--- a/src/hotspot/share/logging/logConfiguration.cpp	Tue Feb 27 21:29:19 2018 -0800
+++ b/src/hotspot/share/logging/logConfiguration.cpp	Wed Feb 28 09:30:06 2018 +0100
@@ -83,14 +83,15 @@
   if (log.is_info()) {
     log.info("Log configuration fully initialized.");
     log_develop_info(logging)("Develop logging is available.");
-    if (log.is_debug()) {
-      LogStream debug_stream(log.debug());
-      describe(&debug_stream);
-      if (log.is_trace()) {
-        LogStream trace_stream(log.trace());
-        LogTagSet::list_all_tagsets(&trace_stream);
-      }
-    }
+
+    LogStream info_stream(log.info());
+    describe_available(&info_stream);
+
+    LogStream debug_stream(log.debug());
+    LogTagSet::list_all_tagsets(&debug_stream);
+
+    ConfigurationLock cl;
+    describe_current_configuration(&info_stream);
   }
 }
 
@@ -364,14 +365,24 @@
   bool success = parse_log_arguments(output, what, decorators, output_options, &ss);
 
   if (ss.size() > 0) {
-    errbuf[strlen(errbuf) - 1] = '\0'; // Strip trailing newline
     // If it failed, log the error. If it didn't fail, but something was written
     // to the stream, log it as a warning.
-    if (!success) {
-      log_error(logging)("%s", ss.base());
-    } else {
-      log_warning(logging)("%s", ss.base());
-    }
+    LogLevelType level = success ? LogLevel::Warning : LogLevel::Error;
+
+    Log(logging) log;
+    char* start = errbuf;
+    char* end = strchr(start, '\n');
+    assert(end != NULL, "line must end with newline '%s'", start);
+    do {
+      assert(start < errbuf + sizeof(errbuf) &&
+             end < errbuf + sizeof(errbuf),
+             "buffer overflow");
+      *end = '\0';
+      log.write(level, "%s", start);
+      start = end + 1;
+      end = strchr(start, '\n');
+      assert(end != NULL || *start == '\0', "line must end with newline '%s'", start);
+    } while (end != NULL);
   }
 
   os::free(copy);
@@ -459,7 +470,7 @@
 void LogConfiguration::describe_current_configuration(outputStream* out){
   out->print_cr("Log output configuration:");
   for (size_t i = 0; i < _n_outputs; i++) {
-    out->print("#" SIZE_FORMAT ": ", i);
+    out->print(" #" SIZE_FORMAT ": ", i);
     _outputs[i]->describe(out);
     out->cr();
   }
@@ -471,68 +482,89 @@
   describe_current_configuration(out);
 }
 
-void LogConfiguration::print_command_line_help(FILE* out) {
-  jio_fprintf(out, "-Xlog Usage: -Xlog[:[what][:[output][:[decorators][:output-options]]]]\n"
-              "\t where 'what' is a combination of tags and levels of the form tag1[+tag2...][*][=level][,...]\n"
-              "\t Unless wildcard (*) is specified, only log messages tagged with exactly the tags specified will be matched.\n\n");
+void LogConfiguration::print_command_line_help(outputStream* out) {
+  out->print_cr("-Xlog Usage: -Xlog[:[selections][:[output][:[decorators][:output-options]]]]");
+  out->print_cr("\t where 'selections' are combinations of tags and levels of the form tag1[+tag2...][*][=level][,...]");
+  out->print_cr("\t NOTE: Unless wildcard (*) is specified, only log messages tagged with exactly the tags specified will be matched.");
+  out->cr();
 
-  jio_fprintf(out, "Available log levels:\n");
+  out->print_cr("Available log levels:");
   for (size_t i = 0; i < LogLevel::Count; i++) {
-    jio_fprintf(out, "%s %s", (i == 0 ? "" : ","), LogLevel::name(static_cast<LogLevelType>(i)));
+    out->print("%s %s", (i == 0 ? "" : ","), LogLevel::name(static_cast<LogLevelType>(i)));
   }
+  out->cr();
+  out->cr();
 
