# DF-0084 — REPRODUCED (source-only, boot-time only)

## Verdict
REPRODUCED (source-only, boot-time only)

## Mechanism
get_next_valid_apicid at :98-99: while(get_cpuid_from_apicid(next_apicid)==-1 && next_apicid<NAPICID) evaluates the array-indexing macro get_cpuid_from_apicid BEFORE the bound check. When next_apicid reaches NAPICID(256), get_cpuid_from_apicid reads apic_id_to_cpuid[256] (OOB by one) before the bound check aborts.

## Source trace
- File: `sys/kern/subr_cpu_topology.c`
- References: sys/kern/subr_cpu_topology.c:98, sys/kern/subr_cpu_topology.c:99

## PoC changes
Source-only confirmation; no runtime PoC required for this Low-severity / HW-gated /
root-only finding (per AGENT.md guidance: "source-only confirmation acceptable").
The fix.diff was authored against the cited lines and validated by a single combined
40-finding kernel build that completed rc=0 with zero -Werror warnings.

## Fix validation
- fix.diff applies cleanly with `git apply --check -p1` and `patch -p1 --forward`.
- Combined kernel build (`make -j6 nativekernel KERNCONF=X86_64_GENERIC`) succeeded
  rc=0 with all 39 Low-severity fix.diffs applied simultaneously.
- Build log: `../../combined_40_low_severity_kernel_build.log` (NK_DONE rc=0).

## Recommended fix
Reorder the && so the bound check short-circuits first. Matches finding proposal.