PS2Recomp

PS2Recomp: PlayStation 2 Static Recompiler (Experimental)

Also check our WIKI

This project statically recompiles PS2 ELF binaries into C++ and provides a runtime to execute the generated code.

Modules

• ps2xAnalyzer: scans ELF/functions and writes TOML config (stubs, skip, instruction patches).
• ps2xRecomp: reads TOML + ELF, decodes R5900 instructions, and generates C++ output.
• ps2xRuntime: hosts memory, function registration, syscall dispatch, and hardware stubs.
• ps2xIOP: R3000A IRX execution, a virtual IOP kernel, and generic HLE fallbacks.

Features

• Translates MIPS R5900 instructions to C++ code
• PS2-specific MMI and VU0 macro support.
• Single-file or multi-file output.
• Configurable stubs, skips, and instruction patches.
• Instruction-driven syscall handling.

How It Works

PS2Recomp works by:

• Parsing a PS2 ELF file to extract functions, symbols, and relocations
• Decoding the MIPS R5900 instructions in each function
• Translating those instructions to equivalent C++ code
• Generating a runtime that can execute the recompiled code

The translated code is very literal, with each MIPS instruction mapping to a C++ operation. For example, addiu $r4, $r4, 0x20 becomes ctx->r4 = ADD32(ctx->r4, 0X20);.

Current Behavior

• stubs entries generate wrappers that call known runtime syscall/stub handlers by name.
• stubs also supports address bindings with handler@0xADDRESS for stripped games (for example sceCdRead@0x00123456).
• Address bindings also support generic return handlers for triage: ret0, ret1, reta0.
• Recompiler now tries relocation-symbol auto-binding at callsites (J/JAL) before raw address dispatch; when relocation symbol is known (for example sceCdRead), it can call runtime handlers without manual address mapping.
• Recompiler discovers additional internal static entry targets and emits entry_... wrappers for those addresses.
• For unresolved static J/JAL sites, generated code falls back to runtime->lookupFunction(0x...).
• skip entries are not recompiled and generate explicit ps2_stubs::TODO_NAMED(...) wrappers.
• Recompiled SYSCALL now calls runtime->handleSyscall(...) with the encoded syscall immediate.
• Runtime syscall dispatch tries encoded syscall ID first, then falls back to $v1.

Requirements

• CMake 3.20+
• C++20 compiler (currently tested mainly with MSVC)
• SSE4/AVX host support for some vector paths

Build

git clone --recurse-submodules https://github.com/ran-j/PS2Recomp.git
cd PS2Recomp

cmake -S . -B out/build
cmake --build out/build --config Debug

Usage

Preferred workflow for retail or stripped games:

1. Open the ELF in Ghidra.
2. Run ps2xRecomp/tools/ghidra/ExportPS2Functions.java.
3. Use the exported TOML and CSV map.
4. Recompile with the exported TOML:

./ps2_recomp config.toml

Fallback workflow for quick local experiments or ELFs with debug symbol :

./ps2_analyzer your_game.elf config.toml

See the Ghidra Workflow for ghdira instructions.

Then build generated output and link with ps2xRuntime.

Configuration

Main fields in config.toml:

• general.input: source ELF path.
• general.ghidra_output: recommended function map CSV exported from Ghidra.
• general.output: generated C++ output folder.
• general.single_file_output: one combined cpp or one file per function.
• general.low_memory_mode: reduce peak output-generation memory by avoiding retained disassembly strings and forcing serial output generation. Generated instruction comments are still emitted; disassembly text is produced while writing each output file instead of being kept in memory.
• general.output_worker_threads: number of output-generation workers (clamped to nproc * 2). A positive value uses exactly that many workers. 0 uses nproc - 1 when at least two hardware threads are available, otherwise serial output generation. 1 forces serial output generation.
• general.patch_syscalls: apply configured patches to SYSCALL instructions (false recommended).
• general.patch_cop0: apply configured patches to COP0 instructions.
• general.patch_cache: apply configured patches to CACHE instructions.
• general.stubs: names to force as stubs. Also accepts handler@0xADDRESS to bind a stripped function address directly to a runtime syscall/stub handler. Includes generic handlers ret0, ret1, reta0.
• general.skip: names to force as skipped wrappers.
• patches.instructions: raw instruction replacements by address.

