HelloWorld.asm

 %macro IO 4  ; simple macro ,
mov rax,%1   ;  param 1 ->  system call number                             
mov rdi,%2    ;  param 2 ->  file descriptor                              
mov rsi,%3     ;  param 3 ->  message                       
mov rdx,%4      ;  param 4 ->  length                         
syscall                                     
%endmacro  
section .data
    m1 db "enter string",10    ;10 ->line feed 
    l1 equ $-m1                         
    m2 db "Entered",10    
    l2 equ $-m2                         
    m3 db "Length is ",10            
    l3 equ $-m3 
    m4 db "Write an X86/64 ALP to accept a string and to display its length" ,10  
    l4 equ $-m4
    m5 db "Exiting now" ,10    
    l5 equ $-m5
    m6 db "Exp second" ,10    
    l6 equ $-m6
    m7 db 10    
section .bss
    string resb 50                      ;string array of size 50
    strl equ $-string 
    count resb 1
    _output resb 20
section .text
    global _start

_start:
    IO 1,1,m6,l6    ; display
    IO 1,1,m4,l4    ; display
    IO 1,1,m1,l1    ; display
 input:
    IO 0,0,string,strl
    mov [count],rax ;count now points to rax 
 output:
    IO 1,1,m2,l2    ; display
    IO 1,1,string,strl
    IO 1,1,m3,l3    ; display 
    mov rax,[count] ; value of count passed into rax   
    call hex_to_dec
    IO 1,1,_output,16
    IO 1,1,m7,1
 exit:
    IO 1,1,m5,l5     
    mov rax, 60     ; system call for exit
    mov rdi, 0      ; exit code 0
    syscall

hex_to_dec:
        mov rsi,_output+15  ; max size of display , for convinience set to 16 and rsipoints to output[16]
        mov rcx,2           ; loop count , or number of digits displayed , 2 digits (unlikely we will enter string > 99)(prints preceding zeros otherwise)
    letter2:	
        xor rdx,rdx         ; setting rdx to null without setting a null byte (a tip i saw on reddit) needed to clean dl for use 
        mov rbx,10          ; conversion base
        div rbx             ; dividing by conversion base
        cmp dl,09h          ; comparing 09h with dl , since the division remainder ends up in dx and since its one digits its in dl
        jbe add30           ; if value under in 0-9 , we directly add 30h to get ascii 0-9
    add30:	
        add dl,30h          ; adding 30h
        mov [rsi],dl        ; moving the ascii we generated to rsi
        dec rsi             ; rsi now points to the next place in display or output[n-1]
        dec rcx             ; loop 
        jnz letter2
ret

created 3 years ago by Tssm Kirti Kamble 75

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