the sysconfig/ulimit text says: 

## Type:        integer(0:99)
## Default:     0
#
# Limit the size of the stack that a single process may allocate.
# Normally, it should be enough to limit virtual and resident size.
# Note that with NPTL, the stack limit determines the stack SIZE
# of multithreaded programs and should thus better not be set.
# Soft limit: Can be increased by non-root up to the hard limit.
# This value corresponds to ulimit -Ss
# Parameter is in percent of physical memory, 0 means no adjustment
# (unlimited).
#
SOFTSTACKLIMIT=0


which reads as if you leave it at the default, you get no stack limit. What actually happens however is that you get the kernel default ulimit, which is arch-dependant (mostly 8MB).