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psxrecomp/docs/ARCHITECTURE.md
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Shokunin 36bd80cefc Compile overlay shards for the runtime's architecture, not the host's 
An x86_64 macOS runtime under Rosetta compiled every overlay shard for
arm64. The runtime's shell and the bundled Python inherit x86_64, so
compile_overlays.py named the cache macos-x64, but it ran the compiler
without -arch and Xcode's clang is an arm64-only binary that defaults to
arm64. The arm64 shards landed in the macos-x64 cache, the runtime could
not load any of them, and every overlay ran interpreted. The BIOS module
builder had the same compile line.

- overlay_loader.h now defines PSX_OVERLAY_ARCH_ABI (moved from
  overlay_loader.c), and autocompile.c exports it to every compile it
  spawns, next to PSX_OVERLAY_FLAVOR. It is the running slice of a
  universal binary.
- compile_overlays.py adopts it (env wins over the new --arch-abi), names
  the cache with it, and passes -arch on macOS. Without a pin it builds
  for its own interpreter, still with an explicit -arch.
- Shards are validated by loading them into the Python that built them,
  so a Python that cannot run as the runtime's architecture now refuses
  up front instead of writing shards nothing loads. The Python's
  architecture is its process's: platform.machine() on macOS and Linux,
  the interpreter's build (sysconfig.get_platform()) on Windows, where
  platform.machine() reports the machine. So an x64 Python emulated on
  Windows on ARM still builds the x64 runtime's shards.
- psx_bios_module.c passes --arch-abi to bios_module_build.py, which
  applies the same rules.
- Windows and Linux compile lines are unchanged, and so are their cache
  directories, except that the x64 build on Windows on ARM now uses the
  runtime's win-x64 instead of the machine's win-arm64.

overlay_compile_arch_test (CTest) pins the handoff, the flags, the refusal,
the Windows process architecture and the unchanged Windows/Linux commands;
with a real cc it builds a shard for each slice the Mac can run and loads
it in a process of that architecture.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2026-10-01 00:31:51 -07:00

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# Architecture
How PSXRecomp is put together, end to end. For the higher-level "why three ways
of running code" story, read [`EXECUTION_MODEL.md`](EXECUTION_MODEL.md) first;
this doc is the component-level view.
## Two programs: the recompiler and the runtime
PSXRecomp is split into two CMake projects that are built and run separately:
```
recompiler/ runtime/
─────────── ────────
MIPS ──▶ C C + hardware simulation ──▶ native game binary
(build-time tool) (linked with the generated C)
```
- **`recompiler/`** (C++20) is an offline tool. It reads MIPS R3000A machine code
and emits C source files under `generated/`.
- **`runtime/`** (C99 + C++17) is the engine. It loads the game's assets into an
emulated PS1 address space, links the generated C in as native functions, and
simulates the console's hardware around them.
A **game repository** (e.g. TombaRecomp) contains no framework source — it links
this framework in (as a submodule) and provides the game's config, seeds, and
build glue. See [`BUILDING.md`](BUILDING.md#linking-the-framework).
## The recompiler (`recompiler/`)
Two entry points share the same translation core:
- `src/main_bios.cpp` — ingests the flat BIOS ROM (`SCPH1001.BIN`, loaded at
`0xBFC00000`) and emits `generated/SCPH1001_*.c`.
- `src/main_psx.cpp` — ingests a `PS-X EXE` extracted from a game disc and emits
`generated/<serial>_*.c`.
The translation pipeline:
| Stage | File | Job |
|---|---|---|
| Decode | `mips_decoder.cpp` (+ vendored `rabbitizer`) | Decode MIPS instructions |
| Control flow | `control_flow.cpp`, `basic_block.cpp` | Build basic blocks / CFG |
| Discovery | `function_discovery.cpp`, `function_analysis.cpp` | Find function entry points (seeded from Ghidra exports) |
| Codegen | `code_generator.cpp`, `full_function_emitter.cpp`, `strict_translator.cpp` | Emit C: one function per guest function, plus a dispatch table |
Output is **two files** per program: a `_full.c` (the function bodies) and a
`_dispatch.c` (the address→function dispatch table). Both are build artifacts and
are **never hand-edited** — if the C is wrong, the fix is in the recompiler.
