05/05/86 Linkage Errors

Linkage errors occur when the Multics dynamic linker is unable to
find an external reference.  Usually the system error handler
prints a message indicating what was wrong; this help file
explains some of the possible problems in more detail.


Segment not found:
    One of the most common messages is "Segment not found.".  This
usually happens because the target segment doesn't exist, or the
name was misspelled, or there is insufficient access.  If none of
these reasons apply, the user should check the search rules (using
the print_search_rules command).


External symbol not found:
    Another common message is "External symbol not found.".  This
means that the linker found the segment but could not find the
specified entry point or externally referenceable data.  This
could be due to misspelling or to an error or omission in the
target segment.  In particular, if the segment is bound, the
bindfile should be checked, since not all the entry points in the
component segments are necessarily retained after binding.


Linkage section not found:
    The message "Linkage section not found." usually means that
the target found is not an object segment and hence has no entry
points or externally referenceable data.  Such segments can be
referenced only by names ending in "$".


Variable or common too big:
    The message "External variable or common block is not the same
size as other uses of the same name." means that the latest
reference to a common block or external variable (one to be
created by the linker) specified a larger size than that already
allocated.  Type "help external_storage.gi" for more information
about this case.


Duplicate entry name:
    The message "Duplicate entry name in bound segment." means
that there is more than one entry point with the same name and the
linker cannot resolve the reference.  This happens with bound
segments when the segment name used does not specify which
component is meant and several components have entry points with
the same name.  Either the reference should be made more precise
or the target segment should be rebound with the bindfile changed
to include the referenced name as a synonym on the desired
component.


No room for allocations:
    The message "There is no room to make requested allocations."
means that the size associated with a common block of external
variable to be created is too large; in this case, the program
must be changed.


Allocation not performed:
    The message "Allocation could not be performed." occurring
when attempting to allocate space for an external variable, means
that the area used by the linker has been clobbered.  If the
process doesn't terminate first, try telling the linker to use a
different area by using the set_user_storage command, giving it
the name of another area.  The create_area command can be used to
create the area, which should be extensible.


Illegal link info:
    Sometimes the program making the reference has been clobbered;
usually recompilation cures the problem.  The messages associated
with this case are:
 "Illegal type code in type pair block."
 "Illegal self reference type."


Bad definitions:
    The messages "Looping searching definitions." and "Bad class
code in definitions." usually mean that target has been clobbered
and should be recompiled.
    The message "Bad definitions pointer in linkage." means that
the copy of the referencing segment's linkage section, which
contains the actual snapped links, etc., has been clobbered.
Terminating the referencing segment and starting over may work,
although it is likely that enough damage has been done that a
new_proc may be necessary.


Bad fault tag 2 location:
    Occasionally the linker is invoked because the processor
encounters the link fault bit pattern at a location other than an
unsnapped link.  When the linker detects this, it returns one of
the following messages:
  "Attempt to execute instruction containing a fault tag 2."
  "Attempt to indirect through word pair containing a fault
   tag 2 in the odd word."


Malformed list template entry:
    The message "A compiler has generated incorrect list template
initialization ..." implies that the initialization information
for an external variable has been damaged in some manner.  The
routines containing the erroneous structure should be recompiled.


Invalid Pointer Target:
    The message "Unable to initialize a pointer used as the
initial of an external variable." implies that the target of a
pointer initialization can not be initialized.  This can be caused
by an error occurring in the initialization structure or by the
segment containing the initialization information being damaged.
This can also be caused by not being able to find the target
specified by the initialziation information.
    The latter case is most likely to happen with references to
external variables that are not defined within the (possibly
multi-segment) object.  The user should check all such references
and the links generated by the compiler and either correct the
reference or make sure that the link target is accessible.  If no
such error is found, the program should be recompiled.


   The problem may actually have occurred in a different variable
from the one associated with the message.  If an external variable
references another external variable, the initialization of the
second may be completed before the initialization of the first,
with any errors being reported with the first.


Segment Unknown:
    The message "Segment not known to process." implies that the
execution environment has been damaged.  The user should initiate
the segments required for their execution or perform a new_proc.


Inconsistent object MSF:
    The message "Object MSF is inconsistent" states that a
component of an Object MSF has been damamged. The segment in
question should be recreated.


First reference trap:
    The message "A first reference trap was found..." specifies
that the first reference traps for the executing segment have not
been executed. The segment should be terminated and then initiated
again with a -fc.


Resolve linkage error:
    There is a command which can often be used to snap a link to
an arbitrary target; type "resolve_linkage_error new_target_name;
start" to continue with the desired reference.  This is most
useful for misspelling cases or when the search rules weren't
adequate.  It does not work for common blocks or external
variables to be created.


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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