diff -r f5a7d413638d Lib/test/test_gdb.py
--- a/Lib/test/test_gdb.py	Thu Jul 21 19:41:04 2011 +0200
+++ b/Lib/test/test_gdb.py	Thu Jul 21 17:00:03 2011 -0400
@@ -639,6 +639,64 @@
 foo\(1, 2, 3\)
 ''')
 
+    def test_threads(self):
+        'Verify that "py-bt" indicates threads that are waiting for the GIL'
+        cmd = '''
+from threading import Thread
+
+class TestThread(Thread):
+    # These threads would run forever, but we'll interrupt things with the
+    # debugger
+    def run(self):
+        i = 0
+        while 1:
+             i += 1
+
+t = {}
+for i in range(4):
+   t[i] = TestThread()
+   t[i].start()
+
+# Trigger a breakpoint on the main thread
+id(42)
+
+'''
+        # Verify with "py-bt":
+        gdb_output = self.get_stack_trace(cmd, import_site=True,
+                                          breakpoint='builtin_id',
+                                          cmds_after_breakpoint=['thread apply all py-bt'])
+        self.assertIn('Waiting for a lock', gdb_output)
+
+    def test_gc(self):
+        'Verify that "py-bt" indicates if a thread is garbage-collecting'
+        cmd = ('from gc import collect\n'
+               'id(42)\n'
+               'def foo():\n'
+               '    collect()\n'
+               'def bar():\n'
+               '    foo()\n'
+               'bar()\n')
+        # Verify with "py-bt":
+        gdb_output = self.get_stack_trace(cmd, import_site=True,
+                                          breakpoint='builtin_id',
+                                          cmds_after_breakpoint=['break update_refs', 'continue', 'py-bt'])
+        self.assertIn('Garbage-collecting', gdb_output)
+
+    def test_pycfunction(self):
+        'Verify that "py-bt" displays invocations of PyCFunction instances'
+        cmd = ('from time import sleep\n'
+               'def foo():\n'
+               '    sleep(1)\n'
+               'def bar():\n'
+               '    foo()\n'
+               'bar()\n')
+        # Verify with "py-bt":
+        gdb_output = self.get_stack_trace(cmd, import_site=True,
+                                          breakpoint='time_sleep',
+                                          cmds_after_breakpoint=['py-bt'])
+        self.assertIn('#0 <built-in function sleep', gdb_output)
+
+
 class PyPrintTests(DebuggerTests):
     def test_basic_command(self):
         'Verify that the "py-print" command works'
diff -r f5a7d413638d Tools/gdb/libpython.py
--- a/Tools/gdb/libpython.py	Thu Jul 21 19:41:04 2011 +0200
+++ b/Tools/gdb/libpython.py	Thu Jul 21 17:00:03 2011 -0400
@@ -884,10 +884,13 @@
         newline character'''
         if self.is_optimized_out():
             return '(frame information optimized out)'
-        with open(self.filename(), 'r') as f:
-            all_lines = f.readlines()
-            # Convert from 1-based current_line_num to 0-based list offset:
-            return all_lines[self.current_line_num()-1]
+        try:
+            with open(self.filename(), 'r') as f:
+                all_lines = f.readlines()
+                # Convert from 1-based current_line_num to 0-based list offset:
+                return all_lines[self.current_line_num()-1]
+        except IOError:
+            return None
 
     def write_repr(self, out, visited):
         if self.is_optimized_out():
@@ -1186,6 +1189,23 @@
             iter_frame = iter_frame.newer()
         return index
 
+    # We divide frames into:
+    #   - "python frames":
+    #       - "bytecode frames" i.e. PyEval_EvalFrameEx
+    #       - "other python frames": things that are of interest from a python
+    #         POV, but aren't bytecode (e.g. GC, GIL)
+    #   - everything else
+
+    def is_python_frame(self):
+        '''Is this a PyEval_EvalFrameEx frame, or some other important
+        frame? (see is_other_python_frame for what "important" means in this
+        context)'''
+        if self.is_evalframeex():
+            return True
+        if self.is_other_python_frame():
+            return True
+        return False
+
     def is_evalframeex(self):
         '''Is this a PyEval_EvalFrameEx frame?'''
         if self._gdbframe.name() == 'PyEval_EvalFrameEx':
@@ -1202,6 +1222,46 @@
 
