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[[warning: this documentation is incomplete and may be outright
misleading. The most recent changes are at the end of the
file. The first and biggest part of the file is from the
old TENEX User's Guide.]]
IDDT is a new debugger for TENEX programs. It has many
of the same commands as the standard DDT10X (SDDT and UDDT)
and ordinarily may be used without regard to the fact that
it is a different debugger. The user is directed to the DDT
section of the DECsystem-10 ASSEMBLY LANGUAGE HANDBOOK for
information regarding the basic features and use of DDT.
The primary feature of IDDT is that it operates on user
programs which run in an inferior fork under IDDT. Thus, an
errant user program cannot destroy the debugger or its
symbol table because the debugger is in a totally different
address space. This relation between the program being
debugged and IDDT is much the same as the relation between
current user programs (including IDDT) and the EXEC.
Because of this, IDDT must simulate many of the services
ordinarly provided by the EXEC, such as @GET, @LOADER, @RUN,
The following describes the new features in IDDT and
how they may be used for debugging. Some of the features
are bound to change, and others will be added.
2. Using IDDT
IDDT may be called into service either before or after
programs have been loaded into memory. This is done by
telling the EXEC
This command causes the EXEC to splice a fork
containing IDDT in between itself and the program to be
debugged. This operation is done in a way that preserves
the state of the user's program including its fork
structure. It is possible to ^C out of a running program
and get IDDT. If this is done, a $P (Proceed) command will
resume running the user program.
The EXEC command "NO IDDT" will unsplice the fork
containing IDDT in the event the user wishes to continue his
program without having an IDDT above it.
A fairly common practice is to get IDDT first and use
it to load the program to be debugged. One of three IDDT
TENEX USER'S GUIDE JANUARY 1973 Page 85
commands may be used to load the object program: $L (run the
LOADER in the user fork), ;L (Loadgo of named file), or ;Y
Yank the named file). The first of these is essentially the
same as the EXEC command, @LOADER. The second is comparable
to @RUN, while the last is similar to @GET.
3. Symbol Table Considerations
When initially started, and after successful execution
of a ;L or ;Y command, IDDT will obtain a new symbol table
if it exists. It does this by copying (and sometimes
sharing) pages of the user fork. Thus, those user programs
which need access to their own symbols will behave the same,
and IDDT will have its own copy of the symbol table which is
protected from the user.
The $L command causes IDDT to run the LOADER in the
user's address space. Upon completion, the LOADER returns
control to IDDT. At this point IDDT will have the LOADER's
symbol table. In order to switch to the symbols of the
program which was loaded, the ;S command should be typed.
;S tells IDDT to look for a standard symbol table pointer in
location 116 (.JBSYM). If the user has merged in a file
which contains its own symbols, he may switch to that table
by typing a;S where "a" is the address of the location
containing a pointer to the new table.
;O Obtains a symbol file directly into IDDT without
modifying the user's memory. The old symbol table is
replaced, and a new entry vector is taken only if there was
no old one. This makes it possible to debug one file with
symbols obtained from a different file.
Symbols may be written out on a specified file by using
the ;W command. This saves the symbols in a way that they
may be obtained later with the ;O command. Along with the
main symbol table, the undefined symbol table is saved in
symbol files. One should be careful that symbol files and
core image (;U) files are kept paired if any undefined
symbols exist. Executing an GET JSYS on a symbol file will
get both tables. The default file extension for symbol
files written by IDDT is .SYMBOLS.
Note: Symbols added to or deleted from IDDT's symbol table
by commands to IDDT will not be seen by the user program.
TENEX USER'S GUIDE JANUARY 1973 Page 86
4. EXEC-like Features
For convenience, the EXEC has several commands which
provide the same services as some EXEC commands. These are:
;A TYPES THE USER'S ADDRESS SPACE. (MEMSTAT)
;F DOES A FORKSTAT ON THE USER FORK. (THIS
FEATURE WILL BE OPERATIONAL AS SOON
AS JSYS 166 IS IMPLEMENTED.)
