Re: [Python] Add methods reference_value and const_value to gdb.Value

Doug Evans
2015-05-07T23:30:57Z

Siva Chandra writes:
> This will help address libstdc++/65840:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65840
>
> gdb/ChangeLog:
>
> 2015-04-27 Siva Chandra Reddy <sivachandra@google.com>
>
> * NEWS (Python Scripting): Mention the new gdb.Value methods.
> * python/py-value.c (valpy_reference_value): New function.
> (valpy_const_value): Likewise.
> (value_object_methods): Add new methods.
> * value.c (make_cv_value): New function.
> * value.h (make_cv_value): Declare.
>
> gdb/doc/ChangeLog:
>
> 2015-04-27 Siva Chandra Reddy <sivachandra@google.com>
>
> * python.texi (Values From Inferior): Add descriptions of new
> methods gdb.Value.reference_value and gdb.Value.const_value.
>
> gdb/testsuite/ChangeLog:
>
> 2015-04-27 Siva Chandra Reddy <sivachandra@google.com>
>
> * gdb.python/py-xmethods.cc: Enhance test case.
> * gdb.python/py-xmethods.exp: New tests.
> * gdb.python/py-xmethods.py (A_indexoper): New xmethod worker
> function.
> (B_indexoper): Likewise.
> (global_dm_list) : Add new xmethod worker functions.

Thanks again for the ping.

LGTM with two nits below. grep for ====.

One more nit might be that we already have gdb.Value.referenced_value,
and now we'll also have gdb.Value.reference_value.
I'm ok with it.

> diff --git a/gdb/NEWS b/gdb/NEWS
> index b711553..627afd0 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -52,6 +52,9 @@
> which is the name of the objfile as specified by the user,
> without, for example, resolving symlinks.
> ** You can now write frame unwinders in Python.
> + ** gdb.Value objects have new methods "reference_value" and
> + "const_value" which return a reference to the value and a
> + "const" version of the value respectively.
>
> * New commands
>
> diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
> index 448fa8b2..1b1079d 100644
> --- a/gdb/doc/python.texi
> +++ b/gdb/doc/python.texi
> @@ -781,6 +781,16 @@ The @code{gdb.Value} object @code{py_val} is
identical to that
> corresponding to @code{val}.
> @end defun
>
> +@defun Value.reference_value ()
> +Return a @code{gdb.Value} object which is a reference to the value
> +encapsulated by this instance.
> +@end defun
> +
> +@defun Value.const_value ()
> +Return a @code{gdb.Value} object which is a @code{const} version of the
> +value encapsulated by this instance.
> +@end defun
> +
> @defun Value.dynamic_cast (type)
> Like @code{Value.cast}, but works as if the C@t{++} @code{dynamic_cast}
> operator were used. Consult a C@t{++} reference for details.
> diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
> index 6622d11..94ff9ba 100644
> --- a/gdb/python/py-value.c
> +++ b/gdb/python/py-value.c
> @@ -236,6 +236,60 @@ valpy_referenced_value (PyObject *self, PyObject
*args)
> return result;
> }
>
> +/* Return a value which is a reference to the value. */
> +
> +static PyObject *
> +valpy_reference_value (PyObject *self, PyObject *args)
> +{
> + PyObject *result = NULL;
> +
> + TRY
> + {
> + struct value *self_val;
> + struct cleanup *cleanup = make_cleanup_value_free_to_mark
(value_mark ());
> +
> + self_val = ((value_object *) self)->value;
> + result = value_to_value_object (value_ref (self_val));
> +
> + do_cleanups (cleanup);
> + }
> + CATCH (except, RETURN_MASK_ALL)
> + {
> + GDB_PY_HANDLE_EXCEPTION (except);
> + }
> + END_CATCH
> +
> + return result;
> +}
> +
> +/* Return a "const" qualified version of the value. */
> +
> +static PyObject *
> +valpy_const_value (PyObject *self, PyObject *args)
> +{
> + PyObject *result = NULL;
> +
> + TRY
> + {
> + struct value *self_val, *res_val;
> + struct type *const_type;

====
const_type can be deleted.

