Re: [lwip-users] Struct packing/alignment problems

[Leon Woestenberg]

Hello all,

Timmy Brolin wrote:
> Why would they be put on 4 byte boundaries? The natural boundary of u16s 
> is 2 bytes, not 4 bytes. Putting a u16 on a 4 byte boundary changes 
> nothing.
>
OK, we all seem to agree on the fact that types should always be aligned 
on their natural alignment boundaries.

The real question is whether the compiler is allowed to add *extra*
padding (for performance reasons or whatever). If a compiler is free
to add extra padding (i.e. other than for alignment reasons) we need
to keep it from doing this (through packing).

Can we give live examples of extranous padding?

I remember the packing stuff being added for *some* reason, although
I cannot remember the specific compiler or platform.

Regards,

Leon.