The DEBUG utility is useful for editing binary files in an environment where only DOS is installed without anything else. This method can be used to create or edit binary files from batch files. ĭEBUG can also be used as a 'DEBUG script' interpreter using the following syntax.Ī script file may contain DEBUG subcommands and assembly language instructions. The user can then enter one of several one or two-letter subcommands, including 'A' to enter the assembler mode, 'D' to perform a hexadecimal dump, 'T' to trace and 'U' to unassemble (disassemble) a program in memory. When DEBUG is started without any parameters the DEBUG prompt, a '-' appears. Andreas 'Japheth' Grech, the author of the HX DOS extender, developed enhanced DEBUG versions 0.98 to 1.25, and former PC DOS developer Vernon C. Ī 32-bit clone 'DEBUGX' version supporting 32-bit DPMI programs exists as well. The FreeDOS version of DEBUG was developed by Paul Vojta and is licensed under the MIT License. Some versions also utilized DPMS to function as a 'stealth mode' protected-mode debugger.

It is fully compatible with the DEBUG command line syntax of MS-DOS/PC DOS, but offers many enhancements, including supporting 16-bit and 32-bit opcodes up to the Pentium, an extended mode (/X) with dozens of additional commands and sub-modes, a much enhanced command line syntax with user-definable macros and symbolic debugging facilities with named registers, loaded symbol tables, mathematical operations and base conversions, as well as a commenting disassembler. When the 'N' subcommand for naming files is used, the filename is stored from offset DS:5D to DS:67 (the Program Segment Prefix File Control Block area), meaning that the program can only save files in FAT 8.3 filename format.Įnhanced DEBUG packages include the DEBUG command in Novell DOS 7, OpenDOS 7.01 and DR-DOS 7.02 and higher, a reimplementation of Digital Research's former Symbolic Instruction Debugger SID/SID86, which came with former versions of DR DOS.It can only access 16-bit registers and not 32-bit extended registers.In assembly/disassembly modes it only supports 8086 opcodes.The MS-DOS/PC DOS DEBUG has several limitations: The 16-bit DOS commands are not available on 64-bit editions of Windows. Windows XP and later versions included DEBUG for the MS-DOS subsystem to maintain MS-DOS compatibility. Originally named DEBUG.COM, the executable was renamed into DEBUG.EXE with MS-DOS 3.2. DEBUG was part of DOS 1.00 and has been included in MS-DOS/ PC DOS and certain versions of Microsoft Windows. When Paterson began working for Microsoft in the early 1980s he brought the program with him. DEBUG was originally written by Tim Paterson to serve this purpose in 86-DOS. Traditionally, all computers and operating systems have included a maintenance function, used to determine whether a program is working correctly. The Microsoft Windows 95 DEBUG.EXE command Overview DEBUG.COM (among other commands) in IBM PC DOS 1.0. It also has several subcommands which are used to access specific disk sectors, I/O ports and memory addresses. The line-oriented debugger DEBUG.EXE is an external command in operating systems such as DOS, OS/2 and Windows (only in 16-bit/32-bit versions ).ĭEBUG can act as an assembler, disassembler, or hex dump program allowing users to interactively examine memory contents (in assembly language, hexadecimal or ASCII), make changes, and selectively execute COM, EXE and other file types. Reg_ebx= 0x7c00 //Real code probably uses bx to load the imageīut when I run the boot command, it doesn't stop.Microsoft, IBM, Digital Research, Novell, Caldera Void DEBUG_AddBreakpoint(Bit16u seg, Bit32u off, bool once)ĬBreakpoint::AddBreakpoint(seg, off, once) I've found the '' code in dos_programs.cpp, and I've found the debugger stuff in debug.cpp. I would like to add an option to the BOOT command (-D maybe?), that would break at 0000:7C00.

Being a booter like it is, that means that the boot sector is loaded into 0000:7C00, and jumped to.

I have an image of the original boot disk (Booter as you guys call it), and it runs under DOSBox. I'm an old school DOS games cracker, and throughout my career one thing that I always heard was 'But did you ever crack Pirates!'? And the answer was always 'No'.

Dosbox debugger bootcom