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LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)
August 1979




LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)           Page 2


LINK is the linking loader  for  the  DECsystem-10  and  DECSYSTEM-20.
LINK  version  4A  is  a maintenance release designed to get bug fixes
made since the last release of LINK distributed to  the  field.   Very
few new features are present, but LINK 4A should be significantly more
reliable than LINK 4 when loading user programs.

LINK 4A supercedes all previous versions.  It runs under all supported
monitors,  and  has been tested under TOPS-10 6.03A an 7.00, and under
TOPS-20 releases 3A and 4.  All patches  published  through  21-Aug-79
have been incorporated into LINK 4A.

LINK is documented in the  LINK  Reference  Manual.   This  manual  is
available  to  DECsystem-10  sites as part of volume 11 of the TOPS-10
Software  Notebooks,  or  separately  as  order  number   AA-0988C-TB.
DECSYSTEM-20  sites  can  find  this manual in volume 4 of the TOPS-20
Software Notebooks, or it can be ordered separately  as  order  number
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)           Page 3


2.1  Changes To LINK

The following sections contain summaries  of  all  externally  visible
changes  that  have  been made to LINK since version 4(765).  Refer to
the file LINK.PCO for more information on specific edits.

2.1.1  EXE File Generation By Default - Previous  versions   of   LINK
loaded  certain  types of programs incorrectly if the user did not ask
for an EXE file with /SAVE.  For example, programs containing embedded
nonexistent pages due to gaps between psect were loaded with the pages
existent, and programs with very low high segment origins did not load
at  all.  These problems were all due to LINK's inability to exit with
the user program set up in memory correctly, and  they  could  all  be
bypassed by typing /SAVE to LINK.

LINK version 4A will automatically generate an EXE file when  programs
of  this  class  are detected.  As part of this change, the old LNKNCL
and LNKNCX messages have been deleted, and LINK will now issue the new
LNKPCL  or LNKPCX messages whenever it decides to generate an EXE file
on its own.  For more information, see the PCL and PCX messages in the
file LNKMSG.MAN.  This was edit 1146 to LINK, PCO 10-LINK-264.

2.1.2  The .HIGH. Psect - Declaring a psect with the name  .HIGH.  is
now  equivalent  to declaring a high segment via REL block type 3 (the
MACRO  HISEG  or  TWOSEG  pseudo-ops).   This  provides  a  convenient
mechanism  for  mixing  psect  and high segment code in the same MACRO
source file, since you can now put the  high  segment  code  into  the
.HIGH. psect.  This was edit 1155 to LINK, PCO 10-LINK-271.

2.1.3  Loading Large Programs - LINK  now  catches  attempts  to  load
programs that extend beyond location 777777, and issues the new LNKPTL
message.  Previous versions of LINK got  various  internal  errors  if
this occurred.  This was edit 1204 to LINK, PCO 10-LINK-293.

2.1.4  Searching FORLIB - LINK  will  now  search  SYS:FORLIB.REL   in
/SEGMENT:LOW  mode when loading FORTRAN program, unless the program is
being loaded in /OTS:NONSHAR mode.  This allows subroutines in  FORLIB
to  be  written with two segments without forcing FOROTS to be read in
at load time.  This was edit 1200 to LINK, PCO 10-LINK-289.
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)           Page 4

2.1.5  Symbol Table Differences - LINK   4A   generates   a   slightly
different  runtime  DDT  symbol table than its predecessors, which may
lead to differences detected by FILCOM if old and new EXE files loaded
with symbols are compared.  The differences are as follows:

     1.  The module length of the module PAT.. is now set up just like
         all  other  modules.   This  will show up as the left half of
         some word in the symbol table changing from zero to 777774.

     2.  Psect names are no longer put into the runtime  symbol  table
         as  empty  modules.   This will make the runtime symbol table
         generated by LINK 4A somewhat smaller than that generated  by
         previous versions of LINK for programs that use psects, since
         the word pairs that  represented  the  psect  names  will  be

This was edit 1127 to LINK, PCO 10-LINK-250.

2.1.6  High Segment Code In Overlays - LINK 4A does not allow any high
segment  code  when  loading into an overlay.  If it sees any, it will
issue the new LNKHCL message.  Previous versions of LINK allowed  this
without  complaint,  but  then proceeded to generate a non-working EXE
file.  This is a common error, since it is what  happens  if  a  COBOL
program  compiled  with  /R  is loaded into an overlay.  This was edit
1115 to LINK, PCO 20-LINK-9.

2.1.7  /OTS:NONSHAR By Default - In addition to the reasons listed  on
page  D-39  of the LINK manual, LINK version 4 assumed /OTS:NONSHAR if
the low segment exceeded 256P in  size  at  the  time  system  library
searching  started,  since  the  OTS  cannot  be  read in at 400000 at
runtime if the low segment extends beyond that address.  With LINK 4A,
this  check  has  been extended so that /OTS:NONSHAR is assumed if the
low segment extends beyond 330000.  This allows for the low segment to
grow  somewhat as a result of system library searching without causing
high segment overlap.

