The exception return mechanism is triggered using a special return address (EXC_RETURN). This address is generated during exception entry and it is stored in the Link Reigster (LR). In example, when the processor is in thread mode and the processor uses the Processor Stack Pointer (PSP) as its stack pointer, whenever an exception occurs, the processor does the stacking operations mentioned using PSP, and LR register is loaded with the EXC_RETURN. The way exception return happens, is by writing the value LR into the program counter (PC). By writing the LR value into the PC, exception return can be triggered. When that happens, the processor actually does an unstacking operation and comes to a normal execution. The EXC_RETURN is not an actual address, it includes different fields that are decoded by the processor (Stack frame type, return to thread mode or handler mode, return with MSP or PSP and so on...) so that the processor knows to which mode it should return.