linux-kernel - [PATCH v1] perf symbol-elf: Avoid a weak cxx_demangle

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Message-Id: <20241119031754.1021858-1-irogers@google.com>
Date: Mon, 18 Nov 2024 19:17:54 -0800
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...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>, 
	Kan Liang <kan.liang@...ux.intel.com>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: [PATCH v1] perf symbol-elf: Avoid a weak cxx_demangle_sym function

cxx_demangle_sym is weak in case demangle-cxx.c replaces the
definition in symbol-elf.c. When demangle-cxx.c is built
HAVE_CXA_DEMANGLE_SUPPORT is defined, as such the define can be used
to avoid a weak symbol. As weak symbols are outside of the C standard
their use can lead to strange behaviors, in particular with LTO, as
well as causing issues to be hidden at link time.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/symbol-elf.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index e398abfd13a0..66fd1249660a 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -287,8 +287,9 @@ static bool want_demangle(bool is_kernel_sym)
  * Demangle C++ function signature, typically replaced by demangle-cxx.cpp
  * version.
  */
-__weak char *cxx_demangle_sym(const char *str __maybe_unused, bool params __maybe_unused,
-			      bool modifiers __maybe_unused)
+#ifndef HAVE_CXA_DEMANGLE_SUPPORT
+char *cxx_demangle_sym(const char *str __maybe_unused, bool params __maybe_unused,
+		       bool modifiers __maybe_unused)
 {
 #ifdef HAVE_LIBBFD_SUPPORT
 	int flags = (params ? DMGL_PARAMS : 0) | (modifiers ? DMGL_ANSI : 0);
@@ -302,6 +303,7 @@ __weak char *cxx_demangle_sym(const char *str __maybe_unused, bool params __mayb
 	return NULL;
 #endif
 }
+#endif /* !HAVE_CXA_DEMANGLE_SUPPORT */
 
 static char *demangle_sym(struct dso *dso, int kmodule, const char *elf_name)
 {
-- 
2.47.0.338.g60cca15819-goog