kme.1

.       @(#)kme.1 $Revision$ $Date$
.TH KME 1 "$Revision$ $Date$"
.SH NAME
kme \- Kernel Memory Editor
.SH SYNOPSIS
.TP 7
\fBkme
\fB[\-ahirstx\fB]
\fB[\-A\ \fRaddrsca\fBl
\fB[\-b\ \fRbase\fB]
\fB[\-c\ \fRcorefile\fB]
\fB[\-d\ \fRdefsnames\fB]
\fB[\-D\ \fRdefspaths\fB]
\fB[\-e\ \fRemuldev\fB]
\fB[\-f\ \fRfepdev\fB]
\fB[\-g\ \fRhost[:port][,...]\fB]
\fB[\-g\ \fRdevice[:baud][,...]\fB]
\fB[\-k\ \fRboard_index\fB]
\fB[\-L\ \fRextension\fB]
\fB[\-m\ \fRhostlist\fB]
\fB[\-M\ \fRoffset:len\fB]
\fB[\-n\ \fRnamelist\fB]
\fB[\-p\ \fRrow\fB]
\fB[\-P\ \fRpid\fB]
\fB[\-S\ \fRaddressmask\fB]
\fB[\-u\ \fRuptime\fB]
\fB[\-U\ \fRudp_port\fB]
\fB[\-w\ \fRcolwidth\fB]
\fB[\fRparams ...\fB]
.SH DESCRIPTION
\fIKme\fR is a general purpose screen-oriented
tool for viewing and modifying memory (such as UNIX kernel memory).
Upon invokation, the program continuously displays and updates
one or more sections of memory in a spreadsheet-like format.
The memory range and display format may be defined
on the command line or entered on the screen.
Thereafter the corresponding memory contents are continuously
displayed and updated on the screen,
and may be modified by field entry.
Available builtin display formats are character,
hex and decimal in
various byte, word and longword combinations.
The file \fIkme_defs\fR in the current directory may contain
user-defined display formats for composite memory structures.
.PP
By default, \fIkme\fP displays UNIX memory using the \fI/dev/kmem\fP
pseudo file.  But \fIkme\fP can display memory in any file or by
using a number of alternative access methods, such as its own
RW protocol, the GDB remote serial protocol (over TCP or serial),
or several other lesser-used methods.
.PP
Command line options include:
.TP 15n
.BI -a
Do not display address expressions.
.TP
.BI \-A \ addrscale
Scale input addresses by multiplying them by \fIaddrscale\fR
before accessing the \fIcorefile\fR.  Scale displayed addresses
by dividing them by \fIaddrscale\fP before displaying them.
.sp 1
The default value for \fIaddrscale\fP is 1 (no scaling).
.sp 1
This feature is useful for displaying memory on devices that
are not byte addressable, such as DSP memory.  For example,
when displaying memory on an Analog Devices 2187 DSP, a
scale factor of 2 can be used for data memory and a scale factor
of 4 can be used for program memory (4 is used instead of 3
because the underlying DSP interface is 32 bits wide, not 24
bits wide).
.sp 1
NOTE: this feature is not very well tested.
.TP
.BI \-b \ base
Add the hex number \fIbase\fR to all addresses
before accessing kernel memory.
.TP
.BI \-c \ corefile
Use the file \fIcorefile\fR for memory accesses.
If the environment variable \fIKME_CORE\fR is defined,
it contains the default file name.  Otherwise the
default is \fI/dev/kmem\fR.
.TP
.BI \-d \ defsnames
Read user-defined display definitions from
the colon-separated list of file names given in
\fIdefsnames\fR.
If the environment variable \fIKME_DEFS\fR is defined,
it contains the list of default file names.
Otherwise the default is \fIkme_defs\fR in the current directory.
The search path can be modified using the -D option.
If a file can't be opened, a warning will be printed except
that no warning will be printed if the file \fIkme_defs\fP
can't be found.
.TP
.BI \-D \ defspaths
When searching for display definition files which aren't
absolute file names (see -d), use
\fIdefspaths\fR as a colon separated list of directories to
search.
If the environment variable \fIKME_PATH\fR is defined,
it contains the list of default directory names.
Otherwise the default is the current directory.
.TP
.BI \-f \ fepdev
Access kernel memory using DIGI_KME ioctl() calls directed
to tty device \fIfepdev\fR.
.TP
.BI \-g \ gdblist
Specifies a comma-separated list of TCP/IP hostnames and/or
serial port devices where memory should be displayed.
Each host/device must provide a GDB remote serial protocol server.
An optional \fB:\fIport\fR may be
appended to each TCP/IP hostname to override the default GDB port of 9000.
