Disassembling an unknown DOS MZ executable using radare2

Question

How do I specify to radare2 that what I'm disassembling when I know it is a DOS MZ executable?

As it does not auto-detect this for me.

Answer 1

You can disassemble a DOS 16-bit executable using radare2 as follows:

Example using TEXTINST.EXE from the FreeDOS 1.1 CDROM image:

bash$ radare2 TEXTINST.EXE
SS : 214f
SP : 4c00
IP : 0
CS : 0
NRELOCS: 1
RELOC  : 1c
CHKSUM : 0
[0000:0020]> aa
[0000:0020]> pd 10
   ;      [0] va=0x00000020 pa=0x00000020 sz=67272 vsz=67272 rwx=-rwx .text
            ;-- section..text:
            0000:0020    b93b03       mov cx, 0x33b
            0000:0023    be7406       mov si, 0x674
            0000:0026    89f7         mov di, si
            0000:0028    1e           push ds
            0000:0029    a9b580       test ax, 0x80b5
        |   0000:002c    8cc8         mov ax, cs
        |   0000:002e    050510       add ax, 0x1005
        |   0000:0031    8ed8         mov ds, ax
        |   0000:0033    05f010       add ax, 0x10f0
        |   0000:0036    8ec0         mov es, ax
(etc)

If required, you can force the disassembler, etc. to assume DOS as follows:

e asm.arch=x86
e asm.os=dos

If you think you have a DOS executable and the above doesn't work, there may be something more subtle going on, and you should post a question showing specifically what you tried, what you expect and what is not working.

Note: showing what you tried, etc. is more likely to elicit answers on the SE sites...