April 1, 1981 e Save Area for Low Storage executing, DEBUG saves the first 160 bytes of low storage in a NUCON field called LOWSAVE. LOWSAVE begins at X'CO'. Register Save Area DMSABN, the abend routine, saves the user's floating-point and
general registers. Kielg FPRLOG GPRLOG ECRLOG Device 1ocati2!! X'160' X'1S0' X'1CO' contents User floating-point registers User general registers User extended control registers
The name of the device causing the last I/O interrupt is in the DEVICE field at X'26C'. Last Two Commands or procedures Executed Figlg LASTCMND PREVC!1ND LASTEXEC PREVEXEC 1Qcati2!! X'2AO' X'2A'S' X'2BO' X' 2BS' Last CMS command issued
Next to last CMS command issued
Last EXEC procedure invoked
Next to last EXEC procedure invoked 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 LASTL!10D (location X'2CO'). The name of the last module
loaded into the transient area via a LOADMOD is in the field LASTTMOD (location X'2CS'). Pointer to CMSCB The pointer to the CMSCB is in the FCBTAB field located at X'SCO'. CMSCB contains the simula·ted as control blocks. These simulated as blocks are in free storage. The CMSCB contains a PLIST for CMS 1/0 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'7AO'), and its corresponding PLIST is stored at CMNDLIST (X'S4S'). Interrupt Work Area EXTSECT (X'1SS0') is a work area for the external interrupt handler.
It contains: The PSW, EXTPSW (X'1SFS') Register save areas, EXSAVE1 (X'1SBSI) separate area for timer interrupts, EXSAVE (X'1SS0') Part 1. Debugging with VM/370 71
Paqe of GC20-1807-7 As Updated April 1, 1981 by TNL GN25-0829 I/O Interrupt Work Area IOSECT (X'1620') is a work area for the I/O interrupt
oldest and newest PSW and CSW are saved. Also, there
save area.
handler. The
is a register Program Check Interrupt Work Area PGMSECT (X'16BO') is a work area for the program check
handler. The old PSW and the address of register 13 save
stored in PGMSECT. SVC Work Area
area are SVCSECT (X'1748') is a work area for the SVC interrupt handler. It
also contains the first four register save areas assigned. The SFLAG (X'1758') indicates the mode of the called routine. Value of __ X'80' X'40' X'20' X'Ol' Description SVC protect key is zero
Transient area routine
Nucleus routine
Invalid reentry flag
Also, the SVC abend code, SVCAB, is located at X'1751'. Simulated CVT (Communications Vector Table)
The CVT, as supported by CMS, is CVTSECT (X'lCC8'). Only the fields
supported by CMS are filled in. Active Device Table and Active File Table
For file system problems, examine the ADT (Active Device Table), or 1FT (Active File Table) in NUCON. REGISTER USAGE In order to trace control blocks and modules, it is important to know
the CMS reqister usaqe conventions. GRl GR12
GR15 Address of the PLIST proqram'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 eMS dump. If it
becomes necessary to trace file system control blocks, refer to Figure
37 in "Part 3. Conversational Monitor System" 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.
72 IBM VM/370 System Guide
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