??: PR 1098: "struct ipovly" not packed.

[Aaron J. Grier]

On Tue, Jul 11, 2006 at 12:52:06PM -0500, Jay Monkman wrote:
> If __attribute__((packed)) is so wrong, what's the correct way to
> ensure a data structure is packed? If you look at the latest code in
> netbsd, they use it on their network data structures:
> http://cvsweb.netbsd.org/bsdweb.cgi/~checkout~/src/sys/netinet/tcp.h?rev=1.19.4.1&content-type=text/plain

the original commits for the packed changes were done in 1999, and in a
couple cases, these changes have been backed out.
http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/netinet/ip_icmp.h?rev=1.23&content-type=text/x-cvsweb-markup

gcc4's builtin memcpy recently demonstrated trouble on MIPS with packed
structs and misalignment as well, prompting a re-examining of the use of
__attribute__ ((packed)).
http://mail-index.netbsd.org/tech-toolchain/2006/05/16/0005.html

explicitly performing direct copies from/to members of a struct (of
default alignment) to/from an array of desired alignment (8/16/32)
appears to me the most robust way.

-- 
  Aaron J. Grier  |   Frye Electronics, Tigard, OR   |  aaron at frye.com