openwatcom2irc

A fork of Open Watcom v2 that adds a native x86-64 C backend (wcc64) while keeping the original 16-bit and 32-bit compilers intact.

One C front end drives three code generators:

Compiler	Target	Status
wcc	i8086 16-bit real mode	stock upstream, unchanged
wcc386	i386 32-bit	stock upstream, unchanged
wcc64	x86-64 (ELF64)	new in this fork

What works

x86-64 backend (wcc64) — new

wcc64 -bt=linux64 compiles C to x86-64 ELF64 objects. 61/61 runtime tests pass. Coverage includes return values, arithmetic, switch/case, loops, recursion, globals, arrays, structs, function pointers, unions, long long shifts, nested struct arrays, pointer initialisers, multi-file linking, string routines, and 5+ argument functions with intervening calls.

Pointers are 8 bytes. The backend uses a 386 code generator feeding an OMF-to-ELF64 post-processor (x64obj.c) that rewrites i386-incompatible encodings, adds REX prefixes where the frame register requires them, and resolves relocations with a real x86 instruction-length decoder.

Run the suite:

export OWROOT=$(pwd)
tests/x64/run_tests.sh $OWROOT      # 61/61

DOS targets — 16-bit and 32-bit

The stock compilers cover DOS unchanged:

Model	Compiler	Extender
16-bit real mode	wcc	none
32-bit flat	wcc386	DOS/32A (open source, bundled)

16-bit real mode is the target for the BBS software in the related repos (PCBoard, QFront). No extender is used there. DOS/32A is available for any 32-bit flat-model program that needs it.

Real-world validation

As a large real-world test, the compilers build a full 3dfx Glide3x SST-1 driver (~23k lines) from original source. That work — the driver builds, libraries, and DOS test harness — lives in a separate repository, not here, to keep this repo a clean compiler toolchain.

i386 / OS/2 / Win32 — unchanged from upstream

The original 32-bit targets are not modified: DOS, DOS/4G, Pharlap, OS/2 16-/32-bit, and Win32 (OMF to PE32) all behave exactly as pristine upstream. Object output is byte-identical to the unmodified compiler across 80+ comparisons.

Note: 16-bit targets do not run on 64-bit Windows (no NTVDM); use DOSBox.

Quick start

export OWROOT=$(pwd)
export OWTOOLS=GCC OWOBJDIR=binbuild OWTOOLSVER=13
. cmnvars.sh
export PATH="$OWROOT/build/binbuild:$OWROOT/rel/binl64:$PATH"
export WATCOM="$OWROOT/rel"

# x86-64 (freestanding, no libc)
printf 'extern int puts(const char*);\nint main(void){ puts("hello"); return 42; }\n' > hello.c
bwcc64 hello.c -fo=hello.o -i=$WATCOM/h -bt=linux64 -ox -s
ld -o hello bld/clib/linux/x64/crt0_x64.o hello.o
./hello        # prints "hello", exits 42

# 16-bit DOS
printf 'int main(void){ return 42; }\n' > dos.c
wcc dos.c -fo=dos.o -bt=dos -ms

Pre-built tools

rel/binl64/
  wcc       C compiler (16-bit real mode)
  wcc386    C compiler (32-bit)
  wlink     linker
  wasm      assembler
  wlib      librarian
  wsplice   text preprocessor
  wrc       resource compiler
build/binbuild/
  bwcc64    C compiler (x86-64)

Testing

tests/x64/run_tests.sh $OWROOT      # wcc64: 61/61 x86-64 runtime tests
tests/x64/difftest.sh               # gcc oracle vs wcc64, behavioural diff
tests/x64/gapscan.sh                # structural section/relocation diff

difftest.sh runs each case under both gcc and wcc64 and compares exit status and stdout — no hand-written expected values.

Architecture

The x64 path post-processes OMF into ELF64:

1. Front end — -bt=linux64 selects x64 macros and codegen settings.
2. Code generator — the 386 code generator emits OMF, with pointer sizes and frame handling adjusted for the 64-bit ABI.
3. Post-processor (x64obj.c) — reads OMF, length-decodes each instruction, applies REX prefixes and encoding fixups, extracts symbols from PUBDEF/LPUBDEF, resolves relocations, and writes ELF64 with .text/.data/.bss/.rela.text/.rela.data.

The instruction-length decoder is what lets the relocation pass skip whole instructions safely, rather than walking byte-by-byte and mistaking a ModRM or displacement byte for an opcode.

Related repos

Repo	What
verta1878/pcbirc	PCBoard 15.3/15.4 revival (16-bit DOS)
verta1878/fpc264irc	Free Pascal 2.6.4 fork (architecture reference)
verta1878/netmodem2irc	FOSSIL/TCP bridge
verta1878/mystic-bbs-irc	Mystic BBS fork

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the crew 4free — x86 little endian