The principle result of this edit is that some large user programs may
now be loaded with the appropriate OTS built in, even though they were
built to bring in the OTS at runtime with previous versions  of  LINK.
If this is objectionable and the program's low segment does not extend
beyond 400000, the /OTS:SHARE switch  can  be  used  to  override  the
default action.  This was edit 1131 to LINK, PCO 10-LINK-252.
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)           Page 5

2.1.8  /NOINCLUDE, Changes To /INCLUDE - There  is   a   new   switch,
/NOINCLUDE.   This  switch  turns  off  include mode set by a previous
/INCLUDE switch seen in a global context.  Unlike  /INCLUDE,  the  new
/NOINCLUDE switch takes no arguments.

The /INCLUDE switch has also been changed to always set  include  mode
for  the  rest  of the line when it is seen in a global context.  This
change restores the behavior of /INCLUDE from  LINK  3A  and  earlier.
The switch was changed in LINK 4 to only set include mode for the rest
of the line if it was seen in a global context, and had no  arguments.
This was edit 1117 to LINK, PCO 10-LINK-242.

2.1.9  CPU Type Conflict Checking - The routines in LINK that  process
modules  built  for a certain type of CPU (with /KA or /KI to FORTRAN,
or .DIRECTIVE KA10, KI10, or KL10 to MACRO) have been  generalized  to
understand  the  KL10  declaration, and to allow for future CPU types.
As part of this change, the LNKKIA message  as  been  changed  to  the
LNKCCD  message, and the CPU types that the loaded program will run on
are now printed  in  the  map.   This  was  edit  1120  to  LINK,  PCO

2.1.10  Change To /UPTO - The /UPTO: switch will  now  take  a  global
symbol  as  an  argument.  The symbol does not need to be defined when
the switch is typed, but must be defined by the end of the  load.   If
it  is  not,  LINK  will  issue  the new LNKUUA message and ignore the
switch.  This was edit 1175 to LINK, PCO 10-LINK-286.

2.1.11  Size Of Overlay Files - Due to a bug,  LINK  version  4  wrote
overlay files that were considerably larger than those written by LINK
3A.  This bug has now been fixed, so overlay files written by LINK  4A
are  comparable  in  size  to those written by LINK 3A.  This was edit
1205 to LINK, PCO 10-LINK-294.

2.1.12  Generated Module Name - If any symbols are  defined  before  a
module  has  been loaded, LINK 4A will start a module of the same name
as the symbol.  Previous versions of LINK just dumped  the  symbol  to
the  map  and runtime symbol table with no preceeding module name.  If
some module has already been loaded, LINK 4A will continue  to  append
the  symbol  to  the  last module loaded, just as previous versions of
LINK did.  This mainly affects symbols defined  with  switches  (/SET,
/DEFINE),  and can only happen if /NOINITIAL is used, since the module
JOBDAT is normally loaded by default.  This was edit 1143 to LINK, PCO
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)           Page 6

2.1.13  Change To REL Block Type 24 - With LINK 4A, REL block type  24
just  declares a new psect.  Under previous versions of LINK, this REL
block also took the  actions  of  REL  block  type  22,  so  that  any
following  low  segment code went in to the psect just declared.  This
was edit 1137 to LINK, PCO 10-LINK-259.

2.1.14  .JBEDV - LINK 4A contains a new JOBDAT symbol, .JBEDV.   This
symbol  will be used in future releases of TOPS-10 and TOPS-20 in exec
mode only for communication with  EDDT  and  other  indepenently-built
exec routines.  This was edit 1151 to LINK, PCO 10-LINK-267.

2.1.15  /SAVE/EXECUTE On TOPS-20 - LINK 4A no longer leaves PA1050  in
memory on /SAVE/EXECUTE.  PA1050 is still left in on /EXECUTE (this is
a known problem).  As part of  this  edit,  several  of  the  messages
generated  during  the  final  phase of LINK have been cleaned up, and
long forms of the messages have been added.  This  was  edit  1144  to

2.1.16  Global Definitions Of Psect Names - For  each  psect   loaded,
LINK will automatically generate a global symbol with the same name as
the psect name, and with the psect origin as its value.  With LINK 4A,
the  psect  name will now be suppressed to DDT typeout.  This was edit
1157 to LINK, PCO 10-LINK-273.

2.1.17  Symbol Names As Switch Arguments - LINK now  requires  symbols
typed as arguments to those switches that accept symbol names to begin
with a letter or special character.  Previous versions of LINK allowed
the  first  character  to be a digit.  This was edit 1167 to LINK, PCO

2.1.18  Error Message Changes - Several  of   LINK's   messages   have
changed  as  the result of an error message cleanup project.  The most
noticeable difference is that most of LINK's errors will now print the
module and file being processed when the error occurred, but there are
many other minor changes.  Most of LINK's messages  were  affected  by
this edit in some way.
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)           Page 7

The file LNKMSG.MAN contains an updated version of the  error  message
portion of the LINK manual (Appendix B).  We recommend using this file
instead of the LINK version  4  manual  for  documentation  on  LINK's
messages,  since  so  many  of  them  have  changed  since  LINK 4 was

The error message cleanup was edit 1174 to LINK, PCO 10-LINK-285.

2.2  Changes To The Overlay Handler

The following sections contain summaries  of  all  externally  visible
changes  that  have  been made to OVRLAY (the runtime overlay handler)
since  version  4(37).   Refer  to  the  file  OVRLAY.PCO   for   more
information on specific edits.