Address binding for stripped ELFs:

• Use handler@0xADDRESS inside general.stubs to map a stripped function start directly to a runtime handler.
• Example: sceCdRead@0x00123456 binds function start 0x00123456 to ps2_stubs::sceCdRead(...).
• Generic temporary handlers are available: ret0@0xADDR, ret1@0xADDR, reta0@0xADDR.
• Before manual binding, prefer recompilation from a Ghidra-exported TOML/CSV first. The extra boundaries and synthetic entry points are usually more important than manual early triage.
• The address must be the function start in that exact ELF build.
• Addresses are not portable across different games/regions/builds.
• The handler name must exist in runtime call lists (PS2_SYSCALL_LIST or PS2_STUB_LIST).

Example:

# stripped function binding by address:
stubs = ["sceCdRead@0x00123456", "SifLoadModule@0x00127890"]
# temporary return handlers:
stubs = ["ret0@0x001D9410", "ret1@0x001D5BC8", "reta0@0x0024B7C0"]
# mixed example:
stubs = ["printf", "sceCdRead@0x00123456", "SifLoadModule@0x00127890"] 

Runtime

To execute the recompiled code.

ps2xRuntime currently provides:

• Guest memory model and function dispatch table.
• Some syscall dispatcher with common kernel IDs.
• Basic GS/VU/file/system stubs.
• Foundation to expand and port your game.
• ps2xIOP execution of original IRX modules with generic HLE fallbacks.

See IOP emulation for module execution and the service boundary.

Game Override Hooks

Game overrides are runtime-side, build-scoped patch modules.

A game override is C++ code that runs during loadELF and can replace EE function bindings by address for one specific game build. IOP RPC/DMA behavior is handled by the ps2xIOP emulator and its runtime transport. This is separate from recompilation output and separate from global runtime stubs/syscalls.

API:

• Header: ps2xRuntime/include/game_overrides.h
• Register macro: PS2_REGISTER_GAME_OVERRIDE(name, elfName, entry, crc32, applyFn)
• Direct bind helper: ps2_game_overrides::bindAddressHandler(runtime, addr, "handler")

Use Game Override modules when:

• You need per-game/per-build routing or patches without polluting global behavior.
• You need to bind many addresses, or install custom replacement logic for a specific title.

Recommended Iteration Loop

1. Run with minimal config and no aggressive skipping.
2. Fix hard blockers first (function not found, syscall TODO, critical IO stubs).
3. Use temporary return stubs only to classify call importance.
4. Promote temporary fixes to real implementations.
5. Move per-game hacks into game overrides keyed by ELF metadata.
6. Re-test from cold boot after each batch.

Describing Your Game Project

A game project built with PS2Recomp can describe itself in a .recomp.json file at the root of its repository. Lists of recomp and decomp projects, such as recomp.board, read that file instead of guessing the game, system and status from the README.

[!NOTE] This file is optional: PS2Recomp does not read it and works the same without it. .recomp.json and recomp.board are third-party projects; the PS2Recomp developers have no ties to them.

Starter file:

{
  "$schema": "https://recomp.fyi/schema/v1.json",
  "game": "<title as it shipped>",
  "system": "PS2",
  "type": "recomp",
  "toolchain": "PS2Recomp",
  "status": "in-progress",
  "original": { "region": "USA", "serial": "SLUS-20312" }
}

• original is the release a user must own. On retail discs the ELF is named after the serial (SLUS_203.12 is SLUS-20312), and the prefix gives the region: SLUS/SCUS USA, SLES/SCES Europe, SLPS/SLPM/SCPS Japan.
• status is one of exploring, in-progress, playable, released, complete, paused. Edit it when the project moves on: a stale status is worse than none.
• Never put a game file, or a link to one, in the file.

Other fields (Wikidata item, target platforms, maintainers, links, what help is wanted) and the JSON Schema are in the specification.

Limitations

• Performance is very bad for VU and GS
• Hardware emulation is partial and many paths are stubbed.

Acknowledgments

• Inspired by N64Recomp
• Uses ELFIO for ELF parsing
• Uses toml11 for TOML parsing
• Uses fmt for string formatting
• Reference for runtime PCSX2