An optional \fB:\fIbaudrate\fR may be
appended to each serial device to override the default baudrate of 38400.
Please note that GDB protocol over TCP/IP can be terribly slow on networks
with latencies larger than a few milliseconds; serial devices may be faster.
.TP
.BI -h
Suppress the one-line help memu normally displayed
at screen bottom.
.TP
.BI -i
Allow curses to use insert/delete line sequences when
updating the screen.
.TP
.BI \-k \ board_conc
Default board and concentrator for DigiBoard devices.  This is a
two digit decimal number.
.TP
.BI \-L \ extend.so
Dynamically load a shared object as an extension to the
display format capabilities of "kme".  Not supported on
all operating systems.
.TP
.BI \-m \ hostlist
Specifies a colon-separated list of TCP/IP hostnames where memory
should be displayed.
Each host must provide a kme/udp memory read/write (RW) server,
as specified in the
.B services
file.
.TP
.BI \-M \ offset:len
Access memory by using the mmap() system call to map the \fIcorefile\fP
directly into kme's address space.  Memory is mapped beginning at
\fIoffset\fP bytes from the beginning of \fIcorefile\fP for a length
of \fIlen\fP bytes.  Note that \fIcorefile\fP
is typically set to \fB/dev/pmem\fP when this option is used.
\fIOffset\fP and \fIlen\fP
are specified using the conventions of strtol(), e.g. 0x500000:0x1000.
.TP
.BI \-n \ namelist
Read symbol definitions from the colon separated list of
file names given in \fInamelist\fR.
If the environment variable \fIKME_SYMS\fR is defined,
it contains the default file list.
Otherwise the default is \fIkme_syms\fR in the current directory.
Each file may be either a binary file (defined by the ld library)
or an ASCII file where each line contains a hexidecimal symbol
value followed by a alphanumeric symbol name.
.TP
.BI \-p
Position the initial display so
\fIrow\fR is at the top of the screen.
.TP
.BI \-P \ process_id
Access the memory space of the running process with the
specified  \fIprocess_id\fR.
Best when combined with the \fI-n\fR option.
Note that KME uses PTRACE to view the memory of the process,
so viewing is invasive.
KME must stop the process each screen refresh,
and KME must catch and rethrow all exceptions handled by the process.
.TP
.BI \-r
Open \fIcorefile\fR read-only, and prohibit all
attempts to modify memory.
.TP
.BI \-s
Swap multiple-byte quantities displayed from and written to the
core file.
.TP
.BI \-S \ addressmask
All addresses read from the symbols file (ascii, coff, or nlisted)
will be binary masked with \fIaddressmask\fR.   
.TP
.BI \-t
Normally, indexed arrays are displayed in the form of "foo+0xb4".
This flag changes it to display the index into the array instead
of the offset.  The example may then display as "foo[4]".  Same
as ^T within the program.
.TP
.BI \-u \ uptime
Wait \fIuptime\fR tenths of a second after refreshing
the screen before beginning a new refresh cycle.
Default is 2, limiting screen refresh time to 5/second.
An update time of zero suppresses refresh until a command key
is depressed.
.TP
.BI \-U \ port
When accessing memory over a network (option \fI-m\fR or \fI-g\fR),
use the specified \fIport\fP rather than the normal default port.
.TP
.BI -V
Print version and other information determined by the configuration
process when kme was built.
.TP
.BI \-w \ colwidth
Set the kme column width to the desired value. The current default is 9,
up from the traditional 8.
.TP
.BI -x
Print debugging information to \fIstderr\fR.
.PP
Additional parameters specify initial screen
display requests, or user format defines.  The form:
.PP
.RS
\fIline_number \fB= \fImemory_address \fB/ \fIdisplay_format\fR
.RE
.PP
says to display data at screen \fIline_number\fR
from \fImemory_address\fR
according to \fIdisplay_format\fR.  If \fIline_number\fR is 0 
this data will display on the line following the first blank line 
after the previous \fIdisplay_format\fR has completed.   This 
method of determining format positioning may affect subsequent 
absolutely anchored references.  

