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Hello World in Assembly

Discussion in 'Assembly Language Programming (ALP) Tutorials' started by lionaneesh, Feb 9, 2011.

  1. lionaneesh

    lionaneesh New Member

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    Assembly language is one of the oldest low-level programming language for computers , micro-processors etc etc...It implements a symbolic representation of the Machine Opcodes needed to program a given CPU Architecture...Its a language based on mnemonics , labels , instructions , memory addresses and Registers... A major disadvantage of programming in assembly is that it is not at all platform independent and thus , cannot be ported to other architectures...

    The Code



    In this article we'll be learning about a simple Hello World Program in x86 Unix Assembly and Will be using basic syscall table to accomplish our tasks...

    We'll be using write() function to write 'Hello World' to STDIN

    Syntax

    Code:
    write(int fd, char *Buff, int NumBytes);
    
    In a Assembly program the arguments can be passed on to the function via a simple call stack or via registers..

    We'll be using registers to pass the arguments...

    Points to remember
    1. eax should contain the syscall number
    2. ebx should point to the first
    3. ecx should point to the second
    4. edx should point to the third
    5. esx should point to the fourth
    6. edi should point to the fifth
    Syscall(system call) table can be looked up in /usr/include/asm/unistd_32.h

    helloworld.asm
    Code:
    segment .data
    
    helloWorldString  db	"Hello World",0xA ; 0xA is ascii code for line feed
    
    helloWorldStringlen equ $ -  helloWorldString ; it contains the length of string
    
    
    
    segment .text
    
    global _start
    
    
    
    _start :
    
    	mov eax,4 			;syscall of write is 4
    
    	mov ebx,1 			;int fd = STDIN is 1
    
    	mov ecx,helloWorldString	;char *
    
    	mov edx,helloWorldStringlen	;int len
    
    	int 0x80			;shift to kernel mode
    
    
    ; exit call
    
    
    	mov eax,1 			;syscall of exit
    
    	mov ebx,0
    			; exit(0)
    	int 0x80
    			; shift to kernel mode
    
    segment .data

    The first 2 lines simply define a db string containing 'Hello World' and the length of string

    segment .text

    First we delare a global declaration of _start lable so as to provide a entry point to the program..

    The main code have been commented above for explanation , so as to provide a better understanding.

    Lets now Assemble and link the program

    Code:
    aneesh@aneesh-laptop:~/Programming/ASM$ nasm -f elf32 helloworld.asm -o helloworld.o
    
    aneesh@aneesh-laptop:~/Programming/ASM$ ld helloworld.o -o helloworld
    
    Now lets run the program

    Code:
    aneesh@aneesh-laptop:~/Programming/ASM$ ./helloworld 
    
    Hello World
    
    
    That's enough for this Article … Stay tuned for more...
     
    shabbir likes this.
  2. lionaneesh

    lionaneesh New Member

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    Thanks for reading and accepting..
     
  3. davidriched

    davidriched New Member

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    This is a wonderful opinion. The things mentioned are unanimous and needs to be appreciated by everyone. The initiative taken for the concern is very serious and need an attention of every one. This
     
  4. lionaneesh

    lionaneesh New Member

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    Sorry Couldn't understand you!!!!

    Maybe you have posted your reply in the wrong thread!!!
     
  5. sudha06

    sudha06 New Member

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    very nice post world in assembly
     
  6. lionaneesh

    lionaneesh New Member

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    Thanks and finally i am over with my boards and now ready to post some great articles to G4E
     

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