$$nG @START AT n-TH ENTRY VECTOR LOCATION
;U @SSAV 0 777 (I.E. "UNGET")
;O OBTAIN SYMBOL FILE -- NO EXEC EQUIVALENT
;W WRITE SYMBOL FILE -- NO EXEC EQUIVALENT
;H @QUIT (HALT, RETURN TO EXEC)
;W, ;M, ;Y, ;O, ;L, and ;U ask for a file name from the
user. The default extention will be .SAV or .SYMBOLS as
TENEX USER'S GUIDE JANUARY 1973 Page 87
5. Access Control
An EXEC-like feature has been included in IDDT which
has no analogy in the current EXEC. This is the $U command
(UNPROTECT), which allows the user to manually change the
protection on various pages of his fork. This command has
a<b$nU CHANGE PROTECTION ON PAGES a
THROUGH b INCLUSIVE
a$nU CHANGE protection of page a
$nU CHANGE PROTECTION OF THE CURRENT PAGE
(WHERE POINT "." IS)
N is always a three-bit number (0-7). The 4-bit means allow
read access, the 2-bit should be on to allow write access,
and the 1-bit for execute access. If N is not specified at
all, it will be taken as 7. Thus, the command $U frees up
the current page, giving it read, write and execute access.
$U changes the protection on pages of the user's fork.
It does not affect the protection of a file page which might
be mapped into that fork. Because it is sometimes
convenient to change the contents of fork pages which have
write-protected files mapped into them, $U commands which
ask for write access will either get it, or will get
While IDDT is running, it temporarily changes the
access of each page that it maps to have read, write, and
execute access. The user's access is reset when the page is
mapped out. This allows IDDT to insert breakpoints,
retrieve trapping instructions, etc. The $U command allows
the user to protect pages from his own program by effecting
a permanent change in the page access.
IDDT arms the RUBOUT button as an interrupt character.
If a user program has been started under IDDT, pressing
RUBOUT will gracefully suspend that process and give control
to IDDT which then types a message of the form
XXX:FOO+5/ MOVE A,DAT+21
The interrupt is understood to have occurred immediately
before this instruction, and that if a $P (proceed) command
is typed, this instruction will be the next one executed by
TENEX USER'S GUIDE JANUARY 1973 Page 88
RUBOUT's typed while in IDDT behave much the same as
they do in normal DDT's. That is, the current command is
aborted. This is particularly convenient for stopping long
searches ($W, $N and $E COMMANDS), with IDDT because it is
an interrupt and does not have to be read by a PBIN to
initiate action as it does with old-style DDT's. RUBOUT's
typed while IDDT is in control cause the terminal output
buffer to be cleared.
7. "GO" Commands
IDDT has several variations of the standard $G command
available. GO commands with two ALTMODES, such as $$G,
FOO$$G, and $$2G, cause the user's pseudo interrupt system
to be cleared before they take effect. If there is a number
between the ALTMODE(s) and the G, this number is taken as an
index into the entry vector of the user's fork, and the
program is restarted as indicated by the corresponding entry
vector element. Thus, $$0G is the same as the EXEC command
"START", while $$1G is equivalent to "REENTER". The command
$$G is an abreviation for $$0G.
Ordinary GO commands still exist. They look like FOO$G
and BEGIN$$G. The user's program counter is stored in the
"GO" register, which is named $G. This can be examined by
commands such as $G/ .
The user may wish to debug programs (such as TECO)
which assign RUBOUT as their own terminal interrupt
character. So that the user always has a way to get back to
IDDT, IDDT has an alternate RUBOUT or "ESCAPE" character.
Initially this is control-T. It may be changed by using the
;E command, which asks the user to type in a new escape
character. Almost any control character will do including
The ESCAPE character behaves exactly as RUBOUT does,
but its only real use is to cause a transition from the
user's program to IDDT. Once IDDT is running, it
temporarily acquires the RUBOUT terminal code from the user.
If the ESCAPE character is changed from ^T to something
else, the EXEC will automatically resume handling ^T
interrupts in the normal way.
TENEX USER'S GUIDE JANUARY 1973 Page 89
9. Interface with the EXEC
The EXEC command "FORK n" may be used to switch the
EXEC's attention between the fork containing IDDT and the
one containing the user's program. This may be done for the
purpose of doing a "MEMSTAT" or ^T. The EXEC examine and
deposit commands (/ and \) also pertain to the currently
Regardless of which fork has been selected, a
"CONTINUE" will always resume a ^C . If the user has
returned to the EXEC by typing ;H to IDDT, IDDT may be
resumed by a "CONTINUE". A HALTF in the user's program will
return to IDDT. It may be continued by a $P to IDDT.