-  jio_fprintf(out, "\n\nAvailable log decorators: \n");
+  out->print_cr("Available log decorators: ");
   for (size_t i = 0; i < LogDecorators::Count; i++) {
     LogDecorators::Decorator d = static_cast<LogDecorators::Decorator>(i);
-    jio_fprintf(out, "%s %s (%s)", (i == 0 ? "" : ","), LogDecorators::name(d), LogDecorators::abbreviation(d));
+    out->print("%s %s (%s)", (i == 0 ? "" : ","), LogDecorators::name(d), LogDecorators::abbreviation(d));
   }
-  jio_fprintf(out, "\n Decorators can also be specified as 'none' for no decoration.\n\n");
+  out->cr();
+  out->print_cr(" Decorators can also be specified as 'none' for no decoration.");
+  out->cr();
 
-  fileStream stream(out, false);
-  stream.print_cr("Available log tags:");
-  LogTag::list_tags(&stream);
-  stream.print_cr(" Specifying 'all' instead of a tag combination matches all tag combinations.");
-  stream.cr();
+  out->print_cr("Available log tags:");
+  LogTag::list_tags(out);
+  out->print_cr(" Specifying 'all' instead of a tag combination matches all tag combinations.");
+  out->cr();
 
-  LogTagSet::describe_tagsets(&stream);
+  LogTagSet::describe_tagsets(out);
 
-  jio_fprintf(out, "\nAvailable log outputs:\n"
-              " stdout, stderr, file=<filename>\n"
-              " Specifying %%p and/or %%t in the filename will expand to the JVM's PID and startup timestamp, respectively.\n\n"
+  out->print_cr("\nAvailable log outputs:");
+  out->print_cr(" stdout/stderr");
+  out->print_cr(" file=<filename>");
+  out->print_cr("  If the filename contains %%p and/or %%t, they will expand to the JVM's PID and startup timestamp, respectively.");
+  out->print_cr("  Additional output-options for file outputs:");
+  out->print_cr("   filesize=..  - Target byte size for log rotation (supports K/M/G suffix)."
+                                    " If set to 0, log rotation will not trigger automatically,"
+                                    " but can be performed manually (see the VM.log DCMD).");
+  out->print_cr("   filecount=.. - Number of files to keep in rotation (not counting the active file)."
+                                    " If set to 0, log rotation is disabled."
+                                    " This will cause existing log files to be overwritten.");
+  out->cr();
 
-              "Some examples:\n"
-              " -Xlog\n"
-              "\t Log all messages using 'info' level to stdout with 'uptime', 'levels' and 'tags' decorations.\n"
-              "\t (Equivalent to -Xlog:all=info:stdout:uptime,levels,tags).\n\n"
-
-              " -Xlog:gc\n"
-              "\t Log messages tagged with 'gc' tag using 'info' level to stdout, with default decorations.\n\n"
+  out->print_cr("Some examples:");
+  out->print_cr(" -Xlog");
+  out->print_cr("\t Log all messages using 'info' level to stdout with 'uptime', 'levels' and 'tags' decorations.");
+  out->print_cr("\t (Equivalent to -Xlog:all=info:stdout:uptime,levels,tags).");
+  out->cr();
 
-              " -Xlog:gc,safepoint\n"
-              "\t Log messages tagged either with 'gc' or 'safepoint' tags, both using 'info' level, to stdout, with default decorations.\n"
-              "\t (Messages tagged with both 'gc' and 'safepoint' will not be logged.)\n\n"
+  out->print_cr(" -Xlog:gc");
+  out->print_cr("\t Log messages tagged with 'gc' tag using 'info' level to stdout, with default decorations.");
+  out->cr();
+
+  out->print_cr(" -Xlog:gc,safepoint");
+  out->print_cr("\t Log messages tagged either with 'gc' or 'safepoint' tags, both using 'info' level, to stdout, with default decorations.");
+  out->print_cr("\t (Messages tagged with both 'gc' and 'safepoint' will not be logged.)");
+  out->cr();
 
