* Szabolcs Nagy <nsz@port70.net> [2013-03-31 22:51:39 +0200]:
> 1) parse /proc/self/maps which gives the current [low,high] mapping
> and 'prev' the high end of the last mapping below the stack
> 2) if we are the main thread check if low <= sp <= high
> 3) check rlimit
> 
> lowend = min(max(prev, high-rlimit, high-1G), low)

attached a getstack for the main thread