Re: [PATCH v7 1/5] Provide counted_by attribute to flexible array member field (PR108896)

[Qing Zhao <qing.zhao@oracle.com>]

> On Mar 26, 2024, at 13:20, Joseph Myers <josmyers@redhat.com> wrote:
> 
> On Tue, 26 Mar 2024, Qing Zhao wrote:
> 
>>> What happens when there are multiple counted_by attributes on the same 
>>> field?  As far as I can see, all but one end up being ignored (by the code 
>>> that actually uses the attribute).
>> 
>> In general, is there any rule for handling multiple same attributes in 
>> GCC? i.e, from left to right, the last one wins? Or something else? I’d 
>> like to following the consistent rule with other places in GCC.
> 
> Sometimes, they are meaningful and all can be respected.  (An example is 
> the format_arg attribute, where ngettext legitimately has two such 
> attributes.)
> 
> When not meaningful, an error is appropriate.  For example, with section 
> attributes you can get
> 
>        error ("section of %q+D conflicts with previous declaration",
>               *node);
> 
> if different sections are named.  I think that's a suitable model for the 
> new attribute here: allow duplicates if they name the same field, but give 
> errors if they name different fields, just as with the section attribute.
> 
> Once you give an error for multiple attributes naming different fields, 
> which one wins is just a question of error recovery; the specific choice 
> doesn't matter much, as long as you don't get an ICE in later processing.

Agreed and fixed as suggested.

Thanks.

Qing
> 
> -- 
> Joseph S. Myers
> josmyers@redhat.com