Python: fetch value when building gdb.Value object

Paul Koning
2011-09-21T15:54:32Z

GDB sometimes lazily evaluates operations on values, and py-value.c wasn't taking that into account. The result was that assigning a Value object to a Python variable could assign a lazy value, so that any errors in accessing the data would occur at a later time, and sometimes would not be handled right. (For example, the "nonzero" operation would fail without a Python traceback.)

The attached patch cures this by fetching any lazy values when the gdb.Value object is built, and adds a test in the testcases to verify this.

Ok to submit?

paul

ChangeLog:

2011-09-21 Paul Koning <paul_koning@dell.com>

* python/py-value.c (valpy_get_address): Use Py_XINCREF.
(value_to_value_object): Fetch value if it was lazy.

testsuite/ChangeLog:

2011-09-21 Paul Koning <paul_koning@dell.com>

* gdb.python/py-value.exp: Add test for null pointer reference
assigned to a variable.

Index: python/py-value.c
===================================================================
RCS file: /cvs/src/src/gdb/python/py-value.c,v
retrieving revision 1.25
diff -u -r1.25 py-value.c
--- python/py-value.c 27 Jun 2011 19:21:51 -0000 1.25
+++ python/py-value.c 21 Sep 2011 15:45:12 -0000
@@ -209,7 +209,7 @@
val_obj->address = value_to_value_object (res_val);
}

- Py_INCREF (val_obj->address);
+ Py_XINCREF (val_obj->address);

return val_obj->address;
}
@@ -1045,7 +1045,15 @@
value_to_value_object (struct value *val)
{
value_object *val_obj;
+ volatile struct gdb_exception except;

+ TRY_CATCH (except, RETURN_MASK_ALL)
+ {
+ if (value_lazy (val))
+ value_fetch_lazy (val);
+ }
+ GDB_PY_HANDLE_EXCEPTION (except);
+
val_obj = PyObject_New (value_object, &value_object_type);
if (val_obj != NULL)
{
Index: testsuite/gdb.python/py-value.exp
===================================================================
RCS file: /cvs/src/src/gdb/testsuite/gdb.python/py-value.exp,v
retrieving revision 1.22
diff -u -r1.22 py-value.exp
--- testsuite/gdb.python/py-value.exp 26 Jul 2011 18:38:55 -0000 1.22
+++ testsuite/gdb.python/py-value.exp 21 Sep 2011 15:45:13 -0000
@@ -218,6 +218,7 @@

# Test memory error.
gdb_test "python print gdb.parse_and_eval('*(int*)0')" "gdb.MemoryError: Cannot access memory at address 0x0.*"
+ gdb_test "python inval = gdb.parse_and_eval('*(int*)0')" "gdb.MemoryError: Cannot access memory at address 0x0.*"

# Test string fetches, both partial and whole.
gdb_test "print st" "\"divide et impera\""