02/06/84  prepare_mc_restart_

The prepare_mc_restart_ subroutine checks machine conditions for
restartability, and makes modifications to the machine conditions (to
accomplish user modifications to process execution) before a condition
handler returns.

The prepare_mc_restart_ subroutine should be called by a condition
handler, which was invoked as a result of a hardware-detected
condition, if the handler wishes the process to:

1.  retry the faulting instruction.
2.  skip the faulting instruction and continue.
3.  execute some other instruction instead of the faulting instruction
    and continue.
4.  resume execution at some other location in the same program.


When a condition handler is invoked for a hardware-detected condition,
it is passed a pointer to the machine-conditions data at the time of
the fault.  If the handler returns, the system attempts to restore
these machine conditions and restart the process at the point of
interruption encoded in the machine-conditions data.  After certain
conditions, however, the hardware is unable to restart the processor.
In other cases, an attempt to restart always causes the same condition
to occur again, because the system software has already exhausted all
available recovery possibilities (e.g., disk read errors).


Entry points in prepare_mc_restart_:
   (List is generated by the help command)


:Entry:  replace:  02/06/84 prepare_mc_restart_$replace


Function: modifies machine-conditions data so that the process
executes a specified machine instruction, instead of the faulting
instruction, and then continues normally.


Syntax:
declare prepare_mc_restart_$replace entry (ptr, bit(36),
     fixed bin(35));
call prepare_mc_restart_$replace (mc_ptr, new_ins, code);


Arguments:
mc_ptr
   is a pointer to the machine conditions.  (Input)  The format of
   the machine conditions is described in the Programmer's Reference
   Manual.
new_ins
   is the desired substitute machine instruction.  (Input)


code
   is a standard status code.  If it is nonzero on return, the machine
   conditions cannot be restarted.  (Output)  The following codes can
   be returned:
   error_table_$badarg
      an invalid mc_ptr was provided.
   error_table_$no_restart
      the machine conditions cannot be restarted.
   error_table_$bad_ptr
      the restart location is not accessible.
   error_table_$useless_restart
      the same error will occur again if restart is attempted.


:Entry:  retry:  02/06/84 prepare_mc_restart_$retry


Function: prepares the machine conditions for retry at the point of
the hardware-detected condition.  For example, this operation is
appropriate for a linkage error signal, resulting from the absence of
a segment, that the condition handler has been able to locate.


Syntax:
declare prepare_mc_restart_$retry entry (ptr, fixed bin(35));
call prepare_mc_restart_$retry (mc_ptr, code);


Arguments:
mc_ptr
   is a pointer to the machine conditions.  (Input)  The format of
   the machine conditions is described in the Programmer's Reference
   Manual.


code
   is a standard status code.  If it is nonzero on return, the machine
   conditions cannot be restarted.  (Output)  The following codes can
   be returned:
   error_table_$badarg
      an invalid mc_ptr was provided.
   error_table_$no_restart
      the machine conditions cannot be restarted.
   error_table_$bad_ptr
      the restart location is not accessible.
   error_table_$useless_restart
      the same error will occur again if restart is attempted.


:Entry:  tra:  02/06/84 prepare_mc_restart_$tra


Function: modifies machine conditions data so that the process resumes
execution, taking its next instruction from a specified location.  The
instruction transferred to must be in the same segment that caused the
fault.


Syntax:
declare prepare_mc_restart_$tra entry (ptr, ptr, fixed bin(35));
call prepare_mc_restart_$tra (mc_ptr, newp, code);


Arguments:
mc_ptr
   is a pointer to the machine conditions.  (Input)  The format of
   the machine conditions is described in the Programmer's Reference
   Manual.
newp
   is used in replacing the instruction counter in the machine
   conditions.  (Input)


code
   is a standard status code.  If it is nonzero on return, the machine
   conditions cannot be restarted.  (Output)  The following codes can
   be returned:
   error_table_$badarg
      an invalid mc_ptr was provided.
   error_table_$no_restart
      the machine conditions cannot be restarted.
   error_table_$bad_ptr
      the restart location is not accessible.
   error_table_$useless_restart
      the same error will occur again if restart is attempted.


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Historical Background

This edition of the Multics software materials and documentation is provided and donated
to Massachusetts Institute of Technology by Group BULL including BULL HN Information Systems Inc. 
as a contribution to computer science knowledge.  
This donation is made also to give evidence of the common contributions of Massachusetts Institute of Technology,
Bell Laboratories, General Electric, Honeywell Information Systems Inc., Honeywell BULL Inc., Groupe BULL
and BULL HN Information Systems Inc. to the development of this operating system. 
Multics development was initiated by Massachusetts Institute of Technology Project MAC (1963-1970),
renamed the MIT Laboratory for Computer Science and Artificial Intelligence in the mid 1970s, under the leadership
of Professor Fernando Jose Corbato. Users consider that Multics provided the best software architecture 
for managing computer hardware properly and for executing programs. Many subsequent operating systems 
incorporated Multics principles.
Multics was distributed in 1975 to 2000 by Group Bull in Europe , and in the U.S. by Bull HN Information Systems Inc., 
as successor in interest by change in name only to Honeywell Bull Inc. and Honeywell Information Systems Inc. .

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Permission to use, copy, modify, and distribute these programs and their documentation for any purpose and without
fee is hereby granted,provided that the below copyright notice and historical background appear in all copies
and that both the copyright notice and historical background and this permission notice appear in supporting
documentation, and that the names of MIT, HIS, BULL or BULL HN not be used in advertising or publicity pertaining
to distribution of the programs without specific prior written permission.
    Copyright 1972 by Massachusetts Institute of Technology and Honeywell Information Systems Inc.
    Copyright 2006 by BULL HN Information Systems Inc.
    Copyright 2006 by Bull SAS
    All Rights Reserved