Step 3: Create a Hello World Application

Objective: Walk through the complete process of creating a hello world application using assembly code.

Assembling and compiling an .asm code file is a two part process:

  1. nasm -f win32 file.asm

    • nasm is the assembler program

    • -f specifies the format, which is win32

    • file.asm is the file to parse and then create the .obj file

  2. gcc file.obj -o file.exe

    • gcc is the compiler

    • file.obj is the assembled file used to create the executable

    • -o file.exe specifies the output file in the form of an executable

Assembly-Compile Process

  1. Create a helloworld.asm file using Visual Studio Code or your favorite text editor.

  2. Add this code:

    ; ------------------------------------------------------------------
    ; helloworld.asm
    ; This is a Win32 console program that writes "Hello World"
    ; on a single line and then exits.
    ; To assemble to .obj: nasm -f win32 helloworld.asm
    ; To compile to .exe:  gcc helloworld.obj -o helloworld.exe
    ; ------------------------------------------------------------------
            global    _main                ; declare main() method
            extern    _printf              ; link to external library
            segment  .data
            message: db   'Hello world', 0xA, 0  ; text message
                        ; 0xA (10) is hex for (NL), carriage return
                        ; 0 terminates the line
            ; code is put in the .text section
            section .text
    _main:                            ; the entry point! void main()
            push    message           ; save message to the stack
            call    _printf           ; display the first value on the stack
            add     esp, 4            ; clear the stack
            ret                       ; return
  3. Save it someplace on your computer. Be sure to keep the file extension as .asm.


  4. Go back to your command prompt

  5. cd to the directory where you saved helloworld.asm

  6. Use NASM to assemble the file and create the .obj file:

  7. Type: nasm -f win32 helloworld.asm.


    • NASM does not give you a message if the operation was successful.

    • Take note of any message that NASM displays.


    • Common Errors

      1. If you get a parser error, then you have an error in your code file. The first part of the text tells you the the line number of the error.


      2. If you a not recognized error, then your path is not set correctly. Go back to the previous section and verify that the locations of the assembler and compile are correctly added to the system path variable.


  8. If successful, the assembler would have created the helloworld.obj file. Verify that it exists.

    image17 image18

  9. Now, compile the file to create an executable file using GCC using command: gcc helloworld.obj -o helloworld.exe

    • If successful, the compiler would have created file helloworld.exe.


  10. Finally, execute the .exe file by running helloworld.exe to verify that it display Hello world.


  11. To get lab credit, show your instructor that your assembly environment works.