GTE (the PS1 geometry coprocessor) instructions are emitted inline;
COP0 kernel-mode instructions the BIOS needs are handled in codegen.
## The runtime (`runtime/`)
The runtime is assembled by one CMake helper, `psxrecomp_add_runtime_target()`
(defined in `runtime/runtime.cmake`), which a game's `CMakeLists.txt` calls with
the paths to its generated C. The runtime provides:
- **Memory & address space** (`memory.c`) — the 2 MB main RAM, scratchpad, BIOS
ROM, and MMIO regions, with the dispatch that routes a guest PC to its native
function (static, overlay, or interpreter).
- **Hardware simulation via MMIO handlers** — GPU (`gpu.c`, `gpu_sw_renderer.c`,
`gpu_gl_renderer.c`), DMA (`dma.c`), timers (`timers.c`), CD-ROM
(`cdrom.c`, `iso_reader.cpp`), MDEC, SIO0 controllers/memory cards
(`sio.c`, `memcard.c`), SPU (`spu.c`), GTE (`gte.cpp`), and interrupt delivery
(`interrupts.c`).
- **Host services** — window/input/audio via SDL3 by default (SDL2 is an
explicit compatibility backend), a cooperative-thread
scheduler on host fibers (`psx_fiber.c`: Win32 Fibers / POSIX `ucontext`), and
the optional debug TCP server (`debug_server.c`).
### BIOS: LLE baseline + a swappable HLE tier
The recompiled `SCPH1001.BIN` is the **low-level (LLE) baseline**: it *is* the
kernel, and it is the reference implementation and the correctness oracle. There
are no per-vector HLE shims replacing it.
On top of that, PSXRecomp carries an optional **HLE tier** (`bios_hle`, on by
default for player convenience) that skips the BIOS boot sequence and intercepts
a small set of BIOS services — always falling through to the recompiled BIOS for
anything it doesn't implement. LLE stays fully linked and is what every accuracy
check runs against. Turn it off with `[runtime] bios_hle = false` or
`PSX_BIOS_HLE=0`; with it off the build behaves as pure LLE. (Design notes:
[`docs/internal/HLE_SCHEDULER_CARVEOUT_PLAN.md`](internal/HLE_SCHEDULER_CARVEOUT_PLAN.md).)
Those are **two independent axes**, and the distinction matters because a build
links more than one BIOS ([`BIOS_SELECTION.md`](BIOS_SELECTION.md)):
| axis | what it needs from the image | on retail SCPH-1001 | on bundled OpenBIOS |
|---|---|---|---|
| boot-skip | `shell_entry_phys` — works under pure LLE | yes | yes |
| kernel-call HLE | `deliver_event_ret` — the kernel's own DeliverEvent `$ra` | yes | refused, loudly |
So **"skip the BIOS and go straight to the game" means the same thing on every
BIOS**: the boot-skip is not synthesis, it just returns immediately from the
shell call, so it needs nothing BIOS-specific beyond knowing where the shell is
entered. Whether the *kernel-call* tier is additionally available is a separate,
per-image question, and refusing it must never cancel the boot-skip — deriving
one from the other is the bug fixed in 2026-07. Both axes are decided in one pure
place, `psx_bios_hle_plan()`
([`runtime/include/bios_hle_plan.h`](../runtime/include/bios_hle_plan.h)), which
is unit-tested over the whole matrix.
### Static / overlay / interpreter dispatch
This is the heart of the system and has its own doc,
[`EXECUTION_MODEL.md`](EXECUTION_MODEL.md). In brief: a guest PC resolves to
statically-recompiled native code (BIOS + main EXE), a runtime-compiled **native
overlay** (`overlay_capture.c` → `tools/compile_overlays.py` →
`overlay_loader.c`), or the small **dirty-RAM interpreter**
(`dirty_ram_interp.c`) — in that priority order.
### Overlay compile backend
When an overlay needs compiling, the runtime spawns a C compiler on the
recompiler-emitted C and loads the resulting DLL — it does not JIT in-process.
