Re: -var-update @

[Vladimir Prus <vladimir@codesourcery.com>]

On Friday 04 April 2008 00:04:03 Nick Roberts wrote:
> Vladimir Prus writes:
>  > On Sunday 30 March 2008 07:54:08 Nick Roberts wrote:
>  > >  > So, we still don't know why the current code does not work? I think
>  > >  > we still get to figure out, to make sure that whatever bug there is
>  > >  > does not affect other cases.
>  > > 
>  > > My patch didn't do the right thing (it always marked a floating variable
>  > > object as changed) but it's along the right lines.  How about this one?
>  > 
>  > This patch seem to go in the right direction. I'm somewhat surprised that
>  > evaluating previous expression gets bogus value, as opposed to getting value
>  > in the frame where varobj was originally created. Any ideas why is that?
> 
> I've not tried to understand _exactly_ what value was being retrieved, but
> basically var->root->exp was obtained once from gdb_parse_exp_1 in
> varobj_create and this has symbol information in var->root->exp->elts[2].
> Previously this would be the symbol information for the variable in the frame
> for which the variable object was created.  At the same time var->value was
> being updated relative to the selected frame, which gave an incorrect address
> value in value->address.  I guess a variable's numeric value on the stack is
> computed using both the frame address and an address in the symbol table and
> these were inconsistent.
> 
> 	  /* Update expression to new frame.  */
> 	  tmp_exp = var->root->exp;
> 	  var->root->exp = tmp_var->root->exp;
> 	  tmp_var->root->exp = tmp_exp;
> 
> Moving var->root->exp into tmp_var->root->exp just ensures that this memory
> gets freed when tmp_var is deleted:
> 
> 	  varobj_delete (tmp_var, NULL, 0);
> 
>  > Do you think you can write some test to go along this patch?
> 
> We need some tests and documentation at some stage before the next release
> but perhaps Bogdan can confirm that this patch works for him first.

Well, if your patch fixes the issue that *you* saw, then it's already an improvement,
and we better get it into the tree as soon as possible.

- Volodya