linux-kernel - Re: [PATCH 04/48] perf dwarf-aux: Fix die_get

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Date:   Sat, 4 Nov 2023 19:52:02 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Stephane Eranian <eranian@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-toolchains@...r.kernel.org, linux-trace-devel@...r.kernel.org
Subject: Re: [PATCH 04/48] perf dwarf-aux: Fix die_get_typename() for void *

On Wed, 11 Oct 2023 20:50:27 -0700
Namhyung Kim <namhyung@...nel.org> wrote:

> The die_get_typename() is to return a C-like type name from DWARF debug
> entry and it follows data type if the target entry is a pointer type.
> But I found void pointers don't have the type attribte to follow and
> then the function returns an error for that case.  This results in a
> broken type string for void pointer types.
> 
> For example, the following type entries are pointer types.
> 
>  <1><48c>: Abbrev Number: 4 (DW_TAG_pointer_type)
>     <48d>   DW_AT_byte_size   : 8
>     <48d>   DW_AT_type        : <0x481>
>  <1><491>: Abbrev Number: 211 (DW_TAG_pointer_type)
>     <493>   DW_AT_byte_size   : 8
>  <1><494>: Abbrev Number: 4 (DW_TAG_pointer_type)
>     <495>   DW_AT_byte_size   : 8
>     <495>   DW_AT_type        : <0x49e>
> 
> The first one at offset 48c and the third one at offset 494 have type
> information.  Then they are pointer types for the referenced types.
> But the second one at offset 491 doesn't have the type attribute.

This looks good to me!

Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Thanks!

> 
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/perf/util/dwarf-aux.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
> index 2941d88f2199..4849c3bbfd95 100644
> --- a/tools/perf/util/dwarf-aux.c
> +++ b/tools/perf/util/dwarf-aux.c
> @@ -1090,7 +1090,14 @@ int die_get_typename(Dwarf_Die *vr_die, struct strbuf *buf)
>  		return strbuf_addf(buf, "%s%s", tmp, name ?: "");
>  	}
>  	ret = die_get_typename(&type, buf);
> -	return ret ? ret : strbuf_addstr(buf, tmp);
> +	if (ret < 0) {
> +		/* void pointer has no type attribute */
> +		if (tag == DW_TAG_pointer_type && ret == -ENOENT)
> +			return strbuf_addf(buf, "void*");
> +
> +		return ret;
> +	}
> +	return strbuf_addstr(buf, tmp);
>  }
>  
>  /**
> -- 
> 2.42.0.655.g421f12c284-goog
> 


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