[PATCH v1] perf build: Don't compile demangle-cxx.cpp if not necessary

[Ian Rogers]

demangle-cxx.cpp requires a C++ compiler, but feature checks may fail
because of the absence of this. Add a CONFIG_CXX_DEMANGLE so that the
source isn't built if not supported. Copy libbfd and cplus demangle
variants to a weak symbol-elf.c version so they aren't dependent on
C++. These variants are only built with the build option
BUILD_NONDISTRO=1.

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/Makefile.config   |  1 +
 tools/perf/util/Build        |  2 +-
 tools/perf/util/symbol-elf.c | 27 +++++++++++++++++++++++++++
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index 71442c54c25f..5f0f24b56f50 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -923,6 +923,7 @@ ifndef NO_DEMANGLE
     EXTLIBS += -lstdc++
     CFLAGS += -DHAVE_CXA_DEMANGLE_SUPPORT
     CXXFLAGS += -DHAVE_CXA_DEMANGLE_SUPPORT
+    $(call detected,CONFIG_CXX_DEMANGLE)
   endif
   ifdef BUILD_NONDISTRO
     ifeq ($(filter -liberty,$(EXTLIBS)),)
diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index bd18fe5f2719..f9df1df1eec0 100644
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build
@@ -214,7 +214,7 @@ perf-$(CONFIG_ZSTD) += zstd.o
 
 perf-$(CONFIG_LIBCAP) += cap.o
 
-perf-y += demangle-cxx.o
+perf-$(CONFIG_CXX_DEMANGLE) += demangle-cxx.o
 perf-y += demangle-ocaml.o
 perf-y += demangle-java.o
 perf-y += demangle-rust.o
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 35724f6a84fa..cd08bdb9824f 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -31,6 +31,13 @@
 #include <bfd.h>
 #endif
 
+#if defined(HAVE_LIBBFD_SUPPORT) || defined(HAVE_CPLUS_DEMANGLE_SUPPORT)
+#ifndef DMGL_PARAMS
+#define DMGL_PARAMS     (1 << 0)  /* Include function args */
+#define DMGL_ANSI       (1 << 1)  /* Include const, volatile, etc */
+#endif
+#endif
+
 #ifndef EM_AARCH64
 #define EM_AARCH64	183  /* ARM 64 bit */
 #endif
@@ -271,6 +278,26 @@ static bool want_demangle(bool is_kernel_sym)
 	return is_kernel_sym ? symbol_conf.demangle_kernel : symbol_conf.demangle;
 }
 
+/*
+ * 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)
+{
+#ifdef HAVE_LIBBFD_SUPPORT
+	int flags = (params ? DMGL_PARAMS : 0) | (modifiers ? DMGL_ANSI : 0);
+
+	return bfd_demangle(NULL, str, flags);
+#elif defined(HAVE_CPLUS_DEMANGLE_SUPPORT)
+	int flags = (params ? DMGL_PARAMS : 0) | (modifiers ? DMGL_ANSI : 0);
+
+	return cplus_demangle(str, flags);
+#else
+	return NULL;
+#endif
+}
+
 static char *demangle_sym(struct dso *dso, int kmodule, const char *elf_name)
 {
 	char *demangled = NULL;
-- 
2.40.0.634.g4ca3ef3211-goog