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STATUS_WX86_FLOAT_STACK_CHECK
The status points specifically at legacy x86 floating-point stack state
STATUS_WX86_FLOAT_STACK_CHECK is the one remaining WX86 status whose published name adds a concrete technical dimension: floating-point stack checking. On x86, Microsoft's C runtime documentation for _statusfp and _statusfp2 explicitly distinguishes x87 and SSE2 floating-point status and notes x87 stack overflow and underflow conditions. This is relevant because x87 uses a stack-oriented register model that is different from SSE scalar/vector state.
The NTSTATUS catalog identifies this value as part of the Win32 x86 emulation subsystem. It does not document the exact emulator instruction or internal handler that produced the check, so the page does not claim that a specific x87 opcode always triggers the code. The defensible evidence is the emulated x86 floating-point context: x87 control/status words, stack/tag state if available, current instruction, and whether the application or compatibility layer also uses SSE2.
For diagnosis, avoid clearing floating-point state before it is captured. Microsoft warns that floating-point operations between a known state and reading the status can change the result, and recommends separating x87 and SSE2 status with _statusfp2 on applicable x86 processors. In an emulation trace, capture the equivalent state at the fault boundary. This code is not a generic “float value is invalid” result and should not be fixed by changing numeric precision without identifying the stack condition and instruction sequence.
What to inspect
- Capture x87 control/status and stack/tag state before cleanup or additional FP operations.
- Record the emulated x86 instruction and whether the path also uses SSE2 state.
- Do not reduce the status to generic NaN/precision handling without stack evidence.
References
- Microsoft Open Specifications: NTSTATUS values
- Microsoft: _status87, _statusfp, and _statusfp2
- Microsoft DbgShell source: WX86 exception filters
- Microsoft: Controlling Exceptions and Events
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