Type SVC 202 or 203 Other o -1 Same as
callerSame as
caller
2 -11I I I IUnpredict-1 lable I I I I I Same as
caller
12 13 14
AddressUser Return
of save address
called area to
routineDftSITS Address User Return
of save address
called area to
routineDftSITS Figure 11. Register Contents when Called Routine is Started 15
Address
of
called
routineSame as
callerpossibly modifying the address field. How the address field is modified depends upon the type of SVC call, and on whether the called routine
indicated an error return address.
ForSVC 202 and 203, the called routine indicates a normal return by means of a zero returned in register and an error return by means of
a nonzero in register 15. If the called routine indicates anormal return, then DftSITS makes a normal return to the caller. If the called
routine indicates an error return, thenDftSITS returns to the caller's
error return address, if one was specified, and abnormally terminates if
none was specified.
ForSVC 202 not followed by "DC AL4(address}ft, a normal return is made to the instruction following the SVC instruction, and an error
return causes an abnormal termination. ForSlC 202 followed by nDC lL4 (address)", a normal return is made to the instruction following the
DC, and an error return ismade to the address specified in the DC. In
either case, register 15 contains the return code passed by the called
routine.
ForSVC 203 with a positive halfword code, a normal return is made to the instruction following the halfword code, and an error return
causes anahnormal termination. For SVC 203 with a negative halfword
code, bothnormal and error returns are made to the instruction
following the halfword code. In any case, register 15 contains the
return code passed hack by the called routine.
ForOS macro simulation SVC calls, and for user-handled SVC calls, no
error return is recognized byDftSITS. As a result, DftSITS always
returns to the caller by loading theSVC old PSi that was saved when DMSITS was first entered. Upon entry to DMSITS, all registers are saved as
they were when theSVC instruction was first executed. Upon exiting from DMSITS, all registers are restored to the values that were saved at entry_ The exception to this is register
return to the caller, register 15
register 15 when the called routine
completed processing.SYSTEM AND USER SAVE AREA FORMATS 15 for SVC 202 and 203. Upon contains the value that was in
returned toDftSITS after it had
Whenever anSVC call is made, DMSITS allocates two save areas for that
particularSVC call. 2-70 IBM VM/370 System Logic and Program 2
caller
caller
2 -11
caller
12 13 14
Address
of save address
called area to
routine
of save address
called area to
routine
Address
of
called
routine
caller
indicated an error return address.
For
a nonzero in register 15. If the called routine indicates a
routine indicates an error return, then
error return address, if one was specified, and abnormally terminates if
none was specified.
For
return causes an abnormal termination. For
DC, and an error return is
either case, register 15 contains the return code passed by the called
routine.
For
causes an
code, both
following the halfword code. In any case, register 15 contains the
return code passed hack by the called routine.
For
error return is recognized by
returns to the caller by loading the
they were when the
return to the caller, register 15
register 15 when the called routine
completed processing.
returned to
Whenever an
particular