Interlanguage Calls - Stack Floor

The stack floor is a system-defined address below which the stack cannot grow.

Other system invariants related to the stack must be maintained by all compilers and assemblers:

No data is saved or accessed from an address lower than the stack floor.
The stack pointer is always valid. When the stack frame size is more than 32767 bytes, take care to ensure that its value is changed in a single instruction, so that there is no timing window in which a signal handler would either overlay the stack data or erroneously appear to overflow the stack segment.