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FLDENV

Stores the contents of the current FPU environment—including the control word, status word, tag word, and the current floating-point instruction pointer—into a specified memory location.

The following table covers what the source and destinations can be.

DO NOT support LOCK

This instruction is supported in 64-bit mode and compatibility mode. It operates specifically on the x87 FPU state regardless of the current processor mode.

The destination memory region m28 MUST be aligned to a dword boundary to avoid potential performance penalties or alignment checks. Writing the FPU environment to memory is typically used before performing a context switch or when implementing exception handlers to preserve the floating-point state. Failure to allocate exactly 28 bytes of contiguous memory will result in a buffer overflow.