Re: [MI] lvalues and variable_editable

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

On Tuesday 10 July 2007 04:49, Nick Roberts wrote:
>  > > + static int
>  > > + variable_editable_pv (struct varobj *var)
>  > 
>  > Can we probably use "varobj_editable_pv". Using
>  > varobj in some places, and "variable" in others
>  > makes for confusing code.
> 
> (I meant variable_editable_p.)
> 
> It looks like you renamed type_changeable to varobj_value_is_changeable_p
> following Apple's version.  I agree that there should be some consistency
> 
> variable_editable_p,  variable_changeable_p?
> 
> var_editable_p, var_changeable_p?
> 
> or, probably better
> 
> varobj_editable_p,  varobj_changeable_p?

This last seems best to me. I think that the "varobj_value_changeable"
is more accurate than varobj_changeable, because it specifically means
that var->value never changes, but that's probably not important.

>  > Also, why is_root_p check? It is possible to create varobj for
>  > an expression the creates rvalue of structure type. The children of 
>  > such varobj won't be lvalues, and won't be editable, but this code
>  > won't catch this case.
> 
> I'm not sure what you mean by "won't catch this case" but this is in
> variable_editable_p which is called by varobj_set_value.  If the user
> tries to assign a value to a child this check means GDB won't need to
> test if it's not an lvalue.

Well, ideally if I have a varobj for rvalue structure, I want the children
of such varobj to be reported as non-editable. It does not seem to happen,
IIUC.

>  > > *************** varobj_value_is_changeable_p (struct var
>  > > *** 1819,1837 ****
>  > > --- 1822,1842 ----
>  > > 
>  > > type = get_value_type (var);
>  > > 
>  > > +
>  > > switch (TYPE_CODE (type))
>  > > {
>  > > case TYPE_CODE_STRUCT:
>  > > case TYPE_CODE_UNION:
>  > > case TYPE_CODE_ARRAY:
>  > > ! ? ? case TYPE_CODE_FUNC:
>  > > ! ? ? case TYPE_CODE_METHOD:
>  > > ! ? ? ? return 0;
>  > 
>  > In current gdb, assuming this declaration:
>  > 
>  >         void (*fp)();
>  > 
>  > I can create varobj for *fp:
>  > 
>  >         -var-create V * *fp
>  > 
>  > and V will be updated if fp changes. With your patch,
>  > I get this:
>  > 
>  >         -var-create V * *fp
>  >         ~"varobj.c:2180: internal-error: c_value_of_variable: Assertion `varobj_value_is_changeable_p (var)' failed.\n"
>  >         ~"A problem internal to GDB has been detected,\n"
>  >         ~"further debugging may prove unreliable.\n"
>  >         ~"Quit this debugging session? (y or n) "
> 
> OK.  I had just thought about fp being TYPE_CODE_PTR.
> 
>  > So, probably TYPE_CODE_FUNC should be handled in variable_editable_p.
>  > I'm not sure about TYPE_CODE_METHOD -- I don't know how to construct
>  > an object of that type using any possible expression.
> 
> That's where they came from.  OK, I'll investigate.  It occurs to me that you
> might be create problems with pointers to structs, unions and arrays too.

We should not have any problems, because we never try to get varobj->value
for object of struct, union or array type.

- Volodya



>