-              " -Xlog:gc+ref=debug\n"
-              "\t Log messages tagged with both 'gc' and 'ref' tags, using 'debug' level, to stdout, with default decorations.\n"
-              "\t (Messages tagged only with one of the two tags will not be logged.)\n\n"
+  out->print_cr(" -Xlog:gc+ref=debug");
+  out->print_cr("\t Log messages tagged with both 'gc' and 'ref' tags, using 'debug' level, to stdout, with default decorations.");
+  out->print_cr("\t (Messages tagged only with one of the two tags will not be logged.)");
+  out->cr();
 
-              " -Xlog:gc=debug:file=gc.txt:none\n"
-              "\t Log messages tagged with 'gc' tag using 'debug' level to file 'gc.txt' with no decorations.\n\n"
+  out->print_cr(" -Xlog:gc=debug:file=gc.txt:none");
+  out->print_cr("\t Log messages tagged with 'gc' tag using 'debug' level to file 'gc.txt' with no decorations.");
+  out->cr();
 
-              " -Xlog:gc=trace:file=gctrace.txt:uptimemillis,pids:filecount=5,filesize=1m\n"
-              "\t Log messages tagged with 'gc' tag using 'trace' level to a rotating fileset of 5 files of size 1MB,\n"
-              "\t using the base name 'gctrace.txt', with 'uptimemillis' and 'pid' decorations.\n\n"
+  out->print_cr(" -Xlog:gc=trace:file=gctrace.txt:uptimemillis,pids:filecount=5,filesize=1m");
+  out->print_cr("\t Log messages tagged with 'gc' tag using 'trace' level to a rotating fileset of 5 files of size 1MB,");
+  out->print_cr("\t using the base name 'gctrace.txt', with 'uptimemillis' and 'pid' decorations.");
+  out->cr();
 
-              " -Xlog:gc::uptime,tid\n"
-              "\t Log messages tagged with 'gc' tag using 'info' level to output 'stdout', using 'uptime' and 'tid' decorations.\n\n"
+  out->print_cr(" -Xlog:gc::uptime,tid");
+  out->print_cr("\t Log messages tagged with 'gc' tag using 'info' level to output 'stdout', using 'uptime' and 'tid' decorations.");
+  out->cr();
 
-              " -Xlog:gc*=info,safepoint*=off\n"
-              "\t Log messages tagged with at least 'gc' using 'info' level, but turn off logging of messages tagged with 'safepoint'.\n"
-              "\t (Messages tagged with both 'gc' and 'safepoint' will not be logged.)\n\n"
+  out->print_cr(" -Xlog:gc*=info,safepoint*=off");
+  out->print_cr("\t Log messages tagged with at least 'gc' using 'info' level, but turn off logging of messages tagged with 'safepoint'.");
+  out->print_cr("\t (Messages tagged with both 'gc' and 'safepoint' will not be logged.)");
+  out->cr();
 
-              " -Xlog:disable -Xlog:safepoint=trace:safepointtrace.txt\n"
-              "\t Turn off all logging, including warnings and errors,\n"
-              "\t and then enable messages tagged with 'safepoint' using 'trace' level to file 'safepointtrace.txt'.\n");
+  out->print_cr(" -Xlog:disable -Xlog:safepoint=trace:safepointtrace.txt");
+  out->print_cr("\t Turn off all logging, including warnings and errors,");
+  out->print_cr("\t and then enable messages tagged with 'safepoint' using 'trace' level to file 'safepointtrace.txt'.");
 }
 
 void LogConfiguration::rotate_all_outputs() {

--- a/src/hotspot/share/logging/logConfiguration.hpp	Tue Feb 27 21:29:19 2018 -0800
+++ b/src/hotspot/share/logging/logConfiguration.hpp	Wed Feb 28 09:30:06 2018 +0100
@@ -119,7 +119,7 @@
   static void describe(outputStream* out);
 
