Wireshark-dev: Re: [Wireshark-dev] Structure sizes change between Linux and Windows help
From: Bill Meier <[email protected]>
Date: Thu, 28 Jul 2011 17:39:00 -0400
On 7/28/2011 5:27 PM, Alex Lindberg wrote:
I am creating a dissector that overlays a complicated struct (bit
fields, unions, etc) on the the tvb.
Unfortunately, you can't do that;   :)

From doc/README.developer

Don't use structures that overlay packet data, or into which you copy
packet data; the C programming language does not guarantee any
particular alignment of fields within a structure, and even the
extensions that try to guarantee that are compiler-specific and not
necessarily supported by all compilers used to build Wireshark.  Using
bitfields in those structures is even worse; the order of bitfields
is not guaranteed.