The form:
.PP
.RS
\fIuser_display_char \fB= \fIdisplay_format\fR
.RE
.PP
defines the upper-case single \fIuser_display_char\fR
to be an abbreviation for the \fIdisplay_format\fR string which follows.
.PP
As a special case when using the \fB-f\fR
option, the memory address field may be prefixed by one or two
hexadecimal digits and a (\fB:\fR) to designate the address space
of a particular DigiBoard device.
The first digit specifies the PC-bus board,
while the second digit (if present) further specifies a
concentrator attached to that host adapter.
For example the prefix \fB03:1000\fR specifies address 0x1000
in the 3rd concentrator attached to the 1st host adapter board.
.PP
As a special case when using the \fB-m\fR
option, the memory address field may be prefixed by one or two
hexadecimal digits and a (\fB:\fR) to designate the hostname and
\fBkmed\fP corefile of a particular device.
The first digit specifies the nth hostname in the \fB-m\fP hostlist option,
while the second digit (if present) further specifies the nth
corefile given with \fBkmed\fP's \fB-c\fP corelist option.
For example the prefix \fB01:1000\fR specifies address 0x1000
in the 2nd corefile attached to the \fBkmed\fP ruuning on the 1st hostname.
.SH SCREEN\ DISPLAY
The CRT screen display is tabular, with a line number leftmost,
the hex memory address next, and memory data fields every
8 columns thereafter across the screen.
On a 24 by 80 CRT screen, the display is 23 address
lines tall by 8 data columns wide,  with a help menu on
the bottom line.
.PP
Regardless of the screen size, \fIkme\fR supports 200
virtual display lines.
At any given time,
only a subset of these lines may be viewed through the
screen window.
The screen window follows the cursor, so the user may
scroll through the range in the manner of an editor or
spreadsheet.
.PP
Through command line parameters, or by screen entry, the
user selects the data to be displayed on each address line.
From the screen there are two methods to accomplish this.
The user may type an \fBm\fR and enter a memory
display string or user format character definition
just as it would appear on a command line.
He may also position the cursor to the desired
address field, type the letter \fBc\fR for change,
or \fBe\fR for edit,
and then enter a string of the form:
.PP
.RS
\fIaddress_expression\fR \fB/ \fIdisplay_format\fR
.RE
.PP
In either case, the memory \fIaddress_expression\fR value
immediately appears on the specified display line,
followed by zero or more data fields according to
the \fIdisplay_format\fR given.
If more data fields are specified than fit across the
screen, the data is extended to multiple lines,
and the memory address of the first data field on each line
is displayed in the corresponding address field.
.SS "Address Expression"
The \fIaddress_expression\fR may include decimal (0t prefix)
and hexidecimal numbers,
symbols defined in the namelist file,
and the operators listed below.
Precedence is modeled after the C-language.
.TP 8
.B .
Structure element designator.
Performs a simple binary add,
but with much higher precedence.
.TP 8
.B {}
2-byte Subscript.
The form
.IB a { b }
returns the 16-bit quantity at address
.IB a \(pl b
in the corefile.
.TP
.B []
4-byte Subscript.
The form
.IB a [ b ]
returns the 32-bit quantity at address
.IB a \(pl b
in the corefile.
.TP
.B \(**
Unary 32-bit indirection.
.TP
.B @
Unary 16-bit indirection.
.TP
.B #
Unary 8-bit indirection.
.TP
.B $
Fetch temporary value.
The size of the current display item is available in temporary 0,
although it will always be zero the first time the item is displayed.
Other temporaries are stored with the
.B $
display operator.
.TP
.B \(pl
Unary plus.
.TP
.B \(mi
