8162419: closed/com/oracle/jfr/runtime/TestVMInfoEvent.sh failing after JDK-8155968

Summary: Under error conditions, always return -1 and perform null termination regardless of the behavior of underlying vsnprintf() implementation.
Reviewed-by: dholmes, cjplummer

src/share/vm/prims/jvm.cpp

 /*
- * Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2016, 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
@@ -2868,7 +2868,18 @@ ATTRIBUTE_PRINTF(3, 0)
 int jio_vsnprintf(char *str, size_t count, const char *fmt, va_list args) {
   // see bug 4399518, 4417214
   if ((intptr_t)count <= 0) return -1;
-  return vsnprintf(str, count, fmt, args);
+
+  int result = vsnprintf(str, count, fmt, args);
+  // Note: on truncation vsnprintf(3) on Unix returns number of
+  // characters which would have been written had the buffer been large
+  // enough; on Windows, it returns -1. We handle both cases here and
+  // always return -1, and perform null termination.
+  if ((result > 0 && (size_t)result >= count) || result == -1) {
+    str[count - 1] = '\0';
+    result = -1;
+  }
+
+  return result;
 }
 
 ATTRIBUTE_PRINTF(3, 0)

src/share/vm/runtime/deoptimization.cpp

@@ -1881,8 +1881,6 @@ const char* Deoptimization::format_trap_state(char* buf, size_t buflen,
                        trap_reason_name(reason),
                        recomp_flag ? " recompiled" : "");
   }
-  if (len >= buflen)
-    buf[buflen-1] = '\0';
   return buf;
 }
 
@@ -1952,8 +1950,6 @@ const char* Deoptimization::format_trap_request(char* buf, size_t buflen,
     len = jio_snprintf(buf, buflen, "reason='%s' action='%s' index='%d'",
                        reason, action, unloaded_class_index);
   }
-  if (len >= buflen)
-    buf[buflen-1] = '\0';
   return buf;
 }
 

src/share/vm/runtime/java.cpp

 /*
- * Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2016, 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
@@ -773,25 +773,36 @@ int JDK_Version::compare(const JDK_Version& other) const {
 }
 
 void JDK_Version::to_string(char* buffer, size_t buflen) const {
+  assert(buffer && buflen > 0, "call with useful buffer");
   size_t index = 0;
   if (!is_valid()) {
     jio_snprintf(buffer, buflen, "%s", "(uninitialized)");
   } else if (is_partially_initialized()) {
     jio_snprintf(buffer, buflen, "%s", "(uninitialized) pre-1.6.0");
   } else {
-    index += jio_snprintf(
+    int rc = jio_snprintf(
         &buffer[index], buflen - index, "%d.%d", _major, _minor);
+    if (rc == -1) return;
+    index += rc;
     if (_micro > 0) {
-      index += jio_snprintf(&buffer[index], buflen - index, ".%d", _micro);
+      rc = jio_snprintf(&buffer[index], buflen - index, ".%d", _micro);
+      if (rc == -1) return;
+      index += rc;
     }
     if (_update > 0) {
-      index += jio_snprintf(&buffer[index], buflen - index, "_%02d", _update);
+      rc = jio_snprintf(&buffer[index], buflen - index, "_%02d", _update);
+      if (rc == -1) return;
+      index += rc;
     }
     if (_special > 0) {
-      index += jio_snprintf(&buffer[index], buflen - index, "%c", _special);
+      rc = jio_snprintf(&buffer[index], buflen - index, "%c", _special);
+      if (rc == -1) return;
+      index += rc;
     }
     if (_build > 0) {
-      index += jio_snprintf(&buffer[index], buflen - index, "-b%02d", _build);
+      rc = jio_snprintf(&buffer[index], buflen - index, "-b%02d", _build);
+      if (rc == -1) return;
+      index += rc;
     }
   }
 }