#ifdef TEST
.globl strcspn_
strcspn_:
#else
.globl strcspn
strcspn:
#endif
#ifdef __x86_64__
    mov %rsi, %rcx
    xor %rax, %rax
1:
    movb    (%rsi), %cl
    cmp (%rdi), %cl
    je  3f
    inc %rsi
    cmp $0, (%rsi)
    jne 1b
2:
    mov %rcx, %rsi
    inc %rdi
    inc %rax
    cmp $0, %rdi
    jne 1b
3:
    ret
#endif


--------------------------------------------------------------------

Breakpoint 2, strcspn_ () at ../../src/string/strcspn.S:16
16      cmp $0, (%rsi)
(gdb) x/c $rsi
0x4010b4:   0 '\000'
(gdb) b 18
Breakpoint 3 at 0x400cf8: file ../../src/string/strcspn.S, line 18.
(gdb) c
Continuing.

Breakpoint 2, strcspn_ () at ../../src/string/strcspn.S:16
16      cmp $0, (%rsi)
(gdb)