helloGAS.s

# hello world in GAS syntax
# to compile and run
# $ yasm -f elf -p gas helloGAS.s 2>&1
.text                           # section declaration

                                      # we must export the entry point to the ELF linker or
    .global _start              # loader. They conventionally recognize _start as their
                                      # entry point. Use ld -e foo to override the default.

_start:

                                # write our string to stdout

      movl    $len,%edx           # third argument: message length
      movl    $msg,%ecx           # second argument: pointer to message to write
      movl    $1,%ebx             # first argument: file handle (stdout)
      movl    $4,%eax             # system call number (sys_write)
      int     $0x80               # call kernel

                                # and exit

      movl    $0,%ebx             # first argument: exit code
      movl    $1,%eax             # system call number (sys_exit)
      int     $0x80               # call kernel

.data                           # section declaration

msg:
    .ascii    "Hello, GAS world!\n"   # our dear string
    len = . - msg                 # length of our dear string