Index: libcxx/trunk/include/__config
===================================================================
--- libcxx/trunk/include/__config
+++ libcxx/trunk/include/__config
@@ -1447,6 +1447,17 @@
 
 #define _LIBCPP_UNUSED_VAR(x) ((void)(x))
 
+// Configures the fopen close-on-exec mode character, if any. This string will
+// be appended to any mode string used by fstream for fopen/fdopen.
+//
+// Not all platforms support this, but it helps avoid fd-leaks on platforms that
+// do.
+#if defined(__BIONIC__)
+#  define _LIBCPP_FOPEN_CLOEXEC_MODE "e"
+#else
+#  define _LIBCPP_FOPEN_CLOEXEC_MODE
+#endif
+
 #endif // __cplusplus
 
 #endif // _LIBCPP_CONFIG
Index: libcxx/trunk/include/fstream
===================================================================
--- libcxx/trunk/include/fstream
+++ libcxx/trunk/include/fstream
@@ -508,34 +508,34 @@
   switch (__mode & ~ios_base::ate) {
   case ios_base::out:
   case ios_base::out | ios_base::trunc:
-    return "w";
+    return "w" _LIBCPP_FOPEN_CLOEXEC_MODE;
   case ios_base::out | ios_base::app:
   case ios_base::app:
-    return "a";
+    return "a" _LIBCPP_FOPEN_CLOEXEC_MODE;
   case ios_base::in:
-    return "r";
+    return "r" _LIBCPP_FOPEN_CLOEXEC_MODE;
   case ios_base::in | ios_base::out:
-    return "r+";
+    return "r+" _LIBCPP_FOPEN_CLOEXEC_MODE;
   case ios_base::in | ios_base::out | ios_base::trunc:
-    return "w+";
+    return "w+" _LIBCPP_FOPEN_CLOEXEC_MODE;
   case ios_base::in | ios_base::out | ios_base::app:
   case ios_base::in | ios_base::app:
-    return "a+";
+    return "a+" _LIBCPP_FOPEN_CLOEXEC_MODE;
   case ios_base::out | ios_base::binary:
   case ios_base::out | ios_base::trunc | ios_base::binary:
-    return "wb";
+    return "wb" _LIBCPP_FOPEN_CLOEXEC_MODE;
   case ios_base::out | ios_base::app | ios_base::binary:
   case ios_base::app | ios_base::binary:
-    return "ab";
+    return "ab" _LIBCPP_FOPEN_CLOEXEC_MODE;
   case ios_base::in | ios_base::binary:
-    return "rb";
+    return "rb" _LIBCPP_FOPEN_CLOEXEC_MODE;
   case ios_base::in | ios_base::out | ios_base::binary:
-    return "r+b";
+    return "r+b" _LIBCPP_FOPEN_CLOEXEC_MODE;
   case ios_base::in | ios_base::out | ios_base::trunc | ios_base::binary:
-    return "w+b";
+    return "w+b" _LIBCPP_FOPEN_CLOEXEC_MODE;
   case ios_base::in | ios_base::out | ios_base::app | ios_base::binary:
   case ios_base::in | ios_base::app | ios_base::binary:
-    return "a+b";
+    return "a+b" _LIBCPP_FOPEN_CLOEXEC_MODE;
   default:
     return nullptr;
   }