Different stack pointers for different modes?

You wold not ask this question if you knew at least a little about MIPS. First, MIPS has NO real stack pointer, so it cannot switch something it doesn't have.

Read the 3rd volume of MIPS32 Architecture for Programmers, available from

BTW. Actually the architecture in its new version supports register shadowing.

Please understand that the ARM stack pointer in just a software convention in native ARM (32 bit) mode. The Thumb instruction set requires that r13 is used in push and pop instructions.

The ARM addressing requires that there is at least one register free for storing the baseline registers when handling an interrupt. Also, there has to be storage places for the baseline program counter and status register. This is precisely what most ARM exception modes do with banked SPSR, r13 and r14. FIQ is a bit different, as there are more banked registers to enable exception handling without any register save / restore.

In many RISC designs, there is no idea of a stack pointer in hardware at all.