Re: SV: [lwip-users] Alignment problem i pbuf_alloc()

[K.J. Mansley]

On Tue, 2004-05-25 at 07:05, Lars Thorup wrote:
> Fra: K.J. Mansley [mailto:address@hidden 
> > Looks like it, but I'm not sure which bit is wrong.  Out of 
> > interest, where does the "6" bytes in the offset come from?  
> > I'm guessing some physical layer header?
> 
> Yes, we are running on top of an ARCNET, and we use a 6 byte header on the
> physical layer.
> 
> > I can think of a number of work-arounds, but does anyone have 
> > a suggestion for a solid fix?
> 
> This is the original code from pbuf_alloc():
> 
> case PBUF_RAM:
>   /* If pbuf is to be allocated in RAM, allocate memory for it. */
>   p = mem_malloc(MEM_ALIGN_SIZE(sizeof(struct pbuf) + length + offset));
> 
> I have changed the third line to
> 
>   p = mem_malloc(MEM_ALIGN_SIZE(sizeof(struct pbuf) + offset) +
> MEM_ALIGN_SIZE(length));

Would it be better to have:

p = mem_malloc(MEM_ALIGN_SIZE(sizeof(struct pbuf)) + MEM_ALIGN_SIZE(offset + 
length));

This makes more sense to me, as "offset" and "length" go together to
make the payload of the pbuf, but it may mean the payload pointer starts
off pointing at a non-word aligned address, which might cause problems?

Thanks

Kieran