ppsspp/AGENTS.md

PPSSPP Agent instructions

These rules apply to this repository by default.

Ignore the folder ai_instructions in the root directory, it's old stuff from contributors.

General instructions

1. Keep style changes minimal unless requested. Follow existing code patterns and conventions.
2. Keep cross-platform parity in mind when changing shared code. See below for more multiplatform tips
3. Never git push (to any remote) without asking the user first. Committing locally is fine when asked; pushing requires explicit approval.

Core Safety Checks

1. For HLE, CPU, GPU, timing, threading, and memory changes, call out regression risks explicitly.
2. Consider savestate compatibility when changing serialized state.

Build and Validation

To verify that things build on Linux/Mac, use ./b.sh --debug. For Windows, use the Visual Studio solution in the Windows subdirectory (Windows/PPSSPP.sln) - always build through it, even if a stray CMake-generated build/ directory exists at the repo root (e.g. left over from WSL/MSYS2 experimentation); that directory is not the supported Windows build path and may not have a working compiler toolchain wired up.

An agent can drive the VS solution non-interactively with MSBuild.exe instead of opening the devenv GUI. Locate it via vswhere.exe (same tool/gotchas as described in the libretro section below) and build a specific project with /t:, e.g.:

$installPath = & "C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe" -latest -property installationPath
$msbuild = "$installPath\MSBuild\Current\Bin\MSBuild.exe"
& $msbuild "Windows\PPSSPP.sln" /t:UnitTest /p:Configuration=Debug /p:Platform=x64 /m

(swap /t:UnitTest for /t:PPSSPPWindows or another project name as needed; drop it entirely to build the whole solution).

In addition to the pspautotests runner (test.py), there is a separate binary with C++ unit tests in the /unittest subdirectory. After substantial changes (at the end of a chunk of work, not necessarily after every edit), run these too:

• Windows: build the UnitTest project (unittest/UnitTests.vcxproj), then run Windows/x64/Debug/UnitTest.exe all
• Linux/Mac: configure with -DUNITTEST=ON, then run build/PPSSPPUnitTest all

This runs all tests in availableTests in unittest/UnitTest.cpp. You can run a single test by passing its name instead of all; no arguments lists the available tests.

Multiplatform considerations

The emulator has multiple platform-specific entry points. Some of these will be merged or removed in the future, but are all still there. To verify that a change works, technically we need to compile for all these systems, but in practice we'll just compile locally and test the platform we are currently on, and let CI handle the cross platform considerations.

System_-prefixed wrapper functions implement kind of a platform wrapper for some functionality, and are implemented in the following list of files for each system. If we change one, we need to change them all.

Windows/main.cpp ios/main.cpp SDL/SDLMain.cpp UWP/PPSSPP_UWPMain.cpp android/jni/app-android.cpp libretro/libretro.cpp

Legacy Android build (android/jni)

There is a legacy Android build using the raw NDK build system (android/jni/Android.mk + ndk-build), separate from the gradle build in android/. It's hooked up on CI (see .github/workflows/build.yml, the android matrix entries) and is useful for quick test builds (it can build ppsspp_headless and the unit tests for Android). You do not need to build it by default, but if you want to test-build it locally:

• The NDK path is hardcoded in android/ab.cmd (Windows) or passed via the NDK env var to android/ab.sh (POSIX). It should match the ndkVersion in android/build.gradle.kts. The scripts copy assets first, then run ndk-build with a core count derived from the machine (nproc / %NUMBER_OF_PROCESSORS%).
• Example (POSIX): cd android && NDK=/path/to/ndk ./ab.sh APP_ABI=arm64-v8a HEADLESS=1
• The ppsspp_headless executable ends up in android/libs/<abi>/.

libretro core build (Windows)

Canonical instructions are in libretro/README_WINDOWS.txt - read that first, this is a summary plus agent-specific gotchas. The libretro core (ppsspp_libretro.dll) is built with a real make, not the Visual Studio solution, even on Windows - it uses cl.exe/link.exe as the compiler/linker (via platform=windows_msvc2019_desktop_x64), but orchestrated through GNU Make running inside an MSYS2 shell (a plain MSYS2 install, not "Git Bash" - typically at C:\msys64, needs pacman -S make).

cd libretro
make DEBUG=1 platform=windows_msvc2019_desktop_x64 -j32

(drop DEBUG=1 for a release build; -j count doesn't need to match logical CPUs exactly). To test the result, copy ppsspp_libretro.* into wherever the local RetroArch install reads cores from (e.g. its cores/ directory) and load it from within RetroArch.

