Re: [patch] Compilation regression with python-2.6 [Re: [PATCH 24/28] introduce gdb_pymodule_addobject]

[Pedro Alves <palves@redhat.com>]

On 05/21/2013 05:36 PM, Tom Tromey wrote:
>>>>>> "Pedro" == Pedro Alves <palves@redhat.com> writes:
> 
> Pedro> I notice that py_decref could actually be using Py_XDECREF instead
> Pedro> of doing the explicit 'if (py)' check.
> 
> Pedro> -  /* Note that we need the extra braces in this 'if' to avoid a
> Pedro> -     warning from gcc.  */
> Pedro>    if (py)
> Pedro> -    {
> Pedro> -      Py_DECREF (py);
> Pedro> -    }
> Pedro> +    Py_DECREF (py);
> 
> The X is missing.

Oh, I did not intend to do that change in the 7.6 workaround patch.
I was leaving that patch concerned only with the scoping issue.

> 
> Also, as discussed on irc, if you do this you might as well zap
> make_cleanup_py_xdecref and py_xdecref.

Yeah.  As discussed on irc, given the existence of py_xdecref, I
think py_decref calling Py_XDECREF would be odd.  Given the only difference
between Py_DECREF and Py_XDECREF is that the latter allows passing
in a NULL object, while the former prohibits it, it's natural to expect
the same from py_decref vs py_xdecref.

> I think having one set of cleanup functions is plenty.  The NULL check
> can't cost much, either in performance or clarity.

I removed the NULL check from py_decref, and ran the testsuite.
It caused a GDB crash in py-pp-maint.exp.  I did that before seeing your
note...  See below.  The issue is of course that make_cleanup_py_decref
is installed on a NULL object.  I could have used make_cleanup_py_xdecref,
but I actually went the other way...  I didn't mean to get myself
into Python hacking.  :-)  If you think this is not good, then I'll
just file a PR.

> Really I would prefer to get rid of decref cleanups at all, since they
> mess with the checker.  But this is a pain, and probably not worth the
> effort unless we think we could really get to 0 false reports.

---

 gdb/python/py-prettyprint.c |    6 +++++-
 gdb/python/py-utils.c       |    3 +--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/gdb/python/py-prettyprint.c b/gdb/python/py-prettyprint.c
index 8c45cd6..8fa2f42 100644
--- a/gdb/python/py-prettyprint.c
+++ b/gdb/python/py-prettyprint.c
@@ -735,8 +735,12 @@ apply_val_pretty_printer (struct type *type, const gdb_byte *valaddr,
   /* Find the constructor.  */
   printer = find_pretty_printer (val_obj);
   Py_DECREF (val_obj);
+
+  if (printer == NULL)
+    goto done;
+
   make_cleanup_py_decref (printer);
-  if (! printer || printer == Py_None)
+  if (printer == Py_None)
     goto done;

   /* If we are printing a map, we want some special formatting.  */
diff --git a/gdb/python/py-utils.c b/gdb/python/py-utils.c
index 80bacf7..7c7c5ca 100644
--- a/gdb/python/py-utils.c
+++ b/gdb/python/py-utils.c
@@ -31,8 +31,7 @@ py_decref (void *p)
 {
   PyObject *py = p;

-  if (py)
-    Py_DECREF (py);
+  Py_DECREF (py);
 }

 /* Return a new cleanup which will decrement the Python object's

-- 
Pedro Alves