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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:

  p   Sets or displays the current option setting for the parent process

  s   Sets or displays the current option setting for the system

  The following keywords are used with the p option:

  reset
      Reset the current option settings to the default for the parent process

  noprint
      Do not print the unaligned access warning message for the parent
      process

  nofix
      Do not fix the unaligned access for the parent process

  sigbus
      Deliver a SIGBUS signal to the parent process

  The following keywords are used with the s option:

  reset
      Reset the current option settings to the default for the system

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

	    # uac p noprint

   2.  Both of the following commands enable messages for the system:
	    # uac s 1

	    # uac s reset

   3.  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

Index for Section 1

Alphabetical listing for U

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