An agent can drive this non-interactively by invoking C:\msys64\usr\bin\bash.exe -lc "..." directly as a subprocess (the -l login-shell flag matters - it's what sets up MSYS2's own PATH, make, cygpath, etc. correctly). In a sandboxed/agentic invocation (as opposed to a normal interactive MSYS2 terminal a human opens), two Windows environment variables the Makefile's VS-detection logic depends on may not be inherited by the spawned process - COMSPEC (breaks the cmd //c "bash VSWhere.sh ..." call used to locate Visual Studio) and ProgramFiles(x86) (which VSWhere.sh itself needs to find vswhere.exe). If VS auto-detection fails this way, skip it by overriding VsInstallRoot directly on the make command line (GNU Make command-line variables take precedence over the Makefile's own := assignment of the same name):

make VsInstallRoot="/c/Program Files/Microsoft Visual Studio/<year>/<edition>" DEBUG=1 platform=windows_msvc2019_desktop_x64 -j32

(path in MSYS2/cygpath POSIX form, not a raw Windows path; find the real value via vswhere -latest -property installationPath if unsure of <year>/<edition>). This is a real full compile+link - prefer it over trying to syntax-check libretro-specific files with a standalone cl.exe /Zs invocation, which can miss real bugs (e.g. an include-order issue that leaves a platform macro like VK_USE_PLATFORM_WIN32_KHR undefined before vulkan.h's first, include-guarded inclusion, since a narrower manual include-path/define set used for a syntax-only check may not reproduce the actual build step's ordering).

Command-line parsing

All command-line parsing for both the main app and headless builds belongs in Core/CmdLine.cpp / Core/CmdLine.h (CommandLineOptions), not in the platform entry points (Windows/main.cpp, headless/Headless.cpp, UI/NativeApp.cpp, etc.). Don't re-parse argv manually in those files - add a field to CommandLineOptions instead.

• Most options are declared in the g_autoParams table in CmdLine.cpp as {offsetof(...), type, longName, shortName, docString, mode}. mode gates the option to CmdLineMode::Application, ::Headless, or ::Both (the default if the field is omitted from the initializer) - the same long name can be reused for both modes with different types/meanings (e.g. --log is a String "log to FILE" option in Application mode but a Bool "full log output" option in Headless mode; they don't collide because a given Parse() call only matches params whose mode is Both or equal to the current mode).
• Options that can be repeated (e.g. --ignore TESTNAME, collected into a std::vector<std::string>) or that don't fit the generic single-value table need manual handling in the else if chain inside CommandLineOptions::Parse(), similar to how --graphics= and boot Filenames are handled.
• ApplyToConfig() is where parsed options get pushed into g_Config/g_logManager; prefer wiring a new option through there so all platforms get it for free, rather than reading CommandLineOptions fields ad-hoc at each call site.
• NativeInit() in UI/NativeApp.cpp still takes argc/argv (several platform entry points pass them in), but it shouldn't read them directly - by the time NativeInit() runs, CommandLineOptions should already have everything.

File formats, codecs, and other format handlers

Before implementing any file format handler, decompressor, codec, or similar from scratch, search the codebase first - PPSSPP already has implementations of many formats (CSO, LZRC, zlib-based loaders, ISO handlers, PBP, SevenZip, etc.), possibly in several places. Reuse or extend an existing one instead of writing a new one (e.g. there is an LZRC decompressor in Core/FileSystems/tlzrc.cpp).