Unary minus.
.TP
.B ~
Unary NOT.
.TP
.B ^
Swap 2 byte operand.
.TP
.B %
Swap 4 byte operand.
.TP
.B \(**
Multiply.
.TP
.B /
Divide.  This operator is recognized only in parenthesized expressions,
so it is not confused with the
.B /
separator character.
.TP
.B %
Modulus.
.TP
.B \(pl
Binary add.
.TP
.B \(mi
Binary subtract.
.TP
.B <<
Shift left.
.TP
.B >>
Shift right.
.TP
.B <
Less than.
.TP
.B >
Greater than.
.TP
.B <=
Less equal.
.TP
.B >=
Greater equal.
.TP
.B ==
Equal.
.TP
.B !=
Not equal.
.TP
.B &
Bitwise AND.
.TP
.B ^
Bitwise Exclusive OR.
.TP
.B |
Bitwise Inclusive OR.
.TP
.B ?:
C-language style if-else conditional value operator.
.TP
.B <be16>
Conditional swap 2 byte operand.
On a big-endian CPU, this operator is a NOP.
On a little-endian CPU, this operator is the same as the
.B ^
operator.
.TP
.B <be32>
Conditional swap 4 byte operand.
On a big-endian CPU, this operator is a NOP.
On a little-endian CPU, this operator is the same as the
.B %
operator.
.TP
.B <le16>
Conditional swap 2 byte operand.
On a little-endian CPU, this operator is a NOP.
On a big-endian CPU, this operator is the same as the
.B ^
operator.
.TP
.B <le32>
Conditional swap 4 byte operand.
On a little-endian CPU, this operator is a NOP.
On a big-endian CPU, this operator is the same as the
.B %
operator.
.SS "Display Format"
Builtin format characters are lower-case letters,
punctuation marks, and text strings delimited by
single and double quotes.
As a special case, text strings containing \'\\h\' are
used to toggle highlighting in the displayed string.
You may want to use this for section headers or elsewhere
for emphasis.
User-defined format characters are upper case alpha
letters.
Format characters, and format strings enclosed in parens
may be preceeded by a decimal repetition
.I count,
and concatenated to form a display string of
arbitrary complexity.
User-defined format characters may include other
user-defined characters to a recursive limit of 10.
.PP
The builtin format characters are given below.
Except as otherwise described, a preceeding decimal repetition
behaves exactly as though the following character were
repeated that number of times.
.TP 8
.B \(pl
Increment the working memory address.
.TP
.B \(mi
Decrement the working memory address.
.TP
\fB\'\fItext\fB\'\fR
Display \fItext\fR.  If \fItext\fR is more than 8 characters, use multiple
fields as required.  Ignore any repetition count.
.TP
\fB"\fItext\fB"\fR
Same as above.
.TP
.B \.
Display a blank data field.
.TP
.B :
Display nothing, but fetch subsequent blocks of display data from the
memory device in blocks of
.I count
bytes.
The effect continues until the end of the format string.
This is often useful when reading device registers.
.TP
.B $
Display nothing, but store the current display address in the
temporary value given by
.I count.
.TP
.B % 
Display nothing, but toggle the endianness swap flag.
If enclosed in parenthesis, the effect ends at the next
right paren.  Otherwise the effect continues until the end of
the format string.
.TP
.B =
Display nothing, but set an internal variable called
.I width
to the value of
.I count.
.TP
.B *
Display nothing, but set the new
.I count
to the temporary value stored in temporary register number
.I count.
.TP
.B &
Display nothing, but store the value at the current display
address in temporary register number
.I count.
The width of the value fetched is determined by the current
setting of
.I width
(see = format).
.TP
.B ^ 
Display nothing, but roundup the value in temporary register
number
.I count.
The value is rounded up to the next multiple of the current
value of
.I width.
.TP
.B #
Display nothing.
If enclosed in parenthesis, set the working memory address to