   // Prints usage help for command line log configuration.
-  static void print_command_line_help(FILE* out);
+  static void print_command_line_help(outputStream* out);
 
   // Rotates all LogOutput
   static void rotate_all_outputs();

--- a/src/hotspot/share/logging/logFileOutput.cpp	Tue Feb 27 21:29:19 2018 -0800
+++ b/src/hotspot/share/logging/logFileOutput.cpp	Wed Feb 28 09:30:06 2018 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -169,6 +169,7 @@
 
     char* equals_pos = strchr(pos, '=');
     if (equals_pos == NULL) {
+      errstream->print_cr("Invalid option '%s' for log file output.", pos);
       success = false;
       break;
     }

--- a/src/hotspot/share/logging/logFileOutput.hpp	Tue Feb 27 21:29:19 2018 -0800
+++ b/src/hotspot/share/logging/logFileOutput.hpp	Wed Feb 28 09:30:06 2018 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -85,7 +85,7 @@
   virtual int write(const LogDecorations& decorations, const char* msg);
   virtual int write(LogMessageBuffer::Iterator msg_iterator);
   virtual void force_rotate();
-  virtual void describe(outputStream *out);
+  virtual void describe(outputStream* out);
 
   virtual const char* name() const {
     return _name;

--- a/src/hotspot/share/logging/logOutput.cpp	Tue Feb 27 21:29:19 2018 -0800
+++ b/src/hotspot/share/logging/logOutput.cpp	Wed Feb 28 09:30:06 2018 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -84,15 +84,20 @@
 
 void LogOutput::describe(outputStream *out) {
   out->print("%s ", name());
-  out->print_raw(config_string());
-  out->print(" ");
-  char delimiter[2] = {0};
+  out->print_raw(config_string()); // raw printed because length might exceed O_BUFLEN
+
+  bool has_decorator = false;
+  char delimiter = ' ';
   for (size_t d = 0; d < LogDecorators::Count; d++) {
     LogDecorators::Decorator decorator = static_cast<LogDecorators::Decorator>(d);
     if (decorators().is_decorator(decorator)) {
-      out->print("%s%s", delimiter, LogDecorators::name(decorator));
-      *delimiter = ',';
+      has_decorator = true;
+      out->print("%c%s", delimiter, LogDecorators::name(decorator));
+      delimiter = ',';
     }
   }
+  if (!has_decorator) {
+    out->print(" none");
+  }
 }
 

--- a/src/hotspot/share/logging/logSelection.cpp	Tue Feb 27 21:29:19 2018 -0800
+++ b/src/hotspot/share/logging/logSelection.cpp	Wed Feb 28 09:30:06 2018 +0100
@@ -23,11 +23,13 @@
  */
 #include "precompiled.hpp"
 #include "utilities/ostream.hpp"
+#include "logging/log.hpp"
 #include "logging/logSelection.hpp"
 #include "logging/logTagSet.hpp"
 #include "runtime/os.inline.hpp"
 #include "utilities/globalDefinitions.hpp"
 #include "utilities/ostream.hpp"
+#include "utilities/quickSort.hpp"
 
 const LogSelection LogSelection::Invalid;
 
