Use the demangle-rust-v0 APIs to see if symbol is Rust mangled and
demangle if so. The API requires a pre-allocated output buffer, some
estimation and retrying are added for this.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/Build        |  5 +++-
 tools/perf/util/symbol-elf.c | 47 ++++++++++++++++++++++++++----------
 2 files changed, 38 insertions(+), 14 deletions(-)

diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index 4f7f072fa222..7910d908c814 100644
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build
@@ -241,9 +241,12 @@ perf-util-y += cap.o
 perf-util-$(CONFIG_CXX_DEMANGLE) += demangle-cxx.o
 perf-util-y += demangle-ocaml.o
 perf-util-y += demangle-java.o
-perf-util-y += demangle-rust.o
+perf-util-y += demangle-rust-v0.o
 perf-util-$(CONFIG_LIBLLVM) += llvm-c-helpers.o
 
+CFLAGS_demangle-rust-v0.o += -Wno-shadow -Wno-declaration-after-statement \
+    -Wno-switch-default -Wno-switch-enum -Wno-missing-field-initializers
+
 ifdef CONFIG_JITDUMP
 perf-util-$(CONFIG_LIBELF) += jitdump.o
 perf-util-$(CONFIG_LIBELF) += genelf.o
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index fbf6d0f73af9..3fc87309746f 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -16,13 +16,14 @@
 #include "demangle-cxx.h"
 #include "demangle-ocaml.h"
 #include "demangle-java.h"
-#include "demangle-rust.h"
+#include "demangle-rust-v0.h"
 #include "machine.h"
 #include "vdso.h"
 #include "debug.h"
 #include "util/copyfile.h"
 #include <linux/ctype.h>
 #include <linux/kernel.h>
+#include <linux/log2.h>
 #include <linux/zalloc.h>
 #include <linux/string.h>
 #include <symbol/kallsyms.h>
@@ -308,6 +309,9 @@ char *cxx_demangle_sym(const char *str __maybe_unused, bool params __maybe_unuse
 
 static char *demangle_sym(struct dso *dso, int kmodule, const char *elf_name)
 {
+	struct demangle rust_demangle = {
+		.style = DemangleStyleUnknown,
+	};
 	char *demangled = NULL;
 
 	/*
@@ -318,21 +322,38 @@ static char *demangle_sym(struct dso *dso, int kmodule, const char *elf_name)
 	if (!want_demangle(dso__kernel(dso) || kmodule))
 		return demangled;
 
-	demangled = cxx_demangle_sym(elf_name, verbose > 0, verbose > 0);
-	if (demangled == NULL) {
-		demangled = ocaml_demangle_sym(elf_name);
-		if (demangled == NULL) {
-			demangled = java_demangle_sym(elf_name, JAVA_DEMANGLE_NORET);
+	rust_demangle_demangle(elf_name, &rust_demangle);
+	if (rust_demangle_is_known(&rust_demangle)) {
+		/* A rust mangled name. */
+		if (rust_demangle.mangled_len == 0)
+			return demangled;
+
+		for (size_t buf_len = roundup_pow_of_two(rust_demangle.mangled_len * 2);
+		     buf_len < 1024 * 1024; buf_len += 32) {
+			char *tmp = realloc(demangled, buf_len);
+
+			if (!tmp) {
+				/* Failure to grow output buffer, return what is there. */
+				return demangled;
+			}
+			demangled = tmp;
+			if (rust_demangle_display_demangle(&rust_demangle, demangled, buf_len,
+							   /*alternate=*/true) == OverflowOk)
+				return demangled;
 		}
+		/* Buffer exceeded sensible bounds, return what is there. */
+		return demangled;
 	}
-	else if (rust_is_mangled(demangled))
-		/*
-		    * Input to Rust demangling is the BFD-demangled
-		    * name which it Rust-demangles in place.
-		    */
-		rust_demangle_sym(demangled);
 
-	return demangled;
+	demangled = cxx_demangle_sym(elf_name, verbose > 0, verbose > 0);
+	if (demangled)
+		return demangled;
+
+	demangled = ocaml_demangle_sym(elf_name);
+	if (demangled)
+		return demangled;
+
+	return java_demangle_sym(elf_name, JAVA_DEMANGLE_NORET);
 }
 
 struct rel_info {
-- 
2.49.0.901.g37484f566f-goog