MSA2 x86 assembler for real-mode DOS

 ooo        ooooo  .oooooo..o       .o.         .oooo.
 `88.       .888' d8P'    `Y8      .888.      .dP""Y88b
  888b     d'888  Y88bo.          .8"888.           ]8P'
  8 Y88. .P  888   `"Y8888o.     .8' `888.        .d8P'
  8  `888'   888       `"Y88b   .88ooo8888.     .dP'
  8    Y     888  oo     .d8P  .8'     `888.  .oP     .o
 o8o        o888o 8""88888P'  o88o     o8888o 8888888888

MSA2 is a old and free 8086 two-pass assembler for DOS targets. It targets the Intel 8086 instruction set. A handful of 186/286-era mnemonics inherited from the original codebase (PUSHA, POPA, ENTER, LEAVE, BOUND) are also accepted; no further 186+ extensions are planned.

Initialy written by a 14-year old Swedish programmer Robert Ostling (in 2000-2001) in Borland C++ 2.0. Now, MSA2 is ported to Watcom C and GCC (and/or mingw).

MSA2 Consume to small piece of memory - i think, will be enougth just 128K. MSA2 does not require DPMI.

MSA2 is pretty fast and the only file you'll need to build a program is MSA2.EXE (50 KB). It runs fine on my old 286.

I had not test MSA2 in FreeDOS, Linux, windows yet, but there should not be any difference where running MSA2.

To compile your source with MSA2 just type:

MSA2 coolprog.asm -o coolprog.com

Output formats

MSA2 produces next formats:

• -f bin flat binary output
• -f com .com file
• -f texe .exe file with tiny memory model
• -f rdf RDOFF2 relocatable object file (NASM-compatible -f rdf), with relocations, exported globals and BSS.

The -f rdf target supports a SECTION (or SEGMENT) directive switching between .text, .data and .bss. Use RESB, RESW, RESD inside .bss to reserve uninitialised storage; use DB, DW, DD in .data for initialised storage. See original/doc/rdoff2-spec.md for the file format.

Preprocessor

NASM-style directives:

• %define NAME body — single-line text alias for use in operands.
• %undef NAME — remove a previously-defined alias.
• %macro NAME N ... %endmacro — multi-line block macros with up to 9 positional args (%1..%9) and per-invocation labels (%%name).
• %include "file.asm" — inline another source file. Nestable up to 8 levels deep; diagnostics inside an included file point at the included file and its line, not the parent.

Storage is unbounded (linked lists) — no compile-time cap on macro count, define count, or include depth besides the explicit limits above. See original/doc/DOC.TXT for the full reference.

Differences with MSA

• Added missed opcodes
• Added .exe generation
• Added .rdf generation
• Added macros
• Added defines
• Added including file

Differences with NASM

• Limited macros / defines
• No conditional jumps optimization (near/short)

Build MSA2

MSA2 could be compiled for DOS, Linux and windows with Open Watcom C, GCC, GCC/MINGW.

DOS

To build DOS version with Watcom C, just type (in original/src/)

cd original\src
make

or

cd original\src
wmake

Linux / macOS (POSIX)

A separate POSIX GNU-make file is provided so it does not collide with the Watcom MAKEFILE (both file names are DOS 8.3-compliant):

cd original/src
make -f MAKEGNU.MAK          # build the msa2 binary
make -f MAKEGNU.MAK test     # build and run the C89 unit tests

windows

To build win32 version with mingw:

i686-w64-mingw32-gcc -m32 -O3 -funsigned-char MSA.C TABLES.C ASSEMBLR.C MISC.C LEX.C EXPR.C RDF.C -o MSA2W.EXE
strip MSA2W.EXE

License

This is free software: you can redistribute it and/or modify it under the terms of the MIT license. See LICENSE file.