From d93ba6ef1dffada47acae6d8a4ea0bda70ddaba0 Mon Sep 17 00:00:00 2001
From: Thomas Stuefe <stuefe@openjdk.org>
Date: Mon, 24 Oct 2016 14:51:16 +0200
Subject: [PATCH] 8168542: os::realloc should return a valid pointer for input
 size=0

Reviewed-by: dholmes, cjplummer, dsamersoff, rehn
---
 hotspot/src/share/vm/runtime/os.cpp | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/hotspot/src/share/vm/runtime/os.cpp b/hotspot/src/share/vm/runtime/os.cpp
index 47a7b5672a4..b48edb441fb 100644
--- a/hotspot/src/share/vm/runtime/os.cpp
+++ b/hotspot/src/share/vm/runtime/os.cpp
@@ -649,6 +649,12 @@ void* os::realloc(void *memblock, size_t size, MEMFLAGS memflags, const NativeCa
     return NULL;
   }
 
+  if (size == 0) {
+    // return a valid pointer if size is zero
+    // if NULL is returned the calling functions assume out of memory.
+    size = 1;
+  }
+
 #ifndef ASSERT
   NOT_PRODUCT(inc_stat_counter(&num_mallocs, 1));
   NOT_PRODUCT(inc_stat_counter(&alloc_bytes, size));
@@ -669,9 +675,6 @@ void* os::realloc(void *memblock, size_t size, MEMFLAGS memflags, const NativeCa
   // NMT support
   void* membase = MemTracker::malloc_base(memblock);
   verify_memory(membase);
-  if (size == 0) {
-    return NULL;
-  }
   // always move the block
   void* ptr = os::malloc(size, memflags, stack);
   if (PrintMalloc && tty != NULL) {