For leaf-node functions (functions which do not call any other function(s)), a 128-byte space is stored just beneath the stack pointer of the function. The space is called the red zone. This zone will not be clobbered by any signal or interrupt handlers. Compilers can thus utilize this zone to save local variables. Compilers may omit some instructions at the starting of the function (adjustment of RSP, RBP) by utilizing this zone. However, other functions may clobber this zone. Therefore, this zone should only be used for leaf-node functions. and offer the flag to disable red-zone optimizations.