ref: 7fa5db9d6a8d3b7d1430cab7df9fda9b8ee1ec0b dir: /sys/src/libc/amd64/strlen.s/
TEXT strlen(SB),$0 MOVL $0, AX MOVQ $-1, CX CLD /* * look for end of string */ MOVQ RARG, DI REPN; SCASB MOVQ DI, AX SUBQ RARG, AX SUBQ $1, AX RET