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uac(1)									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  instruction
       set  computers  (RISC)  do  not	attempt	 to handle unaligned accesses.
       Instead, they generate an unaligned access trap and let	the  operating
       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  Programmer'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 deliv‐
	      ery of a SIGBUS signal to the parent  process:  #	 uac  p	 nofix
	      noprint sigbus

SEE ALSO
       getsysinfo(2), setsysinfo(2)

       Programmer's Guide

									uac(1)
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