uac(1) [osf1 man page]
uac(1) General Commands Manual 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 instruc- tion set computers (RISC) do not attempt to handle unaligned accesses. Instead, they generate an unaligned access trap and let the operat- ing 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 Program- mer'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 delivery of a SIGBUS signal to the parent process: # uac p nofix noprint sigbus SEE ALSO
getsysinfo(2), setsysinfo(2) Programmer's Guide uac(1)
Check Out this Related Man Page
iec(1) General Commands Manual iec(1) NAME
iec - Instruction Emulator Control SYNOPSIS
iec p | s [value] iec p | s [keyword] OPTIONS
The following options are used with the iec 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: Resets the current option settings to the default settings for the parent process. Does not print the instruction emulation warning message for the parent process. Disables instruction emulation. Any programs that attempt to execute instructions that are not implemented in the host processor will receive the SIGILL (illegal instruction) signal. Prints the instruction emulation warning messages for all instances of instruction emulation. By default, a message is only printed for the first instance. The following keywords are used with the s option: Resets the current option settings to the default settings for the system. Does not print the instruction emulation warning message for the system. 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 that it is used with. Usually, the parent process is the shell. DESCRIPTION
Some processors in the Alpha processor family do not implement all of the instructions defined in the Alpha architecture. The operating system provides an instruction emulator that permits all programs written for the Alpha architecture to run, regardless of the Alpha pro- cessor being used. When the operating system encounters an instruction that is not implemented by the host processor, the default action is to emulate the instruction and print a message informing the user process that the emulation has occurred. By default, the operating system prints a mes- sage only for the first instance of emulation, although it continues to emulate any other non-implemented instructions that it encounters. The message has the form: "inst emulated pid=nnn <prog_name> va=0xvirtual_addrpc=0xpc_addr inst=0xactual_instr". Receiving this message tells you that your application will run at less than its optimal level of performance. You may wish to recompile your program to get bet- ter performance. For information on how to compile for a specific hardware platform, see the compiler manpage for the language you are using. In addition, the default action for the operating system is to not deliver a SIGILL signal to the parent process when an emulated instruc- tion is encountered. These defaults are satisfactory for most users, but some users require a different behavior and want to specify their own Instruction Emu- lator Control (IEC). The iec command enables or disables the display of "inst emulated" messages. The command sets or displays the IEC_NOPRINT, IEC_NOEMUL, and IEC_VERBOSE flags, as defined in setsysinfo(2). RESTRICTIONS
You must be superuser to set the system option. EXAMPLES
Both of the following commands disable messages for the parent process: # iec p 0 # iec p noprint Both of the following commands enable messages for the system: # iec s 1 # iec s reset The following command enables the printing of a message for each emulated instruction: # iec p verbose SEE ALSO
getsysinfo(2), setsysinfo(2) iec(1)