Query regarding extracting instruction which caused a data-abort exception

[Stefan Kalkowski]

On 06/20/2017 04:42 PM, rijurekha at ...71... wrote:
> Analyzed the following files:
> (a) base-hw/src/core/spec/arm/kernel/cpu.cc (calls init trustzone)
> (b) base-hw/src/core/spec/imx53/trustzone/platform_support.cc (defines
> init trustzone where monitor exception entry is assigned with
> _mon_kernel_entry)
> (c) base-hw/src/core/spec/arm_v7/trustzone/mode_transition.s defines
> _mon_kernel_entry, which is the exception vector table in monitor mode.
> The exception handlers call "_nonsecure_to_secure exception_type,
> pc_adjust", which sets the appropriate pc based on lr values.
> (d) base-hw/src/core/include/spec/arm_v7/macros_support.s has the register
> bank save and restore macros.
> 
> For my doubt (1) above, does each precise external abort go through this
> monitor exception handler function? How does that explain _state->ip is
> the correct variable (since pc is already adjusted based on lr)?

As previously said, its hard to reason about this, because the whole
peripheral connection and behaviour is largely board/vendor specific.
Probably almost all external data-aborts are taken to monitor mode, but
I can also imagine that some access (e.g. misaligned access on a device
granted to the normal world) might trigger an appropriated data-abort to
the normal world.

When a data-abort is taken by the monitor mode, it goes through that
exception handler.

> For my doubt (2) above, are the _state variables mapped to the memory
> addresses where the normal world registers are restored from?

Yes.

> Is that how
> any change made by vmm is reflected in the normal world registers?

Yes.

Regards
Stefan

> 
> Thanks!
> Riju
> 
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-- 
Stefan Kalkowski
Genode Labs

https://github.com/skalk · http://genode.org/