Development:Setting up Thunks

Build Dependencies

• g++-x86-64-linux-gnu (For building thunks)
• Development libraries for various thunks

Setting cmake to build thunks

Pass in to cmake the option to enable thunk building.

• -DBUILD_THUNKS=True

FEX thunk options

• 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/

How to use Thunks

Once Thunks are built and installed then you can can set the three configuration options to the correct 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.

ThunkConfig example

This is just an example for how one could lay out the thunks.

• Save this to a file somewhere and point ThunkConfig option to it
  • $HOME/.fex-emu/ThunkConfigs/ isn't a bad choice for consistency.

 {
  "thunks": {
   "libGL-guest.so": ["/lib/x86_64-linux-gnu/libGL.so.1", "/usr/lib/x86_64-linux-gnu/libGL.so.1"],
   "libasound-guest.so": ["/lib/x86_64-linux-gnu/libasound.so.2", "/usr/lib/x86_64-linux-gnu/libasound.so.2"],
   "libX11-guest.so": ["/lib/x86_64-linux-gnu/libX11.so.6", "/usr/lib/x86_64-linux-gnu/libX11.so.6"],
   "libXrender-guest.so": ["/lib/x86_64-linux-gnu/libXrender.so.1", "/usr/lib/x86_64-linux-gnu/libXrender.so.1"],
   "libXext-guest.so": ["/lib/x86_64-linux-gnu/libXext.so.6", "/usr/lib/x86_64-linux-gnu/libXext.so.6"],
   "libXfixes-guest.so": ["/lib/x86_64-linux-gnu/libXfixes.so.3", "/usr/lib/x86_64-linux-gnu/libXfixes.so.3"]
   }
 }

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.