Open Watcom Assembler or WASM is an x86 assembler produced by Watcom and included as part of the Watcom C/C++ compiler. Further development is being done on the 32- and 64-bit JWASM project, which more closely matches the syntax of Microsoft's assembler.
There are experimental assemblers for PowerPC, Alpha AXP, and MIPS.
Technical details 
- Native support for output formats Intel OMF output formats
- Supports Intel x86 (Pentium MMX, Pentium III-4, 3DNow!, SSE and SSE2) instruction sets.
- Supports Microsoft macro assembler (MASM) 5 and 6 syntax (incomplete).
There is an associated Watcom disassembler, wdis. The assembler does not have listing facilities; instead the use of wdis for generating listings is recommended. wdis can read OMF, COFF and ELF object files and PE and ELF executables. It supports 16-bit and 32-bit x86 instruction set including MMX, 3DNow!, SSE, SSE2, and SSE3. Support for PowerPC, Alpha AXP, MIPS, and SPARC V8 instruction sets is also built in.
It is a fork of Wasm by Japheth with following features:
- Native support for output formats Intel OMF (16/32-bit), MS Coff (32-bit and 64-bit), Elf (32-bit and 64-bit), Bin and DOS MZ.
- Precompiled JWasm binaries are available for DOS, Windows and Linux. For OS/2 and FreeBSD, makefiles are supplied.
- Supports Intel x86 (8086, 80186, 80286, 80386, 80486, Pentium, Pentium Pro), x86-64 instruction sets with SIMD (MMX, 3DNow!, SSE, SSE2, SSE3 and SSSE3, SSE4.1/2 (since Jwasm), AVX (since JWasm 2.06), VMX (Intel VT-x; AMD SVM, the latter though already implemented, currently still inactive) extensions (since JWasm 2.09)).
- JWasm is written in C. The source is portable and has successfully been tested with Open Watcom, MS VC, GCC and more.
- On Windows, JWasm can be used with both Win32Inc and Masm32. Since v2.01, it will also work with Sven B. Schreiber's SBS WALK32 Win32 Assembly Language Kit
- C header files can be converted to include files for JWasm with Japheth's own dedicated h2incX.
- JWasm's source code is released under the Sybase Open Watcom Public License, which allows free commercial and non-commercial use.
- Fully supports Microsoft macro assembler 6 syntax, all MASM 8 instructions sets.
- ^ Randall Hyde. "WASM: The Open Watcom Assembler". Retrieved 2010-02-02.
- ^ Leiterman, James (2005). "MASM vs. NASM vs. TASM vs. WASM". 32/64-bit 80x86 assembly language architecture. Wordware Publishing, Inc. p. 481. ISBN 978-1-59822-002-5. Retrieved 2010-02-01.
- ^ JWASM project page
- ^ Fog, Agner (2009), Optimizing subroutines in assembly language (2009-09-26 ed.), p. 13
- ^ a b Open Watcom website: Assembler
- ^ OpenWatcom: "No listing files are generated [by the assembler]. Producing full listings may be a waste of effort because wdis (the Open Watcom disassembler) does a very good job. However, it could be extremely helpful to produce a dump of the internal symbol table the way MASM does, especially for diagnostic purposes."
- ^ Open Watcom website: Disassembler
- ^ The 1996 "WALK32 consists of the following main components:
- A full-featured PE (Portable Executable) file linker called W32Link.
- A main include file, containing Win32 constant, type, and structure definitions.
- Another include file, containing the application and DLL startup source code.
- Segment and PE section management macros.
- Macros related to Unicode support.
- Several demo applications and DLL’s.
- A collection of programming utilities for various purposes." walk32.doc in walk32_1.zip
External links 
- wasm at openwatcom.com
- JWASM, a 32/64 bit assembler based on WASM with syntax similar to MASM.