MoBetta

Custom Wine engine for running World of Warcraft 3.3.5a (WotLK) on Apple Silicon Macs. It might work for other old 32-bit games too, but only 3.3.5a has been tested (see Requirements).

The Problem

WoW 3.3.5a crashes at character select when running under Wine on Apple Silicon:

ERROR #132 (0x85100084) Fatal Exception
Exception: 0xC000001D (ILLEGAL_INSTRUCTION)

This affects all old WoW clients (1.12, 2.4.3, 3.3.5a) because Rosetta 2 doesn't implement certain legacy x86 instructions.

The Solution

MoBetta is a Wineskin engine. Everything happens inside Wine:

• The crash: Wine's signal handler emulates the instructions Rosetta 2 rejects (ARPL and nine undocumented x87 opcodes), exactly as real x86 hardware runs them
• The frame rate: game processes start under x87sidecar, which makes Rosetta translate the game's x87 floating point to native ARM code instead of a slow software path. 20 FPS -> 80 FPS average (106 max)
• Graphics buffers: Wine's OpenGL keeps the low-memory view of a graphics buffer between maps instead of rebuilding it every time. Up to ~20% more FPS, 127 max
• DEP stays on under Rosetta, as on Windows
• Direct3D 9 on Metal: our build of mtld3d, without the hooks its release puts into the game's memory, with HDR off and its logs kept out of the game folder. ~140 FPS at the inn (was 60-80), ~170 in a light view

Key constraint: No game file modifications, nothing injected into the game process. This engine is designed for use with servers that run anti-cheat systems. A SHA-256 baseline of the game folder is checked before and after every test.

Why MoBetta

Other tools already run 3.3.5a on Apple Silicon. The best known, WoWSilicon, is a full launcher for 1.12, 2.4.3 and 3.3.5a with addon and mod managers. It gets there by patching the game folder: for a 3.3.5a client it adds d3d9.dll, mtld3d.conf, libDllLdr.dll, mods/winerosetta.dll and mods/libSiliconPatch.dll, lists them in dlls.txt, and patches the game's own DivxDecoder.dll so those DLLs load into the game (WoWSilicon's PatchService.swift, October 2026).

MoBetta is for players who want the client left exactly as Blizzard shipped it:

• The game folder is untouched. No files added, none patched. A SHA-256 of every file in the game folder is checked before and after each test
• Nothing is added to the game process. No extra DLLs, no DLL loader, no hooks or patches in the game's code. The crash fix lives in Wine's own exception handling, and Direct3D is the engine's own d3d9, in place of Wine's
• It's an engine, not a launcher. Your Porting Kit or Wineskin wrapper switches to it in a few clicks, and switching back undoes it
• Open and reproducible. Built from pinned sources; build_engine.sh rebuilds the release byte for byte

MoBetta can't promise how any server's rules or anti-cheat treat a Mac client. What it does promise is an unmodified client. If you'd rather have an all-in-one launcher with addon management and several game versions, WoWSilicon is a good choice; both build on x87sidecar and mtld3d.

Performance

In game with the v1.0.0 engine on a MacBook M3, windowed, medium-high graphics settings, FPS from the in-game counter (Ctrl+R). Shattrath and Booty Bay in the rain run lowest.

Place	FPS
Loch Modan, Valley of Kings (Ironforge gate)	191
Stormwind, Trade District	155
Duskwood	149
Orgrimmar, Valley of Strength	138
Durotar, zeppelin tower	135
Howling Fjord, Kamagua	135
Booty Bay, rain	97
Shattrath City	86

Loch Modan, 191 FPS	Stormwind, 155 FPS
Duskwood, 149 FPS	Orgrimmar, 138 FPS
Durotar, 135 FPS	Howling Fjord, 135 FPS
Booty Bay, 97 FPS	Shattrath City, 86 FPS

Chat and character names are blurred in the screenshots.

Status

• Phase 1: Confirm faulting instructions
• Phase 2: Reproducible engine build
• Phase 3: Instruction emulation (in game: past character select, playing in the world)
• Phase 3b: Performance (20 -> 80 FPS average, 30+ minute sessions; buffer mapping up to ~20% more)
• Engine package WS12WineCX26.3_Mobetta
• mtld3d (Direct3D 9 on Metal) in the engine package (~140 FPS at the inn)
• One build script for the whole engine, reproducible from any directory
• Release: download, install guide, checksums
• Phase 4: Wider testing

See CHANGELOG.md for details.

