Brian Degenhardt
9eb93d4dcd
Remove() stamped a removed block's entry with B JITCompile, and Link() routed not-yet-compiled targets there too. JITCompile unconditionally recompiles from cpuRegs.pc — so when a block was removed and later recompiled at a new address, any orphaned link site still branching to the old entry re-entered recRecompile on an already-compiled block: fnptr assert on Devel, and on Release a spurious in-place recompile that superseded live code and stranded other orphaned callers in the stale pre-SMC compile (the NFS Carbon SLUS-21493 post-FMV deadlock, localized by twindiff against the pre-transplant build). Every link tail in both recs already stores the target guest pc before its branch, so the correct stale-site policy is re-DISPATCH, never re-COMPILE: divert to DispatcherReg, which routes through the recLUT (the single SMC-invalidation rewrite point) to the current code, or to compilation via the LUT's own JITCompile slot when genuinely uncompiled. Both AetherSX2's Remove() and the pre-transplant linker enforce this same fallback-to-dispatcher policy; the recRecompile fnptr assert becomes a true invariant again. Zero hot-path cost: the dispatcher hop is paid only by a cold first execution of an unresolved link (repatched direct by New()) or by a stale site after SMC churn. Remove() keeps its signal-safety contract (single atomic 4-byte B patch, no link-map access). recompiler_tests: 1415/1415. Carbon twincompare free-runs 200 frames where it previously aborted on the recRecompile assert.
ARMSX2 — Native ARM64 JIT Fork of PCSX2
ARMSX2 is a free and open-source PlayStation 2 (PS2) emulator based on PCSX2. Its purpose is to emulate the PS2's hardware, using a combination of MIPS CPU Interpreters, Recompilers and a Virtual Machine which manages hardware states and PS2 system memory. This allows you to play PS2 games on your phone, PC, or gaming handheld, with many additional features and benefits.
Thank You
The ARMSX2 team is eternally indebted to the PCSX2 project it is based on. We are so fortunate to build on their 20 years of hardcore development.
About This Fork
The upstream PCSX2 project ships an ARM64 interpreter build for ARM, but its high-performance JIT recompilers (EE, IOP, VU0, VU1, and vtlb fast memory) are x86-64 only.
This fork exists to close that gap. The goal is to preserve the correctness features of 20 years of PCSX2 development, while generating the fastest native ARM performance possible.
Current status:
- ✅ EE (Emotion Engine) recompiler — integer, float, MMI, COP0/COP1/COP2, branches, load/store
- ✅ IOP (I/O Processor / R3000A) recompiler — full integer, load/store, branches, coprocessors
- ✅ VU (Vector Unit) recompiler — microVU skeleton + Upper FMAC vector ISA complete; Lower ISA and runtime complete
- ✅ vtlb fast memory
- ✅ Native ARM64 binary builds and boots the PS2 BIOS
- ✅ 2D games are already playable
- ✅ 3D games run
Why LLMs / AI Were Used
A word on methodology:
The x86-64 JIT code in upstream ARMSX2 is already proven correct — it has run thousands of PS2 titles for years. The challenge in this port is not emulator design or JIT theory; it is mechanical translation of a large, well-understood x86-64 assembly codebase into equivalent ARM64 assembly (via VIXL) while preserving the exact same register-allocation contracts, block lifecycle, and recompiler semantics.
Large language models (LLMs) were used as an accelerant for this translation work — pattern-matching x86 JIT boilerplate to ARM64 equivalents, scaffolding emit routines, and keeping the porting velocity high. The JIT logic (block compiler, dispatcher, analysis passes, flag pipelines, clamping rules, Tri-Ace hacks, etc.) is taken directly from the upstream x86 implementation and validated against it. Nothing was hallucinated from scratch.
In other words: the hard engineering was done by the PCSX2 team over two decades. The hard typing — translating ~50k lines of x86 emitter code into ARM64 — is what AI helped compress.
System Requirements
ARMSX2 targets ARM64 across desktop (macOS, Windows, Linux) and mobile (Android, iOS/iPadOS), all from the single shared core. Our setup documentation page contains additional details on software and hardware requirements.
Please note that a BIOS dump from a legitimately-owned PS2 console is required to use the emulator. For more information, visit this page.
Building
Check out our github actions for the latest build recipe