Headless and unittest builds

We have additional PPSSPPHeadless and unit test builds (/headless and /unittest), that have their own separate main functions (and also stub out most of the System_ functions as needed). Take these into account when making cross platform changes.

New unit tests are added by listing them in availableTests in unittest.cpp. If they are large, put them in separate files in the unittest subdirectory. Remember to update both CMakeLists.txt and the visual studio project.

pspautotests are a large set of tests of the PSP OS's API surface, and thus tests our HLE implementation.

See docs/pspautotests.md for a workflow for running pspautotests and improving PPSSPP with the results.

Framedump rendering tests (frametests)

There is a rendering test system that replays GE frame dumps (.ppdmp) through PPSSPPHeadless and compares the output against reference images, driven by the frametests.py script and a JSON config per test set. When changing rendering code, consider running these tests. See docs/frametest.md for full documentation.

Note: headless/Compare.cpp reads back framebuffers top-down; the flip to bottom-up is only applied when writing BMPs (and when reading BMP references). TranslateDebugBufferToCompare also exists as a copy in libretro/LibretroGraphicsContext.cpp - keep the two in sync.

Adding HLE modules

HLE module implementations live in Core/HLE/sce<ModuleName>.cpp / .h (e.g. sceOpenPSID.cpp, scePauth.cpp are good small examples to copy from). A module is a const HLEFunction <name>[] table of {nid, &WrapX_YYY<func>, "funcName", retChar, argString} entries, registered via RegisterHLEModule("<name>", ARRAY_SIZE(table), table) inside a Register_<name>() function declared in the header.

• FunctionWrappers.h has generic WrapX_YYY<func> templates for common signatures (return type X, args YYY) - add new wrappers there if you need a new signature.
• Format string legend for the retmask/argmask chars: x = u32 (shown as hex), i = int/s32, f = float, X = u64, I = s64, v = void.
• For functions of genuinely unknown purpose (only known by NID), name them <moduleName>_<NID> and stub them with return hleLogError(Log::HLE, 0, "UNIMPL"); - an established pattern (see scePauth.cpp, sceOpenPSID.cpp).
• New modules must be registered at the very end of the registration function in Core/HLE/HLETables.cpp (look for the // add new modules here. comment near the end of that function) - not inserted alphabetically/logically among the existing Register_*() calls. Module registration order affects numeric IDs used in savestates, so inserting a new module earlier in that list would break save-state compatibility for saves made with older builds.
• Remember to add any new .cpp/.c file to five places: Core/CMakeLists.txt, Core/Core.vcxproj, Core/Core.vcxproj.filters, android/jni/Android.mk, and libretro/Makefile.common. New .h files only need the first three (Android.mk/Makefile.common are plain compiled-source lists so headers don't go in them). Only the CMakeLists.txt change can be verified from a Linux/Mac build - the rest can't be build-tested here, so double check them by hand against how an existing neighboring file (e.g. sceVaudio.cpp) is listed in each. Note: New files in the unittest project have to be updated in the unittest part in android/jni/Android.mk.

WebSocket debugger

PPSSPP has a JSON/WebSocket debugger and automation API (connect, read/write memory, search memory for values or byte patterns, set breakpoints, step the CPU, label data symbols, read GPU state, inject input, tail logs, etc.), served on the same port as Remote ISO sharing at /debugger with subprotocol debugger.ppsspp.org. Implementation is in Core/Debugger/WebSocket.cpp and Core/Debugger/WebSocket/*Subscriber.cpp (one file per feature area, each documented at the top). Enable it via Settings > Tools > Developer Tools > "Allow remote debugger", RemoteDebuggerOnStartup in the config, or --debugger=PORT on the command line (0 = pick a port automatically) - works on both the application and headless builds. On headless it also forces a break at start (startBreak), so the CPU halts before anything runs. The bundled web GUI at /debugger/ comes from the assets/debugger submodule (unknownbrackets/ppsspp-debugger, bundled branch).

Before touching this interface, read docs/WebSocketDebugger.md - it has the full protocol reference and event catalog (including which events are read-only vs. require cpu.stepping first). Don't guess event names or parameters from memory; the doc (and each *Subscriber.cpp file's per-handler comments) is the source of truth, and new events get added over time (e.g. memory.search, hle.data.*).

