Alyssa Rosenzweig
bd4464bd5e
Instruction count CI has transformed the way we work on FEX… I love the system and want to make it better. there’s one part of instruction count CI that isn’t so lovable: the problematic “optimal” flag on instructions. There are several issues with this flag, both philosophical and practical. – it is tedious to update the optimal flag when making an implementation optimal. The effect of that is discouraging people from making instructions, optimal, or encouraging people to fail to update the flag, and dilute the value of it. Either way, since we care far more about optimal implementations, then we do about updating the flag, clearly we should prioritize the implementation and not the flag. This issue was not obvious at the outset, when instruction count, CI was introduced, and still quite small. The problem magnified when we started duplicating instructions in bulk for different combinations of CPU features (flagm, AFP, etc.) that intern multiplies the manual work required to update the flags by the corresponding constant factor. if it comes down to a choice between removing this extra coverage and removing the flag, I think we all agree that removing the flag is the lesser evil. – The definition of “optimal” is fundamentally problematic. I have often improved the instruction count of an instruction that was already “optimal”. This is all kinds of silly, and calls into question whether there’s any value whatsoever in the existing classifications of the flag. Furthermore, it is often unknowable, whether an implementation really is optimal. Is it possible to implement BZHI (with flag calculations) in fewer than eight instructions? We don’t know, and it’s silly to pretend that we do. – as a consequence of the problematic definitions , there are so many errors in both directions that I don’t think there’s much value in preserving the existing classification at the expense of +progress. Being able to say “32% of instructions are translated optimally” is neat, but it really doesn’t tell us anything whatsoever when you dig a little deeper. So, as the flag is misleading at best and perhaps harmful at worst, let’s remove it and make the instruction count CI, more useful overall. let’s let the expected count and the assembly speak for themselves, and cut away the chaff. if we want a meaningless number to report to management, we can instead calculate the average blowup factor ;-) Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
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
