Jan Engelhardt wrote:
On Jun 3 2007 12:14, Bernhard R. Link wrote:
* David Miller <davem@xxxxxxxxxxxxx> [070602 22:09]:
Types must be aligned on their natural size, and GCC can assume
this everywhere you reference such types unless you use the
"packed" GCC attribute.
And even with packed, the struct itself must be naturally aligned
(unless itself is in a packed struct, if course).
It is not a struct actually. It is a bytestream that is reinterpreted
as an integer, that is, for example (it does not really need to be
skb_network_header),
unsigned char *p = skb_network_header(skb);
uint32_t value = *(uint32_t *)(p[9]);
I suppose this won't work, so one would have to...
uint32_t value = (p[0] << 24) | (p[1] << 16) | (p[2] << 8) | p[3];
One of the reasons portable network code tends to be filled with macros
for accessing values of length N at alignment M.
--Adam
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