2.2.1  Changes To RUNOVL And REMOVL - The   manual   call   subroutine
REMOVL  has  been  changed  to only accept one argument:  the name (or
number) of the top link to be removed.  OVRLAY will remove  this  link
and all of its inferiors from memory.  REMOVL has also been changed to
not allow the caller to remove itself, a check  which  was  documented
but not implemented.

The manual call subroutine RUNOVL has been changed to allow the caller
to  be  overlaid.   The  documentation stated that this was legal, but
OVRLAY did not permit it.

These changes were edit 43 to OVRLAY, PCO 20-OVRLAY-5.

2.2.2  JSYS Names Changed - The JSYS names used in the TOPS-20 version
of  OVRLAY  have  been  changed  to be the new name% form that will be
present in release 4 of TOPS-20.  This change was  made  because  JSYS
names  are  global symbols, and the TIME and SIN JSYSes in the overlay
handler were conflicting with FORLIB subroutines  of  the  same  name.
This was edit 41 to OVRLAY, PCO 20-OVRLAY-3.

2.2.3  Symbol Table Pointer Update - The TOPS-20 version of OVRLAY has
been  changed  to keep DDT's symbol table pointer (@770001) up to date
whenever it brings in or removes a link and the  corresponding  symbol
table.   Before  this  change was made, bringing in a link would cause
DDT to lose some or all of the program's symbol table.  This was  edit
40 to OVRLAY, PCO 20-OVRLAY-2.
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)           Page 8

2.2.4  Overlay Files In SFDs - The  TOPS-10  version  of  the  overlay
handler  will  now  attempt  to  obtain  the path in which to find the
overlay file by issuing GETTAB UUOs, which can return the entire path,
including  SFDs.   If  the necessary GETTABs are not implemented, LINK
will continue to use the path information  left  in  the  ACs  by  the
monitor.  This was edit 46 to OVRLAY, PCO 10-OVRLAY-20.
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)           Page 9


The following list  includes  all  known  problems  with  LINK  as  of
31-Jul-79.   The  list is divided into two parts.  The first is a list
of those bugs for which a solution is not currently known.  These will
be  fixed  roughly  in  order  of  their  importance,  and the patches
published in the appropriate Software Dispatch.  The second part is  a
list  of  those  problems for which there are no current plans to fix.
These are restrictions in the product.

3.1  Problems To Be Fixed In The Near Future

     1.  When LINK cannot find an input file, it does not always clear
         typeahead  before asking the user to provide the correct file

     2.  LINK will leave  PA1050  in  memory  on  TOPS-20  if  program
         execution  is  requested.   This  happens  on  the  @DEBUG or
         @EXECUTE commands, or on /EXECUTE to LINK.

     3.  Loading TOPS-10 DDT.REL version 40(220) specifying /ONLY:HIGH
         results  in  an illegal memory reference.  This is indicative
         of several problems with /ONLY.

     4.  Erroneous LNKUGS messages sometimes result when using /ONLY.

     5.  /BACKSPACE does not skip over the file mark after backspacing
         a magtape.  This leaves the tape incorrectly positioned.

     6.  The LNKIMM message does not increment .JBERR, nor does it use
         LINK's  internal  message  facility.  Thus, it cannot cause a
         load to fail if some included modules were  missing,  nor  be
         controlled by the usual LINK message switches.

     7.  The LNKDNS  message  has  various  problems.   The  offending
         switch  is  not ignored if the message is fatal, nor does the
         message get printed when it should.

     8.  The handling of /DDEBUG:(MACRO,FORTRAN) is inconsistent.

     9.  The /NOENTRY: switch assumes that the symbol specified is not
         an  inter-link  entry  point.  If another link does reference
         this symbol then  the  program  being  loaded  will  fail  at

    10.  /USERLIB:(x,y,z) does not work.

    11.  TTY:/MAP:NOW when loading an overlaid program does not work.

    12.  /CPU:x is ignored.  Also, it only takes a single CPU type  as
         its argument when it should take a set of allowed CPU types.
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)          Page 10

    13.  The T.1 routine (and many others) uses  P2  incorrectly.   It
         should  be the last location desired, but is sometimes set up
         as the first free instead.   Common  side  effects  are  that
         location  777777  cannot always be loaded, or that LINK reads
         in too many pages from its overflow files.

    14.  LINK has some problems putting the .EXE file  in  the  proper
         place.   If an ersatz device was specified to /SAVE, and LINK
         must overflow the HC area to disk, then the .EXE file may end
         up  on the wrong path.  Also, if /EXECUTE was specified, then
         LINK looks only on  the  user's  default  path  or  connected
         directory, in spite of any contrary specification to /SAVE.

    15.  The LNKLNS message does not print a carriage-return line-feed
         at the end of the line.

    16.  LINK does not accept commands on the monitor command line, as

              .R LINK (commands) or @LINK commands

    17.  /LINK when specified in a global context has problems.

    18.  /SET specified without an  argument  results  in  the  LNKISN

    19.  The /NOREQUESTS: switch does not accept the complete radix-50
         character set.

    20.  The /SEVERITY: switch takes an  octal  argument,  but  should
         take a decimal one to be consistent with /ERRORLEVEL: and the
         LINK manual.

