ref: 2d56837b2fabf6a7cc11f02b51f20a1e35128c57
dir: /sys/src/libc/arm64/cycles.s/
#define SYSREG(op0,op1,Cn,Cm,op2) SPR(((op0)<<19|(op1)<<16|(Cn)<<12|(Cm)<<8|(op2)<<5)) #define CNTVCT_EL0 SYSREG(3,3,14,0,2) TEXT cycles(SB), 1, $-4 MRS CNTVCT_EL0, R1 MOV R1, (R0) RETURN