ref: e81e1a4aeddad2bc612c9c5243573250b6ff33a4 dir: /sys/src/ape/lib/ap/amd64/cycles.s/
TEXT _cycles(SB),1,$0 /* time stamp counter; cycles since power up */ RDTSC MOVL AX, 0(RARG) /* lo */ MOVL DX, 4(RARG) /* hi */ RET