30天自制操作系统书中fin和putloop没看到哪里调用了，能帮我详细解释一下这个是怎么运行的吗？

; hello-os
; TAB=4

    ORG     0x7c00          

    JMP     entry
    DB      0x90
    DB      "HELLOIPL"  
    DW      512             
    DB      1           
    DW      1           
    DB      2           
    DW      224         
    DW      2880            
    DB      0xf0        
    DW      9       
    DW      18          
    DW      2           
    DD      0       
    DD      2880        
    DB      0,0,0x29        
    DD      0xffffffff      
    DB      "HELLO-OS   "
    DB      "FAT12   "  
    RESB    18              

entry:
MOV AX,0

MOV SS,AX
MOV SP,0x7c00
MOV DS,AX
MOV ES,AX

    MOV     SI,msg

putloop:
MOV AL,[SI]
ADD SI,1

CMP AL,0
JE fin
MOV AH,0x0e

MOV BX,15

INT 0x10

JMP putloop

fin:
HLT

JMP fin

msg:
DB 0x0a, 0x0a

DB "hello, world"
DB 0x0a

DB 0

    RESB    0x7dfe-$    

    DB      0x55, 0xaa

https://blog.csdn.net/bahunj93679/article/details/101090235