(IBM Mainframe Discussion List) wrote:
All it needs is an IOSB -- which contains pointers to the
channel program and UCB. Using STARTIO, you can construct a channel
program to read or write any records anywhere on any device. This puts
you one subtle programming error away from "wiping out" something
important that isn't yours.
Which is why you test your STARTIO code, and anything else you build that is
authorized, on "test" systems that everyone else knows may not survive your
test. You can also wipe out something that is not yours with an incorrect
real address on a read command using the much "safer" EXCPVR. When you are
building authorized code, you must write each instruction with the awareness
that you can unexpectedly hose almost any conceivable part of MVS if you err.
The "wiping out" I was talking about was when writing to the disk.
STARTIO does no prefixing. EXCPVR does. So, unless you do something to
overlay the DEB extent information, or set the flag in the DEB to tell
the system you will provide your own prefix, you are saved by MVS from
accidentally writing on something important when you use EXCPVR.
I agree that if you supply bad buffer addresses for read CCWs, you will
"clobber" storage. That goes without saying. Obviously, mistakes with
real storage addresses have worse (more random) ill effects and are
harder to track down than mistakes with virtual addresses. Good thing we
have GTF.
--
Edward E Jaffe
Phoenix Software International, Inc
5200 W Century Blvd, Suite 800
Los Angeles, CA 90045
310-338-0400 x318
[EMAIL PROTECTED]
http://www.phoenixsoftware.com/
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