From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <dev-bounces@dpdk.org>
Received: from mails.dpdk.org (mails.dpdk.org [217.70.189.124])
	by inbox.dpdk.org (Postfix) with ESMTP id 2492443E39;
	Thu, 11 Apr 2024 05:20:07 +0200 (CEST)
Received: from mails.dpdk.org (localhost [127.0.0.1])
	by mails.dpdk.org (Postfix) with ESMTP id A26B2402A8;
	Thu, 11 Apr 2024 05:20:06 +0200 (CEST)
Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189])
 by mails.dpdk.org (Postfix) with ESMTP id DF0A8402A7
 for <dev@dpdk.org>; Thu, 11 Apr 2024 05:20:04 +0200 (CEST)
Received: from mail.maildlp.com (unknown [172.19.163.174])
 by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4VFPyd2d1XzNnbY;
 Thu, 11 Apr 2024 11:17:45 +0800 (CST)
Received: from dggpeml500024.china.huawei.com (unknown [7.185.36.10])
 by mail.maildlp.com (Postfix) with ESMTPS id 3DC381404D9;
 Thu, 11 Apr 2024 11:20:02 +0800 (CST)
Received: from [10.67.121.161] (10.67.121.161) by
 dggpeml500024.china.huawei.com (7.185.36.10) with Microsoft SMTP Server
 (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id
 15.1.2507.35; Thu, 11 Apr 2024 11:20:01 +0800
Subject: Re: Strict aliasing problem with rte_eth_linkstatus_set()
To: Tyler Retzlaff <roretzla@linux.microsoft.com>,
 =?UTF-8?Q?Morten_Br=c3=b8rup?= <mb@smartsharesystems.com>
CC: Stephen Hemminger <stephen@networkplumber.org>, Ferruh Yigit
 <ferruh.yigit@amd.com>, <dev@dpdk.org>, Dengdui Huang
 <huangdengdui@huawei.com>
References: <8175c905-e661-b910-7f20-59b6ab605c38@huawei.com>
 <20240410082704.4691d7df@hermes.local>
 <98CBD80474FA8B44BF855DF32C47DC35E9F391@smartserver.smartshare.dk>
 <20240410195834.GA25134@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
From: fengchengwen <fengchengwen@huawei.com>
Message-ID: <84929ae8-54cc-43e7-b37e-f38a8963b259@huawei.com>
Date: Thu, 11 Apr 2024 11:20:01 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101
 Thunderbird/68.11.0
MIME-Version: 1.0
In-Reply-To: <20240410195834.GA25134@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Content-Type: text/plain; charset="utf-8"
Content-Language: en-US
Content-Transfer-Encoding: 8bit
X-Originating-IP: [10.67.121.161]
X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To
 dggpeml500024.china.huawei.com (7.185.36.10)
X-BeenThere: dev@dpdk.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: DPDK patches and discussions <dev.dpdk.org>
List-Unsubscribe: <https://mails.dpdk.org/options/dev>,
 <mailto:dev-request@dpdk.org?subject=unsubscribe>
List-Archive: <http://mails.dpdk.org/archives/dev/>
List-Post: <mailto:dev@dpdk.org>
List-Help: <mailto:dev-request@dpdk.org?subject=help>
List-Subscribe: <https://mails.dpdk.org/listinfo/dev>,
 <mailto:dev-request@dpdk.org?subject=subscribe>
Errors-To: dev-bounces@dpdk.org

Hi All,

On 2024/4/11 3:58, Tyler Retzlaff wrote:
> On Wed, Apr 10, 2024 at 07:54:27PM +0200, Morten Brørup wrote:
>>> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
>>> Sent: Wednesday, 10 April 2024 17.27
>>>
>>> On Wed, 10 Apr 2024 17:33:53 +0800
>>> fengchengwen <fengchengwen@huawei.com> wrote:
>>>
>>>> Last： We think there are two ways to solve this problem.
>>>> 1. Add the compilation option '-fno-strict-aliasing' for hold DPDK
>>> project.
>>>> 2. Use union to avoid such aliasing in rte_eth_linkstatus_set (please
>>> see above).
>>>> PS: We prefer first way.
>>>>
>>>
>>> Please send a patch to replace alias with union.
>>
>> +1
>>
>> Fixing this specific bug would be good.

OK for this,
and I already send a bugfix which use union.

Thanks

>>
>> Instinctively, I think we should build with -fno-strict-aliasing, so the compiler doesn't make the same mistake with similar code elsewhere in DPDK. I fear there is more than this instance.
>> I also wonder if -Wstrict-aliasing could help us instead, if we don't want -fno-strict-aliasing.
> 
> agree, union is the correct way to get defined behavior. there are
> valuable optimizatons that the compiler can make with strict aliasing
> enabled so -Wstrict-aliasing is a good suggestion as opposed to
> disabling it.
> 
> also the union won't break the abi if introduced correctly.
> .
>