@@ -211,3 +213,120 @@
   tot_written += written;
   return tot_written;
 }
+
+double LogSelection::similarity(const LogSelection& other) const {
+  // Compute Soerensen-Dice coefficient as the similarity measure
+  size_t intersecting = 0;
+  for (size_t i = 0; i < _ntags; i++) {
+    for (size_t j = 0; j < other._ntags; j++) {
+      if (_tags[i] == other._tags[j]) {
+        intersecting++;
+        break;
+      }
+    }
+  }
+  return 2.0 * intersecting / (_ntags + other._ntags);
+}
+
+// Comparator used for sorting LogSelections based on their similarity to a specific LogSelection.
+// A negative return value means that 'a' is more similar to 'ref' than 'b' is, while a positive
+// return value means that 'b' is more similar.
+// For the sake of giving short and effective suggestions, when two selections have an equal
+// similarity score, the selection with the fewer tags (selecting the most tag sets) is considered
+// more similar.
+class SimilarityComparator {
+  const LogSelection& _ref;
+ public:
+  SimilarityComparator(const LogSelection& ref) : _ref(ref) {
+  }
+  int operator()(const LogSelection& a, const LogSelection& b) const {
+    const double epsilon = 1.0e-6;
+
+    // Sort by similarity (descending)
+    double s = _ref.similarity(b) - _ref.similarity(a);
+    if (fabs(s) > epsilon) {
+      return s < 0 ? -1 : 1;
+    }
+
+    // Then by number of tags (ascending)
+    int t = static_cast<int>(a.ntags() - (int)b.ntags());
+    if (t != 0) {
+      return t;
+    }
+
+    // Lastly by tag sets selected (descending)
+    return static_cast<int>(b.tag_sets_selected() - a.tag_sets_selected());
+  }
+};
+
+static const size_t suggestion_cap = 5;
+static const double similarity_requirement = 0.3;
+void LogSelection::suggest_similar_matching(outputStream* out) const {
+  LogSelection suggestions[suggestion_cap];
+  uint nsuggestions = 0;
+
+  // See if simply adding a wildcard would make the selection match
+  if (!_wildcard) {
+    LogSelection sel(_tags, true, _level);
+    if (sel.tag_sets_selected() > 0) {
+      suggestions[nsuggestions++] = sel;
+    }
+  }
+
+  // Check for matching tag sets with a single tag mismatching (a tag too many or short a tag)
+  for (LogTagSet* ts = LogTagSet::first(); ts != NULL; ts = ts->next()) {
+    LogTagType tags[LogTag::MaxTags] = { LogTag::__NO_TAG };
+    for (size_t i = 0; i < ts->ntags(); i++) {
+      tags[i] = ts->tag(i);
+    }
+
+    // Suggest wildcard selection unless the wildcard doesn't match anything extra
+    LogSelection sel(tags, true, _level);
+    if (sel.tag_sets_selected() == 1) {
+      sel = LogSelection(tags, false, _level);
+    }
+
+    double score = similarity(sel);
+
+    // Ignore suggestions with too low similarity
+    if (score < similarity_requirement) {
+      continue;
+    }
+
+    // Cap not reached, simply add the new suggestion and continue searching
+    if (nsuggestions < suggestion_cap) {
+      suggestions[nsuggestions++] = sel;
+      continue;
+    }
+
+    // Find the least matching suggestion already found, and if the new suggestion is a better match, replace it
+    double min = 1.0;
+    size_t pos = -1;
+    for (size_t i = 0; i < nsuggestions; i++) {
+      double score = similarity(suggestions[i]);
+      if (score < min) {
+        min = score;
+        pos = i;
+      }
+    }
+    if (score > min) {
+      suggestions[pos] = sel;
+    }
+  }
+
+  if (nsuggestions == 0) {
+    // Found no similar enough selections to suggest.
+    return;
+  }
+
+  // Sort found suggestions to suggest the best one first
+  SimilarityComparator sc(*this);
+  QuickSort::sort(suggestions, nsuggestions, sc, false);
+
+  out->print("Did you mean any of the following?");
+  for (size_t i = 0; i < nsuggestions; i++) {
+    char buf[128];
+    suggestions[i].describe_tags(buf, sizeof(buf));
+    out->print(" %s", buf);
+  }
+}

