diasm - simple x86 16-bit real mode instruction subset disassembler, for MS-DOS operating system

diasm is a simple x86 16-bit real mode instruction subset disassembler, for MS-DOS operating system. Written in assembly with tasm compiler, basically proof of concept of writing disassembler in assembly.

• mov all 6 scenarios
• out 2 scenarios
• not 4 scenarios
• rcr 4 scenarios
• xlat 1 scenarios

Actually most interesting aspect of this program is code itself, for example

process_not:
    @PRINT_STR(offset not_str)

    mov w_val, al
    @MASK_VALUE(w_val, 00000001b)

    @RETRIEVE_NEXT_BYTE

    mov rm_val, al
    @MASK_VALUE(rm_val, 00000111b)

    mov mod_val, al
    @MASK_VALUE(mod_val, 11000000b)
    shr mod_val, 3

    @JMP_EQL(mod_val, 00000000b, not_scenario_mod_00)
    @JMP_EQL(mod_val, 00001000b, not_scenario_mod_01)
    @JMP_EQL(mod_val, 00010000b, not_scenario_mod_10)
    @JMP_EQL(mod_val, 00011000b, not_scenario_mod_11)

    not_scenario_mod_00:
        call process_mod_xxx_rm_scenario_00
        jmp not_continue

    // process scenarios 01 - 11, same as 00

    not_continue:

    @PRINT_STR(offset endl_str)

    jmp inst_loop

Note that for an assembly code is pretty readable, now it is very easy to even add support for new instructions.

Main benefit comes from @JMP_EQL(), @MASK_VALUE() and other macros. Tasm itself does not support such macros, these macros are resolved by my own preprocessor link.

Probably no one will build this project, so I will not include or release this preprocessor, if you really need it, just open an issue in this repository.

Sadly this time diasm is a asm framework ?

Cool looking widgets

1. Build manually
   First of all requirements:
   • Dosbox (an x86 emulator with Dos)
   • tasm (Should be installed in Dosbox)
   • tlink (Should be installed in Dosbox)

diasm is free and open source thing. All code in this repository is licensed under

• MIT License (LICENSE.md or https://opensource.org/license/mit/)