pTAL Reference Manual (H06.08+)

Data Alignment
HP pTAL Reference Manual—523746-006
4-3
Misalignment Handling
Misalignment Handling
Misalignment handling is determined by the following SCF attributes, which are set
system-wide (that is, for all processors in the node) by the persons who configure the
system:
•
MISALIGNLOG
•
TNSMISALIGN (applies only to programs running in TNS mode or TNS
accelerated mode, and therefore, does not apply to pTAL programs)
•
NATIVEATOMICMISALIGN
MISALIGNLOG enables or disables the tracing facility (see Misalignment Tracing
Facility on page 4-1).
NATIVEATOMICMISALIGN applies to atomic routines in programs running in TNS/R
native mode; that is, the pTAL and TAL routines whose names begin with “$ATOMIC_”
For normal, nonatomic access in TNS/R native mode, the system uses the operand’s
full address (never rounded down) to complete the operation.
For normal, nonatomic access in TNS/R native mode, the system uses the operand’s
full address (never rounded down) to complete the operation.
Table 4-1 on page 4-3 lists and describes the possible settings for
NATIVEATOMICMISALIGN. Each setting represents a different misalignment handling
method. For more information about NATIVEATOMICMISALIGN, see the SCF
Reference Manual for the Kernel Subsystem .
The method that you choose does not apply to every misaligned address, only to those
that would have been rounded down in earlier RVUs.
Table 4-1. TNS/R Native Atomic Misalignment Handling Methods
Method Description
ROUND
(default)
After rounding down a misaligned address, the system proceeds to access
the address atomically, as in G06.16 and earlier RVUs.
FAIL Instead of rounding down a misaligned address, the system considers the
call to have failed.
This failure generates a SIGILL signal
(signal #4). By default, this signal
causes process termination, but the program can specify other behavior (for
example, entering the debugger or calling a specified signal-handler
procedure). The signal cannot be ignored. For information about signal
handling, see the explanation of the sigaction() function in the Open
System Services System Calls Reference Manual .
Note. ROUND misalignment handling is intended as a temporary solution, not as a substitute
for changing your atomic calls to ensure that they have only aligned addresses. ROUND
misalignment handling cannot be migrated to past and future NonStop OS platforms
.