tests: add more granular ELF OS detection tests, data-driven (#3098)

to better support ports of this logic to other languages/runtimes

CHANGELOG.md

@@ -133,6 +133,7 @@
 - replace black/isort/flake8 with ruff @mike-hunhoff #2992
 - ci: update GitHub Actions to support Node.js 24 (deprecate Node.js 20) @mr-tz #2984
 - tests: add snapshot tests for feature extraction @williballenthin #3069
+- tests: add more tests to exercise ELF OS detection @williballenthin #3098
 
 ### Raw diffs
 - [capa v9.4.0...master](https://github.com/mandiant/capa/compare/v9.4.0...master)

tests/test_elf_os_detection.py

@@ -0,0 +1,139 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import json
+from pathlib import Path
+
+import pytest
+
+import capa.features.extractors.elf as elf
+
+CD = Path(__file__).resolve().parent
+
+ALGORITHM_FUNCTIONS = {
+    "osabi": elf.guess_os_from_osabi,
+    "ph_notes": elf.guess_os_from_ph_notes,
+    "sh_notes": elf.guess_os_from_sh_notes,
+    "ident_directive": elf.guess_os_from_ident_directive,
+    "linker": elf.guess_os_from_linker,
+    "abi_versions_needed": elf.guess_os_from_abi_versions_needed,
+    "needed_dependencies": elf.guess_os_from_needed_dependencies,
+    "symtab": elf.guess_os_from_symtab,
+    "go_buildinfo": elf.guess_os_from_go_buildinfo,
+    "go_source": elf.guess_os_from_go_source,
+    "vdso_strings": elf.guess_os_from_vdso_strings,
+}
+
+FIXTURES = json.loads(
+    """
+[
+    {
+        "path": "2f7f5fb5de175e770d7eae87666f9831.elf_",
+        "os": "linux",
+        "algorithms": {
+            "sh_notes": "linux",
+            "ident_directive": "linux",
+            "vdso_strings": "linux"
+        }
+    },
+    {
+        "path": "7351f8a40c5450557b24622417fc478d.elf_",
+        "os": "linux",
+        "algorithms": {
+            "ph_notes": "linux",
+            "sh_notes": "linux",
+            "ident_directive": "linux",
+            "linker": "linux",
+            "abi_versions_needed": "linux"
+        }
+    },
+    {
+        "path": "b5f0524e69b3a3cf636c7ac366ca57bf5e3a8fdc8a9f01caf196c611a7918a87.elf_",
+        "os": "hurd",
+        "algorithms": {
+            "sh_notes": "hurd",
+            "abi_versions_needed": "hurd",
+            "needed_dependencies": "hurd"
+        }
+    },
+    {
+        "path": "bf7a9c8bdfa6d47e01ad2b056264acc3fd90cf43fe0ed8deec93ab46b47d76cb.elf_",
+        "os": "hurd",
+        "algorithms": {
+            "sh_notes": "hurd",
+            "abi_versions_needed": "hurd"
+        }
+    },
+    {
+        "path": "2bf18d0403677378adad9001b1243211.elf_",
+        "os": "linux",
+        "algorithms": {
+            "symtab": "linux"
+        }
+    },
+    {
+        "path": "1038a23daad86042c66bfe6c9d052d27048de9653bde5750dc0f240c792d9ac8.elf_",
+        "os": "android",
+        "algorithms": {
+            "ph_notes": "android",
+            "needed_dependencies": "android"
+        }
+    },
+    {
+        "path": "3da7c2c70a2d93ac4643f20339d5c7d61388bddd77a4a5fd732311efad78e535.elf_",
+        "os": "linux",
+        "algorithms": {
+            "go_buildinfo": "linux",
+            "go_source": "linux",
+            "vdso_strings": "linux"
+        }
+    }
+]
+"""
+)
+
+
+def _generate_algorithm_params():
+    params = []
+    for fixture in FIXTURES:
+        path = fixture["path"]
+        short_id = path[:8]
+        algorithms = fixture.get("algorithms", {})
+        for alg_name in ALGORITHM_FUNCTIONS:
+            expected = algorithms.get(alg_name)
+            test_id = f"{short_id}-{alg_name}"
+            params.append(pytest.param(path, alg_name, expected, id=test_id))
+    return params
+
+
+def _generate_detection_params():
+    return [pytest.param(f["path"], f["os"], id=f["path"][:8]) for f in FIXTURES]
+
+
+@pytest.mark.parametrize("path,algorithm,expected", _generate_algorithm_params())
+def test_elf_os_algorithm(path, algorithm, expected):
+    with (CD / "data" / path).open("rb") as f:
+        e = elf.ELF(f)
+        result = ALGORITHM_FUNCTIONS[algorithm](e)
+    if expected is None:
+        assert result is None, f"{algorithm} should return None, got {result}"
+    else:
+        assert result is not None, f"{algorithm} should return {expected}, got None"
+        assert result.value == expected
+
+
+@pytest.mark.parametrize("path,expected_os", _generate_detection_params())
+def test_elf_os_detection(path, expected_os):
+    with (CD / "data" / path).open("rb") as f:
+        assert elf.detect_elf_os(f) == expected_os