Basic System Problem Analysis - August 2003

System Globals

System globals is centralized table of information used by all parts of the OS. As was

mentioned earlier, the KSO table is located at the top of System Globals.

At the end of the system globals structure is an array of 32 entries, one for each active

processor (type “SPSD_ENTRY_TYPE”) that tracks information about the process

active on each CPU.

The macro “SYSGLOB” is an easy way to get information out of the system globals

structure but you need to know the name of the field you want to see. The macro also

only handles individual fields within a structure and not structures themselves. So you

could use SYSGLOB to display the highest PIN number used so far, whose field is

PM_HIGHEST_PIN

$22c ($70) nmdat > wl SYSGLOB ("PM_HIGHEST_PIN")

$223

But you could not use it to display the “SG_SPSD_ENTRY” structure for CPU 3 by

doing

$22d ($70) nmdat > wl SYSGLOB ("SG_SPSD_ARRAY[3]")

Error while retrieving the requested data from SYMVAL

Your best bet is to use FT to find the field or structure within system globals that you

want to format and just use the FV command, for example:

$22e ($70) nmdat > fv c0000000 'system_globals_type.sg_spsd_array[3]'

Finally, it is worth noting that the short pointer to system globals “C0000000” can be

constructed with a single instruction. The ZDEPI or zero and deposit, immediate

instruction

ZDEPI 3,1,2,rx

Where “rx” is R1 to R31. This says zero the target register and deposit the value 3

beginning in bit 1 for 2 bits to the left. Bits are numbered left to right, 0 to 31. So bit 1

would be the 2

bit from the left and the quantity 3 in binary is “11”. The resulting value

in binary is “11” followed by 30 zeros and when represented in hexadecimal you have

“C0000000”.

When you see this sequence followed by the target register “rx” being used in a load or

store with an offset you can match that to the offsets found by doing an FT

“system_globals_type, m” remembering that the offsets are in hex from FT and decimal

in the instruction. You can then see which field of system globals is being referenced.