diff -uprN src/string/riscv64/strlen.S src/string/riscv64/strlen.S
--- src/string/riscv64/strlen.S	1970-01-01 08:00:00.000000000 +0800
+++ src/string/riscv64/strlen.S	2023-04-18 13:37:22.644057680 +0800
@@ -0,0 +1,82 @@
+# size_t strlen(const char *str)
+# a0 holds *str
+.global strlen
+.type strlen,@function
+strlen:
+#ifdef __riscv_vector
+    mv      t0, a0      # Save start
+    csrr    t1, vlenb 
+    addi    t1, t1, -1
+    add     a3, t0, t1
+    not     t1, t1
+    and     a3, a3, t1
+    sub     a4, a3, t0
+    beq     a3, t0, loop # if already aligned
+
+unaligned:
+    lbu     t1, 0(t0)
+    beqz    t1, found
+    addi    t0, t0, 1
+    blt     t0, a3, unaligned
+
+loop:
+    vsetvli  a1, x0, e8, m8, ta, ma  # Vector of bytes of maximum length
+    vle8ff.v v8, (t0)      # Load bytes
+    csrr     a1, vl           # Get bytes read
+    vmseq.vi v0, v8, 0    # Set v0[i] where v8[i] = 0
+    vfirst.m a2, v0       # Find first set bit
+    add      t0, t0, a1        # Bump pointer
+    bltz     a2, loop         # Not found?
+
+    add    a3, a3, a1        # Sum start + bump
+    add    t0, t0, a2        # Add index
+    sub    a3, t0, a3        # Subtract start address+bump
+    add    a0, a3, a4
+    ret
+
+found:
+    sub    a0, t0, a0
+    ret
+
+#else
+    mv     a5, a0      
+    andi   a4, a0, 7         
+    beqz   a4, aligned  # if already aligned
+
+unaligned:
+    lbu    a4, 0(a5)
+    beqz   a4, count
+    addi   a5, a5, 1
+    andi   a4, a5, 7
+    bnez   a4, unaligned
+
+aligned:
+    la     t0, magic
+    ld     a1, 0(t0)
+    ld     a2, 8(t0)
+
+loop:
+    ld     a3, 0(a5)   
+    add    a4, a3, a1
+    not    a3, a3
+    and    a4, a4, a3
+    and    a4, a4, a2
+    bnez   a4, found
+    addi   a5, a5, 8
+    j      loop
+
+found:
+    lbu    a4, 0(a5)
+    beqz   a4, count
+    addi   a5, a5, 1
+    j      found
+
+count:
+    sub    a0, a5, a0
+    ret
+
+.section .data
+magic:
+    .dword 0xfefefefefefefeff
+    .dword 0x8080808080808080
+#endif