Ryan Houdek
c75778abeb
When running on a system with a 48-bit VA, if FEX does any allocations between us reserving the upper 128TB and the application running, then /technically/ we are intersecting with the application's memory region in the lower 47-bits. This didn't typically result in any problems due to how ASLR works, but if we did any large allocations (like #4291 wants with 128MB VMA region) then these typically get pushed higher in the VA space. Again not usually a problem, but if you happen to be running an application that is using MAP_FIXED with hardcoded addresses then this can stomp over FEX-Emu memory causing problems. This is what happens with Wine, it reserves the upper-32MB of its 47-bit VA space, which is /highly/ likely to stomp on FEX memory. In-fact it likely occurs all the time, we just got lucky with whatever it was clobbering wasn't used at the time. On 39-bit VA systems this isn't a problem because the mmap fails outright with a warning message from WINE. Because we are already reserving the upper 128TB of VA space, instead just always enable our allocator and use the regions that were reserved. We need to be a little bit careful to ensure we don't accidentally allocate more memory post-reservation but that just requires a small adjustment to our unique_ptr and constructor for the 64BitAllocator. This means /all/ FEX-Emu allocations will be in the upper 128TB VA space when running 64-bit applications on a 48-bit VA system. Which is kind of nice. Fixes WINE in #4291 when the allocator stats are bumped to 128MB per process.
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
