Re: [PATCH v2 2/4] perf dwarf-aux: Add die_has_flex_array() helper

[Namhyung Kim <namhyung@kernel.org>]

Hello,

On Mon, Sep 14, 2026 at 08:14:56PM +0800, Tengda Wu wrote:
> 
> 
> On 2026/9/14 14:45, Namhyung Kim wrote:
> > The die_has_flex_array() returns true when the given type is a compound
> > type and contains an array at the end.  To prevent an infinite recursion
> > add a depth field to the internal function.
> > 
> > Cc: Masami Hiramatsu <mhiramat@kernel.org>
> > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> > ---
> >  tools/perf/util/dwarf-aux.c | 77 +++++++++++++++++++++++++++++++++++++
> >  tools/perf/util/dwarf-aux.h |  3 ++
> >  2 files changed, 80 insertions(+)
> > 
> > diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
> > index d7160f87ac7d7ab3..465824e6513eb0ac 100644
> > --- a/tools/perf/util/dwarf-aux.c
> > +++ b/tools/perf/util/dwarf-aux.c
> > @@ -2180,3 +2180,80 @@ Dwarf_Die *die_deref_ptr_type(Dwarf_Die *ptr_die, int offset,
> >  
> >  	return die_get_member_type(&type_die, offset, die_mem);
> >  }
> > +
> > +static bool is_flex_array_member(Dwarf_Die *mb_die)
> > +{
> > +	Dwarf_Die type_die;
> > +	Dwarf_Word size;
> > +
> > +	/* get the type of the member */
> > +	if (die_get_real_type(mb_die, &type_die) == NULL)
> > +		return false;
> > +
> > +	if (dwarf_tag(&type_die) != DW_TAG_array_type)
> > +		return false;
> > +
> > +	return dwarf_aggregate_size(&type_die, &size) < 0 || size == 0;
> > +}
> > +
> > +#define MAX_FLEX_ARRAY_RECURSION  256  /* arbitrary */
> > +
> > +static bool die_has_flex_array_recurse(Dwarf_Die *parent_die, int depth)
> > +{
> > +	Dwarf_Die die_mem, last_mb;
> > +	int tag = dwarf_tag(parent_die);
> > +
> > +	if (tag != DW_TAG_structure_type && tag != DW_TAG_union_type)
> > +		return false;
> > +
> > +	/* prevent infinite recursion */
> > +	if (depth > MAX_FLEX_ARRAY_RECURSION)
> > +		return false;
> > +
> > +	if (dwarf_child(parent_die, &die_mem))
> > +		return false;
> > +
> > +	do {
> > +		if (dwarf_tag(&die_mem) != DW_TAG_member)
> > +			continue;
> > +
> > +		if (tag == DW_TAG_union_type) {
> > +			if (is_flex_array_member(&die_mem))
> > +				return true;
> > +
> > +			if (die_get_real_type(&die_mem, &last_mb) &&
> > +			    die_has_flex_array_recurse(&last_mb, depth + 1))
> > +				return true;
> > +		}
> > +
> > +		if (tag == DW_TAG_structure_type)
> > +			memcpy(&last_mb, &die_mem, sizeof(last_mb));
> > +
> > +	} while (dwarf_siblingof(&die_mem, &die_mem) == 0);
> > +
> > +	if (tag == DW_TAG_structure_type) {
> > +		if (is_flex_array_member(&last_mb))
> 
> Not sure if this case can actually happen, but adding a check for whether
> last_mb is valid is probably better. (I see Sashiko flagged this too.)

Right, will fix in v3.

Thanks for your review!
Namhyung