++USERMOD(ZP60023)             /* SUPPORT DAS AT THE TASK LEVEL */  .
++VER(Z038) FMID(FBB1221) PRE(UZ61148,UZ36571,UZ30139,UZ25668)
 /*
   PROBLEM DESCRIPTION:
     NO OPERATING SYSTEM SUPPORT FOR THE DUAL ADDRESS SPACE FACILITY.
       IN ORDER TO EXPLOIT THE DUAL ADDRESS SPACE FACILITY (DAS)
       APPLICATIONS MUST USE DISABLEMENT FOR SERIALIZATION AND
       MANAGE THE CONTENTS OF THE RELEVANT CONTROL REGISTERS.
       THIS IS NOT CONDUCIVE TO GOOD SYSTEM STABILITY, RELIABLITY
       AND PERFORMANCE.

       THIS USERMOD UPDATES THE PROGRAM CHECK FIRST LEVEL INTERRUPT
       HANDLER (PCFLIH) SUCH THAT IF A SPECIAL-OPERATION EXCEPTION
       IS CAUSED BY AN SSAR INSTRUCTION WHEN RUNNING UNDER A TASK,
       THE SPECIFIED SECONDARY ADDRESS SPACE NUMBER (SASN) IS
       VALIDATED, AND IF VALID IS SET UP TO BE THE TASK'S SECONDARY
       ADDRESS SPACE.

       THE PCFLIH STORES THE SECONDARY ASID IN THE PREVIOUSLY
       RESERVED FIELD TCBRV326.

       ALL TASKS CAN USE SSAR TO SET SASN=PASN.  ALL TASKS CAN
       ISSUE SSAR WITH THE SPECIAL SASN VALUE OF ZERO WHICH CAUSES
       ALL DAS SETTINGS TO BE CLEARED FROM CONTROL REGISTERS.
       (SPECIFYING A SASN OF ZERO IS DIFFERENT FROM USING GENERAL
       PURPOSE REGISTER 0 IN THE SSAR INSTRUCTION.)

       SETTING THE SECONDARY ADDRESS SPACE TO ONE OTHER THAN THE
       CURRENT PRIMARY ADDRESS SPACE REQUIRES THAT THE SSAR
       INSTRUCTION IS EXECUTED IN SUPERVISOR STATE.

       THIS USERMOD ALSO CHANGES THE DISPATCHER TO RESTORE THE
       SECONDARY ASID OF A TASK EACH TIME IT IS DISPATCHED.  THE
       DISPATCHER WILL RESET THE DAS ENVIRONMENT, AND REVALIDATE
       THE ASID STORED IN TCBRV326, AND IF FOUND TO BE VALID WILL
       SET THAT ASID AS THE TASK'S SECONDARY ASID BEFORE THE TASK
       RESUMES PROCESSING.

       THE ASID IS CONSIDERED VALID IF IT SPECIFIES AN ASSIGNED
       SWAPPED-IN ADDRESS SPACE.  WHEN A SECONDARY ASID IS SET
       UP FOR A TASK BY THE PCFLIH, OR RESTORED BY THE DISPATCHER,
       THE SECONDARY ASN IS SET INTO CONTROL REGISTER 3, THE
       PRIMARY ASN IS SET INTO CONTROL REGISTER 4, THE SECONDARY
       SEGMENT TABLE ORIGIN AND LENGTH ARE SET INTO CONTROL
       REGISTER 7, AND THE EXTRACTION-AUTHORITY CONTROL AND THE
       SECONDARY-SPACE CONTROL BITS ARE SET ON IN CONTROL REGISTER 0.

   SPECIAL CONDITIONS:
     ACTION:
       AN IPL MUST BE PERFORMED FOR THIS SYSMOD TO BECOME ACTIVE.

     DOC:
       SYSTEM ABEND 0D7 INDICATES THAT THE PC FLIH FOUND AN ADDRESS
       SPACE TO NOT BE BOTH ASSIGNED AND SWAPPED IN.  THE VALUE OF
       GENERAL PURPOSE REGISTER 15 IS 1 IF THE PRIMARY ADDRESS
       SPACE WAS FOUND TO BE INVALID AFTER A PAGE FAULT IN THE
       SECONDARY ADDRESS SPACE WAS RESOLVED, AND 2 IF A PAGE-
       TRANSLATION EXCEPTION OCCURRED FOR AN INVALID SECONDARY
       ADDRESS SPACE.

   COMMENTS:
     PRYCROFT SIX P/L PUBLIC DOMAIN USERMOD FOR MVS 3.8 NUMBER 23.

     REWORK HISTORY:
       2008-11-01: INITIAL RELEASE.
       2012-01-07: SAVE FLOATING POINT REGISTER CONTENTS CORRECTLY.
       2015-06-09: FIX CONDITION CODE SETTING AND BRCL BRANCH ADDRESS.
                   ALSO ADD TRTT, TRTO, TROT, TROO, MSFI AND TP.
       2016-08-06: REMOVE NON-370 INSTRUCTION OPCODE SUPPORT RESIDENT
                   IN THE PCFLIH OPERATION EXCEPTION HANDLER, AND SO
                   PSARV022 IS NO LONGER USED AS A RECURSION FLAG.

     THE FOLLOWING MODULES AND/OR MACROS ARE AFFECTED BY THIS USERMOD:
     MODULES:
       IEAVEDS0
       IEAVEPC
     MACROS:
       IKJTCB
 */.