This seems to work OK as well. I have always been keen to make use of the MMX registers when they are just about useless for much else.
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NOSTACKFRAME
testme proc
movq mm0, rbx
movq mm1, r12
movq mm2, r13
movq mm3, r14
movq mm4, r15
movq mm5, rsi
movq mm6, rdi
movq mm7, rbp
mov rbx, 1
mov r12, 2
mov r13, 3
mov r14, 4
mov r15, 5
mov rsi, 6
mov rdi, 7
mov rbp, 8
movq rbx, mm0
movq r12, mm1
movq r13, mm2
movq r14, mm3
movq r15, mm4
movq rsi, mm5
movq rdi, mm6
movq rbp, mm7
ret
testme endp
STACKFRAME
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