 section .data
	hello:     db 'Hello world!',10    ; 'Hello world!' plus a linefeed character
	helloLen:  equ $-hello             ; Length of the 'Hello world!' string

section .text
	global _start
	
main:
        endbr64 
        push   rbp          # save the base pointer to the stack
        mov    rbp,rsp      # put the previous stack pointer into the base pointer
        sub    rsp,0x10     # 0x10 => 16 byte, balance the stack onto a 16-byte boundary
        # DWORD PTR means Double-word property which is 32,
        mov    DWORD PTR [rbp-0x8],0x10     # so this instruction is saying "move 16 to the 32 bits of the stack in a place which address starts with rbp-8
        mov    DWORD PTR [rbp-0x4],0x0  # and this instruction is saying "move 0 to the 32 bits of the stack in a place which address starts with rbp-4
        mov    eax,DWORD PTR [rbp-0x4]  # this copies in the value at the address rbp-0x4 into eax (local)
        mov    edx,0x1  # this copies in the value of 1 into register edx
        mov    ecx,eax  # this copies in the value of eax into register ecx
        shl    edx,cl   # this shifts edx left by 1 bit
        mov    eax,edx  # value of eax is overwritten with copied value from register edx
        mov    DWORD PTR [rbp-0xc],eax  # address of eax is copied into rbp-c
        mov    eax,DWORD PTR [rbp-0xc]  # this copies in the value at the address rbp-0xc into address eax
        cmp    eax,DWORD PTR [rbp-0x8]  # this compares the value stored in rbp-0x8 to the value in eax
        jg     0x11c6 <shift+93>    # jump to line 38 (nop) if eax is greater than
        mov    eax,DWORD PTR [rbp-0x8]  # move the value of 32-bit pointed to by rbp-0x8 into eax
        and    eax,DWORD PTR [rbp-0xc]  # move the value of 32-bit pointed to by rbp-0xc into eax
        mov    edx,eax      #  mov the value stored in eax into edx
        mov    eax,DWORD PTR [rbp-0x4]  # move the value of 32-bit pointed to by rbp-0x4 into eax
        mov    ecx,eax  # move value stored in eax into ecx
        sar    edx,cl   # short-hand, moves value in address edx to one opcode
        mov    eax,edx  # moves value stored in edx to eax
        mov    esi,eax  # moves value stored in eax into esi
        lea    rdi,[rip+0xe4e]        # 0x2004  
        mov    eax,0x0
        call   0x1070 <printf@plt>      # call print function
        add    DWORD PTR [rbp-0x4],0x1
        jmp    0x1183 <shift+26>
        nop
        nop
        leave  
        ret

created 4 years ago by RAMMY

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