linux-kernel - [PATCH 04/52] perf dwarf-aux: Fix die_get

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Message-ID: <20231110000012.3538610-5-namhyung@kernel.org>
Date:   Thu,  9 Nov 2023 15:59:23 -0800
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     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>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-trace-devel@...r.kernel.org, linux-toolchains@...r.kernel.org
Subject: [PATCH 04/52] perf dwarf-aux: Fix die_get_typename() for void *

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.

Acked-by: Masami Hiramatsu (Google) <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);
 }
 
 /**
-- 
2.42.0.869.gea05f2083d-goog