linux-kernel - Re: [PATCH v4 8/9] perf annotate: Improve type comparison from different scopes

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Message-ID: <aP0M95FMF0fB48x9@google.com>
Date: Sat, 25 Oct 2025 10:46:31 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Zecheng Li <zecheng@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Xu Liu <xliuprof@...gle.com>, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 8/9] perf annotate: Improve type comparison from
 different scopes

On Mon, Oct 13, 2025 at 06:16:05PM +0000, Zecheng Li wrote:
> When comparing types from different scopes, first compare their type
> offsets. A larger offset means the field belongs to an outer
> (enclosing) struct. This helps resolve cases where a pointer is found
> in an inner scope, but a struct containing that pointer exists in an
> outer scope. Previously, is_better_type would prefer the pointer type,
> but the struct type is actually more complete and should be chosen.

Wouldn't the size check be sufficient?  I think we need to get read of
the pointer preference.

> 
> Prefer types from outer scopes when is_better_type cannot determine
> a better type. This sometimes helps pick a more complete type.

This code has a loop for the scopes so detecting larger struct would
work well?

Thanks,
Namhyung

> 
> Signed-off-by: Zecheng Li <zecheng@...gle.com>
> ---
>  tools/perf/util/annotate-data.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
> index 4b08331b9dd3..4b510eb29a5f 100644
> --- a/tools/perf/util/annotate-data.c
> +++ b/tools/perf/util/annotate-data.c
> @@ -1629,7 +1629,9 @@ static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
>  				pr_debug_dtp("type_offset=%#x\n", type_offset);
>  			}
>  
> -			if (!found || is_better_type(type_die, &mem_die)) {
> +			if (!found || dloc->type_offset < type_offset ||
> +				(dloc->type_offset == type_offset &&
> +				 !is_better_type(&mem_die, type_die))) {
>  				*type_die = mem_die;
>  				dloc->type_offset = type_offset;
>  				found = true;
> -- 
> 2.51.0.788.g6d19910ace-goog
>