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

[Doug Evans <dje at google dot com>]

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 */