuf_refcnt_set(). The functionality of these functions (atomic,
>>> -	 * or non-atomic) is controlled by the
>> CONFIG_RTE_MBUF_REFCNT_ATOMIC
>>> -	 * config option.
>>> -	 */
>>>  	RTE_STD_C11
>>>  	union {
>>> -		rte_atomic16_t refcnt_atomic; /**< Atomically accessed
>> refcnt */
>>> -		/** Non-atomically accessed refcnt */
>>> -		uint16_t refcnt;
>>> -	};
>>> -	uint16_t nb_segs;         /**< Number of segments. */
>>> +		/* next 8 bytes are initialised on RX descriptor rearm */
>>> +		uint64_t rearm_data[1];
>> We are using zero length array as markers only and know what we are doing
>> with them,
>> what would you think disabling the warning instead of increasing the
>> complexity
>> in mbuf struct?
> Okay, I will add -Wno-zero-length-bounds to the compiler toolchain flags. 

This would be my preference but I would like to get more input, can you please
for more comments before changing the implementation in case there are some
strong opinion on it?




  reply	other threads:[~2020-03-09 11:30 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-03 16:27 [dpdk-stable] [PATCH v1] " Gavin Hu
2020-03-04 12:32 ` [dpdk-stable] [dpdk-dev] " Kevin Traynor
2020-03-07 14:52   ` Gavin Hu
2020-03-07 15:56 ` [dpdk-stable] [PATCH v2] " Gavin Hu
2020-03-09  8:55   ` [dpdk-stable] [dpdk-dev] " Ferruh Yigit
2020-03-09  9:45     ` Gavin Hu
2020-03-09 11:29       ` Ferruh Yigit [this message]
2020-03-09 13:30         ` Morten Brørup
2020-03-09 14:16           ` Richardson, Bruce
2020-03-09 14:50             ` [dpdk-stable] [dpdk-dev] [PATCH v2] mbuf: replace zero-length markerwith " Morten Brørup
2020-03-11  7:50           ` [dpdk-stable] [dpdk-dev] [PATCH v2] mbuf: replace zero-length marker with " Gavin Hu
2020-03-11  9:04             ` Morten Brørup
2020-03-11 12:07               ` Bruce Richardson
2020-03-13  7:36                 ` Gavin Hu
2020-03-13  9:22                 ` Gavin Hu
2020-04-07 17:13                   ` Kevin Traynor
2020-04-08 15:04                     ` Gavin Hu
2020-04-08 15:22                       ` David Marchand
2020-04-09  9:48                         ` Gavin Hu
2020-04-09 10:49                           ` Thomas Monjalon
2020-04-09 16:09                             ` Ray Kinsella
2020-04-11  2:50                             ` Gavin Hu
2020-05-14 13:24                         ` Kevin Traynor
2020-03-09 15:47     ` Stephen Hemminger

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