DEBUG is a clone of the MS-DOS DEBUG command. Some minor things aren't
implemented. DEBUG does not only support the 8086/8088 and 8087 registers
and instruction sets but also the 32bit register and the instruction
sets till PentiumPro CPU - except the MMX extensions.
DEBUG is a relatively advanced DOS tool but has many uses. For instance,
it can be used to:
* find bugs in programs,
* create programs from assembly code,
* inspect and edit binary files.
DEBUG [[drive:][path]filename [arglist]]
[drive:][path]filename Specifies the file you want to test. It
doesn't have to be an executable - it
could be a binary or text file.
Since it can be any file, the file
extension has to be specified.
arglist Specifies command-line information
required by the file you want to test.
See Program Execution below for more
information on running executables.
Once Debug is started, the Debug command prompt is displayed. Enter Q to
quit Debug, and ? to display the list of Debug commands.
Inspecting and Editing Memory:
C range address Compare two memory ranges, displaying the
differences. Only the starting address of the
second range is required, Debug will assume the
second range will be the same size as the first.
C 100,110 200
will compare the range 100,110 to 200,210.
D [range] Display the contents of a memory range. If no
range is specified, dump will display 128 bytes,
starting where the last dump finished or at the
beginning of the loaded file.
DM Display the DOS memory control block (MCB) chain
and the current PSP.
E address [list] Write over part of memory, beginning at address,
with the list of bytes. To enter a string of text
characters, enclose the text in double quotes.
E 100 "Hello!"
F range list Write over a memory range with a repeating list
of bytes. For instance, to set a memory range to
zero, you might put
E 100,110 0
and to set a memory range to "brumbrum":
E 100,107 "brum"
M sourcerange destaddress
Copies the range sourcerange into another range
that begins at destaddress.
S range list Searches for all occurences of the list of bytes
in the specified range. The starting address of
each occurence is displayed.
Calculating Numbers in Hexadecimal:
H value1 value2 Displays two numbers, the first being
value1+value2, the second being value1-value2.
H can handle dword values.
Loading and Saving Files:
LOAD PROGRAM OR FILE:
L [address] Load program.
L address drive sector count
N [[drive:][path]progname [arglist]]
Set the name for the current file/program.
WRITE PROGRAM OR FILE:
W [address] Write the current program/file to disk. Use N to
change the name if you do not wish to overwrite
the original file.
W address drive sector count
Assembling and Disassembling:
A [address] Assemble.
U [range] Unassemble.
M[setting] The current processor (for the purposes of
assembler and disassembler warnings, above) can
be declared to be something else via the following
m0 Declare current processor to be an 8088
m1 Declare 80186
m2 Declare 286
m3 Declare 386
m4 Declare 486
m5 Declare Pentium
m6 Declare Pentium Pro
MC Declare the existence of a math coprocessor.
MNC Declare the absence of a math coprocessor.
MC2 Declare that the math coprocessor is a 287
(only valid if the current processor is a 386)
M? Print currently declared processor type
G [=address] [breakpoints]
Begin execution of the loaded program or the
machine code at the specified address.
Execution is suspended at the breakpoint
addresses, allowing you to inspect memory etc.
P [=address] [count]
Proceed with execution in steps.
R [register [value]]
Display all CPU registers, or display/set a
particular register. Accepts 32-bit register
names (for cpu 80386+).
RN Displays FPU register status (currently for cpu
80386+ only). Just the raw hex values of the
registers are displayed, though.
RX Switches among 8086 and 80386 register display
(for cpu 80386+).
T [=address] [count]
TM [0|1] Set trace command mode, 0=process INTs (default),
1=single-step INTs (the MS-DOS Debug compatible
I port Input from a port
IW port Input from a WORD port
ID port Input from a DWORD port
DWORD values require a 80386+ cpu.
O port value Output to a port
OW port value Output to a WORD port
OD port value Output to a DWORD port.
DWORD values require a 80386+ cpu.
Expanded memory (EMS) commands (only if an EMM v4.0 is present):
XA count Allocate an 'empty' EMS handle with zero pages.
XD handle Deallocate.
XM logical-page physical-page handle
XR handle count Reallocate an EMS handle.
XS Show status.
X? Show help about X commands.
DEBUG uses hexadecimal (base 16). Memory addresses are displayed in
segment:offset form, e.g. 0D00:0100. The last four hexadecimal digits,
which specify the offset from the segment, can go from 0000 to FFFF,
a range of 64 Kilobytes.
Executables with the .com extenstion have all their data and code in
one segment. Hence for .com files, you can usually just write the offset
when specifying memory addresses in DEBUG commands. DEBUG will assume
the program segment. The same is also true of text/binary files that
are < 64K long.
To specify a memory range, seperate two addresses with a comma.
Loading of .HEX files is not implemented in DEBUG.
The assembler and disassembler support all publicly documented
instructions for Intel chips through the Pentium Pro (P6), except for
the MMX instructions. The assembler and disassembler inform you if
any instruction is inappropriate for the current processor.
FPU Opcodes are supported.
Creating a backup of the bootsector (sector number 0 with 512 bytes
=0x200) of drive C: (number 2) to the file BOOT_C.BIN on diskette A:
echo L 100 2 0 1 >BOOT_C.TXT
echo RCX >>BOOT_C.TXT
echo 200 >>BOOT_C.TXT
N BOOT_C.BIN >>BOOT_C.TXT
Looking with DEBUG into the RAM of the graphics card to find some special
characters such as year to identify the card:
S C000:0000,07FF "BIOS"
S C000:0,7FF "(C)"
S c000:0,7ff "199"
s c000:0,7ff "200"
Please read this command's lsm file also.
You will find the updated version (internet) here and
the version described in this manual page here.
The lsm file contains information about the name of the programmer,
the download site, and some other command related information.
Copyright © 2003 Robert Platt, updated 2008 by W. Spiegl.
This file is derived from the FreeDOS Spec Command HOWTO.
See the file H2Cpying for copying conditions.