linux-kernel - Re: [PATCH v4 7/9] perf dwarf-aux: Preserve typedefs in match_var

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Message-ID: <aP0LkimOCj389dNl@google.com>
Date: Sat, 25 Oct 2025 10:40:34 -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 7/9] perf dwarf-aux: Preserve typedefs in
 match_var_offset

On Mon, Oct 13, 2025 at 06:16:04PM +0000, Zecheng Li wrote:
> Since we are skipping the check_variable, we need to preserve typedefs
> in match_var_offset to match the results by __die_get_real_type. Also
> move the (offset == 0) branch after the is_pointer check to ensure the
> correct type is used, fixing cases where an incorrect pointer type was
> chosen when the access offset was 0.
> 
> Signed-off-by: Zecheng Li <zecheng@...gle.com>
> ---
>  tools/perf/util/dwarf-aux.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
> index b57cdc8860f0..b2189de07daf 100644
> --- a/tools/perf/util/dwarf-aux.c
> +++ b/tools/perf/util/dwarf-aux.c
> @@ -1395,24 +1395,24 @@ static bool match_var_offset(Dwarf_Die *die_mem, struct find_var_data *data,
>  	Dwarf_Word size;
>  	s64 offset = addr_offset - addr_type;
>  
> -	if (offset == 0) {
> -		/* Update offset relative to the start of the variable */
> -		data->offset = 0;
> -		return true;
> -	}
> -
>  	if (offset < 0)
>  		return false;
>  
> -	if (die_get_real_type(die_mem, &data->type) == NULL)
> +	if (__die_get_real_type(die_mem, &data->type) == NULL)
>  		return false;

If the type was a typedef of a pointer, then the following check for a
pointer cannot detect the target type.

Thanks,
Namhyung

>  
>  	if (is_pointer && dwarf_tag(&data->type) == DW_TAG_pointer_type) {
>  		/* Get the target type of the pointer */
> -		if (die_get_real_type(&data->type, &data->type) == NULL)
> +		if (__die_get_real_type(&data->type, &data->type) == NULL)
>  			return false;
>  	}
>  
> +	if (offset == 0) {
> +		/* Update offset relative to the start of the variable */
> +		data->offset = 0;
> +		return true;
> +	}
> +
>  	if (dwarf_aggregate_size(&data->type, &size) < 0)
>  		return false;
>  
> -- 
> 2.51.0.788.g6d19910ace-goog
>