# DF-4883 VERDICT

**Status: inconclusive** — the algorithmic defect is PROVEN on the guest
with the file's verbatim code; the kernel-level manifestation could not be
exercised because the guest has no AMD DC hardware and no in-vintage
caller currently passes a nonpositive argument to `dc_fixpt_log`.

## What was reproduced (guest, DragonFly 6.5-DEVELOPMENT, cc)
`fixpt_harness.c` embeds the verbatim library code with production ASSERT
semantics (no-op, matching os_types.h:76) and integer 64-bit division
standing in for `div64_u64_rem`. Results (run.log):

- `dc_fixpt_log(2.0)` → 0.693147180 in 9 iterations (baseline sanity:
  the library and harness behave correctly for in-domain input).
- `dc_fixpt_log(0.0)` → after ~21 iterations the Newton descent drives
  `dc_fixpt_exp(res)` to exactly 0 and the subsequent
  `dc_fixpt_div(0, 0)` traps **integer divide-by-zero (SIGFPE)** —
  the userspace mirror of the kernel's #DE through
  `complete_integer_division_u64` (fixpt31_32.c:43-55), i.e. the same
  unprotected sink as DF-1949, reached through a *different, new* root
  cause: log's missing domain check (fixpt31_32.c:385) and raw-unit exit
  test (fixpt31_32.c:404).
- `dc_fixpt_log(-1.0)` → diverges immediately, SIGFPE after ~2 iterations.

Key analytical detail (why log(0) loops at all): the exit condition
compares `abs_i64(error.value) > 100ULL` in RAW units; each iteration for
arg=0 changes res by exactly 1.0 fixpt = 2^32 raw, so the condition can
never be satisfied — the loop is unbounded by construction until the
div0 preempts it. On an architecture where the underflow never yields an
exact 0 divisor, this is a permanent kernel loop instead.

## What was NOT demonstrated
Kernel impact. The only in-tree consumers are the color module
(modules/color/color_gamma.c, compiled into amdgpu.ko per
sys/dev/drm/amd/amdgpu/Makefile:339): its direct log call is domain-
guarded, and its pow-based paths feed strictly positive bases
(coordinates_x grid starts at a positive power of two, color_gamma.c:52-
66). No AMD GPU exists on the guest (env.txt), so the DC pipeline cannot
be driven. Hence: behavior certain, kernel reachability latent.

## Impact ceiling (if a caller ever passes arg ≤ 0)
Kernel panic (#DE) or an unkillable 100%-CPU loop inside a DRM ioctl /
commit path. Realistic ceiling today: latent defect of a vendored
library, hardening priority. Low severity.

## Fix validation
Not applicable on this guest (no AMD hardware to build/boot a DC path
against). fix.diff implements the file's own TODO guard (return -INF-ish
saturation for arg ≤ 0), which by harness inspection makes log(0)/log(-1)
return immediately. fix_status: not_applicable.

## Fix status (batch validation)
Applied with the 36 sibling fix.diffs of this batch in findings/poc/_batch41/all_fixes.patch; single in-guest `make -j6 nativekernel KERNCONF=X86_64_GENERIC` completed RC=0 with zero errors under -Werror (full log: findings/poc/_batch41/fix_build8.log). Behavior A/B intentionally skipped for this Info-tier item.