michi-jung opened a new pull request #2944:
URL: https://github.com/apache/incubator-nuttx/pull/2944
## Summary
With TrustZone support in armv8-m the bit-fields in EXC_RETURN have been
extended. Bit 6 ('S') now specifies whether the interrupted program was
running in the Non-Secure (S=0) or Secure (S=1) security state.
Furthermore, Bit 0 ('ES' - Exception Secure) specifies the
security state athe exception is taken to (0: Non-Secure, 1: Secure).
When NuttX is run together with TrustedFirmware-M as the application in
the non-secure world both the S and the ES bits have to be set to '0'.
For armv8-m those are also the correct values if TrustZone is not
implemented on the respective MCU or if it is disabled.
## Impact
Required change to run NuttX in the TrustZone non-secure security state.
Should have no impact if NuttX is run with TrustZone disabled.
I am not aware of any configuration that is running NuttX in the TrustZone
secure security state. If there are any then this change will probably break
them. In this case we should probably make this configurable.
## Testing
Tested with TrustZone disabled and with running NuttX in the non-secure
world of TrustedFirmware-M
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