Hole in 64-bit Linux kernel provides root rights

[JD]

On 09/20/2010 05:06 AM, fiedorow at math.ohio-state.edu wrote:
> Story at
> http://www.h-online.com/security/news/item/Hole-in-Linux-kernel-provides-root-rights-Update-1081317.html
>
> There is a link to exploit code at:
> http://sota.gen.nz/compat2/robert_you_suck.c
>
> I compiled this, ran it and got a root shell.  I am running:
> kernel-2.6.34.6-54.fc13.x86_64
>
>

What is  ORIG_RAX  in the code?
It is undefined! Explain how you could have possibly compiled it let 
alone run it.