Re: -var-update and address changes

[Vladimir Prus <ghost at cs dot msu dot su>]

On Tuesday 02 May 2006 17:14, Nick Roberts wrote:
> Vladimir Prus writes:
>  > On Friday 14 April 2006 23:49, Jim Ingham wrote:
>  > > Note as an aside, that we had to add another varobj type which is
>  > > evaluated in the selected frame, whatever that happens to be.  That
>  > > was useful for a general "variable inspector" window.  People wanted
>  > > to put some expression there, and have it re-evaluated in the topmost
>  > > frame whenever they stopped.  So we added that functionality.  But
>  > > that is clearly distinct from what the "*" varobj type is supposed to
>  > > mean.
>  >
>  > Hi Jim,
>  > is this "variable inspector" the same thing that's called "watches" in
>  > other IDEs? Well, I really wish that gdb did support variable objects
>  > that are reevaluated in the current frame. As it stands now, I have to
>  > re-create variable objects on each step.
>
> Assuming some ambiguity with current/selected, have you tried (not
> documented):
>
> "-var-create - @ NAME"
>
> which behaves a bit differently to "-var-create - * NAME".

Wow, that's exactly what I'm looking for. Except that it's buggy :-(
When I have code like this:

  int foo()
  {
      long i = 15;
      printf("foo\n");
  }

  int main()
  {
    int i = 5;
    printf("hi 1\n");
    foo();
  }

and I use

  -var-create I @ i

right before call to 'foo()', then when I enter 'foo', -var-update correctly 
notices the change in value and in type. However, when I have:

  int foo()
  {
      long i = 15;
      printf("foo\n");
  }

  int main()
  {
    int i = 5;
    printf("hi 1\n");
    foo();
  }

then -var-update inside 'foo' does not report anything and 
-var-evaluate-expression still reports the value of 'i' from 'main'. Here's 
the faulty code (varobj.c: value_of_root):

    tmp_var = varobj_create (NULL, var->name, (CORE_ADDR) 0,
			       USE_SELECTED_FRAME);
     if (tmp_var == NULL)
	{
	  return NULL;
	}
     new_type = varobj_get_type (tmp_var);
     if (strcmp (old_type, new_type) == 0)
	{
	  varobj_delete (tmp_var, NULL, 0);
	  *type_changed = 0;
	}
     else

In other words, if the type of 'i' in the current frame happens to be the 
same, the newly created varobj is immediately deleted. What about patch along 
the following lines, that will create new varobj even if type is the same?

@@ -1641,28 +1741,14 @@
 	  return NULL;
 	}
       new_type = varobj_get_type (tmp_var);
-      if (strcmp (old_type, new_type) == 0)
-	{
-	  varobj_delete (tmp_var, NULL, 0);
-	  *type_changed = 0;
-	}
-      else
-	{
-	  if (*type_changed)
-	    {
-	      tmp_var->obj_name =
-		savestring (var->obj_name, strlen (var->obj_name));
-	      varobj_delete (var, NULL, 0);
-	    }
-	  else
-	    {
-	      tmp_var->obj_name = varobj_gen_name ();
-	    }
-	  install_variable (tmp_var);
-	  *var_handle = tmp_var;
-	  var = *var_handle;
-	  *type_changed = 1;
-	}
+      *type_changed = (strcmp (old_type, new_type) != 0);
+
+      tmp_var->obj_name =
+          savestring (var->obj_name, strlen (var->obj_name));
+      varobj_delete (var, NULL, 0);
+      install_variable (tmp_var);
+      *var_handle = tmp_var;
+      var = *var_handle;
     }

- Volodya