Latest revision as of 10:05, 14 July 2025

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>"
         ]
       }
     }
 }

@@ Line 1: / Line 1: @@
+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 =
-== Build dependencies ==
+Install the dependencies below and enable the <code>BUILD_THUNKS</code> CMake option:
+* <code>cmake -DBUILD_THUNKS=True .</code>
+If your distribution is not listed below, there is a generic fallback that requires Nix or a [https://lix.systems/install/#on-any-other-linuxmacos-system compatible alternative].
+=== Ubuntu dependencies ===
 * g++-x86-64-linux-gnu (For building thunks)
 * pkg-config
@@ Line 23: / Line 31: @@
 * libxshmfence-devel
 * libdrm-devel
+* xorg-x11-server-devel
-== Setting CMake to build thunks ==
+=== Generic Nix fallback ===
-Pass in to CMake the option to enable thunk building.
-* -DBUILD_THUNKS=True
+With Nix installed, run <code>../Data/nix/cmake_enable_libfwd.sh</code> from your build folder. This will set up a cross-compiler, install the required dependencies, and enable the required CMake option.
 = Configuration =
-== FEX thunk options ==
+FEXConfig can be used to enable/disable individual libraries.
+=== Per-app overrides ===
+* Filename in '''$HOME/.fex-emu/AppConfig/Balatro.exe.json'''
+* Change the filename as necessary for your application
+  {
+    "ThunksDB": {
+      "GL": 1,
+      "Vulkan": 1
+    }
+  }
+= Advanced configuration =
+=== FEX environment variables and command-line arguments ===
 * FEX_THUNKHOSTLIBS, -t <Thunk Host Libs Path>, --thunkhostlibs=<Thunk Host Libs path>, JSON: '''ThunkHostLibs:<Path>'''
 ** Folder to find the host-side thunking libraries.
@@ Line 40: / Line 64: @@
 ** If the filename isn't a path then FEX will search for the file in '''$HOME/.fex-emu/ThunkConfigs/'''
-== How to use Thunks ==
+===Overriding paths for library wrappers ===
-Once Thunks are built and installed then you can can set the three configuration options to the correct paths
+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
-* Setting the global application profile for '''ThunkConfig''' is useful for testing but not recommended for long term use
-** Due to the unstable nature of thunks, it is recommended to use application specific profiles to enable thunks
-** This allows the user to test applications first using the global config, then once confirmed it works, generating an application profile
-** Recommended to reduce the application profile to the minimum set of options. FEXConfig will save a full config.
-== Thunks Database format ==
-FEX provides a ThunksDB.json file which allows the user to describe a thunk mapping. '''$prefix/share/fex-emu/ThunksDB.json'''
-The user can also provide a '''$HOME/.fex-emu/ThunksDB.json''' which will overlay the system installed path
-This allows the user to configure the thunk file mapping once, since it is unlikely to change between applications. The user can also mix and match ThunksDB and regular thunks configuration if a complex configuration is 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'''.
-* ThunksDB.json example
+Example:
    {
        "DB": {
@@ Line 73: / Line 89: @@
    }
-Look at the FEX provided library for a real implementation, or just use the provided configuration.
-Once the user has a viable ThunksDB provided, now configure FEX with a ThunkConfig filepath with the application thunk configuration.
-This thunks configuration file can now enable Thunk definitions using the user defined names.
-* ThunkConfig example
-  {
-    "ThunksDB": {
-      "GL": 0,
-      "xcb": 1,
-      "xcb-dri2": 1,
-      "xcb-dri3": 1,
-      "X11": 0,
-      "xcb-xfixes": 1,
-      "xcb-shm": 1,
-      "xcb-sync": 1,
-      "xcb-randr": 0,
-      "xcb-present": 0,
-      "xcb-glx": 1,
-      "xshmfence": 1,
-      "drm": 0,
-      "Xrender": 0,
-      "Xext": 0,
-      "Xfixes": 0,
-      "Vulkan-lavapipe": 1,
-      "Vulkan-radeon": 1,
-      "Vulkan-freedreno": 1,
-      "Vulkan-intel": 1,
-      "Vulkan-panfrost": 1,
-      "Vulkan-virtio": 1,
-      "asound": 0
-    }
-  }
-= Further notes =
-== Limitations and problems ==
-* 32-bit thunks aren't available currently
-** Requires kernel patches for ARM64 support
-* Thunks aren't fully stable. Expect missing symbols and crashes.
 [[Category:Development]]

Difference between revisions of "Development:Setting up Library Forwarding"