On 6/27/2013 7:39 AM, Tom Marchant wrote:
On Wed, 26 Jun 2013 22:45:50 -0700, Ed Jaffe wrote:
AFAIK, there is only one 4K range of virtual addresses guaranteed to
generate 0C4 now and forever: 7FFFF000 - 7FFFFFFF.
I didn't know that. Is it documented anywhere?
Documented? Unlikely. But Jim Mulder stated in an IBM-MAIN post back in
2007 that it has been that way since MVS/XA and is not going to change.
If you disassemble or otherwise look at IBM source code in VPL, they use
this value often.
We load 7FFFF000 instead of zero (or negative one) into a "unused"
register any time we want to avoid accidental overlay. Our
infrastructure task launcher/subroutine linkage does this automatically
for _all_ registers not used as part of the "system" linkage.
In addition, it launcher loads AR2-AR13 with FFFFFFFF and, if the target
code is 31-bit mode, the high halves of R2-R13 with FFFFFFFF.
--
Edward E Jaffe
Phoenix Software International, Inc
831 Parkview Drive North
El Segundo, CA 90245
http://www.phoenixsoftware.com/
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