Add separate mechanism to load libc

ctypes.util.find_library() always returns None for systems which do not have the
tools installed to determine the location of a given shared library (i.e.
ldconfig, gcc, objdump). If find_libary() fails attempt to load known libc by
SONAME.

Signed-off-by: Frank Vanbever <frank.vanbever@essensium.com>

Author: frankvanbever

iptc/ip4tc.py

@@ -9,7 +9,7 @@
 import struct
 import weakref
 
-from .util import find_library, load_kernel
+from .util import find_library, load_kernel, find_libc
 from .xtables import (XT_INV_PROTO, NFPROTO_IPV4, XTablesError, xtables,
                       xt_align, xt_counters, xt_entry_target, xt_entry_match)
 
@@ -26,7 +26,7 @@
 
 _IFNAMSIZ = 16
 
-_libc = ct.CDLL("libc.so.6")
+_libc = find_libc()
 _get_errno_loc = _libc.__errno_location
 _get_errno_loc.restype = ct.POINTER(ct.c_int)
 _malloc = _libc.malloc

iptc/util.py

@@ -109,3 +109,19 @@ def find_library(*names):
             major = int(m.group(1))
         return lib, major
     return None, None
+
+
+def find_libc():
+    lib = ctypes.util.find_library('c')
+    if lib is not None:
+        return ctypes.CDLL(lib, mode=ctypes.RTLD_GLOBAL)
+
+    libnames = ['libc.so.6', 'libc.so.0', 'libc.so']
+    for name in libnames:
+        try:
+            lib = ctypes.CDLL(name, mode=ctypes.RTLD_GLOBAL)
+            return lib
+        except:
+            pass
+
+    return None

iptc/xtables.py

@@ -6,7 +6,7 @@
 import weakref
 
 from . import version
-from .util import find_library
+from .util import find_library, find_libc
 from .errors import *
 
 XT_INV_PROTO = 0x40  # invert the sense of PROTO
@@ -792,7 +792,7 @@ class xtables_target(ct.Union):
                 ("v12", _xtables_target_v12)]
 
 
-_libc, _ = find_library("c")
+_libc = find_libc()
 _optind = ct.c_long.in_dll(_libc, "optind")
 _optarg = ct.c_char_p.in_dll(_libc, "optarg")