NAME    [Toc]    [Back]

       uac - Unaligned Access Message Control

SYNOPSIS    [Toc]    [Back]

       uac p | s [value]

       uac p | s [keyword]

OPTIONS    [Toc]    [Back]

       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    [Toc]    [Back]

       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    [Toc]    [Back]

       You must be superuser to set the system option.

EXAMPLES    [Toc]    [Back]

       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    [Toc]    [Back]

       getsysinfo(2), setsysinfo(2)

       Programmer's Guide



                                                           uac(1)