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From: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>
To: Luc Pelletier <lucp.at.work@gmail.com>
Cc: "Richardson, Bruce" <bruce.richardson@intel.com>,
	"dev@dpdk.org" <dev@dpdk.org>,
	"Li, Xiaoyun" <xiaoyun.li@intel.com>,
	"stable@dpdk.org" <stable@dpdk.org>,
	"stephen@networkplumber.org" <stephen@networkplumber.org>,
	"Yigit, Ferruh" <ferruh.yigit@intel.com>,
	"Morten Brørup" <mb@smartsharesystems.com>,
	"Georg Sauthoff" <mail@gms.tf>
Subject: RE: [PATCH v5] eal: fix unaligned loads/stores in rte_memcpy_generic
Date: Mon, 14 Feb 2022 13:41:18 +0000	[thread overview]
Message-ID: <DM6PR11MB4491AA6111EB57693E95FCD09A339@DM6PR11MB4491.namprd11.prod.outlook.com> (raw)
In-Reply-To: <CAFeRdtDcSEKwtzPcpHGtCy_Q93z7whGF9zFBZa5QiDbBSwmnMw@mail.gmail.com>


Hi Luc,
 
> > Indeed it looks like a problem.
> > Thanks for pointing it out.
> > Was able to reproduce it with gcc 11 (clang 13 seems fine).
> > Actually, adding ' __attribute__ ((__may_alias__))' for both dst and src
> > didn't quire the problem.
> 
> __may_alias__ works if it's applied to a typedef, see the following
> for a modified version of my original example that works and uses
> __may_alias__:
> 
> https://godbolt.org/z/W83zzoePq

Interesting, I played with '__may_alias__' attribute a bit more,
and yes, as you said, it seems to wok properly only with typedefs.
If so, then we probably can add a new typedefs (in rte_common.h or so),
and use it in rte_memcpy and probably few other places, where we
think it will be necessary. 
 
> The documentation I found for __may_alias__ is quite sparse, so I'm a
> little wary of assuming it'll always work.
> I'm hoping someone with
> more experience with the attribute would be able to add more
> confidence to the assumption that it'll work in all cases.

Agree, would like to see more input too.
CC-ing to other guys, who seemed to be interested in that discussion before.

Thanks
Konstantin



  reply	other threads:[~2022-02-14 13:41 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-15 19:41 [PATCH] " Luc Pelletier
2022-01-15 21:39 ` [PATCH v2] " Luc Pelletier
2022-01-15 22:13   ` Stephen Hemminger
2022-01-16 14:09     ` Luc Pelletier
2022-01-16 16:32       ` Stephen Hemminger
2022-01-24 23:21         ` Georg Sauthoff
2022-01-25  7:59           ` Morten Brørup
2022-01-25 19:57           ` Luc Pelletier
2022-01-16 14:13 ` [PATCH v3] " Luc Pelletier
2022-01-16 14:33   ` Luc Pelletier
2022-01-16 16:34     ` Stephen Hemminger
2022-01-16 17:59       ` Morten Brørup
2022-01-16 20:33 ` [PATCH v4] " Luc Pelletier
2022-01-17 15:37 ` [PATCH v5] " Luc Pelletier
2022-02-04 16:42   ` Luc Pelletier
2022-02-04 17:16   ` Ananyev, Konstantin
2022-02-08 16:53     ` Thomas Monjalon
2022-02-09 15:05     ` Luc Pelletier
2022-02-10 14:04       ` Ananyev, Konstantin
2022-02-10 16:56         ` Luc Pelletier
2022-02-11 15:51           ` Ananyev, Konstantin
2022-02-13 22:31             ` Luc Pelletier
2022-02-14 13:41               ` Ananyev, Konstantin [this message]
2022-02-25 15:51 ` [PATCH v6] eal: fix rte_memcpy strict aliasing/alignment bugs Luc Pelletier
2022-02-25 16:38 ` [PATCH v7] " Luc Pelletier
2022-03-10 14:55   ` Ananyev, Konstantin
2022-04-07 15:24     ` David Marchand
2022-04-07 15:32       ` David Marchand
2022-04-07 15:40         ` David Marchand
2022-05-13 19:15           ` Luc Pelletier
2022-05-19 16:41             ` David Marchand
2022-04-08 13:47       ` Luc Pelletier
2022-05-19 16:47       ` David Marchand

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