64bit - Unable to find length of String in Assembly(nasm Linux) -

i have made program takes string input user , calculates length , display it. getting error segmentation fault (core dumped) when run program. code shown below

str_len:                    ;procedure calculate length of string     xor rdx,rdx     xor rcx,rcx             ;i want store length in rcx     mov rdx,[string]        ;string contains input taken user     mov rsi,rdx     mov rcx,'0'             ;by default rcx contain '0' decimal  up: cmp byte[rsi],0         ;compare if end of string     je str_o                ;if yes jump str_o      inc rcx                 ;increment rcx i.e., length     inc rsi                 ;point next location of rdx i.e.,string     jmp                  ;repeat till end of string  str_o:  mov rax,1           ;print final length         mov rdi,1         mov rsi,rcx         mov rdx,1         syscall ret 

i can guarantee rest of program correct. error in above part of code. error ?

the error here:

mov rdx,[string] ; string contains input taken user 

you loading rdx first 8 bytes of string content , not address of string. better use

lea rdx, string  ; lea = load effective address 

another problem output routine tries print number not converted ascii with

mov rax,1      ; sys_write - print final length mov rdi,1      ; stdout handle mov rsi,rcx    ; rsi should point buffer mov rdx,1      ; length of buffer - value of 1 prints 1 char syscall 

this doesn't work way. you'd have convert qword number in rcx ascii string before , pass address of string in rsi. search stack overflow questions this.