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

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Message-ID: <20121027014249.GA4008@neilslaptop.think-freely.org>
Date:	Fri, 26 Oct 2012 21:42:49 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	David Miller <davem@...emloft.net>
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

On Fri, Oct 26, 2012 at 05:10:19PM -0400, David Miller wrote:
> 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.
> 
If thats the case, then I'll need to duplicate the memset in all three call
sites.  I've got a busy weekend comming up, but I'll respin this monday barring
no objections or counter-arguments

Best
Neil
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