    21.  Defining a common block with the  name  of  .COMM.  does  not
         result in a definition of blank common.

    22.  On TOPS-20, overlay plots are generally 2.54 times too large.
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)          Page 11

3.2  Problems For Which No Solution Is Currently Planned.

     1.  If code or  data  that  contains  fixups  (external,  Polish,
         inter-psect  references,  etc.)  is overwritten at load time,
         LINK can get an illegal memory reference or go into  a  loop.
         This  can  happen  if  psects  overlap,  or  if  LOC or RELOC
         statements are used incorrectly in a MACRO program.  This  is
         a restriction.

     2.  Generation of  a  symbol  file  via  /SYFILE:  requires  that
         symbols be loaded with the program.  This is a restriction.

     3.  LINK does not read SWITCH.INI on a LOAD-class command.   This
         is a SCAN restriction.

     4.  On TOPS-20, logical names pointing  to  files  do  not  work.
         This is a restriction.
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)          Page 12


4.1  TOPS-10

To install LINK version 4A on your system, copy  the  files  LINK.EXE,
LNK???.EXE,  and  OVRLAY.REL  from  the distribution tape to SYS:, and
then copy the file LINK.HLP from the distribution tape to HLP:.   Note
that all of LINK's EXE files must be on the same disk structure.

The batch control file LINK.CTL contains all necessary instructions to
assemble  and load LINK, and to produce listings and storage maps.  It
will normally have to  be  modified  slightly  to  correspond  to  the
installation configuration.

4.2  TOPS-20

To install LINK version 4 on your system, copy the files LINK.EXE  and
OVRLAY.REL  from the distribution tape to SYS:, and then copy the file
LINK.HLP from the distribution tape to HLP:.   This  can  be  done  by
mounting the tape labelled Distribution Tape on MTA0:, then typing the
following commands:

     TAPE MTA0:
     DENSITY 1600-BPI
     SKIP 2
     RESTORE DSK*:<*>LINK.EXE (TO) SYS:*.*.-1, -
     DSK*:<*>OVRLAY.REL (TO) SYS:*.*.-1, -
     DSK*:<*>LINK.HLP (TO) HLP:*.*.-1

To rebuild LINK from sources, mount  the  tape  labelled  Distribution
Tape on MTA0:, then type the following commands:

     TAPE MTA0:
     DENSITY 1600-BPI
     SKIP 3
     RESTORE DSK*:<*>*.*.* (TO) <self>*.*.*
     !At this point, you should TYPE LINK.CTL to see what it does.

The batch control file LINK.CTL contains the procedures  necessary  to
rebuild  LINK  and  OVRLAY  from  sources.  It may have to be modified
slightly to run at your installation, so you should  type  it  to  see
what it does before typing the SUBMIT command above.
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)          Page 13


5.1  Changes To LINK

All  changes  made  to  LINK  4(765)  to  produce  LINK  4A(1220)  are
summarized  below.   Refer  to  the  file  LINK.PCO  for more detailed
information on specific edits.

766      MCHC    17-MAR-78
         Store correct KL code(offset calculated by JFFO) for inconsistancy
         check of modules to come.

767      MCHC    17-MAR-78
         Clear AC P2(required size) when coing forced dump of LC area,
         which returns through LNKCOR and will cause looping if
         garbage is in it.

770      MCHC    17-MAR-78
         Add code to allow paging for the first time in routine to
         output undefined symbols(especially if undefined symbol table
         does not begin at end of a chunk of code.)

771      MCHC    23-MAR-78
         Fix bug in doing large( > 400000) pop loop in 2 chunks.

772      MCHC    23-MAR-78
         Edit 770 did not adjust start of symbol table that came after
         the undefined symbol table.
         If /SET:FOO:nnnnnn/SYMSEG:PSECT:FOO is used so that a psect
         was created just for the symbol table, the following should
                 .JBUSY (117)/   -U,,PAT..+100 
                                 where U is the length of undefined symbol table
                 .JBSYM (116)/   -L,,PAR..+100+U
                                 where L is the length of the symbol table

773      JNG     30-Apr-78
         Fix GSDLT in LNKXIT to not leave some area's UB
         pointing beyond .JBREL if the GS area is already gone.
         Routines: LNKXIT

774      JNG     30-Apr-78       SPR 10-25711
         Fix bad calculation of UW in EXE file writer.
         Routines: LNKXIT

775      DZN     1-May-78        SPR 20-11396
         Make sure /DEBUG:FORTRAN loads the starting address of
         FORDDT and not the user's program (unless explicit /START).
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)          Page 14

         Routines: LNKWLD

776      DZN     4-May-78        SPR 10-23733
         Fix address check and lost .JBVER when loading small programs
         with /SAVE and no data in core-image pages 0 or 1.
         Routines: LNKXIT

777      DZN     18-May-78       SPR 10-24008
         Fix allocation of COMMON blocks when a COMMON block is first
         referenced but not defined, then later defined. Also document
         SY.RF as destroying P1-P4.
         Routines: LNKOLD, LNKLOD

1000 to 1077     Reserved for Development.

1100     DZN     23-May-78       SPR 10-24042
         Fix LNKMAP to correctly free the index blocks it uses for sorting,
         to keep the integrity of the DY area.
         Routines: LNKMAP

1101     JNG     29-May-78       SPR 10-23623
         Fix LINK to correctly load indexed libraries that contain modules
         which have no entry points and thus do not appear in the index
         when indexed with MAKLIB.

