Processor modes in Armv6‑M, Armv7‑M, and Armv8‑M
The processor modes available in Armv6‑M, Armv7‑M, Armv8‑M Baseline, and Armv8‑M Mainline are Thread mode and Handler mode.
Thread mode is the normal mode that programs run in. Thread mode can be privileged or unprivileged software execution. Handler mode is the mode that exceptions are handled in. It is always privileged software execution.