python2: fix ctypes.util.find_library with gcc10

Fixes NixOS#108243

pkgs/development/interpreters/python/cpython/2.7/default.nix

@@ -114,6 +114,9 @@ let
       # libuuid, slowing down program startup a lot).
       ./no-ldconfig.patch
 
+      # Fix ctypes.util.find_library with gcc10.
+      ./find_library-gcc10.patch
+
     ] ++ optionals stdenv.hostPlatform.isCygwin [
       ./2.5.2-ctypes-util-find_library.patch
       ./2.5.2-tkinter-x11.patch

pkgs/development/interpreters/python/cpython/2.7/find_library-gcc10.patch

@@ -0,0 +1,79 @@
+Backport https://github.com/python/cpython/commit/82df3b3071bb003247c33eac4670775e9883c994
+and https://github.com/python/cpython/commit/27ac19cca2c639caaf6fedf3632fe6beb265f24f
+
+Fixes the check phase of python2Packages.cffi.
+
+--- a/Lib/ctypes/util.py
++++ b/Lib/ctypes/util.py
+@@ -87,6 +87,12 @@ elif os.name == "posix":
+     # Andreas Degert's find functions, using gcc, /sbin/ldconfig, objdump
+     import re, tempfile, errno
+
++    def _is_elf(filename):
++        "Return True if the given file is an ELF file"
++        elf_header = b'\x7fELF'
++        with open(filename, 'rb') as thefile:
++            return thefile.read(4) == elf_header
++
+     def _findLib_gcc(name):
+         # Run GCC's linker with the -t (aka --trace) option and examine the
+         # library name it prints out. The GCC command will fail because we
+@@ -110,10 +116,17 @@ elif os.name == "posix":
+                 # the normal behaviour of GCC if linking fails
+                 if e.errno != errno.ENOENT:
+                     raise
+-        res = re.search(expr, trace)
++        res = re.findall(expr, trace)
+         if not res:
+             return None
+-        return res.group(0)
++
++        for file in res:
++            # Check if the given file is an elf file: gcc can report
++            # some files that are linker scripts and not actual
++            # shared objects. See bpo-41976 for more details
++            if not _is_elf(file):
++                continue
++            return file
+
+
+     if sys.platform == "sunos5":
+@@ -237,8 +250,37 @@ elif os.name == "posix":
+         def _findSoname_ldconfig(name):
+             return None
+
++        def _findLib_ld(name):
++            # See issue #9998 for why this is needed
++            expr = r'[^\(\)\s]*lib%s\.[^\(\)\s]*' % re.escape(name)
++            cmd = ['ld', '-t']
++            libpath = os.environ.get('LD_LIBRARY_PATH')
++            if libpath:
++                for d in libpath.split(':'):
++                    cmd.extend(['-L', d])
++            cmd.extend(['-o', os.devnull, '-l%s' % name])
++            result = None
++            try:
++                p = subprocess.Popen(cmd, stdout=subprocess.PIPE,
++                                     stderr=subprocess.PIPE,
++                                     universal_newlines=True)
++                out, _ = p.communicate()
++                res = re.findall(expr, out)
++                for file in res:
++                    # Check if the given file is an elf file: gcc can report
++                    # some files that are linker scripts and not actual
++                    # shared objects. See bpo-41976 for more details
++                    if not _is_elf(file):
++                        continue
++                    return file
++            except Exception:
++                pass  # result will be None
++            return result
++
+         def find_library(name):
+-            return _findSoname_ldconfig(name) or _get_soname(_findLib_gcc(name))
++            # See issue #9998
++            return _findSoname_ldconfig(name) or \
++                   _get_soname(_findLib_gcc(name)) or _get_soname(_findLib_ld(name))
+
+ ################################################################
+ # test code