         return False
 
+    def is_other_python_frame(self):
+        '''Is this frame worth displaying in python backtraces?
+        Examples:
+          - waiting on the GIL
+          - garbage-collecting
+          - within a CFunction
+         If it is, return a descriptive string
+         For other frames, return False
+         '''
+        if self.is_waiting_for_lock():
+            return 'Waiting for a lock (e.g. GIL)'
+        elif self.is_gc_collect():
+            return 'Garbage-collecting'
+        else:
+            # Detect invocations of PyCFunction instances:
+            older = self.older()
+            if older and older._gdbframe.name() == 'PyCFunction_Call':
+                # Within that frame:
+                #   "func" is the local containing the PyObject* of the
+                # PyCFunctionObject instance
+                #   "f" is the same value, but cast to (PyCFunctionObject*)
+                #   "self" is the (PyObject*) of the 'self'
+                try:
+                    # Use the prettyprinter for the func:
+                    func = older._gdbframe.read_var('func')
+                    return str(func)
+                except RuntimeError:
+                    return 'PyCFunction invocation (unable to read "func")'
+
+        # This frame isn't worth reporting:
+        return False
+
+    def is_waiting_for_lock(self):
+        '''Is this frame waiting for a lock?'''
+        return self._gdbframe.name().startswith('PyThread_acquire_lock')
+
+    def is_gc_collect(self):
+        '''Is this frame "collect" within the the garbage-collector?'''
+        return self._gdbframe.name() == 'collect'
+
     def get_pyop(self):
         try:
             f = self._gdbframe.read_var('f')
@@ -1218,8 +1278,22 @@
 
     @classmethod
     def get_selected_python_frame(cls):
-        '''Try to obtain the Frame for the python code in the selected frame,
-        or None'''
+        '''Try to obtain the Frame for the python-related code in the selected
+        frame, or None'''
+        frame = cls.get_selected_frame()
+
+        while frame:
+            if frame.is_python_frame():
+                return frame
+            frame = frame.older()
+
+        # Not found:
+        return None
+
+    @classmethod
+    def get_selected_bytecode_frame(cls):
+        '''Try to obtain the Frame for the python bytecode interpreter in the
+        selected GDB frame, or None'''
         frame = cls.get_selected_frame()
 
         while frame:
@@ -1235,11 +1309,17 @@
             pyop = self.get_pyop()
             if pyop:
                 sys.stdout.write('#%i %s\n' % (self.get_index(), pyop.get_truncated_repr(MAX_OUTPUT_LEN)))
-                sys.stdout.write(pyop.current_line())
+                line = pyop.current_line()
+                if line is not None:
+                    sys.stdout.write(line)
             else:
                 sys.stdout.write('#%i (unable to read python frame information)\n' % self.get_index())
         else:
-            sys.stdout.write('#%i\n' % self.get_index())
+            info = self.is_other_python_frame()
+            if info:
+                sys.stdout.write('#%i %s\n' % (self.get_index(), info))
+            else:
+                sys.stdout.write('#%i\n' % self.get_index())
 
 class PyList(gdb.Command):
     '''List the current Python source code, if any
@@ -1275,9 +1355,10 @@
         if m:
             start, end = map(int, m.groups())
 
-        frame = Frame.get_selected_python_frame()
+        # py-list requires an actual PyEval_EvalFrameEx frame:
+        frame = Frame.get_selected_bytecode_frame()
         if not frame:
-            print 'Unable to locate python frame'
+            print 'Unable to locate gdb frame for python bytecode interpreter'
             return
 
         pyop = frame.get_pyop()
@@ -1323,7 +1404,7 @@
         if not iter_frame:
             break
 
-        if iter_frame.is_evalframeex():
+        if iter_frame.is_python_frame():
             # Result:
             if iter_frame.select():
                 iter_frame.print_summary()
@@ -1377,7 +1458,7 @@
     def invoke(self, args, from_tty):
         frame = Frame.get_selected_python_frame()
         while frame:
-            if frame.is_evalframeex():
+            if frame.is_python_frame():
                 frame.print_summary()
             frame = frame.older()