gdb/python: print name of unwinder that claimed frame in debug message

If we have multiple registered unwinders, this will helps identify which
unwinder was chosen and make it easier to track down potential problems.
Unwinders have a mandatory name argument, which we can use in the
message.

First, make gdb._execute_unwinders return a tuple containing the name,
in addition to the UnwindInfo.  Then, make pyuw_sniffer include the name
in the debug message.

I moved the debug message earlier.  I think it's good to print it as
early as possible, so that we see it in case an assert is hit in the
loop below, for example.

gdb/ChangeLog:

	* python/lib/gdb/__init__.py (_execute_unwinders): Return tuple
	with name of chosen unwinder.
	* python/py-unwind.c (pyuw_sniffer): Print name of chosen
	unwinder in debug message.

Change-Id: Id603545b44a97df2a39dd1872fe1f38ad5059f03

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index d9e0a3a4f4da860f61529c2572e34eeb8e003db3..995c8a1a3756aedc5cd55e83d78dbafc34cb43ea 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,10 @@
+2021-06-22  Simon Marchi  <simon.marchi@polymtl.ca>
+
+       * python/lib/gdb/__init__.py (_execute_unwinders): Return tuple
+       with name of chosen unwinder.
+       * python/py-unwind.c (pyuw_sniffer): Print name of chosen
+       unwinder in debug message.
+
 2021-06-22  Andreas Schwab  <schwab@suse.de>
 
        PR symtab/27999

diff --git a/gdb/python/lib/gdb/__init__.py b/gdb/python/lib/gdb/__init__.py
index d748b3a5827e7842e970afe6c730c781b633a76e..f2f38b32af9604886919d9943fc0d3c389e3a0c0 100644 (file)
--- a/gdb/python/lib/gdb/__init__.py
+++ b/gdb/python/lib/gdb/__init__.py
@@ -90,27 +90,33 @@ def _execute_unwinders(pending_frame):
 
     Arguments:
         pending_frame: gdb.PendingFrame instance.
+
     Returns:
-        gdb.UnwindInfo instance or None.
+        Tuple with:
+
+         [0] gdb.UnwindInfo instance
+         [1] Name of unwinder that claimed the frame (type `str`)
+
+       or None, if no unwinder has claimed the frame.
     """
     for objfile in objfiles():
         for unwinder in objfile.frame_unwinders:
             if unwinder.enabled:
                 unwind_info = unwinder(pending_frame)
                 if unwind_info is not None:
-                    return unwind_info
+                    return (unwind_info, unwinder.name)
 
     for unwinder in current_progspace().frame_unwinders:
         if unwinder.enabled:
             unwind_info = unwinder(pending_frame)
             if unwind_info is not None:
-                return unwind_info
+                return (unwind_info, unwinder.name)
 
     for unwinder in frame_unwinders:
         if unwinder.enabled:
             unwind_info = unwinder(pending_frame)
             if unwind_info is not None:
-                return unwind_info
+                return (unwind_info, unwinder.name)
 
     return None
 

diff --git a/gdb/python/py-unwind.c b/gdb/python/py-unwind.c
index d3ef1911ab8204d74e180e889590706a10696e62..18ea2434f87e63e495f7a403800c8e6346f06d8e 100644 (file)
--- a/gdb/python/py-unwind.c
+++ b/gdb/python/py-unwind.c
@@ -556,33 +556,56 @@ pyuw_sniffer (const struct frame_unwind *self, struct frame_info *this_frame,
     }
   gdbpy_ref<> pyo_execute (PyObject_GetAttrString (gdb_python_module,
                                                   "_execute_unwinders"));
-  if (pyo_execute == NULL)
+  if (pyo_execute == nullptr)
     {
       gdbpy_print_stack ();
       return 0;
     }
 
-  gdbpy_ref<> pyo_unwind_info
+  /* A (gdb.UnwindInfo, str) tuple, or None.  */
+  gdbpy_ref<> pyo_execute_ret
     (PyObject_CallFunctionObjArgs (pyo_execute.get (),
                                   pyo_pending_frame.get (), NULL));
-  if (pyo_unwind_info == NULL)
+  if (pyo_execute_ret == nullptr)
     {
       /* If the unwinder is cancelled due to a Ctrl-C, then propagate
         the Ctrl-C as a GDB exception instead of swallowing it.  */
       gdbpy_print_stack_or_quit ();
       return 0;
     }
-  if (pyo_unwind_info == Py_None)
+  if (pyo_execute_ret == Py_None)
     return 0;
 
+  /* Verify the return value of _execute_unwinders is a tuple of size 2.  */
+  gdb_assert (PyTuple_Check (pyo_execute_ret.get ()));
+  gdb_assert (PyTuple_GET_SIZE (pyo_execute_ret.get ()) == 2);
+
+  if (pyuw_debug)
+    {
+      PyObject *pyo_unwinder_name = PyTuple_GET_ITEM (pyo_execute_ret.get (), 1);
+      gdb::unique_xmalloc_ptr<char> name
+       = python_string_to_host_string (pyo_unwinder_name);
+
+      /* This could happen if the user passed something else than a string
+        as the unwinder's name.  */
+      if (name == nullptr)
+       {
+         gdbpy_print_stack ();
+         name = make_unique_xstrdup ("<failed to get unwinder name>");
+       }
+
+      pyuw_debug_printf ("frame claimed by unwinder %s", name.get ());
+    }
+
   /* Received UnwindInfo, cache data.  */
-  if (PyObject_IsInstance (pyo_unwind_info.get (),
+  PyObject *pyo_unwind_info = PyTuple_GET_ITEM (pyo_execute_ret.get (), 0);
+  if (PyObject_IsInstance (pyo_unwind_info,
                           (PyObject *) &unwind_info_object_type) <= 0)
     error (_("A Unwinder should return gdb.UnwindInfo instance."));
 
   {
     unwind_info_object *unwind_info =
-      (unwind_info_object *) pyo_unwind_info.get ();
+      (unwind_info_object *) pyo_unwind_info;
     int reg_count = unwind_info->saved_regs->size ();
 
     cached_frame
@@ -613,7 +636,6 @@ pyuw_sniffer (const struct frame_unwind *self, struct frame_info *this_frame,
   }
 
   *cache_ptr = cached_frame;
-  pyuw_debug_printf ("frame claimed");
   return 1;
 }