gsm_utils: call gnutls_global_init() as constructor

gnutls_global_init must be called at least once for
gnutls < 3.3.0. It doesn't hurt calling it twice, except
a reference counter is increased.
gnutls >= 3.3.0 will call it automatic.

Fixes: OS#2986
Change-Id: I241b6ae5aa8df13dd78f04658cf0953e9561c9e2
diff --git a/src/gsm/gsm_utils.c b/src/gsm/gsm_utils.c
index 5d8c834..7e6c794 100644
--- a/src/gsm/gsm_utils.c
+++ b/src/gsm/gsm_utils.c
@@ -112,6 +112,25 @@
 #pragma message ("including GnuTLS for getrandom fallback.")
 #include <gnutls/gnutls.h>
 #include <gnutls/crypto.h>
+
+/* gnutls < 3.3.0 requires global init.
+ * gnutls >= 3.3.0 does it automatic.
+ * It doesn't hurt calling it twice,
+ * as long it's not done at the same time (threads).
+ */
+__attribute__((constructor))
+static void on_dso_load_gnutls(void)
+{
+	if (!gnutls_check_version("3.3.0"))
+		gnutls_global_init();
+}
+
+__attribute__((destructor))
+static void on_dso_unload_gnutls(void)
+{
+	if (!gnutls_check_version("3.3.0"))
+		gnutls_global_deinit();
+}
 #endif
 
 /* ETSI GSM 03.38 6.2.1 and 6.2.1.1 default alphabet