When adding new commands, don't forget to update docs/WebSocketDebugger.md,

To quickly get a live session going for manual testing (e.g. after adding/changing an event): build PPSSPPWindows (see Build and Validation above), then run it with --debugger=PORT and something that keeps running/looping so the CPU stays alive, so requests get a response instead of "CPU not started"/"CPU not active" errors. Any homebrew or game works; PSP homebrew isn't checked into this repo, so if you don't already have something installed under memstick/PSP/GAME/, ask the user for a .iso/.cso/.elf/EBOOT.PBP to boot, or to install one via the in-app Homebrew Store. Watch the log output (--log=somefile.log) for the line Listening on port N, then point Tools/wsdbg/ at that port (cargo run -- N <event> [key=value...] for one-shot, or cargo run -- N for a REPL). Most mutating events (hle.func.*, hle.data.*, memory writes while paused, etc.) require the CPU to be stopped first - send cpu.stepping and cpu.resume to pause/unpause.

Alternatively use the headless build, Windows/{arch}/Debug/PPSSPPHeadless.exe or build/PPSSPPHeadless on CMake-based platforms. Where arch is x64 or ARM64.

Debugger threading model (Core_RunOnCPUThread / g_frameMutex)

CPU-thread-owned debugger state (g_breakpoints, g_symbolMap, g_disassemblyManager, registers, memory, kernel threads) used to be touched directly from other threads (the WebSocket handler thread, and the legacy Win32 debugger's message-pump thread) with no synchronization. Two mechanisms now exist for doing this safely - pick based on whether you're mutating or just reading:

• Core_RunOnCPUThread(func) (Core.h/Core.cpp) - queues func to run on the CPU thread, blocking the caller until it's done. Use for mutations (breakpoint add/remove, register/memory writes, symbol map edits, stepping requests, thread wake/kill). Drained at the top of every Core_RunLoopUntil() iteration, so it's reached whether the CPU is running or stepping/paused; runs immediately if already called from the CPU thread. Two hard rules learned the hard way: never put a modal Win32 dialog call (MessageBox, DialogBoxParam, InputBox_GetString, SomeDialog::exec()) inside the queued lambda - it would block the CPU thread on user input, so split the function into "read/decide", "show modal", "mutate" pieces instead. And never call SendMessage() targeting one of your own GUI-thread windows from inside the lambda - the calling GUI thread is blocked waiting on the CPU thread rather than pumping messages, so a cross-thread SendMessage() back to it deadlocks; keep such calls outside the lambda instead.
• g_frameMutex (Core.h/Core.cpp) - a plain std::mutex, held by NativeFrame() (UI/NativeApp.cpp) only across the span where it actually touches that state (g_breakpoints.Frame() through g_screenManager->render() - where Core_RunLoopUntil()/actual CPU stepping happens - through runImDebugger/renderImDebugger), not across input handling or the present/frame-pacing waits. Use for reads invoked very frequently (WM_PAINT, a list reload triggered on every debugger-state-changed notification) where routing through Core_RunOnCPUThread would be too slow/heavy. The legacy Win32 debugger windows do this now - see CtrlRegisterList::onPaint, CtrlDisAsmView::onPaint, CtrlMemView::onPaint, CtrlBreakpointList::reloadBreakpoints, CtrlThreadList::reloadThreads, etc. in Windows/Debugger/*.cpp.

