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Re: Python: fetch value when building gdb.Value object

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
kept there.

> 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  <>

	* 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.

--- a/gdb/python/py-value.c
+++ b/gdb/python/py-value.c
@@ -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)
 	return NULL;
+  back_to = make_cleanup (xfree, field);
       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;

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