Hello world without using libraries

Question

This was an onsite interview question and I was baffled.

I was asked to write a Hello world program for linux.. That too without using any libraries in the system. I think I have to use system calls or something.. The code should run using -nostdlib and -nostartfiles option..

It would be great if someone could help..

Answer 1

$ cat > hwa.S
write = 0x04
exit  = 0xfc
.text
_start:
        movl    $1, %ebx
        lea     str, %ecx
        movl    $len, %edx
        movl    $write, %eax
        int     $0x80
        xorl    %ebx, %ebx
        movl    $exit, %eax
        int     $0x80
.data
str:    .ascii "Hello, world!\n"
len = . -str
.globl  _start
$ as -o hwa.o hwa.S
$ ld hwa.o
$ ./a.out
Hello, world!