Technical data

SDA Description
Figure SDA–4 Stack Following an Illegal Page-Fault Error
R4
ZK−1923−GE
R5
Reason Mask
Virtual Address
PC
PSL
Six longwords describe the error:
Longword Contents
R4 Contents of R4 at the time of the bugcheck.
R5 Contents of R5 at the time of the bugcheck.
Reason mask Longword mask. If bit 0 of this longword is set, the failing
instruction (at the PC saved below) caused a length violation.
If bit 1 is set, it referred to a location whose page table entry is
in an ‘‘access’’ page. Bit 2 indicates the type of access used by
the failing instruction: it is set for write and modify operations
and clear for read operations.
Virtual address Virtual address being referenced by the instruction that caused
the page fault.
PC PC containing the address of the instruction that caused the
page fault.
PSL PSL at the time of the page fault.
If the operating system detects a page fault while the IPL is higher than IPL$_
ASTDEL, you can obtain the address of the instruction that caused the fault by
examining the PC pushed onto the current operating stack. Follow the steps
outlined in Section 9.3 to determine which module issued the instruction.
9 A Sample System Failure
This section steps through the analysis of a system failure using, as an example,
a printer driver. Three events lead up to this failure:
1. The line printer goes off line for 3 hours.
2. The line printer comes back on line.
3. The operating system signals a bugcheck, writes information to the system
dump file, and shuts itself down.
The following sections describe the actions to take in investigating the causes of
this system crash.
SDA–24