Preloading custom strchr() - ubuntu crashes

Question

I implemented that strchr()

        global  strchr
strchr:
        cmp     byte[rdi], 0
        je      end
        cmp     [rdi], sil
        je      end
        add     rdi, 1
        jmp     strchr
end:    mov     rax, rdi
        ret

When I preload it as .so using,

export LD_PRELOAD=abs/path/to/lib.so

Ubuntu 16.04 crashes. Sometimes it completly crahses, sometimes it displays SIGILL (corrupted data ?).

When I preload it using opensuse 4, it works.

Any idea why ?

Answer 1

Thanks to Michael Petch :

That strchr() doesn't conform to manual for it doesn't return NULL when character is not found.

Fixed strchr() :

global  strchr
strchr:
        cmp     [rdi], sil;first check for character (useful if user searches '\0')
        je      end
        cmp     byte[rdi], 0;then if it is EoS and the character is not in the string, return NULL
        je      eos
        add     rdi, 1
        jmp     strchr
eos:    mov     rax, 0
        ret
end:    mov     rax, rdi
        ret