--- old/src/share/vm/runtime/arguments.cpp	Wed Sep  4 19:27:24 2013
+++ new/src/share/vm/runtime/arguments.cpp	Wed Sep  4 19:27:24 2013
@@ -1850,7 +1850,7 @@
         (NumberOfGCLogFiles == 0)  ||
         (GCLogFileSize == 0)) {
       jio_fprintf(defaultStream::output_stream(),
-                  "To enable GC log rotation, use -Xloggc:<filename> -XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=<num_of_files> -XX:GCLogFileSize=<num_of_size>\n"
+                  "To enable GC log rotation, use -Xloggc:<filename> -XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=<num_of_files> -XX:GCLogFileSize=<num_of_size>[k|K|m|M|g|G]\n"
                   "where num_of_file > 0 and num_of_size > 0\n"
                   "GC log rotation is turned off\n");
       UseGCLogFileRotation = false;
@@ -1864,6 +1864,42 @@
   }
 }
 
+// This function is called for -Xloggc:<filename>, it can be used 
+// to check if a given file name(or string) conforms to the following
+// specification: 
+// A valid string only contains "[A-Z][a-z][0-9].-_%[p|t]"
+// %p and %t only allowed once.
+bool is_filename_valid(const char *file_name) {
+  const char* p = file_name;
+  int count_p = 0;
+  int count_t = 0;
+  while (*p != '\0') {
+    if ((*p >= '0' && *p <= '9') ||
+        (*p >= 'A' && *p <= 'Z') ||
+        (*p >= 'a' && *p <= 'z') ||
+         *p == '-'               ||
+         *p == '_'               ||
+         *p == '.') {
+       p++;
+       continue;
+    }
+    if (*p == '%') {
+      if(*(p + 1) == 'p') {
+        p += 2;
+        count_p ++;
+        continue;
+      }
+      if (*(p + 1) == 't') {
+        p += 2;
+        count_t ++;
+        continue;
+      }
+    }
+    return false;
+  }
+  return count_p < 2 && count_t < 2;
+}
+
 // Check consistency of GC selection
 bool Arguments::check_gc_consistency() {
   check_gclog_consistency();
@@ -2817,6 +2853,12 @@
       // ostream_init_log(), when called will use this filename
       // to initialize a fileStream.
       _gc_log_filename = strdup(tail);
+     if (!is_filename_valid(_gc_log_filename)) {
+       jio_fprintf(defaultStream::output_stream(),
+                  "Filename can only cantain [A-Z][a-z][0-9]-_.%%[p|t]\n"
+                  "%%p and %%t can only show up once\n" );
+        return JNI_EINVAL;
+      }
       FLAG_SET_CMDLINE(bool, PrintGC, true);
       FLAG_SET_CMDLINE(bool, PrintGCTimeStamps, true);