+# if defined(__FreeBSD__) && defined(KERN_ARND)
+/*
+ * sysctl_random(): Use sysctl() to read a random number from the kernel
+ * Returns the size on success, 0 on failure.
+ */
+static size_t sysctl_random(char *buf, size_t buflen)
+{
+ int mib[2];
+ size_t done = 0;
+ size_t len;
+
+ /*
+ * Old implementations returned longs, newer versions support variable
+ * sizes up to 256 byte. The code below would not work properly when
+ * the sysctl returns long and we want to request something not a multiple
+ * of longs, which should never be the case.
+ */
+ ossl_assert(buflen % sizeof(long) == 0);
+
+ mib[0] = CTL_KERN;
+ mib[1] = KERN_ARND;
+
+ do {
+ len = buflen;
+ if (sysctl(mib, 2, buf, &len, NULL, 0) == -1)
+ return done;
+ done += len;
+ buf += len;
+ buflen -= len;
+ } while (buflen > 0);
+
+ return done;
+}
+# endif
+
+/*
+ * syscall_random(): Try to get random data using a system call
+ * returns the number of bytes returned in buf, or <= 0 on error.
+ */
+int syscall_random(void *buf, size_t buflen)
+{
+# if defined(OPENSSL_HAVE_GETRANDOM)
+ return (int)getrandom(buf, buflen, 0);
+# endif
+
+# if defined(__linux) && defined(SYS_getrandom)
+ return (int)syscall(SYS_getrandom, buf, buflen, 0);
+# endif
+
+# if defined(__FreeBSD__) && defined(KERN_ARND)
+ return (int)sysctl_random(buf, buflen);
+# endif
+
+ /* Supported since OpenBSD 5.6 */
+# if defined(__OpenBSD__) && OpenBSD >= 201411
+ return getentropy(buf, buflen);
+# endif
+
+ return -1;
+}
+