1102     DZN     18-Jun-78       SPR 20-11085
         Fix paging routines to detect moving a window past 512P. In this
         case, make the end of the window set right at 512P.
         Routines: LNKLOD

1103     DZN     19-Jun-78
         See that the list of .REQUEST/.REQUIRE blocks is not freed twice,
         to preserve the integrety of the DY area.
         Routines: LNKLOD

1104     JNG     20-Jun-78
         Fix address checks when dumping LC or HC area to disk.  Remove
         edit 750 in LH.DMP, so we will never try to shrink the current
         area by more pages than the area has.
         Routines: LNKCOR

1105     JNG     20-Jun-78
         Fix edit 740 to not destroy an AC that held the input file's PPN.
         This caused LINK to not be able to find a file when the user gave
         an explicit path including SFDs.
         Routines: LNKFIO

1106     JNG     27-Jun-78       QAR RDH
         Update HL.S1 from RC.CV of the highest PSECT loaded at the end of
         loading.  This causes the EXE file generator to allocate all of
         the pages that it should if the last PSECT ends with a BLOCK statement.
         Routines: LNKLOD
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)          Page 15

1107     MCHC    3-Aug-78
         Fix bug in .SETEX--routine to expand RC.TB and RC.NTB tables
         in DY area by obtaining bigger spaces, copying the data from
         the old tables, and freeing the old table spaces.
         The bug was in address calculation in freeing one of the tables.
         The code is re-arranged to do a DY.GET followed by DY.RET
         then another DY.GET and DY.RET

1110     MCHC    7-Aug-78
         Type out the PSECT name as part of the error message when a
         non-existent one is used with /SYMSEG in GETSST routine.
         Don't clear the name from memory cell, loop back without restoring the
         stack and treat this case as a default case.

1111     MCHC    7-Aug-78
         Fix LNKXIT core management bug introduced by edit 772.

1112     JNG     15-Aug-78       SPR 10-25902
         Fix one off bugs in map printing segment lengths in K/P and
         words free.
         Routines: LNKPAR, LNKMAP

1113     DZN     25-Aug-78       SPR 20-12001
         Fix memory management problems when plotting the overlay
         tree. See that LINK never shrinks back on TOPS-20 until final
         placement of the loaded program. Add LNKPOT message to tell user
         when LINK is plotting the overlay tree.

1114     DZN     1-Sep-78        SPR 20-11999
         Zero count of COBOL symbol words and ALGOL OWNs loaded when
         done loading a module, so they don't get counted in subsequent
         modules in the same file.
         Routines: LNKOLD, LNKLOD

1115     DZN     2-Sep-78        SPR 20-11997
         Add LNKHCL message to complain when loading high segment code
         into a link other than the root in an overlaid program.
         Routines: LNKERR, LNKOLD

1116     JNG     7-Sep-78
         Put back part of the code removed by edit 716.  Performance
         improvements are only kosher as long as the code removed is
         Routines: LNKLOD

1117     DZN     14-Sep-78
         Make /INCLUDE:args also set include mode, as it did long ago.
         But also add /NOINCLUDE to turn off include mode but not
         delete the original args.
         Routines: LNKPAR, LNKWLD
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)          Page 16

1120     DZN     22-Sep-78       SPR 10-26135
         Fix CPU mismatch checks so that they work. Remove edit 766,
         revamp all CPU check code to use a bit mask of valid CPUs,
         delete the LNKKIA message and add LNKCCD, and change the
         map to include the correct information. Also, make the map
         show which CPUs the entire program can be run on.

1121     JNG     4-Oct-78        QAR JMF
         Fix LNKXIT bug so .JBSYM ptr won't include the undefined symbol
         table.  This was broken by edit 772.
         Routines: LNKXIT

1122     DZN     5-Oct-78        SPR 10-26222
         Remove edit 740, which attempted to use SCAN's /VERSION switch,
         rather than LINK's. SCAN's switch is a file-specific switch, which
         is not the way LINK wants it to work. However, still fix the original
         problem (having to type /VERSION to 6 characters to work) by making
         LINK's /VERSION switch unique to any abbreviation.

1123     DZN     10-Oct-78       SPR 10-26580
         Use HRLI instead of HRL to load ENTER error flag.
         Routines: LNKFIO

1124     DZN     11-Oct-78       SPR 10-26712
         Edit 636 broke LINK's ability to be run execute-only. Fix
         this by making the TTY log routine once more return into the
         potentially execute-only high segment properly.
         Routine: LNKINI

1125     JNG     1-Nov-78        SPR 10-26379
         Don't try to run the high segment file on /SAVE/RUN (or /SAVE/DEBUG)
         when generating an EXE file.  This fixes ?nnnLHC.EXE not found when
         the user types the above switches and the HC area has overflowed.
         Routines: LNKXIT

1126     JNG     1-Nov-78        SPR 10-26433
         If all 7.01 GETTABs to determine where we came from are not available,
         use the contents of the ACs to do GETSEG UUOs.
         Routines: LNKINI

1127     JNG     14-Nov-78       QAR DIB
         Set up the module length for PAT.. in the runtime symbol table.
         Routine: LNKXIT

1130     DZN     26-Jan-79       SPR 10-27212
         Make LINK honor /MAXCOR correctly when a request for memory in a
         pagable area is made. In this case, edit 650 made LINK count the
         memory request toward the /MAXCOR value, even though the window
         can simply be moved.
         Routine: LNKCOR

