shared: add tests for shared library contents

shared/BUILD.bazel

@@ -22,14 +22,33 @@ cc_shared_library(
 )
 
 assert_linking_test(
-    name = "check_libthree_so",
+    name = "check_libthree_linking",
     lib_root_name = "three",
     require = [
         "libone.so",
         "libtwo.so",
     ],
 )
 
+py_test(
+    name = "check_libthree_dynsyms",
+    srcs = ["check_symtab.py"],
+    args = [
+        "--sut",
+        "libthree.so",
+        "--undefined",
+        "_Z3onev",
+        "--undefined",
+        "_Z3twov",
+        "--defined",
+        "_Z5threev",
+        "--",
+        "$(locations :three_so)",
+    ],
+    data = [":three_so"],
+    main = "check_symtab.py",
+)
+
 # Expected to pass
 cc_test(
     name = "test1",

shared/check_symtab.py

@@ -0,0 +1,61 @@
+#!/usr/bin/env python3
+from argparse import ArgumentParser
+from collections.abc import Iterable
+from os.path import basename
+from re import split
+from shlex import quote
+from subprocess import check_output
+from typing import Optional
+
+
+def _fmt(v: Optional[Iterable[str]]) -> Optional[str]:
+    return ("\n  " + "\n  ".join(sorted(v))) if v else None
+
+
+def assert_empty(entries: set[str], tag: str) -> None:
+    assert not entries, f"{tag} entries ({len(entries)}): {_fmt(entries)}"
+
+
+def main():
+    ap = ArgumentParser()
+    ap.add_argument("--sut")
+    ap.add_argument("--undefined", action="append")
+    ap.add_argument("--defined", action="append")
+    ap.add_argument("files", metavar="FILE", nargs="+")
+    args = ap.parse_args()
+
+    sut = None
+    for fn in args.files:
+        if basename(fn) == args.sut:
+            sut = fn
+            break
+
+    assert sut, f"SUT {args.sut} not found in files args {args.files}"
+    print("sut:", sut)
+
+    cmd = ["readelf", "--dyn-syms", sut]
+    print("+", " ".join(map(quote, cmd)))
+    out = check_output(cmd, text=True)
+    defined = set()
+    undefined = set()
+    for line in out.splitlines():
+        parts = split(r"\s+", line)
+        try:
+            defState = parts[7]
+            name = " ".join(parts[8:])
+        except IndexError:
+            continue
+        if not name.strip():
+            continue
+        if defState == "Ndx":
+            continue
+        (undefined if defState == "UND" else defined).add(name)
+
+    print("undefined:", _fmt(undefined))
+    print("defined:", _fmt(defined))
+
+    assert_empty(set(args.undefined) - undefined, "missing undefined")
+    assert_empty(set(args.defined) - defined, "missing defined")
+
+
+main()