Re: Comments about IPT_ALIGN

[Thomas Heinz <creatix@hipac.org>]

Hi Laszlo

You wrote:
> This is not too surprising. Both of them are RISC processors with
> strict alignment restrictions. I guess even with a 32bit sparc
> gcc, a 64bit unsigned integer gets aligned to 64bit just to make life
> easier

Yes, in fact this is the case. Just take a look at the output of
struct t64 on sparc64 in my first posting.

> Now the problem comes if you have only 32bit integers in the first
> structure and 64bit integers in the second one: you have to either
> use IPT_ALIGN again (which we would like to get rid of), or we
> have to make sure the first structure gets aligned to 64bit.
> We could introduce an extra variablke just for this at the end
> like:
> 
> 	u_int64_t dummy[0];
> }
> 
> Or we could do something like that in netfilter:
> 
> 	struct ipt_entry entries[0];
> }
> 
> This latter version is better if we know what kind structure will follow,
> because it will not increase the size of the structure unnecessarily on
> platforms without alignment restrictions.

Yes, very good point. Another way would be to introduce a new type
for this purpose which is u_int32_t on 32 bit architectures and
u_int64_t on 64 bit architectures or just use long instead if
sizeof(long) always works the expected way.

Anyway this is just a question of personal taste.


Thomas