Re: [RFC PATCH 32/77] dtc-parser: Introduce last_header_flags

On Thu, 15 Jan 2026 17:31:24 +1100
David Gibson <[email protected]> wrote:

> On Mon, Jan 12, 2026 at 03:19:22PM +0100, Herve Codina wrote:
> > The parser needs to get header flags value in different places.
> > 
> > It relies on the fact that the rule used to parse the dts file is always
> >   headers memreserves devicetree
> > 
> > With that only rule to parse the file, it uses '$<flags>-1' construct to
> > get the flags value.
> > 
> > With the future introduction of import symbols parsing, this rule will
> > change and the parser couldn't rely anymore on '$<flags>-1' to get flags
> > value. Indeed, import symbols parsing will add a new optional symbol in
> > this rule leading to two possible rules (with and without the new
> > symbol) to parse the source file.
> > 
> > Introduce the last_header_flags variable to explicitly keep track of
> > flags while also being agnostic of the rule structure and use this new
> > variable instead of '$<flags>-1'.  
> 
> I'm not sure this approach is safe: I'm not sure bison guarantees that
> semantic rules will always be executed in the same order, so using
> global variables is risky.

if rules were not executed in the same order '$<flags>-1' construct would
not work.

The problem is not the order. I don't think the order will change. The
problem is related to the number of items on stack.

With import symbols, that the stack will be:
  header memreserved devicetree
or
  header memreserved importsyms devicetree

Using '$-1' will no more be possible. Indeed, '$-1' from the devicetree
rule will reference 'header' in one case and 'memreserved' in the other
case.

Without a global variable, I don't know how to reference 'header' (or flags
value) in all cases.

Any better ideas are welcome.

Best regards,
Hervé