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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:

  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 pro-
      cess

  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 com-
  puters (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"	mes-
  sages. 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 pro-
       cess:
	    # 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