Technical data

SDA Description
When the system fails, the operating system reports the approximate cause of the
failure on the console terminal. SDA displays a similar message when you issue
a SHOW CRASH command. For instance, for a fatal exception, SDA can display
one of these messages:
FATALEXCPT, Fatal executive or kernel mode exception
INVEXCEPTN, Exception while above ASTDEL or on interrupt stack
SSRVEXCEPT, Unexpected system service exception
Although several exception conditions are possible, access violations are the most
common. When the hardware detects an access violation, information useful in
finding the cause of the violation is pushed onto either the kernel stack or the
interrupt stack. If the access violation occurs when the hardware is using the
interrupt stack, this information appears on the interrupt stack.
The INVEXCEPTN, SSRVEXCEPT, and FATALEXCPT bugchecks place two
argument lists, known as the mechanism and signal arrays, on the stack.
The SSRVEXCEPT and FATALEXCPT bugchecks push an additional argument
list onto the stack above these arrays; INVEXCEPTN does not. This pointer array
(see Figure SDA–1) contains the number 2 in its first longword, indicating that
the following two longwords complete the array. The second longword contains
the stack address of the signal array; the third contains the stack address of the
mechanism array.
Figure SDA–1 Pointer Argument List on the Stack
00000002
ZK−1920−GE
Mechanism Array Address
Signal Array Address
The first longword of the mechanism array (see Figure SDA–2) contains a 4,
indicating that the four subsequent longwords complete the array. These four
longwords are used by the procedures that search for a condition handler and
report exceptions.
SDA–21