devtools: add script to check symbols from Linux gitian executables

Add a script to check that the (Linux) executables produced by gitian
only contain allowed gcc, glibc and libstdc++ version symbols.  This
makes sure they are still compatible with the minimum supported Linux
distribution versions.

Conflicts:

	contrib/devtools/README.md

contrib/devtools/README.md

@@ -3,7 +3,7 @@ Contents
 This directory contains tools for developers working on this repository.
 
 github-merge.sh
-----------------
+==================
 
 A small script to automate merging pull-requests securely and sign them with GPG.
 
@@ -36,7 +36,8 @@ Configuring the github-merge tool for the bitcoin repository is done in the foll
     git config githubmerge.testcmd "make -j4 check" (adapt to whatever you want to use for testing)
     git config --global user.signingkey mykeyid (if you want to GPG sign)
 
-## fix-copyright-headers.py
+fix-copyright-headers.py
+===========================
 
 Every year newly updated files need to have its copyright headers updated to reflect the current year.
 If you run this script from src/ it will automatically update the year on the copyright header for all

contrib/devtools/symbol-check.py

@@ -0,0 +1,108 @@
+#!/usr/bin/python
+# Copyright (c) 2014 Wladimir J. van der Laan
+# Distributed under the MIT/X11 software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+'''
+A script to check that the (Linux) executables produced by gitian only contain
+allowed gcc, glibc and libstdc++ version symbols.  This makes sure they are
+still compatible with the minimum supported Linux distribution versions.
+
+Example usage:
+
+    find ../gitian-builder/build -type f -executable | xargs python contrib/devtools/symbol-check.py
+'''
+from __future__ import division, print_function
+import subprocess
+import re
+import sys
+
+# Debian 6.0.9 (Squeeze) has:
+#
+# - g++ version 4.4.5 (https://packages.debian.org/search?suite=default&section=all&arch=any&searchon=names&keywords=g%2B%2B)
+# - libc version 2.11.3 (https://packages.debian.org/search?suite=default&section=all&arch=any&searchon=names&keywords=libc6)
+# - libstdc++ version 4.4.5 (https://packages.debian.org/search?suite=default&section=all&arch=any&searchon=names&keywords=libstdc%2B%2B6)
+#
+# Ubuntu 10.04.4 (Lucid Lynx) has:
+#
+# - g++ version 4.4.3 (http://packages.ubuntu.com/search?keywords=g%2B%2B&searchon=names&suite=lucid&section=all)
+# - libc version 2.11.1 (http://packages.ubuntu.com/search?keywords=libc6&searchon=names&suite=lucid&section=all)
+# - libstdc++ version 4.4.3 (http://packages.ubuntu.com/search?suite=lucid&section=all&arch=any&keywords=libstdc%2B%2B&searchon=names)
+#
+# Taking the minimum of these as our target.
+#
+# According to GNU ABI document (http://gcc.gnu.org/onlinedocs/libstdc++/manual/abi.html) this corresponds to:
+#   GCC 4.4.0: GCC_4.4.0
+#   GCC 4.4.2: GLIBCXX_3.4.13, CXXABI_1.3.3
+#   (glibc)    GLIBC_2_11
+#
+MAX_VERSIONS = {
+'GCC':     (4,4,0),
+'CXXABI':  (1,3,3),
+'GLIBCXX': (3,4,13),
+'GLIBC':   (2,11)
+}
+READELF_CMD = '/usr/bin/readelf'
+CPPFILT_CMD = '/usr/bin/c++filt'
+
+class CPPFilt(object):
+    '''
+    Demangle C++ symbol names.
+
+    Use a pipe to the 'c++filt' command.
+    '''
+    def __init__(self):
+        self.proc = subprocess.Popen(CPPFILT_CMD, stdin=subprocess.PIPE, stdout=subprocess.PIPE)
+
+    def __call__(self, mangled):
+        self.proc.stdin.write(mangled + '\n')
+        return self.proc.stdout.readline().rstrip()
+
+    def close(self):
+        self.proc.stdin.close()
+        self.proc.stdout.close()
+        self.proc.wait()
+
+def read_symbols(executable, imports=True):
+    '''
+    Parse an ELF executable and return a list of (symbol,version) tuples
+    for dynamic, imported symbols.
+    '''
+    p = subprocess.Popen([READELF_CMD, '--dyn-syms', '-W', executable], stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
+    (stdout, stderr) = p.communicate()
+    if p.returncode:
+        raise IOError('Could not read symbols for %s: %s' % (executable, stderr.strip()))
+    syms = []
+    for line in stdout.split('\n'):
+        line = line.split()
+        if len(line)>7 and re.match('[0-9]+:$', line[0]):
+            (sym, _, version) = line[7].partition('@')
+            is_import = line[6] == 'UND'
+            if version.startswith('@'):
+                version = version[1:]
+            if is_import == imports:
+                syms.append((sym, version))
+    return syms
+
+def check_version(max_versions, version):
+    if '_' in version:
+        (lib, _, ver) = version.rpartition('_')
+    else:
+        lib = version
+        ver = '0'
+    ver = tuple([int(x) for x in ver.split('.')])
+    if not lib in max_versions:
+        return False
+    return ver <= max_versions[lib]
+
+if __name__ == '__main__':
+    cppfilt = CPPFilt()
+    retval = 0
+    for filename in sys.argv[1:]:
+        for sym,version in read_symbols(filename, True):
+            if version and not check_version(MAX_VERSIONS, version):
+                print('%s: symbol %s from unsupported version %s' % (filename, cppfilt(sym), version))
+                retval = 1
+
+    exit(retval)
+
+