the working memory address at the last left paren plus \fIcount\fR.
Otherwise set the working memory address to
\fIaddress_expression\fR plus \fIcount\fR.
.TP
.B a
Mask the next memory byte with 0x7f and display the result
in ASCII.  Characters below 0x20 are shown with a caret as
control characters.
.TP
.B b
Display the next memory byte in hexadecimal.
.TP
.B c
Display the next byte in an unambiguous character format.
Characters below 0x20 are shown with a caret as control characters.
Characters greater-equal 0x7f are shown in hexadecimal.
.TP
.B d
Display the next 2 bytes as signed decimal.
.TP
.B e
Display the next 4 bytes as an unsigned decimal.  If the number is
too large to fit in one column, the number is truncated, and a plus sign
is displayed on the right.
.RB ( \+ )
followed by the lower 7 digits of the decimal value.
.TP
.B f
Display the next 4 bytes as a float, with
printf mode \fB"%-*.*g"\fR, where the first \fB*\fR is the column width,
and the second \fB*\fR is the column width - 6.
.TP
.B g
Display the next 8 bytes as an unsigned decimal quadword (long long).
If the number is too large to fit in two columns, the number
is truncated, and a plus sign is displayed on the right.
.RB ( \+ )
followed by the lower 15 digits of the decimal value.
.TP
.B h
Display the next 8 bytes as a double, with printf mode \fB"%-*.*g"\fR,
where the first \fB*\fR is double the column width, and the second \fB*\fR
is double the column width - 7.
.TP
.B i
Display the next byte as a character (masked to 7 bits),
and the following byte in hexadecimal.
.TP
.B l
Display the next 4 bytes as an 8-digit hexadecimal number.
.TP
.B n
Advance to the next display line.
.TP
.B q
Display the next 8 bytes as a 16-digit hexadecimal quadword (long long).
.TP
.B s
Display string data with zeroes shown as spaces,
and other unprintable characters shown as periods.
When used with a repeat count, up to \fIcolumn-width\fR characters are
shown per field, using as many fields as necessary to show
the complete string.
.TP
.B t
Display the next byte of memory as unsigned decimal.
.B u
Display the next 2 bytes as an unsigned decimal.
.TP
.B w
Display the next 4 bytes as a float, with
printf mode \fB"%-*.8g"\fR, where \fB*\fR is double the column width.
.TP
.B x
Display the next 2 bytes of memory in hexadecimal.
.TP
.B z
Display the next 4 bytes of memory in decimal.
.SH SCREEN_COMMANDS
Screen commands are all single keystrokes, possibly preceeded by a
repeat count.  Available commands are:
.TP 5
.B ^F
Page forward.
.TP
.B ^U
Page back.
.TP
.B ^D
Scroll down.  The line scroll count is remembered and becomes
the default scroll count next time.
.TP
.B ^T
Normally, indexed arrays are displayed in the form of "foo+0xb4".
This flag changes it to display the index into the array instead
of the offset.  The example may then display as "foo[4]".  Same
as -t on the command line.
.TP
.B ^U
Scroll up.  The line scroll count is remembered and becomes
the default scroll count next time.
.TP
.B ^J
Move down to the beginning of the next line.
.TP
.B =
Makes the current row the \fIindirect row\fR.
After this is done, the line number is highlighted.
This alters the action taken by the \fI*\fR command (below).
When an \fIindirect row\fR is selected,
the selected address field used by the \fB*\fR command is
the first \fBaddress_expression\fR above this row.
Entering this key a second time cancels the effect.
.TP
.B *
When entered over a left column hex address
or a hex data field,
causes the address under the cursor to temporarily replace the
\fIaddress_expression\fR in the selected address field.
The selected address field is the \fIaddress_expression\fR at or above the
