Merge #10301: Check if sys/random.h is required for getentropy.

ee2d10a Check if sys/random.h is required for getentropy on OSX. (James Hilliard)

Pull request description:

  This should check and include sys/random.h if required for osx as mentioned [here](https://github.com/bitcoin/bitcoin/pull/9821#issuecomment-290936636).

Tree-SHA512: e9491f67f2e8b2e6bcdbcbb8063295e844d5627daf5336e3e17b4a8027d888fa65a08e4580a745abdc35ffd8d86b4fc7434daaac172c4a06ab7566a2ed0bfb92

configure.ac

@@ -674,6 +674,14 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <unistd.h>]],
  [ AC_MSG_RESULT(no)]
 )
 
+AC_MSG_CHECKING(for getentropy via random.h)
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <unistd.h>
+ #include <sys/random.h>]],
+ [[ getentropy(nullptr, 32) ]])],
+ [ AC_MSG_RESULT(yes); AC_DEFINE(HAVE_GETENTROPY_RAND, 1,[Define this symbol if the BSD getentropy system call is available with sys/random.h]) ],
+ [ AC_MSG_RESULT(no)]
+)
+
 AC_MSG_CHECKING(for sysctl KERN_ARND)
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/types.h>
   #include <sys/sysctl.h>]],

src/random.cpp

@@ -27,9 +27,12 @@
 #include <sys/syscall.h>
 #include <linux/random.h>
 #endif
-#ifdef HAVE_GETENTROPY
+#if defined(HAVE_GETENTROPY) || (defined(HAVE_GETENTROPY_RAND) && defined(MAC_OSX))
 #include <unistd.h>
 #endif
+#if defined(HAVE_GETENTROPY_RAND) && defined(MAC_OSX)
+#include <sys/random.h>
+#endif
 #ifdef HAVE_SYSCTL_ARND
 #include <sys/sysctl.h>
 #endif
@@ -237,6 +240,15 @@ void GetOSRand(unsigned char *ent32)
     if (getentropy(ent32, NUM_OS_RANDOM_BYTES) != 0) {
         RandFailure();
     }
+#elif defined(HAVE_GETENTROPY_RAND) && defined(MAC_OSX)
+    // We need a fallback for OSX < 10.12
+    if (&getentropy != NULL) {
+        if (getentropy(ent32, NUM_OS_RANDOM_BYTES) != 0) {
+            RandFailure();
+        }
+    } else {
+        GetDevURandom(ent32);
+    }
 #elif defined(HAVE_SYSCTL_ARND)
     /* FreeBSD and similar. It is possible for the call to return less
      * bytes than requested, so need to read in a loop.