> + struct cleanup *cleanup = make_cleanup_value_free_to_mark
(value_mark ());
> +
> + self_val = ((value_object *) self)->value;
> + res_val = make_cv_value (1, 0, self_val);
> + result = value_to_value_object (res_val);
> +
> + do_cleanups (cleanup);
> + }
> + CATCH (except, RETURN_MASK_ALL)
> + {
> + GDB_PY_HANDLE_EXCEPTION (except);
> + }
> + END_CATCH
> +
> + return result;
> +}
> +
> /* Return "&value". */
> static PyObject *
> valpy_get_address (PyObject *self, void *closure)
> @@ -1692,6 +1746,10 @@ reinterpret_cast operator."
> { "dereference", valpy_dereference, METH_NOARGS, "Dereferences the
value." },
> { "referenced_value", valpy_referenced_value, METH_NOARGS,
> "Return the value referenced by a TYPE_CODE_REF or TYPE_CODE_PTR
value." },
> + { "reference_value", valpy_reference_value, METH_NOARGS,
> + "Return a value of type TYPE_CODE_REF referencing this value." },
> + { "const_value", valpy_const_value, METH_NOARGS,
> + "Return a 'const' qualied version of the same value." },
> { "lazy_string", (PyCFunction) valpy_lazy_string,
> METH_VARARGS | METH_KEYWORDS,
> "lazy_string ([encoding] [, length]) -> lazy_string\n\
> diff --git a/gdb/testsuite/gdb.python/py-xmethods.cc
b/gdb/testsuite/gdb.python/py-xmethods.cc
> index aedd1de..98bdb72 100644
> --- a/gdb/testsuite/gdb.python/py-xmethods.cc
> +++ b/gdb/testsuite/gdb.python/py-xmethods.cc
> @@ -173,7 +173,7 @@ int main(void)
>
> for (int i = 0; i < 10; i++)
> {
> - a1.array[i] = a2.array[i] = i;
> + a1.array[i] = a2.array[i] = b1.array[i] = i;
> }
>
> return 0; /* Break here. */
> diff --git a/gdb/testsuite/gdb.python/py-xmethods.exp
b/gdb/testsuite/gdb.python/py-xmethods.exp
> index a83b14d..eacfa0c 100644
> --- a/gdb/testsuite/gdb.python/py-xmethods.exp
> +++ b/gdb/testsuite/gdb.python/py-xmethods.exp
> @@ -100,6 +100,8 @@ gdb_test "p a1.geta()" "From Python
<A_geta>.*5" "After: a1.geta()"
> gdb_test "p ++a1" "From Python <plus_plus_A>.*6" "After: ++a1"
> gdb_test "p a1.getarrayind(5)" "From Python <A_getarrayind>.*5" \
> "After: a1.getarrayind(5)"
> +gdb_test "P a1\[6\]" ".*int &.*6" "After a1\[\]"
> +gdb_test "P b1\[7\]" ".*const int &.*7" "After b1\[\]"
> # Note the following test. Xmethods on dynamc types are not looked up
> # currently. Hence, even though a_ptr points to a B object, the xmethod
> # defined for A objects is invoked.
> diff --git a/gdb/testsuite/gdb.python/py-xmethods.py
b/gdb/testsuite/gdb.python/py-xmethods.py
> index 78935e1..3194e89 100644
> --- a/gdb/testsuite/gdb.python/py-xmethods.py
> +++ b/gdb/testsuite/gdb.python/py-xmethods.py
> @@ -43,6 +43,12 @@ def A_getarrayind(obj, index):
> print('From Python <A_getarrayind>:')
> return obj['array'][index]
>
> +def A_indexoper(obj, index):
> + return obj['array'][index].reference_value()
> +
> +def B_indexoper(obj, index):
> + return obj['array'][index].const_value().reference_value()
> +
>
> type_A = gdb.parse_and_eval('(dop::A *) 0').type.target()
> type_B = gdb.parse_and_eval('(dop::B *) 0').type.target()
> @@ -208,6 +214,16 @@ global_dm_list = [
> '^getarrayind$',
> A_getarrayind,
> type_int),
> + SimpleXMethodMatcher('A_indexoper',
> + '^dop::A$',
> + 'operator\\[\\]',
> + A_indexoper,
> + type_int),
> + SimpleXMethodMatcher('B_indexoper',
> + '^dop::B$',
> + 'operator\\[\\]',
> + B_indexoper,
> + type_int)
> ]
>
> for matcher in global_dm_list:
> diff --git a/gdb/value.c b/gdb/value.c
> index cb56849..242b46c 100644
> --- a/gdb/value.c
> +++ b/gdb/value.c
> @@ -1704,6 +1704,22 @@ value_copy (struct value *arg)
> return val;
> }
>
> +/* Return a "const" and/or "volatile" qualified version of the value V.
> + If CNST is true, then the returned value will be qualified with
> + "const".
> + if VOLTL is true, then the returned value will be qualified with
> + "volatile". */
> +
> +struct value *
> +make_cv_value (int cnst, int voltl, struct value *v)
> +{
> + struct value *cv_val = value_copy (v);
> +
> + cv_val->type = make_cv_type (cnst, voltl, value_type (v), NULL);
> +
> + return cv_val;
> +}

====
I'm not sure the call to value_copy will always produce the desired result,
but I don't have anything specific to say. So let's go with it.
I'd replace the assignment to cv_val->type with a call to
deprecated_set_value_type though.
Do we need to call set_value_enclosing_type too?
For consistency I'd think so.

> +
> /* Return a version of ARG that is non-lvalue. */
>
> struct value *
> diff --git a/gdb/value.h b/gdb/value.h
> index 21baa32..9aeaa4a 100644
> --- a/gdb/value.h
> +++ b/gdb/value.h
> @@ -1040,6 +1040,8 @@ extern struct value *value_non_lval (struct value
*);
>
> extern void value_force_lval (struct value *, CORE_ADDR);
>
> +extern struct value *make_cv_value (int, int, struct value *);
> +
> extern void preserve_one_value (struct value *, struct objfile *,
htab_t);
>
> /* From valops.c */