[llvm.py] Implement interface to object files

It is now possible to load object files and scan over sections, symbols,
and relocations! Includes test code with partial coverage.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152482 91177308-0d34-0410-b5e6-96231b3b80d8

bindings/python/llvm/common.py

@@ -14,23 +14,85 @@ from ctypes import cdll
 import ctypes.util
 
 __all__ = [
-    'LLVMObject',
+    'c_object_p',
     'find_library',
     'get_library',
 ]
 
-LLVMObject = POINTER(c_void_p)
+c_object_p = POINTER(c_void_p)
+
+class LLVMObject(object):
+    """Base class for objects that are backed by an LLVM data structure.
+
+    This class should never be instantiated outside of this package.
+    """
+    def __init__(self, ptr, ownable=True, disposer=None):
+        assert isinstance(ptr, c_object_p)
+
+        self._ptr = self._as_parameter_ = ptr
+
+        self._self_owned = True
+        self._ownable = ownable
+        self._disposer = disposer
+
+        self._owned_objects = []
+
+    def take_ownership(self, obj):
+        """Take ownership of another object.
+
+        When you take ownership of another object, you are responsible for
+        destroying that object. In addition, a reference to that object is
+        placed inside this object so the Python garbage collector will not
+        collect the object while it is still alive in libLLVM.
+
+        This method should likely only be called from within modules inside
+        this package.
+        """
+        assert isinstance(obj, LLVMObject)
+
+        self._owned_objects.append(obj)
+        obj._self_owned = False
+
+    def from_param(self):
+        """ctypes function that converts this object to a function parameter."""
+        return self._as_parameter_
+
+    def __del__(self):
+        if self._self_owned and self._disposer:
+            self._disposer(self)
+
+class CachedProperty(object):
+    """Decorator that caches the result of a property lookup.
+
+    This is a useful replacement for @property. It is recommended to use this
+    decorator on properties that invoke C API calls for which the result of the
+    call will be idempotent.
+    """
+    def __init__(self, wrapped):
+        self.wrapped = wrapped
+        try:
+            self.__doc__ = wrapped.__doc__
+        except: # pragma: no cover
+            pass
+
+    def __get__(self, instance, instance_type=None):
+        if instance is None:
+            return self
+
+        value = self.wrapped(instance)
+        setattr(instance, self.wrapped.__name__, value)
+
+        return value
 
 def find_library():
     # FIXME should probably have build system define absolute path of shared
     # library at install time.
-    for lib in ['LLVM-3.1svn', 'LLVM']:
+    for lib in ['LLVM-3.1svn', 'libLLVM-3.1svn', 'LLVM', 'libLLVM']:
         result = ctypes.util.find_library(lib)
         if result:
             return result
 
-    # FIXME This is a local hack to ease development.
-    return "/usr/local/llvm/lib/libLLVM-3.1svn.so"
+    return None
 
 def get_library():
     """Obtain a reference to the llvm library."""