On Mon, Dec 03, 2001 at 07:39:39AM +0900, [EMAIL PROTECTED] wrote:
> i'm not saying it is a bug in tcpdump. is it mandatory for BPF to
> return an aligned packet? if so, it is a bug in netbsd.
Well, the FreeBSD 3.4 man page for BPF says
The bh_hdrlen field exists to account for padding between the header and
the link level protocol. The purpose here is to guarantee proper align-
ment of the packet data structures, which is required on alignment sensi-
tive architectures and improves performance on many other architectures.
The packet filter insures that the bpf_hdr and the network layer header
will be word aligned. Suitable precautions must be taken when accessing
the link layer protocol fields on alignment restricted machines. (This
isn't a problem on an Ethernet, since the type field is a short falling
on an even offset, and the addresses are probably accessed in a bytewise
fashion).
and the NetBSD-current man page at:
http://www.tac.eu.org/cgi-bin/man-cgi?bpf++NetBSD-current
says the same thing.
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