Native execution oracle¶

crimson_re.dbg.native_oracle runs functions of the original crimsonland.exe under Unicorn x86 emulation, so a port function can be checked bit for bit against native code without a capture. Use it for float math, spawn stat tables and other leaf or near-leaf gameplay code.

How it works¶

• The PE is mapped at its preferred base 0x00400000 with section permissions. Writable .data/.data1 start with their file contents, so globals hold their pre-startup values.
• Each call starts with fninit and control word 0x007F (PC24, round-to-nearest). That is the precision Direct3D 8 leaves during gameplay; see float parity policy. Pass control_word= to override.
• Stack arguments follow cdecl/stdcall: Python float and F32 push a float32, and F64 pushes a double. ecx= covers thiscall. st= preloads the x87 stack for register-argument helpers such as __ftol. CallResult has eax, edx, the exact 80-bit x87 stack (st0) and stack_popped (the callee's ret N).
• run(start, stop, regs=..., frame=...) executes a code fragment of a larger function, for example the spawn block of typo_gameplay_update_and_render.
• run_static_initializers() runs the CRT __xi and __xc tables. This applies C++ defaults such as the weapon-table projectile speeds. The CRT stdio and locale initializers trap and are skipped.
• The CRT runs natively. TlsGetValue returns a fake _tiddata, so crt_rand works, and oracle.rand_state reads or writes its _holdrand. Win32 heap calls come from a scratch heap, and critical sections are no-ops. An FS segment points at a fake TIB, so SEH prologues (fs:[0]) work.
• Any access to unmapped memory, write to read-only memory, jump through an unset pointer or call of an import without a stub raises NativeTrap. The message names the address, the instruction, the registers and the nearest symbol from analysis/ghidra/maps. That tells you which global to seed or which callee to stub.
• stub(name_or_address, fn_or_constant, pop=, returns="eax"|"st0") replaces a native function with a Python callback. stub_import(name, ...) answers an import. trace_memory() records the globals that native code reads and writes. snapshot() and restore() reset state between cases.

from crimson_re.dbg.native_oracle import NativeOracle

oracle = NativeOracle()
oracle.run_static_initializers()
angle = oracle.alloc_f32s(1.0)
oracle.write_f32("frame_dt", 0.016)
oracle.call("angle_approach", angle, 2.0, 3.0)  # angle_approach(float*, float, float)
print(oracle.read_f32(angle))

Running the differential tests¶

The executable lives under the gitignored game_bins/, and Unicorn's JIT does not run inside the agent command sandbox, so locally the tests are opt-in. CI downloads the hash-checked 1.9.93 binaries and runs them on every push:

CRIMSON_NATIVE_ORACLE=1 uv run pytest tests/native_oracle

Without the variable, or without the executable, the tests are skipped. A failure lists mismatching fields grouped by kind. bits means the float32 or integer value differs. unrounded means the float32 bits agree, but the port stores a wider double where native stores a float32.

Limitations¶

• Unicorn evaluates fsin, fcos, fpatan and the other transcendentals with host double libm. PC24 rounding of fadd/fsub/fmul/fdiv/fsqrt is exact. The oracle therefore checks the rounding structure around trig, not extended-precision trig accuracy.
• Code that reaches Direct3D, DirectInput or audio traps. Stub those callees, as the tests stub sfx_play_panned and console_printf. For the grim.dll vtable, install_fake_grim in tests/native_oracle/_support.py installs an interface whose methods return 0 or run per-method handlers.
• Globals start from the executable's file image plus static initializers. Runtime tables that game startup fills, such as perk ids, must be seeded or built by calling their init functions (weapon_table_init, effect_defaults_reset). prepare_gameplay in tests/native_oracle/_support.py seeds what projectile_update and the fire paths need, including binding vec2_normalize_impl to the x87 d3dx_c_vec2_normalize: the lazy D3DX dispatcher would otherwise probe the registry and CPU features.