Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!mcnc!rti!rcb From: rcb@rti.UUCP (Random) Newsgroups: comp.os.vms Subject: Re: transfer vectors Message-ID: <1572@rti.UUCP> Date: Thu, 23-Jul-87 10:08:18 EDT Article-I.D.: rti.1572 Posted: Thu Jul 23 10:08:18 1987 Date-Received: Sat, 25-Jul-87 06:36:27 EDT References: <8707230304.AA14642@ucbvax.Berkeley.EDU> Reply-To: rcb@rti.UUCP (Random) Distribution: world Organization: Research Triangle Institute, NC Lines: 28 >Randy Buckland answers: >>The solution is really simple. Have a section of code that will >>always be at a fixed address and will contain pointers to the data structures. >>The pointers will always be 4 bytes and the addresses won't change. You >>can change the size of the structure and you could even change it >>at run time and the program won't care since it always accesses it through >>the pointer that is in a known location. > >Good point, Randy, but not applicable in this case. If somebody is changing >variable lengths on you, all the indirection in the world won't solve the >problem. You not only have to relink, you have to modify source code and >recompile! > One more time...... The pointer variables (using 4 bytes each) are interleaved with the transfer vectors right at the front of the shared image. Once allocated a space in the transfer vector psect, their address relative to the front of the shared image NEVER moves. The value stored in those four bytes can change as things move around in the body of the shared image, but the pointer is always at a fixed address at the head of the image just like a transfer vector. -- Randy Buckland Research Triangle Institute rcb@rti.rti.org [128.109.139.2] {decvax,ihnp4,seismo}!mcnc!rti-sel!rcb