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Date: Mon, 08 Sep 2014 20:20:49 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: James Bottomley <James.Bottomley@HansenPartnership.com>,
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Subject: Re: bit fields && data tearing
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On 09/08/2014 07:56 PM, James Bottomley wrote:
>>
>> Yeah, the extra requirement I added is basically nonsense, since the
>> only issue is what instructions the compiler is emitting. So if compiler
>> thinks the alignment is natural and combines the writes -- ok. If the
>> compiler thinks the alignment is off and doesn't combine the writes --
>> also ok.
> 
> Yes, I think I can agree that the only real problem is gcc thinking the
> store or load needs splitting.
> 

That seems much saner, and yes, that applies to any architecture which
needs unaligned references.  Now, if the references are *actually*
unaligned they can end up being split even on x86, especially if they
cross cache line boundaries.

	-hpa