On 13/11/2019 12:11, Areligious Republican wrote:
> 1. Out of interest, were there to be a 32 bit application
> running under a 64 bit OS, what actually happens when an
> interrupt comes along, andinterrupt that might have system-wide
> importance?
>
> Is it dealt with by the 32 bit IRQ / FIRQ mechanism or does
> it switch back to the 64 bit?

The interrupt (or any other exception) causes a 64 bit privileged mode
to be entered, and is handled by the 64 bit OS. On exit it may return to
the 32 bit non-privileged mode the application is running in.

Incidentally, it is also possible on the A53 to run 32 bit OS along side
a 64 bit OS using a 64 bit hypervisor. In that case the hypervisor
decides which OS the interrupt or exception should be handled by, and
either passes it to the 64 bit OS, or invokes the 32 bit mode's IRQ/FIRQ
handlers.

---druck

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