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Date: Wed, 10 Apr 2024 12:58:34 -0700
From: Tyler Retzlaff <roretzla@linux.microsoft.com>
To: Morten =?iso-8859-1?Q?Br=F8rup?= <mb@smartsharesystems.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>,
 fengchengwen <fengchengwen@huawei.com>,
 Ferruh Yigit <ferruh.yigit@amd.com>, dev@dpdk.org,
 Dengdui Huang <huangdengdui@huawei.com>
Subject: Re: Strict aliasing problem with rte_eth_linkstatus_set()
Message-ID: <20240410195834.GA25134@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
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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.
> 
> 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.