Improve BSDs support.

src/mem/entropy.h

@@ -1,4 +1,5 @@
 #include "../ds/address.h"
+#include "../pal/pal.h"
 
 #include <cstdint>
 #include <random>

src/pal/pal_dragonfly.h

@@ -25,6 +25,19 @@ namespace snmalloc
      * to add new features that they should add any required feature flags.
      */
     static constexpr uint64_t pal_features = PALPOSIX::pal_features;
+
+    /**
+     * Source of Entropy
+     *
+     * DragonflyBSD does not have getentropy, so use getrandom instead.
+     */
+    static uint64_t get_entropy64()
+    {
+      uint64_t result;
+      if (getrandom(&result, sizeof(result), 0) != sizeof(result))
+        error("Failed to get system randomness");
+      return result;
+    }
   };
 } // namespace snmalloc
 #endif

src/pal/pal_netbsd.h

@@ -22,8 +22,13 @@ namespace snmalloc
      * generic BSD with support for arbitrary alignment from `mmap`.  This
      * field is declared explicitly to remind anyone modifying this class to
      * add new features that they should add any required feature flags.
+     *
+     * We disable the default implementation of randomness on NetBSD as it
+     * does not have the getentropy call. This will currently fallback to
+     * C++ libraries std::random_device.
      */
-    static constexpr uint64_t pal_features = PALBSD_Aligned::pal_features;
+    static constexpr uint64_t pal_features =
+      PALBSD_Aligned::pal_features & ~Entropy;
   };
 } // namespace snmalloc
 #endif