ref: a21f832d454f36386c7e759c9291d3d4e1b09fca dir: /sys/src/libc/riscv64/cycles.s/
#define RARG R8 /* user-accessible CSRs */ #define CYCLO 0xc00 TEXT cycles(SB), 1, $-4 /* cycles since power up */ MOV CSR(CYCLO), RARG RET