Question about the rationale behind disabling FLDCW and similar instructions

[yasmineyuy]

Hello, I have a question regarding the decision to disable certain instructions like FLDCW and FSTSW in the testing environment(xed_util.cc).I understand that these instructions operate on the FPU/SSE control and status registers. Could you please elaborate on the specific technical reasons for excluding them?

And I noticed that FLDCW is explicitly disabled, while LDMXCSR is seemingly allowed.From a high-level perspective, both instructions seem to serve a similar purpose: they load a value to configure the floating-point environment . Could you please help me understand the rationale behind this differential treatment?

Thanks

[ksteuck]

My vague recollection is that fldcw was causing significant divergence between different expected end states, maybe even non-determinism but I'm less sure about this.