Re: [RFC] [C]New syntax for the argument of counted_by attribute for C language

[Qing Zhao]

> On Apr 7, 2025, at 10:31, Michael Matz <m...@suse.de> wrote:
> 
> Hello,
> 
> On Mon, 7 Apr 2025, Martin Uecker wrote:
> 
>>> So, what specifically would the two attributes do different?  FWIW: what 
>>> worries me about accepting a generic expression in counted_by, that isn't 
>>> prefixed by a (possibly empty) decl, is that after seeing a non-type 
>>> identifier the parser doesn't yet know if it's the lone-ident case (look 
>>> up in struct scope) or the expression case (look up everything in global 
>>> scope).  It requires look-ahead to decide this.
>>> 
>>> Would that be the difference between the attributes?  One accepting _only_ 
>>> a lone-ident or the decl+expr syntax, and the other _only_ expressions 
>>> that are never looked up in struct-scope (not even if its lone-ident)?
>> 
>> My understanding is that one accepts only a lone identifier and nothing
>> else, i.e.
>> 
>> counted_by(identifier)
>> 
>> and the other only accepts expressions, possibly including a forward
>> declaration.
>> 
>> counted_by_expr(expression)
>> counted_by_expr(decl; expression)
> 
> What exactly happens when counted_by_expr is used with only an identifier 
> expression, without decl?  Is the ident looked up normally, i.e. not in 
> struct scope.

Yes, with the new counted_by_expr, all identifiers in the expression that are 
not declared before the expression will be looked up normally. 

Qing
>  If so, then good, it would resolve my worry.
> 
> 
> Ciao,
> Michael.