# Command: debug

      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.

## Syntax:

      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.

#### [Main menu] [top] (Syntax) [Options] [Comments] [Examples] [See also] [File]

## Options:

      Q                     Quit
      ?                     Help

      Inspecting and Editing Memory:
        COMPARE:
          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.
                            For instance:
                              C 100,110 200
                            will compare the range 100,110 to 200,210.
        DUMP:
          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.
        ENTER:
          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.
                            For instance:
                              E 100 "Hello!"
        FILL:
          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"
        MOVE:
          M sourcerange destaddress
                            Copies the range sourcerange into another range
                            that begins at destaddress.
        SEARCH:
          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:
        HEX
          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
                            Load sectors.
        SET NAME:
          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
                            Write sectors.

      Assembling and Disassembling:
        ASSEMBLE:
          A [address]       Assemble.
        UNASSEMBLE:
          U [range]         Unassemble.
        80x86 MODE:
          M[setting]        The current processor (for the purposes of
                            assembler and disassembler warnings, above) can
                            be declared to be something else via the following
                            commands:
                              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

      Program Execution:
        GO:
          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.
        PROCEED:
          P [=address] [count]
                            Proceed with execution in steps.
        REGISTER:
          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+).
        TRACE:
          T [=address] [count]
                            Trace
          TM [0|1]          Set trace command mode, 0=process INTs (default),
                            1=single-step INTs (the MS-DOS Debug compatible
                            mode).

      Port I/O:
        INPUT:
          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.
        OUTPUT:
          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
                            Map memory.
        XR handle count     Reallocate an EMS handle.
        XS                  Show status.
        X?                  Show help about X commands.

#### [Main menu] [top] [Syntax] (Options) [Comments] [Examples] [See also] [File]

## Comments:

      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.

#### [Main menu] [top] [Syntax] [Options] (Comments) [Examples] [See also] [File]

## Examples:

      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:
        A:
        cd \
        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
        W                >>BOOT_C.TXT
        Q                >>BOOT_C.TXT
        DEBUG <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:
        DEBUG
        S C000:0000,07FF "BIOS"
        S C000:0,7FF     "(C)"
        S c000:0,7ff     "199"
        s c000:0,7ff     "200"
        D C000:0000,100
        Q

#### [Main menu] [top] [Syntax] [Options] [Comments] (Examples) [See also] [File]

## See also:

      emm386
      jemm386
      undelete

#### [Main menu] [top] [Syntax] [Options] [Comments] [Examples] (See also) [File]

## File:

      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.

#### [Main menu] [top] [Syntax] [Options] [Comments] [Examples] [See also] (File)

      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.