Re: [RFC PATCH 20/77] dtc: Add support for /export/ dts keyword parsing

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Jan 12, 2026 at 03:19:10PM +0100, Herve Codina wrote:
> The /export/ dts keyword is the keyword used to define an exported
> symbol at a given node level.
> 
> This keyword can be present in a node definition (after properties and
> before subnodes) to export a symbol. If several symbols need to be
> exported, several /export/ keywords are present.
> 
> The syntax used is the following:
>   /export/ name: reference;
> 
> with:
>   name: The name of the exported symbol
>   reference: The reference of a node the symbol is pointing to.
> 
> For instance:
>   - Reference by label:
>       /export/ foo: &foo1;
> 
>     The exported symbol foo references the node identified by
>     the label foo1.
> 
>   - Reference by path:
>       /export/ foo: &{/path/to/foo@100};
> 
>     The exported symbol foo references the node at /path/to/foo@100.
> 
> Add support for /export/ dts keyword.
> 
> Signed-off-by: Herve Codina <herve.codina@bootlin.com>
> ---
>  dtc-lexer.l  |  6 ++++
>  dtc-parser.y | 53 ++++++++++++++++++++++++++++++++++
>  dtc.h        |  8 ++++++
>  livetree.c   | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 147 insertions(+)
> 
> diff --git a/dtc-lexer.l b/dtc-lexer.l
> index a4a8e0b..90fe70e 100644
> --- a/dtc-lexer.l
> +++ b/dtc-lexer.l
> @@ -149,6 +149,12 @@ static void PRINTF(1, 2) lexical_error(const char *fmt, ...);
>  			return DT_OMIT_NO_REF;
>  		}
>  
> +<*>"/export/" 	{
> +			DPRINT("Keyword: /export/\n");
> +			BEGIN_DEFAULT();
> +			return DT_EXPORT;
> +		}
> +
>  <*>{LABEL}:	{
>  			DPRINT("Label: %s\n", yytext);
>  			yylval.labelref = xstrdup(yytext);
> diff --git a/dtc-parser.y b/dtc-parser.y
> index 9c93673..a0d0aef 100644
> --- a/dtc-parser.y
> +++ b/dtc-parser.y
> @@ -46,6 +46,8 @@ static bool is_ref_relative(const char *ref)
>  	struct property *proplist;
>  	struct node *node;
>  	struct node *nodelist;
> +	struct symbol *symbol;
> +	struct symbol *exportlist;
>  	struct reserve_info *re;
>  	uint64_t integer;
>  	unsigned int flags;
> @@ -60,6 +62,7 @@ static bool is_ref_relative(const char *ref)
>  %token DT_DEL_PROP
>  %token DT_DEL_NODE
>  %token DT_OMIT_NO_REF
> +%token DT_EXPORT
>  %token <propnodename> DT_PROPNODENAME
>  %token <integer> DT_LITERAL
>  %token <integer> DT_CHAR_LITERAL
> @@ -80,6 +83,8 @@ static bool is_ref_relative(const char *ref)
>  %type <data> bytestring
>  %type <prop> propdef
>  %type <proplist> proplist
> +%type <symbol> exportdef
> +%type <exportlist> exportlist
>  %type <labelref> dt_ref
>  
>  %type <node> devicetree
> @@ -276,6 +281,49 @@ nodedef:
>  		{
>  			$$ = build_node(NULL, $2, NULL, &@$);
>  		}
> +	| '{' proplist exportlist subnodes '}' ';'
> +		{
> +			/*
> +			 * exportlist is created with chain_symbol() and so it
> +			 * is created in reverse order. Reverse it now to have
> +			 * it in correct order
> +			 */
> +			$$ = build_node($2, $4, reverse_symbol($3), &@$);
> +		}
> +	| '{' exportlist subnodes '}' ';'
> +		{
> +			/*
> +			 * exportlist is created with chain_symbol() and so it
> +			 * is created in reverse order. Reverse it now to have
> +			 * it in correct order
> +			 */
> +			$$ = build_node(NULL, $3, reverse_symbol($2), &@$);
> +		}
> +	;
> +
> +exportlist:
> +	  exportdef
> +		{
> +			$$ = chain_symbol($1, NULL);
> +		}
> +	| exportlist exportdef
> +		{
> +			$$ = chain_symbol($2, $1);
> +		}
> +	| exportlist propdef
> +		{
> +			ERROR(&@2, "Properties must precede exports");
> +			YYERROR;
> +		}
> +	;
> +
> +exportdef:
> +	DT_EXPORT DT_LABEL dt_ref ';'
> +		{
> +			$$ = build_exportsym($2, $3, 0, &@$);
> +			free($2);
> +			free($3);

I mostly don't bother with free()s in dtc, on the grounds that it's
generally a short-lived process - essentially using the process
context as a crude pool allocator.

