Index: libcxx/trunk/include/__config
===================================================================
--- libcxx/trunk/include/__config
+++ libcxx/trunk/include/__config
@@ -110,12 +110,22 @@
 # endif
 #endif // __sun__
 
-#if defined(__native_client__)
+#if defined(__CloudABI__)
+  // Certain architectures provide arc4random(). Prefer using
+  // arc4random() over /dev/{u,}random to make it possible to obtain
+  // random data even when using sandboxing mechanisms such as chroots,
+  // Capsicum, etc.
+# define _LIBCPP_USING_ARC4_RANDOM
+#elif defined(__native_client__)
   // NaCl's sandbox (which PNaCl also runs in) doesn't allow filesystem access,
   // including accesses to the special files under /dev. C++11's
   // std::random_device is instead exposed through a NaCl syscall.
 # define _LIBCPP_USING_NACL_RANDOM
-#endif // defined(__native_client__)
+#elif defined(_WIN32)
+# define _LIBCPP_USING_WIN32_RANDOM
+#else
+# define _LIBCPP_USING_DEV_RANDOM
+#endif
 
 #if !defined(_LIBCPP_LITTLE_ENDIAN) || !defined(_LIBCPP_BIG_ENDIAN)
 # include <endian.h>
Index: libcxx/trunk/include/random
===================================================================
--- libcxx/trunk/include/random
+++ libcxx/trunk/include/random
@@ -3475,9 +3475,9 @@
 
 class _LIBCPP_TYPE_VIS random_device
 {
-#if !(defined(_WIN32) || defined(_LIBCPP_USING_NACL_RANDOM))
+#ifdef _LIBCPP_USING_DEV_RANDOM
     int __f_;
-#endif // !(defined(_WIN32) || defined(_LIBCPP_USING_NACL_RANDOM))
+#endif // defined(_LIBCPP_USING_DEV_RANDOM)
 public:
     // types
     typedef unsigned result_type;
Index: libcxx/trunk/src/random.cpp
===================================================================
--- libcxx/trunk/src/random.cpp
+++ libcxx/trunk/src/random.cpp
@@ -7,11 +7,10 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if defined(_WIN32)
+#if defined(_LIBCPP_USING_WIN32_RANDOM)
 // Must be defined before including stdlib.h to enable rand_s().
 #define _CRT_RAND_S
-#include <stdio.h>
-#endif // defined(_WIN32)
+#endif // defined(_LIBCPP_USING_WIN32_RANDOM)
 
 #include "random"
 #include "system_error"
@@ -19,21 +18,27 @@
 #if defined(__sun__)
 #define rename solaris_headers_are_broken
 #endif // defined(__sun__)
-#if !defined(_WIN32)
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#if defined(_LIBCPP_USING_DEV_RANDOM)
 #include <fcntl.h>
 #include <unistd.h>
-#endif // !defined(_WIN32)
-#include <errno.h>
-#if defined(_LIBCPP_USING_NACL_RANDOM)
+#elif defined(_LIBCPP_USING_NACL_RANDOM)
 #include <nacl/nacl_random.h>
-#endif // defined(_LIBCPP_USING_NACL_RANDOM)
+#endif
+
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if defined(_WIN32)
+#if defined(_LIBCPP_USING_ARC4_RANDOM)
 
-random_device::random_device(const string&)
+random_device::random_device(const string& __token)
 {
+    if (__token != "/dev/urandom")
+        __throw_system_error(ENOENT, ("random device not supported " + __token).c_str());
 }
 
 random_device::~random_device()
@@ -43,10 +48,43 @@
 unsigned
 random_device::operator()()
 {
+    return arc4random();
+}
+
+#elif defined(_LIBCPP_USING_DEV_RANDOM)
+
+random_device::random_device(const string& __token)
+    : __f_(open(__token.c_str(), O_RDONLY))
+{
+    if (__f_ < 0)
+        __throw_system_error(errno, ("random_device failed to open " + __token).c_str());
+}
+
+random_device::~random_device()
+{
+    close(__f_);
+}
+
+unsigned
+random_device::operator()()
+{
     unsigned r;
-    errno_t err = rand_s(&r);
-    if (err)
-        __throw_system_error(err, "random_device rand_s failed.");
+    size_t n = sizeof(r);
+    char* p = reinterpret_cast<char*>(&r);
+    while (n > 0)
+    {
+        ssize_t s = read(__f_, p, n);
+        if (s == 0)
+            __throw_system_error(ENODATA, "random_device got EOF");
+        if (s == -1)
+        {
+            if (errno != EINTR)
+                __throw_system_error(errno, "random_device got an unexpected error");
+            continue;
+        }
+        n -= static_cast<size_t>(s);
+        p += static_cast<size_t>(s);
+    }
     return r;
 }
 
@@ -79,44 +117,31 @@
     return r;
 }
 
-#else // !defined(_WIN32) && !defined(_LIBCPP_USING_NACL_RANDOM)
+#elif defined(_LIBCPP_USING_WIN32_RANDOM)
 
 random_device::random_device(const string& __token)
-    : __f_(open(__token.c_str(), O_RDONLY))
 {
-    if (__f_ < 0)
-        __throw_system_error(errno, ("random_device failed to open " + __token).c_str());
+    if (__token != "/dev/urandom")
+        __throw_system_error(ENOENT, ("random device not supported " + __token).c_str());
 }
 
 random_device::~random_device()
 {
-    close(__f_);
 }
 
 unsigned
 random_device::operator()()
 {
     unsigned r;
-    size_t n = sizeof(r);
-    char* p = reinterpret_cast<char*>(&r);
-    while (n > 0)
-    {
-        ssize_t s = read(__f_, p, n);
-        if (s == 0)
-            __throw_system_error(ENODATA, "random_device got EOF");
-        if (s == -1)
-        {
-            if (errno != EINTR)
-                __throw_system_error(errno, "random_device got an unexpected error");
-            continue;
-        }
-        n -= static_cast<size_t>(s);
-        p += static_cast<size_t>(s);
-    }
+    errno_t err = rand_s(&r);
+    if (err)
+        __throw_system_error(err, "random_device rand_s failed.");
     return r;
 }
 
-#endif // defined(_WIN32) || defined(_LIBCPP_USING_NACL_RANDOM)
+#else
+#error "Random device not implemented for this architecture"
+#endif
 
 double
 random_device::entropy() const _NOEXCEPT
Index: libcxx/trunk/test/std/numerics/rand/rand.device/ctor.pass.cpp
===================================================================
--- libcxx/trunk/test/std/numerics/rand/rand.device/ctor.pass.cpp
+++ libcxx/trunk/test/std/numerics/rand/rand.device/ctor.pass.cpp
@@ -23,14 +23,12 @@
 #include <unistd.h>
 
 bool is_valid_random_device(const std::string &token) {
-#if defined(_WIN32)
-  return true;
-#elif defined(_LIBCPP_USING_NACL_RANDOM)
-  return token == "/dev/urandom";
-#else  // !defined(_WIN32) && !defined(_LIBCPP_USING_NACL_RANDOM)
+#if defined(_LIBCPP_USING_DEV_RANDOM)
   // Not an exhaustive list: they're the only tokens that are tested below.
   return token == "/dev/urandom" || token == "/dev/random";
-#endif // defined(_WIN32) || defined(_LIBCPP_USING_NACL_RANDOM)
+#else
+  return token == "/dev/urandom";
+#endif
 }
 
 void check_random_device_valid(const std::string &token) {