require et random_device for cons token test

[Jonathan Wakely]

On Thu, 25 Mar 2021 at 11:38, Jonathan Wakely wrote:

> On 25/03/21 08:00 -0300, Alexandre Oliva wrote:
> >On Mar 24, 2021, Jonathan Wakely <jwakely@redhat.com> wrote:
> >
> >> Does vxworks provide any platform-specific source of randomness, like
> >> Linux getrandom(2) or BSD arc4random(3) or Windows rand_s? If yes, we
> >> should add support for that (in the next stage 1).
> >
> >There appears to be a randNumGenCtl syscall that appears to be relevant
> >to that end, and randAdd to seed and randBytes to obtain random bytes in
> >vxRandLib.  I couldn't find documentation on how to use it, but there
> >seems to be some code using it in openssl.  Sorry, I don't know a lot
> >about vxworks.
>
> Thanks! We could look into that in stage 1.
>

Maybe something like this, completely untested and not ready to commit.
-------------- next part --------------
diff --git a/libstdc++-v3/src/c++11/random.cc b/libstdc++-v3/src/c++11/random.cc
index 70fd520077a..eb092cd0950 100644
--- a/libstdc++-v3/src/c++11/random.cc
+++ b/libstdc++-v3/src/c++11/random.cc
@@ -75,6 +75,14 @@
 # include <unistd.h>
 #endif
 
+#if __has_include(<_vxworks-versions.h>)
+# include <_vxworks-versions.h>
+# if _VXWORKS_MAJOR_GE(7) && __has_include(<randomNumGen.h>)
+#  include <randomNumGen.h>
+#  define USE_RANDBYTES 1
+# endif
+#endif
+
 #if defined _GLIBCXX_USE_CRT_RAND_S || defined _GLIBCXX_USE_DEV_RANDOM \
   || _GLIBCXX_HAVE_GETENTROPY
 // The OS provides a source of randomness we can use.
@@ -221,6 +229,29 @@ namespace std _GLIBCXX_VISIBILITY(default)
     }
 #endif
 
+#if USE_RANDBYTES
+    unsigned int
+    __vx_randBytes(void*)
+    {
+      int retries = 10;
+      unsigned int val;
+      auto bytes = reinterpret_cast<unsigned char*>(&val);
+      while (retries-- > 0)
+	{
+	  RANDOM_NUM_GEN_STATUS status = randStatus();
+	  if (status == RANDOM_NUM_GEN_ENOUGH_ENTROPY
+	     || status == RANDOM_NUM_GEN_MAX_ENTROPY)
+	    {
+	      if (randBytes(bytes, sizeof(val)) == OK)
+		return val;
+	    }
+	  else
+	    taskDelay(5);
+	}
+      std::__throw_runtime_error(__N("random_device: randBytes failed"));
+    }
+#endif
+
 #ifdef USE_LCG
     // TODO: use this to seed std::mt19937 engine too.
     unsigned
@@ -271,6 +302,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
     enum Which : unsigned {
       device_file = 1, prng = 2, rand_s = 4, getentropy = 8, arc4random = 16,
       rdseed = 64, rdrand = 128, darn = 256, rndr = 512,
+      randBytes = 1024,
       any = 0xffff
     };
 
@@ -326,6 +358,11 @@ namespace std _GLIBCXX_VISIBILITY(default)
 	return getentropy;
 #endif
 
+#if USE_RANDBYTES
+      if (func == __vx_randBytes)
+	return randBytes;
+#endif
+
 #ifdef USE_LCG
       if (func == &__lcg)
 	return prng;
@@ -506,6 +543,14 @@ namespace std _GLIBCXX_VISIBILITY(default)
       }
 #endif // _GLIBCXX_HAVE_GETENTROPY
 
+#if USE_RANDBYTES
+    if (which & randBytes)
+      {
+	_M_func = __vx_randBytes;
+	return;
+      }
+#endif
+
 #ifdef _GLIBCXX_USE_DEV_RANDOM
     if (which & device_file)
     {
@@ -666,6 +711,8 @@ namespace std _GLIBCXX_VISIBILITY(default)
     case rand_s:
     case prng:
       return 0.0;
+    case randBytes: // XXX is this a real source of entropy or PRNG?
+      return 0.0;
     case device_file:
       // handled below
       break;