Re: Variable objects: references formatting

[Nick Roberts <nickrob at snap dot net dot nz>]

> At the moment, when using variable objects to display a struct or a class,
> the result of -data-evaluate-expression is "...". However, when displaying
> a reference to a class, the result of -data-evaluate-expression is
> {}-enclosed list of members and their values.

> This disparity does not seem to be reasonable, the attached patch fixes it:

> Changelog:

>   2006-05-03 Vladimir Prus <ghost@cs.msu.su>
>       varobj.c (c_value_of_variable): Ignore top-level references.

> Patch attached.

> Thanks,
> Volodya

There are som many things about this patch that I don't understand:

> Index: varobj.c
> ===================================================================
> RCS file: /cvs/src/src/gdb/varobj.c,v
> retrieving revision 1.58

Version 1.59 has been in the repository for over a month, so how come this
patch is against 1.58?

> diff -u -r1.58 varobj.c
> @@ -2055,8 +2219,14 @@

I'm not used to unified diffs, but as insertion appears to be done at the
same place why is it not something like:

@@ -2055,8 +2055,14 @@

>  {
>    /* BOGUS: if val_print sees a struct/class, it will print out its
>       children instead of "{...}" */
> +  struct type* type = get_type (var);
> +  /* Strip top-level references. */
> +  while (TYPE_CODE (type) == TYPE_CODE_REF)
> +    {
> +      type = TYPE_TARGET_TYPE (type);
> +    }
>  
> -  switch (TYPE_CODE (get_type (var)))
> +  switch (TYPE_CODE (type))
>      {
>      case TYPE_CODE_STRUCT:
>      case TYPE_CODE_UNION:


Most importantly, however, the preamble is about -data-evaluate-expression
but AFAICS this doesn't call c_value_of_variable.

I have tested the output of -data-evaluate-expression on pointers to typedeffed
structures and found that with the latter I get a {}-enclosed list of members
with gcc 3.2 and {...} with gcc 4.1.  More generally, I have found that gcc 4.1
treats typedefs differently, which leads to errors with variable objects.

So clearly I also don't understand how Jim can think that the patch looks
good and he'll apply it.


-- 
Nick                                           http://www.inet.net.nz/~nickrob