Accelerator Manual (G06.27+, H06.04+, J06.03+)

Preparing Your Program for TNS/R Systems
Accelerator Manual—527303-003
2-8
Segment Wrapping
Example
The following TAL procedure tries to use the system value at address SG[0], but on a
TNS system, the procedure uses whatever is at address G[0] in the user data
segment. For more information on how to access the system data segment, refer to the
section on “Privileged Procedures” in the TAL Reference Manual.
INT cpuno = 'SG' + 0; ! SG equivalencing
INT .EXT xcpuno; ! Extended pointer
PROCEDURE foo; ! Nonprivileged procedure
BEGIN
IF cpuno = 1 THEN ! TNS/R system traps
BEGIN ! TNS system accesses G[0]
! Lots of code
END;
@xcpuno := $XADR(cpuno);
IF xcpuno = 1 THEN ! TNS/R system traps
... ! TNS system accesses G[0]
END;
Segment Wrapping
If a nonprivileged program tries to allocate and operate on variables partially lying
across the end of the user data segment, results might differ depending on the system:
•
On TNS systems, the variable reference wraps back to the base of the user data
segment.
•
On TNS/R systems, the variable reference is unpredictable; it might wrap or trap.
Nonprivileged programs cannot access SG.
Required Change
•
Remove any constructs from your programs that result in segment wrapping.
Change addressing operations so that they stay fully within the segment.