--- old/src/os/posix/vm/os_posix.cpp	2017-03-14 12:10:20.382868000 +0100
+++ new/src/os/posix/vm/os_posix.cpp	2017-03-14 12:10:19.841840000 +0100
@@ -1107,6 +1107,12 @@
 
 char* os::Posix::realpath(const char* filename, char* outbuf, size_t outbuflen) {
 
+  if (filename == NULL || outbuf == 0 || outbuflen < 1) {
+    assert(false, "os::Posix::realpath: invalid arguments.");
+    errno = EINVAL;
+    return NULL;
+  }
+
   char* result = NULL;
 
   // This assumes platform realpath() is implemented according to POSIX.1-2008.
@@ -1118,21 +1124,20 @@
       strcpy(outbuf, p);
       result = outbuf;
     } else {
-      errno = EINVAL;
+      errno = ENAMETOOLONG;
     }
     ::free(p); // *not* os::free
   } else {
     // Fallback for platforms struggling with modern Posix standards (AIX 5.3, 6.1). If realpath
     // returns EINVAL, this may indicate that realpath is not POSIX.1-2008 compatible and
-    // that it complains about the NULL we did hand down as user buffer (unless filename
-    // was NULL, in which case it may have been complaining about that).
+    // that it complains about the NULL we did hand down as user buffer.
     // In this case, use the user provided buffer but at least check whether realpath caused
     // a memory overwriter.
-    if (errno == EINVAL && filename != NULL) {
+    if (errno == EINVAL) {
+      outbuf[outbuflen - 1] = '\0';
       p = ::realpath(filename, outbuf);
       if (p != NULL) {
-        assert(p == outbuf, "Unexpected..");
-        guarantee(strlen(p) < outbuflen, "realpath buffer overwriter detected.");
+        guarantee(outbuf[outbuflen - 1] == '\0', "realpath buffer overwriter detected.");
         result = p;
       }
     }