current row, unless an \fIindirect row\fR was chosen with the \fB=\fR key.
Then it is the first address field at or above the \fIindirect row\fR.
Entering this key over an \fIaddress_expression\fR field restores
the original contents.
.TP
.B ^
Move to the address field.
.TP
.B \(pl
Advance the memory address of the current display line
by the size of the data displayed.
.TP
.B \(mi
Decrement the memory address of the current display line
by the size of the data displayed.
.TP
.B !
Prompt for and execute a shell command.
.TP
.B ?
Toggle the appearance of the help menu on the bottom
line of the screen.
.TP
.B a
Toggle address display mode.
.TP
.B b
Prompt for and accept a new memory base address.
.TP
.B c
Change the field under the cursor.
.TP
.B d
Delete the current line, and remember it in the save buffer.
If a repeat count is given, delete and keep all those lines
in a single operation.
.TP
.B e
Edit the contents of the field under the cursor using \fIvi\fR
style editing commands.
.TP
.B f
When using an HP64000 emulator, switch command input to control
port A.  Memory updates will not succeed until switched back
by other means.
.TP
.B g
If no repeat count is given, move the cursor to the last
virtual display line.
If a count is given, move to the line number given in that count.
.TP
.B h
Move left.
.TP
.B i
Insert \fIcount\fR lines before the current one.
.TP
.B j
Move down.
.TP
.B k
Move up.
.TP
.B l
Move right.
.TP
.B m
Prompt for and accept either a display line request or
a user format macro using the command line syntax.
.TP
.B n
Discard all existing symbol definitions and re-read the
\fInamelist\fR files to get a fresh copy.
.TP
.B o
Output (print) the contents of the current screen to a file.
If the first character of the file name is the pipe character (\fB|\fP),
then the output is piped to a program.  If the first two characters
of the file name are \fB>>\fP then the output is appended to the file.
.TP
.B p
Put deleted lines back into the display.
.TP
.B q
Quit the program.
.TP
.B r
Discard all existing macro definitions and re-read
the \fIdefspath\fR files to get a fresh copy.
.TP
.B s
Save the configuration of the current display to a command
file.  Subsequently executing that command file should
automatically recreate the current display.
.TP
.B u
Allow the user to enter a new update interval.
.TP
.B y
Yank (copy) the specified number of screen lines into the
save buffer.
.TP
.B z
Zero the memory location under the cursor.
.PP
During all field entry, the user may invoke vi-style commands to
edit the entry in the style of \fIksh\fR.
This facility supports
the basic line editing command characters \fB$.0abcdDfhiIlrstuwx\fR,
and the history command characters \fB+-/jkn\fR.
The character \fBq\fR quits the field entry w/o change.
.SH USER\ DISPLAY\ FORMATS
On startup, user-defined display formats are read from the
colon-separated list of files defined in \fIdefspath\fR.
In this file, a line beginning with an upper-case letter
defines the corresponding user format character.
Subsequent indented lines are continuations.
Single and double quoted strings are passed verbatim,
otherwise white space is discarded, and everything on a
line after an unquoted (#) is a comment.
.PP
An example file might contain:
.PP
.nf
.TA 4
A	"thead""ttail""tstart""tmax""rhead""rtail""rstart""rmax"
	8xN
	"cport""seg""rlow""rhigh"n
	4xnN
	"tlow""dcdtime""flow""mstat""lstat""status"n
	2x4bnN
	"imask""baud""dtype""hndshk""xoff""xon""hflush""btime"
	4b2c2bN
	"bcount""portnum""dmask""irq""tmask""tval""bstart"n
	6bxnN
	"rr0""rr1""rr3""rr10""wr0""wr1""wr2""wr3"
	8bN
	"wr4""wr5""wr9""wr11""wr12""wr13""wr14""wr15"
	8bN
	"ov/un""dcdlo""dcdhi""portbit"n
	4xnN
	"mcount""m10ms""mand""mor""mval"n
	xxbbbn 49+

