pTAL Reference Manual (H06.03+)

Data Alignment
HP pTAL Reference Manual—523746-005
4-2
Misalignment Tracing Facility
When a misaligned address causes an exception that RVUs prior to G06.17 would
have rounded down, the tracing facility traces the exception.
While a process runs, the tracing facility:
•
Counts the number of misaligned-address exceptions that the process causes (the
exception count)
•
Records the program address and code-file name of the instruction that causes the
first misaligned-address exception
Because a process can run for a long time, the tracing facility samples the process
(that is, checks its exception data) periodically (approximately once an hour). If the
process recorded an exception since the previous sample, the tracing facility records
an entry in the EMS log. If the process ends and an exception has occurred since the
last sample, the operating system produces a final Event Management Service (EMS)
event.
The EMS event includes:
•
The process’s exception count
•
Details about one misaligned-address exception, including the program address,
data address, and relevant code-file names
Sampling is short and infrequent enough to avoid flooding the EMS log, even for a
continuous process with many misaligned-address exceptions. One sample logs a
maximum of 100 events, and at most one event is logged for any process.
If misaligned-address exceptions occur in different periods of a process, the operating
system produces multiple EMS events for the same process, and these EMS events
might have different program addresses.
For more information about EMS events or the EMS log, see the EMS Manual.
Note. The tracing facility does not count and trace every misaligned address, only those that
cause round-down exceptions. Other accesses that use misaligned addresses without
rounding them down do not cause exceptions and are not counted or traced. Also, only a
periodic sample of the counted exceptions are traced by means of their own EMS event
messages.