linux-kernel - [PATCH v2 2/2] perf symbol: Skip recording symbols in '.gnu.warning.*' sections

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Date:   Sun, 24 Jul 2022 10:28:57 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Fangrui Song <maskray@...gle.com>,
        Ian Rogers <irogers@...gle.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Leo Yan <leo.yan@...aro.org>
Subject: [PATCH v2 2/2] perf symbol: Skip recording symbols in '.gnu.warning.*' sections

Some symbols are observed their 'st_value' field are zeros.  E.g.
libc.so.6 in Ubuntu contains a symbol '__evoke_link_warning_getwd' which
resides in the '.gnu.warning.getwd' section, unlike normal symbols, this
kind of symbols are only used for linker warning.

This patch skips to record symbols from '.gnu.warning.*' sections by
detecting the sub string '.gnu.warning' is contained in section name.

Signed-off-by: Leo Yan <leo.yan@...aro.org>
---
 tools/perf/util/symbol-elf.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index ef6ced5c5746..4b621e355c0e 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -1277,6 +1277,14 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
 
 		section_name = elf_sec__name(&shdr, secstrs);
 
+		/*
+		 * A symbol coming from ".gnu.warning.*" sections is used to
+		 * generate linker warnings, its 'sym.st_value' field usually
+		 * is zero, skip to record it.
+		 */
+		if (strstr(section_name, ".gnu.warning"))
+			continue;
+
 		/* On ARM, symbols for thumb functions have 1 added to
 		 * the symbol address as a flag - remove it */
 		if ((ehdr.e_machine == EM_ARM) &&
-- 
2.25.1