Technical data
SDA Description
• The PC of the instruction that referred to the bad virtual address was
8005D003
16
.
Issuing the SDA command EVALUATE/PSL 04080000 makes the following
information apparent:
• The IPL was 8 at the time of the exception (shown by bits 16 through 20 of
the PSL).
• The current operating stack was the interrupt stack (bit 26 of the PSL is set
to 1).
• The process was executing in kernel mode at the time of the exception (shown
by bits 24 and 25 of the PSL).
Use the SHOW PAGE_TABLE command to display the system page table, as
shown in the following example. The page containing location 80069E00
16
is not
available to any access mode (a null page); thus, the virtual address is not valid.
SDA> SHOW PAGE_TABLE
System page table
-----------------
ADDRESS SVAPTE PTE TYPE PROT BITS PAGTYP LOC STATE TYPE REFCNT BAK SVAPTE FLINK BLINK
.
.
.
80068400 80777B08 7C40FFC8 STX UR K
80068600 80777B0C 7C40FFC8 STX UR K
80068800 80777B10 7C40FFC8 STX UR K
80068A00 80777B14 7C40FFC8 STX UR K
80068C00 80777B18 7C40FFC8 STX UR K
80068E00 80777B1C 7C40FFC8 STX UR K
80069000 80777B20 7C40FFC8 STX UR K
80069200 80777B24 7C40FFC8 STX UR K
80069400 80777B28 7C40FFC8 STX UR K
80069600 80777B2C 7C40FFC8 STX UR K
80069800 80777B30 7C40FFC8 STX UR K
80069A00 80777B34 780016C9 TRANS UR K SYSTEM FREELST 00 01 0 0040FFC8 80777B34 03AF 0E15
80069C00 80777B38 78000E15 TRANS UR K SYSTEM FREELST 00 01 0 0040FFC8 80777B38 16C9 2592
-------- 40 NULL PAGES
.
.
.
9.3 Locating the Source of the Exception
Because the printer went off line and then came back on line, as shown on the
console listing in Section 9.2, the problem might exist in the driver code. SDA
can help you determine which driver might contain the faulty code.
9.3.1 Finding the Driver by Using the Program Counter
The first step in determining whether the failing instruction is within a driver
is to examine the PC in the signal array using the EXAMINE/INSTRUCTION
command. This has two results:
• If possible, it displays the contents of the address as a MACRO instruction.
• It identifies the address as an offset from the symbol, nnDRIVER, if the
address lies within the first FFF
16
bytes of such a symbol. SDA defines a
symbol in the form of nnDRIVER for each device driver connected to the
system. This symbol represents the base of the driver prologue table (DPT).
Each DPT is part of the device driver it describes and is immediately followed
by that driver’s code.
SDA–26