2.2.1. Main stack and process stack

Out of reset, all code uses the main stack. An exception handler such as SVC can change the stack used by Thread mode from main stack to process stack by changing the EXC_RETURN value it uses on exit. All exceptions continue to use the main stack. The stack pointer, r13, is a banked register that switches between SP_main and SP_process. Only one stack, the process stack or the main stack, is visible, using r13, at any time.

It is also possible to switch from main stack to process stack while in Thread mode by writing to CONTROL[1] using the MSR instruction, in addition to being selectable using the EXC_RETURN value from an exit from Handler mode.

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