It may be unaligned on certain architectures (e.g. macOS).
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We started seeing this intermittently on Intel Macs after !9060. Since FPU_sig was returning an XMM_SAVE_AREA32*, the compiler assumed it was correctly aligned, and emitted `movaps` for a copy. If the pointer wasn't aligned, that of course failed. Presumably alignment is dodgy on macOS because we're returning a pointer a few fields into the context struct - `__fpu_fcw` is preceded by `int __fpu_reserved[2]`.