Requirements

• Mac: Apple Silicon (M1 or later) with Rosetta 2 installed
• Porting Kit or Wineskin installed: Porting Kit or Wineskin Winery, with a wrapper (port) for the game already set up and working
• Game: WoW 3.3.5a (build 12340)
• Other games: untested. Nothing in the engine is specific to WoW: the instruction emulation and x87sidecar apply to any 32-bit Windows program, and mtld3d to any Direct3D 9 game. It might work for other old games, including WoW 1.12 and 2.4.3, but only 3.3.5a has been tested
• Tested on: MacBook M3, macOS 27
• Base: CrossOver 26.3 Wine (Porting Kit's engine WS12WineCX26.3_DXMT)

Installing

Setting up a new Porting Kit port for the game? Follow the Porting Kit guide with screenshots. For a wrapper you already have:

1. Download WS12WineCX26.3_Mobetta.tar.7z and SHA256SUMS from the latest release
2. Check the download. In Terminal, in the folder you saved both files to:

   shasum -a 256 -c SHA256SUMS      # must print: WS12WineCX26.3_Mobetta.tar.7z: OK

3. Move WS12WineCX26.3_Mobetta.tar.7z into ~/Library/Application Support/Wineskin/Engines/ (in Finder: Go > Go to Folder..., paste the path). This folder comes from Porting Kit or Wineskin Winery, so one of them must be installed first (see Requirements); create the Engines folder if it isn't there. Leave the file packed, as the other engines there are. Library is a hidden folder: if you browse to it in Finder, press Shift + Cmd + . (period) to show hidden folders.
4. Switch the game's wrapper to the engine:
   • Quit the game. In Finder, right-click the game's wrapper app, Show Package Contents, open Contents/Wineskin.app
   • Advanced > Tools > Change Engine Used, pick WS12WineCX26.3_Mobetta, OK
   • With Wineskin Winery you can also pick the engine when you create a new wrapper
5. Start the game as usual. The first start on this engine updates the wrapper's Wine prefix once, as after any engine change

To go back, change the engine to the one the wrapper had before (for a Porting Kit port, usually WS12WineCX26.3_DXMT).

mtld3d writes its log to drive_c/users/<user>/AppData/Local/mtld3d-logs/ in the prefix.

Building

The release engine can be rebuilt from source and compared with the download. Requires Xcode Command Line Tools, Homebrew (bison, cmake, sevenzip, gh, logged in), rustup (stable, targets i686-pc-windows-msvc and x86_64-apple-darwin, llvm-tools) with cargo install --locked xwin, plus the stock engine WS12WineCX26.3_DXMT.tar.7z (SHA-256 7b3f383a2209de5765eef45f1d6fc316682cfcfbb3518d7470e4b51f00e7cd08) in Wineskin's Engines folder. Porting Kit downloads it there when a port is set up with that engine.

bash scripts/build_engine.sh       # -> build/engine/WS12WineCX26.3_Mobetta.tar.7z

It downloads the sources (each pinned by hash or commit), builds Wine's ntdll.so and opengl32.so with patches/ applied, x87sidecar and mtld3d, packages the engine, and checks it against the release SHA-256 in SHA256SUMS. The build gives the same bytes in any directory. The steps also run on their own: build_opengl32.sh, build_x87sidecar.sh, build_mtld3d.sh, package_engine.sh. mtld3d always builds in /private/tmp/mobetta-mtld3d, because its output depends on the build path; on a Mac with several users, only one of them can build there at a time.

Tests

bash scripts/test_emu.sh           # instruction emulation, 4153 checks
bash scripts/test_dep.sh --wine    # DEP patch
bash scripts/test_x87.sh           # x87sidecar start-up and speed
bash scripts/baseline.sh verify    # game folder unchanged

References

• Whisky Issue #537 - WoW crashes on Apple Silicon
• Wine Bug 56441 - FNDISI patch precedent
• x87sidecar - x87 acceleration for Rosetta 2 (MIT), shipped in the engine
• athei/wine - source of the DEP and x87sidecar ntdll patches we ported
• mtld3d - Direct3D 9 on Metal (Zlib), shipped in the engine; we build it without the import-table hooks its release installs (scripts/build_mtld3d.sh, patches/mtld3d/)
• Endfield_FineWine - CrossOver patching example

License

MoBetta (patches, scripts and docs) is licensed under the GNU Lesser General Public License, version 2.1 or later, the same as Wine; see LICENSE.

The engine package contains:

Part	License	Source
Wine (CrossOver 26.3.0), with patches/ in ntdll.so and opengl32.so	LGPL 2.1 or later (share/doc/wine/COPYING.LIB)	crossover-sources-26.3.0.tar.gz + patches/
mtld3d v0.15.1, with patches/mtld3d/	Zlib (share/doc/mtld3d/LICENSE)	athei/mtld3d + patches/mtld3d/
x87sidecar	MIT (share/doc/x87sidecar/LICENSE)	athei/x87sidecar

share/doc/mobetta/SOURCE in the engine lists what changed from the stock engine and the exact source versions. Every other file is Porting Kit's stock WS12WineCX26.3_DXMT, unchanged.

Disclaimer

This project is not affiliated with Blizzard Entertainment, any private server, or CodeWeavers. Use at your own risk.