Re: [PATCH 4/7] perf annotate-data: Bound the member nesting recursion

[Namhyung Kim <namhyung@kernel.org>]

On Sat, Sep 19, 2026 at 05:40:24PM -0300, Arnaldo Carvalho de Melo wrote:
> From: Arnaldo Carvalho de Melo <acme@redhat.com>
> 
> Members are added recursively, and the same kind of broken DIE can make
> a member's type point back at one of its own ancestors, recursing until
> the stack is gone; nothing usable comes out of nesting members 8 deep
> anyway, so stop there, marking the member as truncated (reported by the
> JSON exporter added in a later series) and giving up on member types
> that don't resolve.

I think 8 is too restrictive.  It should be common to have 3 or 4 depth
if you have nested struct or union members.

And some kernel primitives like spinlock also have nested members like

  raw_spinlock_t
    arch_spinlock_t
      union
        atomic_t
	  int

So it'd be easy to hit the limit when the nested members contain a
spinlock.

Thanks,
Namhyung

> 
> Assisted-by: LLM
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> ---
>  tools/perf/util/annotate-data.c | 32 ++++++++++++++++++++++++++------
>  tools/perf/util/annotate-data.h |  3 +++
>  2 files changed, 29 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
> index 2ad6d012e069c522..c67bb6005e23c516 100644
> --- a/tools/perf/util/annotate-data.c
> +++ b/tools/perf/util/annotate-data.c
> @@ -221,6 +221,13 @@ static bool data_type_less(struct rb_node *node_a, const struct rb_node *node_b)
>  	return strcmp(a->self.type_name, b->self.type_name) < 0;
>  }
>  
> +/*
> + * Members are added recursively; bound the nesting so that a broken
> + * type that points back at one of its own ancestors doesn't recurse
> + * until the stack is gone.
> + */
> +#define MAX_MEMBER_DEPTH 8
> +
>  /* Recursively add new members for struct/union */
>  static int __add_member_cb(Dwarf_Die *die, void *arg)
>  {
> @@ -235,6 +242,16 @@ static int __add_member_cb(Dwarf_Die *die, void *arg)
>  	if (dwarf_tag(die) != DW_TAG_member)
>  		return DIE_FIND_CB_SIBLING;
>  
> +	if (__die_get_real_type(die, &member_type) == NULL)
> +		return DIE_FIND_CB_SIBLING;
> +
> +	if (dwarf_tag(&member_type) == DW_TAG_typedef) {
> +		if (die_get_real_type(&member_type, &die_mem) == NULL)
> +			return DIE_FIND_CB_SIBLING;
> +	} else {
> +		die_mem = member_type;
> +	}
> +
>  	member = zalloc(sizeof(*member));
>  	if (member == NULL)
>  		return DIE_FIND_CB_END;
> @@ -242,12 +259,6 @@ static int __add_member_cb(Dwarf_Die *die, void *arg)
>  	strbuf_init(&sb, 32);
>  	die_get_typename(die, &sb);
>  
> -	__die_get_real_type(die, &member_type);
> -	if (dwarf_tag(&member_type) == DW_TAG_typedef)
> -		die_get_real_type(&member_type, &die_mem);
> -	else
> -		die_mem = member_type;
> -
>  	if (dwarf_aggregate_size(&die_mem, &size) < 0)
>  		size = 0;
>  
> @@ -289,10 +300,19 @@ static int __add_member_cb(Dwarf_Die *die, void *arg)
>  	}
>  	member->size = size;
>  	member->offset = loc + parent->offset;
> +	member->depth = parent->depth + 1;
>  	INIT_LIST_HEAD(&member->children);
>  	list_add_tail(&member->node, &parent->children);
>  
>  	tag = dwarf_tag(&die_mem);
> +	if (member->depth >= MAX_MEMBER_DEPTH) {
> +		/* Reported by the JSON exporter so consumers can tell a truncated tree. */
> +		member->truncated = true;
> +		pr_debug_dtp("member nesting limit reached at %s\n",
> +			     member->type_name ?: "(unknown type)");
> +		return DIE_FIND_CB_SIBLING;
> +	}
> +
>  	switch (tag) {
>  	case DW_TAG_structure_type:
>  	case DW_TAG_union_type:
> diff --git a/tools/perf/util/annotate-data.h b/tools/perf/util/annotate-data.h
> index ca2096a9ee62cbfe..cc576232f55b5fb0 100644
> --- a/tools/perf/util/annotate-data.h
> +++ b/tools/perf/util/annotate-data.h
> @@ -57,6 +57,9 @@ struct annotated_member {
>  	char *var_name;
>  	int offset;
>  	int size;
> +	unsigned int depth;
> +	/* Children not expanded because the nesting limit was reached */
> +	bool truncated;
>  };
>  
>  /**
> -- 
> 2.53.0
>