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From: Guenter Roeck <linux@roeck-us.net>
To: "Koenig, Christian" <Christian.Koenig@amd.com>
Cc: "Deucher, Alexander" <Alexander.Deucher@amd.com>,
	Peng Hao <peng.hao2@zte.com.cn>,
	"airlied@linux.ie" <airlied@linux.ie>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>,
	"amd-gfx@lists.freedesktop.org" <amd-gfx@lists.freedesktop.org>
Subject: Re: [PATCH] amdgpu/gmc : fix compile warning
Date: Mon, 8 Oct 2018 10:46:28 -0700	[thread overview]
Message-ID: <20181008174628.GB11442@roeck-us.net> (raw)
In-Reply-To: <c6880c5b-e259-4923-8d5a-80c620563398@amd.com>

On Mon, Oct 08, 2018 at 05:22:24PM +0000, Koenig, Christian wrote:
> Am 08.10.2018 um 17:57 schrieb Deucher, Alexander:
> >>>> One thing I found missing in the discussion was the reference to the
> >>>> C standard.
> >>>> The C99 standard states in section 6.7.8 (Initialization) clause 19:
> >>>> "... all
> >>>> subobjects that are not initialized explicitly shall be initialized
> >>>> implicitly the same as objects that have static storage duration".
> >>>> Clause 21 makes further reference to partial initialization,
> >>>> suggesting the same. Various online resources, including the gcc
> >>>> documentation, all state the same. I don't find any reference to a
> >>>> partial initialization which would leave members of a structure
> >>>> undefined. It would be interesting for me to understand how and why
> >>>> this does not apply here.
> >>>>
> >>>> In this context, it is interesting that the other 48 instances of the
> >>>> { { 0 } } initialization in the same driver don't raise similar
> >>>> concerns, nor seemed to have caused any operational problems.
> >>> Feel free to provide patches to replace those with memset().
> >>>
> >> Not me. As I see it, the problem, if it exists, would be a violation of the C
> >> standard. I don't believe hacking around bad C compilers. I would rather
> >> blacklist such compilers.
> 
> Well then you would need to blacklist basically all gcc variants of the 
> last decade or so.
> 
> Initializing only known members of structures is a perfectly valid 
> optimization and well known issue when you then compare the structure 
> with memcpy() or use the bytes for hashing or something similar.
> 

Isn't that about padding ? That is a completely different issue.

Guenter

  reply	other threads:[~2018-10-08 17:46 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-14 10:05 Peng Hao
2018-10-04 18:52 ` Guenter Roeck
2018-10-05  8:14   ` Koenig, Christian
2018-10-05  8:38     ` Guenter Roeck
2018-10-08  8:00       ` Christian König
2018-10-08 13:33         ` Guenter Roeck
2018-10-08 13:47           ` Koenig, Christian
2018-10-08 14:10             ` Guenter Roeck
2018-10-08 15:57               ` Deucher, Alexander
2018-10-08 17:22                 ` Koenig, Christian
2018-10-08 17:46                   ` Guenter Roeck [this message]
2018-10-08 18:13                     ` Koenig, Christian
2018-10-19  8:53                       ` Daniel Vetter
2018-10-19  8:56                         ` Daniel Vetter
2018-10-19 13:08                         ` Guenter Roeck
2018-10-19 15:30                           ` Alex Deucher
2018-10-08 17:41                 ` Guenter Roeck
2018-10-08 18:24                   ` Deucher, Alexander

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