Architecture fact that makes g_frameMutex correct: regardless of graphics backend, NativeFrame() (and thus CPU emulation via Core_RunLoopUntil(), and the Dear ImGui debugger) always runs on the same thread - see Core/EmuThread.cpp. When a backend needs its own thread for actual graphics API calls (GraphicsContext::NeedsSeparateEmuThread() - true for OpenGL, SDL, headless, libretro, Qt; false for D3D11/Vulkan on Windows), the original thread stays behind purely to pump graphicsContext->ThreadFrame() (i.e. just executes queued graphics API calls), and a newly spawned thread takes over NativeFrame()/game logic/CPU duty. So UI/ImDebugger/*.cpp is always safe to read/write this state directly, without either mechanism - it's always on the same thread as Core_RunLoopUntil(). The legacy Win32 debugger is different: its dialogs are pumped by the original WinMain message-loop thread, which is a genuinely separate OS thread from whichever thread ends up running NativeFrame()/CPU, regardless of backend (this split happens one level above the NeedsSeparateEmuThread() branch) - that's the whole reason it needed this mechanism.

Update (2026-08-08): both BreakpointManager's and SymbolMap's internal mutexes have been removed after auditing every touchpoint across the codebase (WebSocket subscribers, Windows/Debugger/*.cpp, Windows/MainWindowMenu.cpp/Windows/MainWindow.cpp main-window menu items, Core/Core.cpp's free-threaded Core_Break/Core_Resume, UI/ImDebugger/*.cpp, JIT/interpreter backends, Core/Debugger/MemBlockInfo.cpp) and confirming each is covered by one of the two mechanisms above or is already on the CPU/NativeFrame thread. Notably, Windows/main.cpp's SortSymbols() calls (fired from System_Notify(BOOT_DONE)/System_Notify(SYMBOL_MAP_UPDATED)) turned out to already be safe without any change - both notifications are only ever fired from the CPU/NativeFrame thread (UI/EmuScreen.cpp, Core/HLE/sceKernelModule.cpp), despite an old comment there claiming reliance on the (now-removed) internal lock. Qt/mainwindow.cpp/Qt/QtMain.cpp still poke at g_symbolMap directly and unguarded on the Qt UI thread - a pre-existing issue, deliberately left alone since Qt isn't a maintained backend and is slated for removal; removing the lock doesn't change SymbolMap's public API, so Qt still builds, just without that safety net. GPU/Common/GPUDebugInterface.cpp (GE debugger expression evaluation) and Core/MemFault.cpp (crash-time diagnostics) also touch g_symbolMap and were deliberately not audited this round - different subsystem / best-effort-by-nature respectively, follow up if they ever come up.

Two more things found while doing this:

• Core_RunOnCPUThread()'s queue is only drained where Core_RunLoopUntil() runs, which requires a game to be loaded (it's called from EmuScreen::render()). Calling Core_RunOnCPUThread() while at the main menu with nothing loaded used to hang forever. Fixed by also calling the (now public) Core_ProcessCPUQueue() directly from NativeFrame(), right before g_screenManager->render(), inside the same g_frameMutex-locked span - so it always runs, not just while a game is active.
• Lock-ordering rule: because Core_ProcessCPUQueue() is called from inside NativeFrame()'s g_frameMutex-locked span, any Core_RunOnCPUThread() lambda that itself tries to lock g_frameMutex (directly, or indirectly - e.g. by calling something like CDisasm::NotifyMapLoaded(), which locks it internally) will deadlock. Keep such calls outside the queued lambda, same as the modal-dialog and SendMessage() rules above.

Painting-problem design history, in case a similar tradeoff comes up elsewhere: routing every paint through Core_RunOnCPUThread was rejected as too slow for something invoked continuously. A per-window snapshot/cache with a per-row-rechecked Core_IsStepping() guard was tried first and worked, but still had a narrow TOCTOU race (the CPU could resume between the check and that row's reads) and the per-row-recheck pattern itself wasn't liked. Settled on g_frameMutex instead - simpler, and actually race-free rather than just lower-risk. CtrlRegisterList shows live values always now, grayed out by color alone (not cached) while the core is running, since a constantly-moving value isn't meaningful to read closely anyway.

Debugging and breakpoint considerations

It might be worth trying the interpreter - all types of breakpoints are the most reliable with this CPU backend. The JITs are much, much faster and in theory also support breakpoints, but especially from websockets there seem to be trouble.

Quick rebuild on Linux

You don't need to do ./b.sh --debug to verify every single little change, instead use this shortcut:

cd build ; make -j32; cd ..