%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 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.
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.
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.
There are various define directives to allocate space for variables for both initialized and uninitialized data.
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 |
| 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 can be defined using
CONSTANT_NAME EQU regular-exp or value
%assign constant_name value
%define constant_name value
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.
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