--- old/src/hotspot/share/prims/jvm.cpp	2018-05-01 09:30:57.523120776 +0900
+++ new/src/hotspot/share/prims/jvm.cpp	2018-05-01 09:30:57.359120165 +0900
@@ -2719,10 +2719,10 @@
 int jio_vsnprintf(char *str, size_t count, const char *fmt, va_list args) {
   // Reject count values that are negative signed values converted to
   // unsigned; see bug 4399518, 4417214
-  if ((intptr_t)count <= 0) return -1;
+  if ((intptr_t)count < 0) return -1;
 
   int result = os::vsnprintf(str, count, fmt, args);
-  if (result > 0 && (size_t)result >= count) {
+  if (count > 0 && result > 0 && (size_t)result >= count) {
     result = -1;
   }
 
--- old/src/hotspot/share/utilities/events.hpp	2018-05-01 09:30:58.090122885 +0900
+++ new/src/hotspot/share/utilities/events.hpp	2018-05-01 09:30:57.931122294 +0900
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 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
@@ -143,10 +143,10 @@
   }
 };
 
-// A simple ring buffer of fixed size text messages.
-class StringEventLog : public EventLogBase<StringLogMessage> {
+// A simple ring buffer of text messages.
+class StringEventLog : public EventLogBase<FormatBufferDynamic> {
  public:
-  StringEventLog(const char* name, int count = LogEventsBufferEntries) : EventLogBase<StringLogMessage>(name, count) {}
+  StringEventLog(const char* name, int count = LogEventsBufferEntries) : EventLogBase<FormatBufferDynamic>(name, count) {}
 
   void logv(Thread* thread, const char* format, va_list ap) ATTRIBUTE_PRINTF(3, 0) {
     if (!should_log()) return;
@@ -282,9 +282,9 @@
   out->cr();
 }
 
-// Implement a printing routine for the StringLogMessage
+// Implement a printing routine for the FormatBufferDynamic
 template <>
-inline void EventLogBase<StringLogMessage>::print(outputStream* out, StringLogMessage& lm) {
+inline void EventLogBase<FormatBufferDynamic>::print(outputStream* out, FormatBufferDynamic& lm) {
   out->print_raw(lm);
   out->cr();
 }
--- old/src/hotspot/share/utilities/formatBuffer.cpp	2018-05-01 09:30:58.964126137 +0900
+++ new/src/hotspot/share/utilities/formatBuffer.cpp	2018-05-01 09:30:58.493124385 +0900
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 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
@@ -36,3 +36,10 @@
   jio_vsnprintf(_buf, FormatBufferBase::BufferSize, format, argp);
   va_end(argp);
 }
+
+FormatBufferDynamic::~FormatBufferDynamic() {
+  if (_buf != NULL) {
+    os::free(_buf);
+  }
+}
+
--- old/src/hotspot/share/utilities/formatBuffer.hpp	2018-05-01 09:31:00.377131394 +0900
+++ new/src/hotspot/share/utilities/formatBuffer.hpp	2018-05-01 09:31:00.093130337 +0900
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 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
@@ -45,6 +45,22 @@
   FormatBufferResource(const char * format, ...) ATTRIBUTE_PRINTF(2, 3);
 };
 
+// Use malloc() for buffer
+class FormatBufferDynamic : public FormatBufferBase {
+ protected:
+  int bufsz;
+
+ public:
+  inline FormatBufferDynamic();
+  ~FormatBufferDynamic();
+  inline void append(const char* format, ...) ATTRIBUTE_PRINTF(2, 3);
+  inline void print(const char* format, ...) ATTRIBUTE_PRINTF(2, 3);
+  inline void printv(const char* format, va_list ap) ATTRIBUTE_PRINTF(2, 0);
+
+  char* buffer() { return _buf; }
+  int size() { return bufsz; }
+};
+
 class FormatBufferDummy {};
 
 // Use stack for buffer
@@ -69,6 +85,55 @@
   inline FormatBuffer();
 };
 
+FormatBufferDynamic::FormatBufferDynamic() : FormatBufferBase(NULL), bufsz(-1) {
+  // do nothing
+}
+
+void FormatBufferDynamic::append(const char* format, ...) {
+  va_list argp;
+
+  va_start(argp, format);
+  int append_len = jio_vsnprintf(NULL, 0, format, argp) + 1;
+  va_end(argp);
+
+  char *append_str = (char *)os::malloc(append_len, mtInternal);
+  va_start(argp, format);
+  jio_vsnprintf(append_str, append_len, format, argp);
+  va_end(argp);
+
+  if (_buf == NULL) {
+    bufsz = append_len;
+    _buf = append_str;
+  } else {
+    bufsz += append_len - 1;
+    _buf = (char *)os::realloc(_buf, bufsz, mtInternal);
+    strcat(_buf, append_str);
+    os::free(append_str);
+  }
+}
+
+void FormatBufferDynamic::print(const char * format, ...) {
+  va_list argp;
+  va_start(argp, format);
+  printv(format, argp);
+  va_end(argp);
+}
+
+void FormatBufferDynamic::printv(const char * format, va_list argp) {
+  if (_buf != NULL) {
+    os::free(_buf);
+    bufsz = -1;
+  }
+
+  va_list argp_local;
+  va_copy(argp_local, argp);
+  bufsz = jio_vsnprintf(NULL, 0, format, argp_local) + 1;
+  va_end(argp_local);
+
+  _buf = (char *)os::malloc(bufsz, mtInternal);
+  jio_vsnprintf(_buf, bufsz, format, argp);
+}
+
 template <size_t bufsz>
 FormatBuffer<bufsz>::FormatBuffer(const char * format, ...) : FormatBufferBase(_buffer) {
   va_list argp;