Accelerator Manual Data Alignment Addendum

Accelerator Manual Data Alignment Addendum—524963-001
3-1
3 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
•
NATIVEATOMICMISALIGN (applies only to programs running in TNS/R native
mode, and therefore, does not apply to the Accelerator)
MISALIGNLOG enables or disables the tracing facility (see Section 2, Misalignment
Tracing Facility).
TNSMISALIGN applies to all programs running in TNS mode or accelerated mode, but
not to programs running in TNS/R native mode.
Table 3-1 lists and describes the possible settings for TNSMISALIGN. Each setting
represents a misalignment handling method. For more information about
TNSMISALIGN, see the SCF Reference Manual for the Kernel Subsystem.
Table 3-1. TNS Misalignment Handling Methods
Method Description
ROUND
(default)*
After rounding down a misaligned address, the system proceeds to access
the address, as in G06.16 and earlier RVUs.
FAIL Instead of rounding down a misaligned address and proceeding to access
the target, the operating system considers the instruction to have failed.
For a Guardian process, this failure generates an Instruction Failure trap
(trap #1). By default, this trap causes the process to go into the debugger,
but the program can specify other behavior (for example, process
termination or calling a specified trap-handling procedure). For information
about trap handling, see the Guardian Programmer’s Guide.
For a OSS process, 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.
NOROUND The system uses the operand’s given odd address (not rounded down) to
complete the operation. If the operation is an atomic operation, atomicity is
no longer guaranteed.
* Use this method on production systems to avoid changing the semantics of old TNS programs. FAIL could
cause possibly fatal Instruction Failure traps in faulty TNS programs. NOROUND might change the semantics of
some faulty programs.