Library forwarding is a FEX feature that allows redirecting calls to common libraries OpenGL or Vulkan from their emulated x86 builds to their native ARM64 counterparts installed on the host system. This saves emulation overhead and dramatically improves performance for some applications.

Build instructions

Install the dependencies below and enable the BUILD_THUNKS CMake option:

cmake -DBUILD_THUNKS=True .

If your distribution is not listed below, there is a generic fallback that requires Nix or a compatible alternative.

Ubuntu dependencies

g++-x86-64-linux-gnu (For building thunks)
pkg-config
libclang-dev
libssl-dev
Development packages for thunked libraries:
- libdrm-dev
- libxcb-present-dev
- libxcb-dri2-0-dev
- libxcb-dri3-dev
- libxcb-glx0-dev
- libxcb-shm0-dev
- libxshmfence-dev

Fedora dependencies

libXext-devel
libXfixes-devel
libXrender-devel
libXrandr-devel
alsa-lib-devel
libxcb-devel
libxshmfence-devel
libdrm-devel
xorg-x11-server-devel

Generic Nix fallback

With Nix installed, run ../Data/nix/cmake_enable_libfwd.sh from your build folder. This will set up a cross-compiler, install the required dependencies, and enable the required CMake option.

Configuration

FEXConfig can be used to enable/disable individual libraries.

Per-app overrides

Filename in $HOME/.fex-emu/AppConfig/Balatro.exe.json
Change the filename as necessary for your application

 {
   "ThunksDB": {
     "GL": 1,
     "Vulkan": 1
   }
 }

Advanced configuration

FEX environment variables and command-line arguments

FEX_THUNKHOSTLIBS, -t <Thunk Host Libs Path>, --thunkhostlibs=<Thunk Host Libs path>, JSON: ThunkHostLibs:<Path>
- Folder to find the host-side thunking libraries.
- FEX by default installs these files to: /usr/lib/fex-emu/HostThunks/
FEX_THUNKGUESTLIBS, -j <Thunk Host Libs Path>, --thunkguestlibs=<Thunk Host Libs path>, JSON: ThunkGuestLibs:<Path>
- Folder to find the guest-side thunking libraries.
- FEX by default installs these files to: /usr/share/fex-emu/GuestThunks/
FEX_THUNKCONFIG, -k <Thunk Config json path>, --thunkconfig=<Thunk Config json path>, JSON: ThunkConfig:<Path>
- A json file specifying where to overlay the thunks.
- If the filename isn't a path then FEX will search for the file in $HOME/.fex-emu/ThunkConfigs/

Overriding paths for library wrappers

You can can set the three configuration options to custom paths

The user can likely set ThunkHostLibs and ThunkGuestLibs to the global install path
- Unless these are set in the ThunkConfig file, these will be unused
- Overriding these to another location is useful for application specific hacks if necessary

ThunksDB.json schema

FEX provides a ThunksDB.json file which allows the user to describe a thunk mapping. $prefix/share/fex-emu/ThunksDB.json. Normally this does not need to be modified, but an overlay to the default database can be provided at $HOME/.fex-emu/ThunksDB.json.

Example:

 {
     "DB": {
       "<User Defined Name>": {
         "Library": "<Guest Library Name>.so",
         "Depends": [
           "<Other User Defined Name>"
         ],
         "Overlay": [
           "<System Library Path to library>"
         ]
       }
     }
 }

Development:Setting up Library Forwarding

Contents