linux-kernel - [PATCH 2/2] perf-probe: Change function definition check due to broken dwarf

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Date:   Fri, 27 Nov 2020 14:48:55 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Thomas Richter <tmricht@...ux.ibm.com>
Cc:     linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sumanth Korikkar <sumanthk@...ux.ibm.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: [PATCH 2/2] perf-probe: Change function definition check due to broken dwarf

Since some gcc generates a broken DWARF which lacks DW_AT_declaration
attribute from the subprogram DIE of function prototype.
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97060)

So, in addition to the DW_AT_declaration check, we also check the
subprogram DIE has DW_AT_inline or actual entry pc.

Reported-by: Thomas Richter <tmricht@...ux.ibm.com>
Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 tools/perf/util/dwarf-aux.c    |   20 ++++++++++++++++++--
 tools/perf/util/probe-finder.c |    3 +--
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 03c1a39c312a..7b2d471a6419 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -356,9 +356,25 @@ bool die_is_signed_type(Dwarf_Die *tp_die)
 bool die_is_func_def(Dwarf_Die *dw_die)
 {
 	Dwarf_Attribute attr;
+	Dwarf_Addr addr = 0;
+
+	if (dwarf_tag(dw_die) != DW_TAG_subprogram)
+		return false;
+
+	if (dwarf_attr(dw_die, DW_AT_declaration, &attr))
+		return false;
 
-	return (dwarf_tag(dw_die) == DW_TAG_subprogram &&
-		dwarf_attr(dw_die, DW_AT_declaration, &attr) == NULL);
+	/*
+	 * DW_AT_declaration can be lost from function declaration
+	 * by gcc's bug #97060.
+	 * So we need to check this subprogram DIE has DW_AT_inline
+	 * or an entry address.
+	 */
+	if (!dwarf_attr(dw_die, DW_AT_inline, &attr) &&
+	    die_entrypc(dw_die, &addr) < 0)
+		return false;
+
+	return true;
 }
 
 /**
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 2c4061035f77..76dd349aa48d 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -1885,8 +1885,7 @@ static int line_range_search_cb(Dwarf_Die *sp_die, void *data)
 	if (lr->file && strtailcmp(lr->file, dwarf_decl_file(sp_die)))
 		return DWARF_CB_OK;
 
-	if (die_is_func_def(sp_die) &&
-	    die_match_name(sp_die, lr->function)) {
+	if (die_match_name(sp_die, lr->function) && die_is_func_def(sp_die)) {
 		lf->fname = dwarf_decl_file(sp_die);
 		dwarf_decl_line(sp_die, &lr->offset);
 		pr_debug("fname: %s, lineno:%d\n", lf->fname, lr->offset);