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Due to how we use a modified ABI for these indirect functions, we don't have a clean way to say that the host_addr lives in a side-argument. The previous inline asm that moved the value from r11 in to a variable worked up until you hit functions with 8 or more arguments. At that point the compiler was generating code before our inline assembly and using r11 as a temporary, thus destroying our value. Then a crash would occur and it was very hard to determine why. It would end up calling some random function (0x1 in this case) from an indirect call. This made it /look/ like it was calling an invalid function returned from the loader but in reality it was a corrupt register loading bad data. To work around this case, we can use an inline asm register variable and a volatile asm block that "sets" the variable. In this case GCC and Clang both seem to extend the live range of the register from the start of the function to the use of the variable. This resolves the issue for now, and I tested quite a large number of function signatures to see if it would break in the future. Theoretically our functional testing should catch this, but we don't currently have something that abuses all the functions like this currently.
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 5.0 interface to the guest, and supports both AArch64 and x86-64 as hosts. FEX is very much work in progress, so expect things to change.
Quick start guide
For Ubuntu 20.04, 21.04, 21.10, 22.04
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, ARMv8.1+, and x86-64(AVX or newer) hardware. ARMv7 and older x86 hardware will not work. Expected operating system usage is Linux. FEX has been tested with Ubuntu 20.04, 20.10, and 21.04. Also 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