10. Zero-ing core
THE $$Z COMMAND behaves the same as it does with old
DDT except that if it is used to zero whole pages, they are
PMAP-ed out of existence, rather than being actually
cleared. If such a page is brought into existence again by
a reference, it will be cleared by TENEX when created.
If a $$Z command is used to clear any word(s) between
700000 and 712777, compatibility code for the user is
dismissed. Ordinary register operations like slash can be
used to examine or modify the compatibility code (PA1050) as
The Zero command has been generalized so that it can
fill core with a specific number. To fill locations 100
through 177 with the number 3, the user would type
TENEX USER'S GUIDE JANUARY 1973 Page 90
11. Internal Registers
IDDT maintains several "internal registers" which may
be manipulated as if they were in the user's address space.
These are listed below, and will be described in detail in
$G CONTAINS FLAGS,,PC FOR THE USER PROGRAM
$M MASK FOR SEARCHES
$X LOCATION FOR SPECIAL EXECUTE
$W PAGER TRAP STATUS WORD AT MEMORY VIOLATION
$W+1 PAGER WRITE DATA AT MEMORY VIOLATION
$I INTERRUPT CHANNELS WITH BREAKS WAITING
$I+1 INTERRUPT CHANNELS ASSIGNED FOR USER
$I+2 BREAKS IN PROGRESS WORD
$I+3 0 IF USER'S INTERRUPT SYSTEM IS OFF. NON-0 OTHERWISE.
$I+4 IDDT'S FORK HANDLE ON USER
$I+5 SIXBIT OF SAVED USER SUBSYSTEM NAME
(This may be made inaccessible in the future!)
$nB+k BREAKPOINT REGISTERS. n is between 1 and 8
inclusive (i.e., IDDT has eight breakpoints), k is
between 0 and 6. Thus there are seven registers
of information associated with each of the
As an example of an internal register reference, consider
looking at the proceed count of breakpoint 3:
$3B+2/ 105 3
The user changed the proceed count from 105 to 3.
IDDT's current location may be internal to IDDT. This
allows the user to use linefeed and up-arrow to look at
internal registers. IDDT has special address printing
routines that print things like $I+3 instead of this address
TENEX USER'S GUIDE JANUARY 1973 Page 91
Attempts to define address tags when "point" is at an
IDDT internal register will be given IDDT's ubiquitous "?"
error. Also, IDDT will not allow expressions with more than
one mention of an internal symbol name. Thus, $M+3 is
allowed, but $I+$M is not.
12. The User Program PC
The internal register $G contains the user's PC and
FLAGS. This is defined to always point at the next
executable instruction. The proceed command ($P) simply
starts the user at the address in $G. Illegal instruction
traps back up the user's PC so that it points at the
offending instruction, in hopes that he will repair it and
proceed. In such a case, the repaired instruction will be
$G is setup from the entry vector after every ;Y, ;L,
and ;S command. Thus, the user can ;Y (yank) a file and
immediately start it with a $P.
Bit 5 of the "GO" word $G is the user-mode bit which
will normally be on if $G is examined. It may be off due to
an interrupt out of a JSYS or after an illegal instruction.
Because this bit is essential to the restarting of the
user's fork, it is not left entirely under his control. In
particular, the user-mode flag may be turned on by changing
the contents of $G, but it may not be turned off. This
means that if a JSYS (such as GTJFN) has been interrupted,
the usermode flag turned on, and $P typed, that the
interrupted JSYS will be re-executed, rather than resumed.
13. Saving a Core Image
The ;U command asks for a file name and then does an
SSAVE from page 0 through page 777 on this file. The entry
vector will be copied if it exists. If no entry vector has
been declared for the fork, IDDT will set a length one entry
vector at "." . A message is typed to this effect.
14. Single Instruction Executes
When the user types an instruction followed by $X, IDDT
pushes down several words of state information, plants the
instruction in the user's address space followed by three
breakpoints, and restarts the user at this special location.
When the instruction completes, IDDT types the proper number
of $-signs to indicate how many times the instruction
skipped, and pops back the saved state information. The
state information currently includes the program counter
TENEX USER'S GUIDE JANUARY 1973 Page 92
($G), and which breakpoint (if any) the user was stopped at.
This makes it possible to hit a breakpoint, execute an
instruction (which might be a PUSHJ to a subroutine), and
then, upon completion of the $X, do a $P to proceed the
IDDT's $X register points in the user's address space
to the four words which will be used for $X commands. $X
initally contains 777774 so that the top four words are
used. The user is free to change the contents of $X.
