svn commit: r211023 - head/usr.sbin/syslogd

[Oliver Fromme]

Dag-Erling Smørgrav wrote:
 > "M. Warner Losh" <imp at bsdimp.com> writes:
 > > You'll find that a number of structures are potentially already
 > > allocated with less than required alignment.  There's about a dozen
 > > places in the tree that would start to fail if we did this, or the
 > > stronger form of __aligned(8).  We could add that to the other
 > > structures, but then we're breaking ABI rules, I think.
 > 
 > __aligned(4) won't affect struct addrinfo since the sockaddr immediately
 > follows a socklen_t, which is 32 bits wide and has 32-bit alignment.  A
 > sockaddr_* allocated with malloc() will already be aligned, and so will
 > a sockaddr_* created on the stack.  The only problem is sockaddr_un,
 > because its size is not a multiple of 4, so if you allocate an array of
 > sockaddr_un, every other element will be misaligned.

I did a small survey of all the sockaddr_ variants:

struct        align size modulo   where
-------------------------------------------------------------------------
osockaddr         2   16   16  <sys/socket.h>
sockaddr          1   16   16  <sys/socket.h>
sockaddr_at       2   16   16  <netatalk/at.h>
sockaddr_dl       2   54    2  <net/if_dl.h>
sockaddr_hci      1   34    2  <netgraph/bluetooth/include/ng_btsocket.h>
sockaddr_in       4   16   16  <netinet/in.h>
sockaddr_in6      4   28    4  <netinet6/in6.h>
sockaddr_inarp    4   16   16  <netinet/if_ether.h>
sockaddr_ipx      2   16   16  <netipx/ipx.h>
sockaddr_l2cap    2   10    2  <netgraph/bluetooth/include/ng_btsocket.h>
sockaddr_natm     2   22    2  <netnatm/natm.h>
sockaddr_nb       4   56    8  <netsmb/netbios.h>
sockaddr_ng       1   16   16  <netgraph/ng_socket.h>
sockaddr_rfcomm   1    9    1  <netgraph/bluetooth/include/ng_btsocket.h>
sockaddr_sco      1    8    8  <netgraph/bluetooth/include/ng_btsocket.h>
sockaddr_storage  8  128  128  <sys/_sockaddr_storage.h>
sockaddr_un       1  106    2  <sys/un.h>

If we push struct sockaddr to align(4), then we will also
have to do the same with all others that are not already
aligned to at least 4 bytes.  That would be almost all of
them.

I agree that there will be ABI problems with those structs
whose size is not a multiple of 4 (that's the ones with a
value < 4 in the "modulo" column above).  So we cannot do
that, right?

Best regards
   Oliver

-- 
``We are all but compressed light'' (Albert Einstein)