uac(1)							      General Commands Manual							    uac(1)

NAME

       uac - Unaligned Access Message Control

SYNOPSIS

       uac p | s [value]

       uac p | s [keyword]

OPTIONS

       The  following  options	are used with the uac command: Sets or displays the current option setting for the parent process Sets or displays
       the current option setting for the system

       The following keywords are used with the p option: Reset the current option settings to the default for the parent process Do not print the
       unaligned  access  warning message for the parent process Do not fix the unaligned access for the parent process Deliver a SIGBUS signal to
       the parent process

       The following keywords are used with the s option: Reset the current option settings to the  default  for  the  system  Do  not	print  the
       unaligned access warning message for the system

       Usually, the parent process is the shell.

DESCRIPTION

       Most  complex  instruction set computers (CISC) can access unaligned data but only at a significantly reduced speed.  Most reduced instruc-
       tion set computers (RISC) do not attempt to handle unaligned accesses.  Instead, they generate an unaligned access trap and let the operat-
       ing system handle the fault.

       The  default  action for the operating system when an unaligned access fault occurs is to fix the unaligned access fault and then display a
       warning message informing the user process that an unaligned access fault has occurred.	 The  warning  message	has  the  following  form:
       "Unaligned  access  pid=nnn  <prog_name> va=virtual_addr pc=pc_addr". If you want to change the code to prevent the unaligned access faults
       from occurring in the future, the warning message gives you the information you need to locate the code causing a fault. (See the  Program-
       mer's Guide for details on the causes and effects of misaligned data.)

       In  addition,  the default action for the operating system is to not deliver a SIGBUS signal to the parent process when an unaligned access
       fault occurs.

       These defaults are satisfactory for most users, but some users require a different behavior and want to specify their own Unaligned  Access
       Control (UAC).

       The  uac  command  enables or disables the display of "Unaligned access" messages. The command sets or displays the UAC_NOPRINT, UAC_NOFIX,
       and UAC_SIGBUS options, as defined in setsysinfo(2).

       If value is not specified, the current option setting is displayed. You can specify value as either 0 (zero) or 1 (one).   If  value  is  0
       (zero), the option is turned on and messages are not displayed. If value is 1 (one), the option is turned off and messages are displayed.

       Keywords can be used singly, or in any combination.  However, the reset keyword overrides any other keywords it is used with.

RESTRICTIONS

       You must be superuser to set the system option.

EXAMPLES

       Both of the following commands disable messages for the parent process: # uac p 0

	      # uac p noprint Both of the following commands enable messages for the system: # uac s 1

	      #  uac  s  reset	The  following	command disables fixing of an unaligned access fault, disables printing a message for an unaligned
	      access fault to the parent process, and enables delivery of a SIGBUS signal to the parent process: # uac p nofix noprint sigbus

SEE ALSO

       getsysinfo(2), setsysinfo(2)

       Programmer's Guide

																	    uac(1)