ci: Add an errno.h check to CI

Add a very simple check that verifies that new error numbers are added
according to the errno.h file in newlib, in order to maintain
compatibility with it.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>

.github/workflows/errno.yml

@@ -0,0 +1,20 @@
+name: Error numbers
+on:
+  pull_request:
+    paths:
+      - 'lib/libc/minimal/include/errno.h'
+
+jobs:
+  check-errno:
+    runs-on: ubuntu-latest
+    container:
+      image: zephyrprojectrtos/ci:v0.17.1
+
+    steps:
+      - name: checkout
+        uses: actions/checkout@v2
+
+      - name: Run errno.py
+        run: |
+          export ZEPHYR_BASE=${PWD}
+          ./scripts/ci/errno.py

scripts/ci/errno.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python3
+#
+# Copyright (c) 2021 Nordic Semiconductor NA
+#
+# SPDX-License-Identifier: Apache-2.0
+
+"""Check minimal libc error numbers against newlib.
+
+This script loads the errno.h included in Zephyr's minimal libc and checks its
+contents against the SDK's newlib errno.h. This is done to ensure that both C
+libraries are aligned at all times.
+"""
+
+
+import os
+from pathlib import Path
+import re
+import sys
+
+def parse_errno(path):
+    with open(path, 'r') as f:
+        r = re.compile(r'^\s*#define\s+([A-Z]+)\s+([0-9]+)')
+        errnos = []
+        for line in f:
+            m = r.match(line)
+            if m:
+                errnos.append(m.groups())
+
+    return errnos
+
+def main():
+
+    minimal = Path("lib/libc/minimal/include/errno.h")
+    newlib = Path("arm-zephyr-eabi/arm-zephyr-eabi/include/sys/errno.h")
+
+    try:
+        minimal = os.environ['ZEPHYR_BASE'] / minimal
+        newlib = os.environ['ZEPHYR_SDK_INSTALL_DIR'] / newlib
+    except KeyError as e:
+        print(f'Environment variable missing: {e}', file=sys.stderr)
+        sys.exit(1)
+
+    minimal = parse_errno(minimal)
+    newlib = parse_errno(newlib)
+
+    for e in minimal:
+        if e[0] not in [x[0] for x in newlib] or e[1] != next(
+            filter(lambda _e: _e[0] == e[0], newlib))[1]:
+            print('Invalid entry in errno.h:', file=sys.stderr)
+            print(f'{e[0]} (with value {e[1]})', file=sys.stderr)
+            sys.exit(1)
+
+    print('errno.h validated correctly')
+
+if __name__ == "__main__":
+    main()