Printing a number in x86-64 assembly - linux

Question

Okay, all I am trying to do is print a number (up to 18446744073709551616) in x86-64 assembly for Linux. Can anyone please tell me why this program will not work? All that happens is that it runs and exits. Thank you for all the help you can give!
GLOBAL _start
SECTION .text
;PRINTCHAR
; MOV [LETTER],RAX
;
; MOV RAX,1
; MOV RDI,1
; MOV RSI,LETTER
; MOV RDX,1
; SYSCALL
; RET
PRINTDEC:
MOV R9,18 ;SO IT CAN POINT TO THE END OF THE BUFFER
MOV R10,0
START:
MOV R8,NUMBER
MOV RDX,0 ;CLEAR OUT RDX TO AVOID ERRORS
MOV RBX,10 ;WHAT TO DIVIDE BY
DIV RBX ;DIVIDE OUR NUMBER BY TEN
CMP RAX,0 ;IF OUR QUOTENT IS ZERO THEN WE ARE DONE, PRINT THE BUFFER
JE END
JMP ADDBUF
ADDBUF:
ADD R8,R9 ;MOV TO THE CURRENT LOCATION IN OUR BUFFER
ADD RDX,0x30
; ADD R8,R10
MOV [R8],RDX ;MOV THE LAST NUMBER IN OUR BUFFER TO RDX
DEC R9
INC R10
JMP START
END:
ADD R8,R9 ;add the very last digit
MOV [R8],RDX
INC R10
MOV RAX,1
MOV RDI,1
MOV RSI,R8
MOV RDX,R10
SYSCALL
RET
_start:
MOV RAX,55
CALL PRINTDEC
MOV RAX,60
MOV RDI,0
SYSCALL
SECTION .bss
LETTER: RESB 1
NUMBER: RESB 19

Answer 1

PRINTDEC:
LEA R9, [NUMBER + 18] ; last character of buffer
MOV R10, R9 ; copy the last character address
MOV RBX, 10 ; base10 divisor
DIV_BY_10:
XOR RDX, RDX ; zero rdx for div
DIV RBX ; rax:rdx = rax / rbx
ADD RDX, 0x30 ; convert binary digit to ascii
TEST RAX,RAX ; if rax == 0 exit DIV_BY_10
JZ LAST_REMAINDER
MOV byte [R9], DL ; save remainder
SUB R9, 1 ; decrement the buffer address
JMP DIV_BY_10
LAST_REMAINDER:
TEST DL, DL ; if DL (last remainder) != 0 add it to the buffer
JZ CHECK_BUFFER
MOV byte [R9], DL ; save remainder
SUB R9, 1 ; decrement the buffer address
CHECK_BUFFER:
CMP R9, R10 ; if the buffer has data print it
JNE PRINT_BUFFER
MOV byte [R9], '0' ; place the default zero into the empty buffer
SUB R9, 1
PRINT_BUFFER:
ADD R9, 1 ; address of last digit saved to buffer
SUB R10, R9 ; end address minus start address
ADD R10, 1 ; R10 = length of number
MOV RAX, 1 ; NR_write
MOV RDI, 1 ; stdout
MOV RSI, R9 ; number buffer address
MOV RDX, R10 ; string length
SYSCALL
RET