>Then the doc for SVCs 68, 138 should be fixed.

If by "the doc" you mean the information in the diagnosis reference, the 
information for SVC 138 is probably wrong but that book does not document 
requirements.
The documentation for PGSER, for example, correctly documents that there 
is no reg 13 requirement (at least for SVC-entry).

If you're referring to other doc, please clarify.

Apparently for SVC 68 SYNADAF R13 must point to a "save area" but it is 
not used to save/restore the SVC issuer's registers. The real requirement 
appears to be that the word at offset 8 in the area pointed to by R13 be 
updateable (since the service does, in effect, save area chaining to/from 
the new area that is gotten).

>>I quite strongly disagree.
>Why?

For exactly the reasons I described. Further, it is clearer and simpler, 
if you truly need to change AMODEs, just to do so, rather than to branch 
somewhere (BASSM) to accomplish that. Prior to the existence of SAMxx, the 
BSM instruction was the normal way to change AMODE.

Peter Relson
z/OS Core Technology Design

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