 section .data
m1 db 10,13, 'Processor is in real mode'
m1Len equ $-m1
m2 db 10,13, 'Processor is in protected mode'
m2Len equ $-m2


m3 db 10,13, 'Contents of GDTR are: '
m3Len equ $-m3

m4 db 10,13, 'Contents of LDTR are: '
m4Len equ $-m4

m5 db 10,13, 'Contents of IDTR are: '
m5Len equ $-m5

m6 db 10,13, 'Contents of TR are: '
m6Len equ $-m6

m7 db 10,13, 'Contents of MSW are: '
m7Len equ $-m7

colon db ':'
newline db 10

section .bss
 gdt resw 1
 resd 1
 
 ldt resw 1
 
 idt resw 1
 resd 1
 
 tr resw 1
 
 msw resw 1
 
 disp_buff resb 8

%macro disp 2
 mov eax,04
 mov ebx,01
 mov ecx,%1
 mov edx,%2
 int 80h
%endmacro

section .text
      global _start

_start:
 smsw ax
 mov[msw],ax 
 bt ax,0
 jc prm
 disp m1,m1Len
 jmp exit
 
exit:
 mov eax,1 
 mov ebx,0  
 int 80h

prm:
 disp m2,m2Len
 
next1:
 sgdt[gdt]
 sldt[ldt]
 sidt[idt]
 str[tr]
 smsw[msw]
 
 disp m3,m3Len
 mov bx,[gdt+4]
 call disp4
 
 mov bx,[gdt+2]
 call disp4
 
 disp m4,m4Len
 mov bx,[ldt]
 call disp4 
 disp m5,m5Len
 mov bx,[idt]
 call disp4
 
 mov bx,[idt+2]
 call disp4
 
 disp m6,m6Len
 mov bx,[tr]
 call disp4
 
 disp m7,m7Len
 mov bx,[msw]
 call disp4
  disp newline,1
 jmp exit
 
disp4:
 mov ecx,4 
 mov edi, disp_buff
 
up1:
 rol bx,04
 mov al,bl
 and al,0fh
 cmp al,09
 jbe y
 add al,07h
y: 
 add al,30h
 mov[edi],al
 inc edi 
 loop up1
 disp disp_buff,4
 ret

created 4 years ago

Assembly Online Compiler

Write, Run & Share Assembly code online using OneCompiler's Assembly online compiler for free. It's one of the robust, feature-rich online compilers for Assembly language. Getting started with the OneCompiler's Assembly compiler is simple and pretty fast. The editor shows sample boilerplate code when you choose language as Assembly and start coding.

About Assembly

Assembly language(asm) is a low-level programming language, where the language instructions will be more similar to machine code instructions.

Every assembler may have it's own assembly language designed for a specific computers or an operating system.

Assembly language requires less execution time and memory. It is more helful for direct hardware manipulation, real-time critical applications. It is used in device drivers, low-level embedded systems etc.

Syntax help

Assembly language usually consists of three sections,

Data section

To initialize variables and constants, buffer size these values doesn't change at runtime.
bss section

To declare variables
text section

_start specifies the starting of this section where the actually code is written.

Variables

There are various define directives to allocate space for variables for both initialized and uninitialized data.

1. To allocate storage space to Initialized data

Syntax

variable-name    define-directive    initial-value

Define Directive	Description	Allocated Space
DB	Define Byte	1 byte
DW	Define Word	2 bytes
DD	Define Doubleword	4 bytes
DQ	Define Quadword	8 bytes
DT	Define Ten Bytes	10 bytes

2. To allocate storage space to un-initialized data

Define Directive	Description
RESB	Reserve a Byte
RESW	Reserve a Word
RESD	Reserve a Doubleword
RESQ	Reserve a Quadword
REST	Reserve a Ten Bytes

Constants

Constants can be defined using

1. equ

To define numeric constants

CONSTANT_NAME EQU regular-exp or value

2. %assign

To define numeric constants.

%assign constant_name value

3. %define

To define numeric or string constants.

%define constant_name value

Loops

Loops are used to iterate a set of statements for a specific number of times.

mov ECX,n
L1:
;<loop body>
loop L1

where n specifies the no of times loops should iterate.

Procedures

Procedure is a sub-routine which contains set of statements. Usually procedures are written when multiple calls are required to same set of statements which increases re-usuability and modularity.

procedure_name:
   ;procedure body
   ret