1131     DZN     26-Jan-79       SPR 10-27123
         Make LINK decide to load a non-sharable OTS if the low segment
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)          Page 17

         has grown within 40 pages of the origin of the OTS high segment
         rather than letting the low segment grow past it first.
         Otherwise, the low segment may cross the beginning of the OTS
         during the system library search when it is too late to fix it.
         Routine: LNKLOD

1132     JNG     30-Jan-79       SPR 10-26576
         Re-work EXE file writer to fix several problems, including:
         . PSECTs above the high segment not written properly.
         . Absolute code not loaded correctly.
         . Bad EXE directory if loading overlays and small /SPACE switch.
         . PSECT attributes not written into the EXE file.
         . Page 1 written into page 0 if page 1 is lowest page containing code.
         . Address checks when writing the EXE file.
         . Bad EXE file if EXE directory is longer than two pages.
         . ?LNKCNW or bad DDT symbol table when loading PSECTs.

1133     JNG     30-Jan-79       SPR 10-26576
         Add a long message for the LNKSTL message.
         Routine: LNKERR

1134     JNG     30-Jan-79       SPR 10-27024
         Avoid address check in LNKXIT while writing EXE file if lowest
         code loaded is between 2000 and 377777, but the program being
         loaded is not so large that LINK needs to overflow to disk.
         This edit is an extract of part of edit 1132.
         Routines: LNKXIT

1135     DZN     31-Jan-79       SPR 10-26792
         Force PG.SU to expand anyway if a request crosses a page boundary
         and the window is not at least two pages long.
         Routine: LNKLOD

1136     JNG     31-Jan-79       SPR 10-26518
         Avoid IO to unassigned channel in LNKXIT while writing an EXE file
         if segment ends on last word of a page and LINK is not paging to disk.
         This edit is an extract of part of edit 1132.
         Routine: LNKXIT

1137     JNG     1-Feb-79        SPR 20-12411
         Don't change RC.CUR in T.24.  Also set default PSECT name to left-
         justified .LOW. (not right-justified) if name not given in block.
         Routine: LNKOLD

1140     JNG     6-Feb-79        SPR 10-26410
         Clear LSTSYM when a non-loaded local is encountered.
         Routine: LNKOLD

1141     JNG     15-Feb-79       SPR 10-26290
         Make the EXE file writer stop writing when it passes the size
         of the user program, instead of writing the entire LC area.
         This edit supercedes edit 1136 and is an extract of edit 1132.
         Routine: LNKXIT
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)          Page 18

1142     JNG     16-Feb-79
         Fix problems with multiple /SET:.HIGH.s introduced by edit 1132.
         Routine: LNKWLD

1143     JNG     16-Feb-79       QAR CKS
         Make sure symbols never get into the LS area before a module name.
         If they try (/NOINITIAL/SET), dummy up a module name from the symbol.
         Routine: LNKLOD

1144     DZN     16-Feb-79       SPR 20-12473
         Clean up code to run the .EXE file so that PA1050 is not left in
         memory on TOPS-20, and so that more of the final messages use .ERR.
         instead of OUTSTRs.

1145     DZN     22-Feb-79
         Load local symbols and store symbol table pointers on TOPS-20 if
         /DEBUG:DDT and leaving program in memory. Broken by edit 1144.
         Routines: LNKXIT, LNKWLD

1146     DZN     8-Mar-79        SPR 10-26290
         Change the 'Not enough core to load' message to 'Program too complex'.
         Then cause more cases to force .EXE file generation (e.g., PSECTs above
         high segment, gaps between PSECTS).
         Routines: LNKPAR, LNKXIT, LNKERR

1147     JNG     12-Mar-79
         Avoid bad EXE file if lowest location loaded is above 400000, LINK
         is overflowing to disk, and lowest location loaded was not the first
         location loaded (i.e., load was not monotonic).
         Routine: LNKXIT

1150     DZN     14-Mar-79       SPR 10-27632
         Make LOGINI in LNKINI.MAC use standard LKNFIO routines to set up the log
         file, so that the default path of a log file is preserved over the
         Routine: LNKINI

1151     JNG     29-Mar-79
         Add the new Job Data Area location .JBEDV to the initial symbols.
         Routine: LNKINI

1152     JNG     3-Apr-79
         Get EXE file right when loading overlays.  Broken by 1132.
         Routines: LNKOV1, LNKXIT

1153     JNG     12-Apr-79       QAR JBD
         Give LNKIPX message if a Define PSECT block (type 24) contains
         an invalid PSECT index.
         Routine: LNKOLD

1154     JNG     12-Apr-79       QAR JBD
         Re-write T.23 to fix the following problems:
         . Don't re-define the PSECT indices in terms of the order of block 23s.
         . Don't require a name of zero in the first block 23.
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)          Page 19

         . Don't do a set PSECT (block type 22) action on block type 23.
         . Expect PSECT index instead of name in first word (name still works).
         Routine: LNKOLD

1155     JNG     13-Apr-79       QAR JBD
         Allow PSECT .HIGH. to be synonymous with TWOSEG.
         Routines: LNKOLD, LNKWLD

1156     JNG     13-Apr-79       QAR JBD
         Relocate the breaks in block type 5 with respect to .LOW.
         every time, even if the current PSECT is not .LOW..
         Routine: LNKOLD

1157     JNG     13-Apr-79       QAR DZN
         Suppress the PSECT name global symbols to DDT typeout.
         Routine: LNKWLD

1160     JNG     14-Apr-79       QAR TW/JMF
         Don't put junk in runtime undefined symbol table for symbols
         that are used in Polish blocks.
         Routine: LNKXIT

1161     JNG     4-May-79        SPR 10-27727
         Clean up Psect printout in map.
         Routines: LNKSUB, LNKMAP.

