Re: Variable objects: references formatting

Nick Roberts
2006-05-03T23:05:07Z

> 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