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

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Mon, 14 Sep 2026 22:54:19 -0700
Namhyung Kim <namhyung@kernel.org> wrote:

> > > +
> > > +	do {
> > > +		if (dwarf_tag(&die_mem) != DW_TAG_member)
> > > +			continue;
> > 
> > If the member is a "const" member, you may have to use
> > die_get_real_type() to get the actual type.
> > (in this case, you need a cursor DIE for dwarf_siblingof()) 
> 
> Doesn't it belong to a type of the member?  In my simple test program,
> it shows the struct type only has children of members and their types
> including const are referenced from the member DIEs.
> 
> Also I don't think flexible arrays will be const as they cannot be
> initialized.

Ah, indeed. flex array needs to be initialized. :)

> 
> > 
> > > +
> > > +		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));
> > 
> > To find the last member, I think you'd better check the
> > DW_AT_data_member_location and DW_AT_decl_line to ensure the
> > DIE is the last member.
> 
> Good point.  I can add the member location check.  I'm afraid decl line
> may be incorrect if compiler randomized the layout.
> 
> So far I haven't seen DWARF data having unsorted members (by location),
> but it'd be better to make sure it's sorted.

OK, that maybe enough.

Thanks!


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>