1162     JNG     4-May-79        SPR 20-12825
         Set up DDT's symbol table pointers on /DEBUG/SAVE.  This edit is
         an extract of edit 1144.
         Routines: LNKXIT

1163     JNG     8-May-79        QAR DC
         Never mark .HIGH. as relocatable, since we default its origin.
         This was broken by edit 1155.
         Routine: LNKWLD

1164     JNG     8-May-79        SPR 10-27598
         Don't overwrite the first page of the FX area when writing a map
         if the LS area is paging and the last piece of the area exactly
         fits into the window.
         Routine: LNKMAP

1165     DZN     15-May-79       SPR 10-27925
         Zero LSTSYM whenever a call to SY.RLS says a symbol requested for symbol
         table fixup was not the last symbol loaded. This prevents  symbol  fixup
         requests from finding a long-obsolete symbol in LSTSYM that just happens
         to match.

1166     JNG     15-May-79
         Don't allow PSECT indices in Polish blocks unless the first halfword
         was the default PSECT index for the block.
         Routine: LNKOLD.

1167     JNG     17-May-79       QAR 10-3081
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)          Page 20

         Don't allow symbols typed as switch arguments to begin with digits.
         Routines: LNKSCN

1170     JNG     23-May-79       SPR 10-27945, QAR 10-3070, 10-3087
         Fix some memory management problems in LNKXIT when not writing an
         EXE file.
         Routine: LNKXIT

1171     JNG     30-May-79       QAR 10-3049
         Fix edit 1146 to say LNKPCL even on TOPS-10 if it doesn't like
         the PSECT attributes.

1172     JNG     5-Jun-79
         Fix many memory management problems when writing a runtime symbol
         table, especially when psects are involved.

1173     JNG     10-Jun-79
         Update RC.HL on /COMMON.
         Routine: LNKWLD

1174     DZN     10-Jun-79       SPRs 20-12548, 20-12244, QAR 10-03199
         Revamp all error messages.
         . Label  all messages with E$$xxx:: or Ennxxx:: so messages can be found
           when debugging. E$$xxx should be  the  label  of  the  .ERR.  (or  its
           preceeding  PUSH  P,[channel])  that  defines  the  .ERxxx text block.
           Ennxxx should be the label of all other .ERR.s with the same  assigned
           mnemonic, with nn starting at 01.
         . Include the module and file name in which an error was detected in all
           applicable messages.
         . Make  .OERR.  synonamous  with OUTSTR for use in place of .ERR. when a
           message must be printed with an OUTSTR, so that all such messages  can
           be found easily.
         . Make  the  list  of  messages  and  long text in LNKERR and the actual
           messages in LINK agree.
         . Fix log device being a terminal other than the controlling one.
         . Clean up the wording of all messages to be more consistent.
         Routines: All

1175     JNG     12-Jun-79
         Fix /START and /UPTO with symbols as arguments.
         Routines: LNKLOD, LNKWLD, LNKERR

1176     JNG     12-Jun-79
         Disallow /SYMSEG:PSECT:name with /OVERLAY.
         Routine: LNKWLD

1177     JNG     12-Jun-79
         Make /VERSION in global context not lose local switches.
         Routines: LNKPAR, LNKWLD

1200     JNG     13-Jun-79
         If loading reentrant FOROTS, search SYS:FORLIB/SEGMENT:LOW.
         This is required for FOROTS version 6 and later.
         Routine: LNKLOD
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)          Page 21

1201     JNG     13-Jun-79
         Disallow /SEGMENT:PSECT, which worked because it used the same
         keyword table as /SYMSEG.

1202     JNG     14-Jun-79
         Fix /VERSION after 1172, and make LINK assemble on TOPS-20
         after edit 1174.
         Routines: LNKPAR, LNKFIO, LNKLOG, LNKXIT.

1203     JNG     14-Jun-79
         Add support for Extended FORTRAN.

1204     JNG     14-Jun-79
         Check for programs that extend beyond location 777777, and
         issue the LNKPTL message.

1205     JNG/DZN 14-Jun-79       SPR 10-27954
         Re-claim some wasted blocks in .OVL files.
         Routine: LNKOV1

1206     JNG     14-Jun-79
         Fix a NO.COR in LNK999 that edit 1174 missed.
         Routine: LNK999

1207     JNG     29-Jun-79
         Make the LNKCMX message continue loading, so the user can run
         the program if he wants to.
         Routine: LNKLOD

1210     JNG     29-Jun-79
         Allow 1-word block type 5's, so SAIL output will load.  Also
         allow a program break of exactly 1,,0 (bypass the LNKPBI check).
         Routine: LNKOLD

1211     JNG     29-Jun-79       QAR 10-3303
         Fix typo in LNKDRC message, avoid Illegal UUO.  Broken by 1174.
         Routine: LNKWLD

1212     DZN     4-Jun-79
         Fix various typos and other loose ends in the aftermath of 1174.

1213     JNG     5-Jul-79
         Eliminate the ISD message; on multiple partial definitions, just
         ignore them if their values agree, and give the MDS message if
         they don't.

