Assembly code example – square a number

Here is another example of assembly code that would square a number:

#Simple square function in assembly language for x86 architecture
.code32 #tell the assembler we are using 32bit

.section .data #we don't have nothing in the data section
.section .text

.globl _start

    push $9 #fixed value of 9
    # The call updates the eip - instruction pointer
    call square 

    mov %eax, %ebx #the return value would be on register %eax, so pass it on %ebx
    mov $1, %eax #system call for exit on eax register - that would be 1
    int $0x80 #interupt

.type square, @function
    mov 4(%esp), %eax #read the value to square basing from the stack pointer (esp)
    imul %eax, %eax # umm.. whatelse? multiply the value and store it on eax
    ret #return the value 

do the following from the command line to run the code

$ gcc -m32 -nostartfiles -o square square.s 
$ ./square 
$ echo $?

Shall produce 81 on the command prompt

Segmenation fault – core dump error assembly 32bit code on 64bit machine

I have a shiny 64 bit dell machine that tops ubuntu on it.
I working working on some other machine a bit of assemly code and I didn’t have a problem.
But when I run the same code my 64 machine i was getting the a segmentation falut error. Not surprising actually.
here is what I have done to resolve it:

1. Don’t forget to add .code32 at the beginning of your assembly file. [ talking about x86 architecture ]
2. Have the gcc multilib on your machine

sudo apt-get install gcc-4.7-multilib

3. When assembling and linking your file use

gcc -m32 -nostartfiles -o executablename filename.s

Change your executablename and filename.s accordingly