playing about with simpler buffer copying

src/hotspot/share/cds/aotClassLocation.cpp

@@ -708,8 +708,7 @@ bool AOTClassLocationConfig::is_valid_classpath_index(int classpath_index, Insta
       JavaThread* current = JavaThread::current();
       ResourceMark rm(current);
       const char* const class_name = ik->name()->as_C_string();
-      const char* const file_name = ClassLoader::file_name_for_class_name(class_name,
-                                                                          ik->name()->utf8_length());
+      const char* const file_name = ClassLoader::file_name_for_class_name(ik->name());
       if (!zip->has_entry(current, file_name)) {
         aot_log_warning(aot)("class %s cannot be archived because it was not defined from %s as claimed",
                          class_name, zip->name());

src/hotspot/share/cds/filemap.cpp

@@ -2091,10 +2091,7 @@ ClassFileStream* FileMapInfo::open_stream_for_jvmti(InstanceKlass* ik, Handle cl
   ClassPathEntry* cpe = get_classpath_entry_for_jvmti(path_index, CHECK_NULL);
   assert(cpe != nullptr, "must be");
 
-  Symbol* name = ik->name();
-  const char* const class_name = name->as_C_string();
-  const char* const file_name = ClassLoader::file_name_for_class_name(class_name,
-                                                                      name->utf8_length());
+  const char* const file_name = ClassLoader::file_name_for_class_name(ik->name());
   ClassLoaderData* loader_data = ClassLoaderData::class_loader_data(class_loader());
   const AOTClassLocation* cl = AOTClassLocationConfig::runtime()->class_location_at(path_index);
   ClassFileStream* cfs;
@@ -2107,7 +2104,7 @@ ClassFileStream* FileMapInfo::open_stream_for_jvmti(InstanceKlass* ik, Handle cl
     cfs = cpe->open_stream_for_loader(THREAD, file_name, loader_data);
   }
   assert(cfs != nullptr, "must be able to read the classfile data of shared classes for built-in loaders.");
-  log_debug(aot, jvmti)("classfile data for %s [%d: %s] = %d bytes", class_name, path_index,
+  log_debug(aot, jvmti)("classfile data for %s [%d: %s] = %d bytes", file_name, path_index,
                         cfs->source(), cfs->length());
   return cfs;
 }

src/hotspot/share/classfile/classLoader.cpp

@@ -986,21 +986,28 @@ objArrayOop ClassLoader::get_system_packages(TRAPS) {
 }
 
 // caller needs ResourceMark
-const char* ClassLoader::file_name_for_class_name(const char* class_name,
-                                                  int class_name_len) {
+char* ClassLoader::symbol_name_to_padded_buffer(const Symbol* symbol, int padding_len) {
+  assert(symbol != nullptr, "invariant");
+  assert(padding_len >= 0, "invariant");
+
+  // Include terminating nul.
+  int name_len = symbol->utf8_length() + 1;
+  char* const buffer = NEW_RESOURCE_ARRAY(char, name_len + padding_len);
+  symbol->as_C_string(buffer, name_len);
+  return buffer;
+}
+
+// caller needs ResourceMark
+const char* ClassLoader::file_name_for_class_name(const Symbol* class_name) {
   assert(class_name != nullptr, "invariant");
-  assert((int)strlen(class_name) == class_name_len, "invariant");
 
   static const char class_suffix[] = ".class";
-  size_t class_suffix_len = sizeof(class_suffix);
-
-  char* const file_name = NEW_RESOURCE_ARRAY(char,
-                                             class_name_len +
-                                             class_suffix_len); // includes term null
-
-  strncpy(file_name, class_name, class_name_len);
-  strncpy(&file_name[class_name_len], class_suffix, class_suffix_len);
+  static const int suffix_len = strlen(class_suffix);
 
+  // Just suffix length (a trailing nul is already accounted for in the copy).
+  char* const file_name = symbol_name_to_padded_buffer(class_name, suffix_len);
+  // Append over existing trailing nul, so need to copy a new one.
+  strncpy(&file_name[class_name->utf8_length()], class_suffix, suffix_len + 1);
   return file_name;
 }
 
@@ -1081,14 +1088,11 @@ InstanceKlass* ClassLoader::load_class(Symbol* name, PackageEntry* pkg_entry, bo
   ResourceMark rm(THREAD);
   HandleMark hm(THREAD);
 
-  const char* const class_name = name->as_C_string();
-
-  EventMarkClassLoading m("Loading class %s", class_name);
-
-  const char* const file_name = file_name_for_class_name(class_name,
-                                                         name->utf8_length());
+  const char* const file_name = file_name_for_class_name(name);
   assert(file_name != nullptr, "invariant");
 
+  EventMarkClassLoading m("Loading class %s", file_name);
+
   // Lookup stream for parsing .class file
   ClassFileStream* stream = nullptr;
   s2 classpath_index = 0;
@@ -1347,9 +1351,7 @@ void ClassLoader::record_result(JavaThread* current, InstanceKlass* ik,
     assert(classpath_index == -1, "sanity");
   }
 
-  const char* const class_name = ik->name()->as_C_string();
-  const char* const file_name = file_name_for_class_name(class_name,
-                                                         ik->name()->utf8_length());
+  const char* const file_name = file_name_for_class_name(ik->name());
   assert(file_name != nullptr, "invariant");
   record_result_for_builtin_loader(checked_cast<s2>(classpath_index), ik, redefined);
 }

src/hotspot/share/classfile/classLoader.hpp

@@ -247,8 +247,9 @@ class ClassLoader: AllStatic {
   // Canonicalizes path names, so strcmp will work properly. This is mainly
   // to avoid confusing the zip library
   static char* get_canonical_path(const char* orig, Thread* thread);
-  static const char* file_name_for_class_name(const char* class_name,
-                                              int class_name_len);
+
+  static char* symbol_name_to_padded_buffer(const Symbol* symbol, int padding_len);
+  static const char* file_name_for_class_name(const Symbol* class_name);
   static PackageEntry* get_package_entry(Symbol* pkg_name, ClassLoaderData* loader_data);
   static int crc32(int crc, const char* buf, int len);
   static bool update_class_path_entry_list(JavaThread* current,