The backend tier is resolved in `overlay_backend.c` (see `main.cpp` around the
`code_provider` setup):
```
static → gcc → tcc
```
- **static** — the overlay was baked into the binary at build time (best case).
- **gcc** — used when a system `gcc` is on `PATH` (the development default).
- **tcc** — TinyCC, the toolchain-free fallback **bundled beside shipped
executables** in `overlay_toolchain/` (an embedded Python + `tcc.exe`) so
players never need a compiler installed.
Compiled overlays are stored in a content-addressed cache namespaced by
compiler and target ABI (`<game>/gcc/<arch-abi>/…` vs `<game>/tcc/…`); a `gcc`
shard wins over a `tcc` shard for the same region. The `<arch-abi>` is the
runtime's own (`PSX_OVERLAY_ARCH_ABI` in `overlay_loader.h`, the running slice
of a universal macOS binary): the runtime exports it to every compile it spawns
and macOS compiles pass the matching `-arch`, so an x86_64 runtime under Rosetta
gets x86_64 shards even though Xcode's clang defaults to arm64. See
[`docs/FEATURES.md`](FEATURES.md), [`docs/OVERLAY_CACHE_V2.md`](OVERLAY_CACHE_V2.md),
and [`docs/ASYNC_OVERLAY_COMPILE.md`](ASYNC_OVERLAY_COMPILE.md).
## Renderers
Three GPU backends behind one interface:
- **Software rasterizer** — CPU, most portable, the reference look.
- **OpenGL** — GPU-authoritative VRAM/FBO renderer, the default; moves
rasterization and supersampling onto the GPU. Falls back to software if GL
init fails. (See [`docs/internal/GL_RENDERER_HANDOFF.md`](internal/GL_RENDERER_HANDOFF.md).)
- **Vulkan** — experimental. The build option `PSX_ENABLE_VULKAN` defaults **ON**
(compiled when the SDK tools are present), but it is not the runtime default
renderer: selecting it also requires the game to offer Vulkan and the user to
request it, otherwise the runtime falls back to OpenGL.
Widescreen (a genuine wider GTE FOV, not a stretch) is opt-in and gen-time; see
[`WIDESCREEN.md`](WIDESCREEN.md) and
[`docs/internal/NATIVE_WIDE_PLAN.md`](internal/NATIVE_WIDE_PLAN.md).
## The oracle model (how correctness is checked)
PSXRecomp validates itself against **Beetle PSX** (the mednafen-psx libretro
core), run as a **separate process** with an identical TCP JSON debug protocol:
- `psx-runtime` — the recompiled runtime (debug server on port 4370).
- `psx-beetle` — Beetle PSX (debug server on port 4380).
A tool written against one works against the other by switching ports; cross-
checking is done by querying both, never by sharing state in one process. There
is also a first-divergence **co-sim** build that cycle-locksteps the compiled
backend against the interpreter. See
[`docs/internal/COSIM_ORACLE.md`](internal/COSIM_ORACLE.md),
[`docs/config_schema.md`](config_schema.md), and [`TCP_COMMANDS.md`](TCP_COMMANDS.md).
## Configuration
A game is configured by its **game config** (`game.toml`). A **BIOS config**
(`bios/*.toml`) describes a BIOS image's identity and address model.
The two are **not merged.** The BIOS config is consumed only by the recompiler
at build time (`psxrecomp-bios`, and `psxrecomp-game` for the address model);
the shipping runtime never loads it — `runtime/src/main.cpp` contains no call to
`load_bios_config`. `[runtime]` keys therefore take effect only from `game.toml`,
`settings.toml`, the CLI, and the environment. Full schema:
[`docs/config_schema.md`](config_schema.md).
## Where to go next
- [`EXECUTION_MODEL.md`](EXECUTION_MODEL.md) — static/native/interp in depth.
- [`BUILDING.md`](BUILDING.md) — dependencies + build steps.
- [`../CONTRIBUTING.md`](../CONTRIBUTING.md) — dev workflow and rules.
- [`../CLAUDE.md`](../CLAUDE.md) — the exhaustive engineering constitution.
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