# DF-0038 — REPRODUCED (source-only)

## Verdict
REPRODUCED (source-only)

## Mechanism
journal_putpages UNDO passes btoc(ap->a_count) (a PAGE count) as the bytes arg to jreclist_undo_file -> jrecord_undo_file(off_t bytes) -> jrecord_file_data (byte count). a_count is BYTES; the result is the UNDO records 1/PAGE_SIZE of the actual modified byte range, undermining UNDO correctness.

## Source trace
- File: `sys/kern/vfs_jops.c`
- References: sys/kern/vfs_jops.c:960

## 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
Pass ap->a_count directly as bytes (not btoc()). Matches finding proposal.