J1coding
cd40a1f169
Crash report from an iPhone XS on 2.5.0: SIGILL less than a second after launch, in ElfObject::GetCRC during the game list scan. The exception code carries the offending instruction, 0xce000c40, and that decodes as eor3, an ARMv8.2 SHA3 instruction. An A12 has no SHA3. The iOS BuildParameters has been handing clang -mcpu=apple-m1, under a comment claiming iOS devices and Apple Silicon Macs share a minimum spec. They do not. The oldest phone that can install at our deployment target is an iPhone XS, and an M1 baseline lets clang fold the XOR chains in the hash and CRC loops into eor3 and bcax. It is not one unlucky function either. The shipped 2.5.0 binary has 36 eor3 and 16 bcax spread across twelve of them, including LoadBIOS, mVUcomputeProgramHash, the memory card CRC and save paths, and the XXH3 hashing the texture cache leans on. An A12 reaches one of those almost immediately whatever it does, so the app has never really worked on that generation: iPhone XS, XS Max and XR, iPad Air 3, iPad mini 5, iPad 8, and the A12X and A12Z iPad Pros. iOS now builds with -mcpu=apple-a12, the oldest device we accept. macOS and Catalyst keep the M1 baseline, which is correct for them. Picking the oldest supported device rather than switching off the one offending instruction means a future compiler that fancies some other post-A12 feature gets refused at compile time instead of turning into another crash report. Checked with otool either side of the change: the count of eor3, bcax, xar, rax1, sha512, sm3 and sm4 in the binary goes from 52 to zero. Worth knowing for next time, this flag lives in the iOS copy of BuildParameters, not the one at the repo root. The iOS CMakeLists points CMAKE_MODULE_PATH at its own cmake directory, so the root copy has no say in an iOS build at all.
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