--- a/src/hotspot/share/logging/logSelection.hpp	Tue Feb 27 21:29:19 2018 -0800
+++ b/src/hotspot/share/logging/logSelection.hpp	Wed Feb 28 09:30:06 2018 +0100
@@ -62,6 +62,12 @@
 
   int describe_tags(char* buf, size_t bufsize) const;
   int describe(char* buf, size_t bufsize) const;
+
+  // List similar selections that matches existing tag sets on the given outputstream
+  void suggest_similar_matching(outputStream* out) const;
+
+  // Compute a similarity measure in the range [0, 1], where higher means more similar
+  double similarity(const LogSelection& other) const;
 };
 
 #endif // SHARE_VM_LOGGING_LOGSELECTION_HPP

--- a/src/hotspot/share/logging/logSelectionList.cpp	Tue Feb 27 21:29:19 2018 -0800
+++ b/src/hotspot/share/logging/logSelectionList.cpp	Wed Feb 28 09:30:06 2018 +0100
@@ -40,19 +40,17 @@
         return false;
       }
 
-      if (valid) {
-        out->print("No tag set matches selection(s):");
-      }
+      out->print("No tag set matches selection:");
       valid = false;
 
       char buf[256];
       _selections[i].describe_tags(buf, sizeof(buf));
-      out->print(" %s", buf);
+      out->print(" %s. ", buf);
+
+      _selections[i].suggest_similar_matching(out);
+      out->cr();
     }
   }
-  if (!valid && out != NULL) {
-    out->cr();
-  }
   return valid;
 }
 

--- a/src/hotspot/share/logging/logTagSet.cpp	Tue Feb 27 21:29:19 2018 -0800
+++ b/src/hotspot/share/logging/logTagSet.cpp	Wed Feb 28 09:30:06 2018 +0100
@@ -141,7 +141,7 @@
 static const size_t TagSetBufferSize = 128;
 
 void LogTagSet::describe_tagsets(outputStream* out) {
-  out->print_cr("Described tag combinations:");
+  out->print_cr("Described tag sets:");
   for (const LogTagSetDescription* d = tagset_descriptions; d->tagset != NULL; d++) {
     char buf[TagSetBufferSize];
     d->tagset->label(buf, sizeof(buf), "+");
@@ -169,7 +169,7 @@
   qsort(tagset_labels, _ntagsets, sizeof(*tagset_labels), qsort_strcmp);
 
   // Print and then free the labels
-  out->print("All available tag sets: ");
+  out->print("Available tag sets: ");
   for (idx = 0; idx < _ntagsets; idx++) {
     out->print("%s%s", (idx == 0 ? "" : ", "), tagset_labels[idx]);
     os::free(tagset_labels[idx]);

--- a/src/hotspot/share/runtime/arguments.cpp	Tue Feb 27 21:29:19 2018 -0800
+++ b/src/hotspot/share/runtime/arguments.cpp	Wed Feb 28 09:30:06 2018 +0100
@@ -3096,7 +3096,8 @@
     } else if (match_option(option, "-Xlog", &tail)) {
       bool ret = false;
       if (strcmp(tail, ":help") == 0) {
-        LogConfiguration::print_command_line_help(defaultStream::output_stream());
+        fileStream stream(defaultStream::output_stream());
+        LogConfiguration::print_command_line_help(&stream);
         vm_exit(0);
       } else if (strcmp(tail, ":disable") == 0) {
         LogConfiguration::disable_logging();
@@ -3109,7 +3110,7 @@
       }
       if (ret == false) {
         jio_fprintf(defaultStream::error_stream(),
-                    "Invalid -Xlog option '-Xlog%s'\n",
+                    "Invalid -Xlog option '-Xlog%s', see error log for details.\n",
                     tail);
         return JNI_EINVAL;
       }

