assignment -6 - Posts

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 0 th least significant bit from EAX to the carry flag.
jc protected_mode ;if CF is set ,processor is in protected mode

Progressive Education Society's
MODERN COLLEGE OF ENGINEERING, PUNE-05.
Department of Computer Engineering

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