Red Zone is a term designating the fixed size area in memory beyond the stack pointer that has not been "allocated". This region of memory is not to be modified by interrupt

Interrupt handler

An interrupt handler, also known as an interrupt service routine , is a callback subroutine in microcontroller firmware, operating system or device driver whose execution is triggered by the reception of an interrupt...

/exception/signal handlers. This allows the space to be used for temporary data without the extra overhead of modifying the stack pointer. The x86-64

X86-64

x86-64 is an extension of the x86 instruction set. It supports vastly larger virtual and physical address spaces than are possible on x86, thereby allowing programmers to conveniently work with much larger data sets. x86-64 also provides 64-bit general purpose registers and numerous other...

 ABI mandates a 128 byte red zone. The OpenRISC

OpenRISC

OpenRISC is the original flagship project of the OpenCores community. This project aims to develop a series of general purpose open source RISC CPU architectures...

 toolchain

Toolchain

In software, a toolchain is the set of programming tools that are used to create a product...

assumes a 128 byte red zone though it is not documented.