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The FEX-EMU, which enables the execution of x86 and x86-64 binaries on an AArch64 host, has been updated.


Read the blog post at FEX-Emu's Site!

Welcome back everyone! After last month's cancelled release and this month being a bit late we have a lot of changes that happened.

More JIT performance improvements

A lot of the work these paste two months have been optimizing our JIT more. We have run Geekbench and Bytemark for these which showed a marginal
performance improvement in these benchmarks. Bytemark showing the biggest improvement of 16% in one sub-benchmark. A lot of the performance
improvements are targeting real-world applications rather than benchmarks which shows as those games getting more of an improvement.

As typical, explaining each individual optimization would take too long so we're going to spam out a bunch in a list.

  • Removes a vtable indirection for syscalls
  • Fix RCL/RCR wraparound behaviour
  • Remove process-wide lock in JIT
  • Fixes syscall rcx/r11 state
  • Optimize SIB address calculation from three instructions to one
  • Optimize TST instruction with -1
  • Optimize TST more
  • Improve XCHG instructions
  • Optimize rotates
  • Optimize CDQ
  • Optimize shifts
  • Optimize PTEST, VTESTP, PDEP
  • Optimize SHA256 instructions to remove spilling
  • Optimize CMPXCHG
  • Stop zero extending a bunch of instructions where it doesn't matter
  • Optimize ANDN
  • Optimize a bunch of instructions using NZCV flags

Fix glibc clone usage of CLONE_CLEAR_SIGHAND

Newer glibc versions starting with 2.38 have started using this new clone flag for executing a program. We also fixed this in 2312.1 but can now make
a note of it.

Fix VDSO symbol fetching on ARM64

This is a fairly minor change but can have a big performance hit. When FEX was querying for VDSO interface functions we were using the wrong names on
ARM64. Since the wrong names were used, this meant we always fell back to the slower glibc implementation of functions. This in particular fixes a
performance hit when games call clock_gettime excessively.

Fix Proton again

Sometime in December there were some changes to Valve's Proton layer which caused us to break it. This has now been fixed.

Expose Linux 6.6

With some relatively minor changes we now support reporting kernel version 6.6 to the guest application. This gives us a range from v5.0 to v6.6 now.

Workaround hang when process is forking

A long-standing bug in FEX is that sometimes a process can hang when it is forking, usually to execute another program. We have now worked around this
issue to an extent that lets the application continue. It's not a full fix because we can still have a crash but that is easier to see instead of a
program hanging forever in the background.

Commonize some WOW64 code to share with ARM64ec

In preparation for sharing some code with FEX built for ARM64ec, this has shared move some Windows code to a common location to be used.

An absolute ton of work went in to thunking

Over the past couple months this has been one of the more active projects within FEX. Today FEX has support for thunking 64-bit x86 libraries across
to ARM64. A significant portion of this work is doing analysis of API interfaces in order to allow thunking 32-bit x86 libraries over to ARM64
libraries with data repacking. This isn't yet complete but since a ton of work has gone in to this, we wanted to call it out.

NOTE: Memory leak on long-running processes like Steam

We have found a memory leak when a process shuts down a thread that has been around for quite a while. We only identified this memory leak this last month which hasn't been fixed.
We are hoping to fix this bug for the next release but be aware that long running processes like Steam has a relatively aggressive memory leak. This is exacerbated by how Steam spins up threads for
doing work which makes this application particularly heavy.

Raw Changes

FEX Release FEX-2402

  • Arm64

  • Removes a vtable indirection in syscalls ( 743df8d)

  • BranchOps

  • Fix unused-variable warning ( f515b1e)

  • ArmEmitter

  • Support single use forward labels ( 8c31630)


  • Removes Init and just uses constructor ( f5997a0)

  • Config

  • Fixes JSON parsing of "ArgumentHandler" types ( bd1e029)

  • Dispatcher

  • Convert GetCompileBlockPtr to using PMF helper ( 82ce76b)

  • Removes unused asserting CompileBlock function ( 5b4e9c6)

  • Externals

  • Update xbyak to v7.02 and switch away from fork ( 9da08b4)

  • FEX

  • Removes legacy kernel 32-bit allocator ( de2cd46)

  • FEXConfig

  • Initialize paths before trying to read configuration files ( 79526b9)

  • FEXCore

  • Fix RCL/RCR shift wraparound behaviour ( c0be974)

  • Use TMP1-4 for values that need preserving across spills ( 0e97f8f)

  • Decompose some std::function usage to regular pointers ( 615cfe0)

  • Pass thread object to HandleUnalignedAccess ( d488592)

  • Removes SRA option, it's now permanently enabled ( 5467c3e)

  • Removes context wide and map lookup ( eea2e7b)

  • Optimize HostFeatures and CPUID feature calculation ( 0071c1b)

  • Warn if MDWE is set ( 00669a1)

  • Changes ParentThread ownership from the CTX to the frontend, take 2 ( b4b8e81)

  • Describe exit function linking object with a structure ( 93ec676)

  • Removes stale references to x86 JIT ( 8665490)

  • Removes old InternalThreadState header ( 12b72f9)

  • Moves OS thread creation to the frontend ( 0a4e064)

