D325 - A memory fill reports what it filled

Status: decided Date: 2026-09-26

The stack, heap, direct-memory and .bss fills are opt-in diagnostics, each reporting how many regions and bytes it filled, and a fill asked for that never fired says "nothing was tested". Fills touch writable mappings only. The .bss fill writes markers whose low bytes are the slot's own address, and an unparseable fill value leaves the fill off.

Why: a poison that changed nothing and one that never ran produce identical output, and recording an elimination on that evidence stops anyone looking. Writing a read-only mapping would fault inside the emulator and read as the guest's fault. A marker naming its own address turns a use of an unset global into a fault that names it. Zeroed .bss is the C guarantee, so a typo must never turn a diagnostic on.

Rejected:

• Silent fills: an elimination indistinguishable from an untested class.
• A constant .bss fill: shows that a global was used, not which.