L	l.

N	n
.fi
.PP
This file defines format \fBA\fR to display a 128 byte
structure.  The name of each field is displayed immediately
above it.
The \fB49+\fR at the end of the \fBA\fR definition pads out
the size of the structure to be 128 bytes so that the \fB+\fR
and \fB-\fR commands will work as desired.
Normally, double spacing is used between lines,
but the user may make it single spaced by redefining N to be Null.
.PP
When \fBl\fR format fields are displayed side-by-side,
they run together.  The \fBL\fR user format overcomes this by
placing a blank field after the 8-character hexadecimal number.
.PP
The syntax for user defined formats has been enhanced, while
remaining compatible with the mode described above.  In a complex
system, a limit of 26 uppercase user defined formats was restricive and 
difficult to make mnemonic.  You can now also define the above
format like this:

.nf
.TA 4
!channel	"thead""ttail""tstart""tmax""rhead""rtail""rstart""rmax"
	8xN
	...
.fi

You must display this symbolically named format with a
leading \fB!\fR character, so the program knows the difference 
between a symbol named "channel" and a format string consisting
of \fBc\fR, \fBh\fR, and so on.   All alphanumeric (plus underbar) 
characters following the \fB!\fR are interpreted to be part of the format
name.
.SH "EXTENSIONS"
A new feature in kme is the ability to extend display formats
using shared objects.  You can write your own C program to
add an arbitrary display format to kme.  The method to do
this is operating system specific.  With the GNU toolchain,
you would do something like the following:

.nf
.TA 4
	$ cc -c dxbmsg.c -o dxbmsg.o
	$ ld -shared dxbmsg.o -o dxbmsg.so
	$ kme -L dxbmsg.so 1=0/!dxbmsg
.fi

The shared object must have an
.I _init()
routine which calls:

.nf
.TA 4
	typedef char * (*DLFUNC)(ulong *addrp);

	add_format(char *name, char *format, DLFUNC dlfunc);
.fi

for each new format
.I name
that it wants to define.  If
.I format
is not NULL,
then the new format is just a simple string.  This is not
interesting as you can already do this with kme_defs files.
However, if
.I dlfunc
is not NULL, then (*dlfunc)(&addr)
is called whenever the format needs to be displayed.
.I &addr
is a pointer to the variable which holds the current display
address.
.PP
.I (*dlfunc)(ulong *addrp)
can do one of two things.  It can generate
a format string on the fly and return a pointer to it.
In this case, kme will display the format as returned.
Or it can handle doing display updates itself.  In this
case, it returns NULL and must update the current display
address (*addrp) itself.
.PP
An example format that displays a real C-string by returning
a customized display format string is:
.nf
.TA 8
extern unsigned char *mem;
typedef unsigned long ulong;

char *
format(ulong * addrp)
{
	ulong		faddr = *addrp;
	ulong		zaddr;
	static char	fmt[32];

	for (;;)
	{
		if (!getmem(1))
			return " \"????\" ";
		if (*mem == 0)
			break;
		(*addrp)++;
	}
	zaddr = *addrp;
	*addrp = faddr;

	sprintf(fmt, "%d a 1+\n", zaddr - faddr);

	return (fmt);
}

void
_init(void)
{
	add_format("asciiz", NULL, &format);
}
.fi
.PP
The above example, although simple to implement, also shows why there
is a second method for the way that extensions can choose to
operate.  The above example is inefficient, as memory
will be traversed twice (once in the extension, and
once in kme itself).  However, the second method currently
requires some knowledge of how kme is implemented internally.
Translation: we are currently too busy to clean up and
expose a set of functions for your convenient use.
.SH FILES
.TP 20
/usr/lib/kme_defs
User defined formatting commands.
.TP
/dev/kmem
Access to kernel memory.
.TP
/etc/services
Internet Services file.
.SH BUGS
There needs to be a stack of last memory addresses, so that
you can use '-' to step backwards thru memory when a variable
length format from an extension is being used.
.PP