On May 28, 2019, at 4:09 AM, Mouse <mouse%Rodents-Montreal.ORG@localhost> wrote:
More siginificant, to me, is that the addresses are indeed misaligned,
but everyone seems to think they should be aligned. Whether the bug is
in code (this code or other code) or in people's mental model, I don't
know, but I would say it needs fixing.
The Ethernet header is not helping us here... If the Ethernet header starts on a 4-byte boundary, then the IP header will not. Some drivers scoot the start of the packet forward 2 bytes into the receive buffer to ensure IP header alignment, but hooray, the hardware people often forget to talk to the software people, and as a result, some hardware requires buffers to start on a 4-byte boundary. In drivers for such devices, we are forced to copy the packet (lots of expensive memory access) **OR** live with the unaligned IP header if we know the CPU can access it.