FreeDOS help system (hhstndrd 1.0.8 en)[debug]

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.


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.


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? (older versions only): Print currently declared processor type 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. DEBUG will display just the raw hex values of the registers, while DEBUGX will display the values in floating-point format. 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.


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: 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

See also:

(emm386) jemm386 jemmex undelete ------------------------------------------------------------------------------ Copyright (C) 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.