Created a script to extract symbol info from a shared library.

symbolextractor.py

@@ -0,0 +1,65 @@
+#!/usr/bin/python3 -tt
+
+# Copyright 2013 Jussi Pakkanen
+
+# 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.
+
+# This script extracts the symbols of a given shared library
+# into a file. If the symbols have not changed, the file is not
+# touched. This information is used to skip link steps if the
+# ABI has not changed.
+
+# This file is basically a reimplementation of
+# http://cgit.freedesktop.org/libreoffice/core/commit/?id=3213cd54b76bc80a6f0516aac75a48ff3b2ad67c
+
+import sys, subprocess, platform
+
+def dummy_syms(outfilename):
+    """Just touch it so relinking happens always."""
+    open(outfilename, 'w').close()
+
+def write_if_changed(text, outfilename):
+    try:
+        oldtext = open(outfilename, 'r').read()
+        if text == oldtext:
+            return
+    except FileNotFoundError:
+        pass
+    open(outfilename, 'w').write(text)
+
+def linux_syms(libfilename, outfilename):
+    pe = subprocess.Popen(['readelf', '-d', libfilename], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+    output = pe.communicate()[0].decode()
+    if pe.returncode != 0:
+        raise RuntimeError('Readelf does not work')
+    result = [x for x in output.split('\n') if 'SONAME' in x]
+    assert(len(result) == 1)
+    pnm = subprocess.Popen(['nm', '--dynamic', '--extern-only', '--defined-only', '--format=posix', libfilename],
+                           stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+    output = pnm.communicate()[0].decode()
+    result += [x.split()[0] for x in output.split('\n') if len(x) > 0]
+    write_if_changed('\n'.join(result), outfilename)
+
+def gen_symbols(libfilename, outfilename):
+    if platform.system() == 'Linux':
+        linux_syms(libfilename, outfilename)
+    else:
+        dummy_syms(outfilename)
+
+if __name__ == '__main__':
+    if len(sys.argv) != 3:
+        print(sys.argv[0], '<shared library file> <output file>')
+        sys.exit(1)
+    libfile = sys.argv[1]
+    outfile = sys.argv[2]
+    gen_symbols(libfile, outfile)