D408 - Unmodeled firmware handoff fields are zero, not markers

Status: decided Date: 2026-08-31

When a run presents a firmware, handoff structure fields this project does not model are set to zero rather than a marker, and a field known to be a pointer is given a real pointer of the right shape, backed by mapped firmware memory, never a fabricated address in the platform's own unreachable address range.

Why: A guest checking a field against null branches wrongly if it finds a marker there instead; matching zero for an unmodeled field keeps that check honest. Certain fields hold addresses in a range this project's host process cannot map at all, so those are answered with a real, dereferenceable stand-in of the same shape - non-null, and backed by memory a guest can actually read - rather than left as a marker or an address nothing can back.

Rejected:

• Leaving unmodeled fields as markers: a guest that checks a field for null branches incorrectly.
• Fabricating the platform's own unreachable addresses directly: they fall outside what a host process can map at all.