[Feature]: runtime stack allocation for exception stack in aarch64.

Feature Overview

Presently, the aarch64 cpu module sets up an alternate "SP_EL0" stack for exception handling used when the SP from the exception source could be corrupt. This is done by reserving a data area in core\patina_internal_cpu\src\interrupts\aarch64\exception_handler.asm:

  .section .data

  .global sp_el0_end

# Stack for SP_EL0 of 0x10000 bytes. Also set to 8KB aligned, which corresponds to BIT13.
  .align 13
sp_el0_start:
  .space 0x10000
sp_el0_end:

However, this has a couple of dis-advantages: 1) it increases the size of the built core image, and 2) it is fixed at build time, which precludes runtime configuration scenarios (i.e. "I enabled the debugger on this boot and need more exception stack for it").

This feature request is filed to track updating the design point to allow runtime replacement of the alternate exception stack to address above disadvantages.

Solution Overview

Presumably an API to the aarch64 CPU module to allow caller to reallocate/move the alternate exception stack, plus a configuration story so it can be used e.g. by platform integrator or debugger.

Alternatives Considered

status quo: disadvantages noted above.

Urgency

Medium

Are you going to implement the feature request?

Someone else needs to implement the feature

Do you need maintainer feedback?

No maintainer feedback needed

Anything else?

No response