  • Moves XID check to the frontend ( 7524029)

  • FEXLinuxTests

  • Fix build warnings ( d34302a)

  • FEXLoader

  • Moves thread management to the frontend ( 5e26b77)

  • Temporarily disable CLONE_CLEAR_SIGHAND ( 26c9d5d)

  • Fix incorrect format strings ( 3a5ac39)

  • GdbServer

  • Fixes crash on gdb detach ( a1cf14f)

  • HostFeatures

  • Supports runtime disabling of preserve_all ( 235f32c)

  • InstCountCI

  • Fixes test to not use relative data ( 3db31a6)

  • JIT

  • Fixes broken register in VTBX1 ( 9841983)

  • Jitarm64

  • Implements spin-loop futex for JIT blocks ( 750b0b7)

  • Linux

  • Decouple thread object creation and tracking ( 5e5984a)

  • Implements a fault safe memcpy routine ( 8e3d4a3)

  • Adjust when clone allocates stack memory ( bd13052)

  • OpcodeDispatcher

  • Fixes syscall rcx/r11 generation ( 56d8080)

  • Initial support for runtime long-mode switch ( 4b37921)

  • Fixes flags generation in imul ( 3d2cbc5)

  • Optimize SIB addr calculation ( 81c85d7)

  • PassManager

  • Removes unused exit handler ( 12923ba)

  • Scripts

  • More changes to InstallFEX script ( b613576)

  • Updates InstallFEX with supported Ubuntu versions ( eb5cf1a)

  • SpinLockWait

  • Fixes unexpected lock success ( 472a701)

  • SpinWaitLock

  • Removes unused variable in spin-loop fallback ( a4a1d60)

  • TestHarnessRunner

  • Move to its own tool folder ( 68d6cf5)

  • ThreadManager

  • StealAndDropActiveLocks in the child forked process ( 930d265)

  • Thunks

  • Add workarounds for pointers not readable by 32-bit guests ( 60b0852)

  • Allow querying customized functions through vkGetInstanceProcAddr ( 86c6ca3)

  • Tools

  • Adds new FEXpidof tool ( be4d1a8)

  • Moves IRLoader to independent folder ( 9dda960)

  • VDSO

  • Fixes symbol fetching for a few symbols ( 4333261)

  • Windows

  • Commonise WOW64 logic that can be shared with ARM64EC ( 8ff4b52)

  • X86Tables

  • Converts tables to be mostly consteval ( ec89a00)

  • Misc

  • Fix  #3419 ( 780b486)

  • Add NZCV+PF/AF optimization pass ( df3d693)

  • Fixes one mutex hang ( ba41da7)

  • Optimize test -1 ( 806e5b8)

  • Optimize TST ( 4331753)

  • Clean up access to possible nullptr ( cdcc432)

  • Revert "Add cmake option DISABLE_CLANG_PRESERVE_ALL" ( 435b67a)

  • Revert "Revert "FEXLoader: Moves thread management to the frontend"" ( a41ebe2)

  • Eliminate spilling in sha256rnds2 and sha1rnds4 ( 557cb59)

  • Revert  #3303 ( 6993f4f)

  • Improve XCHG operations ( 920a8db)

  • Library Forwarding: Handle cross-architecture differences of integer types ( 9c37c0f)

  • Optimize CDQOp ( cec1814)

  • Optimize rotates ( 4d49ac7)

  • Code cleanup - mainly dead store removal; NFC ( 6d13d9f)

  • Optimize shifts a bit ( ae7dc25)

  • Optimize bit manipulation instructions ( f4086b2)

  • Add cmake option DISABLE_CLANG_PRESERVE_ALL ( 37a611b)

  • Library Forwarding: Don't attempt custom repacking for non-struct types ( 2884337)

  • Check that path arguments to TestHarnessRunner exist ( 3036f3b)

  • Allow upper garbage on a bunch of instructions ( fa33520)

  • Fix typos; NFC ( bc67910)

  • Optimize PTEST and VTESTP ( 31a4158)

  • Optimize PDEP ( 58f3d3c)

  • Library Forwarding: Flip order of nullptr check and custom repacking ( d04f3a2)

  • Library Forwarding: Test interaction of struct repacking and assume_compatible_data_layout ( 3bfb4be)

  • Improvements to the Dockerfile ( 1627331)

  • Library Forwarding: Implement assisted struct repacking ( 6efc4a9)

  • Optimize GPR cmpxchg ( f956f00)

  • Library Forwarding: Implement automatic argument repacking ( 8320723)

  • Fixes some new glibc allocations that cropped up ( dae16aa)

  • Linux uprev to v6.6 ( c333aac)

  • Revert "FEXLoader: Moves thread management to the frontend" ( db7d7a6)

  • FEXCore interface cleaning ( 04a88ed)

  • Removes IRLoader, unittests, and public interface ( f785b38)

  • Support disabling SHA in CPUID ( 058e691)

  • Library Forwarding: Emit layout helpers to allow repacking struct data ( d806db5)

  • Fixes Proton again ( b1c3737)

  • rm andn masking ( 0fe5e3d)

  • instcountci

  • Adds panicspill test from steamwebhelper ( b937885)

Release FEX-2402 · FEX-Emu/FEX