Re: Comments about IPT_ALIGN

[Thomas Heinz <creatix@hipac.org>]

I wrote:
>        - the end of the struct must be marked by:
>              struct ipt_entry next[0];
>          or
>              long next[0];   // I'm not sure about this!

Well, this is plain nonsense (I don't know why I wrote that).
But here is another idea that does not need #ifdefs:

            struct info
            {
                [...]
            } __attribute__((aligned(__alignof__(u_int64_t))));

This hopefully does the trick.

>        - pointers or arrays of pointers should be avoided but if they're
>          really needed (as in limit) a special pointer type should be
>          used: 32 bit arch: union nf_ptr_t {void *p;
>                                             u_int32_t padd;};
>                64 bit arch: union nf_ptr_t {void *p;
>                                             u_int64_t padd;};
>          Maybe there are better ways to achieve the same
>          (__attribute__ ((aligned (__alignof__(long)))) might work).
                                                           ^^^^^^^^^^
                                             Of course it does _not_ :-)

            I don't think there is a way to avoid the union which
            leads to an #ifdef if we don't restrict ourselves to at most
            one pointer at the end.
            The reason for that is that it does not suffice to require
            a certain alignment for void * but it also must have the
            expected size. Otherwise members that come after pointer
            members might have a different offset (just the same
            argument as for long).