Attempt to demangle as a Rust symbol before as C++

#371

demangle.cc

@@ -7,23 +7,34 @@
 namespace mold {
 
 std::string_view demangle(std::string_view name) {
-  if (name.starts_with("_Z")) {
-    static thread_local char *buf;
-    if (buf)
-      free(buf);
+  static thread_local char *buf;
+  if (buf)
+    free(buf);
 
-    int status;
-    buf = abi::__cxa_demangle(std::string(name).c_str(), nullptr, nullptr,
-                              &status);
-    if (status == 0)
-      return buf;
-
-    buf = rust_demangle(std::string(name).c_str(), 0);
-    if (buf)
-      return buf;
-  }
+  // Try to demangle as a Rust symbol.
+  buf = rust_demangle(std::string(name).c_str(), 0);
+  if (buf)
+    return buf;
 
+  // Try to demangle as a C++ symbol.
+  if (std::optional<std::string_view> s = cpp_demangle(name))
+    return *s;
   return name;
 }
 
+std::optional<std::string_view> cpp_demangle(std::string_view name) {
+  static thread_local char *buf;
+  static thread_local size_t buflen;
+
+  if (name.starts_with("_Z")) {
+    int status;
+    char *p = abi::__cxa_demangle(std::string(name).c_str(), buf, &buflen, &status);
+    if (status == 0) {
+      buf = p;
+      return p;
+    }
+  }
+  return {};
+}
+
 } // namespace mold

elf/passes.cc

@@ -1092,8 +1092,9 @@ void apply_version_script(Context<E> &ctx) {
       }
 
       if (!cpp_matcher.empty())
-        if (std::optional<u16> ver = cpp_matcher.find(demangle(name)))
-          sym->ver_idx = *ver;
+        if (std::optional<std::string_view> s = cpp_demangle(name))
+          if (std::optional<u16> ver = cpp_matcher.find(*s))
+            sym->ver_idx = *ver;
     }
   });
 }

mold.h

@@ -554,6 +554,7 @@ std::filesystem::path to_abs_path(std::filesystem::path path);
 //
 
 std::string_view demangle(std::string_view name);
+std::optional<std::string_view> cpp_demangle(std::string_view name);
 
 //
 // compress.cc