Open Watcom Assembler Explained

Author:	Open Watcom Assembler
Operating System:	DOS for x86-based PCs, Microsoft Windows, Linux for x86-based PCs, OS/2 for x86-based PCs, FreeBSD for x86-based PCs.

Open Watcom Assembler or WASM is an x86 assembler produced by Watcom, based on the Watcom Assembler found in Watcom C/C++ compiler and Watcom FORTRAN 77.^[1] ^[2] ^[3] Further development is being done on the 32- and 64-bit JWASM project,^[4] which more closely matches the syntax of Microsoft's assembler.

There are experimental assemblers for PowerPC, Alpha AXP, and MIPS.

Technical details

Assembler

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).^[5]

Disassembler

There is an associated Watcom disassembler, wdis. The assembler does not have listing facilities; instead the use of wdis for generating listings is recommended.^[6] 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.^[7]

WASM forks

JWasm

JWasm is a fork of Wasm originated 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^[8]
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.

Japheth ceased development (or rather, was out of contact) of JWASM in January 2014 with version 2.12pre, but others on the Masm32 forum^[9] picked up where Japheth left off.

HJWasm

HJWasm, adding the prefix H in reference to Masm32 forum member Habran who started off this second WASM development continuation. Version 2.13pre was originally announced in 2016.^[10] New features include:

Instructions:

SIMD:

MOVQ and added in 2.13, to supplement MOVD.

AVX2

VGATHERDPD, VGATHERQPD, VGATHERDPS, VGATHERQPS, VPGATHERDD, VPGATHERQD, VPGATHERDQ, VPGATHERQQ, VEX-encoded general purpose instructions added in 2.13. Remaining instructions added in 2.16.

AVX-512

VCMPxxPD, VCMPxxPS, VCMPxxSD, VCMPxxPD, VCMPxxSS, AVX-512F set, EVEX-encoded instructions added in 2.13; VMOVQ added 2.13, to supplement MOVD. Remaining instructions added in 2.16.

Random Number Generator: RDRAND, RDSEED added in 2.13.

half-precision conversions: F16C(VCVTPH2PS, VCVTPS2PH) added in 2.13.

Intel MPX

Added in 2.31.

Registers: RIP, ZMM registers added in 2.13.
OO language extension added in 2.25.

HASM

HASM is a renamed version of HJWASM, starting in version 2.33. The name was used following a MASM Forum discussion thread that originally proposed a replacement name. The name HASM was proposed by forum member habran in Reply #6,^[11] and was finalized at the end of discussion thread at Reply #33.^[12] No known features are added in HASM's release cycle.

UASM

The name was actually used in version 2.33 (dated 2017-05-20) at Terraspace ltd's product page,^[13] but it was only announced in version 2.34.^[14] Changes to HJWASM includes:^[15]