This is the mail archive of the
mailing list for the GDB project.
Re: Python: fetch value when building gdb.Value object
- From: Jan Kratochvil <jan dot kratochvil at redhat dot com>
- To: Paul Koning <paulkoning at comcast dot net>
- Cc: pmuldoon at redhat dot com, gdb-patches at sourceware dot org
- Date: Sat, 1 Oct 2011 11:04:43 +0200
- Subject: Re: Python: fetch value when building gdb.Value object
- References: <36B29E9D-F2B3-446F-AF8A-97254A3AAEE2@comcast.net> <email@example.com> <D9AC6973-91CF-42D4-AD81-0C4A41D3DD2A@comcast.net>
On Wed, 28 Sep 2011 22:40:50 +0200, Paul Koning wrote:
> If I use RETURN_MASK_ERROR and control/C is hit, does that mean the
> currently running code aborts and the outer handler that does have
> RETURN_MASK_ALL is entered?
> If so, most of the Python code seems to be a candidate for
In fact I do not know, it is a Python thing.
RETURN_MASK_ALL is right if returned PyExc_KeyboardInterrupt will really abort
any execution of Python code. It is probably so, as suggested by:
RETURN_MASK_ERROR is right otherwise, but only if it is safe to longjmp out
from a code called by Python. This may not be true. Python may be C++
exceptions throwing safe but it cannot be safe for the GDB longjmp exceptions.
But this case would mean Python is buggy for CTRL-C on its own so
RETURN_MASK_ERROR probably is not right.
> One exception is valpy_getitem (in py-value.c) since it has an xfree(value)
> after the TRY_CATCH but before the GDB_PY_HANDLE_EXCEPTION (outside the
> TRY_CATCH block, though -- is that right?)
It is right as long as RETURN_MASK_ALL is right. It is more usual to call
make_cleanup though - as shown in the attached change. The change could be
just a code cleanup without functionality change if that RETURN_MASK_ALL is
> Probably related: I just tried an infinite Python loop and found that
> control-C had no effect. I wonder if the Python interpreter is setting up
> its own control-C trap (quite possibly -- that's a Python exception after
> all) and we're losing it somewhere along the lines.
Yes, this is the kind of bug from it, thanks for checking it.
only FYI, not intended for commit:
2011-10-01 Jan Kratochvil <firstname.lastname@example.org>
* python/py-value.c (valpy_getitem): New variable back_to. Register
xfree of field to it. Call do_cleanups for it. Use RETURN_MASK_ERROR
instead of RETURN_MASK_ALL.
@@ -448,6 +448,7 @@ valpy_getitem (PyObject *self, PyObject *key)
char *field = NULL;
struct value *res_val = NULL;
volatile struct gdb_exception except;
+ struct cleanup *back_to;
if (gdbpy_is_string (key))
@@ -456,7 +457,9 @@ valpy_getitem (PyObject *self, PyObject *key)
- TRY_CATCH (except, RETURN_MASK_ALL)
+ back_to = make_cleanup (xfree, field);
+ TRY_CATCH (except, RETURN_MASK_ERROR)
struct value *tmp = self_value->value;
@@ -485,10 +488,10 @@ valpy_getitem (PyObject *self, PyObject *key)
- xfree (field);
+ do_cleanups (back_to);
return res_val ? value_to_value_object (res_val) : NULL;