cis-lclient05:~/2012/system>more hello.s
    .file    "hello.s"
    .text
    .global _start             #must be declared for linker (ld)

_start:                        #tell linker entry point
        movl    $len, %edx  #message length
        movl    $msg, %ecx  #message to write
        movl    $1, %ebx    #file descriptor (stdout)
        movl    $4, %eax    #system call number (sys_write)
        int     $0x80       #call kernel

        movl    $1,%eax     #system call number (sys_exit)
        movl    $22,%ebx    
        int     $0x80       #call kernel

        .data
msg:    .string  "Hello, world!\n"   #our dear string
        .set     len,    .-msg       #length of our dear string
        .size    _start, .-main
cis-lclient05:~/2012/system>as -o hello.o hello.s
cis-lclient05:~/2012/system>ld -o hello   hello.o
cis-lclient05:~/2012/system>hello
Hello, world!
cis-lclient05:~/2012/system>echo $?
22
cis-lclient05:~/2012/system>




cyclops:~/cis72/syscalls>cat hello.s
    .file    "hello.s"
    .text
    .global _start             #must be declared for linker (ld)

_start:                        #tell linker entry point
        movl    $len, %edx  #message length
        movl    $msg, %ecx  #message to write
        movl    $1, %ebx    #file descriptor (stdout)
        movl    $4, %eax    #system call number (sys_write)
        int     $0x80       #call kernel

        movl    $1,%eax     #system call number (sys_exit)
        movl    $22,%ebx    
        int     $0x80       #call kernel

        .data
msg:    .string  "Hello, world!\n"   #our dear string
        .set     len,    .-msg       #length of our dear string
        .size    _start, .-main

as -o hello.o hello.s
ld -o hello   hello.o
hello
Hello, world!
cyclops:~/cis72/syscalls>echo $?
22
cyclops:~/cis72/syscalls>