Field Location LASTCMND X'2AO' PREVCMND X'2A8' LASTEXEC X'2BO' PREVEXEC X'2B8'
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Last command issued from the CMS or XEDIT command line. If a com­
mand issued in a CMS EXEC abnor­
mally terminates, this field contains
the name of the command. When a CMS EXEC completes, this field con­
tains the name 'EXEC.' EXEC 2 and System Product Interpreter do not
update this field.
Next-to-Iast command issued from
the CMS or XEDIT command line. If
a command issued in a CMS EXEC
abnormally terminates, this field con­
tains the name 'EXEC'. When a CMS EXEC completes, this field con­
tains the last command issued from
the CMS EXEC. EXEC 2 and Sys­ tem Product Interpreter do not update
this field.
Last EXEC procedure invoked.
EXEC 2 and System Product Inter­
preter do not update this field.
Next to last EXEC procedure
invoked. EXEC 2 and System Prod­ uct Interpreter do not update this
field. • Last Module Loaded into Free Storage and the Transient Area
The name of the last module loaded into free storage via a LOADMOD is in
the field LASTLMOD (location X'2CO'). The name of the last module loaded
into the transient area via a LOADMOD is in the field LASTTMOD (location
X'2C8'). • Pointer to CMSCB The pointer to the CMSCB is in the FCBTAB field located at X'5CO'. CMSCB contains the simulated OS control blocks. These simulated OS con­
trol blocks are in free storage. The CMSCB contains a PLIST for CMS I/O functions, a simulated Job File Control Block (JFCB), a simulated Data Event
Block (DEB), and the first in a chain of I/O Blocks (lOBs). • The Last Command
The last command entered from the terminal is stored in an area called
CMNDLINE (X'7 AO'), and its corresponding PLIST is stored at CMNDLIST
(X'848').
Debugging With eMS 533

Register Usage External Interrupt Work Area EXTSECT is a work area for the external interrupt handler. It contains:
The PSW, EXTPSW Register save areas, EXSA VE 1 Separate area for timer interrupts, EXSA VE I/O Interrupt Work Area IOSECT is a work area for the I/O interrupt handler. The oldest and newest PSW and CSW are saved. Also, there is a register save area.
Program Check Interrupt Work Area PGMSECT is a work area for the program check interrupt handler. The old PSW and the address of register 13 save area are stored in PGMSECT. SVC Work Area SVCSECT is a work area for the SVC interrupt handler. It also contains the
first four register save areas assigned. The SFLAG indicates the mode of the
called routine. Also, the SVC abend code, SVCAB, is located in this CSECT. Simulated CVT (Communications Vector Table)
The CVT, as supported by CMS, is CVTSECT. Only the fields supported by eMS are filled in.
Active Disk Table and Active File Table
For file system problems, examine the ADT (Active Disk Table), or AFT (Ac­
tive File Table) in NUCON. See a CMS nucleus map for the location of these CSECTs. In order to trace control blocks and modules, it is important to know the CMS reg­
ister usage conventions.
Register
GR1
GR12
GR13
GR14
GR15
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Address of the PLIST Program's entry point
Address of a 12-doubleword work area for an SVC call
Return address
Program entry point or the return code
The preceding information should help you to read a CMS dump. If it becomes
necessary to trace file system control blocks, refer to Figure 71 on page 531 for
more information. With a dump, the control block diagrams, and a CMS load map,
you should be able to find the cause of the abend.
Tips for debugging after receiving a program check abend (e.g. DMSITP141) are
as follows:
534 VM/SP System Programmer's Guide