Add support for arc4random() to random_device.

Nuxi CloudABI (https://github.com/NuxiNL/cloudlibc) does not allow
processes to access the global filesystem namespace. This breaks
random_device, as it attempts to use /dev/{u,}random. This change adds
support for arc4random(), which is present on CloudABI.

In my opinion it would also make sense to use arc4random() on other
operating systems, such as *BSD and Mac OS X, but I'd rather leave that
to the maintainers of the respective platforms. Switching to
arc4random() does change the ABI.

This change also attempts to make some cleanups to the code. It adds a
single #define for every random interface, instead of testing against
operating systems explicitly.

As discussed, also validate the token argument to be equal to
"/dev/urandom" on all systems that only provide pseudo-random numbers.
This should cause little to no breakage, as "/dev/urandom" is also the
default argument value.

Reviewed by: jfb
Differential Revision: http://reviews.llvm.org/D8134

llvm-svn: 231764

1 files changed, 60 insertions, 35 deletions

diff --git a/libcxx/src/random.cpp b/libcxx/src/random.cpp
index 0a1d2a58636..4ab424eaa6e 100644
--- a/libcxx/src/random.cpp
+++ b/libcxx/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 @@ random_device::~random_device()
 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 @@ random_device::operator()()
     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