netdev - Re: [PATCH] sctp: Clean up type-punning in sctp_cmd

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Message-Id: <20121026.171019.702275326710216395.davem@davemloft.net>
Date:	Fri, 26 Oct 2012 17:10:19 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	nhorman@...driver.com
Cc:	vyasevich@...il.com, netdev@...r.kernel.org,
	linux-sctp@...r.kernel.org
Subject: Re: [PATCH] sctp: Clean up type-punning in sctp_cmd_t union

From: Neil Horman <nhorman@...driver.com>
Date: Fri, 26 Oct 2012 16:35:04 -0400

> On Fri, Oct 26, 2012 at 03:12:11PM -0400, Vlad Yasevich wrote:
>> Look at commit 19c7e9ee that introduced this.  I don't remember all
>> the details any more, but the problem only occurred on ia64
>> (probably due its speculative load handling).
>> 
>> -vlad
>> 
> Thanks Vlad, I'll have a look see.

Ok, so this IA64 issue is all about accesses to uninitialized memory.

I think Neil's change is thus the most desirable thing to do.  Simple
memset the object to zero.

Let the compiler optimize or not optimize things as it sees fit, to
make sure the object is completely initialized.

memset() expands to __builtin_memset(), and therefore the compiler
can and will eliminate initializations to overlapping areas if such
eliminations are possible.
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