test-link-abi: fall back to lowest observed glibc version on new architectures

On architectures where glibc support was introduced after our baseline
(e.g. loongarch64, added in glibc 2.36), every imported symbol is
tagged with a version newer than the baseline, so the baseline check
fails spuriously. Detect this by taking the minimum version observed
across all binaries: if it exceeds the baseline, treat that minimum
as the effective baseline instead.

Follow up for d9600a2a

Co-developed-by: Claude Opus 4.7 <noreply@anthropic.com>

test/test-link-abi.py

@@ -86,15 +86,16 @@ def is_libc(name: str) -> bool:
     return name.startswith(LIBC_LIB_PREFIXES)
 
 
-def glibc_violations(path: str, baseline: Version) -> list[tuple[str, str]]:
+def glibc_imports(path: str) -> list[tuple[str, str, Version]]:
-    """Return a sorted list of (symbol, "GLIBC_X.Y") pairs above the baseline."""
+    """Return a sorted list of (symbol, "GLIBC_X.Y", version) triples for every
+    imported GLIBC-versioned symbol referenced by ``path``."""
     out = subprocess.check_output(
         ['readelf', '-W', '--dyn-syms', path],
         text=True,
         stderr=subprocess.DEVNULL,
     )
 
-    found: set[tuple[str, str]] = set()
+    found: set[tuple[str, str, Version]] = set()
     for line in out.splitlines():
         m = GLIBC_RE.search(line)
         if not m:
@@ -106,10 +107,8 @@ def glibc_violations(path: str, baseline: Version) -> list[tuple[str, str]]:
         if len(parts) < 8 or parts[6] != 'UND':
             continue
         ver: Version = (int(m.group(1)), int(m.group(2)))
-        if ver <= baseline:
-            continue
         sym = next((t for t in parts if '@' in t), line.strip())
-        found.add((sym, m.group(0)))
+        found.add((sym, m.group(0), ver))
     return sorted(found)
 
 
@@ -150,23 +149,53 @@ def main() -> int:
     args = ap.parse_args()
 
     baseline: Version = args.baseline
-    checked = 0
+
-    failed = 0
+    # First pass: collect all imports and NEEDED entries so we can derive an
+    # effective baseline before reporting any violations.
+    imports: dict[str, list[tuple[str, str, Version]]] = {}
+    needed: dict[str, list[str]] = {}
     for path in args.paths:
         if not is_elf(path):
             # Some inputs passed by meson may be scripts or non-ELF
             # generators; silently skip those rather than fail.
             continue
-        checked += 1
+        imports[path] = glibc_imports(path)
+        needed[path] = needed_violations(path)
 
-        glibc_bad = glibc_violations(path, baseline)
+    # On architectures where glibc support was added after our baseline (e.g.
-        needed_bad = needed_violations(path)
+    # loongarch64, introduced in glibc 2.36), every imported symbol will be
+    # tagged with a version newer than the baseline, so the baseline check
+    # would spuriously fail. Detect this by taking the minimum version observed
+    # across all binaries: if it exceeds the baseline, treat that minimum as
+    # the effective baseline instead.
+    observed = [v for syms in imports.values() for _, _, v in syms]
+    effective_baseline = baseline
+    if observed:
+        observed_min = min(observed)
+        if observed_min > baseline:
+            effective_baseline = observed_min
+            print(
+                f'Note: lowest observed GLIBC import is '
+                f'GLIBC_{observed_min[0]}.{observed_min[1]}, newer than the requested baseline '
+                f'GLIBC_{baseline[0]}.{baseline[1]}; assuming this architecture has no older '
+                f'symbols available and using GLIBC_{effective_baseline[0]}.{effective_baseline[1]} '
+                f'as the effective baseline.',
+                file=sys.stderr,
+            )
+
+    failed = 0
+    for path, syms in imports.items():
+        glibc_bad = sorted({(sym, ver_str) for sym, ver_str, ver in syms if ver > effective_baseline})
+        needed_bad = needed[path]
 
         if glibc_bad or needed_bad:
             failed += 1
             print(f'{path}:', file=sys.stderr)
         if glibc_bad:
-            print(f'  imports symbols newer than GLIBC_{baseline[0]}.{baseline[1]}:', file=sys.stderr)
+            print(
+                f'  imports symbols newer than GLIBC_{effective_baseline[0]}.{effective_baseline[1]}:',
+                file=sys.stderr,
+            )
             for sym, ver_str in glibc_bad:
                 print(f'    {sym} ({ver_str})', file=sys.stderr)
         if needed_bad:
@@ -174,7 +203,8 @@ def main() -> int:
             for name in needed_bad:
                 print(f'    {name}', file=sys.stderr)
 
-    baseline_str = f'GLIBC_{baseline[0]}.{baseline[1]}'
+    checked = len(imports)
+    baseline_str = f'GLIBC_{effective_baseline[0]}.{effective_baseline[1]}'
     if failed:
         print(f'\nFAIL: {failed} of {checked} ELF objects failed the ABI checks.', file=sys.stderr)
         return 1