> +		}
>  	;
>  
>  proplist:
> @@ -576,6 +624,11 @@ subnodes:
>  			ERROR(&@2, "Properties must precede subnodes");
>  			YYERROR;
>  		}
> +	| subnode exportdef
> +		{
> +			ERROR(&@2, "Exports must precede subnodes");
> +			YYERROR;
> +		}
>  	;
>  
>  subnode:
> diff --git a/dtc.h b/dtc.h
> index 6508694..0bf5ba5 100644
> --- a/dtc.h
> +++ b/dtc.h
> @@ -273,6 +273,9 @@ struct node {
>  	for_each_child_withdel(n, c) \
>  		if (!(c)->deleted)
>  
> +#define for_each_symbol(s0, s) \
> +	for ((s) = (s0); (s); (s) = (s)->next)
> +
>  void add_label(struct label **labels, char *label);
>  void delete_labels(struct label **labels);
>  
> @@ -282,6 +285,11 @@ struct property *build_property_delete(const char *name);
>  struct property *chain_property(struct property *first, struct property *list);
>  struct property *reverse_properties(struct property *first);
>  
> +struct symbol *build_exportsym(const char *name, const char *ref, cell_t phandle,
> +			       struct srcpos *srcpos);
> +struct symbol *chain_symbol(struct symbol *first, struct symbol *list);
> +struct symbol *reverse_symbol(struct symbol *list);
> +
>  struct node *build_node(struct property *proplist, struct node *children,
>  			struct symbol *exportsymlist, struct srcpos *srcpos);
>  struct node *build_node_delete(struct srcpos *srcpos);
> diff --git a/livetree.c b/livetree.c
> index 0050492..4458437 100644
> --- a/livetree.c
> +++ b/livetree.c
> @@ -36,6 +36,57 @@ void delete_labels(struct label **labels)
>  		label->deleted = 1;
>  }
>  
> +struct symbol *build_exportsym(const char *name, const char *ref, cell_t phandle,
> +			       struct srcpos *srcpos)
> +{
> +	struct symbol *new = xmalloc(sizeof(*new));
> +
> +	memset(new, 0, sizeof(*new));
> +
> +	new->name = xstrdup(name);
> +	new->ref = ref ? xstrdup(ref) : NULL;
> +	new->phandle = phandle;
> +	new->srcpos = srcpos_copy(srcpos);
> +
> +	return new;
> +}
> +
> +struct symbol *chain_symbol(struct symbol *first, struct symbol *list)
> +{
> +	assert(first->next == NULL);
> +
> +	first->next = list;
> +	return first;
> +}
> +
> +struct symbol *reverse_symbol(struct symbol *list)
> +{
> +	struct symbol *p = list;
> +	struct symbol *head = NULL;
> +	struct symbol *next;
> +
> +	while (p) {
> +		next = p->next;
> +		p->next = head;
> +		head = p;
> +		p = next;
> +	}
> +	return head;
> +}
> +
> +static void add_symbol(struct symbol **list, struct symbol *new)
> +{
> +	struct symbol **s;
> +
> +	new->next = NULL;
> +
> +	s = list;
> +	while (*s)
> +		s = &((*s)->next);
> +
> +	*s = new;
> +}
> +
>  struct property *build_property(const char *name, struct data val,
>  				struct srcpos *srcpos)
>  {
> @@ -144,6 +195,7 @@ struct node *merge_nodes(struct node *old_node, struct node *new_node)
>  {
>  	struct property *new_prop, *old_prop;
>  	struct node *new_child, *old_child;
> +	struct symbol *new_sym, *old_sym;
>  	struct label *l;
>  
>  	old_node->deleted = 0;
> @@ -217,6 +269,34 @@ struct node *merge_nodes(struct node *old_node, struct node *new_node)
>  			add_child(old_node, new_child);
>  	}
>  
> +	/* Merge exported symbols. If there is a collision, keep the new one */
> +	while (new_node->exportsymlist) {
> +		/* Pop the symbol off the list */
> +		new_sym = new_node->exportsymlist;
> +		new_node->exportsymlist = new_sym->next;
> +		new_sym->next = NULL;
> +
> +		/* Look for a collision, set new value if there is */
> +		for_each_symbol(old_node->exportsymlist, old_sym) {
> +			if (streq(old_sym->name, new_sym->name)) {
> +				old_sym->is_local = new_sym->is_local;
> +				free(old_sym->ref);
> +				old_sym->ref = new_sym->ref;
> +				old_sym->phandle = new_sym->phandle;
> +				old_sym->fullpath = new_sym->fullpath;
> +				srcpos_free(old_sym->srcpos);
> +				old_sym->srcpos = new_sym->srcpos;
> +				free(new_sym);
> +				new_sym = NULL;
> +				break;
> +			}
> +		}
> +
> +		/* if no collision occurred, add symbol to the old node list. */
> +		if (new_sym)
> +			add_symbol(&old_node->exportsymlist, new_sym);
> +	}
> +
>  	old_node->srcpos = srcpos_extend(old_node->srcpos, new_node->srcpos);
>  
>  	/* The new node contents are now merged into the old node.  Free
> -- 
> 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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