1214     DZN     9-Jul-79        QAR 10-03315
         Fix mismatched angle brackets so PIP's /V switch doesn't complain.
         Comments should not contain angle brackets unless they actually
         terminate conditionals, repeats, etc.
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)          Page 22

         Routines: LNKHST, LNKCOR, LNKOV1, LNKXIT

1215     JNG     23-Jul-79       QAR R.ACE
         Use RC.HL for .ABS. and .LOW. for LOWLOC update at CHKLLC, since
         RC.CV may not be correct.  In particular, RC.CV for .ABS. is always
         Routine: LNKLOD

1216     JNG     23-Jul-79       QAR CKS
         Preserve P1/P2 in SYMOUT, avoid illegal memory reference if
         undefined symbols exist.
         Routine: LNKXIT

1217     DZN     25-Jul-79
         Clean up the listings for release. Update all copyright notices.
         Remove all editing lines. Break pages in good places.
         Routines: All

1220     DZN     24-Aug-79
         Release on both TOPS-10 and TOPS-20 as version 4A(1220).
         Routines: All
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)          Page 23

5.2  Changes To OVRLAY

All changes  made  to  OVRLAY  4(37)  to  produce  OVRLAY  4A(50)  are
summarized  below.   Refer  to  the  file OVRLAY.PCO for more detailed
information on specific edits.

40       DZN     15-Sep-78
         On TOPS-20, if DDT exists, set its internal symbol table pointer
         whenever we change .JBSYM.

41       DZN     5-Oct-78
         Use new NAME% form of JSYS names to avoid conflicts with user-defined

42       DZN     5-Oct-78
         Change FTENEX conditional to TOPS20 to be consistent with the rest
         of LINK. Use proper mnemonics for JSYS arguments. Some code cleanup.

43       DZN     13-Oct-78
         Fix link deletion problems. Make REMOV. take only a single argument,
         and delete that link and all of its inferiors (otherwise lost links
         result). Allow RUNOV. to delete the calling link as documented. Also
         remove OVLAOC message (use OVLARC instead).

44       DZN     15-Oct-78
         Fix argument checking for calls to manual subroutines. This involves
         allowing all double and single precision argument types to work,
         making the OVLIAT message fatal and not type junk, and getting
         the correct user PC (see edit 10).

45       DZN     15-Oct-78
         Fix PDL overflow if many calls to RUNOV. RUNOV. now unbinds back
         through the return PC on the stack, allowing replacement of links
         at the same level to succeed without the PDL overflow.

46       JNG     15-Jun-79
         Try GETTABs to determine the full path that we were run from on

47       DZN     25-Jul-79
         Clean up the listing for release.

50       DZN     27-Aug-79
         Release on both TOPS-10 and TOPS-20 as version 4A(50).
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)          Page 24


The following  suggestion  list  has  been  accumulated  from  various
sources,  including  SPRs  and  DECUS  sessions.   The appearance of a
suggestion on this list does not necessarily mean  that  DIGITAL  ever
intends to implement it.

     1.  Search REL: for system libraries if they cannot be  found  on

     2.  Print  an  informational  message  when  searching  a  system
         library,  giving  the  number  of undefined symbols remaining
         when the search starts.

     3.  Implement relocatable psects.

     4.  Support long symbols.

     5.  Support a better symbol character set than RADIX-50.

     6.  Support extended addressing.

     7.  Load programs into another fork on TOPS-20.

     8.  Modify LINK  to  be  callable  as  a  subroutine  from  other

     9.  Make LINK use  the  same  message  convention  as  SCAN.   In
         particular, make LINK recognize SCAN's /MESSAGE switch.

    10.  Sort the symbols listed in LINK's map files.

    11.  Use a better free memory algorithm.  Currently, LINK  uses  a
         best-fit  method.   This is known to be inferior, potentially
         slowing LINK down.

    12.  Use virtual memory more intelligently.  In particular,  don't
         zero  memory  just allocated via CORE or PAGE. UUOs, since it
         is already zero.

    13.  Redesign the structure of the title REL block (block type  6)
         to allow easier upward compatibility of CPU types.

    14.  Print  appropriate   error   messages   if   conflicting   or
         inappropriate   psect   properties   are  detected,  such  as
         concatenate and overlay.

    15.  Implement block  type  11  code  bits  in  the  symbol  store

    16.  Make  overlaid  psects  and  common  blocks  coexist.   Other
         DIGITAL  loaders  actually  handle  common blocks as overlaid
         psects.  One advantage would be that the largest common block
         declaration would not necessarily have to be loaded first.
LINK.DOC -- Changes from LINK 4(765) to LINK 4A(1220)          Page 25

    17.  MACRO and LINK should use some facility (perhaps the proposed
         REL   block   types   1042  and  1043)  to  allow  full  file
         specifications in library requests embedded  in  .REL  files.
         Such  an  implementation  should  preferrably use text rather
         than SIXBIT fields as are now used.

    18.  Make the overlay plotter code able to  write  an  LPT  format
         file to the disk.  This would allow printing with non-default
         parameters, for instance.

    19.  Make the LNKUGS message print something more informative than
         a 0 as the value of a polish expression.

    20.  Add KS10 to the CPU specifications allowed both in MACRO  and

[End of LINK.DOC]