Ethereal-dev: Re: [Ethereal-dev] Buffers and pointers in a dissector

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From: Marco Molteni <molter@xxxxxx>
Date: Fri, 22 Nov 2002 14:08:12 +0100
On Thu, 21 Nov 2002, Gerald Combs <gerald@xxxxxxxxxxxx> wrote:

> On Thu, 21 Nov 2002, Paul Smith wrote:

[..] 

> > struct udp
> > {
> >     unsigned short source_port;
> >     unsigned short destination_port
> >     unsigned short length;
> >     unsigned short checksum;
> > }
> > 
> > struct udp_header *udp_hdr;
> > 
> > udp_hdr=(struct udp_header*)data_buffer
> 
> This will fail if:
> 
>   - One of the structure members isn't properly aligned on a 32-bit
>     boundary, and your processor doesn't like that, e.g. SPARC or
>     MIPS.  Alphas and PowerPCs might be subject to this as well.

Gerald,

I have this same question since I read README.developer, so I'll jump in
to ask.

what's wrong with this:

struct foo {
....
} __attribute__ packed

I think the only problem is that __attribute__ is a ggcism and is not
portable, right?

>   - Your processor's host byte order differs from network byte order,
>     e.g. IA32.

Should be enough to always use ntohs() and ntohl(), right?

[..]

thanks
marco