Functional Information
The most important thing to remember aboutC"S, from a debugging
standpoint, is that it is a one-user system. The supervisor manages one user and keeps track of only one user
1
s file and storage
chains. Thus, everything in a dump of a particular machine relates only
to that virtual machine's activity.You should be familiar with register usage, save area structuring,
and control block relationships before attempting to debug or alterCMS. Register Usage When a C"S routine is called, R1 must point to a valid parameter list (PLIST) for that program. On return. RO mayor may not contain
meaningful information (for eXample, on return from a call to FILEDEF
with no change,RO will contain a negative address if a new FCB has been
set up; otherwise, a positive address of the already existing FCE). R15
will contain the return code. if any. The use of Registers0 and 2
through 11 varies.On entry to a command or routine called by SVC 202 the following are
in effect: 1
12
13
14
15
ContentsThe-address of the PLIST supplied by the caller.
The address entry point of the called routine.
The address of a work area (12 doublewords) supplied bySVCINT. The return address to the SVCINT routine.
The entry point (same as register 12).On return from a routine, Register 15 contains:
Return o <0 )0 No error occurred
Called routine not found
Error occurred
If aC"S routine is called by an SVC 202, registers 0 through 14 are
saved and restored byC"S. Most CMS routines use register 12 as a base register.
Structure ofDMSN UC D"SNUC is the portion of storage in a CMS virtual machine that contains
system control blocks, flags, constants, and pointers.
TheCSECTs in DMSNUC contain only symbolic references. This means
that an update or modification toC"S, which changes a CSECT in DMSNUC. does not automatically force all eMS modules to be recompiled. Only those modules that refer to the area that was redefined must be
recompiled.240 IBM VM/370 System Programmer's Guide
The most important thing to remember about
standpoint, is that it is a one-user system. The supervisor manages
1
s file and storage
chains. Thus, everything in a dump of a particular machine relates only
to that virtual machine's activity.
and control block relationships before attempting to debug or alter
meaningful information (for eXample, on return from a call to FILEDEF
with no change,
set up; otherwise, a positive address of the already existing FCE). R15
will contain the return code. if any. The use of Registers
through 11 varies.
in effect:
12
13
14
15
Contents
The address entry point of the called routine.
The address of a work area (12 doublewords) supplied by
The entry point (same as register 12).
Return
Called routine not found
Error occurred
If a
saved and restored by
Structure of
system control blocks, flags, constants, and pointers.
The
that an update or modification to
recompiled.