Development:Setting up FEX

Build dependencies

• git
• cmake
• ninja-build
• ccache (Recommended if you're rebuilding constantly)
• clang
• lld (For ThinLTO)
• binfmt-support (For AArch64 binfmt_misc support)
• libsdl2-dev (For GUI)
• libepoxy-dev (For GUI)
• g++-x86-64-linux-gnu (For building thunks)
• nasm (only if building tests)
• python3-clang (for struct verifier)
• libstdc++-10-dev-i386-cross (for struct verifier)
• libstdc++-10-dev-amd64-cross (for struct verifier)
• libstdc++-10-dev-arm64-cross (for struct verifier)
• squashfs-tools (For squashfs rootfs support)

Gentoo dependencies

• dev-vcs/git
• cmake
• ninja
• ccache
• clang
• lld
• libsdl2
• libepoxy
• nasm

Use gubbins

• >=media-libs/libglvnd-1.3.4 X

Build Configuration

• Ensure release mode is enabled
• Disable static pie
  • Bug with glibc means static-pie needs to be disabled for thunks to work.
  • This is necessary for chroot and pressure-vessel, but is currently incompatible with thunks
  • If using LLD then you need at least LLD 13.0
  • If using LLD then you need at least glibc 2.35
  • Recommendation: Disable LLD, use binutils ld
• Enable LTO - Currently bugged in some configurations
  • Disable if enabling static-pie
• Disable test building

 git clone --recurse-submodules https://github.com/FEX-Emu/FEX.git
 cd FEX
 mkdir Build
 cd Build
 CC=clang CXX=clang++ cmake -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_BUILD_TYPE=Release -DENABLE_LTO=False -DENABLE_STATIC_PIE=False -DBUILD_TESTS=False -DENABLE_ASSERTIONS=False -G Ninja ..
 ninja

Installation

 sudo ninja install

On AArch64 hosts

You can install a binfmt_misc handler for both 32bit and 64bit x86 execution directly from the environment. If you already have box86's 32bit binfmt_misc handler installed then I don't recommend installing FEX's until it is useful. Make sure to have run install prior to this, otherwise binfmt_misc will install an old handler even if the executable has been updated.

 sudo ninja binfmt_misc_32
 sudo ninja binfmt_misc_64

binfmt_misc problems

• Double check that binfmt_misc has worked
  • `ls /usr/share/binfmts/FEX*` should return files
  • `ls /var/lib/binfmts/FEX*` should return files
  • `/proc/sys/fs/binfmt_misc/status` should exist
    • If it doesn't exist then make sure your kernel has `CONFIG_BINFMT_MISC=y`
    • If it still doesn't exist then make sure systemd isn't disabling it `systemctl enable binfmt-support`

Runtime Configuration

FEXConfig is the application to use for runtime configuration setup.

CTRL+SHIFT+O will open default "global" configuration.

CTLR+S saves it.

Things to ensure to set

On AArch64 host, a rootfs path is mandatory, while it is optional on x86-64 host

• Core: JIT
• RootFS
• Silent Logging (Useful to get FEX information spam out of the way)
• Block Size (500 is a good default. Optimization passes may break things though)
• Multiblock: enabled (Can cause more stuttering)
• Emulated CPU Cores: 1 (threading bugs cause issues with more)

More Details at: Follow the instructions here https://wiki.fex-emu.org/index.php/Development:Configuring_FEX

RootFS generation

AArch64 hosts require a rootfs for running applications Follow the instructions here https://wiki.fex-emu.org/index.php/Development:Setting_up_RootFS

Installing Thunks

Only if you want

Follow the instructions here: https://wiki.fex-emu.org/index.php/Development:Setting_up_Thunks

Additional details here: https://github.com/FEX-Emu/FEX/blob/main/ThunkLibs/README.md

Binaries

• FEXLoader
  • This is useful for development purposes but is generally recommended against using.
  • Allows passing arguments to FEX for configuration purposes, which can break under some execve situations
• FEXInterpreter
  • This is a hardlink to FEXLoader which refuses to treat arguments as configuration options
  • Is recommended to use over FEXLoader; Using FEXConfig to set configuration
  • Requires being a hardlink or executable copy, execve logic sees through a softlink
  • Is the executable used for binfmt_misc for interpreters
• FEXConfig
  • Used for setting configuration options from a GUI
  • Written using Dear ImGui
  • Can load/save global configuration and application configuration files
  • Application configuration files are compared against the executable filename
• FEXMountDaemon
  • This is a mount daemon that will run in the background when you are using a squashfs based rootfs
  • Usually one one instance open at any given moment
  • It usually closes when the FEXInterpreter exits, but not always. See the problems section in setting up a rootfs
    • Has a ten second timeout window in case a another instance of FEX opens and uses it.

Debug binaries

• TestHarnessRunner
  • Used for running FEX's ASM unit tests
  • Runs some binary in a host x86_64 host environment or FEX and checks results
  • Useful for quickly creating ASM based unit tests
• IRLoader
  • Used for running FEX's IR based unit tests
  • Only runs through FEX and checks the results
  • Minimal number of tests
• UnitTestGenerator
  • This is supposed to be an x86-64 instruction generator
  • Has an understanding of x86-64 instruction encoding format
  • Generates hundreds of thousands of instructions
  • Used to be used with a lockstep runner to ensure correct behaviour
  • Largely unsupported, avoiding undefined behaviour is difficult and FEX doesn't need to match undefined behaviour
  • Lockstep hostrunner wasn't ever made to be bug free, hard to support
  • Doesn't ensure correct behaviour on AArch64 device