section .data
    introMsg dw "ALP to detect the operating mode of the microprocessor and display the contents of some system registers"
    introMsgLen equ $ - introMsg
    
    gdtrMsg db 10,10,"Contents of GDTR : ",10
    gdtrMsgLen equ $ - gdtrMsg
    
    ldtrMsg db 10,10,"Contents of LDTR : ",10
    ldtrMsgLen equ $ - ldtrMsg
    
    idtrMsg db 10,10,"Contents of IDTR : ",10
    idtrMsgLen equ $ - idtrMsg
    
    trMsg db 10,10,"Contents of TR : ",10
    trMsgLen equ $ - trMsg
    
    mswMsg db 10,10,"Contents of MSW (CR0) register : ",10
    mswMsgLen equ $ - mswMsg
    
    protectedMsg db 10,10,"The Microprocessor is in the protected mode"
    protectedMsgLen equ $ - protectedMsg
    
    proMsg db 10,10,"The contents of the system registers are as follows : "
    proMsgLen equ $ - proMsg
    
    realMsg db 10,10,"The Microprocessor is in the real mode"
    realMsgLen equ $ - realMsg
    
    colon db "  :  "
    colonLen equ $ - colon 
    
section .bss
    gdtr resd 1 ;to store 48-bit GDTR value-resd(32-bit) and resw(16-bit).
         resw 1
         
    ldtr resw 1 ;to store 16-bit LDTR
    
    idtr resd 1  ;to store 48-bit LDTR value-resd(32-bit) and resw(16-bit).

         resw 1
         
    tr resw 1
    
    msw resd 1
    
    result resb 4
    
%macro write 2
    mov rax,1
    mov rdi,1
    mov rsi,%1
    mov rdx,%2
    syscall
%endmacro

section .text
    global _start

_start:
         write introMsg,introMsgLen
        
         smsw eax   ; This instruction is used to store the contents of the MSW register into the EAX register.
         bt eax,0     ; copy the 0th  least significant bit from EAX to the carry flag.
         
         jc protected_mode	;if CF is set ,processor is in protected mode
         
         write realMsg,realMsgLen
         
         jmp endOfProgram
         
protected_mode :
         write protectedMsg , protectedMsgLen
         
         write proMsg , proMsgLen
         
         sgdt [gdtr]   ; Stores the content of the global descriptor table register (GDTR) in the destination operand gdtr
         sldt [ldtr]  ;store LDTR
         str [tr]  
         smsw [msw]
         
         write gdtrMsg,gdtrMsgLen
         mov bx,[gdtr+4]  ;move upper half of gdtr in bx reg.
         call disp
         mov bx,[gdtr+2] 
         call disp
         write colon , colonLen
         mov bx,[gdtr]
         call disp
         
         write ldtrMsg,ldtrMsgLen
         mov bx,[ldtr]
         call disp
         
         write idtrMsg,idtrMsgLen
         mov bx,[idtr+4]
         call disp
         mov bx,[idtr+2]
         call disp
         write colon , colonLen
         mov bx,[idtr]
         call disp
         
         write trMsg,trMsgLen
         mov bx,[tr]
         call disp
         
         write mswMsg,mswMsgLen
         mov bx,[msw+2]   ;upper half of CR0 or MSW
         call disp
         mov bx,[msw]
         call disp
         
endOfProgram:    
    mov rax, 60
    mov rdi, 0
    syscall
    
disp:
        mov rdi, result ;point rdi to result variable
        mov cx,04 ;load count of rotation in cl
up1:
        rol bl,04 ;rotate number left by four bits
        mov dl,bl ;move lower byte in dl
        and dl,0fh ; get only LSB
        cmp dl,09h ;compare with 39h
        jg add_37 ;if greater than 39h skip add 37
        add dl,30h
        jmp skip1 ;else add 30
add_37: add dl,37h
skip1:  mov [rdi],dl ;store ascii code in result variable
        inc rdi ;point to next byte
        dec cx ;decrement the count of digits to display
        jnz up1 ;if not zero jump to repeat
        
        write result , 4
        
        ret
by