> Although SSE2 is always available on x86-64, I also disabled the cpuid bit for SSE2 and SSE to see if it could nudge glibc into using scalar registers to copy data. I immediately got a kernel panic. Ah, well.

I think you need to recompile your compiler, or disable those explicitly via link / cc flags. Compilers are fairly hard to get to coax / dissuade SIMD instructions, IMHO.