If a RUBOUT has interrupted the program being debugged
while it was in the middle of a JSYS -- usually a "long"
JSYS like SOUT or PBIN -- and then an instruction executed
with the $X command, a $P will not resume the original
sequence back in the middle of the interrupted JSYS. Flag
bit 5 will be off if the interrupt came out of a JSYS. A
proceed ($P) immediately after a RUBOUT, with no
intermediate $X will always resume exactly at the interrupt
Associated with each breakpoint are seven internal
registers. The first four of these are the same as those in
older DDT's, while the last three have been added. Taking
breakpoint three as an example:
$3B+1/ 0 OR CONDITIONAL BREAK SKIP
$3B+2/ PROCEED COUNT (>0 for normal, <0 for auto, 0 for none)
$3B+3/ 0 OR STRING POINTER (fed to IDDT when this BPT breaks)
***Not implemented yet***
$3B+4/ SAVED INSTRUCTION WHILE USER IS RUNNING
$3B+5/ 0 OR ELSE -1 FOR AUTOPROCEED MODE
$3B+6/ ASCII NAME OF THIS BREAKPOINT, USUALLY "$3B"
Usually these values are changed only by setting and
clearing breakpoints with the $B command. if he wishes, the
user may change these quantities. For instance, if he wants
hits on breakpoint three to print as
TENEX USER'S GUIDE JANUARY 1973 Page 93
he would type the following:
This stores the ASCII string for the new name in the print
name cell of breakpoint three.
Proceeding after a breakpoint hit happens much in the
same way as a single instruction execute command ($X).
Again four words of memory are written into. However, in
this case the four words are the instruction at the break
location and three JRST's to the three locations following
the break location. The JRST's account for possible skips
by the break instruction.
If a breakpoint is hit, and the user changes the
contents of $G, and then proceeds (with $P), the break
instruction is not executed. Control simply resumes at the
new location given by $G. Old DDT's execute the instruction
under the breakpoint, and then transfer control to the new
16. JSYS Typeout Format
When IDDT attempts to print an opcode 104 instruction
symbolically, it first looks for an exact match in the
user's symbols. If one is found, the corresponding
user-supplied name is printed. Otherwise, IDDT checks its
own internal JSYS symbol table (hopefully, the same as
JSYS's defined in <SYSTEM>STENEX.MAC) for an exact match.
If none is found in either place, the instruction will print
as JSYS 501, i.e., "JSYS" and address.
17. Other Features
The search commands ($W, $N, and $N) have been
generalized to take an argument which specifies the maximum
number of "finds" that shall occur before the search will
terminate. An example is:
This command will stop after typing five instructions lying
between locations "FOO" and "BAR" which have an effective
address of "QQZZ".
Internal register $I+4 contains the fork handle that
IDDT uses to reference the user. This register is
TENEX USER'S GUIDE JANUARY 1973 Page 94
$Q has the value of the last quantity typed, as always.
$$Q has this value with halves swapped. Thus, ($$Q)= will
type the same value as $Q= will.
$V is the value of the left half of the last quantity
typed. $$V is the same with the sign extended. Thus,
assuming the last value typed to be -3,,FOO , $V= would
yield 0,,-3 whereas, $$V= would type -3.
Overview of changes
A. Changed Commands
;J(obstat) is now ;;J
;F(ilstat) is now ;J(fnstat) [;F is forkstat]
also <num>;J just gives the status of jfn num
;P(sistat) is now ;I(nterrupt stat) [;P is patch again]
B. Multiple fork commands
;F gives a hierarchical list of the jobs fork's
<num>;F gives the status of fork num
<num>;;F makes fork num iddt's current fork
C. Single step commands
0$Y - Toggle the single-step verbose switch
$J -- fetch the next instruction and excecute it, no interpretation
$Y -- excecute only one instruction, if the instruction is a jump of some sort
it will be simulated in software (very slow!!)
<num>$J (or $Y) excecute the next num instructions
<num>(<loc>)$J excecute the next num instructions or until an attempt is
made to change the contents of loc.
<loc>$$J procede single stepping until an attempt is made to change the value
I. ;A (Address space command) & ;J (Jfn status)
;A alone still gives a "MEMSTAT" typeout. If an argument
is supplied ( 123;A ), only a single line will be typed, giving the
information about just that page number.
