Masm2c

Masm2c is a 16-bit assembly to C translator that can be used to port DOS x86 assembler code to C and SDL. It is a Source-to-source translator that generates fake-assembler instructions which can be compiled with a C compiler and executed. To convert your masm source to C, you can use the masm2c.py command. Masm2c also has scripts that can help convert DOSBOX run-time traces into IDA annotations to simplify disassembly.

(Since there is no working decompiler for 16 bit DOS code yet. Because of DOS segmentation model, etc) 32 bit is partially supported.

It can make IDA Pro output assembler listing to be recompilable by exeting on instrumented emulator and compare each instruciton with emulation libdosbox.

etc

The following assembler example:

_DATA   segment use16 word public 'DATA'
_msg    db 'Hello World!',10,13,'$'

_DATA   ends

_TEXT   segment use16 word public 'CODE'
  assume  cs:_TEXT,ds:_DATA
start proc near

sti                             ; Set The Interrupt Flag
cld                             ; Clear The Direction Flag
push _data
pop ds
mov ah,9                        ; AH=09h - Print DOS Message
mov dx,offset _msg             ; DS:EDX -> $ Terminated String
int 21h                         ; DOS INT 21h

mov ax,4c00h                    ; AH=4Ch - Exit To DOS
int 21h                       ; DOS INT 21h
start endp

_TEXT   ends
end start

Converts to a compilable and working C++ code:

start:
    R(STI); // 12 sti
    R(CLD); // 13 cld
    R(PUSH(seg_offset(_data))); // 14 push _data
    R(POP(ds)); // 15 pop ds
    R(ah = 9;); // 16 mov ah,9
    R(dx = offset(_data,_msg););    // 17 mov dx,offset _msg
    R(_INT(0x21));  // 18 int 21h
    R(ax = 0x4c00;);    // 20 mov ax,4c00h
    R(_INT(0x21));  // 21 int 21h

struct Memory m = {
{0}, // padding
{0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}, // segment _data
{'H','e','l','l','o',' ','W','o','r','l','d','!','\n','\r','$'}, // _msg
...

Optionally you can compile output of masm2c (C code) for 32 bit plarform with optimization and decompile to get cleaner C code without dead code like x86 flags update.

Key features:

• 386 instructions (except FPU) are supported (well tested with QEMU tests). x86 flags: Carry, Zero, Sign, Overflow are supported

• Segment memory model and 16bit offsets

• Internal SDL target: some BIOS/DOS Int 10h, 21h interrupts, DOS memory manager, and stack emulation CGA text mode is supported using Curses (PDcurses or NCurses). VGA 320x200x256 support (partial)

• Libdosbox target: Full interrupts, hardware support.

• structures support

• parser is based on Masm EBNF grammar

• segment can be merged same as Masm do it during linking: Many .asm sources can be converted individually and linked together using modern linker

(3rd-party code used from: ASM2C (x86 instruction emulation), tasm-recover (from SCUMMVM project; highly modified), QEMU x86 instructions test suit, FreeDOS memory manager.)

License: GPL2+

TODO:

• full macros support

• add FPU instructions support (may use linux 387 emulator)

For easier disassembling (exe to asm) you may need to collect run-time information from dosbox or other emulator to annotate IDA disassembly. Maybe modify dosbox debugger tracing mechanism to collect: - current instruction is code - access to memory (offset of which segment) - segment register values In other repo there are scripts which can help to convert DOSBOX run-time traces into IDA annotations to simplify disassembly.

Assembler source code for Stunts game https://github.com/xor2003/restunts

Assembler source code for Tornado flight sim https://github.com/xor2003/tornado-dos-flightsim

See list of DOS games with debug information http://bringerp.free.fr/forum/viewtopic.php?f=1&t=128

How to convert your masm 16 bit source to C++

Prerequisite: your code should be compilable with uasm(jwasm)/masm6, link5/tlink and work under DOS.

You need at least Python 3.9

pip install -r requirements.txt
masm2c.py <some.asm>

(Small source code modification might also be required to translate)

IDA Pro Free you can find here https://www.scummvm.org/news/20180331/

Inertia Player 1.22 source code

Famous reverse engenerred MOD, S3M player. Currently platform DOS (ASM), SDL2 © There is disassembled source code for MASM, Nasm, C which can be built and running

TODO: finish sound support on SDL, finish porting (keyboard, graphics mode,...)

Building Inertia for SDL from source:

1. get PDCurses or other curses library+headers, SDL2, mingw32 + a lot of luck

2. build_mingw.bat

3. execute: iplay_m_.exe HACKER4.S3M

Or just get prebuilt from release page

If you want to help me please contribute or send BTC to:

BTC: bc1qyaxs8dqn7mglp9w9zyvkfpz888x3aknr0jnsmx