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uac(1) General Commands Manual uac(1) NAME uac - Unaligned Access Message Control SYNOPSIS uac p | s [value] uac p | s [keyword] FLAGS The following flags are used with the uac command: Sets or displays the current flag setting for the parent process Sets or displays the cur- rent flag setting for the system The following keywords are used with the p flag: Reset the current flag settings to the default for the parent process Do not print the un- aligned 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 flag: Reset the current flag settings to the default for the system Do not print the unaligned ac- cess 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. In- stead, 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: "Un- aligned 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 oc- curring 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 de- liver 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 flags, as defined in setsysinfo(2). If value is not specified, the current flag setting is displayed. You can specify value as either 0 (zero) or 1 (one). If value is 0 (zero), the flag is turned on and messages are not displayed. If value is 1 (one), the flag 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 flag. 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 RELATED INFORMATION getsysinfo(2), setsysinfo(2) Programmer's Guide delim off uac(1)