Fix null pointer dereference in MethodMeta::uses_backend()

[bharqav]

Fixes #22404

Summary

MethodMeta::uses_backend() dereferenced ExecutionPlan::delegates() without a null check. Per schema/program.fbs, delegates has no default and can be legitimately unset. num_backends(), six lines below in the same file, already guards this exact condition — this PR applies the same guard to uses_backend().

See #22404 for the full root-cause writeup, reproduction, and crash output.

Test plan

Added MethodMetaTest.UsesBackendOnUnsetDelegatesReturnsFalse to runtime/executor/test/method_meta_test.cpp, constructing a minimal, self-contained, schema-valid Program (via flatbuffers::FlatBufferBuilder + BufferDataLoader) where delegates is left unset, then asserting uses_backend() returns false instead of crashing.

Verified locally (Clang, Debug, -fsanitize=address,undefined):

• Without the fix: the new test crashes with an ASan/UBSan SIGSEGV on flatbuffers::Vector::size() inside uses_backend().
• With the fix: the new test passes, and the full method_meta_test suite (7/7 tests) passes with no regressions.
• Also ran the neighboring program_test, method_test, and memory_manager_test suites via ctest — all passing, no side effects from this change.

Commands used:

cmake --build build-test --target method_meta_test
.\build-test\runtime\executor\test\method_meta_test.exe
ctest --test-dir build-test -R "method_meta_test|memory_manager_test|program_test|method_test" --output-on-failure

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/22405

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• ✅ login: bharqav / name: bharqav (83da422)

[Copilot]

Pull request overview

This PR hardens MethodMeta::uses_backend() against schema-valid programs where ExecutionPlan.delegates is unset, preventing a null-pointer dereference in the runtime. It also adds a regression test that constructs a minimal FlatBuffer Program with delegates == nullptr and verifies uses_backend() returns false rather than crashing.

Changes:

• Add a null check in MethodMeta::uses_backend() for ExecutionPlan::delegates() == nullptr.
• Add a new MethodMetaTest that loads a schema-valid FlatBuffer program with unset delegates and asserts uses_backend() returns false.
• Initialize the runtime in the test fixture setup to avoid PAL timer issues when logging is triggered during tests.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
runtime/executor/method_meta.cpp	Adds a null guard for delegates in MethodMeta::uses_backend() to prevent a crash on unset delegates.
runtime/executor/test/method_meta_test.cpp	Adds a regression test that loads a minimal FlatBuffer program with delegates left unset and validates uses_backend() behavior; adds runtime initialization for tests.

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[bharqav]

Fixed, added //executorch/extension/data_loader:buffer_data_loader and //executorch/schema:program to the method_meta_test deps in targets.bzl.

[bharqav]

right, method_meta_test was disabled behind TODO(T191569140). Re-enabled it in CMakeLists.txt with the required extension_data_loader/program_schema libs.

[bharqav]

@pytorchbot label "release notes: runtime"

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.