Skip to content

ADR-1099: Propagate -fsycl via sycl_dependency to fix test-binary SIGSEGV

  • Status: Accepted
  • Date: 2026-06-07
  • Supersedes: —
  • Superseded by: —

Context

test_sycl_motion_add_uv_parity crashed with SIGSEGV on every run after two previous fix attempts (PRs #768, #796). The test was marked should_fail: true in core/test/meson.build (ADR-1093) to keep CI green while the root cause remained under investigation.

Root cause 1 — missing -fsycl at link time for test executables

SYCL source files are compiled with icpx -fsycl, which embeds SPIR-V device images in the resulting .o files. At link time, icpx must also see -fsycl to invoke clang-offload-wrapper, which registers those device images with the SYCL runtime's ProgramManager during shared-library or executable initialization. Without -fsycl at link, the registration step is silently skipped.

When a test executable links libvmaf.a (the static archive containing all SYCL-compiled .o files) without -fsycl, ProgramManager::getDeviceKernelInfo receives a CompileTimeKernelInfoTy whose backing program was never registered. This produces a null-dereference SIGSEGV at the first queue.submit() call — specifically inside ProgramManager::getDeviceKernelInfo in libsycl.so.

The libvmaf.so shared library was unaffected because vmaf_link_args (a library-only variable in core/src/meson.build) already carried -fsycl. Test executables declared sycl_dependency but received no -fsycl from it, so only the .so link was correct.

Root cause 2 — wrong feature name in vmaf_feature_score_at_index calls

After fixing root cause 1, a secondary failure appeared: vmaf_feature_score_at_index returned -EINVAL (-22) for both the SYCL and CPU score queries.

The VMAF feature-name system (core/src/feature/feature_name.c:vmaf_feature_name_from_opts_dict) transforms feature names when any non-default VMAF_OPT_FLAG_FEATURE_PARAM option is active:

  1. It replaces the raw name with its canonical alias (VMAF_integer_feature_motion2_score → integer_motion2, VMAF_feature_motion2_score → float_motion2).
  2. It appends each active option's alias as a suffix (motion_add_uv=true, alias mau, type BOOL → appends _mau).

So with motion_add_uv=true, the feature-collector stores scores under integer_motion2_mau (SYCL) and float_motion2_mau (CPU), not under the raw VMAF_*_score names. The original test queried the raw names, obtaining "not found" (-EINVAL) for every lookup.

Note: when no FEATURE_PARAM option is non-default, opts_dict is empty, the !sorted_dict branch fires, and the raw name is stored unchanged — which is why other parity tests that use default options query successfully with the raw name.

Decision

Fix 1: Move -fsycl from vmaf_link_args (library-only) into sycl_dependency.link_args in core/src/meson.build. Every Meson target that declares dependencies: [sycl_dependency] — the shared library, the static library, and all SYCL test executables — now automatically receives -fsycl at link time. The vmaf_link_args variable is retained as an empty list for future library-only link flags.

Fix 2: Update core/test/test_sycl_motion_add_uv_parity.c to query the correct aliased names:

  • SYCL path (motion_sycl, motion_add_uv=true): query "integer_motion2_mau"
  • CPU path (float_motion, motion_add_uv=true): query "float_motion2_mau"
  • SYCL Y-only baseline (default options): query "VMAF_integer_feature_motion2_score" (raw name; no aliasing when all FEATURE_PARAM options are at default)

Fix 3: Remove should_fail: true and the ADR-1093 bypass comment from core/test/meson.build. The test must pass unconditionally on SYCL-capable hosts and skip cleanly on hosts without a SYCL device.

Fix 4: Clean up lint warnings in the test file introduced by touching it: remove unused #include <errno.h>, <stdlib.h>, <string.h>; split VmafPicture ref, dist; multi-declaration statements; add NOLINT comments with ADR-0141 citations for the two functions that exceed the size threshold due to their unavoidable test-harness structure.

Alternatives considered

1. Per-target -fsycl in core/test/meson.build: Add link_args: ['-fsycl'] to each SYCL test executable individually instead of centralizing in sycl_dependency. Rejected: error-prone — every future SYCL test must remember the flag, and omitting it produces a silent runtime crash rather than a build error. Centralization in the dependency is the correct Meson idiom.

2. Keep vmaf_link_args with -fsycl AND add it to sycl_dependency: This passes -fsycl twice to the library link. icpx accepts duplicate flags silently, so it is technically safe, but it is redundant and confusing. Removing it from vmaf_link_args is cleaner.

3. Query raw feature names everywhere: Instrument vmaf_feature_collector_get_score to resolve aliases before lookup. Rejected: the aliased-name storage is load-bearing behaviour that other parts of the system depend on (model scoring, score pooling); changing it would have wide blast radius and is out of scope for a bug fix.

4. Add an alias-resolution helper for tests: Expose a helper that maps a raw feature name + options to the aliased name at test time. Rejected: over-engineered for a two-string constant fix; test code should document the aliasing contract explicitly so future readers understand what name is stored.

References

  • req: user direction — reproduce locally, real fix, remove should_fail, draft PR (2026-06-07)
  • PRs #768, #796 (prior incomplete attempts)
  • ADR-1093 (test-disable policy that this ADR supersedes for this test)
  • ADR-0989 (SYCL motion_add_uv implementation)
  • ADR-0141 (touched-file lint-clean rule)
  • ADR-0214 (cross-backend tolerance places=4)
  • T-SYCL-MOTION-ADD-UV-SIGSEGV-2026-06-07 in docs/state.md