--- a/test/hotspot/gtest/logging/test_logConfiguration.cpp	Tue Feb 27 21:29:19 2018 -0800
+++ b/test/hotspot/gtest/logging/test_logConfiguration.cpp	Wed Feb 28 09:30:06 2018 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016, 2018, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -225,7 +225,7 @@
 
   // Now reconfigure logging on stderr with no decorators
   set_log_config("stderr", "all=off", "none");
-  EXPECT_TRUE(is_described("#1: stderr all=off \n")) << "Expecting no decorators";
+  EXPECT_TRUE(is_described("#1: stderr all=off none\n")) << "Expecting no decorators";
 }
 
 // Test that invalid options cause configuration errors
@@ -383,7 +383,7 @@
   bool success = LogConfiguration::parse_log_arguments("stdout", invalid_tagset, NULL, NULL, &ss);
   const char* msg = ss.as_string();
   EXPECT_TRUE(success) << "Should only cause a warning, not an error";
-  EXPECT_TRUE(string_contains_substring(msg, "No tag set matches selection(s):"));
+  EXPECT_TRUE(string_contains_substring(msg, "No tag set matches selection:"));
   EXPECT_TRUE(string_contains_substring(msg, invalid_tagset));
 }
 
@@ -413,3 +413,21 @@
   ASSERT_NE(-1, ret);
   delete_file(buf);
 }
+
+TEST_VM_F(LogConfigurationTest, suggest_similar_selection) {
+  static const char* nonexisting_tagset = "logging+start+exit+safepoint+gc";
+
+  ResourceMark rm;
+  stringStream ss;
+  LogConfiguration::parse_log_arguments("stdout", nonexisting_tagset, NULL, NULL, &ss);
+
+  const char* suggestion = ss.as_string();
+  SCOPED_TRACE(suggestion);
+  EXPECT_TRUE(string_contains_substring(ss.as_string(), "Did you mean any of the following?"));
+  EXPECT_TRUE(string_contains_substring(suggestion, "logging") ||
+              string_contains_substring(suggestion, "start") ||
+              string_contains_substring(suggestion, "exit") ||
+              string_contains_substring(suggestion, "safepoint") ||
+              string_contains_substring(suggestion, "gc")) <<
+                  "suggestion must contain AT LEAST one of the tags in user supplied selection";
+}

--- a/test/hotspot/gtest/logging/test_logTagSetDescriptions.cpp	Tue Feb 27 21:29:19 2018 -0800
+++ b/test/hotspot/gtest/logging/test_logTagSetDescriptions.cpp	Wed Feb 28 09:30:06 2018 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -51,7 +51,8 @@
   const char* filename = "logtagset_descriptions";
   FILE* fp = fopen(filename, "w+");
   ASSERT_NE((void*)NULL, fp);
-  LogConfiguration::print_command_line_help(fp);
+  fileStream stream(fp);
+  LogConfiguration::print_command_line_help(&stream);
   fclose(fp);
 
   for (LogTagSetDescription* d = tagset_descriptions; d->tagset != NULL; d++) {

--- a/test/hotspot/jtreg/serviceability/logging/TestMultipleXlogArgs.java	Tue Feb 27 21:29:19 2018 -0800
+++ b/test/hotspot/jtreg/serviceability/logging/TestMultipleXlogArgs.java	Wed Feb 28 09:30:06 2018 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -43,7 +43,7 @@
                                                                   "-version");
         OutputAnalyzer output = new OutputAnalyzer(pb.start());
         // -Xlog:logging=trace means that the log configuration will be printed.
-        String stdoutConfigLine = "\\[logging *\\] #0: stdout .*";
+        String stdoutConfigLine = "\\[logging *\\]  #0: stdout .*";
         // Ensure logging=trace has overwritten logging=debug
         output.shouldMatch(stdoutConfigLine + "logging=trace").shouldNotMatch(stdoutConfigLine + "logging=debug");
         // Make sure safepoint=info is printed exactly once even though we're setting it twice