;J with an argument likewise types out the status of that jfn.
II. ;V (set View cell)
A command such as FOO+5;V or 123456;V will define the
"view cell". When IDDT fields a ^T interrupt, the address and contents
of the view cell will be typed. The view cell may be undefined and
consequently removed from the ^T typeout by ;V (no argument).
Note: It is the contents of the view cell in whatever fork IDDT's
attention has been directed to which is typed out.
III. Multi-fork Feature
A breakpoint may be set in any fork. The breakpoint is
distinguished by its address and the "owning" fork. The owning
fork is determined by chasing through indirect map entries until
a non-indirect entry is found. The fork or file thus found is
A breakpoint set in one fork may be hit by another fork having
the same address space. If the result of chasing indirect chains
backward doesn't yield the same owner as the original chase did,
the BPT will be considered illegal. This can happen if you mess
around with map entries for pages having breakpoints in them.
When a fork hits a breakpoint, IDDT's handle on the breaking fork
is printed in parens before the breakpoint name unless it is the
the top fork. E.g. (2)$1B>>105.
IDDT's attention can be shifted to any fork in the program being
debugged using the ;;F command. In the form: n;;F, fork n becomes
current and all examines, deposits, BPTs etc pertain to it. n is
a small number (actually the low bits of IDDT's fork handle on
the fork in question). 0 always means the top fork of the
debugee. In the form m<n;f, attention is switched to the m-th
inferior of fork n. Again, n is IDDT's handle on some fork in the
debugee. m is the low bits of fork n's relative handle on some
fork (IDDT executes GFRKH(400000+n, 400000+m) to get the new
handle). The relative handle so gotten is printed.
Instructions may be executed in any fork using the $X command.
Caution must be exercised, however, since all the forks in the
program will get a chance to run while the $X is in progress. If
some other fork then hits a BPT, IDDT will most likely get fouled
up when it tries to proceed the BPT and then field the $X
The "owner" of a BPT may be discovered by examining the location
7 beyond the BPT register (e.g. $1B+7/). When doing examines,
IDDT chases down indirect chains and can thus look at see memory
that is already as far away from the program as possible. In
fact, it can see further, so, just because IDDT says the program
is there, doesn't necessarily mean it can be executed without
memory traps due to excessive indirection. I'm not sure what ;Y
or ;M will do if the current fork is not the top fork.
IV. ;F (Forkstat command)
;F will print the tree of forks below (and including) IDDT.
num;F will print just the information about the named fork.
(The monitor change for implementing ;F will be made in the
near future. Until then ;F with no argument will be illegal.)
V. Single stepping
There are two falvours of single stepping, $Y and $J:
$J just fetches the next instruction and excecutes it, so if that
next instruction is a subroutine call, the entire subroutine will be
excecuted, and if that instruction is a jrst, the program will be continued.
$Y fetches the next instruction and if it is a jump of any sort,
it is interpreted to that in fact only one instruction is excecuted at a time,
so that if the instruction is a subroutine call, the program counter will be
set to the beginning of the subroutine.
Both commands have the same syntax:
$J single steps
<num>$J will step num times
<num>(<loc>)$J will step num instruction or until the contents of location
loc are changed, in which case it will stop and say
(WP)PC LOC/ new contents of loc, where pc is the instruction after
the one that attempted to change the value of loc. Note, however the contents
of loc will not be changed.
<loc>$$J is equivalent to infinity(<loc>)$J, ie it will single step until an
attempt is made to change the contents of loc.
If the verbose switch is on, the instruction being excecuted and
any AC's or the view cell (see above) that change will be typed out.
Both instruction are extremely slow.
1) ^N - ITS style ^N
2) $^N - Single step over subroutine; done by setting three temporary
breakpoints at the next three "reasonable" instructions
3) $. - Returns current PC ($./ examines next instruction to be ^N'ed,
4) $<TAB> - Opens left-half of location rather then right-half.
5) Initialization dialouge now prompts for .EXE filename.
6) $<CR> pops ring buffer and closes patch, $$<CR> just closes patch
7) ;.<internal symbol name> inserts the value of the internal symbol into the
expression. Currently, internal symbols are:
SYMOFS Maximum offset from symbol printed
<nnn> of <symbol>+<nnn>
Default value is 777 octal
PC Current PC (readable also by $., and setable
8) $<LF> pops ring buffer and goes to next location
9) $^ pops ring buffer and goes to previous location
10) ^L clears the screen
11) <adr>$0G sets the start address to <adr> and opens <adr> as if ^N'ing.
