The stack base is used by the collector as one extreme of the region of
stack conservatively scanned during mark phase, the stack frame that invokes
GC being taken as the other extreme. How you set the stack base determines
what region of the C stack acts as storage for GC roots.
How that region should be set really depends on your application. You
must ask yourself which stack frames might contain GC roots and then
be sure that those frames are enclosed in the conservatively scanned region.
Good Luck!
-t