DOSbox compiled with --enable-debug=heavy option becomes a powerful reversing tool. Anytime I feel like checking the disassembly and memory state I just hit Alt+Pause.

But, what if I want to see the very first instructions of the program ? How do I start the application so that it immediately enters debug mode before even starting execution ?

  • I can't find anything about the debug mode on the wiki page. The only place where I found any info was this post on VOGONS.
    – ScumCoder
    Commented Aug 7, 2014 at 15:30
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    DOSBox may be heavily documented and open source. But, i think "How do i accomplish (X) in (Y)", where (Y) is a reverse engineering tool, is a valid question even if (Y) is heavily documented and open source. Commented Aug 7, 2014 at 15:43
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    @GuntramBlohm: Fair enough; I've retracted my close-vote and my previous comments. Thanks for presenting a reasonable argument. Commented Aug 7, 2014 at 16:54

1 Answer 1


If you build with --enable-debug[=heavy] and run the program via debug.com, it automatically breaks on the first instruction. See the DOS_Execute function in src/dos/dos_execute.cpp and DEBUG_CheckExecuteBreakpoint in src/debug/debug.cpp.

  • 1
    Whoa, thank you SO much. I didn't read your answer in time and out of despair made an ugly patch to the DOSbox source which does exactly the same.
    – ScumCoder
    Commented Aug 10, 2014 at 11:57

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