This command is used to set an address break in the process
being debugged. <loc> is the address (cannot be an AC), <n>
is a 3-bit value specifying the type of access to break on
(read, write, xct). Default for <n> is 2 (break on write).
If <loc> is ommitted, existing address break is removed.
When the address break is hit, a break is typed out with the
prefix "ABK:". $P can be used to proceed.
If an attempt is made to store into a read-only location, a
private copy of the page will be made automatically and
<pagenum>$U typed to indicate this.
The ;R command can be used to insert text into the RSCAN
buffer. If the program expects to be run by the exec with
arguments in the same line, this will allow it to be debugged.
The default interrupt (escape) character is ^D. It can be
changed with the ;E command.
Text typein/typeout is now done in ITS-DDT style, namely:
The "0" refers to the low-order bit, and can be "1" to turn it
The ITS patching commands have been implemented. The
following documentation is from the ITS DDT doc:
^\ begins a patch at the location open (the location "being
patched"). It is a convenient way to replace one instruction
(at the open location) by several (the patch). The
instructions in the patch are stored in the job's "patch
area", a spare area allocated specifically to such use. Every
program should allocate one. The beginning of the patch area
is the value of PATCH if it is defined, or the value of PAT if
it is defined, or 50 . As patches are made, PATCH will be
redefined to point to the next free location in the patch
A patch started with ^\ must be terminated with some variety
of ^] command, which will store first the JUMPAs back from the
patch to the patched routine (two of them, in case the patch
skips), and then a JUMPA from the location being patched to
the patch itself. This order of actions guarantees that the
patch will never appear to be "half made" in any way that that
might cause trouble in a running program.
^\ begins by typing and opening the first location of the
patch area. Then the contents of the location being patched
are typed out and left as the argument to the next command.
If you wish to include that instruction as the first
instruction of the patch, type ^J. If you wish to get rid of
it, type <rubout>. Then deposit the other instructions of the
patch, and finish with a ^] (which see).
While patching, the pseudo-location ..PATCH contains
<location being patched>,,<start of patch>.
Note to users of relocatable programs, and MIDAS or FAIL block
structure: PATCH is redefined in the same symbol block that
it was found in. This permits some obscure hackery, but
normally the whole program will have only one patch area, and
it must be visible to ^\ no matter which symbol block is
currently selected for type in. That can be guaranteed by
defining PATCH as a global symbol (eg, using PATCH": in
deposits <arg> in the open location, then does ^\. Equivalent
to ^\<rubout><arg>, except that with <arg>^\, <arg> will be
present in the location being patched while the patch is being
$$^\ unmakes the patch previously made to the open location. $$^\
uses the JUMPA to the patch to find the instruction that the
patch replaced. This works only for patches made by ^\, which
were either closed by $^], or closed by ^] and having the old
instruction as the first instruction of the patch.
^] ends a patch started by ^\. Two JUMPAs back to the locations
following the one being patched are stored in the two words
starting with the open location (or in location .+1 if no
location is open). Then in the location being patched is
stored a JUMPA to the beginning of the patch. Finally, PATCH
is redefined to point at the word after the second JUMPA back
(the first free location of the patch area).
<arg>^] stores <arg> in the open location, opens the next location,
then does ^].
$^] is like ^] but first stores the contents of the place the
patch was made from in the open location and linefeeds. It is
useful for putting a patch "before" an existing instruction.
stores <arg> in the open location, opens the next location,
then does $^].
$$^] is like $^] but omits the JUMPAs back to the place that the
patch was made from. It is useful when a patch is put on top
of a JRST or POPJ - it will store an identical JRST or POPJ,
and nothing else. $$^\ (unpatch) can't work after $$^]
because necessary information isn't there; it can however
figure out that it can't win and will complain. If this is
important, use $^] instead of $$^].
stores <arg> in the open location, if any, then moves down
one word and does $$^].
Recent bug fixes
TIW words are saved and restored.
Release 4 fork handling fixes.
It now knows about quota exceeded interrupts (they type out as QOT:)
Added Release 4 JSYI to the table
Patching commands will use PAT.. if PATCH not found