linux-kernel - Re: [RFC PATCH 32/77] dtc-parser: Introduce last_header

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Message-ID: <aWiJvEEgjl44h6vd@zatzit>
Date: Thu, 15 Jan 2026 17:31:24 +1100
From: David Gibson <david@...son.dropbear.id.au>
To: Herve Codina <herve.codina@...tlin.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Ayush Singh <ayush@...gleboard.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	devicetree-compiler@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree-spec@...r.kernel.org,
	Hui Pu <hui.pu@...ealthcare.com>,
	Ian Ray <ian.ray@...ealthcare.com>,
	Luca Ceresoli <luca.ceresoli@...tlin.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [RFC PATCH 32/77] dtc-parser: Introduce last_header_flags

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.

> 
> Signed-off-by: Herve Codina <herve.codina@...tlin.com>
> ---
>  dtc-parser.y | 28 +++++++++-------------------
>  1 file changed, 9 insertions(+), 19 deletions(-)
> 
> diff --git a/dtc-parser.y b/dtc-parser.y
> index 4e46e9d..48c40e8 100644
> --- a/dtc-parser.y
> +++ b/dtc-parser.y
> @@ -24,6 +24,8 @@ extern void yyerror(char const *s);
>  extern struct dt_info *parser_output;
>  extern bool treesource_error;
>  
> +unsigned int last_header_flags;
> +
>  static bool is_ref_relative(const char *ref)
>  {
>  	return ref[0] != '/' && strchr(&ref[1], '/');
> @@ -122,14 +124,17 @@ header:
>  	  DT_V1 ';'
>  		{
>  			$$ = DTSF_V1;
> +			last_header_flags = $$;
>  		}
>  	| DT_V1 ';' DT_PLUGIN ';'
>  		{
>  			$$ = DTSF_V1 | DTSF_PLUGIN;
> +			last_header_flags = $$;
>  		}
>  	| DT_V1 ';' DT_ADDON ';'
>  		{
>  			$$ = DTSF_V1 | DTSF_ADDON;
> +			last_header_flags = $$;
>  		}
>  	;
>  
> @@ -179,12 +184,7 @@ devicetree:
>  		}
>  	| dt_ref nodedef
>  		{
> -			/*
> -			 * We rely on the rule being always:
> -			 *   versioninfo plugindecl memreserves devicetree
> -			 * so $-1 is what we want (plugindecl)
> -			 */
> -			if (!($<flags>-1 & DTSF_PLUGIN))
> +			if (!(last_header_flags & DTSF_PLUGIN))
>  				ERROR(&@2, "Label or path %s not found", $1);
>  			else if (is_ref_relative($1))
>  				ERROR(&@2, "Label-relative reference %s not supported in plugin", $1);
> @@ -197,7 +197,7 @@ devicetree:
>  		{
>  			struct node *target = get_node_by_ref($1, $3);
>  
> -			if (($<flags>-1 & DTSF_PLUGIN) && is_ref_relative($3))
> +			if ((last_header_flags & DTSF_PLUGIN) && is_ref_relative($3))
>  				ERROR(&@2, "Label-relative reference %s not supported in plugin", $3);
>  
>  			if (target) {
> @@ -209,12 +209,7 @@ devicetree:
>  		}
>  	| devicetree DT_PATH_REF nodedef
>  		{
> -			/*
> -			 * We rely on the rule being always:
> -			 *   versioninfo plugindecl memreserves devicetree
> -			 * so $-1 is what we want (plugindecl)
> -			 */
> -			if ($<flags>-1 & DTSF_PLUGIN) {
> +			if (last_header_flags & DTSF_PLUGIN) {
>  				if (is_ref_relative($2))
>  					ERROR(&@2, "Label-relative reference %s not supported in plugin", $2);
>  				add_orphan_node($1, $3, $2);
> @@ -235,12 +230,7 @@ devicetree:
>  			if (target) {
>  				merge_nodes(target, $3);
>  			} else {
> -				/*
> -				 * We rely on the rule being always:
> -				 *   versioninfo plugindecl memreserves devicetree
> -				 * so $-1 is what we want (plugindecl)
> -				 */
> -				if ($<flags>-1 & DTSF_PLUGIN)
> +				if (last_header_flags & DTSF_PLUGIN)
>  					add_orphan_node($1, $3, $2);
>  				else
>  					ERROR(&@2, "Label or path %s not found", $2);
> -- 
> 2.52.0
> 
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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