CORBA25 — Urgent issue: Alignment of LocateReply body

In CORBA 2.3, a GIOP 1.2 LocateReply message made no requirements as to
the alignment of the LocateReply body. This meant that the LocateReply
body needed to be aligned only on a 4-byte boundary. With the resolution
for issue 2521, published with CORBA 2.4, the spec was changed to require
alignment of the LocateReply body on an 8-byte boundary.

The change is incompatible with the CORBA 2.3 definition because the receiver
must know where to look for the ReplyBody in the the byte stream following
the message header. (The LocateReply header is 12 bytes long, so changing
the alignment rules means that the LocateReply body has to start at offset 12
for CORBA 2.3, but has to start at offset 16 for CORBA 2.4.)

The change in alignment did not result in a version change of GIOP,
despite the incompatibility, so it appears that the change is simply illegal.

There are already deployed products that use the CORBA 2.3 alignment
rule; therefore, we cannot deploy a CORBA 2.4 compliant product without
breaking interoperability with already deployed CORBA 2.3 compliant products.

So, I'd like to request that we back out the change and continue to
permit a LocateReply body to be aligned on a 4-byte boundary. There was
never any need to change the alignment of the LocateReply body anyway because
a LocateReply header has fixed length and, therefore, cannot ever cause
remarshaling of the body due to a size change in the header. In other
words, the motivation quoted in the spec for the 8-byte alignment rule
isn't founded on fact, and the change should never have been made in the first
place. (See issue 4309 for details.)

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