Date: Tue, 18 Sep 2012 16:30:02 -0700 From: John-Mark Gurney <jmg@funkthat.com> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: arch@freebsd.org Subject: Re: Aliasing issue with TAILQ on ppc64 ? Message-ID: <20120918233002.GE19036@funkthat.com> In-Reply-To: <95608.1347973160@critter.freebsd.dk> References: <95608.1347973160@critter.freebsd.dk>
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Poul-Henning Kamp wrote this message on Tue, Sep 18, 2012 at 12:59 +0000:
> It may be a good idea to find some way to make sure the compiler
> spots the potential aliasing, but I am not sufficiently up to
> date on compiler optimizations to know a safe and reliable way
> to do that. (Would explicitly casting throuh a void do it ?)
Try casting the access through a char pointer. The C99 spec states
that you can only access an object through a pointer that is type
compatible, or through a char type, though, it isn't clear that from
the C99 spec that casting through a char type is enough to break
the aliasing...
I'm waiting for an answer from a friend who knows this much better
than myself...
The relevant part of the C99 standard is section 6.5, paragraphs 6 & 7...
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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