Re: Iptables error

[Harald Welte <laforge@netfilter.org>]

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On Fri, Jan 20, 2006 at 11:46:13AM -0800, David S. Miller wrote:

> Your struct won't be 8-byte aligned either as far as I can tell on
> x86_64.

According to my tests, the struct is 8-byte-aligned on x86_64, and
that's how I'd like it to be. 

Please don't ask me why it happens, I know that the alignment constraint
of a u64 on x86_64 is only 4.  But at least gcc-3.3.6 and gcc-4.0.3
(debian) result in __alignof__ of that test structure (and a 'u_int64_t
alone') to 8 bytes.  

When it comes to these things, I can only do trial+error.

Maybe it's because __alignof__ returns the recommended alignment, not
the required alignment.

> We need to use the aligned_u64 thing if you want that.

That should make sure that we always get what we want, yes.  

-- 
- Harald Welte <laforge@netfilter.org>                 http://netfilter.org/
============================================================================
  "Fragmentation is like classful addressing -- an interesting early
   architectural error that shows how much experimentation was going
   on while IP was being designed."                    -- Paul Vixie

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