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@google.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

On Mon, Nov 18, 2024 at 7:17 PM Ian Rogers <irogers@google.com> wrote:
>
> 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@google.com>

Ping.

Thanks,
Ian

> ---
>  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
>

On Thu, Jan 09, 2025 at 09:58:34AM -0800, Ian Rogers wrote:
> On Mon, Nov 18, 2024 at 7:17 PM Ian Rogers <irogers@google.com> wrote:
> >
> > 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@google.com>
> 
> Ping.

Thanks, applied to perf-tools-next,

- Arnaldo