Skip to main content

NASM Assembly - Hello World

Whenever you start programming, there is usually the first program that prints the phrase "Hello world" to the screen.  Well, let us keep that tradition and write an entire assembly program that print that message to the screen.


;Our Assembly Program file
SECTION .data
SECTION .bss
SECTION .text


The preceding is the standard file format of an assembly program using the Netwide assembler, or NASM.



To write something to the screen, we first need to store the value of what we want to render to the screen by declaring variables.




;Our Assembly Program file
SECTION .data
ourHelloMsg: db "Hello world, we are in assembly", 10, 0 ;our simple message
SECTION .bss
SECTION .text






Next, we want to use some real world practical assembly coding to print this message to the screen.  We could simple using the Linux int80h instruction to tell the operating system to print this message (if you aren't sure what I mean by this, do not worry), however we will use the printf function which is part of the C standard library.   This method will teach us how to mix assembly and C.



So let us get started:








;Our Assembly Program file
SECTION .data
ourHelloMsg: db "Hello world, we are in assembly", 10, 0 ;our simple message
SECTION .bss
SECTION .text
extern printf  ;this tell our compiler that printf is available remotely
global main    ;this tells our compiler to make "main" available to others 

main:
 ;create the stack frame
 push ebp
 mov ebp, esp


 ;push the address of the msg onto the stack
 ;-->NOTE: label are aliases for memory address
 push msg ;so here, msg stands in place of something like 0x3048503
 call printf
 ;destroy the stack frame
 mov esp, ebp
 pop ebp
 ret














Now to compile this program, pop open a terminal and bash out these commands:



nasm -f elf -o asm1.o asm1.asm
gcc -o asmProgram asm1.o
./asmProgram




















Labels:







































Comments











Post a Comment






























Popular posts from this blog





















Creating local variables In Assembly




























Lets go over how to create local variables inside of a pure assembly source code.   Much like always, you will start with a *.asm file that looks like this:   source code   SECTION .data  SECTION .bss  SECTION .text global main                    ;make main available to operating system(os) main:      ;create the stack frame      push ebp      push mov ebp, esp        ;destroy the stack frame      mov esp, ebp      pop ebp      ret   So, the above is the general layout of an NASM source file.  Our goal here is to create a local variable inside of the main method.  The only way to create a local variable is by using the stack.  Why?  Because we can only declare variable in storage locations and the only available storage locations are: text, bss, and data.  However, text section is only for code, so it is out of the question.  The bss and data sections are appealing, but to declare our "local" variable in these sections will defeat the purpose of these variables being local, t




















2 comments









Read more




























NASM Programming




























Many of you, if you are like me, might be interested in how assembly works.  You will be very surprised that assembly is very very easy, especially after you write a couple of simple programs.  But don't get me wrong, you will be frustrated at first, however that frustration, if you channel it right, will lead to serious life long learning and will give you a deeper appreciation of the beauty of assembly.   For more tutorial on assembly and visualization of these information, visit my youtube channel .   Okay so lets get started.  We will be using Netwide Assembler (NASM) to write our program.  The general format of NASM file is this:  ;This is a comment  SECTION .data  ;declare variable here    SECTION .bss  ;declare actual, dynamic variable    SECTION .text  ;where your program code/assembly code lives    ;  Working with Data Section  In your .data section, you can declare variables like this:   nameOfVariable: db  32  ;this declares a variable names nameOfVariable with byte valu




















Post a Comment









Read more






























Introduction to Linux Kernel Programming




























The Linux kernel is designed as a mixture of a monolithic binary image and a micro-kernel.  This combination allows for the best of both worlds.  On the monolithic side, all the code for the kernel to work with the user and hardware is already installed and ready for fast access, but the downside is that to add more functionality you need to rebuild the entire kernel.   In a different manner, a micro-kernel is composed of small pieces  of code that can be meshed today and more pieces can be added or removed as needed.  However, the downside to micro-kernel is a slower performance.     Adding a module to the Kernel   Linux is organized as both monolithic, one huge binary, and micro-kernel, as you can add more functionality to it.  The process of adding more functionality to the kernel can be illustrated by the crude image to the left.   The process begins by using the command insmod with the name of the kernel module you want (which usually ends with extension *.ko).  From here, the mod




















4 comments









Read more