How about 31 bytes?
http://www.returninfinity.com/baremetal-helloworld.html
Why use ELF or Linux? Flat binaries (and a custom OS) to the rescue! :)
Why limit yourself to an OS? Design your own instruction set, with a single-bit 'hw' instruction!
As with all games (even Nomic) a game is only a game if there are rules that limit what one can do.
The esoteric language HQ9+ does this.
Indeed, except that one doesn't print "Hello world". :)
http://www.muppetlabs.com/~breadbox/software/tiny/teensy.htm...