Page of GC20-1807-7 As Updated Aug 1, 1979 by TNL GN25-0492 • control registers • Program status word (PSW) • Channel address word (CAW) • Channel status word (CSW) The DCP and DMCP commands of CP are privilege class C and E commands
and are used to display real storage locations. The DMCP command spools
the contents of real storage to your virtual printer. The DCP command
displays at your terminal the contents of real storage locations.
The class G VMDUMP command dumps virtual storage to a specified
reader spool file. VMDUMP provides the same dump information that the DUMP command provides but in a different format. For example, if a tyte of storage contains X'OC', DUMP records it in printable format, X'FOFO'; VMDUMP records it as it appears in storage, X'OO'. The VM/lnteractive Problem Control System Extensions program product can process records
written by VMDUMP. For a description of the format and contents of the VMDUMP records, see "VMDUMP Records: Format and Content" in this
section. COMMANDS THAT SET AND QUERY SYSTEM FEATURES, CONDITIONS, AND EVENTS The SYSTEM and SET commands set system-controlled functions and events;
the QUERY command allows you to determine the status of those settingse
The SYSTEM command is a privilege class G command that simulates the RESET and RESTART buttons on the real computer console. It can also be
used to clear storage.
The functions of the SET command are described in detail in the YlU370 fR f om .!Q3: nd fo£ g.§neral. Qsef:.§. For debugging, the SET command provides the MSG, WNG, and EMSG operands. These provide
messages that may be useful while you are debugging.
The SET MSG function determines whether you receive messages set by
other users via the MSG command. Also, the MSG operand determines
whether you receive messages from CP when other users spool reader,
printer, or punch files to your virtual machine.
The SET SMSG command turns on or off a virtual machines special
message flag. If the virtual machine has issued DIAGNOSE Code X'68'
(Authorize), this flag determines whether the virtual machine accepts or
rejects messages sent via the SMSG command --when the flag is on,
messages are accepted.
The SET WNG function determines whether you receive warning messages
from the system operator.
The
operand
message
specify
spooled SET EMSG function controls error message handling. The EMSG gives you the ability to specify that you want message code,
text, or both to be displayed at your terminal. You can also
that no messages be displayed (except in the case where you have
your console output). When you are debugging, it is useful to have all messages displayed
a t your terminal.
The QUERY command displays the status of features and conditions set
by the SET command for your virtual machine. ON is the default for the MSG, WNG, and EMSG operands of the SET command; OFF is the default for
the SMSG operand. To verify these settings, use the QUERY command. Part 1. Debugging with VM/370 39

Aug 1, 1979 COMMANDS TO COLLECT AND ANALYZE SYSTEM INFORMATION This section discusses five commands to collect and analyze
information when you are debugging. These are the ADSTOP and
commands and the LOCATE, MONITOR, and TRACE commands.
syste m
BEGIN
The ADS TOP command stops the execution of a virtual machine at a
specific address; causes the virtual machine to resume execution.
Execution halts when the instruction at the address specified in the ADSTOP command is reached. At this point, you may invoke other CP debugging commands.
The address stop should be set after the program is loaded but before
it executes. When the specified location is reached during program
execution, execution halts and the CP command environment is entered. You may then enter other CP commands to examine and alter the status of
the program. Set an address stop at a location where you suspect the error in the
program. You can then display the registers, control words, and data
areas to check the program at that point in its execution. This
procedure helps you locate program errors. You may be able to alter the
contents of storage in such a way that the program will execute
correctly. You can then correct the error you have detected and, if
necessary, compile and execute the program again.
To successfully set an address stop, the virtual instruction address
must be in real storage at the time the ADSTOP command is issued. Use the LOCATE command to find the address of CP control blocks
associated with a particular user, a user's device, or a real system
device. The control blocks and their functions are described in the XnLllQ £Qnt£Ql Blg£! Logic. Once you know the location of the control blocks, you can examine (DUMP or DISPLAY) the block you want to look at. When you want to
examine specific control blocks, use the LOCATE and DUMP or DISPLAY commands to examine the control blocks instead of taking a dump. A
discussion of the most important fields of the VMBLOK, VCUBLOK, VDEVBLOK, RCHBLOK, RCUBLOK, and RDEVBLOK are included in "Reading CP Abend Dumps." COMMANDS THAT TRACE EVENTS IN VIRTUAL MACHINES Use the TRACE command to trace the following virtual machine events: • SVC interruption • I/O interruption • Program interruption • External interruption 40 System Programmer's Guide