Ryan Houdek
dcfbc2f20e
When #2722 implemented this initially and #4271 switched over to signed int16_t there was assumptions made that int16_t was a reasonable trade-off in encoding size versus needing to deal with 8-bit values being too small in some cases. In the common case we are almost always encoding 8-bit values because instructions are typically linear (and less than 15-bytes in size), but 16-bit was chosen because optimizing JIT and multiple instructions that don't cause exceptions can add up to larger than 8-bit. Instead of hardcoding 16-bit values, implement a variable length integer class where ~96.8% of values are 8-bit encoded, and the remaining 3.19% are encoded using 16-bit. Due to some constraints that #4271 put in place, we can basically guarantee currently that branch targets are within 16-bit. The VL class does support 32-bit and 64-bit as well so if we change behaviour then nothing needs to change. Some stats when running Sonic Mania with multiblock enabled. Encoded integers: 3,504,907 Encoded 8-bit: 3,393,095 (96.8%) Encoded 16-bit: 111,812 (3.19%) Encoded 32/64-bit: 0 Encoded Size: 3,615,181 bytes (3.44MiB) Fixed encoded size: 7,007,604 bytes (6.68MiB) Definitely worth using and saves the headache of large RIP/PC offsets causing problems.
FEX - Fast x86 emulation frontend
FEX allows you to run x86 and x86-64 binaries on an AArch64 host, similar to qemu-user and box86. It has native support for a rootfs overlay, so you don't need to chroot, as well as some thunklibs so it can forward things like GL to the host. FEX presents a Linux 5.15+ interface to the guest, and supports only AArch64 as a host. FEX is very much work in progress, so expect things to change.
Quick start guide
For Ubuntu 22.04, 24.04 and 24.10
Execute the following command in the terminal to install FEX through a PPA.
curl --silent https://raw.githubusercontent.com/FEX-Emu/FEX/main/Scripts/InstallFEX.py --output /tmp/InstallFEX.py && python3 /tmp/InstallFEX.py && rm /tmp/InstallFEX.py
This command will walk you through installing FEX through a PPA, and downloading a RootFS for use with FEX.
Ubuntu PPA is updated with our monthly releases.
For everyone else
Please see Building FEX.
Getting Started
FEX has been tested to build and run on ARMv8.0+ hardware. ARMv7 hardware will not work. Expected operating system usage is Linux. FEX has been tested with the following Linux OSes:
- Ubuntu 22.04
- Ubuntu 24.04
- Ubuntu 24.10
- Arch Linux
On AArch64 hosts the user MUST have an x86-64 RootFS Creating a RootFS.
Navigating the Source
See the Source Outline for more information.
Building FEX
Follow the guide on the official FEX-Emu Wiki here.
RootFS generation
AArch64 hosts require a rootfs for running applications. Follow the guide on the wiki page for seeing how to set up the rootfs from scratch https://wiki.fex-emu.com/index.php/Development:Setting_up_RootFS
